Sentence stringlengths 143 2.75k | video_title stringlengths 12 103 |
|---|---|
Then maybe the most abstract definition would be a significant influence from the sun's gravitational pull. All of those ways are to imagine the extent of the solar system, but they all kind of leave a gray area for what is and what is not in the solar system. My whole point here, what I want to do is start exploring a... | Scale of distance to closest stars Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
If we go right over here, this shows our local neighborhood from a stellar point of view. Even though these stars look pretty big, if you actually were to draw, this is our solar system right here. You might be saying, oh, maybe that's the sun. No, the sun, if you were to draw it here, it wouldn't even make up one pixe... | Scale of distance to closest stars Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
No, the sun, if you were to draw it here, it wouldn't even make up one pixel. In fact, the entire orbit of Pluto, everything inside of it, still would not make up one pixel on the screen right here. What we see right here, which is a radius of about, give or take, a light year, this is roughly maybe the radius of the O... | Scale of distance to closest stars Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
We saw in the last video how huge that was, especially relative to the radius of, say, Pluto's orbit, which is roughly like that. That itself is a huge, huge diameter or a huge distance away from the sun. That wouldn't even make a pixel on this diagram right over here. Just to give you an idea of how far we are, we're ... | Scale of distance to closest stars Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Just to give you an idea of how far we are, we're a speck of a speck of a speck inside here, of a pixel of a pixel in the center here. We're in the center here to make it from our solar system, or in particular from Earth maybe, to the nearest star, or maybe the nearest cluster of stars, the Alpha Centauri. They're the... | Scale of distance to closest stars Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
There's three stars, Alpha Centauri A, which is the largest, Alpha Centauri B, and then there's one that you can't observe with the naked eye, Alpha Proximus, or I think it's Proximus Centauri, I think is what it's called, not Alpha Proximus. Proximus Centauri. That's a much smaller star, but that's the closest star. Y... | Scale of distance to closest stars Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
You can view it as this whole cluster of stars right here. They're the closest. It's about 4.2 light years away. Or another way to think about it, if someone were to shine a light on one of these planets, and assuming that light could get to us, it would take 4.2 years to get to us. If these guys just disappeared or bl... | Scale of distance to closest stars Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Or another way to think about it, if someone were to shine a light on one of these planets, and assuming that light could get to us, it would take 4.2 years to get to us. If these guys just disappeared or blew up, we wouldn't know it for 4.2 years. We'd say, hey, that's not too bad. We should take a trip over there and... | Scale of distance to closest stars Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
We should take a trip over there and check them out, see if there are any other people there that we can meet and exchange technologies with or whatnot. But this is a huge distance. Just this 4.2 light years is an unbelievably ridiculous distance. Just to give you a sense, the Voyager 1 and 2, we talked about in the la... | Scale of distance to closest stars Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Just to give you a sense, the Voyager 1 and 2, we talked about in the last video, and we can even see how far they've gotten. They've gotten pretty much to the heliopause. These guys are traveling at 60,000 kilometers an hour, which is the same thing as 17 kilometers per second. If we were able to get up to those type ... | Scale of distance to closest stars Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Obviously, the sun's gravity isn't so strong that it keeps light from escaping. So why would something, or even a star that's two or three solar masses, its gravity isn't so strong that it keeps light from escaping. Why would a black hole that has the same mass, why would that keep light from escaping? And to understan... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
And to understand that, let's just think a little bit about, and I'll just do Newtonian classical physics right here. I won't get into the whole general relativity of things. And this really will just give us the intuition of why a smaller, denser thing of the same mass can exert a stronger gravitational pull. So let's... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
So let's imagine, so let's take two examples. Let's say I have some star here. Let's just call that mass m1. And let's say that its radius, let's just call this r. And let's say that I have some other mass right at the surface of this star. It's somehow able to survive those surface temperatures. And this mass over her... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
And let's say that its radius, let's just call this r. And let's say that I have some other mass right at the surface of this star. It's somehow able to survive those surface temperatures. And this mass over here has a mass of m1. This mass over here has a mass of m2. The universal law of gravitation tells us that the ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
This mass over here has a mass of m2. The universal law of gravitation tells us that the force between these two masses is going to be equal to the gravitational constant times the product of the masses. So m1 times m2, all of that over the square of the distance. Now let me be very clear. You might say, wait, this mag... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
Now let me be very clear. You might say, wait, this magenta mass right here is touching this larger mass. Isn't the distance 0? And you have to be very careful. This is the distance between their center of masses. So the center of mass of this large mass over here is r away from this mass that's on the surface. Now wit... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
And you have to be very careful. This is the distance between their center of masses. So the center of mass of this large mass over here is r away from this mass that's on the surface. Now with that said, let's take another example. Let's say that this large, massive star, or whatever it might be, eventually condenses ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
Now with that said, let's take another example. Let's say that this large, massive star, or whatever it might be, eventually condenses into something 1,000 times smaller. So let me draw it like this. And obviously I'm not drawing it to scale. So let's say we have another case like this. And I'm not drawing it to scale.... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
And obviously I'm not drawing it to scale. So let's say we have another case like this. And I'm not drawing it to scale. So this object, maybe it's the same object, or maybe it's a different object, that has the exact same mass as this larger object, but now it has a much smaller radius. It now has a much smaller radiu... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
So this object, maybe it's the same object, or maybe it's a different object, that has the exact same mass as this larger object, but now it has a much smaller radius. It now has a much smaller radius. So that radius now, the radius is 1 over, let's just say it's 1,000th of this radius over here. So it's 1, maybe I'll ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
So it's 1, maybe I'll just call it r over 1,000. So if this had a million kilometer radius, so that would make it roughly about twice the radius of the sun. If this was a million kilometer radius right over here, this would be 1,000 kilometer radius. So maybe we're talking about something that's approaching a neutron s... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
So maybe we're talking about something that's approaching a neutron star. But we don't have to think about what it actually is. Let's just think about the thought experiment here. So let's say I have this thing over here. And let's say I have something on the surface of this. So let's say I have that same mass, it's on... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
So let's say I have this thing over here. And let's say I have something on the surface of this. So let's say I have that same mass, it's on the surface of this thing. So this is m2 right over here. So what is going to be the force between these two masses? How strong are they going to want to, what's the force pulling... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
So this is m2 right over here. So what is going to be the force between these two masses? How strong are they going to want to, what's the force pulling them together? So let's just do the universal law of gravitation again. The force, let's just call this force 1, and let's call this force 2. Once again, it's going to... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
So let's just do the universal law of gravitation again. The force, let's just call this force 1, and let's call this force 2. Once again, it's going to be the gravitational constant times the product of their masses. So the big m1 times the smaller mass, m2, all of that over this distance squared, this radius squared.... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
So the big m1 times the smaller mass, m2, all of that over this distance squared, this radius squared. Remember, it's the distance to the center of masses. This center of mass here, we're considering m2 to kind of be just a point mass right over there. So what's the radius squared? It's going to be r over 1,000 squared... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
So what's the radius squared? It's going to be r over 1,000 squared. Or if we simplify this, what will this be? This is the same thing, and I'll just write it in one color just because it takes less time. Gravitational constant m1, m2 over r squared over 1,000 squared, or over 1 million. Over 1 million. That's just 1,0... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
This is the same thing, and I'll just write it in one color just because it takes less time. Gravitational constant m1, m2 over r squared over 1,000 squared, or over 1 million. Over 1 million. That's just 1,000 squared. Or we can multiply the numerator and the denominator by a million, and this is going to be equal to ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
That's just 1,000 squared. Or we can multiply the numerator and the denominator by a million, and this is going to be equal to 1 million, I'm going to write it out, 1 million, let me scroll to the right a little bit, times the gravitational constant times m1, m2, all of that over r squared. Now what is this thing right... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
That's the same thing as this F1. So this is going to be 1 million times F1. So even though the masses involved are the same, this yellow object right here is the same mass as this larger object over here. It's able to exert a million times the gravitational force on this point mass, and actually vice versa. They're bo... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
It's able to exert a million times the gravitational force on this point mass, and actually vice versa. They're both being attracted. They're both exerting this on each other. And the reality is, is because this thing is smaller, because this m1 on the right here, this one I'm coloring in, because this one is smaller a... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
And the reality is, is because this thing is smaller, because this m1 on the right here, this one I'm coloring in, because this one is smaller and denser, this particle is able to get closer to its center of mass. Now you might be saying, OK, well I can buy that. This just comes straight from the universal law of gravi... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
But wouldn't something closer to this center of mass experience that same thing? If this was a star, wouldn't photons that are over here, wouldn't this experience the same force? If this distance right here is r over 1,000, wouldn't some photon here, or atom here, or molecule, or whatever it's over here, wouldn't that ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
And you've got to remember, all of a sudden when this thing is inside of this larger mass, what's happening? It no longer has the entire mass is no longer pulling on it in that direction. It's no longer pulling it in that inward direction. You now have all of this mass over here. Let me think of the best way of doing i... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
You now have all of this mass over here. Let me think of the best way of doing it. So you could think of it all of this mass over here is pulling it in an outward direction. It's not telling you what that mass out there is doing, since that mass itself is being pulled inward. It is pushing down on this. It is exerting ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
It's not telling you what that mass out there is doing, since that mass itself is being pulled inward. It is pushing down on this. It is exerting pressure on that point. But the actual gravitational force that that point is experiencing is actually going to be less. It's actually going to be mitigated by the fact that ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
But the actual gravitational force that that point is experiencing is actually going to be less. It's actually going to be mitigated by the fact that there's so much mass over here pulling in the other direction. And so you can imagine if you were in the center of a really massive object, there would be no net gravitat... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy (2).mp3 |
In the last video, we talked about the idea that if I dug up a bone someplace, and if I were to measure its carbon-14, and I found that it had half of the carbon-14 that I would expect to find in a living animal or plant, then I said, hey, maybe one half-life has gone by. Or roughly, for carbon-14, one half-life is 5,7... | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
Now, when I did that, I made a pretty big assumption. And some of you all have touched on this in the comments on YouTube on the last video. It's how do I know that this estimate I made is based on the assumption that the amount of carbon-14 in the atmosphere would have been roughly constant from when this bone was liv... | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And so the question is, is the amount of carbon-14 in the atmosphere and in the water and in living plants and animals, is it constant? And if it isn't constant, how do you calibrate your measurement so you can actually figure out how much carbon-14 there is relative to living plants and animals at that time? And the w... | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And I have pictures here of both of them. One is to look at tree rings. And I'm told that this will work up to about 10,000 years old. I don't know of any 10,000-year-old trees. I don't think anyone does. But maybe there are some remains of old trees. And you can look at their tree rings. | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
I don't know of any 10,000-year-old trees. I don't think anyone does. But maybe there are some remains of old trees. And you can look at their tree rings. And I think most of us are familiar with this idea that every year that a tree grows, it forms another layer of bark. And so you can look back to that layer of bark,... | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And you can look at their tree rings. And I think most of us are familiar with this idea that every year that a tree grows, it forms another layer of bark. And so you can look back to that layer of bark, adjust for the half-life of carbon-14, and then figure out how much carbon-14 was there in the atmosphere at that pe... | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And so it's kind of a record of the atmosphere up to 10,000 years. If you want to go even further back, you can look at cave deposits. And the fancy word for these cave deposits are speleothems. You might be familiar with stalagmites. Those are those speleothems that are kind of coming out of the bottom of the cave. Or... | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
You might be familiar with stalagmites. Those are those speleothems that are kind of coming out of the bottom of the cave. Or stalactites, those are the speleothems that are coming from the top of the cave. But the reason why these are useful is these are formed by calcium carbonate. So they have carbon in them. And sl... | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
But the reason why these are useful is these are formed by calcium carbonate. So they have carbon in them. And slowly, over really tens of thousands of years, the water in the cave deposits that calcium carbonate. So it's a record of the fraction of carbon-14 in some of those years. And you can go down to resolutions o... | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So it's a record of the fraction of carbon-14 in some of those years. And you can go down to resolutions of as small as 10 years. And so this will give us pretty good estimates over tens of thousands of years, up to 50,000 years. And frankly, carbon-14 isn't even useful beyond really 50,000 or 60,000 years. So this giv... | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And frankly, carbon-14 isn't even useful beyond really 50,000 or 60,000 years. So this gives us a pretty good record of carbon-14 in the atmosphere, assuming that it's fairly uniform throughout the atmosphere. And all evidence suggests that. And that uniformity through the atmosphere also goes into the water supply and... | Carbon 14 dating 2 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
In the last video, we started with a star in its main sequence, like the sun. And inside the core of that star, you had hydrogen fusion going on. So that is hydrogen fusion. And then outside of the core, you just had hydrogen. You just had hydrogen plasma. And when we say plasma, it's the electrons and protons of the i... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And then outside of the core, you just had hydrogen. You just had hydrogen plasma. And when we say plasma, it's the electrons and protons of the individual atoms have been disassociated because the temperatures and pressures are so high. So they're really just kind of like the soup of electrons and protons, as opposed ... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So they're really just kind of like the soup of electrons and protons, as opposed to proper atoms that we associate with at lower temperatures. So this is a main sequence star right over here. This is a main sequence star right over here. And we saw in the last video that this hydrogen is fusing into helium. So we star... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And we saw in the last video that this hydrogen is fusing into helium. So we start having more and more helium here. And as we have more and more helium, the core becomes more and more dense because helium is a more massive atom. It is able to pack more mass in a smaller volume. So this gets more and more dense. So cor... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
It is able to pack more mass in a smaller volume. So this gets more and more dense. So core becomes more dense until at some point. And so while the core is becoming more and more dense, that actually makes the fusion happen faster and faster because it's more dense, more gravitational pressure, more mass wanting to ge... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And so while the core is becoming more and more dense, that actually makes the fusion happen faster and faster because it's more dense, more gravitational pressure, more mass wanting to get to it, more pressure on the hydrogen that's fusing. So it starts to fuse hotter. So let me write this. So the fusion. So hydrogen ... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So the fusion. So hydrogen fuses faster. And actually, we even see this in our sun. Our sun today is brighter and hotter. It's fusing faster than it was when it was born 4.5 or 4.6 billion years ago. But eventually, you're going to get to the point so that the core, you only have helium. So there's going to be some poi... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Our sun today is brighter and hotter. It's fusing faster than it was when it was born 4.5 or 4.6 billion years ago. But eventually, you're going to get to the point so that the core, you only have helium. So there's going to be some point where the entire core is all helium. And it's going to be way denser than this co... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So there's going to be some point where the entire core is all helium. And it's going to be way denser than this core over here. All of that mass over there has now been turned into helium. Not all of it. A lot of it has been turned into energy. But most of it is now in helium. And it's going to be in a much, much smal... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Not all of it. A lot of it has been turned into energy. But most of it is now in helium. And it's going to be in a much, much smaller volume. And the whole time, the temperature is increasing. The fusion is getting faster and faster. And now that it's in this dense volume of helium that's not fusing, you do have, and w... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And it's going to be in a much, much smaller volume. And the whole time, the temperature is increasing. The fusion is getting faster and faster. And now that it's in this dense volume of helium that's not fusing, you do have, and we saw this in this video, a shell around it of hydrogen that is fusing. So this right her... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And now that it's in this dense volume of helium that's not fusing, you do have, and we saw this in this video, a shell around it of hydrogen that is fusing. So this right here is hydrogen fusion going on. And then this over here is just hydrogen plasma. Now the unintuitive thing, or at least this was unintuitive to me... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Now the unintuitive thing, or at least this was unintuitive to me at first, was what's going on in the core is that the core is getting more and more dense. It's fusing at a faster rate. And so it's getting hotter and hotter. So the core is hotter, fusing faster, getting more and more dense. I kind of imagine it's star... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So the core is hotter, fusing faster, getting more and more dense. I kind of imagine it's starting to collapse. Every time it collapses, it's getting hotter and more dense. But at the same time that's happening, the star itself is getting bigger. The star itself is getting bigger. And this is actually not drawn to scal... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But at the same time that's happening, the star itself is getting bigger. The star itself is getting bigger. And this is actually not drawn to scale. Red giants are much, much larger than main sequence stars, but the whole time that this is getting more dense, the rest of the stars, you can kind of view it as getting l... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Red giants are much, much larger than main sequence stars, but the whole time that this is getting more dense, the rest of the stars, you can kind of view it as getting less dense. And that's because this is generating so much energy that it's able to more than offset, or better offset, the gravitational pull into it. ... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And so that volume is so big that the surface, and we saw this in the last video, the surface of the red giant is actually cooler than the surface of a main sequence star, this right here is hotter. And just to put things in perspective, when the sun becomes a red giant, and it will become a red giant, its diameter wil... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Or another way to view it is, where we are right now will be on the surface, or near the surface, or maybe even inside of that future sun. Or another way to put it, when the sun becomes a red giant, the Earth's going to be not even a speck out here, and it will be liquefied and vaporized at that point in time, so this ... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Just for light to reach the current sun to our point in orbit, it takes 8 minutes. So that's how big one of these stars are. To get from one side of the star to another side of the star, it'll take 16 minutes for light to travel, if it was traveling that diameter. And even slightly longer, if it was to travel in a circ... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And even slightly longer, if it was to travel in a circumference. So these are huge, huge, huge stars. And we'll talk about other stars in the future that are even bigger than this when they become super giants. But anyway, we have the helium in the center. Let me write this down. We have a helium core in the center. W... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But anyway, we have the helium in the center. Let me write this down. We have a helium core in the center. We're fusing faster and faster and faster. We're now a red giant. The core is getting hotter and hotter and hotter, until it gets to the temperature for ignition of helium. So until it gets to 100 million Kelvin. | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
We're fusing faster and faster and faster. We're now a red giant. The core is getting hotter and hotter and hotter, until it gets to the temperature for ignition of helium. So until it gets to 100 million Kelvin. Remember, the ignition temperature for hydrogen was 10 million Kelvin. So now we're at 100 million Kelvin, ... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So until it gets to 100 million Kelvin. Remember, the ignition temperature for hydrogen was 10 million Kelvin. So now we're at 100 million Kelvin, factor of 10. And now, all of a sudden, in the core, you actually start to have helium fusion. And we touched on this in the last video, but the helium is fusing into heavie... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And now, all of a sudden, in the core, you actually start to have helium fusion. And we touched on this in the last video, but the helium is fusing into heavier elements. And some of those heavier elements, and predominantly it will be carbon and oxygen. And you may suspect, this is how heavier and heavier elements for... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And you may suspect, this is how heavier and heavier elements form in the universe. They form literally due to fusion in the core of stars. Especially when we're talking about elements up to iron. But anyway, the core is now experiencing helium fusion. It has a shell around it of helium that is not quite there. Does no... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But anyway, the core is now experiencing helium fusion. It has a shell around it of helium that is not quite there. Does not quite have the pressures and temperatures to fuse yet. So just regular helium. But then outside of that, we do have the pressures and temperatures for hydrogen to continue to fuse. So out here, y... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So just regular helium. But then outside of that, we do have the pressures and temperatures for hydrogen to continue to fuse. So out here, you do have hydrogen fusion. And then outside over here, you just have the regular hydrogen plasma. So what just happened here? When you have helium fusion all of a sudden, now this... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And then outside over here, you just have the regular hydrogen plasma. So what just happened here? When you have helium fusion all of a sudden, now this is once again providing some type of outward support for the core. So it's going to counteract the ever-increasing contraction of the core as it gets more and more den... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So it's going to counteract the ever-increasing contraction of the core as it gets more and more dense. Because now we have energy going outward. Energy pushing things outward. But at the same time that that is happening, more and more hydrogen in this layer is turning into helium. Is fusing into helium. So it's making... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But at the same time that that is happening, more and more hydrogen in this layer is turning into helium. Is fusing into helium. So it's making this inert part of the helium core even larger and larger denser. And even larger and larger. And putting even more pressure on this inside part. And so what's actually going t... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And even larger and larger. And putting even more pressure on this inside part. And so what's actually going to happen within a few moments from, I guess, especially from a cosmological point of view, this helium fusion is going to be burning super, I shouldn't use igniting or fusing, in a super hot level. But it's con... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But it's contained to do all of this pressure. But at some point, that pressure won't be able to contain it and the core is going to explode. But it's not going to be one of these catastrophic explosions where the star is going to be destroyed. It's just going to release a lot of energy all of a sudden into the star. A... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
It's just going to release a lot of energy all of a sudden into the star. And that's called a helium flash. A helium flash. But once that happens all of a sudden, then now the star is going to be more stable. And I'll use that in quotes without writing it down. Because red giants in general are already getting to be le... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But once that happens all of a sudden, then now the star is going to be more stable. And I'll use that in quotes without writing it down. Because red giants in general are already getting to be less stable than a main sequence star. But once that happens, you now will have a slightly larger volume. So it's not being co... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But once that happens, you now will have a slightly larger volume. So it's not being contained in as small of a tight volume. That helium flash kind of took care of that. So now you have helium fusing into carbon and oxygen. And there's all sorts of other combinations of things. Obviously, there's many elements in betw... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So now you have helium fusing into carbon and oxygen. And there's all sorts of other combinations of things. Obviously, there's many elements in between helium and carbon and oxygen. But these are the ones that dominate. And then outside of that, you have helium forming. You have helium that is not fusing. And then out... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But these are the ones that dominate. And then outside of that, you have helium forming. You have helium that is not fusing. And then outside of that, you have your fusing hydrogen. You have over here, you have hydrogen fusing into helium. And then out here in the rest of the radius of our super huge red giant, you jus... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And then outside of that, you have your fusing hydrogen. You have over here, you have hydrogen fusing into helium. And then out here in the rest of the radius of our super huge red giant, you just have your hydrogen plasma out here. Now what's going to happen as this star ages? Well, if we fast forward this a bunch. An... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Now what's going to happen as this star ages? Well, if we fast forward this a bunch. And remember, as the star gets denser and denser in the core and the reactions happen faster and faster in this core, it's expelling more and more energy outward. The star keeps growing. And the surface gets cooler and cooler. So if we... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
The star keeps growing. And the surface gets cooler and cooler. So if we fast forward a bunch, and this is what's going to happen to something the mass of our sun. If it's more massive, then at some point, the core of carbon and oxygen that's forming can start to fuse into even heavier elements. But in the case of the ... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
If it's more massive, then at some point, the core of carbon and oxygen that's forming can start to fuse into even heavier elements. But in the case of the sun, it will never get to that 600 million Kelvin to actually fuse the carbon and the oxygen. And so eventually, you will have a core of carbon and oxygen, or mainl... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But eventually, all of this fuel will run out. All of the hydrogen will run out in the stars. All of this fusing hydrogen will run out. All of this fusing helium will run out. All of this is the fusing hydrogen. This is the inert helium, which will run out. It'll be used in kind of this core being fused into the carbon... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
All of this fusing helium will run out. All of this is the fusing hydrogen. This is the inert helium, which will run out. It'll be used in kind of this core being fused into the carbon and oxygen, until you get to a point where you literally just have a really hot core of carbon and oxygen. And it's super dense. This w... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
It'll be used in kind of this core being fused into the carbon and oxygen, until you get to a point where you literally just have a really hot core of carbon and oxygen. And it's super dense. This whole time, it'll be getting more and more dense as heavier and heavier elements show up in the core. So it gets denser and... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So it gets denser and denser and denser. But this super dense thing will not, in the case of the sun, if it was a more massive star, it would get there. But in the case of the sun, it will not get hot enough for the carbon and the oxygen to form. So it really will just be this dense ball of carbon, super dense ball of ... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So it really will just be this dense ball of carbon, super dense ball of carbon and oxygen. And all of the other material in the sun, remember, was super energetic. It was releasing tons and tons of energy. The more that we progressed down this, the more energy was releasing outward. And the larger the radius of the st... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
The more that we progressed down this, the more energy was releasing outward. And the larger the radius of the star gained. And the cooler the outside of the star became. Until the outside just becomes this kind of cloud, this huge cloud of gas around what once was the star. And in the center, so I could just draw it a... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Until the outside just becomes this kind of cloud, this huge cloud of gas around what once was the star. And in the center, so I could just draw it as this huge, this is now way far away from the star, much even bigger than the radius or the diameter of a red giant. And all we'll have left is a mass, a super dense mass... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
This is in the case of the sun. And at first, when it's hot, and it will be releasing radiation because it's so hot, we'll call this a white dwarf. This right here is called a white dwarf. And it'll cool down over many, many, many, many, many, many, many years until it becomes, when it's no longer, when it's completely... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And it'll cool down over many, many, many, many, many, many, many years until it becomes, when it's no longer, when it's completely cooled down, lost all of its energy, it'll just be this super dense ball of carbon and oxygen. At which point, we would call it a black dwarf. And these are obviously very hard to observe ... | White and black dwarfs Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
It is the dominant place or the most likely place to find mountains or volcanoes on the surface of the earth. But that's not the only place that mountains or volcanoes can form. And probably the biggest example of volcanic activity, or the most popular one, this might be a slightly American, Amerocentric point of view.... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
But the most often cited example of volcanic activity away from a plate boundary is Hawaii. So this right here, these are the Hawaiian islands. This is the big island of Hawaii. And it is experiencing an active volcano. Lava or magma is flowing from underneath the ground. And once it surfaces, we call it lava. And that... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.