When stars die, do their planets die too? What can possibly survive after a supernova explosion? How will the death of the sun affect our solar system? Can zombie planets rise from the dead? I discuss these questions and more in today’s Ask a Spaceman!
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Check this out. The first ever exoplanet ever discovered. I'm talking about the first planet found around a star other than the sun. The first one ever in the whole history of human civilization. We have been wondering about the existence of planets around other stars since forever and the first one finally spotted was around a dead star.
And not just any dead star. I mean, there's a lot of different kinds of dead stars, but a pulsar. And if you're morbidly curious, the pulsar was named PSRB1257Plus12. I'm not in charge of naming things in astronomy as usual, as you already know. And this irks me greatly because I wish I was in charge of naming things because I would name the star to host the first ever discovered exoplanet anything but PSR b one two five seven plus one two.
PSR poser? Like, why did that become the act the short version of never mind. Never mind. That's just a rant for a different day. Anyway, this star, this pulsar is, 2,300 light years away.
And, yeah, it hosts a planet. And think about what just what like, a pulsar is an object that is more massive than the sun, like two or three times more massive than the sun. It is no bigger than your neighborhood. These things are a few miles across. These things spin at up to thousands of revolutions per minute.
That's faster than the blender in your kitchen. These things host some of the strongest magnetic fields, if not the strongest magnetic fields in the entire universe. They are made of exotic matter. They are made of neutrons squished together. They are supported by exotic quantum forces.
These they're just ridiculous. How did it end up with a planet? How did a pulsar get a planet? Especially, when you think about how pulsars form. They are dead stars.
That means there used to be a star and then that star had to die. In order to get pulsars, it is not a quiet, gentle, gentlemanly process. It is a violent, gross, disgusting, and awesome process. They come from supernovae. They come from giant stars literally blowing up and turning themselves inside out, releasing more light in a week than our sun will over its entire lifetime, releasing more light and then an entire galaxy will emit.
These things, they they can be seen from across the universe. We see supernova happen all the time. When supernova happen in our part of the galaxy, they're bright enough to be seen during the daytime. They cast shadows at night. It's been a few hundred years since we've had something that awesome.
I'm hoping in my lifetime I get to see one of those. Come on, Beetlejuice. We're all counting on you. Think of that violence. Think of those energies, and that's just the visible light that gets more energetic output than our entire sun.
That's, like, less than 1% of all the energy dumped out in a supernova explosion. These things are massive. So imagine that happening, and we'll get into the details later in the episode about what would that look like in our own solar system. Here's a hint. It's not pretty.
Imagine a planet surviving that. Planets should die with their parent star, especially when it comes to the most massive stars. But, no. We found an exoplanet. And maybe if we had just seen one exoplanet, we could've chalked it up to one of these weird flukes and coincidence of nature.
Like, okay. Maybe it randomly captured it. You know, just just what are the odds? The first exoplanet we found is just this weird freak of nature, but move on. Move along.
There's nothing nothing more to see here. No mystery to try to solve. No. PSRB one two five seven plus one two has three planets. All of them are within half the distance between the Earth and the sun.
One is tiny, just 2% the mass of the Earth, so that's basically nothing. That one you could chalk up to just being a weird random fluke of nature, but the others are around four times the mass of the Earth. In other words, they're big. Like, they're approaching Neptune mass. So, obviously, planets can survive the death of their parent star.
This is not a fluke. This is not a random of nature. This is something happening. These are real live planets around a real dead star. How does that happen?
Pulsars are the result of the biggest stars dying. And if we wanna answer this general question, which we we do because that's the title of the episode, We want to look at the death of stars in the survivability and habitability of planets around those stars, but there's different kinds of stars. There are little stars, there are medium stars, and there are big stars. So there's three kinds of stars, there are three kinds of cases. The tiny stars are the easiest.
The red dwarf stars, they have the most boring life and the most unspectacular death. They just keep going and going and going. They're fusing hydrogen. Man, the red dwarfs that are around right now, they're just they're babies. They're gonna keep burning hydrogen for trillions of years.
And keep in mind that the age of the universe right now is is thirteen point eight billion years, so they're they're they're barely out of the womb. They're still in diapers. They're still crying all the time. These they're they're babies. Cute little little stars.
They're just gonna keep going for, like, basically forever, and then they don't really do anything spectacular when they start to run out of hydrogen. They just slowly fade down. Just just the lights go out. They're like, alright. You know, I've been alive for about ten trillion years, and, I've seen a lot of stuff, and, bye.
And then that's it. They don't do anything interesting. They don't explode. They don't they don't turn themselves inside out. They're boring, and we we won't be around to see any death of any red dwarf star because, you know, it's gonna take a few hundred more billion years for it to happen.
So, of course, if one of our if a red dwarf has a planet or a planetary system, then, of course, the planets will survive. At least, they'll survive not due to any action or inaction on the part of the star. You know, they may get randomly caked out. Their orbits may be chaetically unstable. The star may pass close in all those hundreds of billions of years of life and may pass close to another star, and that will destabilize the system and the planets.
So there is that, but that's not the fault of the star. That's not the fault of the red dwarf. Like Proxima b, you know, the the planetary system we explored, sometime in the recent past. Yeah. Those planets are just gonna hang on for a really long time unless something some external force, but but the star itself isn't gonna do jack.
But, anyway, bigger stars, like medium stars, it's slightly more complicated, especially the big giant stars. Like, we're let's look at stars bigger than our sun. When stars start to die, when they approach the end of their lives, they start to get bigger. They, you know, they they go through these multiple complicated phases of, becoming red giants and then shrinking back down to somewhat normal size and then reinflating and then again and going back and forth. It's it's a very, very messy process.
As the stars as they enter one of these phases where they start to get bigger and they start to push their outer envelopes to greater radii, bigger distances, this kid this process can push any planets out. They do this because, yes, the interaction between a planet and a star, that gravitational interaction to a large degree can be modeled as just a single point mass interacting with a single point mass. This is all the basis of Newtonian physics, but in reality, it is a little bit more complicated than that. The shape of the objects, the densities of the objects, the matter within the objects, the size of the objects does play a role and gives us cool things like tides. And so, as the star is reshaping itself, the gravitational picture in the rest of the solar system starts to change and look a little bit funky.
Planets generally want to avoid that and so they start to scoot away. And the other thing that big stars start to do once they're near the end of their lives is they just start vomiting outwards. They just start go blah blah blah like these massive wind episodes that eject tons and tons and tons of material out into the solar system. And, yeah, it's just protons. It's just electrons.
It's just plasma, but there's also a lot of it, and it is literally capable of pushing planets. Like, these winds, these outflows, these strong winds, the radiation pressure, you know, just year after year after year of this nudging can push planets outside their orbits. And and sometimes to the point we suspect can completely detach planets from their orbits where they're just like, oh, you know what? I've had enough. I'll catch you later.
I'm I'm gonna take my chances in the interstellar depths rather than hang around this hot mess. And then the star goes boom. And and then the supernova happens, and that's bad news for everyone. Imagine this were to happen in our own solar system. Our own sun is not capable of going supernova.
It's simply not big enough. We'll we'll talk about what happens to sun like stars in a little bit. But if it were, it would be gross. Anything around the distance, the orbital radius of the Earth would simply be obliterated, and it works like this. On a typical day, the Earth absorbs about 10 to the 26 watts from the sun.
That's 10 to the power 26 watts from the sun. That's the total amount of sunlight hitting the surface of the Earth. If we were this far from a supernova, remember supernovas are relatively intense things that are capable of being seen from, you know, across the known universe, kind of a big deal. This position, this orbit, one astronomical unit with 93,000,000 miles, however you wanna count it, million miles, however you wanna count it, the sun would appear to be about 10,000,000 times brighter. This is 100 times more energy needed than is needed to vaporize iron.
So if you're like, how much energy would it take to completely vaporize iron? We've got a hundred times that at this distance. It would take less than a day for the Earth to melt. I'll say that again. If our sun were to go supernova, our entire planet Earth would last less than a day.
It would simply be obliterated. One episode a few episodes ago or maybe it was three years ago, you know, what is time? I talked about binding energy. This is the amount of energy needed to completely dissemble something, disassemble something. This is 10 times the Earth in one day would receive 10 times the amount of energy it needs to unbind itself.
Like, no matter how you count it, no matter how you calculate it, no matter what considerations you make, the Earth does not survive our sun going supernova. Good thing it's not gonna go supernova. But farther planets, they're big, and they're far away, so they could potentially survive. If the planets are far enough away, they might just get ejected from this violent outburst. Like, you can imagine this supernova shockwave, this outburst hitting something like Jupiter or Saturn.
Immediately, all of the hydrogen, all of the helium will get stripped away, but there's a bunch of rocks inside of Jupiter and inside of Saturn. Jupiter has something like at least five to 10 Earth masses worth of rock in its core. That's probably gonna survive, but the blast might be big enough to obliterate that. It might be big enough to eject that planetary core from the system altogether. The planet might hold on for dear life or it might just go away.
It's kind of complicated. It's kind of complicated because this is complicated physics. Right? Think about your thing you're we're talking about stars exploding. We're talking about massive forces, high energies.
We're talking about shock waves. We're talking about intense radiation. We're talking about turbulence. Of course, we're talking about magnetic fields. It's been a while since I've talked about magnetic fields, hasn't it?
I should I should bring that back. It it it the star itself is doing some very intense things, streams of particles, winds, all that. Planets themselves are complicated. They've got these gas envelopes. They've got their own gravity.
They've got their own magnetic field. They've got complicated interiors with different regions. It's hard to predict if a giant planet like, if we're to point to Saturn and ask, would Saturn survive our sun going supernova? The rings wouldn't for sure. They're just made of ice.
They'll just melt away. But would any core would any remnant survive? We honestly don't know. We do have this case of PSRB one two five seven plus one two, which actually we think might be a slightly special case because we don't suspect in general planets to survive a supernova blast. But what we think happened this is crazy to think about this story of all the exoplanets to find first.
This is the one we did. We think PSRB one two five seven plus one two was once two stars. It was once two sun like stars. Maybe these stars had planets. Maybe they didn't.
They probably did. It seems like most stars have planets. These stars lived and then these stars died. And when stars like our sun die, they turn into white dwarfs. And we think what was left behind in the system long ago was two white dwarf stars.
And then they almost certainly, the planets in that system died. It was just, you know, one star dying, you know, you can barely do it and then two stars that you're like, you're just checking out. You're just done over it. Either get ejected or obliterated. We don't think the planet survived.
But then these two white dwarfs, these two remnants of that stars, of those two stars coalesced and merged together. This released a tiny bit of energy when white dwarfs collide. There was a big boom. There was a big explosion. There was a lot of material thrown back into the outer regions of the system.
The material that ended up in the center settled down as a neutron star, but then there was a lot of material left over, a lot of dust, a lot of gas, a lot of iron, a lot of carbon, a lot of silicon just left over. And we suspect that triggered a new round of planetary formation, and that the planets that we see around PSRB one two five seven plus one two were actually formed when the neutron star formed. That these are not the surviving remnants of a system that has always existed and that these planets survived the fate that awaited their stars and made it through and rode out that storm and now are clinging to a meager existence around that neutron star. No. We think these aren't planets, surviving planets, these are zombie planets that have been resurrected from the dead.
We think the original planets in that solar system, if there were any, died, and then now these are reconstituted from their ashes. Yes. I'm getting very morbid and yes, it's a lot of fun. So that's small stars and that's big stars. The answer with small stars is the planets survive unless they get caked out.
Big stars, planets probably don't survive, but it's kind of complicated. Now let's talk about sun like stars, the middle ones. This is where it gets really interesting. In our own solar system, like we're gonna have to answer this question in our own solar system over the next few billion years. As our sun ages, it gets slightly brighter with time.
That's because the fusion reactions happening in the core are leaving behind helium, that's the byproduct of the fusion. That helium is contaminating the core making it harder for fusion to happen, but nothing can stop all that gravity of the sun from crushing inwards, and so the fusion rate goes up in order to compensate for the presence of that contaminating helium. And so the fusion rate goes up, and that means the heat goes up, and that means the luminosity, the brightness of the sun goes up. This has steadily been happening since our sun was born. The dinosaurs knew a slightly dimmer sun than we do know today.
Eventually, within a few hundred million years, it's hard to calculate exactly when. It depends on the trajectory of the sun and some very cool atmospheric models of what will happen to the Earth. But, basically, in a few hundred million years, the Earth is gonna get boiled alive because it will just be too hot. We will turn into another Venus in that few hundred million years. Mars is gonna get very interesting then, and then the red giant comes.
Near the end of the sun's life, it will inflate to be much larger than it is today, then it will undergo a period of contraction as it's as it switches to helium fusion, and then it will reinflate again. When our sun becomes a red giant, Mercury and Venus will just be consumed. Once the sun's atmosphere, once the sun surface hits that planet, they last only a few hours. They will just be obliterated. It's tough to predict the exact red giant size, you know, because it depends on lots of cool complicated physics about the interior of our sun, the exact fusion rates, the exact amount of heavy elements that modify this process, and also it's just if you think about a star turning into a red giant, you can imagine that's probably a somewhat complicated process.
The Earth may get consumed maybe right at the edge. We don't know. We don't know if the Earth will fall into the sun. If the Earth does fall into the sun, it's bye bye. If we're right on the edge, we I don't wanna say we'll survive.
I mean, life won't survive, and the Earth as we know it will won't survive. It'll be hot. Red giants are hot. They have a relatively cool surface temperature, hence the red color, but they're also giant, and so they're pumping out a lot of energy. It will be hot enough to vaporize rock.
All the silicon dioxide and carbon just hanging out is just gonna be gone. The Earth, will only leave behind its iron core. When the sun enters the red giant phase, the same will be true of Mars. All the dirt and rocks will just get burned off. All that will be left will be the core.
And same for all the asteroids too. Like, if there's a random asteroid just hanging out minding its own business, it's gonna be a lot smaller once our sun enters the red giant phase. As for the giant planets, well, for a while, the frozen moons, you know these cool frozen moons in the outer solar system like Europa and and Enceladus in the outer the the orbiting the gas giant planets. These are planets with rocky cores, subsurface liquid water oceans, and then icy layers surrounding that. Yeah.
That's gonna be very interesting place for a while because it will be warm enough out there to melt that ice. The habitable zone of our system, the region around a star where it's not too cold, not too hot, where water can exist, potentially exist in its liquid state is going to steadily move outwards at time. And then when we go into the red giant, it's gonna go way out there. It's gonna go out there to the orbit of Jupiter or Saturn. The icy shells will melt.
Their liquid water oceans will be exposed. It will be nice for a while. It's hard to say how long, like, maybe a couple hundred million years at best. It won't last long. Eventually, it will be too hot for all the ices in the outer solar system.
All the water will evaporate, all the ice will melt, some of the dirt will go away. Titan, whatever the heck is going on with Titan, it's actually gonna be too hot for Titan, so all those interesting methane seas are just gonna evaporate. All the moons of the outer worlds will become barren wastelands. The giant planet this is a pretty picture, isn't it? All the giant planets will lose a lot of their gaseous atmospheres at least at first.
The rings of Saturn will be gone. It's gonna be grotesque. But as for the giant planets themselves, Jupiter, Saturn, Uranus, Neptune. Yes. In these outbursts, when our sun is in its death throes and it's and it's throwing out a lot of material, surely a lot of they're gonna lose a bunch of their atmosphere.
But we see planets around red giants. We've observed exoplanets around red giant stars. It's a real thing. We've been doing this for a while. We've seen plans about around basically everything in the universe.
There's a very short list of objects that we have not seen a planet yet, and that's probably just because we haven't looked yet. We see planets around red giant stars. We see planets around stars that look like what our sun will look like when it's dying. And you know what? These planets tend to be bigger than planets around sun like stars.
In one sense, that's like not exactly crazy because if you're looking at a red giant star now, it likely came from a larger star than our sun and has entered that part of its life cycle sooner than our sun. And so in general, the star was bigger than the sun, which means it had more material to work with, which means any planets are probably gonna be larger. But interestingly, we see no connection between the size of the star and the size of the planet. Like when we look at even bigger red giant stars, we don't see correspondingly big planets around them. They're just big overall, but there's no rhyme or reason to the bigness once you get up in that category.
So it looks like actually the giant planets, the gas giant planets, the ice giant planets around a dying star get beefier. And there's two ways this can work. One is through stellar winds like all this material. Yes. There are gonna be intense blast of radiation that are again they're going to strip gases away from the gas giants, but then there's more material behind it that can just fall on in.
Like you get sandblasted, but then you get some moisturizer. I'm not exactly sure where I'm going with that analogy, but work with me here. The the giant planets lose some material, but then they gain some more because the star itself is constantly oozing out material. And then it can even reach a point where the star is so big in the outer layers of its atmosphere are so tenuous that some of that material can get siphoned down onto the planet. So, like, the the the planet, the gravity of the planet can act like just a big straw and it's like, oh, star, if you don't need this anymore, I think I are you gonna finish that?
I'd yep. You can actually get flows. This this is called Roche lobe overflow, by the way. That's a word and a half. Roche lobe overflow.
When a part of the star is flowing inward, and being sucked down onto a planet. So that we suspect that in this red giant phase, some of the outer planets, if they survive, if they make it, are are actually gonna get bigger. So yay for them. In our own solar system so if we paint the picture of our own solar system, like, five billion years from now, the inner planets are gone. Earth might have a core remaining.
Mars is just gonna be the core. Asteroids are gonna be burnt cinders. The outer planets are gonna probably gonna lose their moons, but in general they're gonna get bigger. The outermost part of the solar system from two to a hundred AU depending on the stage of where the star is in its life cycle could be habitable. That's how hot and intense these red giants are gonna get where something like Pluto is going to be primo real estate in the latter stages of the life of our sun.
And it won't last long. Like, it depends on, like I said, complicated physics. Short side, hundred million years. Long side, two billion years. Like, a while.
Like Pluto's gonna melt. You know all those nitrogen glaciers and water ice mountains, all that's gonna melt. Pluto's gonna be very pretty. Other objects in the Kuiper Belt are also gonna get very pretty, and depending on where you are in the Kuiper Belt, you might last longer or shorter. For sure, the giant planets are gonna get rearranged, maybe even ejected because of all the violence happening to our sun.
The sun will eventually become a white dwarf. It will surround itself, like, it will eject almost all of its atmosphere out into the surrounding system leaving behind the core, leaving behind the remnants of all that fusion which is a lump of carbon and oxygen. That material that surrounds the white dwarf is we call the planetary nebula when we see them all over the place. It's certainly possible for some planets to be swimming around in planetary nebula that we observe, but in general the planets are gonna be dead. In the very last phases, in the formation of this planetary nebula, the winds, the shocks, the outflows of material coming off of the sun will just be too much, and it will drive away almost all the remaining material in around these planets.
Like, for so for a while, they get bigger as the sun becomes a red giant, but then when the sun really goes and really starts spasming and really starts barfing all over the place and spewing its guts throughout the system, that will be too much, and the planets will get stripped of their material. And so you'll end up with a dead star surrounded by the dead remnants of what were once mighty planets. But this star still has a habitable zone. That's one of the craziest things. This star still has a habitable zone.
The white dwarf has a temperature of around a hundred thousand Kelvin, which is kinda hot, but it quickly cools. And by quickly, I mean, within a couple billion years to just, like, a few thousand Kelvin, you know, normal temperature kind of stuff. And after a billion years or so, there will be a habitable zone. There will be a habitable zone around that sun, around that white dwarf. You have to be very close, like within 1% of the current Earth sun distance.
And so any planet there is going to be very vulnerable to tidal disruptions, any changes in gravity. So it's a very unstable, very shaky orbit, but it is still a habitable zone where the temperature at that orbit is just right to support liquid water. So it's perfectly possible for one of these planetary cores to migrate their way inwards and end up within a habitable zone. Small challenge, You you kinda blasted away all the water. But if you fix that, maybe you can make a new Earth around that white dwarf and hang out for billions of years.
Yeah. I'd like to thank my top Patreon contributors. And you know what? I forgot to do a surprise Patreon thing this episode, didn't I? Maybe that was the surprise.
Go to patreon.com/pmsutter. Keep this show going. I really do appreciate it, and I'd like to thank my top Patreon contributors. Matthew k, Justin z, Justin z, Kevin o, Duncan m, Corey d, Barbara k, NooterDoo, Chris c, Robert m, Nate h, Ender f, Chris l, Cameronelle, Nalia, Aaron s, Kirk t, Tom b, Scott m, Billy t, and Rob h for all your contributions and and all the other space cadets. I really appreciate all your contributions.
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It's hilarious. Please leave a review for the book on Amazon that really helps. Please leave a review for this show on iTunes or wherever you get this show. I really do appreciate it. Go to Patreon if you wanna drop some cash my way, and keep those questions coming.
That's hashtag ask a spaceman or ask aspaceman@gmail.com. I'd like to thank Guy r via email for the question that led to today's episode, and I'll see you next time for more complete knowledge of time and space.