What causes the biggest explosions in the universe?

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Speaker 1: Hey, Daniel, do you like looking for shooting stars? I do because sometimes the nice sky is really static, it seems frozen, and so it's exciting to see something streak and flame out across the sky. You know they aren't really stars, right, Um? I am aware, thank you very much. I also know that nobody's actually shooting those stars as far as we know. You know aliens. Hello, you're going to hit the aliens button before me. But it would be cool to actually see a star explode, you know what I mean. You're looking at at the sky and suddenly one of them just goes Yeah, as long as it's not our star, would be pretty fun to watch. Hi am poor handmade cartoonists and the creator of PhD comics. Hi. I'm Daniel Whitson. I'm a particle physicist, and I'm the co author of the book We Have No Idea, A Guide to the Unknown Universe, book about all the things we don't know about the universe. And you wrote it with a really awesome and fun cartoonist, didn't you? I did, in fact, and I was recently contacted by one of our listeners and one of our readers in the Czech Republic, who's reading our book in check, I hope it says the same things. It doesn't English. Well, he actually told me how to translate the title in check literally into English. But how does it translate. Apparently it translates to we don't even know fart about it. Really, the word fart, isn't it? He says. It's a very common expression in check for I don't know fart about that, and that's the expression they chose for the title in check. Wow. I wonder if we had named that, made that the actual title in English, maybe we would assault, we would dislike more copies. I don't know. Maybe the book would kind of stink. But it's a really fun book. It's all about the unanswered questions of the universe, all the things we'd like to know about our lives and where and where we live and how the universe began but don't yet know. And so we hope on this podcast to take you on a tour of what we do and don't know about the universe, and maybe one of you out there, a young budding scientist, will be the one to figure out the answers. That's right. We bring to you all the amazing mysteries of the universe, and all the farts in the universe and all the mysterious farts in the US parts, the ones that fortunately you can't smell through this audio podcast. Well, welcome to Daniel and Jorge Explain the Universe, a production of I Heart Radio in which we examine them the amazing, the mysterious, all the weird and wonderful things in our bonkers universe, and we talk about them in a way we hope entertains you and also teaches you something deep about the physics of our universe. Yeah, we talked about all the sort of a nice and beautiful and wonderful, inspiring things that are out there in universe, the big and the small, but we also talk about some of the crazy things that happened. That's right, because the universe is dramatic and it is violent, and when it wants to make a splash, it goes big, it goes supernova, it goes hyper nova, hypernova. Yeah, So to be on the program, we'll be tackling perhaps one of the most um I don't know, violent or you know, dramatic or you know, maybe interesting events that happened out in the universe. And that happens quite a bit. That's right. It's one of the most interesting and dramatic things that can happen in our universe. One of the things we've seen, the kind of thing that we can even find in historical records that people in ancient times noticed happening in the sky and wondered what it was all about? Right, and then so the question is how much do we know about it? How much do we understand about this incredible event and what we can do if one happens near us? Yeah, and the answer is basically dig a hole and pray. All right, let's get into that. So to be on the podcast will be asking the question what makes a supernova blow explode? I guess super what makes a supernova explode? Or what makes a supernova a supernova? What makes a supernova so super? Yeah? Yeah, why isn't it a super dupernova? Or well, you know, the name nova is actually quite fascinating. It means new and so super. So supernova is like something super and new in the sky. It comes from people looking at the sky and saying, hey, that wasn't there before, or that's different, and it's pretty rare to see something change in the sky. I mean, we're used to the patterns of the seasons and the days and the nights and all that stuff. But otherwise the stars, you know, their lifespan is much longer than ours, and so to see one dies pretty unusual. We'll be talking talking about supernovas and what how what causes a supernova and how that works. But it's basically the biggest explode shin you can have in space? Right? Is that true? The whole universe? That's the biggest explosion that happens. It's the biggest explosion we've seen so far. I mean, the stars are one of the biggest things out there. I guess you can imagine a galaxy exploding, but it's hard to see how that would happen. A galaxy nova. Nobody's ever seen that yet. What would you call that an uber nova or over nova? But I guess maybe it's the biggest explosion because you know, stars are some of the most you know, energy pack things out there, right, I mean that that can explode like you don't see a black hole exploding. You don't yet see black holes exploding. That would be fascinating. And yeah, the key to having a big explosion is not just being massive, having a lot of energy, but releasing it very very rapidly. Right, That's basically what an explosion is. It's like it's like a bomb. You want to deposit a lot of energy and you want to do really quickly, so you got a shock wave of action. And that's the thing that makes supernova is exciting that they happen ly. It also is the thing that makes them hard to understand and hard to spot because we don't know it precisely what causes the star to go supernova, and they don't happen that often, so it's pretty rare to see one's start to go oh wow. Really, we don't know what cosses these supernovas. No, we have some general sense for what happens during the supernova, and we'll dig into it on today's podcast. But what makes it go now and not next week. To predict when an individual star will go supernova is not something we know how to do. Nobody's pressing a switch that you can see. Yeah, they don't annow it's a big countdown like NASA. You know, t's not taking time bomb. No, and astronomers would love to see a star like five seconds before superno, one second before supernova the first moments, you know, that would be fascinating, so you can catch it as it as it's happening. Yeah, And there's actually a guy who was watching the skies in two thousand and sixteen, an astronomer, an amateur astronomer. He was just happen to be looking at one star her through his telescope and he saw it go supernova, like in real time. Wow. What are the chances of that? Well, they're pretty low because it's actually not that many stars that will go supernova, Like, not every star ends up in a supernova. And of course stars lived for a really long long time, and so they calculated the odds is like one in ten million or one in a hundred million that if you're looking at a star or through a telescope, that you'll be watching it go supernova. Oh. So this person was looking at the star through his telescope or her telescope and it went supernova as he was looking at it. As he was looking at it. Now, of course this time delay went supernova a long long time ago, but the images from that supernova arrived on Earth as his eyeballs were pointed at it. Oh wow, And so how did he prove this. Did he have a about his cell phone and took a picture of it? Yea, all good amateur astronomers have cameras attached to their telescopes, so he snapped some photos. Then, of course he alerted astronomers who all pointed their telescopes at it to try to catch a glimpse of the first moment to the star going nova. What is that true? He actually took pictures of it? Oh yeah, Oh wow, that's pretty interesting. Wow. And so supernovas are sort of famous, like people have heard of them. People know that they're a thing. They're pretty dramatic. Their pr campaigns have been pretty good. Yeah, they're there's sort of in the general consciousness for sure, of I think culture and society. I mean, everyone knows him as his stars exploding. Yeah, but I was curious, you know, how much did people actually know about a supernova? Did they know what really happens inside? Do they know what causes it? Do they know whether we understand supernovas? So I walked around campus here at you see Irvine, and I asked folks what they knew about supernovas. Yeah, so think about it for a second. You've probably heard of supernovas, But do you know what causes them and how they actually explode? Here's what people had to say. I guess it's something to do with the star exploding. When a star explodes, What makes it happened? Um, the death of the star. Supernovas usually like an exploding star, right, so what makes its age? Are you going to explode when you get over? Who knows? I know that supermanovas are when a star reaches the end of its life and eventually the force of gravity overcomes the push from the inside of the star and it collapses and then explodes. I know they're in space and it's is it? Is it when a star like implodes or something more? I know that they are the final stage and stars. Okay, what makes it happen? Eventually, the the it becomes too dense, the elements that it creates in the in the middle. At that point it collapses in on itself. And there's a few things that can happen. But a supernova is one of them. A supernova No, I don't alright? Cool, So I think it sounds like everyone knows what it means, Like it means the death or the explosion of a star. Yeah, they knew that it marks the end of the life of a star, but a few people have really a sense for like what's going on inside the supernova? What makes it happen? Why do stars die that way? Why do stars die at all? Why don't they just burn forever? So it's a big e explosion in space. And you're saying it's rare, so only about one to three supernova's per century or something like that in a typical galaxy. Yeah, we have seen a lot of supernovas from Earth, but almost all of them have been in other galaxies. And that's because most stars will not go supernova. In a galaxy like the Milky Way that has about a hundred billion stars, only about one or two, maybe three will go supernova in a hundred years. So it's not it's pretty rare. Most stars don't go supernova. Most stars do not go supernova. The fact that we've seen hundreds is only because there are so many stars and so many galaxies out there. But you know, we're lucky and we're glad actually that they're not a lot of supernovas, because they're pretty devastating. Oh I see, So if a supernova goes off in a galaxy far away, we'll will actually see it, like it'll outshine the whole galaxy and we'll see it, uh, you know, take over the light from the galaxy. That's right. It's a really dramatic event. It can be as bright as the entire sum of all the light from the rest of the stars in the galaxy. And so it's like it like doubles the brightness of a galaxy when it happens. And the most amazing thing is that most of the energy from the supernova doesn't even come out in the form of light, so you're seeing a tiny fraction of this incredible explosion in the visual spectrum. So if you see if you're looking at a galaxy at any point and you see it certainly bright up, it's because of a supernova inside of it, like one of its hundred billion stars went boom. Yeah, precisely. Well, let's get into it, Daniel, all right, um, and explain. Let's explain to people what a supernova is. I guess what's the technical definition of a supernova. Yeah, so technically a supernova is the end of the life of some kinds of stars. Now not all stars. In fact, most stars will not go supernova. But it's essentially the star explodes and it sends out most of the energy that's stored inside of it out into space in the form of electromagnetic radiation, so visible light, which is a tiny fraction, and an enormous number of neutrinos, just like gobs and gobs and gobs of neutrinos, and then also an enormous amount of matter. This is like shock wave of just stuff that gets spewed across the universe, like the shrapnel and the grenade. Yeah, like the shrapnel and the grenade. And it's good that that happens because that goes out and that seeds other stars to form, and it spreads the heavy metals that were burned inside that star out into the universe, so you can get interesting things like a rocky planets then life on them. Well that's interesting. So it's not Supernova is not like an accident that happens to a star. It thought like um, a star is suddenly gets out of balance. It's like it's like in the DNA of the star. You know, like once you once you know what kind of story you are, you will most likely go supernova or if you know the kind of star you know you'll never get you'll never go supernova. Yeah, it's sort of like that, and it's not totally under good, but it's something like if you know how much master is to a star and you know what it's made out of, Like did it start just from burning hydrogen because you're one of the first stars in the universe, or do you already collect the burning remnants of other dead stars and so you have helium and oxygen and nitrogen and carbon and all that stuff already. If you know that starting point, you can almost always predict the life cycle of a star, including whether it's going to become a black hole or a neutron star, or goes supernova, become a white dwarf or whatever. That's basically what determines it is like how big a scoop of stuff did you get of the universe? And what's in that scoop? Wow? And that the terms your your whole life cycle. If you're a star, like you're born and everyone already knows how you're gonna die. Here's a baby. Oh, this baby is going to be a rock star and it's going to you know, shine brightly, but then it's going to go out in a blaze of glory when he or sheet turns thirty two. Stars are not nearly as exciting and variable as people are. Right. They're much bigger, and they're much more dramatic, but they're also simpler, and also they don't really interact with each other. Like a star is pretty isolated. It's got its own little pocket of stuff and it just sits there and burns it until it can't burn it anymore. We know it's gonna go supernova, but you can't predict when it's going to go supernova. Yeah, these stars have some something of a variable lifetime, and you know these events, the supernov event happens really quickly. Remember that the like the time scale for stars can be millions and billions of years, but the supernova events, the time scale for that is days and so days, days, and so it happens really quickly, especially the first bit the explosion. We're talking seconds and minutes, and so what triggers that to happen? Is it like a clock that ticking down. Eventually it's just gonna happen like that. You could predict it a million or a billion years in advance, if you knew well enough. What was happening inside the star or is there some like quantum mechanical randomness that's happening, or is it triggered by some external event, like the star becomes really fragile and then you know, a path seeing shock away from something else makes it go. We just don't really understand those moments or you know, um like a planet falls into it and that triggers it. Perhaps, Yeah, there are stars like that that do get triggers from in falling material, but we don't know exactly like when that happens. All right, well, let's get into the mystery of what triggers supernovas and what's actually happening when they explode. But first let's take a quick break. Right, So we we've seen a couple of these supernovas in the night sky, like without telescopes. Right, there's a historical record of supernovas and in humanity's history. Yeah, it's a big event in the night sky when something blows. And back before people really understood what stars were, they were still interested in looking at them and commenting about them. And so you can go back in the historical record and can find ancient astronomers writing about this and the earliest one. It's called h B nine is from b C and we see this an ancient ancient texts. They talk about the appearance of a new star in the sky. So they just called it HB nine. What were those ancient people thinking they had acronyms and numbers for I don't know, we don't know who was We know it was some unnamed Indian astronomers. We call it h B nine. But you know they wrote about it as a as a new object in the sky. Well, what would we see if if I happened to be looking at the nice guy and a Superno, what just happened to you know, occur while I'm looking at this guy? What would I see? Would I see a star suddenly grow bright and fill the sky with light? Or would just would it just be a star that gets a little bit brighter. Well, it depends on how close it is. Of course, the star is gonna get millions and millions or even billions of times brighter than it normally is. Like, would it be dangerous to look at it? Yes, if you are looking at a star that's going supernova in our galaxy, it could be very dangerous. I mean, you could fry all life on Earth. That's kind of dangerous. So yes, looking at it would be bad, all right, Um, and then what would would I see it go bright for like a few seconds, for a few hours, for a few days. So the light curve of a supernova looks like very rapidly getting brighter and brighter over the period of a few days and then gradually fading over the period of a few weeks outter a few months. So it wouldn't be like a sudden flash. You would get a little bit of warning. You would get brighter and brighter and brighter over a couple of days. Yeah, And you can actually get a warning before the flash arrives because we see neutrinos arrive before the photons. Neutrinos get here first and they tell you watch out a supernova's coming three hours later. Oh really, it's like an early warning system, it is. And you can actually sign up for an early warning emails there instead of neutrino detectors here on Earth, and you can go to a website called s News and they will send you an email when they detect a big flux of neutrinos coming to the Earth. Oh wow, cool, So that you can run outside and not look at it, just so you can know. Man who doesn't want to know, so you can go down down to your bunker and not look up at the sky like our president. It might mean that in three minutes you are that's going to fry. Yeah, it could be. That would be the first warning. And the neutrinos get here first because they're the only ones that can escape the star. Photons, of course, travel faster than neutrinos because neutrinos are not massless like photons are. But neutrinos can fly out of the star, whereas the photons get absorbed inside the star as it's happening, and so photons don't leave the supernova until like the shock wave reaches the surface, which is a few hours after the beginning of the explosion. Yeah, the the the explosion itself. Yeah, they get sort of reabsorbed, and it takes a little while for the photons that will reach Earth to be omitted. So that's why the neutrinos get here first, not because they're faster, but because they sort of left first and didn't get socked. All right, Well, let's get into what's happening here. It's super fun to think about this stuff, you know, because it's a it's a dramatic event, and so people really like thinking not just about how stars form and how they burned, but how they blow up and what makes it happen. And as far as we know, there are sort of two totally different kinds of supernovas that happened. Both of these kinds of supernova reflect this classic Titanic battle between gravity and fusion. In one case, fusion winds and in the other case, it's gravity that comes out on top. The first one we call a runaway fusion, and the second one is probably better well known, is the core collapse supernova. But they're really very different kinds of events. Would you classify them both as supernovas? Like, it's still a star exploding, it just happens in in very different ways. Yeah, And there's lots of different categories of supernovas. You might have heard of type one A, type two, type two C or whatever those described basically what they look like in the sky, what the sort of energy spectrum from them looks like. But there's two fundamental mech isms, this runaway fusion and this core collapse. That's cool, Let's let's get into the first one here runaway fusion. That sounds like um, like an experiment that got away from you. I thought you were gonna say it sounds like a physics based romcom movie, Julia Roberts. So this is what happens when a star. It sort of has like a resurgence. It's a star that's had its day and then sort of died, and then it has a bit of a comeback, really like it had a nice long life as a regular star, and it was already waning, but then it rallied at the end precisely, and it's sort of in retirement and then it sort of brought back for one last explosion. And so what happens here is you have a very normal kind of star, a big star, a red giant. And remember what's happening inside a star is that gravity is pushing in, it's squeezing everything, and because of all that pressure, you're getting fusion. You're turning hydrogen into helium and helium and heavier stuff and heavier stuff into even heavy your stuff. Right, You're you're squeezing stuff together so much it's it's burning and exploding and fusion ng and releasing energy at the same time. That's right. And you might wonder, like, why doesn't an object like that immediately collapse into a black hole. And the reason is that there's outwards pressure and that pressure comes from the explosions, right, it's burning, that's shooting stuff out. And also because matter doesn't like to get squeezed that far, so you know, you squeeze stuff together, it doesn't like to compress, so there's some pressure back out and that's what keeps the star alive. Is this balance between gravity squeezing in and pressure pushing out to keep it alive. Right. It's kind of like if you're squeezing a bag of of of corn kernels, like you would squeeze them, but that would someone would be popping at the same time, so you wouldn't automatically just collapse or explode. You might reach this balance, which is a star. I've heard of fusion, and I've heard of cold fusion, but I've never, until today, heard of corn fusion. I think you might be a brand of pop corn. It's a brand of popcorn physics snacks corn fusions, right, Yeah, there you go. Well, I'm waiting for candy corn fusion. But that's why I think that's what you mean. It's like you squeeze something and then it pops. And so if you have a whole bunch of that and you're squeezing them, David, some of them keep popping until you it's hard to sort of like keep compressing them. I know we're supposed to be talking about supernovous, but now I'm desperately curious. What would happen if you actually squeeze that much popcorn? Would they pop? I bet they would. Bet you'd be heating and pressuring, and uh yeah, you might get a self sustaining corn reaction. That's exactly the idea. And what happens inside the stars that you're fusing the stuff and it's making heavier stuff, and that heavier stuff can then, if you're big enough, and if you're hot enough, can also get squeezed and burned and fused. But as the stuff gets heavier and heavier, you need higher and higher temperatures to keep the reaction going. Oh, I see, at some point you sort of run out of fuel, Right, at some point you can't keep this up forever. You can't keep it up forever. And for some kind of stars, the ones we're talking about red giants, they keep burning until they sort of make carbon, and it's basically like ash, and so it burns all the fuel, but it's not big enough to burn carbon, and that's sort of the end of its life. It's like, Okay, I'm done. I've burned as far as I could, as hot as I could. I reached my pinnacle. Now I'm a big ball of hot carbon. I don't have it in me to make this carbon fuses. It's just not big enough. Like if there were more of it right then there would be enough gravitational pressure to squeeze it, make it hotter and to ignite that carbon, but there isn't and so it just sort of stops there, Okay, and then it sort of cools off. Yeah, and what you have there or something called a white dwarf, which is a fascinating object because it's not fusing anymore. It's just sort of like a big hot lump of carbon, but it's still glowing. It's glowing because it's super duper hot. It's literally white hot carbon. It's glowing in the infrared, are also invisible light. In the visible light, yeah, you can see white dwarfs, but they're not shining because of fusion. They're shining because they're just sort of left overheat from their past life when they were fusing. And my favorite bit about this is that white dwarfs, because there's no more energy coming in there, eventually they're cooling off, and eventually they'll just sort of snuff out and turn into something called a black dwarf. Oh, I see, if you it's red hot, it's white hot, and so that's somebody it can just cool off and it just becomes like a giant ball of rock. Yeah, but that's never happened yet in the universe. We estimate that they would take about ten to the fifteen years, that's how hot this thing is to cool off. But the universe isn't old enough for any black dwarfs to exist. So we have this like category of stars that we haven't sort of achieved yet, haven't unlocked yet as a universe, like a like a video game. Yeah, like a video game, like a video game achievement. I see. So we know what's going to happen to them, but none, none of none of them have actually done it. None of them have actually done it, and some small fraction of them sort of step off that path, right, So you might be thinking, Okay, how's this d up in a supernova? Well, what happens is that some of these guys they think they're at the end of their career, but then they get a sudden dose of extra fuel. To say, for example, you're in a binary star system and you're a white dwarf, and then the other star starts expanding because it gets older and you start sucking up some of its material, or for some other reason, a bunch of new material comes by and you accrete it and you suck it in. Is it that little bit of extra energy or you know gravity, It needs to start cooking that carbon precisely, and so you get enough extra fuel, right, you get all this extra stuff, then you can get hot enough to burn carbon. And what happens then is that it just goes nuts because it's like volatile, like carbon is volatile. Yeah, and this is what we call runaway fusion. It's not like very slowly cooking gently over millions and billions of years. It's like it burns all that really fast, all at once. And in the usual star, you know, you have these shells different temperatures and different densities. You have the heavier stuff in the middle and the lighter stuff on the outside. But here you have basically a ball of carbon with some oxygen in it, and it's just ready to go. And you deposit enough fuel on that thing and it will explode like ten to the forty four jewels, all within just a few seconds. It unbinds the star. It's really incredible. It really literally like blows up from the inside here. Fusion wins and gravity just can't keep the star together anymore. Imagine what would happen if every part of the Earth suddenly had a huge amount of energy like it had, It's enough energy to escape the Earth's gravity. Well, that's what happens to this star, Like every element of the star now has escape velocity from the star. Gravity is overcome and it's just like spews itself over the cosmos. So how does it start. It starts in the middle, like some of the carbon starts to fuse, and then that releases energy with it, which then fuses the carbon in the in the outer layers, and so the whole thing just suddenly has enough energy to fuse and explode. Yeah, and you know, this is sort of the simplified model for what we think might be happening and runaway stars, and we've seen some of them, and but you know, it's hard to really know those first moments because again you can only spot the star after it started to go superno, but we don't know which white dwarfs are about to go. So we really haven't seen the very beginning moments very often, and so it's really difficult to study until compare our simulations to data because it happens within a few seconds. Like it's like it would like be trying to figure out what made a grenade explode or something, because you know, it just explodes. Yeah, it's like if you're looking at a huge field of grenades and you don't know which one is going to explode. All you can do is like snap your neck around as soon as one blows, But then you've missed it. So you never get to see those first moments. And so you might think, well, why don't we just image all the stars all the time, And yeah, I'd love to do that, right, that would be a great strategy. Just as just as signed some grad students to each star in the in the universe, how many grad students do we have, and we do have have some really big survey missions UM that scanned the whole sky and try to spot these things. But again, you can only notice them, you know, after they happen. We'd love to study them just before they happen, so we can see what's causing it, right, because I guess we UM. I mean, they do surveys of the sky that they're always looking at stars, but to get enough of information from the one that blew up is hard because you have to sort of focus on it. Yeah, and you'd love to use our most powerful telescopes. And we have sort of two kinds of telescopes. Ones that are really broad they can image the whole night sky, but they're not that powerful, and ones that can look really deeply at one object, like the hubble, you know, but it can't really scan the whole night sky because it's it has to point really carefully at one thing. I see. So even with the early warning system of the neutrinos, we can't that won't tell us which star is gonna blow. That's what we try to do. We try to see the neutrinos and then like whip stuff around. But you know, neutrinos are hard to spot because even a gazillion of them will come through the Earth and not interact. And you know, new tunion detectors are sometimes busy doing other things, are not dedicated to supernova's. They try to hook these things up, and when the neutrinos tell us the superno is coming, they point in that direction. And so we do our best, because remember, the supernovas have taught us a lot about the universe. They're the ones that gave us the clue that the universe is expanding. All right, So that that's the first way that a star can goes supernova is it's happily retired, but then it gets something triggers it, and it just goes out in a blaze of glory, runaway blaze of glory. That's right. It was saving up for one last hurrah. All right, Let's get into the second way in which supernose can happen, But first let's take a quick break, al right, Daniel. So the second way that uh supernova can happen is called core collapse. And I think this is maybe the one that most peop we're familiar with. Why why is this one? More? I guess popular this is the case where gravity wins in the epics struggle with fusion. I think this one's maybe more awesome. I mean, I don't mean anything negative about runaway fusion the size of a star glowing five billion times brighter than the sun. But this one involves implosion and explosion, so maybe it's like double awesome. Okay, so there's some implosion involved in this one, right, I guess it's in the word core collapse. Yeah. So in this scenario, again, you start as a really big star. You've gotta be our big enough star to even consider going supernova, like a star like our Sun is never going to go supernova. Hey, that's good to know, and be what do you mean big? Like, what's the threshold for supernova? Is it like many times the size of our sun or a little bit more. It's like five to eight times in the mass of the Sun is like the bare minimum you need to have a supernova. Beyond that, you can't even get an agent to return your phone. Yeah, you're forever be list which I think is a good thing. But this sort of core collapse superno requires a really big star. And we were talking earlier about what's happening inside the stars. You have this fusion and you're creating heavier and heavier stuff. Well, in some stars they are big enough to fuse carbon, and then they fuse the byproducts of carbon and make heavier stuff, and the byproduct of that make even heavier stuff. So it's a bigger factory, and it goes beyond what these other stars that we talked about can do. They can actually fuse carbon and and uh and make heavier and heavier elements. But it's sort of a more controlled process because it's happening gradually. It's like an equilibrium. Stuff is slashing back and forth, and the carbon fuses and turns into the next thing. And these guys confuse all the way up to iron. Remember that up to iron, when you have fusion, you release energy. Above iron or nickel or so when you fuse it absorbs energy and so it would cool the star down. So like what comes right before iron. Yes, so iron is number twenty six and nicholas, and that's about as high as you can go. I mean below that you have oxygen at eight you can make you make magnesium a twelve aluminum silicon. Anything below iron, when you fuse it together, releases energy so that that sustains the explosion of the star. But you're saying, after iron, if I want to fuse more things, I have to sink energy into it. Yeah, and so it actually sucks energy out of the star. It starts to cool it. And this is the enemy of the star. The star remembers trying to well, it doesn't like feel anything or want anything. But if a star is going to continue to burn, it needs to exert outward pressure against gravity. But it's sort of working against itself because it's making heavier and heavier stuffed. And so you know, as it's making heavier and heavier stuff, it's making the gravity stronger and more powerful because it's getting denser at its core. And so if you're then also cooling down your own reaction, then you're fighting against yourself. Wow. So and eventually what happens. It winds like you run out of things to fuse. Everything's iron, and then gravity wins. Yeah, eventually gravity wins and it pulls itself together and it collapses and gravity says, all right, I'm blowing past you. And there's this point it's called the Chandra Shaker limit. It's essentially when matter cannot be squeezed anymore. Let's see when all the electrons are pushed down into their lowest orbitals, and everything is tucked as close as possible, and that's what like a white dwarf for a neutron star is sitting at. But when gravity has enough power to overcome that, that electron degenerously. When you have too much stuff, then it collapses and gravity takes over, meaning that um, whatever is keeping the star kind of fluffy, it's no longer enough. Burned too much, and now it's it's too heavy. Yeah, there's not enough outwards pressure and there's growing gravitational pressure inwards, and so eventually gravity just overwhelms it, and that's when you get this core collapse. I guess collapse means that it it's just sort of like folds folds in or what does that mean? Like all the Adams were happy sort of bunched together, but now they crunched in together more. Yeah, and you actually get an inwards going shock wave. And so people sometimes talk about supernovas as implosions and that's why, because you get this shock wave of stuff rushing in towards the center. Wow, because the in the innerts of the star are I guess collapsing before they were sort of fluffy from all the energy. But now they're just they're out of energy, so that everything's just crunching together. To think about the surface of the star, what's happening there is it's constantly getting pulled in by all the heavy stuff inside the star, and it's getting pushed out by the burning. Eventually, if the burning is not strong enough, you know, if it passes this limit, then that stuff gets pulled in and it compresses the next layer, which compresses the next layer, which compresses the next layer. And it's a runaway process because the more you compress something, the higher density it is, the stronger the gravitational force, right, because as you get closer, the gravity stronger. Yeah, so the whole thing just it just falls inwards. It falls inwards, and then what happens depends on how much stuff you started with. And if you're like super duper big, like more than forty times the mass of our Sun, then that's basically it. You just collapse into a black hole without even making a peep. The star just kind of bloop turns into a black hole. Yeah, you can just go and suck itself into a black hole without a supernova, like you can skip the supernova stuff. If you're big, Okay, so that's if you're really big. If you're really big, But if you're not big enough, then the core collapse sort of goes inwards and then it bounces off the hot, dense core of the start, like the shock wave comes in and it reaches a point where the stuff is so dense that it can reflect that shock wave back out, and that's when the supernova happens. That's when like stuff flies out from the star. Oh, it's all this energy of stuff falling in. It's the balance. That's actually the explode. Yes, it's the bounce. And if you're too big, you don't get the bounce, right because it just like turns into a black hole and then nothing can escape. But if you're if you're below that, if you're like around thirty times the mass of the Sun, then you get a bounce that goes out with a supernova and the core becomes a black hole. Oh really, only the core that the other stuff bounces away. Yeah, you get the supernova, this huge shock you know, expus plasma through the universe and neutrinos and light and energy, but the core of it remains and becomes a black hole, and that's different than the other kind of runaway fusion, which didn't form a black hole. That's right, Those don't usually form a black hole. Sometimes those can end with a really dense neutron star, but a lot of times it's just blowing out most of the mass of the star in the runaway fusion. In this case, if you're more than forty times the mass of the Sun, you go straight to black hole. If you're more than thirty times the mass of the Sun, you've got a huge supernova when the bounce turns around and you get a black hole the core. If you're a little smaller than that, it's the same story. Things bounce off the center and then explode down to a supernova, but instead of a black hole the center, and you get a neutron star, which is like a really dense massive material, but not quite dense enough to form a black hole. I see you just you just become a like a compact star. Yes, you just become a really compact blob. And then there's a little window between like seven and ten times the mass of our Sun where um when the gravitational collapse happens. Then it causes runaway fusion and the whole thing just blows um in a huge explosion. So there's all these like pockets like if you're this big, then you'll go supernova if you but if you're a little bit smaller you won't. But then if you're a little bit smaller still you will. Like we said, the fate of the star depends almost entirely on its mass, and so there these little windows like if you're in this window, this happens. If you're in this window, that happens. It's like, oh, man, I shouldn't have eaten that last planet now, now now I'm gonna explode. Literally. Wow, that's interesting. But again, sort of the common thing about all of these scenarios is that it's the it's a collapsing star that becomes a supernova, right, And sometimes it's at the bound. Sometimes it's just it creates a runaway explosion. Yea. For all these core collapse they start with really big stars have been big enough to burn a lot of heavy stuff to go past the carbon limit and uh, and then to pass this gender's say, card limit and collapse gravitationally, right, and then a couple of different things might happen after that. To be a supernova or not. Yeah, you could be black hole. You can be black hole plus supernova. You can be just supernova. You could have as a neutron star. There's lots of different options there, all right, So I guess the next question is should we worry about supernova? Is Daniel, is this something that might happen like with three minute warning, we'll find out that the star next to us is going supernova and then and then goodbye Planet Earth? Or is it unlikely to happen around us? Well, we sort of trying to calculate two different things. One is how close would a supernova have to be to be dangerous? And they figured that if ones within like twenty five light years or so, it would basically destroy half of the Earth's ozone layer, because the half that's facing that star would be fried. And that would be bad because we'd be suddenly like totally exposed to space. An amount of X rays deposited on the planet would like sterilize half the population and or give them cancer instant, Oh my god, within minutes or within days or very quickly. Yeah, I mean, does it really matter if it takes days or minutes to get cancer? You've got cancer. Well, but everything else would stay the same, like a solar system would still be here and we'd be going around the same orbit. Yeah, and you know, that's an interesting question. People wonder if there are gravitational waves from supernova, but we've never seen one before. But it wouldn't affect like the gravity of the Earth. We'd still be orbiting the Sun the same way. Would just be like you know, mostly toast. But fortunately, we've looked around and we haven't spotted anything that we think is going to go supernova, anything anywhere within the nearest five light years. Now, again, we don't have a great understanding of when a stargo supernova, but we think we have a sense for the which kind of star can go supernova, and we don't see any of those nearby. And you know, supernovas are not just bad news, right, supernova is they're sort of part of the life cycle of the galaxy. You know how we learned that forest fires aren't all bad because they helped like clean out dead wood and provide space for new animals. You know, well, they're good as long as you don't live in your house is not next to you. Yeah, exactly that way. It's a sign of a healthy forest to have occasional small fires. In the same way it's a sign of a healthy galaxy to occasionally, know, clear out some of the clutter in the dust and blow up the old stuff and make room for something new. Because that is kind of how um heavier materials like we wouldn't be you and I wouldn't be here if if it's not for a supernova, and it's not just the supernova throw that stuff out into the universe. That is true. But also we wonder about like what makes a star begin, Like give a big cloud of gas and dust. Is gravity just like very gradually pulling it together over billions of years. Some people think that it's the shock wave from a nearby supernova that sort of triggers that gravitational collapse of that cloud into a star. So it might be that the death of a star the supernova is what you need to form new stars. Stars begetting stars. It's all cycle, man, it's the circle of life. Somebody que Elton John, But who who made the first star? Then, Daniel, what came for as the star or the supernova? The eternal question? I believe that one for the philosopher's all right, well, I feel like I learned a lot about supernovas today. You know, I thought that they only did the supernova through core collapse. They didn't know that there were all these other ways that they can happen. Yeah, supernovura fascinating and we're constantly studying them because they are dramatic and they're awesome to learn about, and because we'd like to know, you know, what happens at the end of life of a star. It's it's fascinating, it's dramatic, but it's also still mysterious. Yeah, and it's a big part of how the universe works, right, like how you make metals and everything all around this, everything around us is was basically made in a supernova. Would you say that, like all the metal and components in your phone, in your car, that all came from a supernova. All that stuff was fused inside a hot star billions of years ago. Yes. All right, Well, we hope you enjoyed that. And the next time you look up at the night sky and see something getting brighter, duck or at least close your eyes. At least close your eyes and look it up online later. All right, thanks for joining us, See you next time. Before you still have a question after listening to all these explanations, please drop us a line. We'd love to hear from you. You can find us on Facebook, Twitter, and Instagram at Daniel and Jorge That's one Word, or email us at Feedback at Daniel and Jorge dot com. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. For more podcast from my heart Radio, visit the I heart Radio Apple Podcasts, or wherever you listen to your favorite shows. Yeah,