How can a supernova become even more powerful? Why do we have such a hard time studying them, let alone defining them? What happens when you let a giant star unleash its full potential? I discuss these questions and more in today’s Ask a Spaceman!
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EPISODE TRANSCRIPTION (AUTO-GENERATED)
Now that we all have that nonsense egghead string theory nerd business out of the way, You know my favorite thing to do after I do a long series like I did on string theory is to blow something up. I mean, it just just releases all that energy we spend talking about arcane mathematics. Now we could just now now we could just blow something up. And then my most favorite thing to blow up, of course, is stars. Let's blow up some stars.
And let's because it's special, let's try to find a way to blow up a star in the most magnificent way possible. I'm talking bigger than a nova, bigger than a kilonova, which is another episode if you if you wanna ask. Bigger than a supernova. I'm talking about a hypernova. Yes.
A hypernova. We sorted out the definitions of nova and supernova about a hundred years ago, but, of course, mother nature outwitted us because we thought we had taken the most extreme, the most powerful explosions in the known universe, called those supernova, and we're done with it, wiped our hands, and moved on. But, of course, mother nature outwitted us, and all it took was enough observations to reveal how much more powerful these explosions can be. How big is a hypernova? Up to 100 times more powerful than a supernova, which, if you'll recall, are already brighter than a hundred billion individual stars.
So a single hypernova can outshine a hundred galaxies. That's a lot of energy. Okay? It's 10 to the 46 joules. And if that number means nothing to you, which why should it, 10 to the 46 joules is enough power to run the entire world, all of our electricity needs for a billion, billion, billion years.
It's enough energy to unbind, which if you'll recall earlier episodes is our fancy science word for saying destroy. It's enough energy to unbind the sun 100,000 times over. That's pretty awesome. But they're rare. We only see of them a few per year, which is why it took us so long to actually find them.
And so whatever's making them can't be all that common. What the heck is going on with these hypernova? First, the nomenclature. I like to say hypernova. You like to say hypernova.
Everybody likes to say hypernova. Why? Because it's an awesome word, but the astronomers don't like to say hypernova. Why? And I don't know.
Just to be different, when hypernova were first identified in the nineteen eighties, and they realized this isn't just a weird fluke, this is actually a real thing. These explosions that are a hundred times more powerful than a supernova actually occur on the regular, they were called hypernova. Then for some reason known only to astronomers, they started giving them a new name. They started calling them superlumina supernova or SLSN. And so what you and me think of as a ridiculously powerful supernova isn't called a hypernova, but it's called a superluminous supernova.
Fine. But because jargon is jargon and astronomers never miss an opportunity to be confusing, the term hypernova is still in use, but it refers specifically to supernovas or superluminous supernovas with large kinetic energies that were not necessarily bright or powerful, just fast. In other words, they were referred to big kablooies. I'm well, sometimes. You see, sometimes SLSN is used interchangeably with hypernova, and sometimes it's different.
And then there are the gamma ray bursts, which will mostly be a different show. Please ask. It's a fun shout topic. But the short version, a gamma ray burst is a burst of gamma rays in the sky of unknown origins that just happens like, here you go. Gamma rays.
Okay. We call them gamma ray bursts. There could be all sorts of mechanisms, and some of them might or might not be related to hypernova or SLSN. And sometimes these ridiculously powerful explosions are just listed as obscure subtypes of the regular supernova. So it's confusing.
The jargon is confusing. The nomenclature is confusing. And if you read an article about it, you're likely to be even more confused. But in this case of jargon nonsense, I'm willing to give the astronomers a pass because as we're about to see, we have no idea what's going on. You can call them super luminous supernova.
You can call them obscure subtypes of regular supernova. I'm going to call them hypernova because I believe in awesomeness. Now that we've gotten that out of the way, how do you make a hypernova? Well, let's ask ourselves, how do you make a supernova? We suspect it has something alike how to make a supernova, but more so.
Stars go kablooey in two different ways. They can do it alone or they can do it with a friend. If they're with a friend, there are these things called nova, and that's when you have a white dwarf star, this carbon and oxygen remnant from a star like our sun, orbiting another star or vice versa. And this other star goes into its red giant phase, it inflates, it gets really big, and its atmosphere spills down onto the surface of the white dwarf. And if that layer, that little that thick atmospheric layer on top of the white dwarf, it's made of all hydrogen.
This atmosphere, if it reaches a certain critical density, it goes kablooey, and we get a nova, but the white dwarf still hangs on. But sometimes, so much material can compress too much without going nova, without having that pressure release, that release valve. And the white dwarf just sits there getting more and more and more stressed out, more and more under pressure until finally it just snaps, and the whole thing goes nuts. And it's a big kablooey. And, yes, my notes say to use the word kablooey a lot in this episode, so that's exactly what I'm gonna do.
That's what happens to stars when they go kablooey with a friend. Now they can also go kablooey alone, and this is something we call core collapse supernova. By the way, the whole white dwarf thing, when that goes all the way supernova, that's a type one a supernova. The core collapse or type two supernova is when iron builds up in the core of a massive star. The star can't pull any energy out of the fusion of iron, and so there's nothing to halt.
Catastrophic gravitational collapse, the whole thing shrinks inward. The iron core compresses, turns into a big giant ball of neutrons. The neutrons say, no more. I'm done. You can't press me anymore, and all that atmosphere just bounces off of that core and kablooey.
That's how stars go kablooey by themselves, a core collapse or type two supernova. So how do we make a hypernova? Well, we don't know, but maybe they could do it alone or with a friend. Either way, we need a lot of mass. Why?
Because these are, in case you weren't paying attention, big giant explosions. These are the big giant kablooies. These are a hundred kablooies. More mass in a star equals more gravity, which means more energy to play around with, which is what we think we need to power these kinds of explosions. We think that the hypernovas only go off with stars greater than 40 times the mass of the sun, which explains why they're so rare because stars bigger than 40 solar masses are rare in the universe.
So there you go. Puzzle solved, maybe. When you have one of these giant stars, a star bigger than 40 times the mass of the sun, when they are about to die, funny things can happen. The first funny thing that can happen, are you ready for this, is called a collapsear. Collapsar.
Say it with me on the count of three, everybody. One, two, three. Collapsar. Collapsar. Collapsar.
A hype who's who makes up these sentences? A hypernova can be caused by a collapsear. We're just making things up now. Okay. Here's the scenario.
If you have a big giant star, a really big giant star bigger than 40 times the mass of the sun. Remember, to to trigger a supernova, you need somewhere around eight times the mass of the sun. So we're talking five times bigger than that to give us a potential hypernova. And in that story of the core collapse where there is that ball of neutrons that formed in the core, this ball of neutrons is about the size of a planet, the entire rest of the star crushes inward onto that that little ball of neutrons, bounces off and triggers a supernova explosion. Sometimes that ball of neutron survives, and we get to see it in the normal everyday universe as a neutron star, the leftover core of a massive star.
But sometimes, all that collapsing in rushing atmosphere material, especially if there's a lot of it, especially if there's 40 solar masses worth, can overwhelm the stopping power of that proto neutron star, of that little ball of neutrons. It can actually squeeze that, and we think that if you squeeze a ball of neutrons hard enough, you make a black hole. You form a singularity, a point of infinite density. It's surrounded by an event horizon, all the black hole goodness that we've explored in so many of our episodes. Okay.
What's the situation when this happens, when you formed a black hole? The neutron ball has been converted into a black hole. So you have a region of infinite density at the center of 40 solar masses of material that are going one place and one place only, and that is in. You have material rushing into the black hole. It's collapsing.
It's crushing in. What happens when you have a ball of material squeezing down into a tight little volume? The temperatures go up. The pressures go up. It goes nuts.
You also form an accretion disk. You form a thin disk of material around that black hole, and it flows and swirls into the black hole. But that accretion disk can carry super strong electric fields, super strong magnetic fields. I mean, these are electric charges rubbing up against each other, flowing at nearly the speed of light. It's nuts in there.
It's it's almost impossible to describe what an accretion disk is like. I've tried to do it before, and I'm not gonna try it again because it's just just accretion disks are just something else. Just the forces on display and the variety of forces on display defy human description. Yeah. You can put numbers on it, which is how we do physics and everything, but you can't really talk about it.
It's nasty. That's my point. Forms an accretion disk. These super strong electric and magnetic fields can funnel some material from the disc away from the black hole before it crosses the event horizon, winding the material around the edge of the black hole, round that event horizon, you know, skirting, flirting with death, and then launching them in long jets. These jets race away from the accretion disk in that newly born black hole at 99.99 of the speed of light.
These jets of superheated material blast into any other remnants of that star that just happened to be hanging out and burst through it. And if those jets are pointed in our direction, we see a hypernova. We see all this energy, this gravitational energy of the star collapsing and dying focused on us like a lighthouse beam. We see a hypernova. In order to make this scenario work, you have a few requirements.
Your star has to be massive, you know, so you have a lot of energy to play with. We've already got that covered. You need a lot of rotation so that you can power up the accretion disk in the jet, and you can't have a lot of heavy elements. You need only light elements that can be easily blasted away so this jet can break out. Once the jet breaks out, it also starts spewing gamma rays because why not?
And it might be one possible source of gamma ray bursts. Hypernova and gamma ray bursts may be the same thing. This is a nice story. Sounds cool, but it doesn't explain all observations. What are the observations?
Well, when we watch supernova or hypernova, we have two things that we pay attention to. One is called the light curve, which is the brightness of the supernova over time. So, boom, there's a supernova. We see a big spike in light, and then it might get brighter and brighter and brighter as the thing goes haywire in total nuclear meltdown mode and then slowly decays and gets dimmer and dimmer and fades into the background. We call those light curves.
In different kinds of physics, different kinds of scenarios will give us different kinds of light curves. They might last longer, and they might be peakier. They might have little bumps and wiggles in them. The second thing we pay attention to is called the spectrum. The spectrum is the fingerprint of all the elements that are inside that explosion.
Each individual element gives off light of a very specific frequency or set of frequencies or wavelengths, little fingerprint of each individual element. And so we can look at the spectrum, we can collect all the light, and we can tell what the thing is made of. This is how, by the way, based on light curves and spectra, this is how we classified supernova in the early nineteen hundreds into the type ones and the type twos and the one a's and the two c's and all that. This was before we understood the mechanisms for making supernova. We just classify them, which is a classic astronomer thing to do, which is classify things before you understand them.
Fine. That's what they do. And so this story of a collapsar creating a hypernova is able to explain, able to match some observations, some of the light curves and some of the spectrum, but not all. So we think like this supernova, there might be more than one way to make a hypernova go off. And here's a funny thing that can happen to giant stars number two, something we call pair instability.
You know that the whole nuclear energy thing, right, that's happening inside the core of every single star in the universe. You have nuclear fusion. You're smashing elements together, making new elements, and getting a little bit of energy left over. Voila. Nuclear power.
That energy comes in the form of radiation, of of high energy light, of photons. But what if that radiation is just, like, too much? Like, that radiation, it it's does an important job inside the star. It powers the star. But what if it's a little bit too much?
What if the photons coming out are a little bit more energetic than the star can really handle? Well, did you know that you can change one kind of particle into another? No? Well, you can change one kind of particle into another. If you line everything up just right, presto, chango, magic, abracadabra, alakazam, or Rico Fermi, poof, you can change one kind of particle into another.
For example, you can take an electron and a positron, which is its antimatter equivalent, same mass, same spin, but opposite charge, and you can push them together. They go away and they turn into one photon. They turn into a bit of light. They turn into a gamma ray. What happened to the electron and positron?
They they disappeared. They disappeared. They became something new. They became a particle of light, a photon. So if it can happen in one direction, if we can smash electrons and prot positrons together to turn them into photons, can we go in the opposite direction?
Can we take a bit of light and turn it into an electron and positron pair? Can we run that reaction in reverse? Sure. I mean, why not? What's stopping us?
You need enough energy. The energy of the photon must equal the masses of the electron and positron, but it can happen. So if we're looking inside of this giant star and fusion is off the charts and the temperatures are super high and the pressures are ridiculous, and these fusion reactions of fusing hydrogen or helium or silicon or magnesium or whatever kind. What happens when fusion in a giant star becomes so furious? Well, Patreon happens.
Go to patreon.com. Okay. So Well, Patreon happens. Go to patreon.com/pmsudder to keep this show and all my outreach and education activities going. It is your contribution.
Seriously, I can't thank you enough. You are the most generous audience I've ever had. You're my only audience, and that's okay too. You still win the prize for most generosity in my audiences. I really appreciate it.
Patreon.com/pmsutter. Also, you do know by now, you should know that I do have another book coming out, How to Die in Space, a Journey Through Dangerous Astrophysical Phenomena. It's coming out June 2 in bookstores and Amazon nationwide. I do have a little promotion going on at Patreon. If you sign up, you might get a free autograph copy shipped to you.
I mean, it's not technically free because you have to contribute to Patreon, but it it's in some vague sense, it's free. Okay? Patreon.com/pmsudder. What happens in a giant star when fusion is too furious and that light that is being produced is just too high energy? What happens when the photons that are being spit out from the fusion process are so energetic that they can just spontaneously split into pairs of positrons and electrons?
Because there's nothing stopping them from doing it. Well, the core of the star is usually propped up by pressure from radiation itself. Imagine a weightlifter holding up a giant dumbbell. That dumbbell is gravity. That's the weight of the star crushing in on the core.
In the muscles, in the weight lift are all the forces from radiation. This is actual light, actual photons smacking into things, keeping them from collapsing. It's that is that struggle of the weightlifter of the of the have the dumbbells, like, nice and high or barbells, nice and high. Pressure from light itself is what is keeping the core of the star propped up when it's fusing like this. This kind of pair production, which is what we call when a photon turns into particles, happens all the time.
As soon as you get high enough energy light, as soon as you start making gamma rays of the required energy, this thing happens. But, usually, those particles that get produced, the positrons and electrons, just find each other again and turn back into photons quickly enough so that nothing is amiss. Like, the weight lifter, like, losing their balance, but then getting it right back, and it's no biggie. But in one of these massive stars, there can be a sudden surge of energy, a sudden surge of fusion with a lot of photons being pumped out in a very short amount of time and these photons turning into pairs of positrons and electrons very, very quickly. And then balance changes, pressure changes, temperature changes in the core prevent these pairs from finding each other again?
Well, it's like that weight lifter losing the balance for just a split second too long, too long to to catch themselves. And what do you get? You get kablooey in a snap of a finger. Like, imagine this, this core of a star which weighs more than the Earth, more than several Earths, this fusion factory that is supported and self sustaining from the pressure of radiation itself, in a blink of an eye, in a snap of a finger, you have almost all the photons just turning into particles and then the particles washing away. There's nothing left to hold up the star.
The core disappears. It's not just the weightlifter losing balance. It's going in and kneecapping the weightlifter. It's hamstringing them. The star collapses instantly, releasing way more energy than a typical supernova, and this is how we get a potential hypernova.
These two cases of a collapse are in a pair instability hypernova, which is what we call when we have this pair production process, we call it the pair instability hypernova. This is when stars are alone and can explain some of the observations, but it can't still explain them all. So for the last bit, let's remember what happens when stars die with a friend. Remember this nova story with, you know, a white dwarf, it's got a companion, the companion spills material onto the nova, it's too much for the nova to take, and then finally they crack? Let's take that and crank it up a notch.
Let's turn the white dwarf into a neutron star so it's a lot heavier, a lot more compact, a lot more material in a smaller volume. And let's turn the red giant companion into, I don't know, its own supernova. So instead of a red giant surrounding a white dwarf, we're gonna have a supernova go off to a neutron star. And this is the point in the story where I'm convinced that all physicists, especially astrophysicists, are just 12 year olds at heart. Because if you ask a 12 year old, like, hey hey hey, kid.
Can you describe the most awesome thing in the universe? And they say, well, what if, what if a supernova went off next to a neutron star? And he's like, got it. Physics. Done.
Write it up. Put it in on the astrophysical journal. We think it can happen. Of course, it's rare, but hypernovae are rare. We're trying to explain a rare thing.
This isn't a common thing. Sometimes a supernova can go off next to a neutron star, and that supernova will plop so much material onto the neutron star that it collapses into a black hole. This collapse releases a lot of energy. There's a lot of accretion. It looks similar to a collapsar, except it's happening on the outside and not on the inside.
And at the end of the day, big kablooey. Is this the end of the story? Is this the three ways we can get hypernova going or super luminous supernova going in our universe? Probably not. We're still detecting hypernova.
We get a few a year. Still trying to classify them, and it's hard because each one seems a little bit more different than the last. And so they don't slot nicely into categories or buckets that we can just plug into physical models and try to understand what's going on. We have some ideas of how the biggest stars die. It's complicated physics.
The observations are rare. And like I said, we kinda have no idea what's going on. And so we're we're just gonna let Hypernova or SLSN be. And the moral of the story, though, if you're gonna go, you might as well go Hypernova because it's awesome. Also, Kablooey.
I'd like to thank Ter b on email at Genghis Gala Galahed two on Twitter, at Rick Winterfell on Twitter, Max Oria on YouTube, Christy on email, Campbell d on email, and at postman pat on Twitter for asking the questions that led to today's episode. And, of course, patreon.com/pmsutter, Matthew k, Justin z, Justin g, Kevin o, Duncan m, Corey d, Barbara k, NooterDude, Chris c, Robert m, Nate h, Andrew f, Chris l, John, Cameron l, Nalia, Aaron s, and Kirk t. Those are the top contributors of this month. There are many more, Many, many more with them, and you can be one too. Patreon.com/pmsudder.
I've got a book out. It's coming out. It's it's happening. That's right. One book wasn't enough.
How to Die in Space, a Journey Through a Dangerous Astrophysical Phenomena. Go to my website, pmSutter.com/book for a link, and, let's let's have a lot of fun. It's it's such a fun book. It's such a fun book. At least it was to write.
I don't know what it's like to read. Thank you again. Keep sending questions to hashtag ask a spaceman over on social media. You can also email askaspaceman@gmail.com. We've got the website, askaspaceman.com.
And I'll see you next time for more complete knowledge of time and space. Kablooey.