Things You Thought You Knew - Fun with Fusion

What is thermonuclear fusion? Neil deGrasse Tyson and comedian Chuck Nice break down the Department of Energy’s breakthrough, thermonuclear fusion at the center of stars, supernovae, and how stars are born.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Neil deGrasse Tyson?

  Welcome to StarTalk. Your place in the universe where science and pop culture collide. StarTalk begins right now.

• 0:15Neil deGrasse Tyson?

  This is StarTalk, a Things You Thought You Knew edition. Chuck, always good to have you, man.

• 0:22Chuck Nice?

  Always a pleasure to be here.

• 0:24Neil deGrasse Tyson?

  All right, this particular episode of Things You Thought You Knew was triggered by the triggering of fusion recently at the Lawrence Livermore National Labs.

• 0:38Chuck Nice?

  Yeah.

• 0:38Neil deGrasse Tyson?

  And, oh my gosh, people couldn't get enough of this. What is fusion? How does it work? How does it relate to astrophysics? Where does it happen? Why does it happen? And so, we've got three consecutive Things You Thought You Knew, all about fusion. And by the end of this, you should be conversant at the next cocktail party.

• 1:01Chuck Nice?

  Okay, I'll take that.

• 1:03Neil deGrasse Tyson?

  All right, so let's do this. Chuck, what's been bugging you lately?

• 1:07Chuck Nice?

  I'll tell you, I don't know if it's bugging me. Maybe I'm happy about it. Maybe, maybe the entire human race has something to be hopeful about. You know how I feel about climate and the climate crisis. But, so, I wake up this morning and it's all about fusion. Fusion everywhere. Everybody's talking about fusion. Fusion, fusion. I'm like, whoa, whoa, is this a good thing? Or are they yanking my chain? Are they just making me? What are they doing? Are they doing the Lucy pulled a football away from me? What are they doing? What is happening? What is happening with the fusion?

• 1:44Neil deGrasse Tyson?

  Oh, okay. So, the highlight is at one of the national laboratories, Lawrence Livermore National Laboratories, where they, among all the national labs, are, one of their major tasks is as shepherds of our nuclear arsenal.

• 2:07Neil deGrasse Tyson?

  Okay, the nuclear fuel, basically, so radioactive materials that might be used in weapons. And it is funded by the Department of Energy, not the Department of Defense. So that in fact, the total amount of money we spend on defense is not only the DOD's budget, but an important fraction of the Department of Energy's budget that involves weaponry, basically. Okay. Right, yes. So there, they have the world's most powerful laser. And what they do with a bunch of these lasers is they aim them all at a tiny target. And they cause the target to explode. All right, that alone is not, okay.

• 2:53Neil deGrasse Tyson?

  Okay, all right. Sounds like America so far.

• 2:59Neil deGrasse Tyson?

  People say, well, what's new about this? Because we've been blowing it up like forever. So if the target is uniformly heated, evenly in all directions, and the material is very uniform in all directions, so that would be a spherical shape, then the explosion creates an implosion on the other side of that explosion, right? You can't just have stuff come out unless the Newton's law for every action is an equal and opposite reaction. Explosion that comes out creates an explosion that points inward. Okay. Very high pressure and very high temperature.

• 3:39Neil deGrasse Tyson?

  And under those conditions, you can take two atoms, light atoms, and merge them into a heavier atom. Sweet. That takes a lot of high temperature to accomplish. Because, let's take the lightest atom of them all, which is what? I don't know, maybe hydrogen? Hydrogen, you got it. So hydrogen in its nucleus has one proton. And helium in its nucleus has two protons, plus two neutrons. So how am I gonna create a helium atom from a hydrogen atom? So you gotta get a bunch of hydrogen atoms together, all right? Together. Together. Well, here's what no one is telling you in the news, but it's obvious when you think about it.

• 4:24Neil deGrasse Tyson?

  What do two protons want to normally do? They're both positive charged.

• 4:29Chuck Nice?

  They don't, they, they like each other, but they don't like each other. Cause they're alike.

• 4:34Neil deGrasse Tyson?

  Okay.

• 4:35Chuck Nice?

  It's like when you, it's like when you meet somebody at a cocktail party and they remind you of yourself. And you're just like, I don't like that dude. Some, I don't really like that. I don't wanna be over there talking to that dude.

• 4:47Neil deGrasse Tyson?

  Chuck is still in therapy, people, just so you know.

• 4:49Chuck Nice?

  I know, exactly. It's like, it's a simple question, Chuck. Where, where do cocktail parties and liking people come in? Yeah, but they, they wanna get away from each other, right?

• 4:59Neil deGrasse Tyson?

  So these are like charges. They're, so in the case of two protons, they repel each other. So, how do you get them to come together as a new helium nucleus if they want to repel? So this is like rolling, rolling a ball up a hill. All right? If you don't give it enough energy, it's not gonna reach the top. It's not gonna reach the top, okay?

• 5:22Chuck Nice?

  There you go, so that, yeah.

• 5:24Neil deGrasse Tyson?

  If you roll it faster and faster, giving it more and more energy, eventually the ball will reach the top and tip and go over and fall on the other side of the hill. That is precisely what's going on with two protons. Here it goes. The two protons wanna come near each other, but they repel. Let's boost the temperature, which speeds everything up. They get closer to each other before they repel. Boost the temperature some more, they get even, even closer. There is a magic temperature at which these protons will come close enough so that an entire new force operates.

• 6:06Neil deGrasse Tyson?

  It would have to be a strong force in the nucleus to keep two protons together. In fact, the name of that-

• 6:13Chuck Nice?

  That's quantum love.

• 6:16Chuck Nice?

  That's called quantum love.

• 6:18Neil deGrasse Tyson?

  Oh, where's that disco, so I remember jungle love, remember jungle love?

• 6:21Chuck Nice?

  Exactly. Oh, jungle love.

• 6:24Neil deGrasse Tyson?

  Yeah, quantum love is like you resist until you cross over the barrier and then you're there. So, when they cross that barrier, a strong force that operates in the nucleus takes over. It's one of the fundamental forces of nature and it's called the strong nuclear force. There it is, okay? What it's called. It only operates on scales as small as the nucleus itself.

• 6:54Neil deGrasse Tyson?

  But you have to get there for it to grab a hold of you and make a new atom. That's why it takes high density, high pressure and high temperature to overcome.

• 7:04Chuck Nice?

  All right, so now I'm with you.

• 7:08Neil deGrasse Tyson?

  That is thermo nuclear fusion. Thermo is hot, nuclear is the nucleus, fusion, they're bringing it together. It turns out that when you do that, your products have less mass than when you started with. Whoa. Oh, my gosh. Where did the mass go?

• 7:28Chuck Nice?

  Exactly.

• 7:29Neil deGrasse Tyson?

  E equals mc squared. My lovely. So the mass on the one side of the equation, if you lose it, it manifests on the other side of the equation as energy.

• 7:42Chuck Nice?

  There you go.

• 7:43Neil deGrasse Tyson?

  There it is. And so they managed. So at the Lawrence Livermore Laboratories using lasers. And by the way, they've led the world in lasers like for decades. In fact, people on the inside call it lasers, lasers and lasers. Okay. Lawrence Livermore National Lab.

• 8:01Chuck Nice?

  Lasers, lasers and lasers.

• 8:03Neil deGrasse Tyson?

  And lasers, right? Right. So, so anyhow, so they have managed to, you can add up how much energy it takes to turn on the lasers and fire them. And then look at how much energy comes out after you've done this. And they got 50% more energy out of this than the energy of the lasers that went into it.

• 8:24Chuck Nice?

  That's amazing because wow, now that, now that's, now that's an energy source now because you got more out than you got in, which is what I want to know, which is what did it measure? Like, is it anything significant? Percentage wise, that's great, but like, what would it take to turn this into an energy?

• 8:41Neil deGrasse Tyson?

  It just broke even. That would be a major milestone unto itself, right? But the fact that they got 50% more energy out than they put in, it's, it says, oh my gosh, we can get the physics to succeed.

• 8:56Neil deGrasse Tyson?

  And for my money, I'm saying if the physics works, then it's just a matter of time before engineers, I got this. I got, I got, I'm gonna make something out of that. I, I got this. And so.

• 9:09Chuck Nice?

  That's amazing.

• 9:09Neil deGrasse Tyson?

  Yeah. And so I very much look forward, there's a civilization pivoting on this result. And by the way, what I just described to you, the sun does every moment of its life. The problem over all these years is that, of course, we've known how to make fusion. We've got, we've known how to make fusion since, what, 1949 or something? When the first fusion bombs were called hydrogen bombs. They're using hydrogen. That's what I just told you. We have two protons merging hydrogen atoms, nuclei together. So we've known how to make fusion forever. The challenge is not how do you make fusion? How do you control it?

• 9:49Chuck Nice?

  Yeah, because you don't want the electric company having to move to a new city because there's no city left.

• 9:54Neil deGrasse Tyson?

  Right, exactly. So while in America, America, we're really good at blowing stuff up. We're less good at controlling that explosion, right? So the holy grail was, can we undergo fusion in a controlled way? Where one day you might be able to throttle it, or contain it, or transport it? And we'll finally get, maybe, that ending scene in Back to the Future.

• 10:25Chuck Nice?

  Right.

• 10:26Neil deGrasse Tyson?

  Here's your cue, Doc. Marty, it's your kid, Spotty. And do you remember how, you know, and, and, and Marty says, but Doc, where are you gonna get the energy? There's no lightning bolt, and there's no room for, you know, what are you gonna do? And remember what he does?

• 10:51Chuck Nice?

  He dumps a bunch of trash into the flux capacitor, which is now powered by fusion.

• 10:59Neil deGrasse Tyson?

  It's Mr. Home Fusion, right? It was like a blender.

• 11:03Chuck Nice?

  That's right.

• 11:04Neil deGrasse Tyson?

  He puts it in and that undergoes nuclear fusion. And so one day, perhaps, we have fusion reactors in every car. And then you could like,

• 11:14Chuck Nice?

  Wow.

• 11:14Neil deGrasse Tyson?

  There it is. So this would transform civilization. Even regardless of the carbon footprint that it doesn't have, it would transform civilization. But it also happens to not have a carbon footprint. So we could stave off this growth of fossil fuel burning and greenhouse gases. And we'll still have to recover from the damage we've already done. Because a lot of the carbon dioxide got up took into the oceans. And if you start removing it from the atmosphere, it begins to come out of the oceans. And it'll do that until it becomes equal again. So you gotta like recover that. But it is the future.

• 11:55Neil deGrasse Tyson?

  And I tip my hat to this science physicist and engineers at the National Labs. And this whole thing was important enough. It was a press conference announced by the Secretary of Energy. So, oh, yeah. Yeah, chomping at the bit.

• 12:11Chuck Nice?

  So then it is good news.

• 12:13Neil deGrasse Tyson?

  Good news. You suspected accurately, yes.

• 12:17Chuck Nice?

  All right.

• 12:17Neil deGrasse Tyson?

  And we've been at it for decades. Just thought I'd tell you that. And so this will be a benchmark day. The first week and first and second week of December in the year 2022. We'll look back on that.

• 12:30Chuck Nice?

  Another day in December that will live not in infamy. What is it when it's a good thing?

• 12:35Neil deGrasse Tyson?

  Femmy.

• 12:37Chuck Nice?

  Just femmy.

• 12:45Neil deGrasse Tyson?

  All right, Chuck, we gotta end it there.

• 12:47Chuck Nice?

  All right.

• 12:48Neil deGrasse Tyson?

  All right, but there's way more about like talk about stars.

• 12:51Chuck Nice?

  Yeah.

• 12:52Neil deGrasse Tyson?

  There's more and why stars explode. All right, I'll leave a teaser here. You ready? Fusion, you get energy by combining little atoms. Fusion, you get energy by splitting big atoms.

• 13:04Chuck Nice?

  Okay.

• 13:05Neil deGrasse Tyson?

  But wait a minute. There's got to be some point in the middle where these two phenomenon meet.

• 13:12Neil deGrasse Tyson?

  What happens then? Therein are the seeds of the undoing of great massive stars in the universe. Chuck, we will get to that in the very next segment of this Things You Thought You Knew Fusion Edition when StarTalk continues.

• 13:37Speaker 02

  Hey, I'm Roy Hill Percival and I support StarTalk on Patreon, Bringing the Universe Down to Earth. This is StarTalk with Neil deGrasse Tyson.

• 13:53Neil deGrasse Tyson?

  We're back, Things You Thought You Knew, the Fusion Edition. This time, Chuck, I'm going to take this into the universe.

• 13:59Chuck Nice?

  Okay.

• 14:00Neil deGrasse Tyson?

  Because we were fusing stuff long before the Lawrence Livermore National Labs were even born.

• 14:05Chuck Nice?

  Oh, okay.

• 14:07Neil deGrasse Tyson?

  In fact, billions of years before they were born. So let's see what the universe has to say about thermonuclear fusion. You know, my people, we astrophysicists, that we're all about fusion. Just want you to know that.

• 14:19Chuck Nice?

  Yes, yes, you guys, you really stick together.

• 14:24Neil deGrasse Tyson?

  That was good.

• 14:24Chuck Nice?

  I'm sorry. That was not... That was awful.

• 14:30Neil deGrasse Tyson?

  So, just so you know where we're coming from, every single star in the universe that is sort of alive, alive in a stellar sense, is undergoing thermonuclear fusion. And that whole word, you can parse it, thermo is heat, that nuclea is the nucleus, and fusion is the bringing together of nuclei. And it happens that when you bring in the quantum physics and into the periodic table of elements... And you slam these nuclei together. You make heavier nuclei that are missing some mass. An atomic mosh pit.

• 15:14Neil deGrasse Tyson?

  And the mass has become energy. Right. So here's what's, here's what's interesting. So cool, so cool. Here's what's interesting. Yeah. Just, I think it's interesting, but you, you and the viewers, listeners will be the judge of this. All right. We lay people. You've heard of nuclear fission. Of course. This is where you take a big atom, such as uranium or plutonium, as we've done in the past. Those are big atoms, all right? Ninety-two, ninety-four protons crammed into its nucleus. Right. And that's like the opposite of hydrogen, which has one proton in its nucleus, right? So the hydrogen we use for fusion and make heavier elements.

• 15:58Neil deGrasse Tyson?

  And fission, we take the big elements and split them apart. So you split them apart. You get other elements when you add up their mass, it's less. And you get energy from that. And this is the foundations of the, the nuclear fission arsenal. The bombs used in the Second World War were fission bombs. Well, if splitting an atom gets you, splitting heavy atoms gets you energy. Mm-hmm. And fusing light atoms gets you energy. Right. Well, then what's going on? Is there some point in the middle? Right? Where, does it know if you split it or fuse it, what can happen?

• 16:42Neil deGrasse Tyson?

  So here, here's what's going on. As you fuse atoms, you get less and less energy out from the fusion. Mm-hmm. As the atoms get bigger. As you split atoms, you get less and less energy out for having split them. Okay. Okay. Gotcha. All right, all right. So it turns out there is a place in the periodic table of elements where that element, if you split it, it absorbs energy. And if you fuse it, it absorbs energy. Oh. So you can't fizz past it.

• 17:27Neil deGrasse Tyson?

  And still expect to make energy and you can't fuse past it. The buck stops there.

• 17:35Chuck Nice?

  Wow.

• 17:36Neil deGrasse Tyson?

  And that element is iron.

• 17:40Chuck Nice?

  Iron.

• 17:40Neil deGrasse Tyson?

  On the periodic table of elements.

• 17:42Chuck Nice?

  See, if this were a Marvel movie, we would call it absorpsion or something like that.

• 17:49Chuck Nice?

  We must get the element absorpsion. So that we can stop this reaction and save the universe.

• 17:56Neil deGrasse Tyson?

  Yes, it would it would stop all freaking reactions. Correct. Correct. You you cannot fizz iron. You cannot fuse iron. Okay, so this effort to undergo nuclear fission, to undergo nuclear fusion, has a stopping point. All right, so stars are born with hydrogen and helium and they start fusing and they work their way up the periodic table, up in mass. Okay, so the the sun, as other stars will do, they start in hydrogen, they make helium. And then they take three helium atoms, bring them together and you get, oh, well, let's figure it out. Uh, helium has two protons. Okay, so you take three of those atoms, how many protons you have? A helium had two protons.

• 18:39Chuck Nice?

  You have six protons. You got six protons.

• 18:42Neil deGrasse Tyson?

  Six, okay. Don't tell me I went to public schools, I don't know.

• 18:48Neil deGrasse Tyson?

  Okay, by the way, I went to public school, K through 12. So, um, so two, two and two, then you have six protons. You go check the periodic table of elements. Who has six protons? Carbon does.

• 18:59Chuck Nice?

  Ah ha.

• 19:00Neil deGrasse Tyson?

  Okay, so, so, uh, we go from hydrogen to helium, there's carbon in there. There are other pathways that get other elements, but these are the primary ones. Okay, so you get to carbon, you get nitrogen, oxygen, and so there's a, there are these fusion pathways that work their way up the periodic table. And at each step, the sun is making energy.

• 19:22Chuck Nice?

  Right.

• 19:23Neil deGrasse Tyson?

  Okay, so the sun can hold itself up. Against gravitational collapse.

• 19:29Chuck Nice?

  Gotcha.

• 19:30Neil deGrasse Tyson?

  Because it wants to collapse. This gravity is a, let, I want to make this sucker as small as possible, but the fusion is saying, no, you're not, no, you're not, no, you're not.

• 19:37Chuck Nice?

  Right.

• 19:38Neil deGrasse Tyson?

  Preventing that.

• 19:39Chuck Nice?

  So there's pressure without and pressure within.

• 19:42Neil deGrasse Tyson?

  Correct.

• 19:42Chuck Nice?

  So the pressure pushing out is the fusion actually propping up the sun in its size and creating-

• 19:50Neil deGrasse Tyson?

  It's a perfect, perfect phrase, propping up the sun. That's exactly what it's doing.

• 19:53Chuck Nice?

  Wow.

• 19:55Neil deGrasse Tyson?

  Now, there are people who misinterpret this because we say it is balanced.

• 19:59Chuck Nice?

  Right.

• 20:00Neil deGrasse Tyson?

  You know, the star is ba, the sun is balanced because it's not shrinking and it's not expanding.

• 20:05Chuck Nice?

  Right.

• 20:05Neil deGrasse Tyson?

  Okay, here's an interesting fact. It is balanced as a ball would be at the bottom of a hill, between two hills, not balanced as it would be at the top of a hill.

• 20:18Chuck Nice?

  Right.

• 20:19Neil deGrasse Tyson?

  These are two different kinds of balance.

• 20:20Chuck Nice?

  Absolutely.

• 20:21Neil deGrasse Tyson?

  At the top of the hill, you can just barely balance it and put it in what we call equilibrium, but it's an unstable equilibrium. That's an official term.

• 20:29Chuck Nice?

  I love it.

• 20:30Neil deGrasse Tyson?

  Unstable because if you just breathe on the marble, it'll fall down the hill.

• 20:34Chuck Nice?

  Right.

• 20:34Neil deGrasse Tyson?

  Okay, all right, now, the ball at the bottom of the, between two hills in a trough, is also a, an equilibrium, but it's a stable equilibrium.

• 20:44Chuck Nice?

  Right.

• 20:44Neil deGrasse Tyson?

  If you blow on it, it'll go up the side and come right back down to where it was.

• 20:48Chuck Nice?

  Right.

• 20:49Neil deGrasse Tyson?

  Stars are not in a delicate balance, they're in a stable balance, okay?

• 20:56Chuck Nice?

  Mm-hmm.

• 20:57Neil deGrasse Tyson?

  So watch what happens. If you compress the star, the star gets hotter, creates more energy and pumps itself back up.

• 21:05Chuck Nice?

  Oh.

• 21:06Neil deGrasse Tyson?

  If you figure, if you somehow manage to puff it up, that releases the pressure on the inside, the nuclear fuel, uh, uh, uh, energy rate drops and then it shrinks back down again.

• 21:17Chuck Nice?

  Look at that.

• 21:19Neil deGrasse Tyson?

  It's, it's, there it is. Stable equilibrium.

• 21:21Chuck Nice?

  That's wonderful.

• 21:22Neil deGrasse Tyson?

  It's, it's a totally wonderful thing, especially if you have long-term civilizations that you wanna sort of-

• 21:28Chuck Nice?

  Yeah.

• 21:28Neil deGrasse Tyson?

  Uh, you've-

• 21:29Chuck Nice?

  If you're, if you're gonna, if you're gonna be a civilization that is smart enough- To use that power and energy, then you have a stable source of power that is always working. And you don't have to worry about it being unstable because it's in a state of stable equilibrium. But, you know, that's kind of, I mean, who could ever do that? That's ridiculous.

• 21:58Neil deGrasse Tyson?

  Yet another public service announcement from Chuck Nice. Okay. All right, so watch what happens. So there's the star. And it is, and there are more details that we have time to get into here. But the star is cranking its way up the periodic table of elements. And each of these new elements creates an onion skin layer in the center of the star. So there's, um, the outer layer has the hydrogen and helium and carbon. And because the sun is only hottest at the center. And it has to be really hot to fuse the bigger elements. Because I need more energy, more temperature, higher speeds to fuse helium than I did hydrogen. Because helium has two protons and two protons. There is more resistive force there

• 22:43Neil deGrasse Tyson?

  than one proton and one proton. If I want to fuse carbon, I got six protons and six pro- So it is, the, the, the center of the star gets hotter and hotter and hotter to, in order to make this happen. I run out of hydrogen in my core because I made it all into helium.

• 22:58Chuck Nice?

  Right.

• 22:59Neil deGrasse Tyson?

  Okay? I'm not hot enough to fuse helium. I'm not. So how do I ever end up fusing helium? I ran out of energy. What does the star do? The star says, gravity is, time for gravity to win. And it, the core collapses.

• 23:12Chuck Nice?

  Right.

• 23:13Neil deGrasse Tyson?

  Increasing the pressure, increasing the temperature, until helium kicks in.

• 23:19Neil deGrasse Tyson?

  Then helium ignites, stabilizing the star once again. You run out of helium in the core and carbon's sitting around doing nothing. Okay, time for the star to collapse. Gravity says, time for us to win again. Carbon says, not so fast. You have now raised my temperature so that I can fuse. And so, stopping the further collapse. Okay? This is, this is the, this is the, the dance that stars do with their thermonuclear fusion in their core. So now watch. Okay, here's the fun part. I now get to iron. In the core. And the star says, we've been down that road before.

• 23:57Chuck Nice?

  Right.

• 23:57Neil deGrasse Tyson?

  Right now, right now, you're not giving us energy. Let's collapse under our own weight. Increase the temperature, then you'll give us energy.

• 24:05Chuck Nice?

  And then you will fuse.

• 24:07Neil deGrasse Tyson?

  You will fuse.

• 24:08Chuck Nice?

  Iron says, ha ha, and pulls up its mask and says, it's me. Absorption.

• 24:16Neil deGrasse Tyson?

  So the star collapses, ready to, for iron to give it new energy. And iron says, no, I absorb energy to fuse.

• 24:25Chuck Nice?

  Uh oh.

• 24:26Neil deGrasse Tyson?

  And so now the star, which is in the business of making energy.

• 24:30Chuck Nice?

  Right.

• 24:31Neil deGrasse Tyson?

  Has a fuel source in the center that is only absorbing energy. So the star collapses some more. And iron says, I will take anything you give me. And any heavier element is going to absorb it as well. And so the star undergoes a catastrophic collapse. Catastrophe, within hours. This is a star that's been alive for millions of years. Millions of years. And within a matter of hours, it's a catastrophic collapse. And in that collapse, the temperature goes to astronomically high temperatures.

• 25:10Chuck Nice?

  Yeah.

• 25:10Neil deGrasse Tyson?

  And here you have this ball of astronomically high temperatures in the collapse. And it only knows one thing to do at that point. And that's explode.

• 25:19Chuck Nice?

  It has to.

• 25:20Neil deGrasse Tyson?

  It has to.

• 25:20Chuck Nice?

  It can't fuse. It's got no other choice but to explode.

• 25:25Neil deGrasse Tyson?

  To explode. And Chuck, thus is the appearance in the universe of a supernova explosion.

• 25:34Chuck Nice?

  Hmm, better known as a several billion year orgasm.

• 25:40Neil deGrasse Tyson?

  What?

• 25:43Neil deGrasse Tyson?

  No, those stars don't live billions of years. They went through this fast, okay? Only the highest mass stars.

• 25:50Chuck Nice?

  Oh, really?

• 25:50Neil deGrasse Tyson?

  Have enough, have enough pressure to take the temperature to get to iron. The sun is not, will never make it to iron.

• 25:56Chuck Nice?

  The sun won't make it because, okay, it's not big enough. Cause you need, you need the pressure without and the pressure within. And it has to be a big enough mass, not big enough in size, but it has to be a large enough mass for that. Oh my God, that's amazing.

• 26:10Neil deGrasse Tyson?

  It's amazing. So the gravity creates the pressure and the temperature. And it's the temperature that matters because temperature makes the particles go at high speeds to overcome their, their repulsion.

• 26:19Chuck Nice?

  That's the only way you can get to the fusion.

• 26:22Neil deGrasse Tyson?

  Fusion so that the strong nuclear force takes over. Gotta get over that hump. Exactly. Then it sticks. That's right. So. Amazing. So this would have happened in millions of years. Some will live billions, some stars live trillions. These, this special category of high mass stars doesn't live very long. 10 million years tops. Wow. They go to iron, they create this onion layer of elements. They explode and they scatter that enrichment across the galaxy. Allowing newly born stars in stellar nurseries to have planets made of ingredients that are not just hydrogen and helium. Made of planets that have carbon, nitrogen, oxygen.

• 27:06Neil deGrasse Tyson?

  The basic ingredients of life itself. That's beautiful, man. We are not. We're not just poetically stardust. We are literally. Literally stardust. Stardust. Correct. And what I say is we're alive in this universe, yes. But think about the universe contributing to who and what we are. Through this process of thermonuclear fusion from hydrogen all the way up to iron. And those stars explode. If those stars didn't explode, the universe would have all those elements locked up with nothing to make planets and people out of. Right. The fact that those stars explode.

• 27:52Neil deGrasse Tyson?

  The fact that the ones that make the elements explode. Allows me to tell you that not only are we alive in this universe. The universe is alive within us.

• 28:05Neil deGrasse Tyson?

  Oh, that's. Why do I feel like I want to take up an offering right now?

• 28:12Neil deGrasse Tyson?

  That was just gorgeous. The collection plate is going. I just want to pass the plate now. That was just beautiful, man. I mean, that's just wonderful. And this was figured out by four scientists. Burbidge, Burbidge, Fowler and Hoyle. Jeff Burbidge, Margaret Burbidge. Willie Fowler and Fred Hoyle.

• 28:32Chuck Nice?

  Burbidge Fowler and Hoyle.

• 28:38Neil deGrasse Tyson?

  Burbidge Fowler and Hoyle. And they really deserved the Nobel Prize for that. But back then, they weren't giving them to astrophysicists as they are today. But I'm just saying, that research paper came out in 1957, I think it was.

• 28:51Chuck Nice?

  Oh, my God. How soon? How recent?

• 28:55Neil deGrasse Tyson?

  Right, mid-century. So this, this understanding of our place in the universe, this cosmic perspective, I think of as the greatest gift that astrophysicists have given to civilization. Because it borders on the spiritual for its meaning and significance and our connectivity to the cosmos.

• 29:16Chuck Nice?

  It really does. And it's such an elegant picture of a closed system where dying stars seed the universe with life itself. And the building blocks for that life. It really is just a lovely, just almost metaphorical depiction, but it's literal at the same time. That's amazing.

• 29:46Neil deGrasse Tyson?

  So I just wanted to complete our fusion session together.

• 29:49Chuck Nice?

  Okay, but see, is it really complete? Because now I gotta know this. Because as you talk about this kind of explosion and these, you know, elements leaving and then going into these stellar nurseries, and then this system starts again. Now I want to know, how does the whole thing get kick-started? What happens that causes the entire thing to kick off in the first place that ignites that first little spark for the fusion?

• 30:19Neil deGrasse Tyson?

  I deeply value your insatiable curiosity. That's why I love you, Chuck.

• 30:24Chuck Nice?

  Well, I appreciate it. And I love you because you have answers and I don't have to read.

• 30:32Neil deGrasse Tyson?

  All right, Chuck, we're going to take a quick break. But when we return, we're going to find out how you give birth to stars in the first place on StarTalk. We'll be right back.

• 30:55Neil deGrasse Tyson?

  We're back. StarTalk, Things You Thought You Knew, Fusion Edition. Chuck, we're gonna round this out with just talking about how stars are born.

• 31:05Chuck Nice?

  Nice.

• 31:06Neil deGrasse Tyson?

  Alright, cuz somewhere in there fusion kicks in. And, uh, let's, let's get some sense of how that happens.

• 31:14Chuck Nice?

  We kinda went Benjamin Button. We started with death and now we're ending with birth.

• 31:19Neil deGrasse Tyson?

  There you go. Here it goes. Chuck, why the emergency call to my hotline?

• 31:24Chuck Nice?

  Because, we left off a place that has really put me in, uh, my peak curiosity.

• 31:33Neil deGrasse Tyson?

  Okay.

• 31:34Chuck Nice?

  Which is, we were talking about how the death of stars seeds the universe with the ingredients of life. Which, by the way, was like, just incredible. Where we, you know, talked about how fusion leads to a point where we get to iron, we can't go anymore, or as I like to call it, absorption.

• 31:55Neil deGrasse Tyson?

  Absorption.

• 31:57Chuck Nice?

  And, and then boom, we have to explode, right?

• 32:00Neil deGrasse Tyson?

  Yes, yes.

• 32:01Chuck Nice?

  And, but then, this is what got me when you said that. And then that is what, when these elements go out into the universe and they seed stellar nurseries and, you know, and they start this process again. And I'm just like, how does that even happen? Like, how does the process itself then get kick-started, you know?

• 32:24Neil deGrasse Tyson?

  Okay, so, uh, so a couple of things. Let me come into that from a back door. So, if you take biology class and one of, every biology class will spend some amount of time trying to define life.

• 32:38Chuck Nice?

  Yes.

• 32:39Neil deGrasse Tyson?

  Okay? And it's hard because we only have one example of it.

• 32:42Chuck Nice?

  Right.

• 32:43Neil deGrasse Tyson?

  So, it's, it's hard to generalize what life requires if you only have one example of life. The day we find another example of life, we can then throw away the things that we thought only applied to us.

• 32:59Neil deGrasse Tyson?

  We can throw away the things that we thought were fundamental to life. That happen to apply to us and just get the basic bottom common denominator of the two life forms that we know about. And if we discover a third life form, an a tenth life form, we can more sharply tune. So for example, does life need liquid water? Well, we know life on Earth needs liquid water, but there's all life. Maybe there's liquid ammonia in another place. Okay, that matters. I saw a comic where there's a crashed alien flying saucer in the desert, right? And the aliens are crawling out and they're saying, ammonia, ammonia. So just a little bit of a cosmic perspective there.

• 33:41Chuck Nice?

  Right.

• 33:41Neil deGrasse Tyson?

  So I'm so life, you don't, I don't think we know. But often what's bandied about is the idea that life has a metabolism. Okay, it, it, it uses energy. It needs a source of energy so that it can use the energy. And then when it uses the energy, it has to continue to replenish the source. And life needs a way to reproduce itself. Otherwise it wouldn't sustain. I guess something can be alive, but not ever reproduce itself. But in, in the full understanding of what life means and does on Earth, it has a metabolism and can reproduce itself. Okay.

• 34:22Neil deGrasse Tyson?

  If you look carefully at stars, they have a metabolism. They're born, they live out their lives, they die, and they reproduce themselves. So by some definitions, even many definitions of life, stars are alive.

• 34:43Chuck Nice?

  Hmm.

• 34:44Neil deGrasse Tyson?

  Just putting it out there.

• 34:45Chuck Nice?

  Ah, okay, I see what you're saying. So in, in, in, in, in the respect of life itself, there is.

• 34:53Chuck Nice?

  There is a facet where stars themselves fit the definition of being alive.

• 35:00Neil deGrasse Tyson?

  That's correct. And the reproducing themselves is their gas clouds waiting for this enrichment that then birth a next generation of stars. So it's, it's just an interesting way to think about stars relative to how we've thought about biology. So now we can ask, how you make a star in the first place?

• 35:18Chuck Nice?

  Mm hmm.

• 35:19Neil deGrasse Tyson?

  All right. Well.

• 35:21Chuck Nice?

  Well, first you gotta get a good agent. Let me just tell you, because you can have all the talent in the world, but if you're not connected correctly, you're gonna have some issues.

• 35:31Neil deGrasse Tyson?

  Okay, so some gas clouds have better agents than others.

• 35:34Chuck Nice?

  Okay.

• 35:35Neil deGrasse Tyson?

  So there are two broad categories of galaxy out there. One of them is elliptically shaped, and we call them elliptical galaxies. And they're sort of round, and they don't have much gas at all. They ate up their gas back when the galaxy was born, leaving hardly anything left to make new generations of stars. Okay? We call those elliptical. Broadly again, another is a very flat version of a galaxy that has spiral arms, and we call those spiral galaxies. All right?

• 36:06Chuck Nice?

  Okay.

• 36:07Neil deGrasse Tyson?

  Very clear and present. All right? Those are very inefficient at making stars, and they're still making stars today. They're as old as the elliptical galaxies, but they're still making stars, and they still have huge repositories of gas. All right? Now, I have a gas cloud minding its own business.

• 36:26Chuck Nice?

  Okay.

• 36:27Neil deGrasse Tyson?

  All right? There are reasons why a gas cloud would just be happy to stay that way its entire life, but here's what happens. Either a star blows up nearby, create a shock wave that literally shocks the gas cloud, or there are other sort of waves that relate to the maintenance of the spiral pattern, and they're called spiral density waves. And the point is, what we have is You have gas clouds moving through a region of the galaxy that because of this, what's called a density wave, it's compressed as it moves through this region before it comes out the other side.

• 37:12Neil deGrasse Tyson?

  Got you. All right. And so what's an example of that? If you're in traffic and you're driving down the street. Right. And then you sort of, if there's a slow-moving car. With his flashers on. Right. It slows everybody down. Yes. And you work your way around it and come out the other side. Right.

• 37:32Neil deGrasse Tyson?

  That's a density wave in the traffic. Awesome. If you see it from a helicopter, the entire traffic pattern is moving. Because the car with his flashers on is moving, it's just moving slower than everybody else. So the traffic is moving fast, it slows down, and it merges out the other side. That is a density wave in the traffic. It's a perfect analogy to what's happening in the galaxy, except the galaxy doesn't have cars. All right. So, here's what happens. If you shock the gas cloud, or create a density wave that'll force some compression, little bits of it will now be denser than other regions. Okay. If you're denser, you have stronger gravity near your surface than other places do.

• 38:17Neil deGrasse Tyson?

  Well, I want to get that next molecule that comes by. And you're going to attach to me. You're not going to be free-floating anymore. Mm-hmm. Okay? All right, I just added a molecule to myself. And you didn't. With every extra molecule, I now have more gravity than I had before. Huh. Okay? And I start clearing out the gas cloud. Because even if you tried, if I started before you, I'm going to win. Because this is a runaway process. For all the new mass that I accumulate, based on the power of my gravity from before, I now have even more gravity.

• 38:57Neil deGrasse Tyson?

  More gravity. Correct. So more gravity gets, breeds more gravity. And this is a runaway process. And so when this happens, you can trigger star formation in a gas cloud. Ah-huh. And typically, there's a whole region of the cloud that starts making stars. And when you do that, you make a star cluster. All the stars with the same birthday. And for another explainer, it's fascinating how we use star clusters to figure out how stars evolve. It's more fascinating than it sounds like than I'm even explaining to you right now.

• 39:38Neil deGrasse Tyson?

  It's just complete, it's the same thing as taking a snapshot of civilization. And all you have is a snapshot. And you have to figure out, well, how are people born and how do they die? You're right, are you born, are we born in the ground?

• 39:54Chuck Nice?

  Right.

• 39:55Neil deGrasse Tyson?

  Shrivelled and we bring you out of the ground and then we feed you and then you flesh out? And then over time, do you then shrink? And then exit back into another human being? The time order is not obvious because we don't have a video of this happening. We just have, because we don't live long enough. We just have snapshots of clusters at different stages of their evolution. And so that's another explainer. I'll get to that. It's very cool. Okay, so, um, but just I'll give you an example. Everybody in a day goes to the bathroom some one way or another, but you don't spend much time there.

• 40:35Chuck Nice?

  Well, um, that's debatable, debatable. Just saying.

• 40:42Neil deGrasse Tyson?

  Relative to other things you do, you don't spend much time there. So a snapshot is not likely to catch you in the bathroom. Are, do only some people live in the bathroom? Well, others don't? Or does everybody go through the bathroom? So these are questions we ask and we answer them brilliantly in the history of this exercise. But my point is, um, this triggering of the gas clouds is what, um, this shocking of the gas clouds is what creates pockets of condensation.

• 41:10Chuck Nice?

  Right.

• 41:11Neil deGrasse Tyson?

  Pockets of convergence of matter that then, as they continue, okay, they get bigger and bigger and bigger. Now, it'll keep doing this. The native temperature of the cloud.

• 41:26Chuck Nice?

  Right.

• 41:27Neil deGrasse Tyson?

  Will sustain it to some level. Okay. But as it gets more and more and more massive, there's greater and greater gravitational pressure on the core.

• 41:41Neil deGrasse Tyson?

  There is the point where.

• 41:46Neil deGrasse Tyson?

  We have ignition.

• 41:48Chuck Nice?

  Got you.

• 41:49Neil deGrasse Tyson?

  Thermonuclear fusion ignition. And in that moment, a star is born. And so that then stabilizes this against any further collapse. And it will continue to accrete material unless the star is of a very high luminosity variety. Because you know what happens? The photons that come out, they exert a pressure onto themselves. And if you're Johnny Come Lately to the party, you just get pushed away. And so this is a fascinating point in the evolution of a star. Because the high mass stars, we see them evacuating the pocket out of which they formed.

• 42:31Chuck Nice?

  Oh wow, yeah.

• 42:31Neil deGrasse Tyson?

  There are these pockets where the gas is not as dense. Because first it had absorbed up the initial amount of gas in that pocket. And anyone who tries to make it later, it ends up getting pushed away.

• 42:42Chuck Nice?

  Sorry, guys, club is full.

• 42:44Neil deGrasse Tyson?

  Club is full.

• 42:44Chuck Nice?

  Club is full, guys. I gotta put the rope down, gotta put the rope down, guys. Listen, now I'm a big fan, I'm a big fan, don't worry, man. I saw your latest work, I'm a big fan. But the club is full, man. We got fire laws, we got fire laws, man. Sorry, no, put your money away, bro, put your money away. I'm serious.

• 43:03Neil deGrasse Tyson?

  So it's a fascinating, and by the way, this is decades and decades of hard earned telescope observation, brilliant people thinking about what's going on. There's the thermodynamics of it, the quantum physics of it, the chemistry of it. There's all of this going on. And that's why in astrophysics, we tap the expertise from people of many different professions. And that's also why astrophysics is, by many, myself included, is considered a gateway subject to teach in school.

• 43:38Chuck Nice?

  Ah, so you can use that as a means of going to, as a portal to go to many different lands in science.

• 43:46Neil deGrasse Tyson?

  Yes, in science, the biology, the chemistry, the physics, the

• 43:50Chuck Nice?

  The geology.

• 43:51Neil deGrasse Tyson?

  The geology on the planets and of course, we send hardware out there. So if you're, if you're an engineering geek and love the universe, we got a place for you too. So.

• 44:04Chuck Nice?

  Nice.

• 44:04Neil deGrasse Tyson?

  Yeah, that's, this is my recruitment.

• 44:08Neil deGrasse Tyson?

  PSA for modern astrophysics. So anyhow, that's, that's how we, that's how.

• 44:12Chuck Nice?

  That's kinda how it's done. That's pretty cool. I, I, I love it.

• 44:16Neil deGrasse Tyson?

  A fast addition. Um, Chuck, do you know when I was in high school in my chemistry class?

• 44:21Chuck Nice?

  Uh huh.

• 44:22Neil deGrasse Tyson?

  I, I had asked, as we learned about the periodic table, I said, where do all these elements come from? Well, did we find them in the earth? That was the answer. It would be a couple of years later when I learned, no, we made these in our stars.

• 44:35Chuck Nice?

  Right.

• 44:36Neil deGrasse Tyson?

  They, they were birthed in stars first and then became part of the earth as the earth formed. Um, and, oh, by the way, uh, borrowing a bit from the earlier explainer where the buck stops at iron.

• 44:52Chuck Nice?

  Yes.

• 44:52Neil deGrasse Tyson?

  Right? And by the way, there's no shortage of iron in the world and in the universe. And earth's core is primarily made of iron.

• 45:00Chuck Nice?

  Mm hmm.

• 45:00Neil deGrasse Tyson?

  All of that comes from, uh, the fact that once the star made iron, there it is. It's a major part of that, a major part of that, uh, process. It makes the heavier elements, it can still make heavier elements, it's just not getting energy out of it. Right? So there's a plenty of energy in a supernova explosion to keep making elements up the periodic table. But you're not sustaining the energy of a star by doing it. You're sucking energy from the explosion and all the energy that's already available to you. So.

• 45:31Chuck Nice?

  Man.

• 45:32Neil deGrasse Tyson?

  Anyhow, that's how it works, Chuck. Some of how that works.

• 45:36Chuck Nice?

  That's fascinating. I love it. I love it. It's, uh, I mean, it makes perfect sense. And the thing that's weird is that you have to think about these in terms of, um, um, atomic terms. Like while you're thinking, I'm trying to think about this, not in terms of like actual things fusing like Lego.

• 46:00Neil deGrasse Tyson?

  Right.

• 46:00Chuck Nice?

  You know?

• 46:02Neil deGrasse Tyson?

  Legos are good, that's a good fusion.

• 46:03Chuck Nice?

  Yeah.

• 46:04Neil deGrasse Tyson?

  You get them close enough, then they just stick.

• 46:06Chuck Nice?

  They just stick, right.

• 46:06Neil deGrasse Tyson?

  They stick in there.

• 46:07Chuck Nice?

  But, yeah, but it's, it's like...

• 46:09Neil deGrasse Tyson?

  No, yeah, it's happening at a, at a, at a, in a, not only atomic, but a nuclear level.

• 46:14Chuck Nice?

  A nuclear level.

• 46:15Neil deGrasse Tyson?

  By the way, the whole universe, which was all energy at one point, as the universe cooled, that energy, um, would, E equals mc squared, the energy becomes the matter out of which everything would later form, and most of that matter is hydrogen and helium. So, so you start out for free from the birth of the universe with the hydrogen and the helium, and these big gas clouds, that's there for free.

• 46:39Chuck Nice?

  For free.

• 46:40Neil deGrasse Tyson?

  That's all.

• 46:40Chuck Nice?

  Wow. Oh, man, this makes me just wanna go, just be there when it happens. Like, why can't we just be there and...

• 46:50Neil deGrasse Tyson?

  Let the world know that Chuck wants to be in the room where it happens. Chuck wants to be... I just wanna be in the room.

• 47:00Chuck Nice?

  I just wanna be in the room where it happens.

• 47:04Neil deGrasse Tyson?

  Is that the name of that song? What's the actual name of that song? It's from Hamilton.

• 47:07Chuck Nice?

  It is from Hamilton, I don't know the name of the song.

• 47:09Neil deGrasse Tyson?

  In the room where it happens.

• 47:10Chuck Nice?

  Yeah.

• 47:11Neil deGrasse Tyson?

  We'll work on it, Chuck.

• 47:11Chuck Nice?

  All right.

• 47:13Neil deGrasse Tyson?

  I'll hook you up with the universe one day.

• 47:16Neil deGrasse Tyson?

  So, this has been a Things You Thought You Knew episode, fusion edition. Always good to have you, Chuck. It's your curiosity that drove this entire show, just want you to know.

• 47:28Chuck Nice?

  Oh, I'm good for something, thank God.

• 47:31Neil deGrasse Tyson?

  I was minding my own business, I saw the bat signal. Feel the fusion helping.

• 47:37Chuck Nice?

  That's right.

• 47:38Neil deGrasse Tyson?

  So, we good here. This has been StarTalk. Neil deGrasse Tyson, your personal astrophysicist, keep looking up.