Daniel and Kelly’s Extraordinary Universe - Can a planet be bigger than its star?

Episode Date: January 21, 2021

What counts as a planet and is it possible for it to outweigh or outsize its parent star? Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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On the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want or gone.

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Listen to the Good Stuff podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Hey, Daniel, are your kids taller than you? You know, that day is not too far off. I've only got a few inches. is on my 13-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-inch 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? Do stars have children? Yeah, I mean, like, they have planets, right? Like, do you think they would feel proud if 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? Hi, I'm Horam. I'm a cartoonist.

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 ordeal 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 Horshawks. Explain the Universe, a production of iHeard Radio. 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. We 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. 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 noticed about our solar, 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 tiniest 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. 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?

Particle-sized children, yeah, cork-sized kids. 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 a 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 moons? And one thing that inspired this question in my mind, at least, was reading about a recent discovery of a really, really strange planet. system. There's a planet out there, about 4,000 light years from Earth that was recently discovered and confirmed by Hubble. And this planet is huge. It's 3,000 times the size of the Earth. It's 10 times the size of Jupiter. This thing is a monster. Wow. That is huge. I mean, Jupiter is like the biggest kid in our block. Now you're saying there's a planet that's 10 times bigger. Yeah. And

it's got a moon that's 10 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, we'll be asking the question. Can planets be bigger than stars? Well, hearing about these huge planets kind of makes me little house jealous. 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 of the butt. Well, it would take away time from your couch sitting denny. 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 this couch in a while. So you just get a rolling couch. Then you can just scoge over to your pool, lounge next to the pool while you clean it. There's always an engineering solution to any. 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 didn't end up spending time together and they moved into a smaller house where they had to share the space

and get along and they actually totally improved their marriage. So there's an n equals one study. Well, again, I think some engineering solutions might have helped. You know, there's walkie-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'm having a hard time wrapping my head around that question. I mean, how could a planet be bigger than its star? Or what does it even mean to be bigger? Like, denser, 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 and answer, please write to us to questions at danielanhorpe.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 although i would also guess that it couldn't be more massive or more dense than a star i'm thinking about a dwarf star they discover that has a planet some planets can be bigger than a dwarf star so yeah i think the size of stars changes over a 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 as 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 it wouldn't pick up other mass. 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 people digging into the masses of things and 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 planets? Like, does it 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 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 it 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'd need like about 10 or 13 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 10 times the mass of Jupiter is definitely a planet because he can't have fusion inside of it. Right. But doesn't it also depends on what it's made out of? Like Jupiter's made mostly out of hydrogen, right? Which would sort of fuse easily. But if you have something like a giant planet made out of iron, you would need a whole lot more to get anything going if you can at 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 mass of 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 crazy? Or would that just turn into like a neutron star at some point? Wow. The size of the galaxy, oh my gosh, if 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 in 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 then on the mass a planet could have, at least in the universe that we see, not in Jorge's imaginary, iron-filled universe. That's right. Up to about, you know, 10 or 15 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 15 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 a mass limit, but we kind of pose a question as bigger. Can a planet be bigger than stars? In which case, it kind of 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 70 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 70 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've seen? Yeah, actually, there's a bunch of them. There's a star out there, Trappist 1A. It's 80 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, as a planet. It's just much, much more dense, right? This thing is so dense. It's mostly hydrogen, but it's like 25 times as dense as granite. Wow. Yeah, that's crazy to think that hydrogen can be that dense. Yeah, there are really weird faces of hydrogen also when it gets so dense. There are these things called like metallic hydrogen. 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 Saturn.

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 counter examples that we don't yet understand. Like there's a planet out there, found called Kelt 11B. This is the one they called the Styrofoam planet because it's one fifth of the mass of Jupiter, but it's actually like 40% larger than Jupiter. So it's like a big fluffy planet. Extra fluff. It's like Jupiter extra fluffy. 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 not 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. So there is kind of a size limit to planets. Because if you keep adding more at some point,

it'll stay 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 100546BN, 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 coalescing. Like the biggest baby in the universe. It's a big dangerous baby, so I'd be 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 would be a lot of rock. There's a larger rocky core in the center of Jupiter than the volume of the Earth, right?

So typically if you get that large Aragy 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 its star? But first, let's take a quick break. 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene.

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Well, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy?

That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professional. and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet.

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Listen to no such thing on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. All right, we're 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 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 it 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 our sun is going to get bigger, much bigger at some point in the future and then shrink.

Yeah, exactly. And so the way a star is 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 10 or 100 or even 1,000 times the mass of Jupiter. And so the early stages of the star is that it just gathers all that stuff.

And then fusion happens in the center of the star. And that push. is 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 going to 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 a 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 its radius is going to almost encapsulate the earth yeah that'll be a nice toasty time for earthlings yeah if we're still here

and this is important to understand the question later about whether or not you can have a planet surrounding a star 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 a 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 of 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 work out. Yeah, 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, they'll might have some heydays where they're huge, but then eventually they all shrink because they run out of fuel, 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 layers of fluff blown out into the solar system. But at the core, what you're left with 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 hot, right? If you 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. Yeah, 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 needed fusion, Daniel, you're confusing me. Oh my God, astronomical names are confusing. What? Newsflash. Well, 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's not fusing. 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 they're no longer a star. You know, it's kind of like a professor emeritus, you know. They're not really professors anymore, but, you know, you don't want to strip away their title. Yeah, exactly. Or last decade's A-list celebrity.

They don't get invited to the parties anymore, but, you know, people still ask for their autograph. But the amazing thing is that you get like 60% 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. Wow. That is that. It sounds tiny. But then there are other possible fates for a star, right? Not just a war dwarf.

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. Wow. Now, but technically that's also not a star because there's no fusion going on anymore. Hold on, I'm going to 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 now because you're confusing at least one cartoonist here, Daniel. 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 sun and the radius of these things is like 10 kilometers. It's like a whole star in Los Angeles. Wow. 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 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, you have more mass, even like stronger gravity, it can collapse into a black hole. Yeah, exactly. The neutron star is 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 overcome 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 a 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 a 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. All right. Well, let's get into now whether or not you could have a planet that's bigger than its star. We talked about how big 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 take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal.

Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop.

Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on. the okay story time podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now hold

up, isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meets. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the Iheart Radio app, Apple Podcasts, or wherever you get your podcast. Imagine that you're on an airplane and all of a sudden you hear this. Attention passengers. The pilot is having an emergency and we need someone, anyone,

to land this plane. Think you could do it? It turns out that nearly 50% of men think that they could land the plane with the help of air traffic control. And they're saying like, okay, pull this. Do this. Pull that. Turn this. It's just, I can do my eyes close. I'm Manny. I'm Noah. This is Devin. And on our new show, no such thing, we get to the bottom of questions like these. Join us as we talk to the leading expert on overconfidence. Those who lack expertise lack the expertise they need to recognize that they lack expertise. And then, as we try the whole thing out for real. Wait, what?

Oh, that's the run right. I'm looking at this thing. See? Listen to no such thing on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. 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 its star? I guess the question, 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 place 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 its 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. 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 guess. You have to make it through your parents' middle age or something. You have to wait it out. Exactly. Wait for them to shrink and then you're taller than your parents.

Right, exactly. And when their life explodes, if you can somehow hold on, then you can outsize them. Well, the trick is to stay away from them when they flare up. That's right. So, Jupiter, you should go like, you know, on a backpacking trip through Europe and then come back when the sun has become a whiteboard. That's right. 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 reds, body is on Jupiter. Maybe it's already done. It's traveling. Oh, 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, all 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,

gloating 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, it may be that it perturbs the orbit of Jupiter so that it also gets flung out into space. 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 a 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 so it totally can't 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've seen? Like, do we have evidence? We actually have seen one. Yeah. NASA's telescope test, which is excellent at looking for these

things that has spotted this solar system in the constellation cancer. And it's about 50. 1,500 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. 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 a 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 John at some point toasting any planet that was near it. And so this planet is like inside the radius

of where the star 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 gone white dwarf. 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. Yeah. 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.

means that it is possible to survive your star's transition to white dwarf or 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 cheat it 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 posed 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 100 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 something that is fusing,

then the thing that's fusing is got to have more mass. Otherwise, it wouldn't be fusing. You just confuse me on that last statement. 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 were saying. Yeah. You just defused the situation. I defused this whole podcast, apparently. But I guess, I mean, it's 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, 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 of 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 its star because then the star kind of shrinks and becomes a dwarf or a neutron star. Yeah. If you think professors emeritus are still professors, 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, cool. Sounds like the universe still has a star. 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 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. Please don't. I'm 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. In the heat of battle, your squad relies on you. Don't let them down. Unlock elite gaming tech at Lenovo.com. Dominate every match with next level speed,

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kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new. season of law and order criminal justice system on the i heart radio app apple podcasts or wherever

you get your podcasts my boyfriend's professor is way too friendly and now i'm seriously suspicious wait a minute sam maybe her boyfriend's just looking for extra credit well dakota luckily it's back to school week on the okay story time podcast so we'll find out soon this person writes my boyfriend's been hanging out with his young professor a lot he doesn't think it's a problem but i don't trust her now he's insisting we get to know each other, but I just want or gone. Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.