Daniel and Jorge Explain the UniverseWhat causes the biggest explosions in the universe?
We're taking a deep dive into the subject of supernovas. What causes them? What do we know about them and can they harm us here on earth.?
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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, I.
Am aware, thank you very much. I also know that nobody's actually shooting those.
Stars as far as we know. You know, Hello, you're.
Going to hit the aliens button before me. But it would be cool to actually see a star explode, you know.
I mean, you're looking at the sky and suddenly one of them just goes, oh.
Yeah, as long as it's not our star, it'd be pretty fun to watch.
H II am poor handmade cartoonist 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, a 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 does in English.
Well, he actually told me how to translate the title in check literally into English.
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, That'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 have sold. You would be slaying 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 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.
Universe, mysterious 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 iHeartRadio.
In which we examine 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. It also teaches you something deep about the physics of our universe.
Yeah, we talk about all the sort of a nice and beautiful and wonderful, inspiring things that are out there in the 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 super nova.
It goes hyper nova.
Hyper nova. Yeah. So to the on the program, we'll be tackling perhaps one of the most I don't know, violent or you know, dramatic or you know, maybe interesting events that happen 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, well, let's get into that. So to be on the podcast, we'll be asking the question what makes a supernova blow explode? I guess 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 duper nova or.
Well, you know, the name nova is actually quite fascinating. It means new and so, 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 die is pretty unusual.
We'll be talking talking about supernovas and what causes the supernova and how that works. But it's basically the biggest explosion 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 could 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 ober nova? Or I call it mega nova an 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 can't 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's exciting that they happen quickly. It also is the thing that makes them hard to understand and hard to spot because we don't know precisely what causes the start to go supernova, and they don't happen that often, so it's pretty rare to see one start to.
Go oh wow. Really, we don't know what causes these supernovas.
No, we have some general sense for what happens during 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 announce a big countdown like NASA, you know, thirty seconds still ticking.
There's no ticking time bomb.
No, And astronomers would love to see a star like five seconds before supernova, one second before supernova, the first moments, you know, that would be fascinating.
So you can catch it as as it's happening.
Yeah, and there's actually a guy who was watching the skies in twenty sixteen, an astronomer, an amateur astronomer. He was just happened to be looking at one star 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 live for a really long long time, and so they calculated the odds as like one in ten million or one in one hundred million that if you're looking at a star 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. 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 those Did he have a whip out his cell phone and took a picture of it?
Yeah, 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 of this 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 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 shod people actually know about a supernova? Do 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.
Is it when a star explodes? What makes it happen?
You know the death of the star.
Supernova is basically like an exploding.
Star, right, So what makes it explode?
Age?
Are you going to explode when you get older?
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?
I know that they are the final stage in the stars.
Okay, what makes them happen?
Eventually?
The it becomes too dense the elements that it creates 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 know, all right, 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 few people had 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 explosion in space. And you're saying it's rare, so only about one to three supernovas 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 one 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 will actually see it, like you'll I'll shine the whole galaxy and we'll see it, 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 one hundred billion stars went boom.
Yeah, precisely.
Well, let's get into it, Daniel, all right, 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 well, 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 enormous amount of matter.
This is like.
Shockwave of just stuff that gets spewed across the.
Universe, like the shrapnel in a 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's not like a star suddenly gets out of balance. It's like in the DNA of the star. You know, like, once you know what kind of star you are, you will most likely go supernova, or if you another 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 understood, 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 goes supernova, become a white dwarf or whatever. That's basically what determines it. It's like how big a scoop of stuff did you get of the universe and what's in that scoop?
Wow, and that determines your your whole life cycle. If you're a star, like you're born and everyone already knows how you're going to die. Right, Yeah, here's a baby. Oh, this baby's 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 she turns thirty two.
Yeah, 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 pocketive stuff and it just sits there and burns it until it can't burn it anymore.
We know it's going to go super nova, but you can't predict when it's going to go super nova.
Yeah, these stars have something of a variable lifetime, and you know these events, the supernova event happens really quickly. Remember that, Like the timescale for stars can be millions and billions of years, but the supernova events, the timescale for that is days and so a 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's ticking down. Eventually it's just going to 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 passing shockwave from something else makes it go. We just don't really understand those moments.
Or you know, like a planet falls into it and that triggers it.
Perhaps, yeah, there are stars like that that do get triggered from infalling material, but we don't know exactly like when that happens.
All right, well, let's get into the mystery of what triggers supernova's and what's actually happening when they explode. But first let's take a quick break.
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Right doneld. So we've seen a couple of these supernovas in the night sky, like without telescopes. Right, there's a historical record of supernovas and then 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 you can find a astronomers writing about this. And the earliest one, it's called HB nine, is from forty five hundred BC. And we see this in 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 it?
I don't know.
We don't know who was. We know some unnamed Indian astronomers. We call it HB 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 sky and a supernova just happened to, you know, occur while I'm looking at the sky. 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 going to 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? And then 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 after a few months, so.
It wouldn't be like a sudden flash. You would sort of 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, huh. It's like an early warning system.
It is. And you can actually sign up for an early warning emails. There are 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 to your bunker and not look up at the sky.
Like our president.
It might mean that in three minutes the Earth is 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 shockwave reaches the surface, which is a few hours after the beginning of the explosion.
Yeah, the explosion itself.
Yeah, they get sort of reabsorbed, and it takes a little while for the photons that will reach Earth to be emitted. 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 soft all right.
Well, to get into what's happening here.
It's super fun to think about this stuff, you know, because it's a dramatic event, and so people really like thinking not just about how stars form and how they burn, 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 happen. Both of these kinds of supernova reflect this classic Titanic battle between gravity and fusion. In one case, fusion wins, 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 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 describe basically what they look like in the sky, what the sort of energy spectrum from them looks like. But there's two fundamental mechanisms. Is run away fusion and this core collapse.
That's cool, let's get into the first one here, runaway fusion. That sounds like like an experiment that got away from you.
I thought you were going to say it sounds like a physics based.
Rom com movie with 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 into heavier stuff, and heavier stuff into even heavier stuff.
You're squeezing stuff together so much it's burning and exploding and fusion ing 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 were squeezing a bag of corn kernels, Like you would squeeze them, but then 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'd never until today, heard of corn fusion. I think you might be.
Corn popcorn, the new brand of popcorn.
Corn physics snacks corn.
Fusion's 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, 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 supernovaus, but now I'm desperately curious. What would happen if you actually squeeze that much popcorn, would they pop? I bet they would. I bet you'd be heating and pressuring, and yeah, you might get a self sustaining corn reaction. That's exactly the idea. And what happens inside the star is 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, So 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.
Oh I don't have it in me to make this carbon fuses.
Yeah, it's just not big enough. Like, if there were more of it, right then there'd 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 which you have there are 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, shining because they're just sort of left over heat 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, they're 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 it's red hot it's white hot, and so at some point it can just cool off. 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 dwarf 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 vide game achievement. Oh, I see, So we know what's going to happen to them, but 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 does this end up in a supernow, 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. So 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 in 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 in 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 literally like blows up from the inside.
Here fusion winds and gravity just can't keep the star together anymore. Imagine what would happen if every part of the Earth suddenly had huge amount of energy, like it had 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 just like spews itself over the cosmos.
What so, how does it start. It starts in the middle, like some of the carbon starts to fuse, and then that releases energy with which then fuses the carbon 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 simple model for what we think might be happening in 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 supernova. 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 and to compare our simulations to data.
Because it happens within a few seconds. Like it's like it'd 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's 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 just assign some grad students to each star in the in the universe.
Yeah, how many grad students do we have? And we do have some really big survey missions that scan 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 can. 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 going to 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, neutrino detectors are sometimes busy doing other things, are not dedicated to supernovas. They try to hook these things up and when the neutrinos tell us the supernoa has come and they point in that direction, and so we do our best because remember, these 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 go 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 supernoas can happen. But first, let's take a quick break.
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All right, Daniel. So the second way that a supernova can happen is called core collapse, and I think this is maybe the one that most people are familiar with. Why is this one more I guess popular.
This is the case where gravity wins in the epic 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 got to be a 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 SUPERNOA? Is it like many times the size of our Sun or a little bit more.
It's like five to eight times 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.
Hey, yeah, you're forever b list, which I.
Think is a good thing. But this sort of core collapse supernova requires a really big star. And we were talking earlier about what's happening inside a star, is 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 byproducts 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 make heavier and heavier elements.
But it's sort of a more control process because it's happening gradually. It's like an equilibrium. Stuff is sloshing back and forth, and the carbon fuses and it turns into the next thing. And these guys can fuse all the way up to iron. Remember that up to iron, when you have fusion, you release energy above iron, nickel or so when you fuse it absorbs energy and so cool the star down.
So like what comes right before iron.
Yeah, so iron is number twenty six and Nicholas twenty eight, 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 at twelve, aluminum, silicon.
Oh.
I see. So 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 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 stuff. 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, gravity wins, 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 shake card limit. It's essentially when matter cannot be squeezed Anymore'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 or a neutron star is sitting at But when gravity has enough power to overcome that that electron degeneracy. When you have too much stuff, then it collapses and gravity takes.
Over, meaning that whatever is keeping the star kind of fluffy, it's no longer enough burn 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 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 shockwave. And so people sometimes talk about supernovas as implosions, and that's why, because you get this shockwave of stuff rushing in towards the center.
Wow, because the inwards of the star are I guess collapsing. Before there was sort of fluffy from all the energy, but now they're just through out of energy, so that everything's just crunching together.
So 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. Yeah, so the whole thing 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 turns into a black hole.
Yeah, it can just go and suck itself into a black hole without a supernova, Like you can skip the supernova step if you're big enough.
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 star, Like the shockwave 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 bounce. That's actually the explosion.
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 below that, if you're like around thirty times the mass of the Sun, then you get a bounce that goes out with the supernova and the core becomes a black hole.
Oh really, only the core. The other stuff bounces away.
Yeah, you get the supernova, this huge shock. You know, it spews 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 get 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 at the center, 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 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 when the gravitational collapse happens, then it causes runaway fusion and the whole thing just blows in a huge explosion.
Huh. So there's all these like pockets, like if you're this big, then you'll go supernova, but if you're a little bit smaller you will. 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 are 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 it's a collapsing star that becomes a supernova, right, And sometimes it's at the bounds. Sometimes it's just it creates a runaway explosion.
M hm.
Yeah. For all these core collapse they start with really big stars that have been big enough to burn a lot of heavy stuff to go past the carbon limit and then to pass this gender say car limit and collapse gravitationally.
Right.
Oh, 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 it 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's 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 try to calculate two different things. One is like how close would a supernova have to be to be dangerous? And they figure that if one's 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, and the amount of X rays deposited on the planet would like sterilize half the population and or give them cancer instantly.
Oh my god, within minutes or within days right very quickly.
Yeah, I mean does it really matter if it takes days or minutes to get cancer?
You got cancer, But everything else would stay the same, like the 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 yeah, it wouldn't affect like the gravity of the Earth. We'd still be orbiting the Sun the same way. We'd 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 hundred light years. Now, again, we don't have a great understanding of when a star goes 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's they're sort of part of the life cycle of the galaxy. You know how we learn that forest fires aren't all bad because they help like clean out deadwood and provide space for new animals.
You know, well, they're good as long as you don't live your house is not nice soon.
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, you 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 heavier materials like we wouldn't be you and I wouldn't be here if if not for a supernova.
Mm hm.
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 shockwave 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 a cycle, man, it's the circle of life. Somebody q 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 philosophers.
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, supernervare 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 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 those was basically made in a supernova. Would you say that, Like all the metal and components in your phone and 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. I'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jhoorge that's one word, or email us at Feedback at Danielandhorge dot com. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.
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