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such a signature, but need to be confirmed by future observations. The second “smoking gun” has been even more exciting to see: the detection of gravitational waves. As will be discussed in Black Holes and Curved Spacetime, gravitational waves are ripples in the fabric of spacetime that general relativity predicts sho... |
useful information about the production of stars in the early universe. Astronomers continue to scan the skies, looking for even more distant events signaling the deaths of stars from even further back in time. 844 Chapter 23 The Death of Stars CHAPTER 23 REVIEW KEY TERMS Chandrasekhar limit the upper limit to the mas... |
a typical diameter of 20 kilometers. The core rebounds and transfers energy outward, blowing off the outer layers of the star in a type II supernova explosion. 23.3 Supernova Observations A supernova occurs on average once every 25 to 100 years in the Milky Way Galaxy. Despite the odds, no supernova in our Galaxy has ... |
a few thousandths of a second. 23.6 The Mystery of the Gamma-Ray Bursts Gamma-ray bursts last from a fraction of a second to a few minutes. They come from all directions and are now known to be associated with very distant objects. The energy is most likely beamed, and, for the ones we can detect, Earth lies in the di... |
. “Speed Matters.” Astronomy (May 2000): 36. On the quick-alert networks for finding afterglows. Zimmerman, R. “Witness to Cosmic Collisions.” Astronomy (July 2006): 44. On the Swift mission and what it is teaching astronomers about gamma-ray bursts. Websites Death of Stars Crab Nebula: http://chandra.harvard.edu/xray_... |
://swift.sonoma.edu/. Videos Death of Stars BBC interview with Antony Hewish: http://www.bbc.co.uk/archive/scientists/10608.shtml. (40:54). Black Widow Pulsars: The Vengeful Corpses of Stars: https://www.youtube.com/watch?v=Fn-3G_N0hy4. A public talk in the Silicon Valley Astronomy Lecture Series by Dr. Roger Romani (S... |
Sirius (the brightest star in our northern skies) has a white-dwarf companion. Sirius has a mass of about 2 MSun and is still on the main sequence, while its companion is already a star corpse. Remember that a white dwarf can’t have a mass greater than 1.4 MSun. Assuming that the two stars formed at the same time, you... |
2. Describe the evolution of a star with a mass like that of the Sun, from the main-sequence phase of its evolution until it becomes a white dwarf. 3. Describe the evolution of a massive star (say, 20 times the mass of the Sun) up to the point at which it becomes a supernova. How does the evolution of a massive star d... |
Questions 16. Arrange the following stars in order of their evolution: A. A star with no nuclear reactions going on in the core, which is made primarily of carbon and oxygen. B. A star of uniform composition from center to surface; it contains hydrogen but has no nuclear reactions going on in the core. C. A star that ... |
. The first cluster contains mainly main-sequence stars, along with some red giant stars and a few white dwarfs. The second cluster also contains mainly main-sequence stars, along with some red giant stars, and a few neutron stars—but no white dwarf stars. What are the relative ages of the clusters? How did you determi... |
than g at the surface of Earth? What would you weigh at the surface of the white dwarf (again granting us the dubious notion that you could survive there)? 36. What is the escape velocity from the white dwarf in Exercise 23.35? How much greater is it than the escape velocity from Earth? 37. What is the average density... |
,000 K and a radius equal to Earth’s, how would its luminosity compare to that of the Sun? 45. A supernova can eject material at a velocity of 10,000 km/s. How long would it take a supernova remnant to expand to a radius of 1 AU? How long would it take to expand to a radius of 1 light-years? Assume that the expansion v... |
ar shown in Figure 23.16 is rotating 100 times per second, how many pulses would be detected in one minute? The two beams are located along the pulsar’s equator, which is aligned with Earth. 852 Chapter 23 The Death of Stars This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 24 Blac... |
of general relativity Recognize that one’s experiences of gravity and acceleration are interchangeable and indistinguishable Distinguish between Newtonian ideas of gravity and Einsteinian ideas of gravity Recognize why the theory of general relativity is necessary for understanding the nature of black holes Most stars... |
) So, when we wrote that the theory of general relativity was Einstein’s work, you may have worried just a bit, convinced that anything Einstein did must be beyond your understanding. This popular view is unfortunate and mistaken. Although the detailed calculations of general relativity do involve a good deal of higher... |
then dropping rapidly for a while. This is how NASA trains its astronauts for the experience of free fall in space; the scenes of weightlessness in the 1995 movie Apollo 13 were filmed in 856 Chapter 24 Black Holes and Curved Spacetime the same way. (Moviemakers have since devised other methods using underwater filmin... |
identical distances from the object(s) responsible for producing the gravitational force. In this case, objects in different locations will experience slightly different accelerations. But this point does not invalidate the principle of equivalence that Einstein derived from this line of thinking. This OpenStax book i... |
�weightless” environment of the International Space Station, moving takes very little effort. Watch astronaut Karen Nyberg (https://openstax.org/l/30ISSzerogravid) demonstrate how she can propel herself with the force of a single human hair. Appearances are misleading, however. There is a force in this situation. Both ... |
strike the front wall at a point higher than the point from which it left. Figure 24.6. Curved Light Path. In a spaceship moving to the left (in this figure) in its orbit about a planet, light is beamed from the rear, A, toward the front, B. Meanwhile, the ship is falling out of its straight path (exaggerated here). W... |
2 SPACETIME AND GRAVITY Learning Objectives By the end of this section, you will be able to: Describe Einstein’s view of gravity as the warping of spacetime in the presence of massive objects Understand that Newton’s concept of the gravitational force between two massive objects and Einstein’s concept of warped spaceti... |
build up a correct picture of the physical world. We examine spacetime a bit more closely in the next subsection. The gist of Einstein’s general theory is that the presence of matter curves or warps the fabric of spacetime. This curving of spacetime is identified with gravity. When something else—a beam of light, an e... |
axis. From A to B he drove at a uniform speed; unfortunately, it was too fast a uniform speed and a police car spotted him. From B to C he stopped to This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 24 Black Holes and Curved Spacetime 861 receive his ticket and made no progress th... |
or warps the rubber sheet very effectively, putting a good sag in it. From our point of view, we can see that the sheet near the paperweight is no longer straight. 862 Chapter 24 Black Holes and Curved Spacetime Figure 24.8. Three-Dimensional Analogy for Spacetime. On a flat rubber sheet, a trained ant has no trouble ... |
ATIVITY Learning Objectives By the end of this section, you will be able to: Describe unusual motion of Mercury around the Sun and explain how general relativity explains the observed behavior Provide examples of evidence for light rays being bent by massive objects, as predicted by general relativity’s theory about th... |
in a slightly different direction as seen from the Sun (Figure 24.9). Figure 24.9. Mercury’s Wobble. The major axis of the orbit of a planet, such as Mercury, rotates in space slightly because of various perturbations. In Mercury’s case, the amount of rotation (or orbital precession) is a bit larger than can be accoun... |
test was something that had not been observed before and would thus provide an excellent confirmation of his theory. Since spacetime is more curved in regions where the gravitational field is strong, we would expect light passing very near the Sun to appear to follow a curved path (Figure 24.10), just like that of the... |
that the next suitable eclipse was on May 29, 1919. The British organized two expeditions to observe it: one on the island of Príncipe, off the coast of West Africa, and the other in Sobral, in northern Brazil. Despite some problems with the weather, both expeditions obtained successful photographs. The stars seen nea... |
. For a clock, the experimenters used the frequency (the number of cycles per second) of gamma rays emitted by radioactive cobalt. Einstein’s theory predicts that such a cobalt clock on the ground floor, being a bit closer to Earth’s center of gravity, should run very slightly slower than the same clock on the top floo... |
its frequency and wavelength. To understand what happens, let’s recall that a wave of light is a repeating phenomenon—crest follows crest with great regularity. In this sense, each light wave is a little clock, keeping time with its wave cycle. If stronger gravity slows down the pace of time (relative to an outside ob... |
1.8 Chapter 24 Black Holes and Curved Spacetime 867 GPS relies on an array of 24 satellites orbiting the Earth, and at least 4 of them are visible from any spot on Earth. Each satellite carries a precise atomic clock. Your GPS receiver detects the signals from those satellites that are overhead and calculates your posi... |
nothing can stop the core from collapsing forever. We will examine this situation from two perspectives: first from a pre-Einstein point of view, and then with the aid of general relativity. Classical Collapse Let’s begin with a thought experiment. We want to know what speeds are required to escape from the gravitatio... |
“thought experiment” to get our bearings). Ultimately, as the Sun shrinks, the escape velocity near the surface would exceed the speed of light. If the speed you need to get away is faster than the fastest possible speed in the universe, then nothing, not even light, is able to escape. An object with such large escape... |
larger than a black hole. All the light paths, except the one straight up, curve back to the surface. When the star shrinks inside the event horizon and becomes a black hole, even a beam directed straight up returns. Keep in mind that gravity is not pulling on the light. The concentration of matter has curved spacetim... |
solution to Einstein’s equations of general relativity. The radius of the event horizon is called the Schwarzschild radius in his memory. Figure 24.15. Karl Schwarzschild (1873–1916). This German scientist was the first to demonstrate mathematically that a black hole is possible and to determine the size of a nonrotat... |
) of the event horizon is RS = 2GM c2 where c is the speed of light, G is the gravitational constant, and M is the mass of the black hole. Note that in this formula, 2, G, and c are all constant; only the mass changes from black hole to black hole. As we will see in the chapter on The Milky Way Galaxy, astronomers have... |
that the gravity of any star some distance away acts as if all its mass were concentrated at a point in the center, which we call the center of gravity. For real stars, we merely imagine that all mass is concentrated there; for black holes, all the mass really is concentrated at a point in the center. So, if you are a... |
reading when compared to time passing on Earth. Her heart will beat more slowly, her hair will grow more slowly, her antique wristwatch will tick more slowly, and so on. She is not aware of this slowing down because all her readings of time, whether made by her own bodily functions or with mechanical equipment, are me... |
ohl and A World out of Time by Larry Niven, also make use of the slowing down of time near black holes as major turning points in the story. For a list of science fiction stories based on good astronomy, you can go to www.astrosociety.org/scifi. A Trip into a Black Hole The fact that scientists cannot see inside black ... |
gravitational redshift, we could say that if the infalling astronaut uses a blue light to send his signals every second, we will see the light get redder and redder until its wavelength is nearly infinite.) As the spacing between clock ticks approaches infinity, it will appear to us that the astronaut is slowly coming... |
toward the right, and the right slightly toward the left, bringing each side closer to the singularity. The astronaut will therefore be slightly squeezed in one direction and stretched in the other. Some scientists like to call this process of stretching and narrowing spaghettification. The point at which the astronau... |
a stellar black hole), and completely black? It turns out that the trick is not to look for the black hole itself but instead to look for what it does to a nearby companion star. As we saw, when very massive stars collapse, they leave behind their gravitational influence. What if a member of a double-star system becom... |
ved Spacetime In our example, the infalling gas that produces the X-ray emission comes from the black hole’s companion star. As we saw in The Death of Stars, stars in close binary systems can exchange mass, especially as one of the members expands into a red giant. Suppose that one star in a double-star system has evol... |
stars can also have accretion disks that produce X-rays, so astronomers must study the properties of these X-rays carefully when trying to determine what kind of object is at the center of the disk. Nevertheless, a number of systems that clearly contain black holes have now been found. The Discovery of Stellar-Mass Bl... |
GRS1009-45 (Nova Vel 1993) XTE J1118+480 XTE J1859+226 Table 24.1 K dwarf K dwarf K dwarf 3.9 5.6 2.8 1.7 1.1 2.6 33.5 6.5 1.5 0.33 0.52 0.43 0.35 0.29 0.17 0.38 10.9 15 6–7 7 9 7 14 12 11 9–13 5–7 7 5–10 8–9 7 5.4 2 As you can tell, there is no standard way of naming these candidates. The chain of numbers is the loca... |
. (If two black holes merge, you just get a black hole with more mass and a larger event horizon.) As a result, black holes in crowded regions can grow, eventually swallowing thousands or even millions of times the mass of the Sun. Ground-based observations have provided compelling evidence that there is a black hole i... |
should spread outward at the speed of light. The big problem with trying to study such waves is that they are tremendously weaker than electromagnetic waves and correspondingly difficult to detect. Proof from a Pulsar We’ve had indirect evidence for some time that gravitational waves exist. In 1974, astronomers Joseph... |
motions within the observing stations and mimic gravitational waves—such as small earthquakes, ocean tides, and even traffic—should affect the two sites differently. Each of the LIGO stations consists of two 4-kilometer-long, 1.2-meter-diameter vacuum pipes arranged in an L-shape. A test mass with a mirror on it is su... |
us. In the cataclysm of the merger, about three times the mass of the Sun was converted to energy (recall E = mc2). During the tiny fraction of a second for the merger to take place, this event produced power about 50 times the power produced by all the stars in the entire visible universe—but the power was all in the... |
�s general theory of relativity where its effects are very strong—close to black holes—and not weak, as they are near Earth. One remarkable result from this first detection is that the signal measured matched so closely the theoretical predictions made using Einstein’s theory. Once again, Einstein’s revolutionary idea ... |
the world outside it—that is, the boundary of the region around a black hole where the curvature of spacetime no longer provides any way out general theory of relativity Einstein’s theory relating gravity and the structure (geometry) of space and time gravitational redshift an increase in wavelength of an electromagne... |
Black Holes Theory suggests that stars with stellar cores more massive than three times the mass of the Sun at the time they exhaust their nuclear fuel will collapse to become black holes. The surface surrounding a black hole, where the escape velocity equals the speed of light, is called the event horizon, and the ra... |
existence of event horizons and thus black holes. Nadis, S. “Black Holes: Seeing the Unseeable.” Astronomy (April 2007): 26. A brief history of the black hole idea and an introduction to potential new ways to observe them. This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 24 Black... |
Astrophysics. Black Holes: Gravity’s Relentless Pull: http://hubblesite.org/explore_astronomy/black_holes/home.html. The Hubble Space Telescope’s Journey to a Black Hole and Black Hole Encyclopedia (a good introduction for beginners). Introduction to Black Holes: http://www.damtp.cam.ac.uk/research/gr/public/bh_intro.... |
52). Death by Black Hole: http://www.openculture.com/2009/02/death_by_black_hole_and_its_kind_of_funny.htm. Neil deGrasse Tyson explains spaghettification with only his hands (5:34). Hearts of Darkness: Black Holes in Space: https://www.youtube.com/watch?v=4tiAOldypLk. 2010 Silicon Valley Astronomy Lecture by Alex Fili... |
group have been convicted (falsely) of high treason. The method of execution is to send everyone into a black hole, but you get to pick which one. Since you are doomed to die, you would at least like to see what the inside of a black hole is like—even if you can’t tell anyone outside about it. Would you choose a black... |
the movie and then try to use your knowledge of black holes from this chapter to explain the plot. (Note that the film also uses the concept of a wormhole, which we don’t discuss in this chapter. A wormhole is a theoretically possible way to use a large, spinning black hole to find a way to travel from one place in th... |
. What would happen? Would this violate the equivalence principle? 12. A monkey hanging from a tree branch sees a hunter aiming a rifle directly at him. The monkey then sees a flash and knows that the rifle has been fired. Reacting quickly, the monkey lets go of the branch and drops so that the bullet can pass harmless... |
stop your fall, you glance at the scale reading. Does the scale show your real weight? An apparent weight? Something else? Figuring For Yourself 20. Look up G, c, and the mass of the Sun in Appendix E and calculate the radius of a black hole that has the same mass as the Sun. (Note that this is only a theoretical calc... |
Association. Chapter Outline 25.1 The Architecture of the Galaxy 25.2 Spiral Structure 25.3 The Mass of the Galaxy 25.4 The Center of the Galaxy 25.5 Stellar Populations in the Galaxy 25.6 The Formation of the Galaxy Thinking Ahead Today, we know that our Sun is just one of the many billions of stars that make up the ... |
galactic equivalent of Times Square. Herschel Measures the Galaxy In 1785, William Herschel (Figure 25.2) made the first important discovery about the architecture of the Milky Way Galaxy. Using a large reflecting telescope that he had built, William and his sister Caroline counted stars in different directions of the... |
Sun. Today we know that this is a very small section of the entire 100,000-light-year-diameter disk of stars that makes up the Galaxy Harlow Shapley: Mapmaker to the Stars Until the early 1900s, astronomers generally accepted Herschel’s conclusion that the Sun is near the center of the Galaxy. The discovery of the Gal... |
not finished high school, Shapley went back and completed a six-year high-school program in only two years, graduating as class valedictorian. In 1907, at age 22, he went to the University of Missouri, intent on studying journalism, but found that the school of journalism would not open for a year. Leafing through the... |
hunts” for communist sympathizers (including such liberal leaders as Shapley), he spoke out forcefully and fearlessly in defense of the freedom of thought and expression. A man of many interests, he was fascinated by the behavior of ants, and wrote scientific papers about them as well as about galaxies. By the time he... |
infrared observations have confirmed that the central bar is composed mostly of old yellow-red stars. The two main spiral arms appear to connect with the ends of the bar. They are highlighted by the blue light from young hot stars. We know many other spiral galaxies that also have bar-shaped concentrations of stars in... |
as a whole was taken at infrared wavelengths (Figure 25.7). Figure 25.7. Inner Part of the Milky Way Galaxy. This beautiful infrared map, showing half a billion stars, was obtained as part of the Two Micron All Sky Survey (2MASS). Because interstellar dust does not absorb infrared as strongly as visible light, this vi... |
Way Galaxy formed. Characteristics of the Milky Way Galaxy Property Thin Disk Thick Disk Stellar Halo (Excludes Dark Matter) Stellar mass 4 × 1010 MSun A few percent of the thin disk mass 1010 MSun Luminosity 3 × 1010 LSun A few percent of the thin disk luminosity 8 × 108 LSun Typical age of stars 1 million to 10 bill... |
back a few centuries, and these starlit sights would have been the norm rather than the exception. Before the advent of electric or even gas lighting, people relied on short-lived fires to illuminate their homes and byways. Consequently, their night skies were typically much darker. Confronted by myriad stellar patter... |
.9. The Milky Way in Myth. (a) Origin of the Milky Way by Jacopo Tintoretto (circa 1575) illustrates the Greek myth that explains the formation of the Milky Way. (b) The Moon of the Milky Way by Japanese painter Tsukioka Yoshitoshi depicts the Chinese legend of Zhi Nu and Niu Lang. To the Quechua Indians of Andean Peru... |
in the disk at visible wavelengths. However, radio waves of 21-cm wavelength pass right through the dust, enabling astronomers to detect hydrogen atoms throughout the Galaxy. More recent surveys of the infrared emission from stars in the disk have provided a similar dust-free perspective of our Galaxy’s stellar distri... |
Spiral Structure At the Sun’s distance from its center, the Galaxy does not rotate like a solid wheel or a CD inside your player. Instead, the way individual objects turn around the center of the Galaxy is more like the solar system. Stars, as well as the clouds of gas and dust, obey Kepler’s third law. Objects farthe... |
the galaxies began to “settle down.” The galaxies that were to become spirals lost their massive clumps and developed a central bulge. The turbulence in these galaxies decreased, rotation began to dominate the motions of the stars and gas, and stars began to form in a much quieter disk. Smaller star-forming clumps beg... |
, orbits the center of the Milky Way. Our star’s orbit is nearly circular and lies in the Galaxy’s disk. The speed of the Sun in its orbit is about 200 kilometers per second, which means it takes us approximately 225 million years to go once around the center of the Galaxy. We call the period of the Sun’s revolution th... |
the amount of luminous matter (meaning any material from which we can detect electromagnetic radiation) both drop off dramatically at distances of more than about 30,000 light-years from the galactic center. Little did we suspect how wrong our assumption was. A Galaxy of Mostly Invisible Matter In science, what seems ... |
higher speeds mean? Kepler’s third law tells us how fast objects must orbit a source of gravity if they are neither to fall in (because they move too slowly) nor to escape (because they move too fast). If the Galaxy had only the mass calculated by Kepler, then the high-speed outer objects should long ago have escaped ... |
distant galaxies. What are our other possibilities? The dark matter cannot be a huge number of black holes (of stellar mass) or old neutron stars, since interstellar matter falling onto such objects would produce more X-rays than are observed. Also, recall that the formation of black holes and neutron stars is precede... |
Stop a moment and consider how astounding the conclusion we have reached really is. Perhaps as much as 95% of the mass in our Galaxy (and many other galaxies) is not only invisible, but we do not even know what it is made of. The stars and raw material we can observe may be merely the tip of the cosmic iceberg; underl... |
ittarius A* (pronounced “Sagittarius A-star” and abbreviated Sgr A*), was the first cosmic radio source astronomers discovered. A Journey toward the Center Let’s take a voyage to the mysterious heart of our Galaxy and see what’s there. Figure 25.14 is a radio image of a region about 1500 light-years across, centered on... |
picture are hundreds of hot white dwarfs, neutron stars, and stellar black holes with accretion disks glowing with X-rays. The diffuse haze in the picture is emission from gas that lies among the stars and is at a temperature of 10 million K. 910 Chapter 25 The Milky Way Galaxy Figure 25.15. Galactic Center in X-Rays.... |
cnx.org/content/col11992/1.8 Chapter 25 The Milky Way Galaxy 911 Finding the Heart of the Galaxy Just what is Sagittarius A*, which lies right at the center our Galaxy? To establish that there really is a black hole there, we must show that there is a very large amount of mass crammed into a very tiny volume. As we saw... |
If we combine observations of their periods and the size of their orbits with Kepler’s third law, we can estimate the mass of the object that keeps them in their orbits. One of the stars has been observed for its full orbit of 15.6 years. Its closest approach takes it to a distance of only 124 AU or about 17 light-hou... |
at the centers of most other large galaxies (see Active Galaxies, Quasars, and Supermassive Black Holes)—even ones that are very young—this collapse probably would have taken place when the Milky Way was just beginning to take shape. The initial mass of this black hole might have been only a few tens of solar masses. ... |
for free at http://cnx.org/content/col11992/1.8 Chapter 25 The Milky Way Galaxy 913 Andrea Ghez A lover of puzzles, Andrea Ghez has been pursuing one of the greatest mysteries in astronomy: what strange entity lurks within the center of our Milky Way Galaxy? Figure 25.18. Andrea Ghez. Research by Ghez and her team has... |
saw) on a gravitational solution that requires the presence of a supermassive black hole with a mass equivalent to 4.6 million Suns—all nestled within a space smaller than that 914 Chapter 25 The Milky Way Galaxy occupied by our solar system. Ghez’s achievements have been recognized with one of the “genius” awards giv... |
see the motion of stars in the Galaxy’s halo in randomly oriented and elliptical orbits. This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 25 The Milky Way Galaxy 915 Two Kinds of Stars The discovery that there are two different kinds of stars was first made by Walter Baade during... |
I stars. Population II stars show no correlation with the location of the spiral arms. These objects are found throughout the Galaxy. Some are in the disk, but many others follow eccentric elliptical orbits that carry them high above the galactic disk into the halo. Examples include stars surrounded by planetary nebul... |
of heavier elements available to new stars. The Real World With rare exceptions, we should never trust any theory that divides the world into just two categories. While they can provide a starting point for hypotheses and experiments, they are often oversimplifications that need refinement a research continue. The ide... |
by supernova explosions in order to recycle it. Low-mass galaxies exert only a modest gravitational force, and the high-speed gas ejected by supernovae can easily escape from them. Which elements a star is endowed with thus depends not only on when the star formed in the history of its galaxy, but also on how many sta... |
later, when the gas from which they were made was already “contaminated” with heavy elements produced in earlier generations of stars. Gravitational forces caused the gas in the thin disk to fragment into clouds or clumps with masses like those of star clusters. These individual clouds then fragmented further to form ... |
plane. The blue outline on either side of the galactic plane corresponds to the infrared image in Figure 25.7. The boxes mark regions where detailed studies of individual stars led to the discovery of this galaxy. (credit: modification of work by R. Ibata (UBC), R. Wyse (JHU), R. Sword (IoA)) Since that discovery, evi... |
a satellite galaxy would stir up the orbits of the stars and gas clouds originally in the thin disk and cause them to move higher above and below the mid-plane of the Galaxy. Meanwhile, the Galaxy’s stars would add to the fluffed-up mix. If such a collision happened about 10 billion years ago, then any gas in the two ... |
distance throughout the sequence of events, as the collision readjusts the orbits of many stars within each galaxy. (credit: NASA; ESA; Z. Levay, R. van der Marel, STScl; T. Hallas, and A. Mellinger) We are thus coming to realize that “environmental influences” (and not just a galaxy’s original characteristics) play a... |
consists of a thin disk containing dust, gas, and young and old stars; a spherical halo containing populations of very old stars, including RR Lyrae variable stars and globular star clusters; a thick, more diffuse disk with stars that have properties intermediate between those in the thin disk and the halo; a peanut-s... |
elements are referred to as population II stars and are found in the halo and in globular clusters. Population I stars contain more heavy elements than globular cluster and halo stars, are typically younger and found in the disk, and are especially concentrated in the spiral arms. The Sun is a member of population I. ... |
. On the history of observations that pinpointed the Sun’s location in the Galaxy. Haggard, D., & Bower, G. “In the Heart of the Milky Way.” Sky & Telescope (February 2016): 16. On observations of the Galaxy’s nucleus and the supermassive black hole and magnetar there. Ibata, R., & Gibson, B. “The Ghosts of Galaxies Pa... |
esigning the Milky Way.” Sky & Telescope (September 2004): 50. On recent multi-wavelength surveys of the Galaxy. Whitt, K. “The Milky Way from the Inside.” Astronomy (November 2001): 58. Fantastic panorama image of the Galaxy, with finder charts and explanations. Websites International Dark Sky Sanctuaries: http://dark... |
near the galactic center showing their motions around the center (3:00). COLLABORATIVE GROUP ACTIVITIES A. You are captured by space aliens, who take you inside a complex cloud of interstellar gas, dust, and a few newly formed stars. To escape, you need to make a map of the cloud. Luckily, the aliens have a complete a... |
. Is there any This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 25 The Milky Way Galaxy 927 relationship between a person’s age and whether they have seen the Milky Way? How important is it that many kids growing up on Earth today never (or rarely) get to see our home Galaxy in th... |
than the spiral arms? C. Which are thought to be very young? D. Which are thought to be very old? E. Which have the hottest stars? 13. The dwarf galaxy in Sagittarius is the one closest to the Milky Way, yet it was discovered only in 1994. Can you think of a reason it was not discovered earlier? (Hint: Think about wha... |
Galaxy in 225 million years at a distance of 26,000 light-years. Given that ⎠ × P2, where a is the semimajor axis and P is the orbital period, what is the mass of the a3 = ⎛ ⎞ ⎝M1 + M2 Galaxy within the Sun’s orbit? 20. Suppose the Sun orbited a little farther out, but the mass of the Galaxy inside its orbit remained ... |
. The best evidence for a black hole at the center of the Galaxy also comes from the application of Kepler’s third law. Suppose a star at a distance of 20 light-hours from the center of the Galaxy has an orbital speed of 6200 km/s. How much mass must be located inside its orbit? 26. The next step in deciding whether th... |
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