Ep. 579: White and Black Dwarfs

Posted on Sep 29, 2020 in Astronomy, Forces, High Energy Physics, Particles, Physics, podcast, Stellar Evolution | 0 comments

I’ve got some bad news for you: stars die. At some point in the next few billion years or so, our Sun is going to start heating up, using up all the fuel in its core, and then eventually die, becoming a white dwarf. It will then slowly cool down to the background temperature of the universe, becoming a black dwarf. Let’s learn about this fascinating process!

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Show Notes:

Ep. 578: Life on Venus?!?

Rocket Lab’s plan to search for life on Venus in 2023 just got more exciting (Space.com)

Breakthrough Initiatives to Fund Study Into Search for Primitive Life in the Clouds of Venus (Breakthrough Initiatives)

Future Missions to Venus (University of Wisconsin-Madison)

Stellar Evolution (Swinburne University)

Proton-Proton Chain (Berkeley Lab) 

Core-collapse (Swinburne University)

Solar Wind (Swinburne University)  

Planetary Nebulae (Center for Astrophysics, Harvard and Smithsonian) 

ALMA Sees Complex Stellar Winds around Red Giant Stars (SciNews)  

Owl Nebula (Messier Objects)

What are brown dwarfs? (EarthSky.org)  

Ep. 290: Failed Stars

White Dwarf Stars (NASA)  

Electron Degeneracy Pressure (Swinburne University)  

Pauli Exclusion Principle (Byju’s) 

Neutron Stars (NASA)  

Carbon Stars (Universe Today) 

VIDEO: Globular Cluster Age: White Dwarfs in M4 (Hubblesite)

On the Spectrum of Zeta Ursae Majoris,” Pickering, American Journal of Science, 3rd Ser., vol. 39, pp. 46-47, 1890  

Why Are Stars Different Colors? (Universe Today)  

Chandrasekhar Limit (Swinburne University)  

Earth-sized diamond in space is coolest white dwarf star (EarthSky.org)  

PDF: “The Transfer of Radiation in Stellar Atmospheres”, S. Chandrasekhar (University of Central Florida)

Black Dwarf (University Today)  

Proton Decay (Boston University)  

Dead star spotted eating planetary leftovers (Nature) 

Planet discovered transiting a dead star (Nature)  

So, um, Maybe the Sun Will Eventually Swallow the Earth. Bummer. (Bad Astronomy, SyFy Wire)  

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Transcriptions provided by GMR Transcription Services

Fraser:                         Astronomy cast: Episode 579; White and Black Dwarf Stars. Welcome to Astronomy Cast for weekly fact-based journey through the cosmos, where we help you understand not only what we know; but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey Pamela, how you doing?

Dr. Gay:                      I’m doing well, how are you doing?

Fraser:                         Doing good. Boy, have I been talking a lot about life on Venus though, that’s, that’s my life. That is the new reality, is just talking about life. How’s the life, what else could be making the life. But the part that I love is the responses now that there are some cool missions in the works that people are thinking of.

Dr. Gay                       Yeah.

Fraser:                         To send. I’ve seen a couple of really great ideas. Now, we got people have something very specific to look at. So, hopefully we’ll be able to follow up in a couple of years with some cool missions, to go to Venus.

Dr. Gay                       I hope so. The thing that really frustrates me is, I know the timescale of going from thinking about a mission, to building and sending the mission.

Fraser:                         Yeah.

Dr. Gay:                      And – it’s like – I want them to go figure this out while I’m alive.

Fraser:                         But the good thing is that Venus only takes a couple of months to reach. So, it’s not like…

Dr. Gay:                      I know.

Fraser:                         … Saturn, or

Dr. Gay:                      I know.

Dr. Gay:                      Mercury.

Fraser:                         Yeah, Mercury is a tough one to get to. But hopefully we’ll get some answers. We’ll get some answers for you, everybody.

Dr. Gay:                      I hope so.

Fraser:                         Now, I got some bad news for you, though. Stars die.

Dr. Gay:                      They do.

Fraser:                         At some point, in the next few billion years, or so our sun is going to start heating up. Using up all of the fuel in its’ core, and then eventually die, becoming a white dwarf. It’ll then slowly cool down to the background temperature of the universe, becoming a black dwarf. Let’s learn about this fascinating process. What’s the timescale? First, why is the sun dying? I mean we’re all dying, you know? We’re all born and then we’re all dying, so why is the sun dying?

Dr. Gay:                      Right. Ultimately, it’s just going to run out of energy. So, the way that stars shine and support themselves is deep in their core, they’re undergoing nuclear reactions. Now, exactly where in the core depends on the stage of evolution. Initially when a star turns on, it’s burning hydrogen, it’s going through the proton-proton process, and all the light that is generated during this fusion, because when the particles come together, they release energy as they fuse into something new, and that energy pushes out against gravity, supporting the outer layers of the star.

Fraser:                         And eventually, it runs out of fuel in the core?

Dr. Gay:                      Yeah. So, it’s eventually going to run out of hydrogen in the core, the star’s going to go through different changes in luminosity, changes in color, changes in size. It’s gonna end up burning hydrogen in a shell, it’s gonna end up burning helium in the core. All sorts of different things are gonna change over the life of a star. And what all happens depends on the mass of the star. If a star is big enough, it’s actually going to eventually get to the point that it has a heart of iron. And it turns out, that when you try and fuse two iron atoms together, they say ‘sure, you can do it, but you have to give us the energy to do it.’

Fraser:                         Right. No free lunch anymore.

Dr. Gay:                      No free lunch anymore. And, since trying to fuse these heavier elements doesn’t release energy, the star doesn’t have anything to push back against the fight with gravity, and it collapses down in this moment that it’s no longer producing enough energy. And this is where things get interesting.

Fraser:                         Now that’s for the stars that are bigger than our sun, right? But for stars that are the mass of our sun, they don’t have that catastrophic end, they just have this quieter, cool down end?

Dr. Gay:                      This is where physics can get interesting. Because, it turns out that stars that are ten solar masses and less, undergo varying amounts of mass loss. And where not always sure how much – in fact we’re never sure how much mass a star is going to lose. And over it’s lifetime, that ten solar mass star may end up – once it’s done bloating off its outermost atmosphere – as something only one solar mass in size. It can lose 9/10 of its material.

Fraser:                         So, sorry – what’s the mechanism that’s actually causing that material to be lost?

Dr. Gay:                      So, you have two different things that happen. The first is regular everyday solar winds, like what we’re experiencing with our own sun. Where the sunlight as it pushes out, interactions with the outer magnetic field of the star. You have both things gradually getting carried off all the time and things getting ejected through coronal mass ejection, solar flares, and all of this is carrying particles. Only atoms, electrons, small bits of matter, but still actual matter is getting carried away from the star.

And the rate at which the star is able to lose mass through mass loss like this, through solar winds, is variable over its lifetime. And elder stars and the most massive young stars, are the ones that give off the absolute largest amount of mass.

Fraser:                         Right. And so, once a star is done blasting off all its’ mass, once its gone through this process of turning into a red giant and then – multiple times, sometimes right? They’ll blow it out and then shrink back down, and then blow it out – and then it’s done.

Dr. Gay:                      Well, and here by ‘done’ it’s more a matter of it’s like ‘I’m just gonna let my outer atmosphere drift away, just gonna exhale it.’

Fraser:                         Right.

Dr. Gay:                      And this is planetary nebula formation. And, here it’s just a matter of the light that the star is generating at this point, and the size of the star make gravity just not quite as strong as it needs to be with those outer layers of the star.

Fraser:                         I don’t know if you saw, a piece of research just came out – a couple of days ago now – that astronomers have been able to, essentially tie down the shape of every single planetary nebula based on just the planets, and any binary companions that are orbiting the star. The different shapes are now are; entirely caused…

Dr. Gay:                      Yeah, I would have phrased it differently.

Fraser:                         … are caused by, the variations are caused by the interactions with whatever is orbiting the star.

Dr. Gay:                      Yes. And they haven’t actually gone through and identified every planetary nebula in existence and matched it with their computer models. But what they figured out is the variations from having stars in various binary systems, stars in various solar system configurations, and stars pretty much on their own. By tweaking all of these different interactions, you’re able to create the nearly infinite diversity of shapes, including all of the nested shells and things that we see planetary nebulae.

Fraser:                         Yeah, yeah. It’s kinda cool though that planets can help make planetary nebulae.

Dr. Gay:                      Oh, yeah. And this is your standard reminder that the name planetary nebula has nothing to do with planets…

Fraser:                         Except now it does!

Dr. Gay:                      Well, fair. The name itself, however…

Fraser:                         Yeah.

Dr. Gay:                      … is based on the fact that so many of these nebulae look like gas giants. The Owl Nebula through a telescope looks like it’s another gas giant.

Fraser:                         Yeah. So then, the planetary nebula blows off and you are left with, a star but it’s not like the kind of star that we were familiar with for the entire time that we’ve lived here on the planet.

Dr. Gay:                      And this is where we have to go back to ‘is it a star, really?’ Because…

Fraser:                         So, what is it? What is left, what is the remnant?

Dr. Gay:                      It’s a core. It’s a dead core, it’s an ember. The basic definition that we have of a star – which is what allows us to say that brown dwarves are temporarily stars – is you have to have that nuclear fusion going on, that is generating energy. With a white dwarf, you have the core of a former star that is no longer generating energy, that is sitting there going ‘Hi. I would collapse except for electron degeneracy pressure.’ The ability of electrons to go to other electrons do not get to close with the Pauli Exclusion Principle.

Fraser:                         Right, this is our atom.

Dr. Gay:                      This is, yeah! So, essentially a white dwarf star says ‘Okay, electrons, align!’ And they line up according to the Pauli Exclusion Principle in all of the allowed states, forming as dense an array as they can, pushing back against gravity.

Fraser:                         Right. And, we have talked about if you have a more massive object, then gravity can overcome that and force the whole thing into a neutron star, but these – today we’re talking the stars that don’t quite make it.

Dr. Gay:                      Yes. And, so with these leftover cores, they start out with a temperature at the surface of 10 million degrees eradiating…

Fraser:                         Wow.

Dr. Gay:                      The radiation, their light in the ultraviolet, it’s the core of a star!

Fraser:                         Right, right, right! Well, let’s just stop for a second because you know when you think about a star like the sun, the surface temperature of the sun is; whatever, 5,700 Kelvin.

Dr. Gay:                      Yeah.

Fraser:                         And, so that’s hot. But that’s not millions of degrees hot.

Dr. Gay:                      Yeah.

Fraser:                         But when the sun has been running, this fusion core down in the middle of it and then it blasts off all those outer layers, and now – is it literally the core of the star is now just revealed to space?

Dr. Gay:                      Yes.

Fraser:                         And it is millions of degrees, hot?

Dr. Gay:                      And, and, so the inside of the star is consistently at this 10 million; but that surface, it’s gonna drop down to 150,000 Kelvin as it radiates. Now, here’s the thing, though, we have a pretty much solid object with a very small surface. This is your standard reminder that a sphere has a surface that is the minimum surface you can have for the amount of stuff inside of it. Which means that it’s not the most effective at radiating away heat.

Fraser:                         Right. So, sorry. So, because it’s got this nice spherical shape, because it’s holding in its atoms in the tightest possible configuration, like a bubble, right?

Dr. Gay:                      Yeah.

Fraser:                         Holds in the amount of air that’s inside of it. It has a really hard time getting that heat out into the universe. But if you took a knife and sliced open a little; took out a little piece of pie…

Dr. Gay:                      10 million degrees inside.

Fraser:                         A 10 million degree, yeah – what would it be? What would you be holding? If you could just pull it out of the white dwarf?

Dr. Gay:                      Something denser than anything that you can generally imagine. We don’t have material like this on Earth. This – I mean you might be able to create it in a lab, if you spent enough money – but, your average person is never going to create something this dense. So, that little snippet you pull out from beneath the surface? You’re looking at elephant in a teaspoon kind of situation.

Fraser:                         Yeah, 15 tons for a teaspoon.

Dr. Gay:                      Yeah, so elephant in a teaspoon scenario. And, you’re looking at something unbelievably hot, and you’re looking at something where the material is arranged so that as it cools, it crystallizes.

Fraser:                         Hmm.

Dr. Gay:                      And this is one of the – to me – most fascinating things about white dwarves. Is they start out as standard plasma that we’re used to thinking of our stars as being, but as they cool; they solidify into a crystal structure, and this affects how they cool. So, it was originally thought that we could just very, very easily use them as – if you look at a cluster of stars, and you see white dwarves at this minimum temperature that is diagnostic of the most massive stars to become white dwarves have already had a chance to cool to this point, therefore this system of stars is this age.

Fraser:                         Right.

Dr. Gay:                      And, we were finding discontinuities, we were finding weird things, we were finding ages that didn’t quite match, and as our chemistry and quantum mechanics got better it was realized that energy periodically was getting absorbed into the phase changes. And so, it was the phase changes of this crystalline matrix, that was changing how the star cools over time.

Fraser:                         Huh. So, I’m just sort of imaging if I – back to that analogy of I slice out a little piece of my white dwarf – I pull it out and it’s this 10-million-degree material.

Dr. Gay:                      Yeah.

Fraser:                         The mass of a, the weight of an elephant in my teaspoon, or on my little cake knife, I quench it…

Dr. Gay:                      … that is melted.

Fraser:                         Yeah, of course. Of course, yeah, no I’ve got my neutron star cake knife, which is even heavier. I quench it in water, and it will crystallize into what?

Dr. Gay:                      Well, this is the awesome part, is white dwarfs are generally either helium or carbon, and crystalized carbon is a diamond. So, these are objects that when you’re looking at a carbon white dwarf star from the more massive stars to become white dwarves, you’re ending up with a solar mass diamond.

Fraser:                         Right.

Dr. Gay:                      That, to be fair, if you tried to stand upon on it, to put your hand against it…

Fraser:                         Yeah.

Dr. Gay:                      …too pretend you were wearing it – it would crush you to its’ surface and destroy you.

Fraser:                         Sure. Right

Dr. Gay:                      Don’t try to wear one.

Fraser:                         And, so at the beginning, at the hot point, it is just this very hot…

Dr. Gay:                      Plasma.

Fraser:                         Plasma, but formed into a very tight ball?

Dr. Gay:                      The electrons are degenerate which means they’re aligned in specific ways…

Fraser:                         Right

Dr. Gay:                      So that their spins are correctly up and down …

Fraser:                         Yeah, they’re marching.

Dr. Gay:                      And their energy. Yeah

Fraser:                         Yeah. Yeah. They’re marching in perfect order.

Dr. Gay:                      Yes.

Fraser:                         But then as it cools down, it freezes almost. It crystalizes…

Dr. Gay:                      Yeah.

Fraser:                         Into this shape that it had arranged itself, just trying to fit into the smallest possible size. And that is a diamond?

Dr. Gay:                      Yes.

Fraser:                         Because it’s made out of carbon?

Dr. Gay:                      Yes.

Fraser:                         Whoa.

Dr. Gay:                      Now, the thing about this to remember is these are the remainders of a lot of different kinds of stars. So, not all white dwarves are identical. You can start off with that we think 10 is the order of the top but it could even meet a larger mass; originally formed stars that have undergone massive amounts of mass loss, and so they lived as hot, bright – not the hottest and brightest – but hot, bright stars hanging out, out there. They’re going to form these carbon white dwarfs.  Now at the same time, this little tiny red dwarf’s out there, someday far in the future after all the rest of the universe is given up the ghost. They’re gonna finally stop undergoing nuclear reactions. They’re undergoing convections.

Fraser:                         Mm-hmm

Dr. Gay:                      …the entire star is eventually going to get used up, it’s going to become pretty much pure helium, and when this occurs – when they can no longer burn anymore, for the lowest mass hydrogen burning stars, they’re just gonna kind of slow down, shrink down. Again, these stars are very different. They don’t undergo all the red giant stuff, they just sort of sit there and go ‘…and I’m done.’ And shrink down.

Fraser:                         So, then do you get a crystal of helium?

Dr. Gay:                      Yeah. And the helium’s just going ‘I’m a noble gas. I don’t behave this way.’

Fraser:                         Right.

Dr. Gay:                      So, there’s no crystallization of the helium.

Fraser:                         Right. Right, it’s not going to lock into a structure in the way that say a diamond; the way carbon would.

Dr. Gay:                      And this is where it gets so interesting, trying to understand the way these things cool over time and to figure out how to accurately use them as what we call Cosmic Chronographers. To measure the age of various star clusters we have to go ‘Okay, so the white dwarves are probably this mass distribution at this point…’

Fraser:                         Right.

Dr. Gay:                      ‘…in this clusters’ evolution, therefore when we’re looking at this band, all right the coolest ones here are from …’ and you have to take all of this into account, if you see an isolated white dwarf, you can’t get its’ mass because it’s isolated it’s not in a binary system.

Fraser:                         Right.

Dr. Gay:                      And, so you can’t figure out what its’ cooling history would be. All you can do is look at it and say ‘well that one’s 10,000 degrees.’

Fraser:                         Right.

Dr. Gay:                      And, I know that it’s old.

Fraser:                         Right, so you can’t say ‘Okay, I know that because it’s 10,000 degrees, then I know that it died 14…’

Dr. Gay:                      Billion years ago.

Fraser:                         Yeah, whatever, before the universe. Okay, so it died a billion years ago.

Dr. Gay:                      Fair.

Fraser:                         I can tell by just looking at the temperature. Astronomers used to think that, right? That you could …?

Dr. Gay:                      Yeah.

Fraser:                         You could measure the temperature of a white dwarf, and that would tell you when it died. But I know that, you look in say globular star clusters and we see – they count the number of white dwarves there to tell them how old the cluster, itself, is overall.

Dr. Gay:                      And this is where it gets so cool with clusters of stars. Because in a cluster you know, those ten solar mass stars had to have existed, they’re the ones that will have evolved first. So, they’re the ones that have been cooling the longest. So, when you have a not-isolated, because it’s in a cluster, versus being in a binary. Two different ways to be isolated. If you have a white dwarf in a cluster of stars, you can look at this stripe of all the different temperatures that white dwarves come in. And you know the ones that are still hot? Those are from smaller stars that took longer to …

Fraser:                         Right.

Dr. Gay:                      Exhale their atmosphere.

Fraser:                         Huh.

Dr. Gay:                      And you look at the coldest, and you go ‘Those! Those are from the most massive stars.’

Fraser:                         That did it very quickly?

Dr. Gay:                      And, so this is a trickstery way to get at the mass.

Fraser:                         Wow.

Dr. Gay:                      It’s just when you see one hanging out by itself, that you can’t do much with.

Fraser:                         Right, it’s only when you have them in a cluster that you can actually use them as a diagnostic tool like this.

Dr. Gay:                      Yes.

Fraser:                         So, then let’s sort of roll the clock forward. I mean, what is the coolest – how cool have white dwarves gotten this far into the universe?

Dr. Gay:                      We’re still seeing them in the tens of thousands of degrees for the most part. They do, occasionally get down to 4,000 Kelvin, 6,000 Kelvin, but for the most part we’re looking at objects that are roughly Earth sized, that are roughly; 0.6 to 0.8 solar masses. And they’re hot, hanging out in the centers of planetary nebulas being a source of light to illuminate those planetary nebulas that we’re looking at. But that’s going to change over time, and this is where white dwarves when they first discovered really kind of broke the brains of the researchers that were looking at them.

And, it was Pickering, at Harvard college observatory, that got people to take spectra of these dwarf companions of a myriad of different binary systems, and realize that something weird is going on; because they saw red dwarf, red dwarf, red dwarf, what is this? Because it was known that it had to be small, because it was super faint – small surface area – but then the color, was that of an A star something that should be massive.

Fraser:                         Right.

Dr. Gay:                      So, they realized there had to be something new. And these discoveries predated Chandra Saykar, figuring out what a white dwarf should, just from doing the math – which he did while sailing to from India to graduate school.

Fraser:                         Right, right.

Dr. Gay:                      So, he got a Nobel Prize for that.

Fraser:                         Yeah, what did you do on your vacation? He got a Nobel Prize.

Dr. Gay:                      Yeah, I can tell you what I did. I did not get a Nobel Prize for it. Other people did, but I did not.

Fraser:                         Oh, okay. Awe. The – I just looked it up – the coolest white dwarf that we know about, is about 3,000 Kelvin.

Dr. Gay:                      So, we’re finding them down at the thousands.

Fraser:                         Yeah, yeah.

Dr. Gay:                      But your average one is gonna tens of thousands of degrees.

Fraser:                         Right, yeah this one’s probably 11 billion years old.

Dr. Gay:                      Yeah. So, it’s had a chance to cool.

Fraser:                         Yeah. And, so astronomers were able to – I mean I love this idea, right – that they find something super weird, they find this star, that is as bright, that has the color of a, of the hottest most powerful stars out there, but clearly is teeny, teeny tiny. And then Chandrasekhar says “Hey, here’s a way a star could form that does that.”

Dr. Gay:                      And one of the things that Chandrasekhar did in beautifully clean math, and if you go through enough used book stores you can find Chandrasekhar’s Penguin House published book. And what he’d been looking at is the dichotomy between gravitational pressure pushing in and light pressure pushing out, and what happens at different phases in a star where you don’t have enough light pressure pushing out, and that’s where you start to get at these white dwarves and the famous Chandrasekhar Limit, where if you put too much mass on a white dwarf, the electrons go ‘I can’t man. I can’t.’

Fraser:                         Kaboom.

Dr. Gay:                      Yeah. And there’s electrons on the protons that they’re associated with come together, there’s tremendous release of energy, neutrinos, other stuff, and what’s left behind is a neutron degenerate gas. A neutron star.

Fraser:                         So, we’ve got sort of two sides to this, right? We’ve got the white dwarf at the beginning; but we’ve got the concept, the theoretical idea of the black dwarf as well.

Dr. Gay:                      Yes.

Fraser:                         So, what is that?

Dr. Gay:                      So, a black dwarf is basically an object that is cold, it is tiny, it is the black ember of our universe. It is something that you might only be able to see in the infrared, initially. But given the fullness of time, and luck avoiding black holes, our universe is going to be littered with these extraordinarily dense objects that will eventually cool down to the background temperature of our universe. And, this also is provided that protons don’t actually decay, which is a concern we have.

But given no proton decay, given the fullness of time, and not getting eaten up by a black hole, our universe is going to be littered by crystallized, no longer radiating temperature on their own, blobs of helium and carbon, and that’s kind of fantastical to imagine. Something like 95% of stars are thought to eventually to evolve into these white dwarfs…

Fraser:                         Right.

Dr. Gay:                      …that can become black dwarves.

Fraser:                         Right. And, so I’m looking at some numbers here; trillions of years, quadrillions of years, some people are talking 1025 years?

Dr. Gay:                      This is where I like to just say, in the fullness of time…

Fraser:                         In the long…

Dr. Gay:                      Given escape from other problems.

Fraser:                         Yeah, in the far, far, far future.

Dr. Gay:                      Yeah.

Fraser:                         And, so, I’m just sort of imagining – I’m trying to wrap my head around that future. You’ve got all the stars that have every lived that didn’t explode a super nova, and didn’t gather up more material…

Dr. Gay:                      Mm-hmm

Fraser:                         Cooled from red dwarfs to larger stars, even larger stars than our sun, turned into some flavor of a white dwarf, and then cooled down to become…

Dr. Gay:                      The background temperature – they’re giant marbles.

Fraser:                         They’re crystal.

Dr. Gay:                      That’s what they are.

Fraser:                         Yeah! They’re crystalline version of whatever they would become. Diamonds, a solid block of helium, other potentially elements, some thin atmosphere maybe surrounding them.

Dr. Gay:                      And, white dwarfs, because they come in so many different masses, they do have weird different behaviors. Some of the lowest mass white dwarves, will as they’re working on collapsing down under gravity, their outer atmosphere is like ‘wait! I’m still gonna try and do some more burning here. Wait, trying to do fusion.’ And they also have this neat way of you can see the imprint of things chemically that go splat on them, on their surface later.

Fraser:                         Right, right.

Dr. Gay:                      So, there’s been a white dwarf discovered that appears to have consumed a rocky world that lost its atmosphere during the stars’ red giant phase. When you see one of these, because it’s supposed to be just the pure core of a star, you don’t expect any heavy elements. Those would have sunk to the very center, and so we’re looking at the outer part of that core. There should not be stuff and things – by which I mean heavy metals –

Fraser:                         Yeah.

Dr. Gay:                      On the outside of a core of a star. And so, we can see, ‘well, that white dwarf ate its solar system.’ And that’s just kinda cool.

Fraser:                         Yeah, that’s amazing. That, that can be seen. You can see the imprint, the bug splatter, of the planets as they fell one by one onto the surface of the white dwarf. And in fact, we don’t have a lot of time but I know that a planet has recently been discovered orbiting a white dwarf.

Dr. Gay:                      Yes, and this gives us some hope for our own solar system. We understand that our particular future involves the sun bloating out, eating Mercury, Venus, probably not Earth, we think it will lose enough mass that we’re fine.

Fraser:                         Apparently Phil, just posted Bad Astronomy today that apparently the sun will eat the Earth. So that’s…

Dr. Gay:                      Okay. So

Fraser:                         So, that’s the science today, as of September 25, 2020; the sun will eat the Earth.

Dr. Gay:                      But as of yesterday, we were still good.

Fraser:                         Yeah. It was the other way, and before that it was back the other way.

Dr. Gay:                      We don’t fully know. Anyways, some number of inner worlds will be eaten. Jupiter and Saturn should be fine, and as the sun puffs off its outer atmosphere, this is going to create all sorts of weird physics. It’s going to potentially create a situation where the outer planets can migrate inwards. It’s going to potentially blow off – blast off – the outer layers of these planets.

We don’t fully understand what’s going to happen, but what we do know is we have now found one, exactly one white dwarf that has a gas giant snuggled up next to it in a 30-something hour orbit. And what’s kind of amazing about this system, is that it’s thought that the star is about four Earth diameters, and the planet is order of 10 Earth diameters.

Fraser:                         So, the planet’s bigger than the star?

Dr. Gay:                      So, the planet – yeah!

Fraser:                         Yeah, yeah.

Dr. Gay:                      It’s a cool system.

Fraser:                         And theoretically, I mean these things are still putting out heat, and it’s a very stable – there’s no …

Dr. Gay:                      Yes.

Fraser:                         There’s no solar flares anymore, there’s no coronal mass ejections, there’s no solar wind, there’s just light coming from your star for trillions, quadrillions of years. As you just snuggle up closer and closer to the star. And so, you can imagine some far, far future.

Dr. Gay:                      You can imagine Endor.

Fraser:                         Yeah, you can imagine some future, where you just take your planet, and you just huddle it up beside you’re your white dwarf and you got a nice dependable source of light and heat for effectively, ever. And without all that testy, solar flares and stuff.

Dr. Gay:                      And, this is where I think we’re more likely to find habitable moons in these kinds of situations because …

Fraser:                         Yeah

Dr. Gay:                      The gas giant would potentially have the ability to grab on to things as they flew by, it would potentially have the ability to have already had Ganymede like moons that have all the stuff necessary for life. There’s so many cool possibilities.

Fraser:                         Yeah. And next week we’re gonna talk about how they explode.

Dr. Gay:                      Yeah.

Fraser:                         So.

Dr. Gay:                      Things need to explode.

Fraser:                         Do you have some names for us?

Dr. Gay:                      I do. So, as always, we are here because of you. We do this because we love talking to you, finding out more, finding out what you’re curious about, but at the end of the day, Fraser and I are lazy and it takes other humans to maintain our website and edit our audio and post our video.

Fraser:                         Or busy!

Dr. Gay:                      Well that too, that too. So, your donations allow us to pay the people behind the scenes that keep us going. To pay Rich, to pay Ally, to pay our servers; because they like electrons. So, I would like this week to thank Paul Jarman, Jos Cunningham, Corey Davoll, Emily Patterson, Adam Anis Brown, Infinitesimal Ripple in Space Time, at Love Science, Gordon Dewis, Bill Hamilton Sinai, Joshua Pierson, Frank Tippin, Richard Rivera, Jack Much, Alexis, Thomas Sepstrup, Silan Wesbi, William Andrews, Jeff Collins, Marek Vydareny, Ben Floss, Steven Shewalter, Articfox, Nate Detwiler, Dave Lackey, Matt Rucker, Elad Avron, and Phillip Walker.

And Elad, I’m sorry, I know it’s Elad – I always say it wrong. I am sorry. Elad Avron.

Fraser:                         Thank you everybody. And we’ll see you all next week. Thanks Pamela.

Dr. Gay:                      Buh bye.

Female Speaker:         Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a creative comments’ attribution license. So, love it, share it, and remix it. But, please, credit it to our hosts; Fraser Cain, and Dr. Pamela Gay. You can get more information on today’s show topic on our website, Astronomy Cast.com. This episode was brought to you, thanks to our generous patrons on Patreon. If you want to help keep this show going, please consider joining our community at Patron.com/Astronomy Cast.

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