Daniel and Jorge Explain the UniverseWhat counts as a planet and is it possible for it to outweigh or outsize its parent star?
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Hey, Daniel, are your kids taller than you?
You know that day is not too far off. I've only got a few inches on my thirteen year old.
Oh man, that's crazy. How about your parents? Are you taller than your parents?
I'm like one quarter inch taller than my dad.
I like how you've measured that precisely. It's like an important quarter end to be taller than your dad.
He's an engineer, so we pulled out the high precision measurement devices when that happened.
I wonder if your dad was happy that he lost that measurement. But you know, it kind of makes me wonder, do you think stars feel the same way.
New stars have children.
Yeah, I mean like they have planets, right, Like, do you think they would feel proud off their planet was bigger than them? Or would they be jealous?
I don't know. I just hope that one day my own kids escape my orbit and start their own solar systems.
That's confusing, though, who would be the sun? You or your son? I am horehand made cartoonists and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle physicist, and I hope my kids never move out of the house.
And do they wish that too? Even after this whole or deal we've been through, you still want them in the house.
You know. It's pretty typical. When they were five or six and they learned that kids grow up and move out, they were like, what, No, we want to live at home forever. But now that they are teens and tweens, they are counting the days until they get to move out of the house.
Wow. But welcome to our podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we take you on a tour of everything that's amazing and crazy. The big things in the universe, the tiny things in the universe, the things that are so huge they blow your mind, and the tiny particles that are hard to wrap our minds around, and we wrap your mind around all of it.
Yeah, a lot of wrapping in this episode. You like to talk about all the amazing things out there that is wrapping us basically. I mean, we're surrounded by mystery and wonderful and incredible things happening in the universe.
And we spend a lot of time as humans looking out there into the universe and trying to understand the way things work. And one deep question we have that we're asking all the time is whether what we see is typical, whether it's usual, or whether there are rule breaking examples out there, whether there are other ways the universe could be arranged.
Yeah, because the universe is full of surprises. And so one thing that we've noticed, or that probably as kids we know it is about our solar system, about planets and moons, is that there's sort of a like a size hierarchy, right, Like you know, suns and stars are bigger than planets, and planets are bigger than moons, and moons are generally bigger than like asteroids, right, and rocks.
Yeah exactly, and it goes all the way down to space dust that we talked about on a recent episode. It's fascinating how our solar system isn't actually filled with just these like different categories of objects, but this whole spectrum of objects from the tin, these little particles out there, all the way up to the Sun. But there does seem to be sort of an order there, stars and planets and moons and then all these other little rocks, and so it's fun to wonder about whether that order could be inverted.
Hmmm.
It'd be kind of weird to think that all kids are shorter than their parents, because how would it end.
It would end with particle children, right.
Particles sized children, yeah, quark size.
Yeah exactly. It actually seems to be going the other way. A lot of people have kids that are taller than them, which means, you know, if you extrapolate that eventually children will be the size of stars.
Oh wow, well my kids are already stars. Daniel in my twinkling eyes walked right into that. But I guess the big question about the universe and our solar system is does it have to be that way? Do stars always have to be bigger than planets, and do planets always have to be bigger than their moods?
And one thing that inspired this question in my mind at least, was reading about a recent discovery of a really really strange planetary system. There's a planet out there four thousand light years from Earth that was recently discovered and confirmed by Hubble. And this planet is huge. It's three thousand times the size of the Earth. It's ten times the size of Jupiter. What this thing is a monster?
Wow? That is huge. I mean, Jupiter is like the biggest kid in our block. And now you're saying there's a planet that's ten times bigger.
Yeah, and it's got a moon that's ten times the size of Neptune. So like, this moon in this other solar system is bigger than most of our planets.
Wow, bigger than us?
Then much bigger than Earth? Yes, absolutely, so we are overshadowed by this moon. And that got me thinking about the question, like, well, is it possible to have a planet so big that could even be bigger than its own star?
Yeah? So today on the program movie asking the question can planets be bigger than stars? Well, hearing about these huge planets kind of makes me a little house jealous.
You know.
It's like when you see somebody with a bigger house, you're like, I wish I had a pool.
Is that what you think? I think? Man, cleaning that pool must be a pain in the butt.
Well, it would take away time from your couch sitting dinner.
That's true, yeah, exactly, unless you have lots of couches and lots of different rooms. But then you know that feels like a chore, Like, oh man, I have to sit on that couch and nobody's on mis couch in a while.
So did you just get a rolling couch? Then you can just scooch over to your pool lounge next to the pool while you clean it. There's always an engineering solution, Danny.
No, I'm a big believer in smaller houses actually, so I like our cozy little planet. I had some friends actually who were on track to getting divorced, and the reason was that their house was too big for real, for real, because they were always shouting each other from across the house, and they did end up spending time together, and they moved into a smaller house or they had to share the space and get along, and they actually totally improved their marriage, So there's an equals of one study.
Well, again, I think some engineering solutions might have helped. You know, there's walking talkies, intercoms that could have saved their marriage as well and kept their big house.
That's too high tech and this is much cheaper anyway. Bigger is not always better, you know. I like our cozy little planet.
Yeah, we don't have to shout at each other to talk. We have cell phones, Daniel, and podcasts.
Yeah.
Well, but it's a big question here about bigness and whether planets can be bigger than stars. I have I'm having a hard time wrapping my head around that question. I mean, how could a planet be bigger than it's star? Or what does it mean to be bigger like Danser size or what.
Yeah, lots of fun stuff we will dig into in this very episode of our podcast.
All right, Well, as usual, Daniel went out there into the wilds of the Internet to ask people if they thought that planets could be bigger than stars.
And so, if you are a denizen of the wilds of the Internet and you are waiting for somebody to ask you tough physics questions for which you have no time to prepare an answer. Please write to us to questions at Daniel and Jorge dot com and we will send you some.
Yeah, so think about it for a second. Do you think planets can be bigger than stars? Here's what people have to say.
Well, I would.
Guess it could be bigger, though I would also guess that it couldn't be more massive or more that a star. I'm thinking about a door star they discovered that has a planet. Some planets can be bigger than a dwarf star. So yeah, I think.
The size of stars changes over its lifetime, and after it's gotten through its red giant phase. There's a few things that could happen afterwards, but I think it can ultimately turn out to be a much smaller size than it was for the majority of its life, and some large gas giant far enough away I think has a chance of being larger than its star at that point in time.
My guess is that if a planet was bigger than its star in the sense that its actual mass was larger than that of its star, the planet's gravity would be bigger than that of the star, and it wouldn't really rotate around the star, but would probably form a kind of binary system.
I think that a planet could be bigger than its sun, but it would have to be secluded so that wouldn't pick up other masks. But I would also wonder if there could be sustainable life on this planet. And also would there be no nighttime on this planet? If the Sun is in place of the moon, but the Sun is also spinning around the Earth, would it be eternal daytime?
All right? Pretty intelligent answers here. A lot of like people digging into the masses of things, different kinds of stars that people could orbit or that planets could orbit around. A lot of interesting answers here.
Yeah, a lot of fun speculation. Thank you especially to Ryan, our nine year old listener, for sharing his speculation about what it would be like to live on such a planet. I love the breadth of ages we have in our listening group.
Yeah, so I guess let's jump into it, Daniel, and let's start with I guess with the basic question, which is like how big could planets get? Like is there a size limit to planet? Like does at some point collapse into a star?
Yeah? This one is not that satisfying because it turns out that the definition of a planet the thing that distinguishes something from being a planet, and a star is really closely connected to the size, so it's a bit arbitrary. And what distinguishes a star from a planet is whether or not there is fusion happening inside. Like you've got a big blob of stuff, but it's just sort of sitting there and not fusing. You call that a planet. If it's got enough stuff so that collapses and causes fusion to happen inside of it, then you call it a star. And the thing that controls whether that happens is basically the mass of stuff you have.
Right, like the gravity, the thing that's compressing all of that mass. It might trigger fusion or not.
It's not dependent on the size of it, right the physical volume. It only depends on the mass. And you do these calculations, and you can talk about things in terms of like the mass of Jupiter. So Jupiter, for example, doesn't have enough stuff to have enough gravity to collapse and cause fusion to happen at its core. You need like a about ten or thirteen times the mass of Jupiter to have a special kind of star called a brown dwarf, which is a special kind of fusion and so anything up to about ten times the mass of Jupiter is definitely a planet because it can't have fusion inside of it.
Right, But it doesn't. It also depends on what it's made out of. Like you know, Jupiter is made mostly out of hydrogen, right, which wouldn't sort of fuse easily. But if you have something, you know, like a giant planet made out of iron, you would need a whole lot more to get anything going if you can't.
All.
Yeah, it does definitely depend on the material. But most of the stuff in the universe is hydrogen, right, So if you're going to get a blob of stuff and coalesce it into an object, it's mostly going to be hydrogen. But you also are sensitive to the kinds of hydrogen you get, Like you can get a brown dwarf only under certain conditions. We have the right ratios of different isotopes of hydrogen to start a particular kind of fusion. To start the kind of fusion we have going on in our sun, for example, you need basically pure hydrogen of the simplest isotope, and then you'd even need more of it. So how much stuff you need to start fusion definitely depends on the amount of stuff you have, And you're right. If you just start with a blob of iron, the massive hydrogen, that wouldn't actually fuse.
Right, Yeah, because it can't. You could have like a giant planet made out of iron. That it could be you know, the whole size of the galaxy. Is that? Is that crazy? Or would that just turn into like a neutron star at some point?
Wow, the size of the galaxy. Oh my gosh, you took like all of the iron in the galaxy and blobbed it up together into a big planet.
Would that start to fuse or do other crazy stuff?
Yeah? I don't know. I don't know anybody's done that calculation. That's really fun. It definitely wouldn't fuse, right because, as you say fusion above, iron actually absorbs energy and so it would cool the object and so it wouldn't create fusion. If you get enough heavy metal in there, then gravity eventually wins. It'll just compress it further and further until it collapses into a neutron star, and if it has even more mass, it'll become a black hole. So a galaxy sized blob of iron would pretty likely turn into a big black hole. But in terms of the stuff that we actually see out there in the galaxy, the materials that are available, most of the stuff out there in the galaxy is still hydrogen. You know, We've been slowly cooking hydrogen into heavier elements and the inside of stars, but it's still a very tiny fraction of the hydrogen in the galaxy that's been turned into heavier metals.
There's kind of an upper limit than on the mass a planet could have, at least in the universe that we see, not in Horhez imaginary iron filled universe.
That's right up to about you know, ten or fifteen times the mass of Jupiter. You can still call it a planet. You can arrange for other ways to get more massive without actually fusing, but that's the typical limit. I see.
Anything more than fifteen times the mass of Jupiter, if it's made out of hydrogen, then it's going to start to fuse and become a.
Sun, and it would become a star exactly.
All right, Well, that's like the mass limit. But we kind of post a question as bigger can a planet be bigger than stars? In which case it can has more to do with the volume, right, Like the measurement of it the size.
Yeah, and this is really weird. Like if you took Jupiter and you started adding mass to it, you had like a hydrogen pump, and you just started dumping hydrogen into Jupiter, then it would get more massive, but it wouldn't actually get larger very quickly because it would mostly just get denser, Like the gravity would get more intense and it would hold itself together and it would get denser and denser. So as you pump hydrogen into it, you could actually get Jupiter up to like seventy times its mass without changing its volume very much.
You're saying Jupiter right now is actually kind of fluffy. Yeah, I mean a lot of it is just like gas, right, A.
Lot of it is just gas. And if you added seventy jupiters and put them all on top of each other, they would just like collapse to a denser object about the same size as Jupiter.
Yeah. Are there any examples of that that we seen?
Yeah, Actually there's a bunch of them. There's a star out there, trappist one A. It's eighty times the mass of Jupiter and it's a star, right, so this thing is burning, it's a star. It's the same size as Jupiter. Right. So right now out there there's a star which is the same size as a planet. It's just much much more dense. Right, this thing is so dense. It's mostly hydrogen, but it's like twenty five times as dense as granite.
Wow. Yeah, that's crazy to think that hydrogen can be that dense.
Yeah, there are really weird phases of hydrogen. Also when it gets so dense. There are these things called like metallic hydrogen, and we can dig into that one time in some other episode. But there are a bunch of these things, Like there's another star out there that's a red dwarf and it's about the size of Sadurll.
Wow, it's tiny, And so it's.
Actually a star that's smaller, smaller than Jupiter, right, And that's just because of these weird effects that as you add more volume, the gravity gets more intense, and so the planet doesn't actually grow in size, it only grows in mass.
But it's still a star, meaning it has fusion at the center. It's just not exploding maybe like our star.
And then there are some other examples. You know, we say that as you add more mass to the planet, it doesn't actually grow in size. That's what we expect, and that's what we see most of the time. But there are some counterexamples that we don't yet understand. Like there's a planet out there they found called Celt eleven B. This is the one they called the styrofoam planet because it's one fifth the mass of Jupiter, but it's actually like forty percent larger than Jupiter. So it's like a big fluffy planet, extra fluff. It's like Jupiter extra fluffy exactly. It's like the whipped up version. Right. Somebody put a mixer in there and set it on high and they're going to fold it into their angel food cake. But this is not something that we understand, like it's thought in the models it shouldn't exist, and so it tells us that there's something about planetary formation we don't understand. Or maybe it's some weird thing and it just exploded and still coalescing. You know, a lot of questions there, but mostly we expect that you can't get a planet much larger than Jupiter by volume.
Oh I see, uh, So there is kind of a size limit to planets because if you keep adding more, at some point it'll stake the same size, but at some point it'll become a star, so you can't have a bigger planet.
Yeah, exactly. Roughly, Jupiter is about the biggest planet you can make that we understand. There's one example out there that the king of planets currently is this planet out there HD one zero zero of five four six b N, which we think has seven times the diameter of Jupiter. So this is the largest known planet. But it still looks like it's forming, like it's in a young solar system, and so it may actually be like a brown dwarf that's still sort of coalescent.
Like the biggest baby in the universe.
It's a big, dangerous baby.
So I may careful what you call it, but I guess the main point is that there's a size limit and a mass limit to planets if we sort of stick to what we see in the universe, which is mostly hydrogen. But I guess the point is that there isn't large enough concentrations of the heavier elements to make bigger planets. Is that kind of it.
Yeah, I mean there might be some really big planets out there that fluctuate into having huge deposits of rock, but you know there'd be a lot of rock. There is a larger rocky core in the center of Jupiter than the volume the Earth right, So typically if you get that large rocky planet, it's also going to have a huge amount of gas around it, as you'll end up with a gas planet.
All right, Well, let's get into the other side of the equation, which are the stars. How small can a star get? And then we'll talk about the question can a planet get bigger than it's star? First, let's take a quick break.
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All right, we're talking about planets and stars and their relative sizes. Can your kid be bigger than you?
Depends on what you feed them I suppose.
Yeah, who knows what they put in milk these days. But yeah, we talked about planets, and now let's talk about stars. Like what's the smallest size that a star can get? Because if you can have a tiny star but it's pretty heavy, then you could imagine it can have much bigger planet orbiting around it.
Yeah, exactly, we're going to talk about the biggest planet. Now we need to talk about the smallest possible star. The thing that's really fascinating about stars is that their size depends on where they are in their life cycle. Like a star isn't just born and then it fizzles out and always stays the same size. It actually evolves a lot. So the size of a star, even like our sun, depends on where it is in its life cycle.
Yeah, it changes size, like it's our sun is going to get bigger, much bigger at some point in the future.
Ye thenk yeah exactly. And so the way the stars formed is that you get a huge blob of gas like hydrogen gas, which most of the stuff when you're forming a solar system goes to the Sun because gravity is a runaway process. You know, the heaviest thing has the most gravity, so it attracts the most stuff, so you get most of the hydrogen sort of falling in towards the center of the Solar system. And that's how it gets big. Right, that's why it doesn't just turn into a planet. It turns into a star because it has much more than ten or one hundred or even a thousand times the mass of Jupiter. And so the early stages of the stars that it just gass all that stuff and then fusion happens in the center of the star and that pushes back against the gravity. Right, you have gravity pulling everything in to form the star, and then fusion shining energy out and keeping it from collapsing any further.
Yeah, So then does that put a limit then to how small or how large a star can be?
Well, in the beginning, it just depends on the mass, Like as you add mass to a star, it gets bigger and bigger and bigger. And our Sun is actually unusually large on average, like most of the stars in the galaxy are smaller than our Sun. But there's no limit really on the size of a star in this phase, like it can get really really big. And we're gonna do a fun podcast episode next week, I think about what is the biggest star in the universe, but we're interested in the smallest star, right, But what happens when a star burns is that fusion pushes all of this stuff out, So you get a big star, which causes this gravity, which collapses stuff in, and then it causes fusion, which works backwards. It's like a back reaction. It pushes all the stuff out. It tends to make the star bigger. So what happens in the life cycle of the star is that it burns for a long time, like billions of years depending on its size, and then it grows like, as you said, our star is going to get much much bigger, and not like twice as big or three times as big, it's going to be huge. It's going to grow so much that it's radius is going to almost encapsulate the Earth.
Yeah, that'll be a nice toasty time for Earth.
If we're still here. And this is important to understanding the question later about whether or not you're gonna have a planet surrounding us, because before a star gets small, it gets really really big, right, and then what happens is that it collapses. Right as you say, what happens in fusion is that you're making these heavier metals, and so you start out with the blob of hydrogen, but soon you have a core of helium which is fused from the hydrogen, and then that helium, if the star is big enough, burns into heavier stuff and you end up with neon and carbon and oxygen and all this stuff. And so now you have increasing density in the center of the star and gravity is sort of pulling on it. Again. I love the dynamics of star formation and star life cycles because it's this like back and forth between fusion that's pushing out on the star and gravity that's like trying to collapse it, and each one sort of trips itself up, Like gravity causes fusion, which pushes stuff out, but then fusion creates denser stuff, which increases the gravity. And so eventually what happens is that the star collapses because you get so much heavy stuff in its center that it can no longer burn.
Yeah, it's a big drama, like a bit of a dysfunctional relationship there between fusion and gravity.
Maybe they should just get a smaller house, you know, maybe that would become.
A smaller universe. Hey, we would all be a lot cozier, be like living in the pandemic all the time forever, all right, But I guess it seems like the inevitable fate of most stars is to shrink. Like theyll might have some heydays where they're huge, but then eventually they all shrink as they run out of field.
Basically, yeah, exactly, they shrink, and what you are left with is some really really dense core. Like they blow out a lot of the stuff and you get some sort of like layers of fluff blown out into the Solar system. But at the core which you're left with, it is a few different options. Depending on the mass you started with, you might end up with a white dwarf, or a neutron star, or actually a black hole.
What's a white dwarf?
A white dwarf is the future of our Sun. It's basically just a huge hot blob of heavy metals and there's no more fusion happening anymore. It's like not big enough, there's not enough compression to cause fusion at its core. But it's still If you like took a scoop out of the center of the Sun and put it in space, it would still be a big hot blob of heavy metals. And that's what a white dwarf is. It's not glowing anymore because it's making fusion, but it's still hot. So they call it a white dwarf because it glows from.
Its heat, right, But it's not technically a star anymore, right, because there's no fusion.
Man, good question, is a white dwarf a star? You're right, there's no fusion happening anymore. It's like a stellar remnant. It's definitely not fusing. But I think you do still call a white dwarf a star.
Really, but we just said earlier that we need a fusion. Daniel, you're confusing me.
Oh my god, astronomical names are confusing. What news flash?
Well, it's they call it a star because it's bright and it's giving of light right in the form of heat, but it's not fusing it. It's kind of somewhere in there.
It's somewhere in there.
Does it become a planet eventually?
Eventually? Sort of What happens is that these things eventually cool and they become a black dwarf. And a black dwarf is just a white dwarf that's had enough time to radiate away its heat into the universe and cool from being white hot to be you know, cooler. The interesting thing is that there aren't any black dwarfs in the universe yet because they think it would take like trillions of years for a white dwarf to cool off, and so there just hasn't been enough time yet to form any of these things.
I guess they sort of become planets, but everyone's too polite to tell them that they're no longer a star. You know, it's kind of like a professor emeritis. You know, they're not really professors anymore, but you know, you don't want to strip away their title.
Yeah, exactly, or last decades a list celebrity. They don't get invited to parties anymore, but you know, people still ask for their autograph. But the amazing thing is that you get like sixty percent of the mass of the original star, but now compacted into an area that's about the volume of the Earth. Our sun will be about the size of the Earth after all this happens, even though it will be much much more dense than the Earth.
Ah, that is, it sounds tiny. But then there are other possible fates for a star, right not just a warp war.
That's right. If the amount of stuff that you end up in the core is large enough that you still have a lot of gravitational pressure, it can collapse those heavy metals even further and you don't get fusion. What you do is you sort of force the electrons and protons together and you end up with forming neutrons. This is called electron capture. You're like push the electron into the proton and you get this interaction in the core that turns all the protons and electrons into neutrons, and then you get a neutron star.
Now po technically that's also not a star because there's no fusion going on anymore.
Hold on, I'm gonna make sure I have a comprehensive list of your objections to astronomical categories so we could submit it to the committee.
Let's get this straight out, because you're confusing. At least one cartoon is here.
Then that's right. Well, I have the official form here, so I'll make sure to fill it out and submit it after we're done. But you're right, it's a neutron star. It's not fusing, right, it's probably still hot like we see neutron stars, but they don't emit light in the same way. Mostly we see them in the X ray. But these things are tiny because they're super duper dense. So you have like one and a half times the mass of the on and the radius of these things is like ten kilometers. It's like a whole star in Los Angeles. Wow.
But it's emitting light just from its heat or from some kind of process or why are we still giving it the honorary title of a star.
It's definitely not fusing, and so it's giving off light the same way everything gives off light that everything with a temperature radiates. It's called black body radiation. And all matter that has electromagnetic interactions will give off light at some frequency that's connected to its temperature. And that's why you know things that get hot glow, even things that you don't see glowing or are actually glowing just at wavelengths that you cannot tell.
All right, And then a star can also end up as a black hole, right, like if you compress we have more mass, even like stronger gravity, it can collapse into a black hole.
Yeah, exactly. The neutron stars prevented from collapsing into a black hole because these neutrons don't want to press against each other even further. They're like pushing back. There's some pressure pushing back, but if you have enough mass, you can also that, and then you've got a total gravitational collapse into a black hole. And because these things are collapsing, right, they're even more dense. And so from white dwarf to neutron star to black hole, the density of matter at the core at least is increasing, and so the radius is decreasing, and so these things get pretty small.
Yeah, and now you're going to tell me that a black hole is also star, Daniel, it's a black hole star? Is that the technical term?
It's a star of science? At least, it's a star of mystery.
It's a stellar performer out there in space. But yeah, then at that point it's no longer star. I mean, come on, it's a black hole.
A black hole is not a star. I think we can definitely rule on that one here today.
Yeah, all right, well let's get into now whether or not you could have a planet that's bigger than it's star. We talked about how big cam planets get and how small stars can get and how to push the limits of what astronomers call things in space. But first, let's tick a quick break.
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All right, we've set up these two topics Daniel stars and planets, and now we're going to ask can a planet be bigger than it's star? I guess the question I just from what we've talked about is yes, right. I mean, you can get tiny stars and you can get big planets, So there must be some point, someplace in the universe where the two are together.
It certainly seems possible, right, But the key thing is can the planet survive? Because the stars tend to be large when they're young, then get even larger before they get smaller, and so for a planet to outsize it's star, it has to survive that transition, and that transition is not an easy one to survive, right, Like going to this red super giant is going to be pretty toasty for any inner planets, and the collapse to like a black hole or a neutron star can involve a supernova. So even if the remnant is smaller than the planet originally was, to satisfy so to say, technically you have to survive that transition.
You have to make it to be bigger than your parents. I get. I guess you have to make it through your parents' middle age or something. You have to wait it out, wait for them to shrink, and then you're taller than your parents.
Right exactly when their life explodes. If you can somehow hold on, then you.
Stay away from them.
Right to Jupiter. Yeah, Jupiter, you should go, like you know, on a backpacking trip through Europe and then come back when the Sun has become a white rider.
Take that job in Asia for sure, and then come back.
I think that is good parenting advice and good astronomical advice. Become a rogue planet at some point in your life.
Get that tattoo, you know.
Maybe that's what the red spot is on Jupiter. Maybe it's already done as traveling man. Maybe it's a tattoo of the sun. You know how some people get like a mom tattoo. Maybe that thought it's red, you know, that makes sense.
We are solving deep, deep questions and old, old ancient mysteries about the universe today on the.
Podcast Physics and Parenting in One Podcast. All right, well, yeah, it's tricky to survive, but it's totally possible, right Like, Jupiter in our Solar system is going to survive our Sun exploding and becoming a white dwarf, right because it's so far away.
It is, but you know, it's going to be pretty crazy and we're going to lose some of the planets, and so it might be that Jupiter doesn't survive. Like Jupiter itself won't be disintegrated, but it will be disturbed. And so, for example, if Neptune takes off, or if Saturn takes off after the Sun goes white dwarf, and maybe that it perturbs the orbit of Jupiter so that it also gets flung out into space. Right, you need like a new stable configuration, and things have changed, and some of these things are a bit fragile.
But it's technically possible though, right Like, isn't it kind of hard to kick a planet out of Sun's orbit?
It's not that easy. But one thing that can do it is having your star grow to red super giant and push off outer layers. And it totally can happen. And that's because what's left of the star when it shed its layers is much smaller than the original star. So it just doesn't have the gravity to hold onto the big planets in the same orbit. So those planets sort of relax and get bigger orbits. And now those orbits are a little bit looser and more chaotic, and so they're more susceptible to tugs from passing stars that can pull them out of their orbits and even out of the Solar system.
All right, well, it might happen in our Solar system. But do we have examples of this configuration of a bigger planet than its star that we seem like, do we have evidence.
We actually have seen one. Yeah, NASA's telescope tests, which is excellent at looking for these things, that has spotted this solar system in the constellation Cancer. It's about fifteen hundred light years away, and at the center is a white dwarf, right, And a white dwarf is something which is a stellar remnant, which means that there used to be a big, powerful star there, which like our Sun, burned for a long time billions of years and then collapsed into a white dwarf. And around this white dwarf they see a planet.
Hmmm, which is bigger than the white dwarf.
It is it's about the size of Neptune. And these white dwarfs, you know, they're about the size of a small rocky planet. Like the white dwarf that's in the future of our star will be about the volume of Earth, and so this one, we think is about the same size. And so this Earth sized star has a planet around it that's the size of Neptune.
Wow. So that's the situation that we're asking about. The star with the planet that's bigger than it flying around and we've seen these, or at least we've detected them using gravity, right.
Yeah, exactly, we have detected this one. It's sort of weird. We don't really understand it. Like the Neptune sized planet, it's pretty close to the star. It's much closer to the star than you would expect because that star must have been like a red super giant at some point toasting any planet that was near it. And so this planet is like inside the radius of where the stars should have been, and so there must have been some crazy gymnastics changing orbital radii after that happened.
Oh, I see, it's like us surviving the flare up of our sun, Like how could we still be there?
Yeah? Exactly, and so probably this planet was somewhere further out and then something crazy happened and it migrated closer after the planet became a white dwarf. So that's sort of like one survival strategy. It's like, maybe you don't go all the way to Asia, but you just have like a really distant orbit and then you come back in closer after.
It's coming on. Then you reconnect with your parents after a lifetime, you.
Move into the city, and then you come back to the suburbs, you know, when they're ready to retire.
All right. So that's one example that we've seen. Are there more?
That's the only one that we've seen. But you know, the fact that we've seen this one means that it is possible to survive your star's transition to white dwarf for neutron star or even black hole, and so it's possible that there are a lot of these things out there. It's probably pretty common. Oh yeah, cool.
Well, I feel like we kind of cheated a little bit though, Daniel, because if I hold you to the technical definition of a star to say that there has to be fusion in it, it sort of becomes a very different question, right, like, it is possible for a white dwarf to have planets that are bigger than it, but a white dwarf doesn't have fusion in it.
That's right, a white dwarf doesn't have fusion in it, and either does a neutron star.
So if I hold you to the definition of that we post earlier about a star that it has to have fusion in it, do you think it's possible still for a fusing star to have a planet that's bigger than it.
No, I don't think so, because a fusing star would have to be pretty big, right, You need to be like one hundred times the mass of Jupiter to get that fusion going, and that would eventually be larger than Jupiter. And if you had a planet in orbit that was that same size, it would also turn into a star. And so what you would get then is a binary star system. And so it sort of comes just out of this definition of what we call a star or a planet. If you're going to have something that's not fusing orbiting around someone that is fusing, then the thing that's fusing has got to have more mass, otherwise it wouldn't be fusing.
You just confused me in that last state. So it doesn't sound possible, right, because if the star has to be fusing, they're usually bigger than the largest planet that you can have without fusion. That's what you're saying.
Yeah, you just defused the situation.
I diffuse this whole podcast apparently, but I guess I mean still possible. You just have to invert what you call who's orbiting who? Like, you could technically have a really heavy planet like it's it's mostly iron or there's a lot of iron in it, so it's very heavy. You could have a star maybe that's bigger than it, but it could be that the star is orbiting the planet.
If the planet had more mass, then you could say the star is orbiting the planet. You know, in reality, it's not the case that a planet is orbiting the star. The two things are sort of orbiting each other, and the point that they orbit is their center of mass. And typically a star is much much heavier than the planet, and so the center of mass is close to the center of the star. But in a binary star system, the center of mass is between them, and so they're both orbiting this point that's between the two of them. So where that point is that they're orbiting depends on the relative mass the two objects. So yeah, in your fantasy system where you get to build up whatever you like, you could make an enormous iron planet that has more mass than the star it's fusing. Of course, it would collapse into a black hole, but the star would mostly be in orbit around Jorge's black hole world.
All right, Well, it sounds like a lot of this depends on the definition of a star. If we let stars keep their honorific even after they stop fusing, then it's totally possible for a planet to be bigger than a star, because then the star kind of shrinks and becomes a dwarf for a neutron star.
Yeah, if you think professors emeritis are still Professor's, then a white dwarf is still a star.
But if not, then it's technically possible, but not likely.
Yeah, but sort of just by definition, because that's what we call a planet and that's what we call a star.
Boy. All right, Well, well, it sounds like the universe still has a lot of surprises in store for us, maybe new and interesting configurations that we didn't think were possible.
Yeah, and there are lots of solar systems out there that we don't understand. Weird planets made out of styrofoam and strange stars is doing things that we don't understand. So this is all based on our current understanding of how planets and stars form and what's going on inside them. But there are lots of surprises out there in the universe, and the only way to learn them is to look, and so we should all be supporting astronomy and building more space telescopes so that we can just sort of buy our way into answers to these questions to revealing what's out there in the universe.
Yeah, the only way is to look or to go out there, which you should tell your kids that's an option if they want to become astronauts and they can get as far away from you as possible.
But nobody out there should take this podcast as advice that you should get a red spot tattoo on yourself.
Sure there are people already out there. All right, Well, thanks for joining us. We hope you enjoyed that. See you next time.
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. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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