What are zombie stars?

00:00:08
Speaker 1: Hey or heey? Do you think we should try to make physics cool? Isn't that an oxymoron? What do you mean, like connected to like the latest fat in the culture. Yeah, I was wondering if it might not be too late to ride the wave of the popularity of zombies. Well, zombies in popular culture just keep coming back like real zombies, So why not You don't think that they've like jumped the shark already. I mean, the Walking Dead came out like ten years ago. Well that that show definitely jumped the zombie shark. But no, it's it's had a little bit of a renaissance lately. Well, then maybe it's a perfect time for physics to get into the zombie game. I don't know if that's such a good idea. Man. Well, you know, we're experts at like giving new, confusing meetings to words that people already understand. You know, we did it for Color, for Spin, for Flavor. Now it's time to do it for zombies. Are you writing a movie called Quantum Zombies or Attack of the Zombie Courks? I am now dumb run Hi, I'm poor Handmay cartoonists and the creator of PhD comics. Hi I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I have never finished a zombie movie. What do you mean you've never finished making one or finished watching one? How many zombie movies have you try to make? I have made zero zombie movies. I have finished watching zero zombie movies. None of the above? Really? Why not? They just haven't been any good? Or you don't like the zombie genre. I haven't seen one yet that really clicks for me. You know, usually it's just ridiculous. The science isn't well explained, the zombies are slow and shuffling, or the action is all the same, like, boom, blow up a zombie's head, Boom, low zombie's head. It's just the same thing over and over again. Oh man, you just haven't been watching the right zombie movies. Tell me what are the right zombie Give me Orges top zombie movies. Well I have. I have a bit of an undead relationship with zombie the zombie Joe. What do you mean you're love for it died and then came back? Yes, kind of. I can't stand them. I hate them, and yet I can't stop watching them. I am fascinated by the whole genre. You're slowly shuffling towards even as you say no, no, Well, I can tell your zombie new because the sort of the latest flavor of zombies. They're fastened, they're lethal, ferocious. Yeah, can they hold a conversation? Some of them now they can yet? Watch Zombies got lines now it must be the Zombie Union has really done some negotia. Yeah, there's something I'll call half beat. If you're watching the latest Netflix zombie show, what did you say? A half beat? Have beat like a zombie, but a half zombie. That sounds like something in a quantum superposition of human and zombie. It does sound like something a physicism would come up with for a zombie show. But anyways, Welcome to our podcast. Daniel and Jorge explain the Zombie Universe, a production of Our Heart Radio in which we hope to infect your brain with the crazy virus that is reality. All of the amazing things that are out there in the universe that we understand, and all the incredible things that are out there in the universe that we do not yet understand, things that are blowing up and things that are blowing our minds we think about all of it, we talk about all of it, we joke about all of it, and we explain all of it to you. That's right. We want to bring back from the dead that fascination you had as a kid about the universe and everything in it, about how everything seemed amazing and wonderful and mysterious. We like to talk about all of those things that you can still see out there when you look out into the night. Kind And so, if I've never lost my love for the universe, does that mean that I'm still dead or I've always been a zombie? How does that work? It means you haven't turned into a zombie physic zombie. That's just in my future. Huh. If you get bitten by a physicist, although if you get bitten by a radio active physicists, maybe that's a whole different genre altogether. Then you get that physicist proportional intelligence or something. Well, it's hard to go down from where you Well, I'll try not to get bitten by a radioactive cartoonist. But you know, I'm not the first person to think about the idea of combining quantum mechanics and zombies. That's right. Yeah, it's a big part of the Marvel universe now, at least in the Marvel multi universe. Yeah, that's right. It's something called the quantum virus, virus that originated in the quantum realm and can turn his host into a quantum zombie. Whatever that is. Wow, I'm surprised you watched that episode of What If? I did say. I watched that episode internet googling. Oh I see, oh I see. You did no research for this episode today, minimal, minimal research, surface level zombie research. As much zombie research as I could stomach. That was a great episode. I think the original Adman went into the quantum realm and somehow got infected by a quantum virus and then turn into a zombie. And then when he came back, everyone turned into a zombie. All the superheroes turned into zombies. So where's the quantum mechanics? It just the virus came from the quantum realm. That's it. Do you need more? What more? Do you say the word quantum and it shuts down the conversation? You know? That's exactly how my son described it after we watched a Marvel movie together. He said, do people just say quantum when they mean you won't understand the science. Wow, and what did you say. I said, that's exactly what they usually. It means they don't understand the science, so they can't explain it to you. Well, it's kind of interesting because now the Marvel universe is all about the multiverse, right, which could be a quantum idea. Yeah. Well, there's millions more universes, so millions more ways to make money. And they mix it up with zombies, so you can see a zombie Captain America taking on a zombie Iron Man. Do zombies go to the movies? I wonder are these just for human audiences only if it's a brainy movie. Well, we are going to try to apply our brains to this universe and to understand whether things out there can die and maybe even come back to life, because there are so many strange things out there in the universe. Every time we look deeper in the universe, we find something weird, something bizarre, something strange, something we never expected to see. Yeah, it is a pretty bizarre universe, and sometimes things sort of come back to life, almost sort of like zombies. Everything in the universe has a second act. And speaking of rebirth and birth, I want to take a moment to wish a very special thirty fifth birthday to one of our listeners, Agnish Sabulci, have a very happy birthday, Agnish, and a very nice week visiting your family. In fact, you are made out of stuff from a star that once exploded and sprayed those heavy elements out into the cosmos. So everything that you were made of was once part of a burning star. So in that sense, we are all cosmic zombies. Are you saying, Daniel, that our son like us? Right now? We're the sequel, We're not the original production. Yeah, we might not even be the sequel. We could be the third generation or the fourth generation. We did an episode about how many generations of stars there might be, and how many generations of stars there might have already been. We could be a mixture. Some of our elements could have been in two or three Stars already, and others could still be fresh from the Big Bang. So we are like a zombie casserole where the reboot, where the slightly warmed up remake exactly the unimaginative castion of intellectual property strip mining. I guess all of Hollywood is full of zombies. Kind of true shuffling about trying to eat your brain. Every canceled TV show eventually comes back to life with a younger cast, better looking casts. Usually sometimes I think there's a new Jurassic Park movie coming out that has the original cast from the first movie. I'm amazed those folks are still alive. Or maybe they're not. Maybe the cost their zombie versions. Maybe the dinosaurs are Oh my goodness, you just give me an idea, dino zombies. I'm sure somebody in Hollywood is it's that to somebody else already. Let me call the Discovery Channel. They we'll have a shared universe with the sharknadoes and alligator Hurricane. I'm already looking forward to the zombie dinosaur Tornado sequel crossover event. That's right, that those would be the quantum dinosaurs. No God, they'll be both brilliant and terrible at the same time. Don't collapse the wave function at your own peril. It's called the Heisenberg Hollywood principle. But anyways, it is a pretty interesting universe full of life cycles. Things that have come into being and then explode or fade away, but then they have a way sometimes of coming back. In this universe, and apparently it happens also with stars. That's right. Stars have lots of different ways to live out their life cycle. They can burn on for trillions of years if they're very small, or they may very rapidly burn up their fuel and end in a cataclysmic explosion, a supernova that tears it apart. And you I think that a super over will always kill a star, would shred it from the inside and destroy any chance of its future burning. But that might not always be the case. So to be on the podcast will be tackling the question what is a zombie star now, Daniel? Is this a star that's a zombie or like a zombie that's also like a Hollywood star? That's right, This is a zombie whose career is really on the rise, and a list zombie was that it's supposed to be a zombie punt? Yeah, exactly. You know, we resurrected their career from the dead. You know, for example John Travolta, he is a zombie career, right. You know these are after physical objects, not folks in Hollywood. This is not, after all, an entertainment podcast, as much as we'd like it to be sometimes, So Zombie Stars, is that the official physics term or is that just what you're calling them. I did not invent this term. This is a term that exists in science. Is the term of those co into by astrophysicists. And as you learn, I think it's actually a pretty good description. Interesting, and these are these related to z bosons? Is that what the z and the z boson is zombie boon? No, that's what zombies exchange when they meet each other. No, this has nothing to do with z bosons. Though. It would be awesome if you could form a star purely out of z boson, So that would be a very weird kind of matter. Interesting. And then it dies and becomes a zz boson star, or it maybe turns into a different kind of court, then it'll be the zz top cor And I don't even know where this is going, but anyways, we're wondering how many people out there had heard of this term zombie star and whether or not it's meet it out into the public like zombie virus. So Daniel went out there into the wilds of the internet to ask people what do they think is a zombie star? So thank you to everybody who volunteers to answer these questions. Whereas on the podcast. It's super helpful. If you're out there and you've been listening to the podcast for a while and you would like to hear your one voice in the podcast. Please don't be shy. Just write to me two questions at Daniel and Jorge dot com and I'll let you know how to participate. To think about it for a second, what comes to mind when you think of a zombie star. Here's what people have to say. I'm gonna take a wild guess and say that a zombie star is a star that continues to live by sucking material, sucking mass out of a nearby star. They can be killed with a neutron bullet to the head. The zombie stars, I think it's the type of remnant star after a supernova. Zombie stars, I suppose, are stars that have used up all of their stellar material but have stayed small enough to not explode or become black holes. And so they maybe are brown dwarf stars that perhaps crash into another star of enough mass that the whole thing will reignite away, reanimating a dead star like a zombie. Zombie stars are stars that blew up and went cold and then got it up. Some yeah, some new materials like new Maybe they went through a field of gas or something of hydrogen and reached critical mass again and fired up again, and yeah, now they're one stead but alive again, basically like rogue dead stars that didn't collapse into a black hole. I have no idea, but I'm going to guess that it has to do with a start dying and not exploding or turning into a black hole. Maybe it's mass is not massive enough to create a singularity, and so that star just burns out and just stays out there, dead, encircling a galaxy. Uh, stars just wandering the universe that don't have, you know, a stable place where they exist. Maybe stars that are appeared to be dead but then they come to back to life or something to do with the cranberries. Of course, there are stars which were dead so after they were super nova they somehow start capturing material and comm alive again. But that would be close to what class hours are, but class ours are for black holes. No idea, stars that are dead but still produced light. All right, it seems pretty much everyone I knew exactly what you were talking about. That that's that's a very powerful thing about the word zombie it's like you you kind of everyone knows what that means. Yeah, I think it's actually a well named phenomena in after physics, right, I don't really believe that they actually call these zombie stars. Show me the paper, all right, will include a link to the paper in the show notes, so that everybody can verify for themselves that I have not fabricated this. But if I did fabricated, then I should get the credit for naming these things zombie stars. So in fact, yeah, sure, I'm happy to take the credit. This was my brilliant idea. Wow. Yeah, I feel like you're gaslighting me. Now you're both asserted that you came up with it and that you didn't come up with it. That's right, it's quantum credit. It's quite quantum plagiarism. No, but everyone seems to sort of kind of know what you're talking about, or at least how I think they have an idea what you're talking about, Like a star that dies and then comes back to life? Daniel stepp us through here. What is a zombie star? How do you define a star that dies and then comes back? Yeah, so a zombie star is exactly that. It's a star that sort of survives its own death. And you might be wondering, well, you know, how do stars die? What does that mean? Well, the most spectacular way for a star to end its life or to die is to blow up, is to go supernova. That's when it stars, gravity can no longer contain it, and it erupts and sprays its material out into space and is extraordinarily bright for a very brief amount of time. Right, But there, I think there are several kinds of supernova's. Right, then one of them it actually happens when it runs out of fuel and gravity takes over. Right, that's right. There's a couple of different varieties of supernova. Actually there's lots of different varieties, but sort of two major categories. The one that people typically think about it is called a core collapse supernova. That's when you have a star that's like ten to a hundred times the mass of the Sun, so a really big massive star. And at the heart of the star, remember what's happening is fusion. You squeeze together hydrogen to make helium, and then if it's a big enough star like these guys, that helium then gets fused to make something heavier, and the net gets fused to make something heavier, and if you keep going far enough, you get all the way up to iron. Problem is, when you fuse iron, it doesn't make any more heat, it doesn't fuel the star, doesn't continue the burning. It sucks up heat, so it cools the star down. So now all of a sudden, this balance between the energy of usuon pushing out on the star and gravity pushing in is disrupted and the star very suddenly collapses and then has this shock wave outwards. So that's a core collapse supernova. And these are really dramatic and they can like trigger the formations of new stars as the shock wave propagates through the universe. It's really pretty incredible. That's the core collapse type of supernova. That's one kind. The kind of we're interesting today is actually not that kind. It's from the star that didn't make it to supernova and then later on gets the material that it did. So that's called the type one A supernova, which is different from this core collapse kind of supernova. And I see, so we're talking today about the type one A. And sometimes that type one A can turn into a zombie. So step us through what's happening in a type one A supernova. So the type one A supernova is when you have a lower mass star, one that's on its own, could never become a supernova. So you have like less than eight times the mass of the Sun, and this thing goes through its normal life cycle, maybe becomes a red giant. It burns, the hydrogen burn is the heavier stuff, but it doesn't have enough mass, for example, to burn carbon inside of it. So the carbon that's inside of it, it just accumulates like ash. And what happens in these stars is that you get a gravitational collapse when it runs out of fuel, when it can no longer burn because now it's just like filled with carbon at its core. You get a gravitational collapse, but you don't get a supernova, and you don't get a black hole, and you know, you don't get a neutron star. What you end up with is a white dwarf. A white dwarf is something that's no longer fusing. It's just like a big hot lump of stuff sitting out there in space. It's like a mix of oxygen and carbon, but again it doesn't have enough mass to keep going, and so most white doors just sit out there, and they can sit in the universe for millions, billions some people think trillions of years, just sort of glowing and not fusing until eventually they become black dwarves. So that's a typical life cycle for a star like that. But sometimes something intervenes. If one of these white dwarfs is actually the member of a binary system, meaning there's another star nearby, then they can start to steal some of the material from that other star and that can trigger a supernova that can give it enough material to get it like over that hump to collapse into a supernova. All right, that was kind of a lot a lot there, but it sounds like it's sort of like a star not much bigger than our It's like only eight times bigger than our sun. And then that kind of happens in the same way that's the other stars that do supernova. It runs out of things to fuse together, it just doesn't have enough gravity, and so it collapses and then it just simmers there. You're saying, well, what happens is that it collapses, but not as a supernova. It just sort of like becomes a white dwarf and it just sits there hot, glowing into the universe until it's a neighbor this binary star. Maybe that one becomes a red giant or gets too close, and then the white dwarf can steal some of the mass from its neighbor, and now the white dwarf. Otherwise we just sit there happily. But when this new material accumulates to the surface of the white dwarf, then it pushes is it over the limit the gravitation limit for a stable white dwarf, and then it collapses. So it's like you didn't have enough mass to go for collapse from the beginning, like a typical core collapse supernova, but instead you've got like a late second helping and it's extra stuff you steal from your binary partner that lets you collapse to a supernova. And this is a type one a supernova, and it's famous because it's helped us understand like the shape and the acceleration of the universe. M I see. So this only happens in binary star systems, like star systems with two stars in it or more. It almost only happens with binary star systems, probably not exclusively, but yeah, that's the best way to accumulate some extra material. So then you have this white dwarf which is just like a ball of oxygen and carbonages simmering, just glowing there from the heat. And then you're saying, like the other it's partner stars somehow falls in or get sucked in or or what happens to it. Yeah, these two things can be near each other, and remember a binary star system. Eventually they get closer and closer and even merge. Sometimes you can them even like one goes inside the other star. But eventually these two stars in the binary system get close enough that the white dwarf can steal some of the material from the other one. You've probably seen these like artistic renditions. You know, you have two stars, one much bigger than the other one and the smaller one having this like trail of material accumulating from the bigger star. And I see they're like rotating around each other. But eventually, over time they orbit collapses and it starts to suck suck it in to the bigger one, which is the white dwarf exactly. And if the white dwarf gets enough material, then it can actually go supernova, and it's really fascinating because these white dwarfs are very regular, like there's a very specific critical mass at which a white dwarf will get triggered to go into one of these type one A supernova, and that makes it very nice to study because that critical mass is like a basic feature of the physics. It's the same everywhere in the universe, and that means that these type one A supernova are very regular. They're sort of easy to standardize. There's a simple relationship between the light curve, like how much light is admitted per time and the true brightness, which is one of the things that allows us to calibrate them, to say, oh, we know how bright it was at its source, and so we can figure out how far away they are. And that's why they played such a crucial role in extending our distance ladder and helping us understand how far away some of these distant galaxies are. I think you're saying that this process for the supernova through the white dwarf is very repeatable, like it always kind of happens at the same time or at the same point in the life cycle of the star YEA. As soon as this white dowarf accumulates enough mass and gets over this threshold boom, that's when it goes supernova. And so that's very repeatable exactly. And so the supernova is really pretty incredible process. You know, it's a supersonic propagation of energy out of the heart of the star. You know, the explosion is happening faster than the speed of sound inside the star, and so it builds up this shock wave which propagates out at you know, some like significant fraction of the speed of light. It can be going like ten kilometers per second through this stellar material. That's like more than five of the speed of light. Wow. All right, well, let's get a little bit more into detail of what's happening when this thing collapses, and let's talk about how that gives rise to zombie stars. But first let's take a quick break. All right, we are back from the dad here talking about zombie stars, stars that come back from the dead, and we talked about how you said that these come usually in in binary star systems, where one of them turns into a white dwarf, meaning it runs out of fuel, it collapses, it's simmering there and then it sucks the mass from its partner star and somehow that gives it enough I don't know, juice to explode. What's happening there, Like it increases. It was nice and stable and simmering, but now it has extra mass. So what happens? Yeah, Well, the white dwarf is stable, and to understand how it becomes unstable and turns into a supernova, you have to understand what the forces are at play. So pushing it in, of course is gravity. Gravity is compressing it. It's very dense, it's very heavy, so there's a lot of force inwards. What's pushing out, what's keeping this thing from collapsing into a black hole or something else, is actually quantum mechanics. This thing is super dense, but the electrons that are inside the white dwarf they don't like to overlap with each other. Electrons are a special kind of particle. They're called fermions that don't like to be in the same quantum states as any other fermion. So they don't like to overlap and they resist, and that's what keeps white dwarfs from collapsing. But that's not infinite. If you put enough gravitational pressure on this thing, it will eventually collapse into a supernova and maybe leave you at the heart with a black hole or a neutron star. So what you need is more gravity. Which you need is more mass. So if you add extra helping of stuff to your white dwarf, then it will actually collapse and create a supernova. But I guess it's keeping the electrons from collapsing into each other. You're saying they don't like being together because of quantum gravity, But what's the actual force there? Is it like an electromagnetic forces kind of repelling each other apart. Yeah, that's a really fun question, like what force is actually at play keeping electrons apart? You know, and you don't have to think about everything in physics has happened as requiring a force. You know, this is just something that like quantum mechanically is suppressed. Electrons don't like to do this. You can overcome it by squeezing these things down and basically having the electrons being captured by the protons that are also inside the star, converting them into neutrons, and so then you can avoid the electron degeneracy pressure. But that takes a lot of energy, a lot of gravitational pressure to basically push the electron inside the nucleus, so it gets captured and gets converted into a neutron. That's not an easy thing to do. Takes a lot of gravitational pressure, all right, So then you had this white dwarf. It was sitting there. Happily it got more stuff, and now it's so heavy that it collapses, like the gravity kind of overcome is this propulsion and it collapses. And then how does that lead to an explosion? Well, it collapses, which is an implosion, right, which creates incredible density at the core, and that triggers basically a thermonuclear explosion. So it happens there is that all of a sudden, you do have the conditions you need to create carbon fusion. Remember the white dwarf died because it accumulated all of this carbon at its core, and it wasn't big enough and hot enough to create the temperature necessary to fuse carbon, so sort of stopped. And then all of a sudden, boom, you have incredible pressure from this implosion, this shock wave that's traveling inwards because the gravitational collapse, and that does create the conditions needed for carbon fusion, and all of a sudden, all that carbon goes up in just like you know, days, So instead of taking millions or billions of years to burn all of it, it's like a huge bomb goes off instead of a self sustaining reaction. Wow, it's like you brun the entire sun in like a matter of a few days. Yeah, it's so much energy that it basically unbinds the star. It just blows up out into space and disperses its material over a huge region. Sometimes it just blows everything out into space. So that's really like the death of a star, or at least one particular death of of this kind of binary star. And you say when it explodes, When this kind of star explodes, the type one A, that's the kind that we use as standard candles right as to kind of measure how far galaxies are. Yeah, because they do so in a very predictable way. The light curve has a very distinctive shape, and so we can spot it was like, oh, that one's a Type one A. We know what happened there. And because the shape of the light curve is easy to relate to the true luminosity, like the actual brightness. So if you look at the light curve, you can say, oh, it's one of these type one A. It's one of those type one A, so you can know exactly how bright it actually is. Sort of similar if you remember to how we first measured cosmic distances, which with these sephids, these variable stars, where their period was related to their brightness, so you can measure the period of their variability and you could use that to deduce how bright they were the source. That's always what you want to do to understand how far away something is is understand how bright is it really if you were right next to it, and then you can compare that to how bright it appears here on Earth and you can know how far away it is. Right. I think what you're saying is that this type of supernova, it almost always explodes with the same brightness, Like you don't have this kind of supernova for a small white dwarf. It only happens for very particular size of a white dwarf. And when it happens, it always happens at the same brightness, which means you can tell where it is. Almost is one little wrinkle there, which is they're not all exactly the same brightness, but you can tell how bright they are by how rapidly they emit light and then fade away. So the shape of that light curve over time tells you what the brightness is. So it's not exactly that they're all the same brightness, but you can figure out how bright they are by measuring this light curve. I see. All right, So that's one way for a start to die. And you're saying, this is the kind of explosion, this kind of death of a star that leads to a zombie star. So this kind of explosion destroys the star that's are dead, dead and never coming back. It's like a big with a big cloud of dust and gas. Yeah, exactly, But what we noticed about twenty years ago is that that's not always what happens. Sometimes, when you have a type one day supernova, it doesn't actually destroy the star. It explodes a little bit differently, and it leaves behind something that has enough stuff to keep glowing, so it can sort of like have a supernova and still survive. Wait what, So it collapses, it creates incredible fusion in the middle. It explodes from that, but not completely like it doesn't. It doesn't all disperse. It stays there and no black hole is for me, that's right, it's sort of like it tries to go supernova but doesn't quite make it. So this peculiar kind of supernova comes from the same sort of basic setup. You have a white dwarf in a binary star system. It accumulates some mass, but for reasons that are not fully well understood, it doesn't actually trigger the same kind of supernova trigger sort of like halfway supernova. It does definitely do a collapse, and there's some carbon fusion that's happening at the core, but not enough to like really ignite it. So it like blows up a little bit, sends out a huge amount of light, but not quite a full on type one A supernova, and it leaves behind something which can still burn. So basically it just collapses. It doesn't actually explode that much. It does create carbon fusion, and that does create a ripple through the star, but the key is that that ripple is not supersonic and so it doesn't create a shock wave. And that's key. I think about what happens as you row your boat through a lake, right you leave ripples, and those ripples passed through the lake. If you're driving a motor boat, for example, you're going super fast you're going faster than the speed of your ripples. Then you create a wig because all those ripples are catching up to each other, they're adding up at the same place. And so that's what happens in a Type one A supernova is the explosion is supersonic, so it creates this incredible shock wave which blows up the star. And a Type one A X supernova this weird version of a Type one A. It doesn't quite me. It doesn't go supersonic, and so it sort of heats up the star. It gets bright, but it doesn't actually blow it up. See now you're confusing me. Now you're saying it's called a one A X. Shouldn't have been like a one It should totally have been a one A Z. I think they must have labeled it one A X because when they saw these, they were like, hold on a second, this is really weird. Type one A supernova usually super regular and predictable. Here's a weird version. So they like X for like X files, So this is like the X file star. And so what's the difference, Like what made this one explode in a different way than the other one. They're not sure, but one theory is that it depends on the kind of stuff that the white dwarf is accumulating. Like if your binary star, the companion, the one that's feeding you this extra material that triggers you, that has a lot of helium instead of just a lot of hydrogen, and that might set off a different kind of reaction. It might only make carbon fusion happen within a specific bubble of the star. It doesn't trigger it well enough. But truth is, we don't really understand the process of a supernova well enough to predict it and to understand it and to disentangle it. So it's sort of like a puzzle. We need to figure this out. We don't know why it didn't blow up like the other ones. Yeah, we don't know. What we do know is that they look different, right, So these things are less bright. There's still really dramatic events, but they're not as bright as type one a supernova. The stuff that flies out of the star as much lower velocity, so you're still like exploding part of the star. You can stand out like half the mass of the star. Or this thing is not just like a little burp, right, it is a big explosion. And they also look different, like there's more helium lines in these stars than in typical type one A supernova, So there's definitely something different happening, is something different going on, but we don't understand the process of a supernova well enough to really pint it down. But you're saying, then that doesn't explode is violently than as a regular type one A supernova, which means it leaves behind some stuff, at least stuff that can still burn. It leaves stuff that can still burn. And this is an incredible object, this zombie star, because it's very small, it's very hot. It might be like only the size of our moon. You know, this is a tiny, little astrophysical object. It's blown away a huge amount of its stuff in this sort of like half formed supernova, but it can still burn because it's dense enough and it's hot enough to glow. So they think that carbon fusion still happens on the inside, but in a more sustainable way, in a way that doesn't explode the star. Wait what so it's not just like a hot thing that glows from being hot it it's actually doing fusion in the middle, and it's only the size of the moon. You can have a sun the size of the moon. Yeah, it's come back to life. Man. It was fusing and it collapsed into a white dwarf and then it's fusing again. It can't do it forever, right, because it's a pretty small lump of stuff relative to other things in the universe. But the conditions that forced it to collapse can get carbon fusing. And what you need is temperature. So if it gets hot enough inside there to fuse carbon, that generates this heat that you need to keep it going, right, But I guess what keeps the star burning if it's not, if it's only the size of the moon, whereas all the gravity coming from to keep the fusion going, well, it's sort of ignited. Right. In order to have that kind of carbon fusion, you just need really high temperatures, and that temperature is now coming from the carbon fusion itself. So it's a kind of thing like once you've gotten it's started, it's easier for it to keep going. In many stars you just can't get carbon fusion started because you never reach that temperature. But in these zombie stars, you like across that threshold because of this collapse, and that ignites the star and then it can burn its carbon, even if there wasn't originally enough carbon to trigger that temperature just from gravitational pressure. Oh, I see, So it's like a self sustaining fusion reaction. No gravity need Well, gravity is still holding it together, but it didn't need the gravity to trigger the carbon fusion. But once that's happening, then it can keep going exactly. So these are really fascinating objects because they're weird, right, because they're different from the kind of tape one a supernova that you typically see. Well, it's kind of weird that you're calling it a zombie star because it's sort of not undead. It's like it's a lively star. It's burning. You know, I might might be even insulted if you call it a zombie, right. I see, you're saying zombies are not back to life, they're undead. That's the distinction. I'm not sure what I'm saying. I'm saying, like, like our son also came from a dead star maybe, but we don't call it a zombie star. It's just a new star, that's true. I guess this is more closely connected to its progenitor than the Sun is. The Sun came from just like a big cloud of gas and dust that swirled together to form the solar system. This is like a white dwarf that's pretty closely connected to the original I mean, in the same sense we're all zombies because we're all made out of organic material that's definitely been used in other beings. But you call a zombie zombie because it's like the same body. So this is like the same body of the original star that was fusing. That's sun corpse, he's saying. It's the same. It's a reanimated corpse, and therefore that's a zombie. Exactly. It's lost some of its mass, you know, part of its face has fallen off, but it's still ca double of shuffling around and entertaining you and and eating sun brains. What does it mean? Carbon? Yeah, well I guess so. Carbon is the brain of the sun, you know, and carbon is the basis of organic life here on Earth, and it's also at the heart of the brains. Yeah, exactly, eat star brains. All right, Well, let's get into how common they are in the universe and where we've seen that and what does it all mean. But first let's take another quick break. All right, we're talking about zombie star stars to have come back from the dead, and so we talked about how some stars sort of try to explode, but they sort of only half explode, I guess because they don't have to write ingredients to explode into a supernova, and so they you just kind of get a little bit of a dead corpse of a star. But it's still burnie. Still, it's shuffling about exactly. It's like a quantum star because it's both exploded and it survived. Oh wait, now you're just confusing whether there's no quantum superposition going on here. No, there's no quantum superposition. Now, it's like half of the stars blown up and the other half decided not to So it's more like a divorce star because you know, the different halves couldn't agree on what to do. That's a different kind of Netflix show. I feel we should maybe stick to one genre before we refuse people. It's a zombie star. It's not a divorce zombie star. It's not a zombie relationship. It's just a star. Isn't there a Netflix show about Mary zombies? There have been movies. Yes, as you can see, I'm an expert on are Apparently you know there have been a movie about zombie romances. Well, anyway, I love zombie stars, even if I don't love zombie movies. Well, that's because you haven't seen one up close or in the middle of the night. I'll consider it. All right. Well, let's talk about how common they are. How often do we see these zombie stars. Are we like surrounded by zombie stars everywhere or is this kind of a rare thing. Well, it's sort of an interesting paradox because we know two things about them. On one hand, we haven't seen very many of these things. Only like a hundred type one A X supernova which leads to zombie stars, have ever been seen. The first one was spotted about twenty years ago, so that's not a whole lot. You know, we've seen a lot more Type one A supernova than that. On the other hand, based on you know, frankly speculative models for how this happens, if we understand what's going on inside supernova and we don't, then these calculations suggest that this should happen more often than you imagine that, like the full Type one A supernova should fail to trigger in like of the cases. But I guess it's all based on whether or not the companion star has the right ingredients. So how do we know what these companions have out there? We don't know for sure, but you know, we do know a lot about what is out there in the universe based on how stars glow. You can look at the light that comes from a star and you can tell mostly what's made out of what it's hydrogen helium mix, because remember that different kinds of materials, different elements like to glow at different frequencies because they can absorb and amid photons that match the various vibrational and rotational and orbital energy levels of that element. So you can tell how much helium and how much hydrogen there is in a star based on how it glows. And so we have some idea for how common it is to have like a very helium ish star, and that lets people do these calculations, but you know, it's totally speculative, and its conflicts with some of the data. The data says, look, we haven't seen that many of these things. Either there's a lot of them out there we haven't spotted, or maybe something's wrong with the calculation I see, because we've only seen kind of a few tents of these, right, like a hundred of these zombies stars. We've only that's how many we've seen. But you're saying there should we should see more. Exactly, we should see more. There should be more of them. Again, if our theory about how this happens is correct, or maybe it's not. And you know, this is the process of science. We see something new, we go what how does that work? They put together a model from maybe what makes it, and then we look at the consequences of that. We say, well, if this model is true, what does it predict about how many more we should see and where we should be able to find them? So let's go look. If we don't find them, that means we've got to go back to the drawing board and come up with a different model for how this happens. I think what you're saying is that we might be surrounded by zombie stars, but maybe they're hiding. Is that what you're saying. It sounds terrifying. They're waiting for nighttime, right, isn't that waiting for you to go to sleep for them to shine their zombie light on me. We should be careful about talking about scary things because I think some people listen to this podcast as they're falling asleep, and we don't want to give them bad dreams unless they're fans of zombie movies, in which case they will sleep very happily. Maybe you could be a fan of zombie movies without being a fan of having zombies in your dreams. I think, do you want to start a zombie movie now? I just want to dream about zombie stars? But that is kind of what might be happening right. There might be a lot of them and they but they might be hiding somehow. Or maybe this failed collapse happens a lot, but maybe just we just don't see it, like maybe it collapses in mud blows up exactly. It might be that happens in a different way that we imagine. And when challenge is that we haven't ever seen one of these in our own galaxy. Remember the Type one A supernova are so bright that we can see them in distant galaxies. In fact, that's why they're so powerful and so useful, because they can shine a light about how far away, really really distant galaxies are. Interesting thing is that we've never seen one of these Type one A X supernova we've never seen a zombie star in our own galaxy until very very recently. I guess you just made me think of a question, which is like, if we haven't seen one in our galaxy, then how do we actually know they happen? Like you see a bright flash in a distant galaxy, and then but then you can't see the zombie star, can you. It's too small? Yeah, the zombies are itself is too small to really see to make out in detail. But you can see that the type one A X supernova has happened. You can see the light curve that's really bright. It's not as bright as a type one A supernova, like ten times less luminous, but it's bright enough to see in other galaxies. And actually one time they caught a type one A X supernova happening accidentally. They were looking for type one A supernova, of course, as they usually do, and so they were using hubble to take pictures of one that had recently happened. And then shortly afterwards there was a type one A X supernova that happened in the same region of space in this distance galaxy. So they were able to go back because they happened to take pictures of it before it exploded, and to see the progenitor, the thing that created this Type one a X supernova. So it helped give them a clue about how this happens. But I guess you haven't actually seen these zombie stars, right, You've only seen like a failed flash, but you're sort of speculating that it leaves behind a zombie star exactly. These zombie stars are not bright enough to see directly. But in this case, it's cool because you can see the binary star system and you can see that the other star in that system is actually a bright blue helium star right next to a white dwarf. And then we see a Type one A X supernova has this characteristic shape. It's different from a Type one A supernova, and so it doesn't have enough energy to like totally destroy that star. But we see that the progenitor, this white dwarf, is no longer there. So it's fascinating because they could see it like before it happened. That's not something we've ever seen for a Type one A supernova. We've never taken a picture of a star system before it went Type one A, which is one of the challenges for understanding how these things happen. Wait, so you're saying, we've never seen a zombie star in our galaxy, isn't that weird? Yeah, it is kind of weird, And again it goes to our lack of knowledge about what forms these things. Some people speculate that it might depend on the age of the galaxy, that only in galaxies of a certain age does this kind of thing happen, because maybe you get more helium stars. But there's all just a lot of speculation in the literature about why this might happen. Recently, people saw something that they think might be a type one A X supernova, and that's very close to the center of the galaxy. There's this thing they're called supernova remnant Sagittarius A East. So it's very close to the black hole of the center of our galaxy, and the light that's coming from it looks consistent with what you would expect from a type one A X supernova. The supernova itself was actually seen on Earth like nine hundred years ago, and it's recorded in history. At the time, of course, they couldn't tell that it was the type one A X supernova. But now by looking at like what's around it, and how it affected the stuff nearby it. They're speculating that that might have been a type one A X supernova and it might have left behind a zombie star. Whoa wait, wait, we saw it here from Earth. There's records of it exactly in one a d for a hundred and eighty five nights. This supernova lit up the sky and Japanese and Chinese astronomers recorded it in history. So something we know half and we can look at the remnant it's very close to the center of the galaxy, and then we can look at stuff nearby it and say, like, what shock wave has impacted on that stuff nearby? What's the velocity of the stuff moving through space? And when they do the calculations, it looks like it's consistent with a type one A X supernova having exploded there like nine hundred years ago. I guess maybe it's a good thing that we haven't seen a supernova in our galaxy, right, Like, if there was a supernova nearby, we we did fried. Yes, supernova release a huge amount of energy, a huge amount of radiation, and so if one of them was too close, absolutely it could sterilize half of the planet. Fascinatingly, though, most of the energy of a supernova is actually carried out in new trinos, Like of the energy released in a supernova comes as new trinos, which of course hardly interact with us. Even that one percent, though that's left over if the supernova is close enough, is enough to sterilize an entire planet. So are we lucky then that the one near the center of the galaxy was a failed supernova? You know, like if it had been a real supernova, would it have affected us. It would have been brighter and so it would have been more dramatic. But even that one is still pretty far away the center of the galaxies, like twenty thousand light years away, so not close enough to really cause any damage, your honor, and I guess also too far for the zombie to come edith, I don't know, it's had nine years. Well, in a way, it's kind of funny because these zombie stars happen because one star eats another star. Oh that's true. Yes, one star is feasting off of the brains of another star, and that's what it brings it back to life. Yeah, that's the lesson. I think, do not eat brains like turn into a zombie or if that's your aspiration in life, eat away. That's right. If you if you endeavor to be a zombie star, that would make you an zalist star. I guess, all right, well, what what does it all mean. I guess it means that we still don't quite understand Supernovaz that will. I thought it was something that was pretty well understood and modeled, but it sounds like there are still a lot of questions about how it happens and in which way it can happen. It's a rapidly moving field, and we're always developing better and better models, which have gone from like two D to three D two much more realistic, and now with our impressive computational power, we're making more and more detailed models. But it's very tricky because we're talking about something that's happening very fast, very high density, and very high intensity, and so the modeling is difficult to get right. We're talking about the strong nuclear force, we're talking about incredible gravitational forces, and so it's difficult, and you know, our measurements are limited. We can see a few things about them here from Earth, but it's not easy to understand, like what's going on inside the supernova. And actually a lot of that information is carried by neutrinos, which can reveal what happened on the inside of the supernova. But neutrinos are so difficult to observe, so it's a real challenge for us to model and for us to understand, right. And it's also I think it's sort of this difficult intersection for physics of quantum mechanics and gravity, right, Like it's it's almost like you're looking at the heart of a black hole. It's like when these supernova happened, the pressure and the gravity, it's all sort of makes us together. So that's something we don't understand. Yeah, and it's very short lived and kind of rare, and even easier problems we still don't understand, like what's going on inside a neutron star. Neutron stars are everywhere, and they last forever and they glow steadily in the X ray, and still we don't understand sort of the equation of state, like what's going on in terms of the pressure and the density and the speed of sound and the inside of a neutron star. So supernova is harder because it's short lived, it's higher intensity, and there are fewer of them, and so we have a lot of work to do to understand what's going on at the heart of these things. But seeing the weird ones, the extremes are really helpful because they help you understand the boundary conditions, like why didn't this one go Type one A supernova? Why didn't that one? Is like examples of ones that survived and came back to tell us a story. So they're really useful clues, and it tells what triggers the type one day supernova and what doesn't. Yeah, that's pretty cool, and I guess also the problem is there are a lot of physicists who hate zombies, and so they won't even touched this stuff, right, Like, I'm surprised to you even finish that paper, Daniel. Anything for the podcast, and anything for the podcast except actually watching zombie movies that I can send you a long list of required zombie genre thanks to watch if you want to catch up. If not, you can just run faster. Alright, and listeners out there, tell us what is your favorite physics zombie movie. That's a that's a sub genre. I guess, I hope, so, I mean, apparently would watch those then yes, there's a physicist involved, you would watch it exactly. Maybe the physicist becomes a zombie and then she has her best ideas and that's when her career really takes off. Yeah, she becomes a zombie star in the physics community. All right, Well, we hope you enjoyed that thinking about what happens out there in the cosmos, and what doesn't happen in the cosmos, and what kinds of interesting new types of stars there can be and are being born every day. Thanks for joining us, See you next time. Yeah, thanks for listening, and remember that Daniel and Jorge explained. The Universe is a production of I Heart Radio. For more podcast For my Heart Radio, visit the I heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. H