StarTalk Radio - Things You Thought You Knew - Fun with Fusion

Episode Date: January 10, 2023

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.NOTE: StarTalk+ Patrons can listen to this entire episode commercial-free here:https://startalkmedia.com/show/things-you-thought-you-knew-fun-with-fusion/Thanks to our Patrons Manny Baez, Carlo Falcigno, jason walsh, Nuno Nebel, and Michael Hart for supporting us this week.Photo Credit: NASA/ESA/ESO/Wolfram Freudling et al. (STECF) Subscribe to SiriusXM Podcasts+ on Apple Podcasts to listen to new episodes ad-free and a whole week early.

Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now. This is StarTalk, a Things You Thought You Knew edition. Chuck, always good to have you, man. Always a pleasure to be here. 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. Yeah. And, oh my gosh, people couldn't get enough of this. What is fusion?

How does it work? How does it relate to astrophysics 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. Okay. I'll take that.

All right. So let's do this. Chuck, what's been bugging you lately? I'll tell 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 they they i wake up this, 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 pull the football away from me? What are they doing? What is happening? What is happening with the fusion?

Oh, okay. me what are they doing what what is happening what is happening with the fusion oh okay so the highlight is at one of the national laboratories uh lawrence livermore national laboratories where they they among all the national labs are one of their major tasks is as shepherds of our nuclear arsenal 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. Okay.

All right. Sounds like America so far. You'll say, well, what's new about this? We've been blowing it up like forever. What's new about this? 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 there 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 Newton's law for every action is an equal and opposite reaction. Explosion that comes out creates an explosion that points inward. Okay. And that creates very high pressure and very high temperature.

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.

Right. And helium in its nucleus has two protons plus two neutrons. So how am I going to create a helium atom from a hydrogen atom? So you got to 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. What do two protons want to normally do? They're both positive charge. They like each other, but they don't like each other because they're alike. Okay. 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. I don't really like that. I won't be over there talking to that dude. Chuck is still in therapy, people, just so you know. I know, exactly. It's like, it's a simple question, Chuck. Where do cocktail parties and liking people come in?

Yeah, but they want to get away from each other, right? So these are like charges. 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 a ball up a hill, all right? If you don't give it enough energy, it's not going to reach the top. It's not going to reach the top, okay? There you go. So, yeah. 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 want to 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 closer. There is a magic temperature at which these protons will come close enough so that an entire new force operates. It would have to be a strong force in the nucleus to keep two protons together. In fact, the name of that... That's quantum love. That's called quantum love.

Oh, where's that disco? So I remember jungle love. Remember jungle love? We know quantum love. Oh, jungle love. 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 the strong nuclear force. There it is. Okay. What it's called. It only operates on scales as small as the nucleus itself.

Wow. 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 this. All right. So, now I'm with you. That is thermonuclear 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? Exactly. products have less mass than when you started with. Whoa. Oh, my gosh. Where did the mass go? Exactly. 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. There you go. There it is. And so they managed. That's fusion. 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. Lasers, lasers, and lasers.

Lasers, right? Right. 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. That's amazing because, wow, 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? If 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 says, oh my gosh, we can get the physics to succeed. And for my money, I'm saying, if the physics works, then it's just a matter of time before engineers say, I got this. I got, then it's just a matter of time before engineers say, I got this. I got this. I'm going to make something out of that. I got this. That's amazing.

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 known how to make fusion we've done we've not made fusion since what 1949 or something when the first fusion bombs are called hydrogen bombs they're using hydrogen that's what i just told you we two protons is 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? Yeah, because you don't want the electric company having to move to a new city because there's no city left. Right, exactly. So while in 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. Right. Here's your cue, Doc. Eh. Marty! It's your kid's body! And do you remember

how, you know, and Marty says, but Doc, where are you going to get the energy? There's no lightning bolt, and there's no room for, you know, what are you going to get the energy? There's no lightning bolt. And there's no room for, you know, what are you going to do? And remember what he does. He dumps a bunch of trash into the flux capacitor, which is now powered by fusion. It's Mr. Home Fusion, right?

It was like a blender. That's right. He puts it in, and that undergoes nuclear fusion. And so one day, perhaps, we'd have fusion reactors in every car. And then you could like, 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 uptook 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 got to like recover that.

But it is the future. And I tip my hat to this 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, we're chomping at the bit for this. So then it is good news. Good news.

You suspected accurately, yes. All right. 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 and second week of December in the year 2022. We'll look back on that. Another day in December that will live, not in infamy.

What is it when it's a good thing? Femi. Just femi. Femi. Okay. All right, Chuck, we got to end it there. All right. All right, but there's way more about, like, talk about stars.

Yeah, we should do that. And why stars explode. All right. I'll leave a teaser here. You ready? Fusion, you get energy by combining little atoms. Vision, you get energy by splitting big atoms. Okay.

But wait a minute there's got to be some point in the middle where these two phenomenon meet what happens then therein is the are the 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. 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. We're back.

Things you thought you knew. The Fusion Edition. This time, Chuck, I'm going to take this into the universe. Okay. Because we were fusing stuff long before the Lawrence Livermore National Labs were even born. Oh, okay. 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, we're all about fusion. Just want you to know that. Yes, yes. You guys, you really stick together. That was good. I'm sorry. That was good. I'm sorry. That was not. That was awful. 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 that you can parse it thermo is heat that nuclear is the nucleus and fusion is the bringing together of 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 moss pit. And the mass has become energy. Right.

So, here's what's interesting. So cool. So cool. Here's what's interesting. Yeah. I think it's interesting. So cool. So cool. Here's what's interesting. Yeah. I think it's interesting, but you and the viewers, listeners will be the judges. 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. And you get 92, 94 protons crammed into its nucleus, okay? And that's like the opposite of hydrogen, which has one proton in its nucleus, all right?

So the hydrogen we use for fusion and make heavier elements. 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 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. 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? So, here's what's going on. As you fuse atoms, you get less and less energy out from the fusion.

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 and still expect to make energy, and you can't fuse past it. The buck stops there. Wow. And that element is iron.

Iron. On the periodic table of elements. See, if this were a Marvel movie, we would call it absorption or something like that. We must get the element absorption so that we can stop this reaction and save the universe. Yes, it would stop all freaking reactions. Correct. Correct. You cannot fizz iron.

You cannot fuse iron. Okay? 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 sun as other stars will do they 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. Helium has two protons, okay? So you take three of those atoms. How many protons do you have?

A helium atom has two protons. You have six protons. You got six protons. Six? Okay. Don't tell me. I went to public school, so I don't know. Okay. By the way, I went to public school, K through 12.

So, two, two, and two, there you have six protons. You go check the periodic table of elements. Who has six protons? Carbon does. Aha. Okay. So, 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, and you get nitrogen, oxygen. And so there are these fusion pathways that work their way up the periodic table. And at each step, the sun is making energy. Right.

Okay? So the sun can hold itself up against gravitational collapse. Gotcha. Because it wants to collapse. This gravity, I don't 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.

I'm preventing that. So there's pressure without and pressure within. Correct. So the pressure pushing out is the fusion actually propping up the sun in its size and creating. That's a perfect phrase, propping up the sun. That's exactly what it's doing. Wow. Now, there are people who misinterpret this because we say it is balanced.

Right. You know the sun is balanced because it's not shrinking and it's not expanding. Right. 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. Right.

These are two different kinds of balance. Absolutely. 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. I love it. Unstable, because if you just breathe on the marble, it'll fall down the hill. Right. Okay. All right. Now, the ball at the bottom of the, between two hills and a trough is also an equilibrium, but it's a stable equilibrium. Right. If you blow on it, it'll go up the side and come right back down to where it was. Right. Stars are not in a delicate balance. They're in a stable balance.

Okay? Mm-hmm. So watch what happens. If you compress the star, the star gets hotter, creates more energy, and puffs itself back up. Oh. If you somehow manage to puff it up, that releases the pressure on the inside,

the nuclear fuel energy rate drops, and then it shrinks back down again. Look at that. There it is. Stable equilibrium. That's wonderful. It's a totally wonderful thing, especially if you have long-term civilizations

that you want to sort of... Yeah. If you're going to 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. 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 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 than one proton and one proton. If I want to fuse carbon, I got six protons and six protons. There is more resistive force there than one proton in one proton. If I want to fuse carbon, I got six protons and six protons. So it is the center of the star gets hotter and hotter and hotter in order to make this happen. I run out of hydrogen in my core because I made it all

into helium. Right. 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, time for gravity to win, and the core collapses, increasing the pressure, increasing the temperature, until helium kicks in. 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 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 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. Right. Right now you're not giving us energy.

Let's collapse under our own weight. Increase the temperature. Then you'll give us energy. And then you will fuse. You will fuse. But then Iron says ha ha and pulls off its mask

and says it's me absorption. Ha ha. Absorption. Ha ha. So the star collapses

ready for Iron to give it new energy and Iron says no I absorb energy to fuse. Uh oh. And so now, no, I absorb energy to fuse. Uh-oh. And so now the star, which is in the business of making energy,

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. 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 yeah 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 it has to because it has to. It can't fuse. It's got no other choice but to explode. To explode. And Chuck, thus is the appearance in the universe of a supernova explosion. Better known as a several billion year orgasm. What?

No, those stars don't live billions of years. They went through this fast, okay? Only the highest mass stars Oh, really? have enough pressure to take the temperature to get to the iron. The sun will never make it to the iron. The sun won't make it

because, okay, it's not big enough. Because 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 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. 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 repulsion. That's the only way you can get to the fusion. The fusion so that the strong nuclear force takes over. You got to get over that hump. Exactly. Then it sticks.

That's right. So. Amazing. So this would have happened in millions of years. Right. The sun will live billions. Some stars live trillions. 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,

the basic ingredients of life itself. That's beautiful, man. We are not just poetically stardust. We are literally stardust. Stardust, correct. It's beautiful. 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, 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. universe, the universe is alive within us. Oh, that's, why do I feel like I want to take up an offering right now? That was just gorgeous. The collection plate is going to pass the plate now. That was just beautiful, man. I mean, that's just wonderful. This was figured out by four scientists, Burbage, Burbage, Fowler, and Hoyle, Jeff Burbage, Margaret Burbage,

Willie Fowler, and Fred Hoyle. Burbage, Burbage, Fowler, and Hoyle. Burbage, Fowler, and Hoyle. And they really deserve 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. Oh, my God. How soon?

I mean, how recent? Right. Mid-century. So 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. 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 ingredients for life the building blocks for for that life it's it's uh it really is just a a lovely just almost metaphorical depiction but it's literal at the same time. That's amazing.

So I just wanted to complete our fusion session together. Okay, but see, is it really complete? Because now I've got to know this. Because as you talk about this kind of explosion and these 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?

I deeply value your insatiable curiosity. That's why I love you, Jack. Oh, I appreciate it. And I love you because you have answers and I don't have to read. 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. StarTalk. We'll be right back. We're back.

StarTalk. Things you thought you knew. Fusion Edition. Chuck, we're going to round this out with just talking about how stars are born. Nice. All right, because somewhere in there, fusion kicks in. And let's get some sense of how that happens.

We kind of went Benjamin Button. We started with death, and now we're ending with birth. There you go. Here it goes. Chuck, why the emergency call to my hotline? Here it goes. Chuck, why the emergency call to my hotline? Because we left off a place that has really put me in my peak curiosity. Okay.

Which is we were talking about how the death of stars seeds the universe with the ingredients of life, which, by the way, was just incredible, where we 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. Absorption. And then, boom, we have to explode, right? Yes, yes. 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? Okay. So, a couple of things. Let me come into that from a back door. So, if you take biology class, and every biology class will spend some amount of time trying to define life. Yes. Okay? And it's hard because we only have one example of it.

Right. So 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. things that we thought were fundamental to life that happen to apply to us and just get the basic common denominator of the two life forms that we know about. And if we discover a third life form and a 10th 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 does 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.

Right. So life, I don't think we know. But often, what's bandied about is the idea that life has a metabolism. 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 the full understanding of what life means and does on Earth, it has a metabolism and can reproduce itself.

Okay? 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 Just putting it out there. Okay, I see what you're saying. So in the respect of life itself, there is a facet where stars themselves fit the definition of being alive. 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 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. All right. Well, first you got to get a good agent. Let me just tell you, because you can have all the talent in the world, but if you're not conducted correctly, you're going to have some issues. Okay. So some gas clouds have better agents than others. Okay.

All right. So there are two broad categories of galaxy out there. One of them is elliptically shaped, and we call them elliptical galaxies. Okay. 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? Okay. We call those elliptical galaxies. Broadly, again, another is a very flat version of a galaxy that has spiral arms, and we call those spiral galaxies, all right? 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. Okay. All right. Now, I have a gas cloud minding its own business. Okay. 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, creating a shock wave that literally shocks the gas cloud.

Okay. 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. Gotcha. 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 its flashers on, it slows everybody down. Yes. And you work your way around it and come out the other side. 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 its 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 climate 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. 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. 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. 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. More gravity. Correct. So more gravity breeds more gravity.

And this is a runaway process. And so when this happens, you can trigger star formation in a gas cloud. Aha. 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. 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. 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 know are you born uh are we born in the ground right shriveled 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'll get to that. It's very cool. Okay. So I'll just 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. Well, that's debatable. Debatable. Just saying. 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 while 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, this shocking of the gas clouds is what creates pockets of condensation. Right. Pockets of convergence of matter that then, as they continue, okay, they get bigger and bigger and bigger. Now, it'll keep doing this. it'll keep doing this. The native temperature of the cloud 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. There is the point where we have ignition. Got you. Thermonuclear fusion. 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. 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's tries to make it later, it ends up getting pushed away. Sorry, guys. Club is full. Club is full. Club is full, guys. I got to put the rope down. Got to put the rope down, guys.

Listen, 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. So it's a um 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 the chemistry of it there's all of this going on and that's why in astysics, 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. Ah, so you can use that as a means of going to, as a portal to go to many different lands in science. Yes, in science. The biology, the chemistry, the physics, the geology, whatever. The geology on the planets. And of course, we send hardware out there. So

if you're an engineering geek and love the universe, we got a place for you too. Nice. This is my recruitment. PSA for modern astrophysics. So anyhow, that's how we begin. That's kind of how it's done. That's pretty cool. I love it.

A fast addition. Chuck, do you know when I was in high school in my chemistry class, I had asked, as we learned about the periodic table, I said, where did 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.

Right. They were birthed in stars first and then became part of the Earth as the Earth formed. And, oh, by the way, borrowing a bit from the earlier explainer, where the buck stops at iron. Yes. 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. All of that comes from the fact that once the star made iron, there it is. It's a major part of that comes from the fact that once the star made iron, there it is. It's a major part of that 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 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, man. Anyhow. That's how it works, Chuck.

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

That's a good fusion. Because you get them close enough, then they just stick. They just stick. Right. They stick in there. Yeah, yeah. But yeah, but it's like. No, yeah.

It's happening at a, not only atomic, but a nuclear level. A nuclear level. By the way, the whole universe, which was all energy at one point, as the universe cooled, that energy with 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 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. For free. That's all. Wow. All right, dude. Oh, man, this makes me just want to go, just be there when it happens.

Why can't we just be there? Let the world know that Chuck wants to be in the room where it happens. Chuck wants to be. I just want to be in the room. I just want to be in the room where it happens.

Is that the name of that song? What's the actual name of that song? It's from Hamilton. It is from Hamilton. happens. Is that the name of that song? What's the actual name of that song? It's from Hamilton. It is from Hamilton. I don't know the name of the song. In the room where it happens. Okay, we'll work on it, Chuck. All right.

I'll hook you up with the universe one day. 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. Oh, to have you, Chuck. It's your curiosity that drove this entire show. Just want you to know. Oh, I'm good for something.

Thank God. Mind my own business. I saw the bat signal. You're in fusion. Help me. That's right. So we good here. This has been StarTalk.

Neil deGrasse Tyson, your personal astrophysicist. Keep looking up.