text stringlengths 26 3.6k | page_title stringlengths 1 71 | source stringclasses 1
value | token_count int64 10 512 | id stringlengths 2 8 | url stringlengths 31 117 | topic stringclasses 4
values | section stringlengths 4 49 ⌀ | sublist stringclasses 9
values |
|---|---|---|---|---|---|---|---|---|
where is the plaintext and the ciphertext, with r being the number of rounds.
Frequently, key whitening is used in addition to this. At the beginning and the end, the data is modified with key material (often with XOR):
Given one of the standard iterated block cipher design schemes, it is fairly easy to construct a block cipher that is cryptographically secure, simply by using a large number of rounds. However, this will make the cipher inefficient. Thus, efficiency is the most important additional design criterion for professional ciphers. Further, a good block cipher is designed to avoid side-channel attacks, such as branch prediction and input-dependent memory accesses that might leak secret data via the cache state or the execution time. In addition, the cipher should be concise, for small hardware and software implementations.
Substitution–permutation networks
One important type of iterated block cipher known as a substitution–permutation network (SPN) takes a block of the plaintext and the key as inputs and applies several alternating rounds consisting of a substitution stage followed by a permutation stage—to produce each block of ciphertext output. The non-linear substitution stage mixes the key bits with those of the plaintext, creating Shannon's confusion. The linear permutation stage then dissipates redundancies, creating diffusion.
A substitution box (S-box) substitutes a small block of input bits with another block of output bits. This substitution must be one-to-one, to ensure invertibility (hence decryption). A secure S-box will have the property that changing one input bit will change about half of the output bits on average, exhibiting what is known as the avalanche effect—i.e. it has the property that each output bit will depend on every input bit.
A permutation box (P-box) is a permutation of all the bits: it takes the outputs of all the S-boxes of one round, permutes the bits, and feeds them into the S-boxes of the next round. A good P-box has the property that the output bits of any S-box are distributed to as many S-box inputs as possible.
At each round, the round key (obtained from the key with some simple operations, for instance, using S-boxes and P-boxes) is combined using some group operation, typically XOR. | Block cipher | Wikipedia | 499 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Decryption is done by simply reversing the process (using the inverses of the S-boxes and P-boxes and applying the round keys in reversed order).
Feistel ciphers
In a Feistel cipher, the block of plain text to be encrypted is split into two equal-sized halves. The round function is applied to one half, using a subkey, and then the output is XORed with the other half. The two halves are then swapped.
Let be the round function and let
be the sub-keys for the rounds respectively.
Then the basic operation is as follows:
Split the plaintext block into two equal pieces, (, )
For each round , compute
.
Then the ciphertext is .
The decryption of a ciphertext is accomplished by computing for
.
Then is the plaintext again.
One advantage of the Feistel model compared to a substitution–permutation network is that the round function does not have to be invertible.
Lai–Massey ciphers
The Lai–Massey scheme offers security properties similar to those of the Feistel structure. It also shares the advantage that the round function does not have to be invertible. Another similarity is that it also splits the input block into two equal pieces. However, the round function is applied to the difference between the two, and the result is then added to both half blocks.
Let be the round function and a half-round function and let be the sub-keys for the rounds respectively.
Then the basic operation is as follows:
Split the plaintext block into two equal pieces, (, )
For each round , compute
where and
Then the ciphertext is .
The decryption of a ciphertext is accomplished by computing for
where and
Then is the plaintext again.
Operations
ARX (add–rotate–XOR)
Many modern block ciphers and hashes are ARX algorithms—their round function involves only three operations: (A) modular addition, (R) rotation with fixed rotation amounts, and (X) XOR. Examples include ChaCha20, Speck, XXTEA, and BLAKE. Many authors draw an ARX network, a kind of data flow diagram, to illustrate such a round function.
These ARX operations are popular because they are relatively fast and cheap in hardware and software, their implementation can be made extremely simple, and also because they run in constant time, and therefore are immune to timing attacks. The rotational cryptanalysis technique attempts to attack such round functions. | Block cipher | Wikipedia | 509 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Other operations
Other operations often used in block ciphers include data-dependent rotations as in RC5 and RC6, a substitution box implemented as a lookup table as in Data Encryption Standard and Advanced Encryption Standard, a permutation box, and multiplication as in IDEA.
Modes of operation
A block cipher by itself allows encryption only of a single data block of the cipher's block length. For a variable-length message, the data must first be partitioned into separate cipher blocks. In the simplest case, known as electronic codebook (ECB) mode, a message is first split into separate blocks of the cipher's block size (possibly extending the last block with padding bits), and then each block is encrypted and decrypted independently. However, such a naive method is generally insecure because equal plaintext blocks will always generate equal ciphertext blocks (for the same key), so patterns in the plaintext message become evident in the ciphertext output.
To overcome this limitation, several so-called block cipher modes of operation have been designed and specified in national recommendations such as NIST 800-38A and BSI TR-02102 and international standards such as ISO/IEC 10116. The general concept is to use randomization of the plaintext data based on an additional input value, frequently called an initialization vector, to create what is termed probabilistic encryption. In the popular cipher block chaining (CBC) mode, for encryption to be secure the initialization vector passed along with the plaintext message must be a random or pseudo-random value, which is added in an exclusive-or manner to the first plaintext block before it is encrypted. The resultant ciphertext block is then used as the new initialization vector for the next plaintext block. In the cipher feedback (CFB) mode, which emulates a self-synchronizing stream cipher, the initialization vector is first encrypted and then added to the plaintext block. The output feedback (OFB) mode repeatedly encrypts the initialization vector to create a key stream for the emulation of a synchronous stream cipher. The newer counter (CTR) mode similarly creates a key stream, but has the advantage of only needing unique and not (pseudo-)random values as initialization vectors; the needed randomness is derived internally by using the initialization vector as a block counter and encrypting this counter for each block. | Block cipher | Wikipedia | 510 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
From a security-theoretic point of view, modes of operation must provide what is known as semantic security. Informally, it means that given some ciphertext under an unknown key one cannot practically derive any information from the ciphertext (other than the length of the message) over what one would have known without seeing the ciphertext. It has been shown that all of the modes discussed above, with the exception of the ECB mode, provide this property under so-called chosen plaintext attacks.
Padding
Some modes such as the CBC mode only operate on complete plaintext blocks. Simply extending the last block of a message with zero bits is insufficient since it does not allow a receiver to easily distinguish messages that differ only in the number of padding bits. More importantly, such a simple solution gives rise to very efficient padding oracle attacks. A suitable padding scheme is therefore needed to extend the last plaintext block to the cipher's block size. While many popular schemes described in standards and in the literature have been shown to be vulnerable to padding oracle attacks, a solution that adds a one-bit and then extends the last block with zero-bits, standardized as "padding method 2" in ISO/IEC 9797-1, has been proven secure against these attacks.
Cryptanalysis
Brute-force attacks
This property results in the cipher's security degrading quadratically, and needs to be taken into account when selecting a block size. There is a trade-off though as large block sizes can result in the algorithm becoming inefficient to operate. Earlier block ciphers such as the DES have typically selected a 64-bit block size, while newer designs such as the AES support block sizes of 128 bits or more, with some ciphers supporting a range of different block sizes.
Differential cryptanalysis
Linear cryptanalysis
A linear cryptanalysis is a form of cryptanalysis based on finding affine approximations to the action of a cipher. Linear cryptanalysis is one of the two most widely used attacks on block ciphers; the other being differential cryptanalysis.
The discovery is attributed to Mitsuru Matsui, who first applied the technique to the FEAL cipher (Matsui and Yamagishi, 1992).
Integral cryptanalysis | Block cipher | Wikipedia | 457 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Integral cryptanalysis is a cryptanalytic attack that is particularly applicable to block ciphers based on substitution–permutation networks. Unlike differential cryptanalysis, which uses pairs of chosen plaintexts with a fixed XOR difference, integral cryptanalysis uses sets or even multisets of chosen plaintexts of which part is held constant and another part varies through all possibilities. For example, an attack might use 256 chosen plaintexts that have all but 8 of their bits the same, but all differ in those 8 bits. Such a set necessarily has an XOR sum of 0, and the XOR sums of the corresponding sets of ciphertexts provide information about the cipher's operation. This contrast between the differences between pairs of texts and the sums of larger sets of texts inspired the name "integral cryptanalysis", borrowing the terminology of calculus.
Other techniques
In addition to linear and differential cryptanalysis, there is a growing catalog of attacks: truncated differential cryptanalysis, partial differential cryptanalysis, integral cryptanalysis, which encompasses square and integral attacks, slide attacks, boomerang attacks, the XSL attack, impossible differential cryptanalysis, and algebraic attacks. For a new block cipher design to have any credibility, it must demonstrate evidence of security against known attacks.
Provable security
When a block cipher is used in a given mode of operation, the resulting algorithm should ideally be about as secure as the block cipher itself. ECB (discussed above) emphatically lacks this property: regardless of how secure the underlying block cipher is, ECB mode can easily be attacked. On the other hand, CBC mode can be proven to be secure under the assumption that the underlying block cipher is likewise secure. Note, however, that making statements like this requires formal mathematical definitions for what it means for an encryption algorithm or a block cipher to "be secure". This section describes two common notions for what properties a block cipher should have. Each corresponds to a mathematical model that can be used to prove properties of higher-level algorithms, such as CBC.
This general approach to cryptography – proving higher-level algorithms (such as CBC) are secure under explicitly stated assumptions regarding their components (such as a block cipher) – is known as provable security.
Standard model
Informally, a block cipher is secure in the standard model if an attacker cannot tell the difference between the block cipher (equipped with a random key) and a random permutation. | Block cipher | Wikipedia | 490 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
To be a bit more precise, let E be an n-bit block cipher. We imagine the following game:
The person running the game flips a coin.
If the coin lands on heads, he chooses a random key K and defines the function f = EK.
If the coin lands on tails, he chooses a random permutation on the set of n-bit strings and defines the function f = .
The attacker chooses an n-bit string X, and the person running the game tells him the value of f(X).
Step 2 is repeated a total of q times. (Each of these q interactions is a query.)
The attacker guesses how the coin landed. He wins if his guess is correct.
The attacker, which we can model as an algorithm, is called an adversary. The function f (which the adversary was able to query) is called an oracle.
Note that an adversary can trivially ensure a 50% chance of winning simply by guessing at random (or even by, for example, always guessing "heads"). Therefore, let PE(A) denote the probability that adversary A wins this game against E, and define the advantage of A as 2(PE(A) − 1/2). It follows that if A guesses randomly, its advantage will be 0; on the other hand, if A always wins, then its advantage is 1. The block cipher E is a pseudo-random permutation (PRP) if no adversary has an advantage significantly greater than 0, given specified restrictions on q and the adversary's running time. If in Step 2 above adversaries have the option of learning f−1(X) instead of f(X) (but still have only small advantages) then E is a strong PRP (SPRP). An adversary is non-adaptive if it chooses all q values for X before the game begins (that is, it does not use any information gleaned from previous queries to choose each X as it goes). | Block cipher | Wikipedia | 411 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
These definitions have proven useful for analyzing various modes of operation. For example, one can define a similar game for measuring the security of a block cipher-based encryption algorithm, and then try to show (through a reduction argument) that the probability of an adversary winning this new game is not much more than PE(A) for some A. (The reduction typically provides limits on q and the running time of A.) Equivalently, if PE(A) is small for all relevant A, then no attacker has a significant probability of winning the new game. This formalizes the idea that the higher-level algorithm inherits the block cipher's security.
Ideal cipher model
Practical evaluation
Block ciphers may be evaluated according to multiple criteria in practice. Common factors include:
Key parameters, such as its key size and block size, both of which provide an upper bound on the security of the cipher.
The estimated security level, which is based on the confidence gained in the block cipher design after it has largely withstood major efforts in cryptanalysis over time, the design's mathematical soundness, and the existence of practical or certificational attacks.
The cipher's complexity and its suitability for implementation in hardware or software. Hardware implementations may measure the complexity in terms of gate count or energy consumption, which are important parameters for resource-constrained devices.
The cipher's performance in terms of processing throughput on various platforms, including its memory requirements.
The cost of the cipher refers to licensing requirements that may apply due to intellectual property rights.
The flexibility of the cipher includes its ability to support multiple key sizes and block lengths.
Notable block ciphers
Lucifer / DES
Lucifer is generally considered to be the first civilian block cipher, developed at IBM in the 1970s based on work done by Horst Feistel. A revised version of the algorithm was adopted as a U.S. government Federal Information Processing Standard: FIPS PUB 46 Data Encryption Standard (DES). It was chosen by the U.S. National Bureau of Standards (NBS) after a public invitation for submissions and some internal changes by NBS (and, potentially, the NSA). DES was publicly released in 1976 and has been widely used. | Block cipher | Wikipedia | 443 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
DES was designed to, among other things, resist a certain cryptanalytic attack known to the NSA and rediscovered by IBM, though unknown publicly until rediscovered again and published by Eli Biham and Adi Shamir in the late 1980s. The technique is called differential cryptanalysis and remains one of the few general attacks against block ciphers; linear cryptanalysis is another but may have been unknown even to the NSA, prior to its publication by Mitsuru Matsui. DES prompted a large amount of other work and publications in cryptography and cryptanalysis in the open community and it inspired many new cipher designs.
DES has a block size of 64 bits and a key size of 56 bits. 64-bit blocks became common in block cipher designs after DES. Key length depended on several factors, including government regulation. Many observers in the 1970s commented that the 56-bit key length used for DES was too short. As time went on, its inadequacy became apparent, especially after a special-purpose machine designed to break DES was demonstrated in 1998 by the Electronic Frontier Foundation. An extension to DES, Triple DES, triple-encrypts each block with either two independent keys (112-bit key and 80-bit security) or three independent keys (168-bit key and 112-bit security). It was widely adopted as a replacement. As of 2011, the three-key version is still considered secure, though the National Institute of Standards and Technology (NIST) standards no longer permit the use of the two-key version in new applications, due to its 80-bit security level.
IDEA
The International Data Encryption Algorithm (IDEA) is a block cipher designed by James Massey of ETH Zurich and Xuejia Lai; it was first described in 1991, as an intended replacement for DES.
IDEA operates on 64-bit blocks using a 128-bit key and consists of a series of eight identical transformations (a round) and an output transformation (the half-round). The processes for encryption and decryption are similar. IDEA derives much of its security by interleaving operations from different groups – modular addition and multiplication, and bitwise exclusive or (XOR) – which are algebraically "incompatible" in some sense. | Block cipher | Wikipedia | 451 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
The designers analysed IDEA to measure its strength against differential cryptanalysis and concluded that it is immune under certain assumptions. No successful linear or algebraic weaknesses have been reported. , the best attack which applies to all keys can break a full 8.5-round IDEA using a narrow-bicliques attack about four times faster than brute force.
RC5
RC5 is a block cipher designed by Ronald Rivest in 1994 which, unlike many other ciphers, has a variable block size (32, 64, or 128 bits), key size (0 to 2040 bits), and a number of rounds (0 to 255). The original suggested choice of parameters was a block size of 64 bits, a 128-bit key, and 12 rounds.
A key feature of RC5 is the use of data-dependent rotations; one of the goals of RC5 was to prompt the study and evaluation of such operations as a cryptographic primitive. RC5 also consists of a number of modular additions and XORs. The general structure of the algorithm is a Feistel-like a network. The encryption and decryption routines can be specified in a few lines of code. The key schedule, however, is more complex, expanding the key using an essentially one-way function with the binary expansions of both e and the golden ratio as sources of "nothing up my sleeve numbers". The tantalizing simplicity of the algorithm together with the novelty of the data-dependent rotations has made RC5 an attractive object of study for cryptanalysts.
12-round RC5 (with 64-bit blocks) is susceptible to a differential attack using 244 chosen plaintexts. 18–20 rounds are suggested as sufficient protection.
Rijndael / AES
The Rijndael cipher developed by Belgian cryptographers, Joan Daemen and Vincent Rijmen was one of the competing designs to replace DES. It won the 5-year public competition to become the AES (Advanced Encryption Standard). | Block cipher | Wikipedia | 409 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Adopted by NIST in 2001, AES has a fixed block size of 128 bits and a key size of 128, 192, or 256 bits, whereas Rijndael can be specified with block and key sizes in any multiple of 32 bits, with a minimum of 128 bits. The block size has a maximum of 256 bits, but the key size has no theoretical maximum. AES operates on a 4×4 column-major order matrix of bytes, termed the state (versions of Rijndael with a larger block size have additional columns in the state).
Blowfish
Blowfish is a block cipher, designed in 1993 by Bruce Schneier and included in a large number of cipher suites and encryption products. Blowfish has a 64-bit block size and a variable key length from 1 bit up to 448 bits. It is a 16-round Feistel cipher and uses large key-dependent S-boxes. Notable features of the design include the key-dependent S-boxes and a highly complex key schedule.
It was designed as a general-purpose algorithm, intended as an alternative to the aging DES and free of the problems and constraints associated with other algorithms. At the time Blowfish was released, many other designs were proprietary, encumbered by patents, or were commercial/government secrets. Schneier has stated that "Blowfish is unpatented, and will remain so in all countries. The algorithm is hereby placed in the public domain, and can be freely used by anyone." The same applies to Twofish, a successor algorithm from Schneier.
Generalizations
Tweakable block ciphers
M. Liskov, R. Rivest, and D. Wagner have described a generalized version of block ciphers called "tweakable" block ciphers. A tweakable block cipher accepts a second input called the tweak along with its usual plaintext or ciphertext input. The tweak, along with the key, selects the permutation computed by the cipher. If changing tweaks is sufficiently lightweight (compared with a usually fairly expensive key setup operation), then some interesting new operation modes become possible. The disk encryption theory article describes some of these modes.
Format-preserving encryption | Block cipher | Wikipedia | 461 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Block ciphers traditionally work over a binary alphabet. That is, both the input and the output are binary strings, consisting of n zeroes and ones. In some situations, however, one may wish to have a block cipher that works over some other alphabet; for example, encrypting 16-digit credit card numbers in such a way that the ciphertext is also a 16-digit number might facilitate adding an encryption layer to legacy software. This is an example of format-preserving encryption. More generally, format-preserving encryption requires a keyed permutation on some finite language. This makes format-preserving encryption schemes a natural generalization of (tweakable) block ciphers. In contrast, traditional encryption schemes, such as CBC, are not permutations because the same plaintext can encrypt multiple different ciphertexts, even when using a fixed key.
Relation to other cryptographic primitives
Block ciphers can be used to build other cryptographic primitives, such as those below. For these other primitives to be cryptographically secure, care has to be taken to build them the right way.
Stream ciphers can be built using block ciphers. OFB mode and CTR mode are block modes that turn a block cipher into a stream cipher.
Cryptographic hash functions can be built using block ciphers. See the one-way compression function for descriptions of several such methods. The methods resemble the block cipher modes of operation usually used for encryption.
Cryptographically secure pseudorandom number generators (CSPRNGs) can be built using block ciphers.
Secure pseudorandom permutations of arbitrarily sized finite sets can be constructed with block ciphers; see Format-Preserving Encryption.
A publicly known unpredictable permutation combined with key whitening is enough to construct a block cipher -- such as the single-key Even–Mansour cipher, perhaps the simplest possible provably secure block cipher.
Message authentication codes (MACs) are often built from block ciphers. CBC-MAC, OMAC, and PMAC are such MACs.
Authenticated encryption is also built from block ciphers. It means to both encrypt and MAC at the same time. That is to both provide confidentiality and authentication. CCM, EAX, GCM, and OCB are such authenticated encryption modes. | Block cipher | Wikipedia | 482 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
Just as block ciphers can be used to build hash functions, like SHA-1 and SHA-2 are based on block ciphers which are also used independently as SHACAL, hash functions can be used to build block ciphers. Examples of such block ciphers are BEAR and LION. | Block cipher | Wikipedia | 58 | 4594 | https://en.wikipedia.org/wiki/Block%20cipher | Technology | Computer security | null |
The Boeing 747 is a long-range wide-body airliner designed and manufactured by Boeing Commercial Airplanes in the United States between 1968 and 2023.
After the introduction of the 707 in October 1958, Pan Am wanted a jet times its size, to reduce its seat cost by 30%. In 1965, Joe Sutter left the 737 development program to design the 747. In April 1966, Pan Am ordered 25 Boeing 747-100 aircraft, and in late 1966, Pratt & Whitney agreed to develop the JT9D engine, a high-bypass turbofan. On September 30, 1968, the first 747 was rolled out of the custom-built Everett Plant, the world's largest building by volume. The 747's first flight took place on February 9, 1969, and the 747 was certified in December of that year. It entered service with Pan Am on January 22, 1970. The 747 was the first airplane called a "Jumbo Jet" as the first wide-body airliner.
The 747 is a four-engined jet aircraft, initially powered by Pratt & Whitney JT9D turbofan engines, then General Electric CF6 and Rolls-Royce RB211 engines for the original variants. With a ten-abreast economy seating, it typically accommodates 366 passengers in three travel classes. It has a pronounced 37.5° wing sweep, allowing a cruise speed, and its heavy weight is supported by four main landing gear legs, each with a four-wheel bogie. The partial double-deck aircraft was designed with a raised cockpit so it could be converted to a freighter airplane by installing a front cargo door, as it was initially thought that it would eventually be superseded by supersonic transports. | Boeing 747 | Wikipedia | 348 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Boeing introduced the -200 in 1971, with uprated engines for a heavier maximum takeoff weight (MTOW) of from the initial , increasing the maximum range from . It was shortened for the longer-range 747SP in 1976, and the 747-300 followed in 1983 with a stretched upper deck for up to 400 seats in three classes. The heavier 747-400 with improved RB211 and CF6 engines or the new PW4000 engine (the JT9D successor), and a two-crew glass cockpit, was introduced in 1989 and is the most common variant. After several studies, the stretched 747-8 was launched on November 14, 2005, using the General Electric GEnx engine first developed for the Boeing 787 Dreamliner (the inspiration for the -8 in the name), and was first delivered in October 2011. The 747 is the basis for several government and military variants, such as the VC-25 (Air Force One), E-4 Emergency Airborne Command Post, Shuttle Carrier Aircraft, and some experimental test aircraft such as the YAL-1 and SOFIA airborne observatory.
Initial competition came from the smaller trijet widebodies: the Lockheed L-1011 (introduced in 1972), McDonnell Douglas DC-10 (1971) and later MD-11 (1990). Airbus competed with later variants with the heaviest versions of the A340 until surpassing the 747 in size with the A380, delivered between 2007 and 2021. Freighter variants of the 747 remain popular with cargo airlines. The final 747 was delivered to Atlas Air in January 2023 after a 54-year production run, with 1,574 aircraft built.
, 64 Boeing 747s (%) have been lost in accidents and incidents, in which a total of 3,746 people have died.
Development
Background
In 1963, the United States Air Force started a series of study projects on a very large strategic transport aircraft. Although the C-141 Starlifter was being introduced, officials believed that a much larger and more capable aircraft was needed, especially to carry cargo that would not fit in any existing aircraft. These studies led to initial requirements for the CX-Heavy Logistics System (CX-HLS) in March 1964 for an aircraft with a load capacity of and a speed of Mach 0.75 (), and an unrefueled range of with a payload of . The payload bay had to be wide by high and long with access through doors at the front and rear. | Boeing 747 | Wikipedia | 505 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The desire to keep the number of engines to four required new engine designs with greatly increased power and better fuel economy. In May 1964, airframe proposals arrived from Boeing, Douglas, General Dynamics, Lockheed, and Martin Marietta; engine proposals were submitted by General Electric, Curtiss-Wright, and Pratt & Whitney. Boeing, Douglas, and Lockheed were given additional study contracts for the airframe, along with General Electric and Pratt & Whitney for the engines.
The airframe proposals shared several features. As the CX-HLS needed to be able to be loaded from the front, a door had to be included where the cockpit usually was. All of the companies solved this problem by moving the cockpit above the cargo area; Douglas had a small "pod" just forward and above the wing, Lockheed used a long "spine" running the length of the aircraft with the wing spar passing through it, while Boeing blended the two, with a longer pod that ran from just behind the nose to just behind the wing. In 1965, Lockheed's aircraft design and General Electric's engine design were selected for the new C-5 Galaxy transport, which was the largest military aircraft in the world at the time. Boeing carried the nose door and raised cockpit concepts over to the design of the 747.
Airliner proposal
The 747 was conceived while air travel was increasing in the 1960s. The era of commercial jet transportation, led by the enormous popularity of the Boeing 707 and Douglas DC-8, had revolutionized long-distance travel. In this growing jet age, Juan Trippe, president of Pan American Airways (Pan Am), one of Boeing's most important airline customers, asked for a new jet airliner times size of the 707, with a 30% lower cost per unit of passenger-distance and the capability to offer mass air travel on international routes. Trippe also thought that airport congestion could be addressed by a larger new aircraft.
In 1965, Joe Sutter was transferred from Boeing's 737 development team to manage the design studies for the new airliner, already assigned the model number 747. Sutter began a design study with Pan Am and other airlines to better understand their requirements. At the time, many thought that long-range subsonic airliners would eventually be superseded by supersonic transport aircraft. Boeing responded by designing the 747 so it could be adapted easily to carry freight and remain in production even if sales of the passenger version declined. | Boeing 747 | Wikipedia | 494 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
In April 1966, Pan Am ordered 25 Boeing 747-100 aircraft for US$525 million (equivalent to $ billion in dollars). During the ceremonial 747 contract-signing banquet in Seattle on Boeing's 50th Anniversary, Juan Trippe predicted that the 747 would be "…a great weapon for peace, competing with intercontinental missiles for mankind's destiny". As launch customer, and because of its early involvement before placing a formal order, Pan Am was able to influence the design and development of the 747 to an extent unmatched by a single airline before or since.
Design effort
Ultimately, the high-winged CX-HLS Boeing design was not used for the 747, although technologies developed for their bid had an influence. The original design included a full-length double-deck fuselage with eight-across seating and two aisles on the lower deck and seven-across seating and two aisles on the upper deck. However, concern over evacuation routes and limited cargo-carrying capability caused this idea to be scrapped in early 1966 in favor of a wider single deck design. The cockpit was therefore placed on a shortened upper deck so that a freight-loading door could be included in the nose cone; this design feature produced the 747's distinctive "hump". In early models, what to do with the small space in the pod behind the cockpit was not clear, and this was initially specified as a "lounge" area with no permanent seating. (A different configuration that had been considered to keep the flight deck out of the way for freight loading had the pilots below the passengers, and was dubbed the "anteater".)
One of the principal technologies that enabled an aircraft as large as the 747 to be drawn up was the high-bypass turbofan engine. This engine technology was thought to be capable of delivering double the power of the earlier turbojets while consuming one-third less fuel. General Electric had pioneered the concept but was committed to developing the engine for the C-5 Galaxy and did not enter the commercial market until later. Pratt & Whitney was also working on the same principle and, by late 1966, Boeing, Pan Am and Pratt & Whitney agreed to develop a new engine, designated the JT9D to power the 747. | Boeing 747 | Wikipedia | 453 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The project was designed with a new methodology called fault tree analysis, which allowed the effects of a failure of a single part to be studied to determine its impact on other systems. To address concerns about safety and flyability, the 747's design included structural redundancy, redundant hydraulic systems, quadruple main landing gear and dual control surfaces. Additionally, some of the most advanced high-lift devices used in the industry were included in the new design, to allow it to operate from existing airports. These included Krueger flaps running almost the entire length of the wing's leading edge, as well as complex three-part slotted flaps along the trailing edge of the wing. The wing's complex three-part flaps increase wing area by 21% and lift by 90% when fully deployed compared to their non-deployed configuration.
Boeing agreed to deliver the first 747 to Pan Am by the end of 1969. The delivery date left 28 months to design the aircraft, which was two-thirds of the normal time. The schedule was so fast-paced that the people who worked on it were given the nickname "The Incredibles". Developing the aircraft was such a technical and financial challenge that management was said to have "bet the company" when it started the project. Due to its massive size, Boeing subcontracted the assembly of subcomponents to other manufacturers, most notably Northrop and Grumman (later merged into Northrop Grumman in 1994) for fuselage parts and trailing edge flaps respectively, Fairchild for tailplane ailerons, and Ling-Temco-Vought (LTV) for the empennage.
Production plant
As Boeing did not have a plant large enough to assemble the giant airliner, they chose to build a new plant. The company considered locations in about 50 cities, and eventually decided to build the new plant some north of Seattle on a site adjoining a military base at Paine Field near Everett, Washington. It bought the site in June 1966. | Boeing 747 | Wikipedia | 405 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Developing the 747 had been a major challenge, and building its assembly plant was also a huge undertaking. Boeing president William M. Allen asked Malcolm T. Stamper, then head of the company's turbine division, to oversee construction of the Everett factory and to start production of the 747. To level the site, more than of earth had to be moved. Time was so short that the 747's full-scale mock-up was built before the factory roof above it was finished. The plant is the largest building by volume ever built, and has been substantially expanded several times to permit construction of other models of Boeing wide-body commercial jets.
Flight testing
Before the first 747 was fully assembled, testing began on many components and systems. One important test involved the evacuation of 560 volunteers from a cabin mock-up via the aircraft's emergency chutes. The first full-scale evacuation took two and a half minutes instead of the maximum of 90 seconds mandated by the Federal Aviation Administration (FAA), and several volunteers were injured. Subsequent test evacuations achieved the 90-second goal but caused more injuries. Most problematic was evacuation from the aircraft's upper deck; instead of using a conventional slide, volunteer passengers escaped by using a harness attached to a reel. Tests also involved taxiing such a large aircraft. Boeing built an unusual training device known as "Waddell's Wagon" (named for a 747 test pilot, Jack Waddell) that consisted of a mock-up cockpit mounted on the roof of a truck. While the first 747s were still being built, the device allowed pilots to practice taxi maneuvers from a high upper-deck position.
In 1968, the program cost was US$1 billion (equivalent to $ billion in dollars). On September 30, 1968, the first 747 was rolled out of the Everett assembly building before the world's press and representatives of the 26 airlines that had ordered the airliner. Over the following months, preparations were made for the first flight, which took place on February 9, 1969, with test pilots Jack Waddell and Brien Wygle at the controls and Jess Wallick at the flight engineer's station. Despite a minor problem with one of the flaps, the flight confirmed that the 747 handled extremely well. The 747 was found to be largely immune to "Dutch roll", a phenomenon that had been a major hazard to the early swept-wing jets.
Issues, delays and certification | Boeing 747 | Wikipedia | 494 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
During later stages of the flight test program, flutter testing showed that the wings suffered oscillation under certain conditions. This difficulty was partly solved by reducing the stiffness of some wing components. However, a particularly severe high-speed flutter problem was solved only by inserting depleted uranium counterweights as ballast in the outboard engine nacelles of the early 747s. This measure caused some concern when these aircraft crashed, for example El Al Flight 1862 at Amsterdam in 1992 with of uranium in the tailplane (horizontal stabilizer); detailed investigations showed, however, that the best estimate of the exposure to depleted uranium was ".. several orders of magnitude less than the workers' limit for chronic exposure."
The flight test program was hampered by problems with the 747's JT9D engines. Difficulties included engine stalls caused by rapid throttle movements and distortion of the turbine casings after a short period of service. The problems delayed 747 deliveries for several months; up to 20 aircraft at the Everett plant were stranded while awaiting engine installation. The program was further delayed when one of the five test aircraft suffered serious damage during a landing attempt at Renton Municipal Airport, the site of Boeing's Renton factory. The incident happened on December 13, 1969, when a test aircraft was flown to Renton to have test equipment removed and a cabin installed. Pilot Ralph C. Cokely undershot the airport's short runway and the 747's right, outer landing gear was torn off and two engine nacelles were damaged. However, these difficulties did not prevent Boeing from taking a test aircraft to the 28th Paris Air Show in mid-1969, where it was displayed to the public for the first time. Finally, in December 1969, the 747 received its FAA airworthiness certificate, clearing it for introduction into service.
The huge cost of developing the 747 and building the Everett factory meant that Boeing had to borrow heavily from a banking syndicate. During the final months before delivery of the first aircraft, the company had to repeatedly request additional funding to complete the project. Had this been refused, Boeing's survival would have been threatened. The firm's debt exceeded $2 billion, with the $1.2 billion owed to the banks setting a record for all companies. Allen later said, "It was really too large a project for us." Ultimately, the gamble succeeded, and Boeing held a monopoly in very large passenger aircraft production for many years.
Entry into service | Boeing 747 | Wikipedia | 497 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
On January 15, 1970, First Lady Pat Nixon christened Pan Am's first 747 at Dulles International Airport in the presence of Pan Am chairman Najeeb Halaby. Instead of champagne, red, white, and blue water was sprayed on the aircraft. The 747 entered service on January 22, 1970, on Pan Am's New York–London route; the flight had been planned for the evening of January 21, but engine overheating made the original aircraft (Clipper Young America, registration N735PA) unusable. Finding a substitute delayed the flight by more than six hours to the following day when Clipper Victor (registration N736PA) was used. The 747 enjoyed a fairly smooth introduction into service, overcoming concerns that some airports would not be able to accommodate an aircraft that large. Although technical problems occurred, they were relatively minor and quickly solved.
Improved 747 versions
After the initial , Boeing developed the , a higher maximum takeoff weight (MTOW) variant, and the (Short Range), with higher passenger capacity. Increased maximum takeoff weight allows aircraft to carry more fuel and have longer range. The model followed in 1971, featuring more powerful engines and a higher MTOW. Passenger, freighter and combination passenger-freighter versions of the were produced. The shortened 747SP (special performance) with a longer range was also developed, and entered service in 1976.
The 747 line was further developed with the launch of the on June 11, 1980, followed by interest from Swissair a month later and the go-ahead for the project. The 300 series resulted from Boeing studies to increase the seating capacity of the 747, during which modifications such as fuselage plugs and extending the upper deck over the entire length of the fuselage were rejected. The first , completed in 1983, included a stretched upper deck, increased cruise speed, and increased seating capacity. The -300 variant was previously designated 747SUD for stretched upper deck, then 747-200 SUD, followed by 747EUD, before the 747-300 designation was used. Passenger, short range and combination freighter-passenger versions of the 300 series were produced. | Boeing 747 | Wikipedia | 429 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
In 1985, development of the longer range 747-400 began. The variant had a new glass cockpit, which allowed for a cockpit crew of two instead of three, new engines, lighter construction materials, and a redesigned interior. Development costs soared, and production delays occurred as new technologies were incorporated at the request of airlines. Insufficient workforce experience and reliance on overtime contributed to early production problems on the . The -400 entered service in 1989.
In 1991, a record-breaking 1,087 passengers were flown in a 747 during a covert operation to airlift Ethiopian Jews to Israel. Generally, the 747-400 held between 416 and 524 passengers. The 747 remained the heaviest commercial aircraft in regular service until the debut of the Antonov An-124 Ruslan in 1982; variants of the 747-400 surpassed the An-124's weight in 2000. The Antonov An-225 Mriya cargo transport, which debuted in 1988, remains the world's largest aircraft by several measures (including the most accepted measures of maximum takeoff weight and length); one aircraft has been completed and was in service until 2022. The Scaled Composites Stratolaunch is currently the largest aircraft by wingspan.
Further developments
After the arrival of the , several stretching schemes for the 747 were proposed. Boeing announced the larger 747-500X and preliminary designs in 1996. The new variants would have cost more than US$5 billion to develop, and interest was not sufficient to launch the program. In 2000, Boeing offered the more modest 747X and 747X stretch derivatives as alternatives to the Airbus A38X. However, the 747X family was unable to attract enough interest to enter production. A year later, Boeing switched from the 747X studies to pursue the Sonic Cruiser, and after the Sonic Cruiser program was put on hold, the 787 Dreamliner. Some of the ideas developed for the 747X were used on the 747-400ER, a longer range variant of the .
After several variants were proposed but later abandoned, some industry observers became skeptical of new aircraft proposals from Boeing. However, in early 2004, Boeing announced tentative plans for the 747 Advanced that were eventually adopted. Similar in nature to the 747-X, the stretched 747 Advanced used technology from the 787 to modernize the design and its systems. The 747 remained the largest passenger airliner in service until the Airbus A380 began airline service in 2007. | Boeing 747 | Wikipedia | 487 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
On November 14, 2005, Boeing announced it was launching the 747 Advanced as the Boeing 747-8. The last 747-400s were completed in 2009. , most orders of the 747-8 were for the freighter variant. On February 8, 2010, the 747-8 Freighter made its maiden flight. The first delivery of the 747-8 went to Cargolux in 2011. The first 747-8 Intercontinental passenger variant was delivered to Lufthansa on May 5, 2012. The 1,500th Boeing 747 was delivered in June 2014 to Lufthansa.
In January 2016, Boeing stated it was reducing 747-8 production to six per year beginning in September 2016, incurring a $569 million post-tax charge against its fourth-quarter 2015 profits. At the end of 2015, the company had 20 orders outstanding. On January 29, 2016, Boeing announced that it had begun the preliminary work on the modifications to a commercial 747-8 for the next Air Force One presidential aircraft, then expected to be operational by 2020.
On July 12, 2016, Boeing announced that it had finalized an order from Volga-Dnepr Group for 20 747-8 freighters, valued at $7.58 billion (~$ in ) at list prices. Four aircraft were delivered beginning in 2012. Volga-Dnepr Group is the parent of three major Russian air-freight carriers – Volga-Dnepr Airlines, AirBridgeCargo Airlines and Atran Airlines. The new 747-8 freighters would replace AirBridgeCargo's current 747-400 aircraft and expand the airline's fleet and will be acquired through a mix of direct purchases and leasing over the next six years, Boeing said.
End of production
On July 27, 2016, in its quarterly report to the Securities and Exchange Commission, Boeing discussed the potential termination of 747 production due to insufficient demand and market for the aircraft. With a firm order backlog of 21 aircraft and a production rate of six per year, program accounting had been reduced to 1,555 aircraft. In October 2016, UPS Airlines ordered 14 -8Fs to add capacity, along with 14 options, which it took in February 2018 to increase the total to 28 -8Fs on order. The backlog then stood at 25 aircraft, though several of these were orders from airlines that no longer intended to take delivery. | Boeing 747 | Wikipedia | 478 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
On July 2, 2020, it was reported that Boeing planned to end 747 production in 2022 upon delivery of the remaining jets on order to UPS and the Volga-Dnepr Group due to low demand. On July 29, 2020, Boeing confirmed that the final 747 would be delivered in 2022 as a result of "current market dynamics and outlook" stemming from the COVID-19 pandemic, according to CEO David Calhoun. The last aircraft, a 747-8F for Atlas Air registered N863GT, rolled off the production line on December 6, 2022, and was delivered on January 31, 2023. Boeing hosted an event at the Everett factory for thousands of workers as well as industry executives to commemorate the delivery.
Design
The Boeing 747 is a large, wide-body (two-aisle) airliner with four wing-mounted engines. Its wings have a high sweep angle of 37.5° for a fast, efficient cruise speed of Mach 0.84 to 0.88, depending on the variant. The sweep also reduces the wingspan, allowing the 747 to use existing hangars. Its seating capacity is over 366 with a 3–4–3 seat arrangement (a cross section of three seats, an aisle, four seats, another aisle, and three seats) in economy class and a 2–3–2 layout in first class on the main deck. The upper deck has a 3–3 seat arrangement in economy class and a 2–2 layout in first class.
Raised above the main deck, the cockpit creates a hump. This raised cockpit allows front loading of cargo on freight variants. The upper deck behind the cockpit provides space for a lounge and/or extra seating. The "stretched upper deck" became available as an alternative on the variant and later as standard beginning on the 747-300. The upper deck was stretched more on the 747-8. The 747 cockpit roof section also has an escape hatch from which crew can exit during the events of an emergency if they cannot do so through the cabin.
The 747's maximum takeoff weight ranges from for the -100 to for the -8. Its range has increased from on the -100 to on the -8I. | Boeing 747 | Wikipedia | 448 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The 747 has redundant structures along with four redundant hydraulic systems and four main landing gears each with four wheels; these provide a good spread of support on the ground and safety in case of tire blow-outs. The main gear are redundant so that landing can be performed on two opposing landing gears if the others are not functioning properly. The 747 also has split control surfaces and was designed with sophisticated triple-slotted flaps that minimize landing speeds and allow the 747 to use standard-length runways.
For transportation of spare engines, the 747 can accommodate a non-functioning fifth-pod engine under the aircraft's port wing between the inner functioning engine and the fuselage. The fifth engine mount point was also used by Virgin Orbit's LauncherOne program to carry an orbital-class rocket to cruise altitude where it was deployed.
Operational history
After the aircraft's introduction with Pan Am in 1970, other airlines that had bought the 747 to stay competitive began to put their own 747s into service. Boeing estimated that half of the early 747 sales were to airlines desiring the aircraft's long range rather than its payload capacity. While the 747 had the lowest potential operating cost per seat, this could only be achieved when the aircraft was fully loaded; costs per seat increased rapidly as occupancy declined. A moderately loaded 747, one with only 70 percent of its seats occupied, used more than 95 percent of the fuel needed by a fully occupied 747. Nonetheless, many flag-carriers purchased the 747 due to its prestige "even if it made no sense economically" to operate. During the 1970s and 1980s, over 30 regularly scheduled 747s could often be seen at John F. Kennedy International Airport. | Boeing 747 | Wikipedia | 337 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The recession of 1969–1970, despite having been characterized as relatively mild, greatly affected Boeing. For the year and a half after September 1970, it only sold two 747s in the world, both to Irish flag carrier Aer Lingus.
No 747s were sold to any American carrier for almost three years. When economic problems in the US and other countries after the 1973 oil crisis led to reduced passenger traffic, several airlines found they did not have enough passengers to fly the 747 economically, and they replaced them with the smaller and recently introduced McDonnell Douglas DC-10 and Lockheed L-1011 TriStar trijet wide bodies (and later the 767 and Airbus A300/A310 twinjets). Having tried replacing coach seats on its 747s with piano bars in an attempt to attract more customers, American Airlines eventually relegated its 747s to cargo service and in 1983 exchanged them with Pan Am for smaller aircraft; Delta Air Lines also removed its 747s from service after several years. Later, Delta acquired 747s again in 2008 as part of its merger with Northwest Airlines, although it retired the Boeing 747-400 fleet in December 2017.
International flights bypassing traditional hub airports and landing at smaller cities became more common throughout the 1980s, thus eroding the 747's original market. Many international carriers continued to use the 747 on Pacific routes. In Japan, 747s on domestic routes were configured to carry nearly the maximum passenger capacity.
Variants
The 747-100 with a range of 4,620 nautical miles (8,556 km), was the original variant launched in 1966. The 747-200 soon followed, with its launch in 1968. The 747-300 was launched in 1980 and was followed by the in 1985. Ultimately, the 747-8 was announced in 2005. Several versions of each variant have been produced, and many of the early variants were in production simultaneously. The International Civil Aviation Organization (ICAO) classifies variants using a shortened code formed by combining the model number and the variant designator (e.g. "B741" for all -100 models).
747-100 | Boeing 747 | Wikipedia | 428 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The first 747-100s were built with six upper deck windows (three per side) to accommodate upstairs lounge areas. Later, as airlines began to use the upper deck for premium passenger seating instead of lounge space, Boeing offered an upper deck with ten windows on either side as an option. Some early -100s were retrofitted with the new configuration. The -100 was equipped with Pratt & Whitney JT9D-3A engines. No freighter version of this model was developed, but many 747-100s were converted into freighters as 747-100(SF). The first 747-100(SF) was delivered to Flying Tiger Line in 1974. A total of 168 747-100s were built; 167 were delivered to customers, while Boeing kept the prototype, City of Everett. In 1972, its unit cost was US$24M (M today).
747SR
Responding to requests from Japanese airlines for a high-capacity aircraft to serve domestic routes between major cities, Boeing developed the 747SR as a short-range version of the with lower fuel capacity and greater payload capability. With increased economy class seating, up to 498 passengers could be carried in early versions and up to 550 in later models. The 747SR had an economic design life objective of 52,000 flights during 20 years of operation, compared to 24,600 flights in 20 years for the standard 747. The initial 747SR model, the -100SR, had a strengthened body structure and landing gear to accommodate the added stress accumulated from a greater number of takeoffs and landings. Extra structural support was built into the wings, fuselage, and the landing gear along with a 20% reduction in fuel capacity.
The initial order for the -100SR – four aircraft for Japan Air Lines (JAL, later Japan Airlines) – was announced on October 30, 1972; rollout occurred on August 3, 1973, and the first flight took place on August 31, 1973. The type was certified by the FAA on September 26, 1973, with the first delivery on the same day. The -100SR entered service with JAL, the type's sole customer, on October 7, 1973, and typically operated flights within Japan. Seven -100SRs were built between 1973 and 1975, each with a MTOW and Pratt & Whitney JT9D-7A engines derated to of thrust. | Boeing 747 | Wikipedia | 480 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Following the -100SR, Boeing produced the -100BSR, a 747SR variant with increased takeoff weight capability. Debuting in 1978, the -100BSR also incorporated structural modifications for a high cycle-to-flying hour ratio; a related standard -100B model debuted in 1979. The -100BSR first flew on November 3, 1978, with first delivery to All Nippon Airways (ANA) on December 21, 1978. A total of 20 -100BSRs were produced for ANA and JAL. The -100BSR had a MTOW and was powered by the same JT9D-7A or General Electric CF6-45 engines used on the -100SR. ANA operated this variant on domestic Japanese routes with 455 or 456 seats until retiring its last aircraft in March 2006.
In 1986, two -100BSR SUD models, featuring the stretched upper deck (SUD) of the -300, were produced for JAL. The type's maiden flight occurred on February 26, 1986, with FAA certification and first delivery on March 24, 1986. JAL operated the -100BSR SUD with 563 seats on domestic routes until their retirement in the third quarter of 2006. While only two -100BSR SUDs were produced, in theory, standard -100Bs can be modified to the SUD certification. Overall, 29 Boeing 747SRs were built.
747-100B
The 747-100B model was developed from the -100SR, using its stronger airframe and landing gear design. The type had an increased fuel capacity of , allowing for a range with a typical 452-passenger payload, and an increased MTOW of was offered. The first -100B order, one aircraft for Iran Air, was announced on June 1, 1978. This version first flew on June 20, 1979, received FAA certification on August 1, 1979, and was delivered the next day. Nine -100Bs were built, one for Iran Air and eight for Saudi Arabian Airlines. Unlike the original -100, the -100B was offered with Pratt & Whitney JT9D-7A, CF6-50, or Rolls-Royce RB211-524 engines. However, only RB211-524 (Saudia) and JT9D-7A (Iran Air) engines were ordered. The last 747-100B, EP-IAM was retired by Iran Air in 2014, the last commercial operator of the 747-100 and -100B.
747SP | Boeing 747 | Wikipedia | 512 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The development of the 747SP stemmed from a joint request between Pan American World Airways and Iran Air, who were looking for a high-capacity airliner with enough range to cover Pan Am's New York–Middle Eastern routes and Iran Air's planned Tehran–New York route. The Tehran–New York route, when launched, was the longest non-stop commercial flight in the world. The 747SP is shorter than the . Fuselage sections were eliminated fore and aft of the wing, and the center section of the fuselage was redesigned to fit mating fuselage sections. The SP's flaps used a simplified single-slotted configuration. The 747SP, compared to earlier variants, had a tapering of the aft upper fuselage into the empennage, a double-hinged rudder, and longer vertical and horizontal stabilizers. Power was provided by Pratt & Whitney JT9D-7(A/F/J/FW) or Rolls-Royce RB211-524 engines.
The 747SP was granted a type certificate on February 4, 1976, and entered service with launch customers Pan Am and Iran Air that same year. The aircraft was chosen by airlines wishing to serve major airports with short runways. A total of 45 747SPs were built, with the 44th 747SP delivered on August 30, 1982. In 1987, Boeing re-opened the 747SP production line after five years to build one last 747SP for an order by the United Arab Emirates government. In addition to airline use, one 747SP was modified for the NASA/German Aerospace Center SOFIA experiment. Iran Air is the last civil operator of the type; its final 747-SP (EP-IAC) was retired in June 2016.
747-200
While the 747-100 powered by Pratt & Whitney JT9D-3A engines offered enough payload and range for medium-haul operations, it was marginal for long-haul route sectors. The demand for longer range aircraft with increased payload quickly led to the improved -200, which featured more powerful engines, increased MTOW, and greater range than the -100. A few early -200s retained the three-window configuration of the -100 on the upper deck, but most were built with a ten-window configuration on each side. The 747-200 was produced in passenger (-200B), freighter (-200F), convertible (-200C), and combi (-200M) versions. | Boeing 747 | Wikipedia | 496 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The 747-200B was the basic passenger version, with increased fuel capacity and more powerful engines; it entered service in February 1971. In its first three years of production, the -200 was equipped with Pratt & Whitney JT9D-7 engines (initially the only engine available). Range with a full passenger load started at over and increased to with later engines. Most -200Bs had an internally stretched upper deck, allowing for up to 16 passenger seats. The freighter model, the 747-200F, had a hinged nose cargo door and could be fitted with an optional side cargo door, and had a capacity of 105 tons (95.3 tonnes) and an MTOW of up to . It entered service in 1972 with Lufthansa. The convertible version, the 747-200C, could be converted between a passenger and a freighter or used in mixed configurations, and featured removable seats and a nose cargo door. The -200C could also be outfitted with an optional side cargo door on the main deck.
The combi aircraft model, the 747-200M (originally designated 747-200BC), could carry freight in the rear section of the main deck via a side cargo door. A removable partition on the main deck separated the cargo area at the rear from the passengers at the front. The -200M could carry up to 238 passengers in a three-class configuration with cargo carried on the main deck. The model was also known as the 747-200 Combi. As on the -100, a stretched upper deck (SUD) modification was later offered. A total of 10 747-200s operated by KLM were converted. Union de Transports Aériens (UTA) also had two aircraft converted.
After launching the -200 with Pratt & Whitney JT9D-7 engines, on August 1, 1972, Boeing announced that it had reached an agreement with General Electric to certify the 747 with CF6-50 series engines to increase the aircraft's market potential. Rolls-Royce followed 747 engine production with a launch order from British Airways for four aircraft. The option of RB211-524B engines was announced on June 17, 1975. The -200 was the first 747 to provide a choice of powerplant from the three major engine manufacturers.
In 1976, its unit cost was US$39M (M today). | Boeing 747 | Wikipedia | 483 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
A total of 393 of the 747-200 versions had been built when production ended in 1991. Of these, 225 were -200B, 73 were -200F, 13 were -200C, 78 were -200M, and 4 were military. Iran Air retired the last passenger in May 2016, 36 years after it was delivered. , five 747-200s remain in service as freighters.
747-300
The 747-300 features a upper deck than the -200. The stretched upper deck (SUD) has two emergency exit doors and is the most visible difference between the -300 and previous models. After being made standard on the 747-300, the SUD was offered as a retrofit, and as an option to earlier variants still in-production. An example for a retrofit were two UTA -200 Combis being converted in 1986, and an example for the option were two brand-new JAL -100 aircraft (designated -100BSR SUD), the first of which was delivered on March 24, 1986.
The 747-300 introduced a new straight stairway to the upper deck, instead of a spiral staircase on earlier variants, which creates room above and below for more seats. Minor aerodynamic changes allowed the -300's cruise speed to reach Mach 0.85 compared with Mach 0.84 on the -200 and -100 models, while retaining the same takeoff weight. The -300 could be equipped with the same Pratt & Whitney and Rolls-Royce powerplants as on the -200, as well as updated General Electric CF6-80C2B1 engines. | Boeing 747 | Wikipedia | 324 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Swissair placed the first order for the on June 11, 1980. The variant revived the 747-300 designation, which had been previously used on a design study that did not reach production. The 747-300 first flew on October 5, 1982, and the type's first delivery went to Swissair on March 23, 1983. In 1982, its unit cost was US$83M (M today). Besides the passenger model, two other versions (-300M, -300SR) were produced. The 747-300M features cargo capacity on the rear portion of the main deck, similar to the -200M, but with the stretched upper deck it can carry more passengers. The 747-300SR, a short range, high-capacity domestic model, was produced for Japanese markets with a maximum seating for 584. No production freighter version of the 747-300 was built, but Boeing began modifications of used passenger -300 models into freighters in 2000.
A total of 81 series aircraft were delivered, 56 for passenger use, 21 -300M and 4 -300SR versions. In 1985, just two years after the -300 entered service, the type was superseded by the announcement of the more advanced 747-400. The last 747-300 was delivered in September 1990 to Sabena. While some -300 customers continued operating the type, several large carriers replaced their 747-300s with 747-400s. Air France, Air India, Japan Airlines, Pakistan International Airlines, and Qantas were some of the last major carriers to operate the . On December 29, 2008, Qantas flew its last scheduled 747-300 service, operating from Melbourne to Los Angeles via Auckland. In July 2015, Pakistan International Airlines retired their final 747-300 after 30 years of service. Mahan Air was the last passenger operator of the Boeing 747-300. In 2022, their last 747-300M was leased by Emtrasur Cargo. The 747-300M was later seized by the US Department of Justice and scrapped in 2024. As of 2024, TransAVIAExport, a Belarusian cargo airline operates one Boeing 747-300F. As of 2024, a former Saudia 747-300 is used for VVIP transport, operated by the Saudi Arabian Government.
747-400 | Boeing 747 | Wikipedia | 468 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The 747-400 is an improved model with increased range. It has wingtip extensions of and winglets of , which improve the type's fuel efficiency by four percent compared to previous 747 versions. The 747-400 introduced a new glass cockpit designed for a flight crew of two instead of three, with a reduction in the number of dials, gauges and knobs from 971 to 365 through the use of electronics. The type also features tail fuel tanks, revised engines, and a new interior. The longer range has been used by some airlines to bypass traditional fuel stops, such as Anchorage. A 747-400 loaded with of fuel flying consumes an average of . Powerplants include the Pratt & Whitney PW4062, General Electric CF6-80C2, and Rolls-Royce RB211-524. As a result of the Boeing 767 development overlapping with the 747-400's development, both aircraft can use the same three powerplants and are even interchangeable between the two aircraft models.
The was offered in passenger (-400), freighter (-400F), combi (-400M), domestic (-400D), extended range passenger (-400ER), and extended range freighter (-400ERF) versions. Passenger versions retain the same upper deck as the , while the freighter version does not have an extended upper deck. The 747-400D was designed for short-range operations with maximum seating for 624. So winglets were not included though they can be retrofitted. Cruising speed is up to Mach 0.855 on different versions of the .
The passenger version first entered service in February 1989 with launch customer Northwest Airlines on the Minneapolis to Phoenix route. The combi version entered service in September 1989 with KLM, while the freighter version entered service in November 1993 with Cargolux. The 747-400ERF entered service with Air France in October 2002, while the 747-400ER entered service with Qantas, its sole customer, in November 2002. In January 2004, Boeing and Cathay Pacific launched the Boeing 747-400 Special Freighter program, later referred to as the Boeing Converted Freighter (BCF), to modify passenger 747-400s for cargo use. The first 747-400BCF was redelivered in December 2005. | Boeing 747 | Wikipedia | 473 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
In March 2007, Boeing announced that it had no plans to produce further passenger versions of the -400. However, orders for 36 -400F and -400ERF freighters were already in place at the time of the announcement. The last passenger version of the 747-400 was delivered in April 2005 to China Airlines. Some of the last built 747-400s were delivered with Dreamliner livery along with the modern Signature interior from the Boeing 777. A total of 694 of the series aircraft were delivered. At various times, the largest 747-400 operator has included Singapore Airlines, Japan Airlines, and British Airways. , 331 Boeing 747-400s were in service; there were only 10 Boeing 747-400s in passenger service as of September 2021.
747 LCF Dreamlifter
The 747-400 Dreamlifter (originally called the 747 Large Cargo Freighter or LCF) is a Boeing-designed modification of existing 747-400s into a larger outsize cargo freighter configuration to ferry 787 Dreamliner sub-assemblies. Evergreen Aviation Technologies Corporation of Taiwan was contracted to complete modifications of 747-400s into Dreamlifters in Taoyuan. The aircraft flew for the first time on September 9, 2006, in a test flight. Modification of four aircraft was completed by February 2010. The Dreamlifters have been placed into service transporting sub-assemblies for the 787 program to the Boeing plant in Everett, Washington, for final assembly. The aircraft is certified to carry only essential crew with no passengers.
747-8
Boeing announced a new 747 variant, the , on November 14, 2005. Referred to as the 747 Advanced prior to its launch, Boeing selected the designation 747-8 to show the connection with the Boeing 787 Dreamliner, as the aircraft would use technology and the General Electric GEnx engines from the 787 to modernize the design and its systems. The variant is designed to be quieter, more economical, and more environmentally friendly. The 747-8's fuselage is lengthened from to , marking the first stretch variant of the aircraft. | Boeing 747 | Wikipedia | 417 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The 747-8 Freighter, or 747-8F, has 16% more payload capacity than its predecessor, allowing it to carry seven more standard air cargo containers, with a maximum payload capacity of of cargo. As on previous 747 freighters, the 747-8F features a flip up nose-door, a side-door on the main deck, and a side-door on the lower deck ("belly") to aid loading and unloading. The 747-8F made its maiden flight on February 8, 2010. The variant received its amended type certificate jointly from the FAA and the European Aviation Safety Agency (EASA) on August 19, 2011. The -8F was first delivered to Cargolux on October 12, 2011.
The passenger version, named 747-8 Intercontinental or 747-8I, is designed to carry up to 467 passengers in a 3-class configuration and fly more than at Mach 0.855. As a derivative of the already common , the 747-8I has the economic benefit of similar training and interchangeable parts. The type's first test flight occurred on March 20, 2011. The 747-8 has surpassed the Airbus A340-600 as the world's longest airliner, a record it would hold until the 777X, which first flew in 2020. The first -8I was delivered in May 2012 to Lufthansa. The 747-8 has received 155 total orders, including 106 for the -8F and 47 for the -8I . The final 747-8F was delivered to Atlas Air on January 31, 2023, marking the end of the production of the Boeing 747 series.
Government, military, and other variants | Boeing 747 | Wikipedia | 347 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
VC-25 – This aircraft is the U.S. Air Force very important person (VIP) version of the 747-200B. The U.S. Air Force operates two of them in VIP configuration as the VC-25A. Tail numbers 28000 and 29000 are popularly known as Air Force One, which is technically the air-traffic call sign for any United States Air Force aircraft carrying the U.S. president. Partially completed aircraft from Everett, Washington, were flown to Wichita, Kansas, for final outfitting by Boeing Military Airplane Company. Two new aircraft, based around the , are being procured which will be designated as VC-25B.
E-4B – This is an airborne command post designed for use in nuclear war. Three E-4As, based on the 747-200B, with a fourth aircraft, with more powerful engines and upgraded systems delivered in 1979 as an E-4B, with the three E-4As upgraded to this standard. Formerly known as the National Emergency Airborne Command Post (referred to colloquially as "Kneecap"), this type is now referred to as the National Airborne Operations Center (NAOC).
Survivable Airborne Operations Center - In April 2024, Sierra Nevada Corporation was awarded a contract to develop and build the Survivable Airborne Operations Center aircraft to replace the Boeing E-4 NAOC. Five 747-8Is were purchased from Korean Air for conversion, with the contract calling for nine in total.
YAL-1 – This was the experimental Airborne Laser, a planned component of the U.S. National Missile Defense.
Shuttle Carrier Aircraft (SCA) – Two 747s were modified to carry the Space Shuttle orbiter. The first was a 747-100 (N905NA), and the other was a 747-100SR (N911NA). The first SCA carried the prototype Enterprise during the Approach and Landing Tests in the late 1970s. The two SCA later carried all five operational Space Shuttle orbiters.
C-33 – This aircraft was a proposed U.S. military version of the 747-400F intended to augment the C-17 fleet. The plan was canceled in favor of additional C-17s. | Boeing 747 | Wikipedia | 454 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
KC-25/33 – A proposed 747-200F was also adapted as an aerial refueling tanker and was bid against the DC-10-30 during the 1970s Advanced Cargo Transport Aircraft (ACTA) program that produced the KC-10 Extender. Before the 1979 Iranian Revolution, Iran bought four 747-100 aircraft with air-refueling boom conversions to support its fleet of F-4 Phantoms. There is a report of the Iranians using a 747 Tanker in H-3 airstrike during Iran–Iraq War. It is unknown whether these aircraft remain usable as tankers. Since then there have been proposals to use a 747-400 for that role.
747F Airlifter – Proposed US military transport version of the 747-200F intended as an alternative to further purchases of the C-5 Galaxy. This 747 would have had a special nose jack to lower the sill height for the nose door. System tested in 1980 on a Flying Tiger Line 747-200F.
747 CMCA – This "Cruise Missile Carrier Aircraft" variant was considered by the U.S. Air Force during the development of the B-1 Lancer strategic bomber. It would have been equipped with 50 to 100 AGM-86 ALCM cruise missiles on rotary launchers. This plan was abandoned in favor of more conventional strategic bombers.
MC-747 – Two separate studies from the 1970s and 2005, the first by Boeing and the second by ATK and BAE Systems, to horizontally store up to four Peacekeeper ICBMs or seven Minutemen above bomb bay-like doors in the first study, and to vertically store twelve Minutemen or 32 JDAM-equipped conventional missiles for launch from in situ tubes in the second.
747 AAC – A Boeing study under contract from the USAF for an "airborne aircraft carrier" for up to 10 Boeing Model 985-121 "microfighters" with the ability to launch, retrieve, re-arm, and refuel. Boeing believed that the scheme would be able to deliver a flexible and fast carrier platform with global reach, particularly where other bases were not available. Modified versions of the 747-200 and Lockheed C-5A were considered as the base aircraft. The concept, which included a complementary 747 AWACS version with two reconnaissance "microfighters", was considered technically feasible in 1973.
Evergreen 747 Supertanker – A Boeing 747-200 modified as an aerial application platform for fire fighting using of firefighting chemicals. | Boeing 747 | Wikipedia | 497 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Stratospheric Observatory for Infrared Astronomy (SOFIA) – A former Pan Am Boeing 747SP modified to carry a large infrared-sensitive telescope, in a joint venture of NASA and DLR. High altitudes are needed for infrared astronomy, to rise above infrared-absorbing water vapor in the atmosphere.
A number of other governments also use the 747 as a VIP transport, including Bahrain, Brunei, India, Iran, Japan, Kuwait, Oman, Pakistan, Qatar, Saudi Arabia and United Arab Emirates. Several Boeing 747-8s have been ordered by Boeing Business Jet for conversion to VIP transports for several unidentified customers. | Boeing 747 | Wikipedia | 123 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Proposed variants
Boeing has studied a number of 747 variants that have not gone beyond the concept stage.
747 trijet
During the late 1960s and early 1970s, Boeing studied the development of a shorter 747 with three engines, to compete with the smaller Lockheed L-1011 TriStar and McDonnell Douglas DC-10. The center engine would have been fitted in the tail with an S-duct intake similar to the L-1011's. Overall, the 747 trijet would have had more payload, range, and passenger capacity than either of the two other aircraft. However, engineering studies showed that a major redesign of the 747 wing would be necessary. Maintaining the same 747 handling characteristics would be important to minimize pilot retraining. Boeing decided instead to pursue a shortened four-engine 747, resulting in the 747SP.
747-500
In January 1986, Boeing outlined preliminary studies to build a larger, ultra-long haul version named the , which would enter service in the mid- to late-1990s. The aircraft derivative would use engines evolved from unducted fan (UDF) (propfan) technology by General Electric, but the engines would have shrouds, sport a bypass ratio of 15–20, and have a propfan diameter of . The aircraft would be stretched (including the upper deck section) to a capacity of 500 seats, have a new wing to reduce drag, cruise at a faster speed to reduce flight times, and have a range of at least , which would allow airlines to fly nonstop between London, England and Sydney, Australia.
747 ASB
Boeing announced the 747 ASB (Advanced Short Body) in 1986 as a response to the Airbus A340 and the McDonnell Douglas MD-11. This aircraft design would have combined the advanced technology used on the 747-400 with the foreshortened 747SP fuselage. The aircraft was to carry 295 passengers over a range of . However, airlines were not interested in the project and it was canceled later that year.
747-500X, -600X, and -700X
Boeing announced the 747-500X and -600X at the 1996 Farnborough Airshow. The proposed models would have combined the 747's fuselage with a new wing spanning derived from the 777. Other changes included adding more powerful engines and increasing the number of tires from two to four on the nose landing gear and from 16 to 20 on the main landing gear. | Boeing 747 | Wikipedia | 487 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The 747-500X concept featured a fuselage length increased by to , and the aircraft was to carry 462 passengers over a range up to , with a gross weight of over 1.0 Mlb (450 tonnes). The 747-600X concept featured a greater stretch to with seating for 548 passengers, a range of up to , and a gross weight of 1.2 Mlb (540 tonnes). A third study concept, the 747-700X, would have combined the wing of the 747-600X with a widened fuselage, allowing it to carry 650 passengers over the same range as a . The cost of the changes from previous 747 models, in particular the new wing for the 747-500X and -600X, was estimated to be more than US$5 billion. Boeing was not able to attract enough interest to launch the aircraft.
747X and 747X Stretch
As Airbus progressed with its A3XX study, Boeing offered a 747 derivative as an alternative in 2000; a more modest proposal than the previous -500X and -600X with the 747's overall wing design and a new segment at the root, increasing the span to . Power would have been supplied by either the Engine Alliance GP7172 or the Rolls-Royce Trent 600, which were also proposed for the 767-400ERX. A new flight deck based on the 777's would be used. The 747X aircraft was to carry 430 passengers over ranges of up to . The 747X Stretch would be extended to long, allowing it to carry 500 passengers over ranges of up to . Both would feature an interior based on the 777. Freighter versions of the 747X and 747X Stretch were also studied.
Like its predecessor, the 747X family was unable to garner enough interest to justify production, and it was shelved along with the 767-400ERX in March 2001, when Boeing announced the Sonic Cruiser concept. Though the 747X design was less costly than the 747-500X and -600X, it was criticized for not offering a sufficient advance from the existing . The 747X did not make it beyond the drawing board, but the 747-400X being developed concurrently moved into production to become the 747-400ER. | Boeing 747 | Wikipedia | 454 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
747-400XQLR
After the end of the 747X program, Boeing continued to study improvements that could be made to the 747. The 747-400XQLR (Quiet Long Range) was meant to have an increased range of , with improvements to boost efficiency and reduce noise. Improvements studied included raked wingtips similar to those used on the 767-400ER and a sawtooth engine nacelle for noise reduction. Although the 747-400XQLR did not move to production, many of its features were used for the 747 Advanced, which was launched as the 747-8 in 2005.
Operators
In 1979, Qantas became the first airline in the world to operate an all Boeing 747 fleet, with seventeen aircraft.
, there were 462 Boeing 747s in airline service, with Atlas Air and British Airways being the largest operators with 33 747-400s each.
The last US passenger Boeing 747 was retired from Delta Air Lines in December 2017. The model flew for almost every American major carrier since its 1970 introduction. Delta flew three of its last four aircraft on a farewell tour, from Seattle to Atlanta on December 19 then to Los Angeles and Minneapolis/St Paul on December 20.
As the IATA forecast an increase in air freight from 4% to 5% in 2018 fueled by booming trade for time-sensitive goods, from smartphones to fresh flowers, demand for freighters is strong while passenger 747s are phased out.
Of the 1,544 produced, 890 are retired; , a small subset of those which were intended to be parted-out got $3 million D-checks before flying again.
Young -400s were sold for 320 million yuan ($50 million) and Boeing stopped converting freighters, which used to cost nearly $30 million.
This comeback helped the airframer financing arm Boeing Capital to shrink its exposure to the 747-8 from $1.07 billion in 2017 to $481 million in 2018.
In July 2020, British Airways announced that it was retiring its 747 fleet. The final British Airways 747 flights departed London Heathrow on October 8, 2020.
Orders and deliveries
Boeing 747 orders and deliveries (cumulative, by year):
Orders and deliveries through to the end of February 2023.
Model summary
Accidents and incidents | Boeing 747 | Wikipedia | 459 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
, the 747 has been involved in 173 aviation accidents and incidents, including 64 hull losses (52 in-flight accidents), causing fatalities. There have been several hijackings of Boeing 747s, such as Pan Am Flight 73, a 747-100 hijacked by four terrorists, causing 20 deaths. The 747 also fell victim to three mid-air bombings, two of which resulted in fatalities and hull losses, Air India Flight 182 in 1985, and Pan Am Flight 103 in 1988.
Few crashes have been attributed to 747 design flaws. The Tenerife airport disaster resulted from pilot error and communications failure, while the Japan Air Lines Flight 123 and China Airlines Flight 611 crashes stemmed from improper aircraft repair due to a tailstrike. United Airlines Flight 811, which suffered an explosive decompression mid-flight on February 24, 1989, led the National Transportation Safety Board (NTSB) to issue a recommendation that the Boeing 747-100 and 747-200 cargo doors similar to those on the Flight 811 aircraft be modified to those featured on the Boeing . Korean Air Lines Flight 007 was shot down by a Soviet fighter aircraft in 1983 after it had strayed into Soviet territory, causing US President Ronald Reagan to authorize the then-strictly-military global positioning system (GPS) for civilian use. South African Airways Flight 295, a 747-200M Combi, which crashed on 28 November 1987 due to an inflight fire, led to the mandate of adding fire-suppression systems on board Combi variants. | Boeing 747 | Wikipedia | 308 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
The lack of adequate warning systems combined with flight crew error led to a preventable crash of Lufthansa Flight 540 in November 1974, which was the first fatal crash of a 747, while an instrument malfunction leading to disorientation of the crew led to the crash of Air India Flight 855 on New Years Day in 1978. TWA Flight 800, a 747-100 that exploded in mid-air on July 17, 1996, was probably caused due to sparking from the old and cracked electrical wires inside the fuel tank, where voltage levels exceeded the maximum limit, causing ignition of the fuel vapors inside the tank. This finding led the FAA to adopt a rule in July 2008 requiring installation of an inerting system in the center fuel tank of most large aircraft, after years of research into solutions. At the time, the new safety system was expected to cost US$100,000 to $450,000 per aircraft and weigh approximately . Two 747-200F freighters - China Airlines Flight 358 in December 1991 and El Al Flight 1862 in October 1992, crashed after the fuse pins for an engine (no. 3) broke off shortly after take-off due to metal fatigue, and instead of simply dropping away from the wing, the engine knocked off the adjacent engine and damaged the wing. Following these crashes, Boeing issued a directive to examine and replace all fuse pins found to be cracked. | Boeing 747 | Wikipedia | 286 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Other incidents did not result in any hull losses, but the planes suffered certain damages and were put back into service after repair. On July 30, 1971, Pan Am Flight 845 struck approach lighting system structures while taking off from San Francisco for Tokyo, Japan; the plane dumped fuel and landed back. The cause was pilot error with improper calculations, and the plane was repaired and returned to service. On June 24, 1982, British Airways Flight 9, a Boeing 747-200, registration G-BDXH, flew through a cloud of volcanic ash and dust from the eruption of Mount Galunggung, suffering an all engine flameout; the crew restarted the engines and successfully landed at Jakarta. The volcanic ash caused windscreens to be sandblasted along with engine damage and paint rip-off; the plane was repaired with engines replaced and returned to service. On December 11, 1994, on board Philippine Airlines Flight 434 from Manila to Tokyo via Cebu, a bomb exploded under a seat, killing one passenger; the plane landed safely at Okinawa despite damage to the plane's controls. The bomber, Ramzi Yousef, was caught on 7 February 1995 in Islamabad, Pakistan, and the plane was repaired, but converted for cargo use.
Preserved aircraft
Aircraft on display | Boeing 747 | Wikipedia | 257 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
As increasing numbers of "classic" 747-100 and series aircraft have been retired, some have been used for other uses such as museum displays. Some older 747-300s and 747-400s were later added to museum collections.
20235/001 – 747-121 registration N7470 City of Everett, the first 747 and prototype, is at the Museum of Flight, Seattle, Washington.
19651/025 – 747-121 registration N747GE at the Pima Air & Space Museum, Tucson, Arizona, US.
19778/027 – 747-151 registration N601US nose at the National Air and Space Museum, Washington, D.C.
19661/070 – 747-121(SF) registration N681UP preserved at a plaza on Jungong Road, Shanghai, China.
19896/072 – 747-132(SF) registration N481EV at the Evergreen Aviation & Space Museum, McMinnville, Oregon, US.
20107/086 – 747-123 registration N905NA, a NASA Shuttle Carrier Aircraft, at the Johnson Space Center, Houston, Texas, US.
20269/150 – 747-136 registration G-AWNG nose at Hiller Aviation Museum, San Carlos, California.
20239/160 – 747-244B registration ZS-SAN nicknamed Lebombo, at the South African Airways Museum Society, Rand Airport, Johannesburg, South Africa.
20541/200 – 747-128 registration F-BPVJ at Musée de l'Air et de l'Espace, Paris, France.
20770/213 – 747-2B5B registration HL7463 at Jeongseok Aviation Center, Jeju, South Korea.
20713/219 - 747-212B(SF) registration N482EV at the Evergreen Aviation & Space Museum, McMinnville, Oregon, US.
20825/223 - 747-200 registration SX-OAB at the site of Ellinikon International Airport, Athens, Greece. After over 20 years sitting at the closed airport, it was moved to a permanent location within the boundaries of the airport and put on display as part of the ongoing regeneration work.
21134/288 – 747SP-44 registration ZS-SPC at the South African Airways Museum Society, Rand Airport, Johannesburg, South Africa. | Boeing 747 | Wikipedia | 488 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
21549/336 – 747-206B registration PH-BUK at the Aviodrome, Lelystad, Netherlands.
21588/342 – 747-230B(M) registration D-ABYM preserved at Technik Museum Speyer, Germany.
21650/354 – 747-2R7F/SCD registration G-MKGA preserved at Cotswold Airport, UK as an event space.
22145/410 – 747-238B registration VH-EBQ at the Qantas Founders Outback Museum, Longreach, Queensland, Australia.
21942/471 – 747-212B registration N642NW nose at the Museum of Aeronautical Science in Narita, Japan, near Narita International Airport.
22455/515 – 747-256BM registration EC-DLD Lope de Vega nose at the National Museum of Science and Technology, A Coruña, Spain.
23223/606 – 747-338 registration VH-EBU at Melbourne Avalon Airport, Avalon, Victoria, Australia. VH-EBU is an ex-Qantas airframe formerly decorated in the Nalanji Dreaming livery, currently in use as a training aircraft and film set.
23719/696 – 747-451 registration N661US at the Delta Flight Museum, Atlanta, Georgia, US. This particular plane was the first in service, as well as the prototype.
24354/731 – 747-438 registration VH-OJA at Shellharbour Airport, Albion Park Rail, New South Wales, Australia.
21441/306 - SOFIA - 747SP-21 registration N747NA at Pima Air and Space Museum in Tucson, Arizona, US. Former Pan Am and United Airlines 747SP bought by NASA and converted into a flying telescope, for astronomy purposes. Named Clipper Lindbergh. | Boeing 747 | Wikipedia | 384 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
Other uses
Upon its retirement from service, the 747 which was number two in the production line was dismantled and shipped to Hopyeong, Namyangju, Gyeonggi-do, South Korea where it was re-assembled, repainted in a livery similar to that of Air Force One and converted into a restaurant. Originally flown commercially by Pan Am as N747PA, Clipper Juan T. Trippe, and repaired for service following a tailstrike, it stayed with the airline until its bankruptcy. The restaurant closed by 2009, and the aircraft was scrapped in 2010.
A former British Airways 747-200B, G-BDXJ, is parked at the Dunsfold Aerodrome in Surrey, England and has been used as a movie set for productions such as the 2006 James Bond film, Casino Royale. The airplane also appears frequently in the television series Top Gear, which is filmed at Dunsfold.
The Jumbo Stay hostel, using a converted 747-200 formerly operated by Singapore Airlines and registered as 9V-SQE, opened at Arlanda Airport, Stockholm in January 2009.
A former Pakistan International Airlines 747-300 was converted into a restaurant by Pakistan's Airports Security Force in 2017. It is located at Jinnah International Airport, Karachi.
The wings of a 747 have been repurposed as roofs of a house in Malibu, California.
In 2023, a Boeing 747-412, retired from Lion Air, was turned into a steak restaurant in Bekasi, Indonesia. The aircraft had been sitting since 2018 but the construction of the restaurant was delayed due to the COVID-19 pandemic.
Specifications
Cultural impact
Following its debut, the 747 rapidly achieved iconic status. The aircraft entered the cultural lexicon as the original Jumbo Jet, a term coined by the aviation media to describe its size, and was also nicknamed Queen of the Skies. Test pilot David P. Davies described it as "a most impressive aeroplane with a number of exceptionally fine qualities", and praised its flight control system as "truly outstanding" because of its redundancy.
Appearing in over 300 film productions, the 747 is one of the most widely depicted civilian aircraft and is considered by many as one of the most iconic in film history. It has appeared in film productions such as the disaster films Airport 1975 and Airport '77, as well as Air Force One, Die Hard 2, and Executive Decision. | Boeing 747 | Wikipedia | 490 | 4614 | https://en.wikipedia.org/wiki/Boeing%20747 | Technology | Specific aircraft_2 | null |
A black hole is a region of spacetime wherein gravity is so strong that no matter or electromagnetic energy (e.g. light) can escape it. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. A black hole has a great effect on the fate and circumstances of an object crossing it, but it has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly.
Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. In 1916, Karl Schwarzschild found the first modern solution of general relativity that would characterise a black hole. Due to his influential research, the Schwarzschild metric is named after him. David Finkelstein, in 1958, first published the interpretation of "black hole" as a region of space from which nothing can escape. Black holes were long considered a mathematical curiosity; it was not until the 1960s that theoretical work showed they were a generic prediction of general relativity. The discovery of neutron stars by Jocelyn Bell Burnell in 1967 sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality. The first black hole known was Cygnus X-1, identified by several researchers independently in 1971.
Black holes of stellar mass form when massive stars collapse at the end of their life cycle. After a black hole has formed, it can grow by absorbing mass from its surroundings. Supermassive black holes of millions of solar masses () may form by absorbing other stars and merging with other black holes, or via direct collapse of gas clouds. There is consensus that supermassive black holes exist in the centres of most galaxies. | Black hole | Wikipedia | 440 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
The presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Any matter that falls toward a black hole can form an external accretion disk heated by friction, forming quasars, some of the brightest objects in the universe. Stars passing too close to a supermassive black hole can be shredded into streamers that shine very brightly before being "swallowed." If other stars are orbiting a black hole, their orbits can be used to determine the black hole's mass and location. Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.
History
The idea of a body so big that even light could not escape was briefly proposed by English astronomical pioneer and clergyman John Michell and independently by French scientist Pierre-Simon Laplace. Both scholars proposed very large stars rather than the modern model of stars with extraordinary density.
Mitchel's idea appeared in a letter published in November 1784. Michell's simplistic calculations assumed such a body might have the same density as the Sun, and concluded that one would form when a star's diameter exceeds the Sun's by a factor of 500, and its surface escape velocity exceeds the usual speed of light. Michell correctly noted that such supermassive but non-radiating bodies might be detectable through their gravitational effects on nearby visible bodies.
In 1796, Laplace mentioned that a star could be invisible if it were sufficiently large while speculating on the origin of the Solar System in his book Exposition du Système du Monde. Franz Xaver von Zach asked Laplace for a mathematical analysis, which Laplace provided and published in journal edited by von Zach.
Scholars of the time were initially excited by the proposal that giant but invisible 'dark stars' might be hiding in plain view, but enthusiasm dampened when the wavelike nature of light became apparent in the early nineteenth century, as if light were a wave rather than a particle, it was unclear what, if any, influence gravity would have on escaping light waves.
General relativity | Black hole | Wikipedia | 469 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
In 1915, Albert Einstein developed his theory of general relativity, having earlier shown that gravity does influence light's motion. Only a few months later, Karl Schwarzschild found a solution to the Einstein field equations that describes the gravitational field of a point mass and a spherical mass. A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the same solution for the point mass and wrote more extensively about its properties. This solution had a peculiar behaviour at what is now called the Schwarzschild radius, where it became singular, meaning that some of the terms in the Einstein equations became infinite. The nature of this surface was not quite understood at the time.
In 1924, Arthur Eddington showed that the singularity disappeared after a change of coordinates. In 1933, Georges Lemaître realised that this meant the singularity at the Schwarzschild radius was a non-physical coordinate singularity. Arthur Eddington commented on the possibility of a star with mass compressed to the Schwarzschild radius in a 1926 book, noting that Einstein's theory allows us to rule out overly large densities for visible stars like Betelgeuse because "a star of 250 million km radius could not possibly have so high a density as the Sun. Firstly, the force of gravitation would be so great that light would be unable to escape from it, the rays falling back to the star like a stone to the earth. Secondly, the red shift of the spectral lines would be so great that the spectrum would be shifted out of existence. Thirdly, the mass would produce so much curvature of the spacetime metric that space would close up around the star, leaving us outside (i.e., nowhere)."
In 1931, Subrahmanyan Chandrasekhar calculated, using special relativity, that a non-rotating body of electron-degenerate matter above a certain limiting mass (now called the Chandrasekhar limit at ) has no stable solutions. His arguments were opposed by many of his contemporaries like Eddington and Lev Landau, who argued that some yet unknown mechanism would stop the collapse. They were partly correct: a white dwarf slightly more massive than the Chandrasekhar limit will collapse into a neutron star, which is itself stable. | Black hole | Wikipedia | 465 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
In 1939, Robert Oppenheimer and others predicted that neutron stars above another limit, the Tolman–Oppenheimer–Volkoff limit, would collapse further for the reasons presented by Chandrasekhar, and concluded that no law of physics was likely to intervene and stop at least some stars from collapsing to black holes. Their original calculations, based on the Pauli exclusion principle, gave it as . Subsequent consideration of neutron-neutron repulsion mediated by the strong force raised the estimate to approximately to . Observations of the neutron star merger GW170817, which is thought to have generated a black hole shortly afterward, have refined the TOV limit estimate to ~.
Oppenheimer and his co-authors interpreted the singularity at the boundary of the Schwarzschild radius as indicating that this was the boundary of a bubble in which time stopped. This is a valid point of view for external observers, but not for infalling observers. The hypothetical collapsed stars were called "frozen stars", because an outside observer would see the surface of the star frozen in time at the instant where its collapse takes it to the Schwarzschild radius.
Also in 1939, Einstein attempted to prove that black holes were impossible in his publication "On a Stationary System with Spherical Symmetry Consisting of Many Gravitating Masses", using his theory of general relativity to defend his argument. Months later, Oppenheimer and his student Hartland Snyder provided the Oppenheimer–Snyder model in their paper "On Continued Gravitational Contraction", which predicted the existence of black holes. In the paper, which made no reference to Einstein's recent publication, Oppenheimer and Snyder used Einstein's own theory of general relativity to show the conditions on how a black hole could develop, for the first time in contemporary physics.
Golden age
In 1958, David Finkelstein identified the Schwarzschild surface as an event horizon, "a perfect unidirectional membrane: causal influences can cross it in only one direction". This did not strictly contradict Oppenheimer's results, but extended them to include the point of view of infalling observers. Finkelstein's solution extended the Schwarzschild solution for the future of observers falling into a black hole. A complete extension had already been found by Martin Kruskal, who was urged to publish it. | Black hole | Wikipedia | 478 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
These results came at the beginning of the golden age of general relativity, which was marked by general relativity and black holes becoming mainstream subjects of research. This process was helped by the discovery of pulsars by Jocelyn Bell Burnell in 1967, which, by 1969, were shown to be rapidly rotating neutron stars. Until that time, neutron stars, like black holes, were regarded as just theoretical curiosities; but the discovery of pulsars showed their physical relevance and spurred a further interest in all types of compact objects that might be formed by gravitational collapse.
In this period more general black hole solutions were found. In 1963, Roy Kerr found the exact solution for a rotating black hole. Two years later, Ezra Newman found the axisymmetric solution for a black hole that is both rotating and electrically charged. Through the work of Werner Israel, Brandon Carter, and David Robinson the no-hair theorem emerged, stating that a stationary black hole solution is completely described by the three parameters of the Kerr–Newman metric: mass, angular momentum, and electric charge.
At first, it was suspected that the strange features of the black hole solutions were pathological artefacts from the symmetry conditions imposed, and that the singularities would not appear in generic situations. This view was held in particular by Vladimir Belinsky, Isaak Khalatnikov, and Evgeny Lifshitz, who tried to prove that no singularities appear in generic solutions. However, in the late 1960s Roger Penrose and Stephen Hawking used global techniques to prove that singularities appear generically. For this work, Penrose received half of the 2020 Nobel Prize in Physics, Hawking having died in 2018. Based on observations in Greenwich and Toronto in the early 1970s, Cygnus X-1, a galactic X-ray source discovered in 1964, became the first astronomical object commonly accepted to be a black hole.
Work by James Bardeen, Jacob Bekenstein, Carter, and Hawking in the early 1970s led to the formulation of black hole thermodynamics. These laws describe the behaviour of a black hole in close analogy to the laws of thermodynamics by relating mass to energy, area to entropy, and surface gravity to temperature. The analogy was completed when Hawking, in 1974, showed that quantum field theory implies that black holes should radiate like a black body with a temperature proportional to the surface gravity of the black hole, predicting the effect now known as Hawking radiation. | Black hole | Wikipedia | 499 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Observation
On 11 February 2016, the LIGO Scientific Collaboration and the Virgo collaboration announced the first direct detection of gravitational waves, representing the first observation of a black hole merger. On 10 April 2019, the first direct image of a black hole and its vicinity was published, following observations made by the Event Horizon Telescope (EHT) in 2017 of the supermassive black hole in Messier 87's galactic centre. , the nearest known body thought to be a black hole, Gaia BH1, is around away. Though only a couple dozen black holes have been found so far in the Milky Way, there are thought to be hundreds of millions, most of which are solitary and do not cause emission of radiation. Therefore, they would only be detectable by gravitational lensing.
Etymology
Science writer Marcia Bartusiak traces the term "black hole" to physicist Robert H. Dicke, who in the early 1960s reportedly compared the phenomenon to the Black Hole of Calcutta, notorious as a prison where people entered but never left alive.
The term "black hole" was used in print by Life and Science News magazines in 1963, and by science journalist Ann Ewing in her article Black Holes' in Space", dated 18 January 1964, which was a report on a meeting of the American Association for the Advancement of Science held in Cleveland, Ohio.
In December 1967, a student reportedly suggested the phrase "black hole" at a lecture by John Wheeler; Wheeler adopted the term for its brevity and "advertising value", and it quickly caught on, leading some to credit Wheeler with coining the phrase.
Properties and structure
The no-hair theorem postulates that, once it achieves a stable condition after formation, a black hole has only three independent physical properties: mass, electric charge, and angular momentum; the black hole is otherwise featureless. If the conjecture is true, any two black holes that share the same values for these properties, or parameters, are indistinguishable from one another. The degree to which the conjecture is true for real black holes under the laws of modern physics is currently an unsolved problem. | Black hole | Wikipedia | 431 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
These properties are special because they are visible from outside a black hole. For example, a charged black hole repels other like charges just like any other charged object. Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analogue of Gauss's law (through the ADM mass), far away from the black hole. Likewise, the angular momentum (or spin) can be measured from far away using frame dragging by the gravitomagnetic field, through for example the Lense–Thirring effect.
When an object falls into a black hole, any information about the shape of the object or distribution of charge on it is evenly distributed along the horizon of the black hole, and is lost to outside observers. The behaviour of the horizon in this situation is a dissipative system that is closely analogous to that of a conductive stretchy membrane with friction and electrical resistance—the membrane paradigm. This is different from other field theories such as electromagnetism, which do not have any friction or resistivity at the microscopic level, because they are time-reversible.
Because a black hole eventually achieves a stable state with only three parameters, there is no way to avoid losing information about the initial conditions: the gravitational and electric fields of a black hole give very little information about what went in. The information that is lost includes every quantity that cannot be measured far away from the black hole horizon, including approximately conserved quantum numbers such as the total baryon number and lepton number. This behaviour is so puzzling that it has been called the black hole information loss paradox.
Physical properties
The simplest static black holes have mass but neither electric charge nor angular momentum. These black holes are often referred to as Schwarzschild black holes after Karl Schwarzschild who discovered this solution in 1916. According to Birkhoff's theorem, it is the only vacuum solution that is spherically symmetric. This means there is no observable difference at a distance between the gravitational field of such a black hole and that of any other spherical object of the same mass. The popular notion of a black hole "sucking in everything" in its surroundings is therefore correct only near a black hole's horizon; far away, the external gravitational field is identical to that of any other body of the same mass. | Black hole | Wikipedia | 475 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Solutions describing more general black holes also exist. Non-rotating charged black holes are described by the Reissner–Nordström metric, while the Kerr metric describes a non-charged rotating black hole. The most general stationary black hole solution known is the Kerr–Newman metric, which describes a black hole with both charge and angular momentum.
While the mass of a black hole can take any positive value, the charge and angular momentum are constrained by the mass. The total electric charge Q and the total angular momentum J are expected to satisfy the inequality
for a black hole of mass M. Black holes with the minimum possible mass satisfying this inequality are called extremal. Solutions of Einstein's equations that violate this inequality exist, but they do not possess an event horizon. These solutions have so-called naked singularities that can be observed from the outside, and hence are deemed unphysical. The cosmic censorship hypothesis rules out the formation of such singularities, when they are created through the gravitational collapse of realistic matter. This is supported by numerical simulations.
Due to the relatively large strength of the electromagnetic force, black holes forming from the collapse of stars are expected to retain the nearly neutral charge of the star. Rotation, however, is expected to be a universal feature of compact astrophysical objects. The black-hole candidate binary X-ray source GRS 1915+105 appears to have an angular momentum near the maximum allowed value. That uncharged limit is
allowing definition of a dimensionless spin parameter such that
Black holes are commonly classified according to their mass, independent of angular momentum, J. The size of a black hole, as determined by the radius of the event horizon, or Schwarzschild radius, is proportional to the mass, M, through
where r is the Schwarzschild radius and is the mass of the Sun. For a black hole with nonzero spin or electric charge, the radius is smaller, until an extremal black hole could have an event horizon close to
Event horizon
The defining feature of a black hole is the appearance of an event horizon—a boundary in spacetime through which matter and light can pass only inward towards the mass of the black hole. Nothing, not even light, can escape from inside the event horizon. The event horizon is referred to as such because if an event occurs within the boundary, information from that event cannot reach an outside observer, making it impossible to determine whether such an event occurred. | Black hole | Wikipedia | 489 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
As predicted by general relativity, the presence of a mass deforms spacetime in such a way that the paths taken by particles bend towards the mass. At the event horizon of a black hole, this deformation becomes so strong that there are no paths that lead away from the black hole.
To a distant observer, clocks near a black hole would appear to tick more slowly than those farther away from the black hole. Due to this effect, known as gravitational time dilation, an object falling into a black hole appears to slow as it approaches the event horizon, taking an infinite amount of time to reach it. At the same time, all processes on this object slow down, from the viewpoint of a fixed outside observer, causing any light emitted by the object to appear redder and dimmer, an effect known as gravitational redshift. Eventually, the falling object fades away until it can no longer be seen. Typically this process happens very rapidly with an object disappearing from view within less than a second.
On the other hand, indestructible observers falling into a black hole do not notice any of these effects as they cross the event horizon. According to their own clocks, which appear to them to tick normally, they cross the event horizon after a finite time without noting any singular behaviour; in classical general relativity, it is impossible to determine the location of the event horizon from local observations, due to Einstein's equivalence principle.
The topology of the event horizon of a black hole at equilibrium is always spherical. For non-rotating (static) black holes the geometry of the event horizon is precisely spherical, while for rotating black holes the event horizon is oblate.
Singularity
At the centre of a black hole, as described by general relativity, may lie a gravitational singularity, a region where the spacetime curvature becomes infinite. For a non-rotating black hole, this region takes the shape of a single point; for a rotating black hole it is smeared out to form a ring singularity that lies in the plane of rotation. In both cases, the singular region has zero volume. It can also be shown that the singular region contains all the mass of the black hole solution. The singular region can thus be thought of as having infinite density. | Black hole | Wikipedia | 452 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Observers falling into a Schwarzschild black hole (i.e., non-rotating and not charged) cannot avoid being carried into the singularity once they cross the event horizon. They can prolong the experience by accelerating away to slow their descent, but only up to a limit. When they reach the singularity, they are crushed to infinite density and their mass is added to the total of the black hole. Before that happens, they will have been torn apart by the growing tidal forces in a process sometimes referred to as spaghettification or the "noodle effect".
In the case of a charged (Reissner–Nordström) or rotating (Kerr) black hole, it is possible to avoid the singularity. Extending these solutions as far as possible reveals the hypothetical possibility of exiting the black hole into a different spacetime with the black hole acting as a wormhole. The possibility of travelling to another universe is, however, only theoretical since any perturbation would destroy this possibility. It also appears to be possible to follow closed timelike curves (returning to one's own past) around the Kerr singularity, which leads to problems with causality like the grandfather paradox. It is expected that none of these peculiar effects would survive in a proper quantum treatment of rotating and charged black holes.
The appearance of singularities in general relativity is commonly perceived as signalling the breakdown of the theory. This breakdown, however, is expected; it occurs in a situation where quantum effects should describe these actions, due to the extremely high density and therefore particle interactions. To date, it has not been possible to combine quantum and gravitational effects into a single theory, although there exist attempts to formulate such a theory of quantum gravity. It is generally expected that such a theory will not feature any singularities.
Photon sphere
The photon sphere is a spherical boundary where photons that move on tangents to that sphere would be trapped in a non-stable but circular orbit around the black hole.
For non-rotating black holes, the photon sphere has a radius 1.5 times the Schwarzschild radius. Their orbits would be dynamically unstable, hence any small perturbation, such as a particle of infalling matter, would cause an instability that would grow over time, either setting the photon on an outward trajectory causing it to escape the black hole, or on an inward spiral where it would eventually cross the event horizon. | Black hole | Wikipedia | 488 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
While light can still escape from the photon sphere, any light that crosses the photon sphere on an inbound trajectory will be captured by the black hole. Hence any light that reaches an outside observer from the photon sphere must have been emitted by objects between the photon sphere and the event horizon. For a Kerr black hole the radius of the photon sphere depends on the spin parameter and on the details of the photon orbit, which can be prograde (the photon rotates in the same sense of the black hole spin) or retrograde.
Ergosphere
Rotating black holes are surrounded by a region of spacetime in which it is impossible to stand still, called the ergosphere. This is the result of a process known as frame-dragging; general relativity predicts that any rotating mass will tend to slightly "drag" along the spacetime immediately surrounding it. Any object near the rotating mass will tend to start moving in the direction of rotation. For a rotating black hole, this effect is so strong near the event horizon that an object would have to move faster than the speed of light in the opposite direction to just stand still.
The ergosphere of a black hole is a volume bounded by the black hole's event horizon and the ergosurface, which coincides with the event horizon at the poles but is at a much greater distance around the equator.
Objects and radiation can escape normally from the ergosphere. Through the Penrose process, objects can emerge from the ergosphere with more energy than they entered with. The extra energy is taken from the rotational energy of the black hole. Thereby the rotation of the black hole slows down. A variation of the Penrose process in the presence of strong magnetic fields, the Blandford–Znajek process is considered a likely mechanism for the enormous luminosity and relativistic jets of quasars and other active galactic nuclei.
Innermost stable circular orbit (ISCO) | Black hole | Wikipedia | 397 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
In Newtonian gravity, test particles can stably orbit at arbitrary distances from a central object. In general relativity, however, there exists an innermost stable circular orbit (often called the ISCO), for which any infinitesimal inward perturbations to a circular orbit will lead to spiraling into the black hole, and any outward perturbations will, depending on the energy, result in spiraling in, stably orbiting between apastron and periastron, or escaping to infinity. The location of the ISCO depends on the spin of the black hole, in the case of a Schwarzschild black hole (spin zero) is:
and decreases with increasing black hole spin for particles orbiting in the same direction as the spin.
Plunging region
The final observable region of spacetime around a black hole is called the plunging region. In this area it is no longer possible for matter to follow circular orbits or to stop a final descent into the black hole. Instead it will rapidly plunge toward the black hole close to the speed of light.
Formation and evolution
Given the bizarre character of black holes, it was long questioned whether such objects could actually exist in nature or whether they were merely pathological solutions to Einstein's equations. Einstein himself wrongly thought black holes would not form, because he held that the angular momentum of collapsing particles would stabilise their motion at some radius. This led the general relativity community to dismiss all results to the contrary for many years. However, a minority of relativists continued to contend that black holes were physical objects, and by the end of the 1960s, they had persuaded the majority of researchers in the field that there is no obstacle to the formation of an event horizon.
Penrose demonstrated that once an event horizon forms, general relativity without quantum mechanics requires that a singularity will form within. Shortly afterwards, Hawking showed that many cosmological solutions that describe the Big Bang have singularities without scalar fields or other exotic matter. The Kerr solution, the no-hair theorem, and the laws of black hole thermodynamics showed that the physical properties of black holes were simple and comprehensible, making them respectable subjects for research. Conventional black holes are formed by gravitational collapse of heavy objects such as stars, but they can also in theory be formed by other processes.
Gravitational collapse | Black hole | Wikipedia | 475 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Gravitational collapse occurs when an object's internal pressure is insufficient to resist the object's own gravity. For stars this usually occurs either because a star has too little "fuel" left to maintain its temperature through stellar nucleosynthesis, or because a star that would have been stable receives extra matter in a way that does not raise its core temperature. In either case the star's temperature is no longer high enough to prevent it from collapsing under its own weight.
The collapse may be stopped by the degeneracy pressure of the star's constituents, allowing the condensation of matter into an exotic denser state. The result is one of the various types of compact star. Which type forms depends on the mass of the remnant of the original star left if the outer layers have been blown away (for example, in a Type II supernova). The mass of the remnant, the collapsed object that survives the explosion, can be substantially less than that of the original star. Remnants exceeding are produced by stars that were over before the collapse.
If the mass of the remnant exceeds about (the Tolman–Oppenheimer–Volkoff limit), either because the original star was very heavy or because the remnant collected additional mass through accretion of matter, even the degeneracy pressure of neutrons is insufficient to stop the collapse. No known mechanism (except possibly quark degeneracy pressure) is powerful enough to stop the implosion and the object will inevitably collapse to form a black hole.
The gravitational collapse of heavy stars is assumed to be responsible for the formation of stellar mass black holes. Star formation in the early universe may have resulted in very massive stars, which upon their collapse would have produced black holes of up to . These black holes could be the seeds of the supermassive black holes found in the centres of most galaxies. It has further been suggested that massive black holes with typical masses of ~ could have formed from the direct collapse of gas clouds in the young universe. These massive objects have been proposed as the seeds that eventually formed the earliest quasars observed already at redshift . Some candidates for such objects have been found in observations of the young universe. | Black hole | Wikipedia | 446 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
While most of the energy released during gravitational collapse is emitted very quickly, an outside observer does not actually see the end of this process. Even though the collapse takes a finite amount of time from the reference frame of infalling matter, a distant observer would see the infalling material slow and halt just above the event horizon, due to gravitational time dilation. Light from the collapsing material takes longer and longer to reach the observer, with the light emitted just before the event horizon forms delayed an infinite amount of time. Thus the external observer never sees the formation of the event horizon; instead, the collapsing material seems to become dimmer and increasingly red-shifted, eventually fading away.
Primordial black holes and the Big Bang
Gravitational collapse requires great density. In the current epoch of the universe these high densities are found only in stars, but in the early universe shortly after the Big Bang densities were much greater, possibly allowing for the creation of black holes. High density alone is not enough to allow black hole formation since a uniform mass distribution will not allow the mass to bunch up. In order for primordial black holes to have formed in such a dense medium, there must have been initial density perturbations that could then grow under their own gravity. Different models for the early universe vary widely in their predictions of the scale of these fluctuations. Various models predict the creation of primordial black holes ranging in size from a Planck mass ( ≈ ≈ ) to hundreds of thousands of solar masses.
Despite the early universe being extremely dense, it did not re-collapse into a black hole during the Big Bang, since the expansion rate was greater than the attraction. Following inflation theory there was a net repulsive gravitation in the beginning until the end of inflation. Since then the Hubble flow was slowed by the energy density of the universe.
Models for the gravitational collapse of objects of relatively constant size, such as stars, do not necessarily apply in the same way to rapidly expanding space such as the Big Bang.
High-energy collisions
Gravitational collapse is not the only process that could create black holes. In principle, black holes could be formed in high-energy collisions that achieve sufficient density. As of 2002, no such events have been detected, either directly or indirectly as a deficiency of the mass balance in particle accelerator experiments. This suggests that there must be a lower limit for the mass of black holes. Theoretically, this boundary is expected to lie around the Planck mass, where quantum effects are expected to invalidate the predictions of general relativity. | Black hole | Wikipedia | 512 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
This would put the creation of black holes firmly out of reach of any high-energy process occurring on or near the Earth. However, certain developments in quantum gravity suggest that the minimum black hole mass could be much lower: some braneworld scenarios for example put the boundary as low as . This would make it conceivable for micro black holes to be created in the high-energy collisions that occur when cosmic rays hit the Earth's atmosphere, or possibly in the Large Hadron Collider at CERN. These theories are very speculative, and the creation of black holes in these processes is deemed unlikely by many specialists. Even if micro black holes could be formed, it is expected that they would evaporate in about 10 seconds, posing no threat to the Earth.
Growth
Once a black hole has formed, it can continue to grow by absorbing additional matter. Any black hole will continually absorb gas and interstellar dust from its surroundings. This growth process is one possible way through which some supermassive black holes may have been formed, although the formation of supermassive black holes is still an open field of research. A similar process has been suggested for the formation of intermediate-mass black holes found in globular clusters. Black holes can also merge with other objects such as stars or even other black holes. This is thought to have been important, especially in the early growth of supermassive black holes, which could have formed from the aggregation of many smaller objects. The process has also been proposed as the origin of some intermediate-mass black holes.
Evaporation
In 1974, Hawking predicted that black holes are not entirely black but emit small amounts of thermal radiation at a temperature ħc/(8πGMk); this effect has become known as Hawking radiation. By applying quantum field theory to a static black hole background, he determined that a black hole should emit particles that display a perfect black body spectrum. Since Hawking's publication, many others have verified the result through various approaches. If Hawking's theory of black hole radiation is correct, then black holes are expected to shrink and evaporate over time as they lose mass by the emission of photons and other particles. The temperature of this thermal spectrum (Hawking temperature) is proportional to the surface gravity of the black hole, which, for a Schwarzschild black hole, is inversely proportional to the mass. Hence, large black holes emit less radiation than small black holes. | Black hole | Wikipedia | 505 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
A stellar black hole of has a Hawking temperature of 62 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrinking. To have a Hawking temperature larger than 2.7 K (and be able to evaporate), a black hole would need a mass less than the Moon. Such a black hole would have a diameter of less than a tenth of a millimetre.
If a black hole is very small, the radiation effects are expected to become very strong. A black hole with the mass of a car would have a diameter of about 10 m and take a nanosecond to evaporate, during which time it would briefly have a luminosity of more than 200 times that of the Sun. Lower-mass black holes are expected to evaporate even faster; for example, a black hole of mass 1 TeV/c would take less than 10 seconds to evaporate completely. For such a small black hole, quantum gravity effects are expected to play an important role and could hypothetically make such a small black hole stable, although current developments in quantum gravity do not indicate this is the case.
The Hawking radiation for an astrophysical black hole is predicted to be very weak and would thus be exceedingly difficult to detect from Earth. A possible exception, however, is the burst of gamma rays emitted in the last stage of the evaporation of primordial black holes. Searches for such flashes have proven unsuccessful and provide stringent limits on the possibility of existence of low mass primordial black holes. NASA's Fermi Gamma-ray Space Telescope launched in 2008 will continue the search for these flashes.
If black holes evaporate via Hawking radiation, a solar mass black hole will evaporate (beginning once the temperature of the cosmic microwave background drops below that of the black hole) over a period of 10 years. A supermassive black hole with a mass of will evaporate in around 2×10 years. Some monster black holes in the universe are predicted to continue to grow up to perhaps during the collapse of superclusters of galaxies. Even these would evaporate over a timescale of up to 10 years. | Black hole | Wikipedia | 483 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Observational evidence
By nature, black holes do not themselves emit any electromagnetic radiation other than the hypothetical Hawking radiation, so astrophysicists searching for black holes must generally rely on indirect observations. For example, a black hole's existence can sometimes be inferred by observing its gravitational influence on its surroundings.
Direct interferometry
The Event Horizon Telescope (EHT) is an active program that directly observes the immediate environment of black holes' event horizons, such as the black hole at the centre of the Milky Way. In April 2017, EHT began observing the black hole at the centre of Messier 87. "In all, eight radio observatories on six mountains and four continents observed the galaxy in Virgo on and off for 10 days in April 2017" to provide the data yielding the image in April 2019.
After two years of data processing, EHT released the first direct image of a black hole. Specifically, the supermassive black hole that lies in the centre of the aforementioned galaxy. What is visible is not the black hole—which shows as black because of the loss of all light within this dark region. Instead, it is the gases at the edge of the event horizon, displayed as orange or red, that define the black hole.
On 12 May 2022, the EHT released the first image of Sagittarius A*, the supermassive black hole at the centre of the Milky Way galaxy. The published image displayed the same ring-like structure and circular shadow as seen in the M87* black hole, and the image was created using the same techniques as for the M87 black hole. The imaging process for Sagittarius A*, which is more than a thousand times smaller and less massive than M87*, was significantly more complex because of the instability of its surroundings. The image of Sagittarius A* was partially blurred by turbulent plasma on the way to the galactic centre, an effect which prevents resolution of the image at longer wavelengths. | Black hole | Wikipedia | 410 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
The brightening of this material in the 'bottom' half of the processed EHT image is thought to be caused by Doppler beaming, whereby material approaching the viewer at relativistic speeds is perceived as brighter than material moving away. In the case of a black hole, this phenomenon implies that the visible material is rotating at relativistic speeds (>), the only speeds at which it is possible to centrifugally balance the immense gravitational attraction of the singularity, and thereby remain in orbit above the event horizon. This configuration of bright material implies that the EHT observed M87* from a perspective catching the black hole's accretion disc nearly edge-on, as the whole system rotated clockwise.
The extreme gravitational lensing associated with black holes produces the illusion of a perspective that sees the accretion disc from above. In reality, most of the ring in the EHT image was created when the light emitted by the far side of the accretion disc bent around the black hole's gravity well and escaped, meaning that most of the possible perspectives on M87* can see the entire disc, even that directly behind the "shadow".
In 2015, the EHT detected magnetic fields just outside the event horizon of Sagittarius A* and even discerned some of their properties. The field lines that pass through the accretion disc were a complex mixture of ordered and tangled. Theoretical studies of black holes had predicted the existence of magnetic fields.
In April 2023, an image of the shadow of the Messier 87 black hole and the related high-energy jet, viewed together for the first time, was presented.
Detection of gravitational waves from merging black holes
On 14 September 2015, the LIGO gravitational wave observatory made the first-ever successful direct observation of gravitational waves. The signal was consistent with theoretical predictions for the gravitational waves produced by the merger of two black holes: one with about 36 solar masses, and the other around 29 solar masses. This observation provides the most concrete evidence for the existence of black holes to date. For instance, the gravitational wave signal suggests that the separation of the two objects before the merger was just 350 km, or roughly four times the Schwarzschild radius corresponding to the inferred masses. The objects must therefore have been extremely compact, leaving black holes as the most plausible interpretation. | Black hole | Wikipedia | 482 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
More importantly, the signal observed by LIGO also included the start of the post-merger ringdown, the signal produced as the newly formed compact object settles down to a stationary state. Arguably, the ringdown is the most direct way of observing a black hole. From the LIGO signal, it is possible to extract the frequency and damping time of the dominant mode of the ringdown. From these, it is possible to infer the mass and angular momentum of the final object, which match independent predictions from numerical simulations of the merger. The frequency and decay time of the dominant mode are determined by the geometry of the photon sphere. Hence, observation of this mode confirms the presence of a photon sphere; however, it cannot exclude possible exotic alternatives to black holes that are compact enough to have a photon sphere.
The observation also provides the first observational evidence for the existence of stellar-mass black hole binaries. Furthermore, it is the first observational evidence of stellar-mass black holes weighing 25 solar masses or more.
Since then, many more gravitational wave events have been observed.
Stars orbiting Sagittarius A*
The proper motions of stars near the centre of our own Milky Way provide strong observational evidence that these stars are orbiting a supermassive black hole. Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source Sagittarius A*. By fitting their motions to Keplerian orbits, the astronomers were able to infer, in 1998, that a object must be contained in a volume with a radius of 0.02 light-years to cause the motions of those stars.
Since then, one of the stars—called S2—has completed a full orbit. From the orbital data, astronomers were able to refine the calculations of the mass to and a radius of less than 0.002 light-years for the object causing the orbital motion of those stars. The upper limit on the object's size is still too large to test whether it is smaller than its Schwarzschild radius. Nevertheless, these observations strongly suggest that the central object is a supermassive black hole as there are no other plausible scenarios for confining so much invisible mass into such a small volume. Additionally, there is some observational evidence that this object might possess an event horizon, a feature unique to black holes.
Accretion of matter | Black hole | Wikipedia | 484 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Due to conservation of angular momentum, gas falling into the gravitational well created by a massive object will typically form a disk-like structure around the object. Artists' impressions such as the accompanying representation of a black hole with corona commonly depict the black hole as if it were a flat-space body hiding the part of the disk just behind it, but in reality gravitational lensing would greatly distort the image of the accretion disk.
Within such a disk, friction would cause angular momentum to be transported outward, allowing matter to fall farther inward, thus releasing potential energy and increasing the temperature of the gas.
When the accreting object is a neutron star or a black hole, the gas in the inner accretion disk orbits at very high speeds because of its proximity to the compact object. The resulting friction is so significant that it heats the inner disk to temperatures at which it emits vast amounts of electromagnetic radiation (mainly X-rays). These bright X-ray sources may be detected by telescopes. This process of accretion is one of the most efficient energy-producing processes known. Up to 40% of the rest mass of the accreted material can be emitted as radiation. In nuclear fusion only about 0.7% of the rest mass will be emitted as energy. In many cases, accretion disks are accompanied by relativistic jets that are emitted along the poles, which carry away much of the energy. The mechanism for the creation of these jets is currently not well understood, in part due to insufficient data.
As such, many of the universe's more energetic phenomena have been attributed to the accretion of matter on black holes. In particular, active galactic nuclei and quasars are believed to be the accretion disks of supermassive black holes. Similarly, X-ray binaries are generally accepted to be binary star systems in which one of the two stars is a compact object accreting matter from its companion. It has also been suggested that some ultraluminous X-ray sources may be the accretion disks of intermediate-mass black holes.
Stars have been observed to get torn apart by tidal forces in the immediate vicinity of supermassive black holes in galaxy nuclei, in what is known as a tidal disruption event (TDE). Some of the material from the disrupted star forms an accretion disk around the black hole, which emits observable electromagnetic radiation. | Black hole | Wikipedia | 494 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
In November 2011 the first direct observation of a quasar accretion disk around a supermassive black hole was reported.
X-ray binaries
X-ray binaries are binary star systems that emit a majority of their radiation in the X-ray part of the spectrum. These X-ray emissions are generally thought to result when one of the stars (compact object) accretes matter from another (regular) star. The presence of an ordinary star in such a system provides an opportunity for studying the central object and to determine if it might be a black hole.
If such a system emits signals that can be directly traced back to the compact object, it cannot be a black hole. The absence of such a signal does, however, not exclude the possibility that the compact object is a neutron star. By studying the companion star it is often possible to obtain the orbital parameters of the system and to obtain an estimate for the mass of the compact object. If this is much larger than the Tolman–Oppenheimer–Volkoff limit (the maximum mass a star can have without collapsing) then the object cannot be a neutron star and is generally expected to be a black hole.
The first strong candidate for a black hole, Cygnus X-1, was discovered in this way by Charles Thomas Bolton, Louise Webster, and Paul Murdin in 1972. Some doubt remained, due to the uncertainties that result from the companion star being much heavier than the candidate black hole. Currently, better candidates for black holes are found in a class of X-ray binaries called soft X-ray transients. In this class of system, the companion star is of relatively low mass allowing for more accurate estimates of the black hole mass. These systems actively emit X-rays for only several months once every 10–50 years. During the period of low X-ray emission, called quiescence, the accretion disk is extremely faint, allowing detailed observation of the companion star during this period. One of the best such candidates is V404 Cygni.
Quasi-periodic oscillations | Black hole | Wikipedia | 426 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
The X-ray emissions from accretion disks sometimes flicker at certain frequencies. These signals are called quasi-periodic oscillations and are thought to be caused by material moving along the inner edge of the accretion disk (the innermost stable circular orbit). As such their frequency is linked to the mass of the compact object. They can thus be used as an alternative way to determine the mass of candidate black holes.
Galactic nuclei
Astronomers use the term "active galaxy" to describe galaxies with unusual characteristics, such as unusual spectral line emission and very strong radio emission. Theoretical and observational studies have shown that the activity in these active galactic nuclei (AGN) may be explained by the presence of supermassive black holes, which can be millions of times more massive than stellar ones. The models of these AGN consist of a central black hole that may be millions or billions of times more massive than the Sun; a disk of interstellar gas and dust called an accretion disk; and two jets perpendicular to the accretion disk.
Although supermassive black holes are expected to be found in most AGN, only some galaxies' nuclei have been more carefully studied in attempts to both identify and measure the actual masses of the central supermassive black hole candidates. Some of the most notable galaxies with supermassive black hole candidates include the Andromeda Galaxy, M32, M87, NGC 3115, NGC 3377, NGC 4258, NGC 4889, NGC 1277, OJ 287, APM 08279+5255 and the Sombrero Galaxy.
It is now widely accepted that the centre of nearly every galaxy, not just active ones, contains a supermassive black hole. The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M–sigma relation, strongly suggests a connection between the formation of the black hole and that of the galaxy itself. | Black hole | Wikipedia | 402 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Microlensing
Another way the black hole nature of an object may be tested is through observation of effects caused by a strong gravitational field in their vicinity. One such effect is gravitational lensing: The deformation of spacetime around a massive object causes light rays to be deflected, such as light passing through an optic lens. Observations have been made of weak gravitational lensing, in which light rays are deflected by only a few arcseconds. Microlensing occurs when the sources are unresolved and the observer sees a small brightening. The turn of the millennium saw the first 3 candidate detections of black holes in this way, and in January 2022, astronomers reported the first confirmed detection of a microlensing event from an isolated black hole.
Another possibility for observing gravitational lensing by a black hole would be to observe stars orbiting the black hole. There are several candidates for such an observation in orbit around Sagittarius A*.
Alternatives
The evidence for stellar black holes strongly relies on the existence of an upper limit for the mass of a neutron star. The size of this limit heavily depends on the assumptions made about the properties of dense matter. New exotic phases of matter could push up this bound. A phase of free quarks at high density might allow the existence of dense quark stars, and some supersymmetric models predict the existence of Q stars. Some extensions of the standard model posit the existence of preons as fundamental building blocks of quarks and leptons, which could hypothetically form preon stars. These hypothetical models could potentially explain a number of observations of stellar black hole candidates. However, it can be shown from arguments in general relativity that any such object will have a maximum mass.
Since the average density of a black hole inside its Schwarzschild radius is inversely proportional to the square of its mass, supermassive black holes are much less dense than stellar black holes. The average density of a black hole is comparable to that of water. Consequently, the physics of matter forming a supermassive black hole is much better understood and the possible alternative explanations for supermassive black hole observations are much more mundane. For example, a supermassive black hole could be modelled by a large cluster of very dark objects. However, such alternatives are typically not stable enough to explain the supermassive black hole candidates. | Black hole | Wikipedia | 481 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
The evidence for the existence of stellar and supermassive black holes implies that in order for black holes not to form, general relativity must fail as a theory of gravity, perhaps due to the onset of quantum mechanical corrections. A much anticipated feature of a theory of quantum gravity is that it will not feature singularities or event horizons and thus black holes would not be real artefacts. For example, in the fuzzball model based on string theory, the individual states of a black hole solution do not generally have an event horizon or singularity, but for a classical/semiclassical observer the statistical average of such states appears just as an ordinary black hole as deduced from general relativity.
A few theoretical objects have been conjectured to match observations of astronomical black hole candidates identically or near-identically, but which function via a different mechanism. These include the gravastar, the black star, related nestar and the dark-energy star.
Open questions
Entropy and thermodynamics
In 1971, Hawking showed under general conditions that the total area of the event horizons of any collection of classical black holes can never decrease, even if they collide and merge. This result, now known as the second law of black hole mechanics, is remarkably similar to the second law of thermodynamics, which states that the total entropy of an isolated system can never decrease. As with classical objects at absolute zero temperature, it was assumed that black holes had zero entropy. If this were the case, the second law of thermodynamics would be violated by entropy-laden matter entering a black hole, resulting in a decrease in the total entropy of the universe. Therefore, Bekenstein proposed that a black hole should have an entropy, and that it should be proportional to its horizon area. | Black hole | Wikipedia | 362 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
The link with the laws of thermodynamics was further strengthened by Hawking's discovery in 1974 that quantum field theory predicts that a black hole radiates blackbody radiation at a constant temperature. This seemingly causes a violation of the second law of black hole mechanics, since the radiation will carry away energy from the black hole causing it to shrink. The radiation also carries away entropy, and it can be proven under general assumptions that the sum of the entropy of the matter surrounding a black hole and one quarter of the area of the horizon as measured in Planck units is in fact always increasing. This allows the formulation of the first law of black hole mechanics as an analogue of the first law of thermodynamics, with the mass acting as energy, the surface gravity as temperature and the area as entropy.
One puzzling feature is that the entropy of a black hole scales with its area rather than with its volume, since entropy is normally an extensive quantity that scales linearly with the volume of the system. This odd property led Gerard 't Hooft and Leonard Susskind to propose the holographic principle, which suggests that anything that happens in a volume of spacetime can be described by data on the boundary of that volume.
Although general relativity can be used to perform a semiclassical calculation of black hole entropy, this situation is theoretically unsatisfying. In statistical mechanics, entropy is understood as counting the number of microscopic configurations of a system that have the same macroscopic qualities, such as mass, charge, pressure, etc. Without a satisfactory theory of quantum gravity, one cannot perform such a computation for black holes. Some progress has been made in various approaches to quantum gravity. In 1995, Andrew Strominger and Cumrun Vafa showed that counting the microstates of a specific supersymmetric black hole in string theory reproduced the Bekenstein–Hawking entropy. Since then, similar results have been reported for different black holes both in string theory and in other approaches to quantum gravity like loop quantum gravity.
Information loss paradox | Black hole | Wikipedia | 415 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
Because a black hole has only a few internal parameters, most of the information about the matter that went into forming the black hole is lost. Regardless of the type of matter which goes into a black hole, it appears that only information concerning the total mass, charge, and angular momentum are conserved. As long as black holes were thought to persist forever this information loss is not that problematic, as the information can be thought of as existing inside the black hole, inaccessible from the outside, but represented on the event horizon in accordance with the holographic principle. However, black holes slowly evaporate by emitting Hawking radiation. This radiation does not appear to carry any additional information about the matter that formed the black hole, meaning that this information appears to be gone forever.
The question whether information is truly lost in black holes (the black hole information paradox) has divided the theoretical physics community. In quantum mechanics, loss of information corresponds to the violation of a property called unitarity, and it has been argued that loss of unitarity would also imply violation of conservation of energy, though this has also been disputed. Over recent years evidence has been building that indeed information and unitarity are preserved in a full quantum gravitational treatment of the problem.
One attempt to resolve the black hole information paradox is known as black hole complementarity. In 2012, the "firewall paradox" was introduced with the goal of demonstrating that black hole complementarity fails to solve the information paradox. According to quantum field theory in curved spacetime, a single emission of Hawking radiation involves two mutually entangled particles. The outgoing particle escapes and is emitted as a quantum of Hawking radiation; the infalling particle is swallowed by the black hole. Assume a black hole formed a finite time in the past and will fully evaporate away in some finite time in the future. Then, it will emit only a finite amount of information encoded within its Hawking radiation. According to research by physicists like Don Page and Leonard Susskind, there will eventually be a time by which an outgoing particle must be entangled with all the Hawking radiation the black hole has previously emitted. | Black hole | Wikipedia | 437 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
This seemingly creates a paradox: a principle called "monogamy of entanglement" requires that, like any quantum system, the outgoing particle cannot be fully entangled with two other systems at the same time; yet here the outgoing particle appears to be entangled both with the infalling particle and, independently, with past Hawking radiation. In order to resolve this contradiction, physicists may eventually be forced to give up one of three time-tested principles: Einstein's equivalence principle, unitarity, or local quantum field theory. One possible solution, which violates the equivalence principle, is that a "firewall" destroys incoming particles at the event horizon. In general, which—if any—of these assumptions should be abandoned remains a topic of debate.
In science fiction
Christopher Nolan's 2014 science fiction epic Interstellar features a black hole known as Gargantua, which is the central object of a planetary system in a distant galaxy. Humanity accessed this system via a wormhole in the outer solar system, near Saturn. | Black hole | Wikipedia | 210 | 4650 | https://en.wikipedia.org/wiki/Black%20hole | Physical sciences | Astronomy | null |
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino; or, conversely a proton is converted into a neutron by the emission of a positron with a neutrino in what is called positron emission. Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus prior to beta decay, but are created in the decay process. By this process, unstable atoms obtain a more stable ratio of protons to neutrons. The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy. The binding energies of all existing nuclides form what is called the nuclear band or valley of stability. For either electron or positron emission to be energetically possible, the energy release (see below) or Q value must be positive.
Beta decay is a consequence of the weak force, which is characterized by relatively long decay times. Nucleons are composed of up quarks and down quarks, and the weak force allows a quark to change its flavour by means of a virtual W boson leading to creation of an electron/antineutrino or positron/neutrino pair. For example, a neutron, composed of two down quarks and an up quark, decays to a proton composed of a down quark and two up quarks.
Electron capture is sometimes included as a type of beta decay, because the basic nuclear process, mediated by the weak force, is the same. In electron capture, an inner atomic electron is captured by a proton in the nucleus, transforming it into a neutron, and an electron neutrino is released.
Description
The two types of beta decay are known as beta minus and beta plus. In beta minus (β−) decay, a neutron is converted to a proton, and the process creates an electron and an electron antineutrino; while in beta plus (β+) decay, a proton is converted to a neutron and the process creates a positron and an electron neutrino. β+ decay is also known as positron emission. | Beta decay | Wikipedia | 494 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Beta decay conserves a quantum number known as the lepton number, or the number of electrons and their associated neutrinos (other leptons are the muon and tau particles). These particles have lepton number +1, while their antiparticles have lepton number −1. Since a proton or neutron has lepton number zero, β+ decay (a positron, or antielectron) must be accompanied with an electron neutrino, while β− decay (an electron) must be accompanied by an electron antineutrino.
An example of electron emission (β− decay) is the decay of carbon-14 into nitrogen-14 with a half-life of about 5,730 years:
→ + +
In this form of decay, the original element becomes a new chemical element in a process known as nuclear transmutation. This new element has an unchanged mass number , but an atomic number that is increased by one. As in all nuclear decays, the decaying element (in this case ) is known as the parent nuclide while the resulting element (in this case ) is known as the daughter nuclide.
Another example is the decay of hydrogen-3 (tritium) into helium-3 with a half-life of about 12.3 years:
→ + +
An example of positron emission (β+ decay) is the decay of magnesium-23 into sodium-23 with a half-life of about 11.3 s:
→ + +
β+ decay also results in nuclear transmutation, with the resulting element having an atomic number that is decreased by one.
The beta spectrum, or distribution of energy values for the beta particles, is continuous. The total energy of the decay process is divided between the electron, the antineutrino, and the recoiling nuclide. In the figure to the right, an example of an electron with 0.40 MeV energy from the beta decay of 210Bi is shown. In this example, the total decay energy is 1.16 MeV, so the antineutrino has the remaining energy: . An electron at the far right of the curve would have the maximum possible kinetic energy, leaving the energy of the neutrino to be only its small rest mass.
History | Beta decay | Wikipedia | 467 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Discovery and initial characterization
Radioactivity was discovered in 1896 by Henri Becquerel in uranium, and subsequently observed by Marie and Pierre Curie in thorium and in the new elements polonium and radium. In 1899, Ernest Rutherford separated radioactive emissions into two types: alpha and beta (now beta minus), based on penetration of objects and ability to cause ionization. Alpha rays could be stopped by thin sheets of paper or aluminium, whereas beta rays could penetrate several millimetres of aluminium. In 1900, Paul Villard identified a still more penetrating type of radiation, which Rutherford identified as a fundamentally new type in 1903 and termed gamma rays. Alpha, beta, and gamma are the first three letters of the Greek alphabet.
In 1900, Becquerel measured the mass-to-charge ratio () for beta particles by the method of J.J. Thomson used to study cathode rays and identify the electron. He found that for a beta particle is the same as for Thomson's electron, and therefore suggested that the beta particle is in fact an electron.
In 1901, Rutherford and Frederick Soddy showed that alpha and beta radioactivity involves the transmutation of atoms into atoms of other chemical elements. In 1913, after the products of more radioactive decays were known, Soddy and Kazimierz Fajans independently proposed their radioactive displacement law, which states that beta (i.e., ) emission from one element produces another element one place to the right in the periodic table, while alpha emission produces an element two places to the left.
Neutrinos | Beta decay | Wikipedia | 321 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
The study of beta decay provided the first physical evidence for the existence of the neutrino. In both alpha and gamma decay, the resulting alpha or gamma particle has a narrow energy distribution, since the particle carries the energy from the difference between the initial and final nuclear states. However, the kinetic energy distribution, or spectrum, of beta particles measured by Lise Meitner and Otto Hahn in 1911 and by Jean Danysz in 1913 showed multiple lines on a diffuse background. These measurements offered the first hint that beta particles have a continuous spectrum. In 1914, James Chadwick used a magnetic spectrometer with one of Hans Geiger's new counters to make more accurate measurements which showed that the spectrum was continuous. The results, which appeared to be in contradiction to the law of conservation of energy, were validated by means of calorimetric measurements in 1929 by Lise Meitner and Wilhelm Orthmann. If beta decay were simply electron emission as assumed at the time, then the energy of the emitted electron should have a particular, well-defined value. For beta decay, however, the observed broad distribution of energies suggested that energy is lost in the beta decay process. This spectrum was puzzling for many years.
A second problem is related to the conservation of angular momentum. Molecular band spectra showed that the nuclear spin of nitrogen-14 is 1 (i.e., equal to the reduced Planck constant) and more generally that the spin is integral for nuclei of even mass number and half-integral for nuclei of odd mass number. This was later explained by the proton-neutron model of the nucleus. Beta decay leaves the mass number unchanged, so the change of nuclear spin must be an integer. However, the electron spin is 1/2, hence angular momentum would not be conserved if beta decay were simply electron emission.
From 1920 to 1927, Charles Drummond Ellis (along with Chadwick and colleagues) further established that the beta decay spectrum is continuous. In 1933, Ellis and Nevill Mott obtained strong evidence that the beta spectrum has an effective upper bound in energy. Niels Bohr had suggested that the beta spectrum could be explained if conservation of energy was true only in a statistical sense, thus this principle might be violated in any given decay. However, the upper bound in beta energies determined by Ellis and Mott ruled out that notion. Now, the problem of how to account for the variability of energy in known beta decay products, as well as for conservation of momentum and angular momentum in the process, became acute. | Beta decay | Wikipedia | 509 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
In a famous letter written in 1930, Wolfgang Pauli attempted to resolve the beta-particle energy conundrum by suggesting that, in addition to electrons and protons, atomic nuclei also contained an extremely light neutral particle, which he called the neutron. He suggested that this "neutron" was also emitted during beta decay (thus accounting for the known missing energy, momentum, and angular momentum), but it had simply not yet been observed. In 1931, Enrico Fermi renamed Pauli's "neutron" the "neutrino" ('little neutral one' in Italian). In 1933, Fermi published his landmark theory for beta decay, where he applied the principles of quantum mechanics to matter particles, supposing that they can be created and annihilated, just as the light quanta in atomic transitions. Thus, according to Fermi, neutrinos are created in the beta-decay process, rather than contained in the nucleus; the same happens to electrons. The neutrino interaction with matter was so weak that detecting it proved a severe experimental challenge. Further indirect evidence of the existence of the neutrino was obtained by observing the recoil of nuclei that emitted such a particle after absorbing an electron. Neutrinos were finally detected directly in 1956 by the American physicists Clyde Cowan and Frederick Reines in the Cowan–Reines neutrino experiment. The properties of neutrinos were (with a few minor modifications) as predicted by Pauli and Fermi.
decay and electron capture
In 1934, Frédéric and Irène Joliot-Curie bombarded aluminium with alpha particles to effect the nuclear reaction + → + , and observed that the product isotope emits a positron identical to those found in cosmic rays (discovered by Carl David Anderson in 1932). This was the first example of decay (positron emission), which they termed artificial radioactivity since is a short-lived nuclide which does not exist in nature. In recognition of their discovery, the couple were awarded the Nobel Prize in Chemistry in 1935.
The theory of electron capture was first discussed by Gian-Carlo Wick in a 1934 paper, and then developed by Hideki Yukawa and others. K-electron capture was first observed in 1937 by Luis Alvarez, in the nuclide 48V. Alvarez went on to study electron capture in 67Ga and other nuclides. | Beta decay | Wikipedia | 487 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Non-conservation of parity
In 1956, Tsung-Dao Lee and Chen Ning Yang noticed that there was no evidence that parity was conserved in weak interactions, and so they postulated that this symmetry may not be preserved by the weak force. They sketched the design for an experiment for testing conservation of parity in the laboratory. Later that year, Chien-Shiung Wu and coworkers conducted the Wu experiment showing an asymmetrical beta decay of at cold temperatures that proved that parity is not conserved in beta decay. This surprising result overturned long-held assumptions about parity and the weak force. In recognition of their theoretical work, Lee and Yang were awarded the Nobel Prize for Physics in 1957. However Wu, who was female, was not awarded the Nobel prize.
β− decay
In decay, the weak interaction converts an atomic nucleus into a nucleus with atomic number increased by one, while emitting an electron () and an electron antineutrino (). decay generally occurs in neutron-rich nuclei. The generic equation is:
→ + +
where and are the mass number and atomic number of the decaying nucleus, and X and X′ are the initial and final elements, respectively.
Another example is when the free neutron () decays by decay into a proton ():
→ + + .
At the fundamental level (as depicted in the Feynman diagram on the right), this is caused by the conversion of the negatively charged () down quark to the positively charged () up quark promoteby by a virtual boson; the boson subsequently decays into an electron and an electron antineutrino:
→ + + .
β+ decay
In decay, or positron emission, the weak interaction converts an atomic nucleus into a nucleus with atomic number decreased by one, while emitting a positron () and an electron neutrino (). decay generally occurs in proton-rich nuclei. The generic equation is:
→ + +
This may be considered as the decay of a proton inside the nucleus to a neutron:
p → n + + | Beta decay | Wikipedia | 428 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
However, decay cannot occur in an isolated proton because it requires energy, due to the mass of the neutron being greater than the mass of the proton. decay can only happen inside nuclei when the daughter nucleus has a greater binding energy (and therefore a lower total energy) than the mother nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron, and a neutrino and into the kinetic energy of these particles. This process is opposite to negative beta decay, in that the weak interaction converts a proton into a neutron by converting an up quark into a down quark resulting in the emission of a or the absorption of a . When a boson is emitted, it decays into a positron and an electron neutrino:
→ + + .
Electron capture (K-capture/L-capture)
In all cases where decay (positron emission) of a nucleus is allowed energetically, so too is electron capture allowed. This is a process during which a nucleus captures one of its atomic electrons, resulting in the emission of a neutrino:
+ → +
An example of electron capture is one of the decay modes of krypton-81 into bromine-81:
+ → +
All emitted neutrinos are of the same energy. In proton-rich nuclei where the energy difference between the initial and final states is less than 2, decay is not energetically possible, and electron capture is the sole decay mode.
If the captured electron comes from the innermost shell of the atom, the K-shell, which has the highest probability to interact with the nucleus, the process is called K-capture. If it comes from the L-shell, the process is called L-capture, etc.
Electron capture is a competing (simultaneous) decay process for all nuclei that can undergo β+ decay. The converse, however, is not true: electron capture is the only type of decay that is allowed in proton-rich nuclides that do not have sufficient energy to emit a positron and neutrino.
Nuclear transmutation
If the proton and neutron are part of an atomic nucleus, the above described decay processes transmute one chemical element into another. For example: | Beta decay | Wikipedia | 456 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
:{|border="0"
|- style="height:2em;"
| || || ||→ || ||+ || ||+ || ||(beta minus decay)
|- style="height:2em;"
| || || ||→ || ||+ || ||+ || ||(beta plus decay)
|- style="height:2em;"
| ||+ || ||→ || ||+ || || || ||(electron capture)
|}
Beta decay does not change the number () of nucleons in the nucleus, but changes only its charge . Thus the set of all nuclides with the same can be introduced; these isobaric nuclides may turn into each other via beta decay. For a given there is one that is most stable. It is said to be beta stable, because it presents a local minimum of the mass excess: if such a nucleus has numbers, the neighbour nuclei and have higher mass excess and can beta decay into , but not vice versa. For all odd mass numbers , there is only one known beta-stable isobar. For even , there are up to three different beta-stable isobars experimentally known; for example, , , and are all beta-stable. There are about 350 known beta-decay stable nuclides. | Beta decay | Wikipedia | 294 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Competition of beta decay types
Usually unstable nuclides are clearly either "neutron rich" or "proton rich", with the former undergoing beta decay and the latter undergoing electron capture (or more rarely, due to the higher energy requirements, positron decay). However, in a few cases of odd-proton, odd-neutron radionuclides, it may be energetically favorable for the radionuclide to decay to an even-proton, even-neutron isobar either by undergoing beta-positive or beta-negative decay. An often-cited example is the single isotope (29 protons, 35 neutrons), which illustrates three types of beta decay in competition. Copper-64 has a half-life of about 12.7 hours. This isotope has one unpaired proton and one unpaired neutron, so either the proton or the neutron can decay. This particular nuclide (though not all nuclides in this situation) is almost equally likely to decay through proton decay by positron emission () or electron capture () to , as it is through neutron decay by electron emission () to .
Stability of naturally occurring nuclides
Most naturally occurring nuclides on earth are beta stable. Nuclides that are not beta stable have half-lives ranging from under a second to periods of time significantly greater than the age of the universe. One common example of a long-lived isotope is the odd-proton odd-neutron nuclide , which undergoes all three types of beta decay (, and electron capture) with a half-life of .
Conservation rules for beta decay
Baryon number is conserved
where
is the number of constituent quarks, and
is the number of constituent antiquarks.
Beta decay just changes neutron to proton or, in the case of positive beta decay (electron capture) proton to neutron so the number of individual quarks doesn't change. It is only the baryon flavor that changes, here labelled as the isospin.
Up and down quarks have total isospin and isospin projections
All other quarks have .
In general
Lepton number is conserved
so all leptons have assigned a value of +1, antileptons −1, and non-leptonic particles 0.
Angular momentum
For allowed decays, the net orbital angular momentum is zero, hence only spin quantum numbers are considered. | Beta decay | Wikipedia | 487 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
The electron and antineutrino are fermions, spin-1/2 objects, therefore they may couple to total (parallel) or (anti-parallel).
For forbidden decays, orbital angular momentum must also be taken into consideration.
Energy release
The value is defined as the total energy released in a given nuclear decay. In beta decay, is therefore also the sum of the kinetic energies of the emitted beta particle, neutrino, and recoiling nucleus. (Because of the large mass of the nucleus compared to that of the beta particle and neutrino, the kinetic energy of the recoiling nucleus can generally be neglected.) Beta particles can therefore be emitted with any kinetic energy ranging from 0 to . A typical is around 1 MeV, but can range from a few keV to a few tens of MeV.
Since the rest mass of the electron is 511 keV, the most energetic beta particles are ultrarelativistic, with speeds very close to the speed of light.
In the case of Re, the maximum speed of the beta particle is only 9.8% of the speed of light.
The following table gives some examples:
β− decay
Consider the generic equation for beta decay
→ + + .
The value for this decay is
,
where is the mass of the nucleus of the atom, is the mass of the electron, and is the mass of the electron antineutrino. In other words, the total energy released is the mass energy of the initial nucleus, minus the mass energy of the final nucleus, electron, and antineutrino. The mass of the nucleus is related to the standard atomic mass by
That is, the total atomic mass is the mass of the nucleus, plus the mass of the electrons, minus the sum of all electron binding energies for the atom. This equation is rearranged to find , and is found similarly. Substituting these nuclear masses into the -value equation, while neglecting the nearly-zero antineutrino mass and the difference in electron binding energies, which is very small for high- atoms, we have
This energy is carried away as kinetic energy by the electron and antineutrino.
Because the reaction will proceed only when the value is positive, β− decay can occur when the mass of atom is greater than the mass of atom .
β+ decay
The equations for β+ decay are similar, with the generic equation
→ + +
giving
However, in this equation, the electron masses do not cancel, and we are left with | Beta decay | Wikipedia | 508 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Because the reaction will proceed only when the value is positive, β+ decay can occur when the mass of atom exceeds that of by at least twice the mass of the electron.
Electron capture
The analogous calculation for electron capture must take into account the binding energy of the electrons. This is because the atom will be left in an excited state after capturing the electron, and the binding energy of the captured innermost electron is significant. Using the generic equation for electron capture
+ → +
we have
which simplifies to
where is the binding energy of the captured electron.
Because the binding energy of the electron is much less than the mass of the electron, nuclei that can undergo β+ decay can always also undergo electron capture, but the reverse is not true.
Beta emission spectrum
Beta decay can be considered as a perturbation as described in quantum mechanics, and thus Fermi's Golden Rule can be applied. This leads to an expression for the kinetic energy spectrum of emitted betas as follows:
where is the kinetic energy, is a shape function that depends on the forbiddenness of the decay (it is constant for allowed decays), is the Fermi Function (see below) with Z the charge of the final-state nucleus, is the total energy, is the momentum, and is the Q value of the decay. The kinetic energy of the emitted neutrino is given approximately by minus the kinetic energy of the beta.
As an example, the beta decay spectrum of 210Bi (originally called RaE) is shown to the right.
Fermi function
The Fermi function that appears in the beta spectrum formula accounts for the Coulomb attraction / repulsion between the emitted beta and the final state nucleus. Approximating the associated wavefunctions to be spherically symmetric, the Fermi function can be analytically calculated to be:
where is the final momentum, Γ the Gamma function, and (if is the fine-structure constant and the radius of the final state nucleus) , (+ for electrons, − for positrons), and .
For non-relativistic betas (), this expression can be approximated by:
Other approximations can be found in the literature.
Kurie plot | Beta decay | Wikipedia | 444 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
A Kurie plot (also known as a Fermi–Kurie plot) is a graph used in studying beta decay developed by Franz N. D. Kurie, in which the square root of the number of beta particles whose momenta (or energy) lie within a certain narrow range, divided by the Fermi function, is plotted against beta-particle energy. It is a straight line for allowed transitions and some forbidden transitions, in accord with the Fermi beta-decay theory. The energy-axis (x-axis) intercept of a Kurie plot corresponds to the maximum energy imparted to the electron/positron (the decay's value). With a Kurie plot one can find the limit on the effective mass of a neutrino.
Helicity (polarization) of neutrinos, electrons and positrons emitted in beta decay
After the discovery of parity non-conservation (see History), it was found that, in beta decay, electrons are emitted mostly with negative helicity, i.e., they move, naively speaking, like left-handed screws driven into a material (they have negative longitudinal polarization). Conversely, positrons have mostly positive helicity, i.e., they move like right-handed screws. Neutrinos (emitted in positron decay) have negative helicity, while antineutrinos (emitted in electron decay) have positive helicity.
The higher the energy of the particles, the higher their polarization.
Types of beta decay transitions
Beta decays can be classified according to the angular momentum ( value) and total spin ( value) of the emitted radiation. Since total angular momentum must be conserved, including orbital and spin angular momentum, beta decay occurs by a variety of quantum state transitions to various nuclear angular momentum or spin states, known as "Fermi" or "Gamow–Teller" transitions. When beta decay particles carry no angular momentum (), the decay is referred to as "allowed", otherwise it is "forbidden".
Other decay modes, which are rare, are known as bound state decay and double beta decay. | Beta decay | Wikipedia | 445 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Fermi transitions
A Fermi transition is a beta decay in which the spins of the emitted electron (positron) and anti-neutrino (neutrino) couple to total spin , leading to an angular momentum change between the initial and final states of the nucleus (assuming an allowed transition). In the non-relativistic limit, the nuclear part of the operator for a Fermi transition is given by
with the weak vector coupling constant, the isospin raising and lowering operators, and running over all protons and neutrons in the nucleus.
Gamow–Teller transitions
A Gamow–Teller transition is a beta decay in which the spins of the emitted electron (positron) and anti-neutrino (neutrino) couple to total spin , leading to an angular momentum change between the initial and final states of the nucleus (assuming an allowed transition).
In this case, the nuclear part of the operator is given by
with the weak axial-vector coupling constant, and the spin Pauli matrices, which can produce a spin-flip in the decaying nucleon.
Forbidden transitions
When , the decay is referred to as "forbidden". Nuclear selection rules require high values to be accompanied by changes in nuclear spin () and parity (). The selection rules for the th forbidden transitions are:
where corresponds to no parity change or parity change, respectively. The special case of a transition between isobaric analogue states, where the structure of the final state is very similar to the structure of the initial state, is referred to as "superallowed" for beta decay, and proceeds very quickly. The following table lists the Δ and Δ values for the first few values of :
Rare decay modes
Bound-state β decay
A very small minority of free neutron decays (about four per million) are "two-body decays": the proton, electron and antineutrino are produced, but the electron fails to gain the 13.6 eV energy necessary to escape the proton, and therefore simply remains bound to it, as a neutral hydrogen atom. In this type of beta decay, in essence all of the neutron decay energy is carried off by the antineutrino. | Beta decay | Wikipedia | 453 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
For fully ionized atoms (bare nuclei), it is possible in likewise manner for electrons to fail to escape the atom, and to be emitted from the nucleus into low-lying atomic bound states (orbitals). This cannot occur for neutral atoms with low-lying bound states which are already filled by electrons.
Bound-state β decays were predicted by Daudel, Jean, and Lecoin in 1947, and the phenomenon in fully ionized atoms was first observed for Dy in 1992 by Jung et al. of the Darmstadt Heavy-Ion Research Center. Though neutral Dy is stable, fully ionized Dy undergoes β decay into the K and L shells with a half-life of 47 days. The resulting nucleus – Ho – is stable only in this almost fully ionized state and will decay via electron capture into Dy in the neutral state. Likewise, while being stable in the neutral state, the fully ionized Tl undergoes bound-state β decay to Pb with a half-life of days. The half-lives of neutral Ho and Pb are respectively 4570 years and years. In addition, it is estimated that β decay is energetically impossible for natural atoms but theoretically possible when fully ionized also for 193Ir, 194Au, 202Tl, 215At, 243Am, and 246Bk.
Another possibility is that a fully ionized atom undergoes greatly accelerated β decay, as observed for Re by Bosch et al., also at Darmstadt. Neutral Re does undergo β decay, with half-life years, but for fully ionized Re this is shortened to only 32.9 years. This is because Re is energetically allowed to undergo β decay to the first-excited state in Os, a process energetically disallowed for natural Re. Similarly, neutral Pu undergoes β decay with a half-life of 14.3 years, but in its fully ionized state the beta-decay half-life of Pu decreases to 4.2 days. For comparison, the variation of decay rates of other nuclear processes due to chemical environment is less than 1%. Moreover, current mass determinations cannot decisively determine whether Rn is energetically possible to undergo β decay (the decay energy given in AME2020 is (−6 ± 8) keV), but in either case it is predicted that β will be greatly accelerated for fully ionized Rn.
Double beta decay | Beta decay | Wikipedia | 488 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Some nuclei can undergo double beta decay (2β) where the charge of the nucleus changes by two units. Double beta decay is difficult to study, as it has an extremely long half-life. In nuclei for which both β decay and 2β are possible, the rarer 2β process is effectively impossible to observe. However, in nuclei where β decay is forbidden but 2β is allowed, the process can be seen and a half-life measured. Thus, 2β is usually studied only for beta stable nuclei. Like single beta decay, double beta decay does not change ; thus, at least one of the nuclides with some given has to be stable with regard to both single and double beta decay.
"Ordinary" 2β results in the emission of two electrons and two antineutrinos. If neutrinos are Majorana particles (i.e., they are their own antiparticles), then a decay known as neutrinoless double beta decay will occur. Most neutrino physicists believe that neutrinoless 2β has never been observed. | Beta decay | Wikipedia | 223 | 4651 | https://en.wikipedia.org/wiki/Beta%20decay | Physical sciences | Nuclear physics | Physics |
Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyletic lineage within the superfamily Apoidea. They are currently considered a clade, called Anthophila. There are over 20,000 known species of bees in seven recognized biological families. Some speciesincluding honey bees, bumblebees, and stingless beeslive socially in colonies while most species (>90%)including mason bees, carpenter bees, leafcutter bees, and sweat beesare solitary.
Bees are found on every continent except Antarctica, in every habitat on the planet that contains insect-pollinated flowering plants. The most common bees in the Northern Hemisphere are the Halictidae, or sweat bees, but they are small and often mistaken for wasps or flies. Bees range in size from tiny stingless bee species, whose workers are less than long, to the leafcutter bee Megachile pluto, the largest species of bee, whose females can attain a length of .
Bees feed on nectar and pollen, the former primarily as an energy source and the latter primarily for protein and other nutrients. Most pollen is used as food for their larvae. Vertebrate predators of bees include primates and birds such as bee-eaters; insect predators include beewolves and dragonflies.
Bee pollination is important both ecologically and commercially, and the decline in wild bees has increased the value of pollination by commercially managed hives of honey bees. The analysis of 353 wild bee and hoverfly species across Britain from 1980 to 2013 found the insects have been lost from a quarter of the places they inhabited in 1980.
Human beekeeping or apiculture (meliponiculture for stingless bees) has been practiced for millennia, since at least the times of Ancient Egypt and Ancient Greece. Bees have appeared in mythology and folklore, through all phases of art and literature from ancient times to the present day, although primarily focused in the Northern Hemisphere where beekeeping is far more common. In Mesoamerica, the Mayans have practiced large-scale intensive meliponiculture since pre-Columbian times. | Bee | Wikipedia | 457 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Evolution
The immediate ancestors of bees were stinging wasps in the family Crabronidae, which were predators of other insects. The switch from insect prey to pollen may have resulted from the consumption of prey insects which were flower visitors and were partially covered with pollen when they were fed to the wasp larvae. This same evolutionary scenario may have occurred within the vespoid wasps, where the pollen wasps evolved from predatory ancestors.
Based on phylogenetic analysis, bees are thought to have originated during the Early Cretaceous (about 124 million years ago) on the supercontinent of West Gondwana, just prior to its breakup into South America and Africa. The supercontinent is thought to have been a largely xeric environment at this time; modern bee diversity hotspots are also in xeric and seasonal temperate environments, suggesting strong niche conservatism among bees ever since their origins.
Genomic analysis indicates that despite only appearing much later in the fossil record, all modern bee families had already diverged from one another by the end of the Cretaceous. The Melittidae, Apidae, and Megachilidae had already evolved on the supercontinent prior to its fragmentation. Further divergences were facilitated by West Gondwana's breakup around 100 million years ago, leading to a deep Africa-South America split within both the Apidae and Megachilidae, the isolation of the Melittidae in Africa, and the origins of the Colletidae, Andrenidae and Halictidae in South America. The rapid radiation of the South American bee families is thought to have followed the concurrent radiation of flowering plants in the same region. Later in the Cretaceous (80 million years ago), colletid bees colonized Australia from South America (with an offshoot lineage evolving into the Stenotritidae), and by the end of the Cretaceous, South American bees had also colonized North America. The North American fossil taxon Cretotrigona belongs to a group that is no longer found in North America, suggesting that many bee lineages went extinct during the Cretaceous-Paleogene extinction event. | Bee | Wikipedia | 422 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Following the K-Pg extinction, surviving bee lineages continued to spread into the Northern Hemisphere, colonizing Europe from Africa by the Paleocene, and then spreading east to Asia. This was facilitated by the warming climate around the same time, allowing bees to move to higher latitudes following the spread of tropical and subtropical habitats. By the Eocene (~45 mya) there was already considerable diversity among eusocial bee lineages. A second extinction event among bees is thought to have occurred due to rapid climatic cooling around the Eocene-Oligocene boundary, leading to the extinction of some bee lineages such as the tribe Melikertini. Over the Paleogene and Neogene, different bee lineages continued to spread all over the world, and the shifting habitats and connectedness of continents led to the isolation and evolution of many new bee tribes.
Fossils
The oldest non-compression bee fossil is Cretotrigona prisca, a corbiculate bee of Late Cretaceous age (~70 mya) found in New Jersey amber. A fossil from the early Cretaceous (~100 mya), Melittosphex burmensis, was initially considered "an extinct lineage of pollen-collecting Apoidea sister to the modern bees", but subsequent research has rejected the claim that Melittosphex is a bee, or even a member of the superfamily Apoidea to which bees belong, instead treating the lineage as incertae sedis within the Aculeata.
The Allodapini (within the Apidae) appeared around 53 Mya.
The Colletidae appear as fossils only from the late Oligocene (~25 Mya) to early Miocene.
The Melittidae are known from Palaeomacropis eocenicus in the Early Eocene.
The Megachilidae are known from trace fossils (characteristic leaf cuttings) from the Middle Eocene.
The Andrenidae are known from the Eocene-Oligocene boundary, around 34 Mya, of the Florissant shale.
The Halictidae first appear in the Early Eocene with species found in amber. The Stenotritidae are known from fossil brood cells of Pleistocene age.
Coevolution | Bee | Wikipedia | 452 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
The earliest animal-pollinated flowers were shallow, cup-shaped blooms pollinated by insects such as beetles, so the syndrome of insect pollination was well established before the first appearance of bees. The novelty is that bees are specialized as pollination agents, with behavioral and physical modifications that specifically enhance pollination, and are the most efficient pollinating insects. In a process of coevolution, flowers developed floral rewards such as nectar and longer tubes, and bees developed longer tongues to extract the nectar. Bees also developed structures known as scopal hairs and pollen baskets to collect and carry pollen. The location and type differ among and between groups of bees. Most species have scopal hairs on their hind legs or on the underside of their abdomens. Some species in the family Apidae have pollen baskets on their hind legs, while very few lack these and instead collect pollen in their crops. The appearance of these structures drove the adaptive radiation of the angiosperms, and, in turn, bees themselves. Bees coevolved not only with flowers but it is believed that some species coevolved with mites. Some provide tufts of hairs called acarinaria that appear to provide lodgings for mites; in return, it is believed that mites eat fungi that attack pollen, so the relationship in this case may be mutualistic.
Phylogeny
External
Molecular phylogeny was used by Debevic et al, 2012, to demonstrate that the bees (Anthophila) arose from deep within the Crabronidae sensu lato, which was thus rendered paraphyletic. In their study, the placement of the monogeneric Heterogynaidae was uncertain. The small family Mellinidae was not included in this analysis.
Further studies by Sann et al., 2018, elevated the subfamilies (plus one tribe and one subtribe) of Crabronidae sensu lato to family status. They also recovered the placement of Heterogyna within Nyssonini and sunk Heterogynaidae. The newly erected family, Ammoplanidae, formerly a subtribe of Pemphredoninae, was recovered as the most sister family to bees.
Internal
This cladogram of the bee families is based on Hedtke et al., 2013, which places the former families Dasypodaidae and Meganomiidae as subfamilies inside the Melittidae. English names, where available, are given in parentheses.
Characteristics | Bee | Wikipedia | 507 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Bees differ from closely related groups such as wasps by having branched or plume-like setae (hairs), combs on the forelimbs for cleaning their antennae, small anatomical differences in limb structure, and the venation of the hind wings; and in females, by having the seventh dorsal abdominal plate divided into two half-plates.
Bees have the following characteristics:
A pair of large compound eyes which cover much of the surface of the head. Between and above these are three small simple eyes (ocelli) which provide information on light intensity.
The antennae usually have 13 segments in males and 12 in females, and are geniculate, having an elbow joint part way along. They house large numbers of sense organs that can detect touch (mechanoreceptors), smell and taste; and small, hairlike mechanoreceptors that can detect air movement so as to "hear" sounds.
The mouthparts are adapted for both chewing and sucking by having both a pair of mandibles and a long proboscis for sucking up nectar.
The thorax has three segments, each with a pair of robust legs, and a pair of membranous wings on the hind two segments. The front legs of corbiculate bees bear combs for cleaning the antennae, and in many species the hind legs bear pollen baskets, flattened sections with incurving hairs to secure the collected pollen. The wings are synchronized in flight, and the somewhat smaller hind wings connect to the forewings by a row of hooks along their margin which connect to a groove in the forewing.
The abdomen has nine segments, the hindermost three being modified into the sting.
The largest species of bee is thought to be Wallace's giant bee Megachile pluto, whose females can attain a length of . The smallest species may be dwarf stingless bees in the tribe Meliponini whose workers are less than in length.
Sociality
Haplodiploid breeding system
According to inclusive fitness theory, organisms can gain fitness not just through increasing their own reproductive output, but also that of close relatives. In evolutionary terms, individuals should help relatives when Cost < Relatedness * Benefit. The requirements for eusociality are more easily fulfilled by haplodiploid species such as bees because of their unusual relatedness structure. | Bee | Wikipedia | 468 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
In haplodiploid species, females develop from fertilized eggs and males from unfertilized eggs. Because a male is haploid (has only one copy of each gene), his daughters (which are diploid, with two copies of each gene) share 100% of his genes and 50% of their mother's. Therefore, they share 75% of their genes with each other. This mechanism of sex determination gives rise to what W. D. Hamilton termed "supersisters", more closely related to their sisters than they would be to their own offspring. Workers often do not reproduce, but they can pass on more of their genes by helping to raise their sisters (as queens) than they would by having their own offspring (each of which would only have 50% of their genes), assuming they would produce similar numbers. This unusual situation has been proposed as an explanation of the multiple (at least nine) evolutions of eusociality within Hymenoptera.
Haplodiploidy is neither necessary nor sufficient for eusociality. Some eusocial species such as termites are not haplodiploid. Conversely, all bees are haplodiploid but not all are eusocial, and among eusocial species many queens mate with multiple males, creating half-sisters that share only 25% of each other's genes. But, monogamy (queens mating singly) is the ancestral state for all eusocial species so far investigated, so it is likely that haplodiploidy contributed to the evolution of eusociality in bees.
Eusociality | Bee | Wikipedia | 338 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Bees may be solitary or may live in various types of communities. Eusociality appears to have originated from at least three independent origins in halictid bees. The most advanced of these are species with eusocial colonies; these are characterized by cooperative brood care and a division of labour into reproductive and non-reproductive adults, plus overlapping generations. This division of labour creates specialized groups within eusocial societies which are called castes. In some species, groups of cohabiting females may be sisters, and if there is a division of labour within the group, they are considered semisocial. The group is called eusocial if, in addition, the group consists of a mother (the queen) and her daughters (workers). When the castes are purely behavioural alternatives, with no morphological differentiation other than size, the system is considered primitively eusocial, as in many paper wasps; when the castes are morphologically discrete, the system is considered highly eusocial.
True honey bees (genus Apis, of which eight species are currently recognized) are highly eusocial, and are among the best known insects. Their colonies are established by swarms, consisting of a queen and several thousand workers. There are 29 subspecies of one of these species, Apis mellifera, native to Europe, the Middle East, and Africa. Africanized bees are a hybrid strain of A. mellifera that escaped from experiments involving crossing European and African subspecies; they are extremely defensive.
Stingless bees are also highly eusocial. They practice mass provisioning, with complex nest architecture and perennial colonies also established via swarming.
Many bumblebees are eusocial, similar to the eusocial Vespidae such as hornets in that the queen initiates a nest on her own rather than by swarming. Bumblebee colonies typically have from 50 to 200 bees at peak population, which occurs in mid to late summer. Nest architecture is simple, limited by the size of the pre-existing nest cavity, and colonies rarely last more than a year. In 2011, the International Union for Conservation of Nature set up the Bumblebee Specialist Group to review the threat status of all bumblebee species worldwide using the IUCN Red List criteria. | Bee | Wikipedia | 457 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
There are many more species of primitively eusocial than highly eusocial bees, but they have been studied less often. Most are in the family Halictidae, or "sweat bees". Colonies are typically small, with a dozen or fewer workers, on average. Queens and workers differ only in size, if at all. Most species have a single season colony cycle, even in the tropics, and only mated females hibernate. A few species have long active seasons and attain colony sizes in the hundreds, such as Halictus hesperus. Some species are eusocial in parts of their range and solitary in others, or have a mix of eusocial and solitary nests in the same population. The orchid bees (Apidae) include some primitively eusocial species with similar biology. Some allodapine bees (Apidae) form primitively eusocial colonies, with progressive provisioning: a larva's food is supplied gradually as it develops, as is the case in honey bees and some bumblebees.
Solitary and communal bees
Most other bees, including familiar insects such as carpenter bees, leafcutter bees and mason bees are solitary in the sense that every female is fertile, and typically inhabits a nest she constructs herself. There is no division of labor so these nests lack queens and worker bees for these species. Solitary bees typically produce neither honey nor beeswax.
Bees collect pollen to feed their young, and have the necessary adaptations to do this. However, certain wasp species such as pollen wasps have similar behaviours, and a few species of bee scavenge from carcases to feed their offspring. Solitary bees are important pollinators; they gather pollen to provision their nests with food for their brood. Often it is mixed with nectar to form a paste-like consistency. Some solitary bees have advanced types of pollen-carrying structures on their bodies. Very few species of solitary bee are being cultured for commercial pollination. Most of these species belong to a distinct set of genera which are commonly known by their nesting behavior or preferences, namely: carpenter bees, sweat bees, mason bees, plasterer bees, squash bees, dwarf carpenter bees, leafcutter bees, alkali bees and digger bees. | Bee | Wikipedia | 460 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Most solitary bees are fossorial, digging nests in the ground in a variety of soil textures and conditions, while others create nests in hollow reeds or twigs, or holes in wood. The female typically creates a compartment (a "cell") with an egg and some provisions for the resulting larva, then seals it off. A nest may consist of numerous cells. When the nest is in wood, usually the last (those closer to the entrance) contain eggs that will become males. The adult does not provide care for the brood once the egg is laid, and usually dies after making one or more nests. The males typically emerge first and are ready for mating when the females emerge. Solitary bees are very unlikely to sting (only in self-defense, if ever), and some (esp. in the family Andrenidae) are stingless.
While solitary, females each make individual nests. Some species, such as the European mason bee Hoplitis anthocopoides, and the Dawson's Burrowing bee, Amegilla dawsoni, are gregarious, preferring to make nests near others of the same species, and giving the appearance of being social. Large groups of solitary bee nests are called aggregations, to distinguish them from colonies. In some species, multiple females share a common nest, but each makes and provisions her own cells independently. This type of group is called "communal" and is not uncommon. The primary advantage appears to be that a nest entrance is easier to defend from predators and parasites when multiple females use that same entrance regularly.
Biology
Life cycle | Bee | Wikipedia | 322 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
The life cycle of a bee, be it a solitary or social species, involves the laying of an egg, the development through several moults of a legless larva, a pupation stage during which the insect undergoes complete metamorphosis, followed by the emergence of a winged adult. The number of eggs laid by a female during her lifetime can vary from eight or less in some solitary bees, to more than a million in highly social species. Most solitary bees and bumble bees in temperate climates overwinter as adults or pupae and emerge in spring when increasing numbers of flowering plants come into bloom. The males usually emerge first and search for females with which to mate. Like the other members of Hymenoptera bees are haplodiploid; the sex of a bee is determined by whether or not the egg is fertilized. After mating, a female stores the sperm, and determines which sex is required at the time each individual egg is laid, fertilized eggs producing female offspring and unfertilized eggs, males. Tropical bees may have several generations in a year and no diapause stage.
The egg is generally oblong, slightly curved and tapering at one end. Solitary bees, lay each egg in a separate cell with a supply of mixed pollen and nectar next to it. This may be rolled into a pellet or placed in a pile and is known as mass provisioning. Social bee species provision progressively, that is, they feed the larva regularly while it grows. The nest varies from a hole in the ground or in wood, in solitary bees, to a substantial structure with wax combs in bumblebees and honey bees. | Bee | Wikipedia | 342 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
In most species, larvae are whitish grubs, roughly oval and bluntly-pointed at both ends. They have 15 segments and spiracles in each segment for breathing. They have no legs but move within the cell, helped by tubercles on their sides. They have short horns on the head, jaws for chewing food and an appendage on either side of the mouth tipped with a bristle. There is a gland under the mouth that secretes a viscous liquid which solidifies into the silk they use to produce a cocoon. The cocoon is semi-transparent and the pupa can be seen through it. Over the course of a few days, the larva undergoes metamorphosis into a winged adult. When ready to emerge, the adult splits its skin dorsally and climbs out of the exuviae and breaks out of the cell.
Flight
Antoine Magnan's 1934 book says that he and André Sainte-Laguë had applied the equations of air resistance to insects and found that their flight could not be explained by fixed-wing calculations, but that "One shouldn't be surprised that the results of the calculations don't square with reality". This has led to a common misconception that bees "violate aerodynamic theory". In fact it merely confirms that bees do not engage in fixed-wing flight, and that their flight is explained by other mechanics, such as those used by helicopters. In 1996 it was shown that vortices created by many insects' wings helped to provide lift. High-speed cinematography and robotic mock-up of a bee wing showed that lift was generated by "the unconventional combination of short, choppy wing strokes, a rapid rotation of the wing as it flops over and reverses direction, and a very fast wing-beat frequency". Wing-beat frequency normally increases as size decreases, but as the bee's wing beat covers such a small arc, it flaps approximately 230 times per second, faster than a fruitfly (200 times per second) which is 80 times smaller.
Navigation, communication, and finding food | Bee | Wikipedia | 425 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
The ethologist Karl von Frisch studied navigation in the honey bee. He showed that honey bees communicate by the waggle dance, in which a worker indicates the location of a food source to other workers in the hive. He demonstrated that bees can recognize a desired compass direction in three different ways: by the Sun, by the polarization pattern of the blue sky, and by the Earth's magnetic field. He showed that the Sun is the preferred or main compass; the other mechanisms are used under cloudy skies or inside a dark beehive. Bees navigate using spatial memory with a "rich, map-like organization".
Digestion
The gut of bees is relatively simple, but multiple metabolic strategies exist in the gut microbiota. Pollinating bees consume nectar and pollen, which require different digestion strategies by somewhat specialized bacteria. While nectar is a liquid of mostly monosaccharide sugars and so easily absorbed, pollen contains complex polysaccharides: branching pectin and hemicellulose. Approximately five groups of bacteria are involved in digestion. Three groups specialize in simple sugars (Snodgrassella and two groups of Lactobacillus), and two other groups in complex sugars (Gilliamella and Bifidobacterium). Digestion of pectin and hemicellulose is dominated by bacterial clades Gilliamella and Bifidobacterium respectively. Bacteria that cannot digest polysaccharides obtain enzymes from their neighbors, and bacteria that lack certain amino acids do the same, creating multiple ecological niches.
Although most bee species are nectarivorous and palynivorous, some are not. Particularly unusual are vulture bees in the genus Trigona, which consume carrion and wasp brood, turning meat into a honey-like substance. Drinking guttation drops from leaves is also a source of energy and nutrients.
Ecology
Floral relationships | Bee | Wikipedia | 391 | 4654 | https://en.wikipedia.org/wiki/Bee | Biology and health sciences | Hymenoptera | null |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.