Daniel and Kelly’s Extraordinary Universe - What are boson stars?

Episode Date: March 9, 2021

Daniel and Jorge talk about whether its possible to have stars made out of bosons! Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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This technology is already solving so many cases. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hey, Daniel, what does it take to be a star? I think you either have to have enormous natural talent or rich and famous parents. I bet that helps But what about a star out there in the universe? Oh, that's easier. All you need is like a lot of gas, like a lot of gas.

Like the burping kind or the other kind of gas? Any kind of gas? Like, can I make a star out of methane? I don't really know how that would smell, but I bet it would burn pretty well. How about a star meant out of laughing gas? That would be pretty funny. Hi, I'm Jorge, I'm a cartoonist and the creator of Ph.D. Comics. Hi, I'm Daniel. I'm a particle physicist, and I'm no kind of star.

But I bet you're a gas. I try to make people laugh. Well, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of I-Hard Radio. in which we try to gas you up about all the incredible things out there in the universe. The things we understand, the things we don't understand, and the things that scientists are still puzzling over, and the things that make you curious about how our universe works. We try to wrap it all up, inject some jokes,

and make it all understandable to you. Yeah, because there is a lot out there in the universe to be curious about, including things that may or may not exist. Those are the best things to be curious about, like, is there a tiny little teacup between here and Venus? Yes. Can you prove it, though? I have faith, Daniel, in the teacup hypothesis.

Well, fortunately, we have better ways of exploring the universe than just faith. We have science, and science encourages us to think creatively, but then ask ourselves questions like, hmm, how do we know that's true and how could we prove it? Yeah, because the universe is full of surprises. Sometimes we think some things are impossible, even though the math says that it's possible, and then we find those things out there in the cosmos. Yeah, we have surprises both experimentally and theoretically. Sometimes we look out in the universe with a new kind of telescope and we see something

totally weird than we never expected and didn't understand, like the Fermi bubbles or all sorts of other weird stuff like pulsars. And then there are theoretical surprises where we find something in the math that says, hmm, this thing could exist in the universe, maybe even should exist. let's go and see if it's real. Yeah, because I feel like there's nothing in the universe that says that what our expectations are of it or what our experience of it is has to dictate what is actually out there. Thank God for that, right? It's nice that the universe is filled with surprises.

It would be boring if the universe was just like the surface of the earth and not much else. Well, you know that old curse that says, I hope you have an interesting life. Yes, I want to live in interesting scientific times, actually. I want to live in times when we discover crazy things that totally upend our knowledge of the universe and our understanding of our place in it. That's the power of science. That's the joy of it. It's revealing the truth and stripping away our intuition and the ideas that came about just from like living on the surface of the earth. Well, today we're going to talk about one such thing that scientists think that could be out there, at least the math says it's possible, but we don't really know if it does exist.

It would be pretty wild if it does. That's right. it turns out that even though we've talked about neutron stars and magnetars and crazy white dwarves and all sorts of other kinds of stars we've done the biggest stars in the universe, the weirdest stars in the universe, it turns out there are even weird or stranger kinds of stars we haven't even scratched the surface of. Yeah. So is this the weirdest star, Daniel episode in our extreme series? This is the most hypotheticalist star. I see, I see. The most imaginative star, maybe. The most bonkersest star.

Yeah, because each of these sort of extreme examples tells something a little bit about what matter can and cannot do, right? They're sort of like, you know, extreme examples of where you can take physics. Yeah, these are really useful thought experiments. You say to yourself, is this possible? And if the laws of physics say that it is, then you go out there and you hunt in the universe to see if you find it. And if you find it, cool, you've learned something about the universe. And if you don't find it, or if you can prove that it doesn't exist somehow, that it should exist in the universe, but we don't see any of it, there's a clue. There's a hint that there's something about physics you don't yet understand.

And those clues are super valuable because those are the ones that lead us down the path to revealing something true about the universe we didn't know before. Yeah, and that's the whole point of science is to find out things we didn't know before. Well, it's not just to make us feel good or make us laugh sometimes or to have interesting careers. Science makes me feel good. You know, I had a tasty breakfast this morning because of science. I slept in a warm house last night because of science. I'm alive because of science. So, yes, science makes me feel good.

I think you mean engineering, Daniel. I don't think a scientist, you know, fix your AC system. This scientist certainly didn't fix my own AC system. That's true. Well, today on the podcast, we'll be asking the question. What is a boson star? Now, Daniel, that doesn't just refer to the press a button when they discovered the Higgs boson, right? That would be me.

Yes, I'm a star in the Higgs boson. No, I was... Did you press the button? I pressed lots of buttons, actually. Yes, because I spent time in the control room at the Large Hadron Collider, which looks a lot like, you know, the way they depict the control room at NASA, where they're launching the shuttle or whatever. It's a bunch of monitors and people at desks looking at screens, and you got buttons in front of you. And so, yeah, sometimes you actually get to press a button.

Yeah. Did you press any buttons? What was your role there? Monitoring the collisions or something? Yeah, you monitor collisions. You make sure the data that's coming in looks reasonable. And then in very rare circumstances, there might be an emergency. I was actually on shift, the large Hadron Collider. When they first turned it on, very early on, it was 2008, if I remember correctly, when we had that accident, when there was a spot that was welded poorly, and there was an arc and liquid helium was ejected and the whole thing broke. And there's this big red button in the control room. that you have to hit in the case of an emergency. And I had sat at that desk for weeks looking at that button, wanting to press that button

because, you know, buttons. They have to be pressed, right? And so I actually got to press that button. Oh, wow. Now, it wasn't just a coincidence that things went wrong when you were on the shift. It was 100% a coincidence that things went wrong when I was on shift.

Absolutely. Nothing to do with me at all. It's not like I knocked coffee onto a critical control panel or something. Right. It was tea. But yeah, we're asking the question. Question, what is a boson star? And I have to say, I've never heard of this concept, a boson star. I mean, I've heard of the Higgs boson. And I think I know what a boson is. It's a kind of particle. But also, but put together with the word star, it's a whole new thing. Yeah, it's fun to just like take two science words and stick them together and say, hey, is this a thing in the universe. I wonder if that's how they came up with this idea. Let's come up with a few. Quantum black hole. That is a thing, man. Thermodynamic Fermion.

Teleporting hamsters. There you go. All right, yeah, this is an interesting concept in physics. Is it kind of like a new thing or is it an old thing that people are rediscovering? What's the context here? It's not that old an idea. It's something people have been thinking about in the last few decades. But it's received a little bit of attention recently because one of the ingredients you need

to make it, a particularly weird kind of boson, has sort of seen a resurgence of interest as a candidate for what might explain the dark matter. All right, well, let's see if people on the internet know what it is. As usual, Daniel went out there and as folks, if they knew what a boson star is. Yeah, and so my deepest gratitude, as usual, for people who are willing to volunteer to speculate without any preparation on tough physics concepts, even Jorge hasn't heard about. So if you would like to participate in the future, please write to me to questions at danielanhorpe.com. All right, well, here's what people had to say. No idea.

No idea. They're the clowns of the star. I do know there's bosons and fermions. Those are two types of particles. What's the difference? I think one adds up to a different charge than the other. So maybe a boson star is just a star just completely made out of bosons. That's my best guess.

Well, I thought we are done with boson. We find a fixed boson and that's it. Moving on. no I don't boson stars no sorry well I've never heard of them but my assumption would be that if you can have a star that's only made of neutrons then you'd be looking at a star that's only made of bosons however what that would look like or how it behaves is completely lost on me boson stars are stars that give off a lot of bosons and I'm going to have to back up a few podcast to remember

what bosons are. All right. A lot of good guesses. I like the one about clowns. Like I wonder how many boson stars can you fit into a small car at the same time. Yeah, a lot. Actually, a lot. You can squeeze a lot of them into there because they're bosons. No, I love hearing

these folks try to work it out on the fly. That's my favorite thing about this. It's not like a gotcha question. I like hearing people think about it and apply their knowledge of physics and try to put these things together and figure it out. You know, in 15, seconds. So thanks everybody for your great ideas. Yeah, well, there are a lot of good ideas here. Some people are saying they're stars that give off a lot of bosons. And some people may be saying,

or thinking that there are stars made out of bosons. Could it be a star that eats bosons? Yeah, and there's one person who suggested that maybe neutron stars are made out of bosons, which is a cool idea. Neutron stars are super awesome, but neutrons are not actually bosons. Even though you can have Objects we call stars made out of only neutrons, that doesn't qualify as a boson star. But good try. All right. Well, let's get into it, Daniel. Step us through it.

What is a boson star? I guess maybe start with the word boson. What does that mean? Yeah, so there are two kinds of particles out there in the universe that we've discovered. There are fermions and there are bosons. And these are not just like cool names for things. These actually have meanings and the meanings are important because fermions and bosons are very, very different kinds of particles. What's the difference?

Well, fermions tend to be the kind of particles that make up matter, and bosons tend to be the kind of particles that transmit forces. So, for example, electrons are fermions. Quarks are fermions. Even when you put three quarks together to make a proton or a neutron, you still get a fermion. And so all the stuff that we're made out of me and you and amsters and most of the stars in the universe are made out of fermions, right?

So all the matter in the universe are made out of fermions. We're Fermion fellas. We are, yes. And all the other kind of stuff like light beams and Higgs bosons and the weak nuclear force and the strong force, these use particles to communicate between fermions. Like what happens when an electron repels another electron is they exchange a photon. That photon is a boson. So all the particles that represent how matter particles interact, those are force particles,

those are the boson particles. So fermion particles are matter particles, and boson particles are the force particles. Right. So is that the criteria, like what they do? Isn't it technically like from a theory point of view that they're all just kind of the same? They're all just like excitations in a quantum field? They are all excitations of quantum fields, but those fields are different. And it's not just about what they do, like what role they serve. They actually have a fundamentally different mathematical structure because all the fermion particles, which are excitation, excitations of Fermion fields have a different quantum spin than all the boson particles, which are excitations of the boson fields.

Remember, we talked about quantum spin once in an episode. It's not like that the particles are actually spinning. It's just that they have this property, which is really closely related to angular momentum. And so we call it quantum spin. But it's a quantum property, which means you can only have a couple values of it. So, for example, an electron has one half spin. can be either spin one half up or spin one half down. So fermions all have these half integer spins, a half, three halves, five halves, whatever.

Bosons all have integer spins, zero, one, or two. So if you can go sort of halfway up or halfway down, you're fermion. And if you are on the integer number is zero, one, or two, then you're a boson. So they have different sort of mathematical structures. And that tells us about like the number of different configurations the field can be in. So fermions and bosons really are fundamentally different kinds of particles. It's like they're part of a different kind of feel altogether. Yes.

Which probably lets them do different things. Yes, exactly. And there's a very important property that makes fermions and bosons different. Now, fermions, they can't hang out in the same state. Like you can't have two electrons hanging out in the same quantum state. You can't have them have the same spin and the same location and the same energy. They just don't get along. They exclude each other.

And that's why, for example, when you have a complicated atom with eight electrons around it, for example, they're not all in the lowest energy state. They stack up on top of each other like a game of connect four. So fermions cannot hang out in the same quantum state, but bosons can. And it's the same for quarks? It's the same for quarks. Yeah, absolutely. For any kind of fermion, they will not hang out in the same state. Like if there's one in that state, it's done.

It's filled in. It's checked off. And the next one that comes in has to settle in. at some other state, either higher energy or a different spin or something. But only if they're really close together or in the same exact spot. Yeah, location is part of your quantum state. And so if you're like isolated in a box, like in a quantum dot or in a hydrogen atom or something, then the energy level or the spin or something else has to distinguish you from the other electrons.

If you're in a different location, that counts as having a different quantum state. But bosons can overlap. Bosons can totally overlap. You can have two bosons in exactly the same quantum state. And, you know, for example, take two flashlights and shine them at each other. The photons don't like bounce off each other, right? You can fill up a room with like light from flashlights and have it be like stuffed full. But fermions repel each other, you know, that's why matter has volume.

That's why things fill up. So bosons, you can have as many of them as you like in the same state. And we've done really interesting experiments that we talked about in the podcast like the Bose-Einstein condensate. which is an extreme example of this when you get a huge number of bosons all together in the same quantum state. All right. So then a boson star, then is a star made out of bosons or that gives off the bosons? Yeah, a boson star is a star made out of boson. The sun, for example, is made out of fermions.

It's made out of quarks and electrons all mixed up in different configurations, but they're all fermions. And a boson star would be a star made out of just boson. Like a star made out of light, pure light. Yeah, so not every boson is capable of making a boson star. But yeah, photons are an example of bosons. They're like the most famous kind of boson. But think about sort of how hard it is to make a star. You can't just make a star out of anything.

We talked on the podcast about the conditions for making a star. It's actually quite tricky, right? Even like stars made out of fermions, you have to have enough mass so that there's gravity that pulls it together and you make like an object, not just like a big fluffy cloud out there in the universe. It has to be gravity pulling it together, but there also has to be something else working in the other direction. So gravity doesn't like run away and give you a black hole. In most stars, that's fusion. Gravity comes together and it makes the core of the star really, really hot. And so you get light and energy flying out and that pushes against gravity. So the key

thing about making a star is this balance. You need something pulling in gravity and you need something pushing out to prevent the collapse. And this is not like an eternally stable thing. So it's not that easy to make it happen. So in most stars, you have fusion and gravity imbalance. And other stars that aren't burning like white dwarfs, you have other weirders not happening. But then the question about boson stars is like, what can you get to balance gravity to make a boson star? Right.

Well, I guess the tricky part is that you say that bosons are the force particles that transmit forces. So are you talking about like the idea that you can make a star? out of force particles? Like, what does that even mean, Daniel? Like a star where you bring things that are pure force? Yeah, well, remember that forces aren't transmitted by particles, but those particles can also be real. You know, photons are what electrons used to talk to each other,

but photons can also just exist, right? They can fly across the universe. They can be part of a laser beam. They're created all the time. And so these particles, you know, that's the role they play in our matter. and sort of in the story we tell about nature, but they can also just exist.

So, yeah, you can get a huge pile of bosons altogether and then ask questions like, what happens to them? Do they form interesting structures, right? That's the physics game we play. We think, what happens when you get a huge pile of hydrogen together? Oh, look, it does this cool thing. It makes a star. And now people are playing that game, like,

what happens if you got a huge number of bosons together? Could you make a star out of them? What would they do? How many could you fit into a small car? Big fundamental questions All right, well let's get into how you might actually make a boson star and if they exist

what would they be like? But first, let's take a quick break. Hola, it's Honey German and my podcast, Grasias Come Again, is back. This season, we're going even deeper into the world of music and entertainment with raw and honest conversations with some of your favorite Latin artists and celebrities.

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All right, we're talking about boson stars, a hypothetical, possible, maybe, theoretically plausible kind of star, but that maybe we haven't seen yet out there in the universe. We talked about how there are stars that might be made out of bosons. I guess my first question is, how would you even, like, get a bunch of bosons together? Like, do they have mass? Would gravity bring them together? Or do you need to capture them somehow? or, you know, lure them with big shoes and retin noses, how do we bring it together?

Really comically sized cookies, I think, and that just pull the ball in. No, that's a fair question. You can ask two different questions. One is, if I had a huge pile of bosons, would they form a star? And the other question is, could I just get or should I expect to see in the universe

a huge pile of bosons, right? It's possible that this thing could potentially exist if you could assemble the ingredients, but that it just doesn't happen in our universe, because it's not a consequence of the Big Bang in any way. So those are two totally interesting, but separate question. Oh, I see. One is like, can it exist?

And the other one is could it exist? Does it exist? Yeah, exactly. And, you know, we talk in this podcast about the infinity of the universe and everything that can happen will happen. And that's mostly true, but there's an important caveat that you need to have the right initial conditions. You know, it might be that even in an infinite universe,

there's no way to start from a hot, dense state that we began from and end up with like a huge pile of bosons all in the same place that then, you know, do whatever they do, maybe make a star. All right. Well, let's play the first game then. What if you certainly have a bunch of bosons all in the same place or the same vicinity or like volume? What are we talking about?

Yeah, that's exactly what you need to do. And you need to think about the two ingredients to make a star. One is gravity and the other is outward pressure. So to have gravity, you need to. to have these objects having some appreciable mass, right? You need to have gravity to be able to work on these things. Now, there are folks out there probably thinking, hold on a second. I know photons don't have mass, but they are affected by gravity because they can't, for example, escape black holes. And that's true. And we talked once on the podcast about how you could like focus enough

photons together to maybe make a black hole. But to make a stable boson star, you'd actually need to have a particle with at least a little bit of mass. So gravity has like a little bit more a handle to pull it together. Right. Well, but isn't it like mass the same thing as energy? Like if I have a lot of photons in one place, wouldn't that warp the space around it just like it, as if it had a lot of mass? Yeah, absolutely it would.

And you could, for example, make a black hole if you concentrated photons together enough. But a star is a little bit different. It's actually harder to make than a black hole. Black hole is just like a bunch of energy in a super tiny space. A star is a balance, right? It has to be a balance to have just the right. amount of gravity and just the right amount of outward pressure.

So these two things match. And the calculations just don't suggest that photons could make a boson star. They don't have enough mass to like pull together in the right density to get the outward pressure you need. I see. I think what you're saying is that for something to be called the star, I mean, it can't be a black hole, basically. And it can't be an explosion either.

It has to like shine and shine consistently. And you're saying that you just can't do that with bosons. Like, they wouldn't stick together if they don't have mass. You can't do that with photons. There are other bosons out there that might be candidates for making a boson star, but we don't think that photons can do it. All right. So which bosons could do it?

Well, let's go through the kinds of bosons there are in the universe. What's on the menu? Next up are gluons, but gluons also have no mass. We've got to scratch them off. We also need a particle that's stable. We don't want our boson star to decay instantaneously. into other kinds of stuff. And so that, for example, removes Higgs bosons.

Higgs bosons exist in the universe, but very, very briefly, they very rapidly decay into pairs of fermions, like a Higgs will decay into two bottom corks or into two muons or something like that. So we need a stable particle. So we don't think there are any Higgs stars out there, which is too bad because that would be kind of awesome. Yeah, pretty good name recognition right there. And so that removes the possibility of a Higgs star.

and also a W star or a Z star. Ws and Zs are the bosons associated with the weak nuclear force, and they're also very massive, and they decay very quickly. Zs decay into a pair of quarks, W's decay also into a pair of quarks or sometimes into leptons. And so you just can't make them out of those particles because they would just decay into a Fermion star. Well, I'm sad that we can't have gluon stars.

But we have glue balls, actually. Glue balls are a stable configuration of just gluons, It's a particle made out of just gluons, which is pretty cool. But you can't have a gluon star, unfortunately. Yeah. Also, that's a sticky subject. So what does that leave us? Which boson particle could we use to make a boson star?

Well, that basically crosses off all the bosons that we know exist. So, well, all right. We're done. But we're not done because there are always more particles on the list, this long, infinite list of hypothetical. particles. Particles that we think might exist. And if they did, could do other weird things that the particles were familiar with don't do. And near the top of that list is a particle, which has gotten a lot of attention recently. Theoretically, it's called the axion. Yeah, we had an episode about that. Maybe remind folks what an axiom is. And by folks, I mean, including myself.

Well, an axon is named after a detergent because it was thought of by Frank Wilcheck and he was doing a grocery shopping while he was thinking about the name. And there's a detergent called Axion. He thought, ooh, that's a cool name. So the Axion particle is one that was thought up to sort of explain a theoretical puzzle in the strong force. People didn't really understand why the strong force was different from the weak force in a subtle way. And so they came up with this axion to explain it. But the reason that axions are interesting recently is that people think they're a good candidate for what might be the dark matter particle. Remember that while we know dark matter is a thing, we know it's out there, we know it's providing

gravity. Most of the gravity in the universe actually comes from dark matter. We still don't know what it's made out of. It could be made out of one particle or many particles or some other weird kind of stuff, but we have this sort of list of candidates. One of the particles on that list is a fermion. It's called the Wimp, the Weekly Interacting Massive Particle. and it's sort of the leading candidate for a long time,

but nobody's found it. We have all these dedicated experiments looking for wimps and not seeing them. So recently people in chart think a little more broadly, dig deeper into that bag of hypothetical particles to find other things, and the idea that the axon might be the dark matter is sort of popular these days. Wow. All right. I'm a little confused now.

So you're saying that dark matter could be made out of something that's not matter. That's a force particle? and that's an axion and that if these things exist you could potentially put them together to make an axiom star yes exactly you totally understood it so much been perfectly clear so we don't know that axions exist right it's an idea it would be sort of beautiful theoretically and solve a bunch of interesting problems if you're interested in that go dig into that podcast episode specifically on that topic we don't know that they exist but they would solve an interesting theoretical problem about the strong force they might also be dark matter and yes they would be the perfect ingredient for making a boson star because they're a boson and they have a little bit of mass and they are stable. Hey, did I tell you that Frank Wilchik retweeted me the other day or mentioned me in a tweet? I didn't know that. I didn't even know he tweeted.

Yeah. I felt like an axon star myself there for a moment there. All right. So then if a boson star exists, it would be potentially made out of axions, which is you're saying are stable. And they do last for a while and they do have mass and so they could get sort of bunched together by gravity. Yeah, that's the requirements to be the dark matter, right? You need to have mass.

Otherwise, you can not explain to the dark matter. And you need to be stable on cosmological timescales because we think dark matter sticks around a long time. It's still here after all. So Axion satisfy both of those requirements. And then you have to ask the question like, well, what makes it a star? And I heard you saying earlier like, well, it has to shine. And I know we talked on this podcast before. about the definition of a star versus a planet.

A star is defined to be something that has fusion happening at its core. Here, though, unfortunately, we're going to have to be inconsistent and relax that definition because a boson star doesn't actually shine. How convenient. So what are we talking about then? If you get a whole bunch of axions together, then gravity would keep it in a ball of axioms, like a sphere of axioms? What would happen if I get a bunch of them together?

Or like even if I get two of them together, do they attract each other by gravity? They would attract each other with gravity. Now, just two particles would have infinitesimal gravitational force. And so that's why we don't think about gravitationally bound particle systems, right? Like the proton, the electron, the gravitational force between them is basically zero, but should compare to the other forces. But if you have a lot of axions near each other, then yeah, you're going to have a lot of mass, and that will make a gravitationally bound system.

And so you can get a huge serving of axions. and they would clump together and they would fall into each other. And then you have to ask the question, well, like, why wouldn't you just make a black hole? Remember, a star has to have two conditions. It needs to have gravity to clump it together and it needs to have something to resist falling into a black hole. The reason why our sun is not a black hole is because it's resisting that through fusion. The reason that white dwarfs, which is the future of our sun, aren't black holes, is not because they're burning.

It's because they're actually made out of fermions. and those fermions don't want to sit on top of each other, right? Fermions have this exclusion principle. And so that's like quantum mechanics at work. The reason that white dwarves don't fall into black holes is because of quantum mechanics of their fermions. But axions are different. Bosons are different.

They can't do either of those things. They can't make fusion to have radiation pressure. They can't rely on the poly exclusion principle because that only applies to fermions. Meaning like if you get a bunch of electrons at some point, they'll repeliorate. tell each other or protons or, you know, balls of dirt. Or neutrons. Yeah, like to make a planet. But bosons, they can sit on top of each other.

So I guess if you get a whole bunch of them together, why wouldn't they just all sit in the same point? That's kind of what you're saying, right? And if they do, then you would form a black hole. Exactly. So you need a boson which would prevent itself somehow from collapsing. And the way you do that here is another property of quantum mechanics. So you were exactly right that the reason a neutron star and a white dwarf

don't collapse into a black hole is because of the firmy pressure, right? It's all these particles not wanting to sit on top of each other. Boson stars can't do that. But there's another property of quantum mechanics, the uncertainty principle that just prevents axions and bosons from being too constrained. If you have a bunch of axions and say they're all within the same sort of location, then that creates a large uncertainty on their position because the uncertainty principle tells us that there's like a minimum amount of uncertainty. in the momentum and the position of these particles. So if you constrain their position,

then their momentum becomes uncertain and then they fly off. The quantum mechanics sort of resists having these things collapse. What do you mean they can't merge? Like they can fuse together? Like fermions, well, not all fermions can fuse together, only some, right? Only some. But yeah, but bosons typically don't interact with themselves. Like photons don't interact with other photons.

Photons don't merge together to form something else. some bosons do like gluons or higgs bosons have a self-interaction but most bosons including axions don't interact with themselves they just like don't even see each other they don't like add up like if you have two in the same spot don't they just add up they don't add up because they don't like fill energy levels right they can all be in the same energy level that's not a problem for bosons and they don't have any interaction you know that field the axion field doesn't interact with itself at all just the same way photons don't Photons, for example, only interact with charged particles, right? They will ignore neutrons and neutrinos and anything else that has zero electric charge, including other photons.

And axions are the same way. They ignore all other axioms. If I have two photons in the same spot, don't they just become a bigger photon? Or are they still technically two photons? There's still two photons, yeah. And I should add here that there are actually a few different flavors of axions, since they are a hypothetical particle. Right now, we're talking about.

talking about the ones that don't interact with themselves or with photons. But there are other versions of these theories where they have some small self-interaction and they can feel photons a little bit. Those variants can also make boson stars and sometimes that self-interaction can help if it's repulsive because the axioms might repel each other and then form that outward pressure to keep the axiom star from collapsing. All right. Well, that's our main imaginary candidate for these imaginary stars, the Axion. And so that's how you would make one. But let's talk about whether or not

we actually see them out there in space and what they would be like. But first, let's take another quick break. A foot washed up a shoe with some bones in it. They had no idea who it was. Most everything was burned up pretty good from the fire that not a whole lot was salvageable. These are the coldest of cold cases. But everything is about to change. Every case that is a cold case that has DNA right now in a backlog will be identified in our lifetime. A small lab in Texas is cracking the code on DNA. Using new scientific tools, they're finding clues in evidence so tiny you might just miss it. He never thought he was going to get caught. And I just looked at my computer screen.

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for this new season of Family Secrets. Listen to Family Secrets Season 12 on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. We're talking about boson stars that may exist out there in the cosmos. And if they do, they might be made out of axions, which themselves may not exist. I feel like we're stacking imaginaries here. Do imaginary concepts exclude each other, Daniel?

Do they add up? I'm so confused. Can they merge? These bonkers concepts are all bosons, so we can have an infinite number. of bonkersness. I see. They don't exclude each other so you can just stack them

infinitely. Exactly. Until we get a bozo star. All right. Well, let's say that the axion does exist and let's say that you could somewhere out there

get them all together enough to make some sort of axione object that still doesn't tell me how that makes it a star. Like, why isn't, wouldn't be called an axion planet

or an axon, you know, ball? Well, if you were around when they were deciding on the name these things, then that would have been a good idea, axiom planet. I think that makes more sense, you know, because a planet is a non-fusing blob of stuff out there in the universe made out of basically whatever. So, yeah, these axions are also, they're not fusing, they're not glowing,

they're not giving off any light. They're just a stable collection of axions that are resisting, collapsing into a black hole. So I think they called it a star just to sort of make it sound awesome, not because it's actually doing it. Really? Was that a physics paper there? I don't know. I mean, in the same way, our neutron stars, stars, right? They're just a big collection of neutrons that aren't collapsing into a black hole yet,

but they're not glowing, right? They're not fusing. There's no radiation being emitted there. So the same way, like white dwarfs, right? We call those stars. So, yeah, astronomy's got some work to do. I think what you're saying is that in physics, there are no standards for being a star. Anyone can be a star.

It's like our society today. You just need an Instagram account. Yeah, or famous parents. Being a physicist is easy. It's no big deal. No, I'm saying I cannot defend the naming of this thing as a star. It's just there's nothing I can say about it. That makes any sense.

But I guess you're saying that it is possible theoretically to have a whole bunch of axions together in the same spot without collapsing into a black hole. And what keeps them from collapsing is this uncertainty principle, you said? Yeah, exactly. as you try to constrain them to be in a smaller and smaller location, the uncertainty grows on their energy. And that essentially resists them being constrained. So the uncertainty principle resists them from being collapsed too far into a tiny little spot. So how big would an Axion planet balls be?

Like if you get a whole bunch of them together, would it be just super tiny or would it actually be the size of a planet? That's a great question. And it depends on the mass of the boson star. And so a more massive boson star would be larger. They have a similar sort of structure to black holes, right? Or a more massive black hole than just becomes larger and larger and larger sort of in volume. And so boson stars in the same way would resist collapsing. And the more bosons you have, the more resistance there is.

And so they would just sort of like grow larger and larger. But the question is like, you know, are there boson stars? And if so, how big are they? Yeah, because I feel like you're saying that it's the uncertainty principle that that keeps him kind of from collapsing. Can you have an uncertainty principle the size of a planet? Like, that's a big ball of uncertainty. That is a big ball of uncertainty.

Yeah, exactly. But you know, it also applies locally and not just globally. So you can have like patches of these things where you have bosons lying on top of each other. So yeah, I think it certainly could apply to something the size of a planet. I mean, it does also for white dwarfs, right? For neutron stars, there you have like quantum mechanics at work, preventing particles from overlapping on top of each other, providing the resistance to collapsing into a black hole. Does that apply to photons, too? Like, can photons also be stacked like that? Does the uncertainty

principle also prevent photons from being on top of each other? Yeah, absolutely. If you try to localize photons in the same way, then it will prevent you from knowing their energy in exactly the same way. The uncertainty principle applies to all quantum particles. It might be easier to understand the uncertainty principle if you think about it in terms of temperature. Quantum mechanics prevents anything from going to absolute zero temperature because there's always a minimum energy. Otherwise, you'd know a particle's momentum and location at once because it'd be frozen in place. So there's a minimum temperature for any collection of particles. And that's quantum mechanics keeping something from collapsing into a single dot. So the way you, for example,

you would make a black hole out of photons is not by trying to squeeze a bunch of photons that already exist into the same location, but by overlapping laser beams on top of of each other. The photons from different directions are all coming together in the same place. Well, let's say that these stars exist, these boson stars exist. What would they be like? Could we see the one? Would we feel attracted to them? Would they, you know, burn our eyes if we look at them? They would actually look a lot like black holes because they are dense gravitational objects. They're contortions in space time, right, due to the mass of all the axions. And they're not glowing. They're not giving off any light. There's no fusion happening in.

inside of them, but they're not black, right? Light can escape them. So there's no event horizon, but they're sort of like transparent. In fact, they're more like transparent holes than black holes. It's weird to think that a hole is transparent because aren't all holes transparent? Technically. I suppose that it would be a non-weird hole for once. They would be essentially invisible, but they would distort the light around them. So it's sort of like just seeing a big lens in the sky. It would look a lot like dark matter. Dark matter you can't see visually, but you can detect that it's there because of its gravity. And so boson stars would be the same. They would distort space around them, bending the path of light, for example. So you would see gravitational lensing

and all sorts of other weird stuff. But there wouldn't be an event horizon. I see. But wouldn't they wouldn't block or reflect light? Like if I have a bunch of axions there and I shoot a laser beam into it, would the laser beam just shoot right through it? It wouldn't interact with the with the If you shot a laser beam into a boson star, then no, nothing would happen to it would go right through because photons and axions don't interact with each other. For some theories of axioms, there are other versions of axioms where the photons and axioms can interact a bit, but here we're thinking about axions as dark matter with no reaction to photons. The only effect would be gravitational.

If you shot your laser beam sort of near the boson star, it might curve the path of your laser. It would bend your laser. But the axions and the photons as quantum particles don't interact. I see. And would these things need to be huge or could you have a small boson star? We don't know, actually. That's a great question. I think they might be really huge.

In fact, there's some speculation that some of the black holes at the center of galaxies might actually just be boson stars. But there's also the possibility that you could make them to be fairly small. In the same way that like black holes, you could make to be really, really, really small. you could also make boson stars in a fairly small helping as long as they were compact enough. All right. Well, so there would be basically transparent planets, kind of. Like could they have planets, other planets, like real planets orbiting around them?

Absolutely, they could. And they might also not be transparent for very long. Because, for example, think about what happens if you toss a banana and a boson star. What happens? Well, it passes through the axions and it falls towards the center because of the gravity. and then it just sort of stays there, right? Like, it would just fall into it and not be able to escape. It has the gravitational pull of something else with the same mass.

And so things would fall into the core of it. It would collect normal matter at its core. It wouldn't like get crushed or anything? Yeah, absolutely. It might get crushed. Your banana might not survive, but it also wouldn't escape. And so if these boson stars are near other matter, then that matter might fall into them and that would be visible.

Oh, you mean like, in the same way that dark matter, for example, kind of helps gather galaxies. Yeah, exactly. And Axion star could help gather bananas. Exactly. The way stars tell us where dark matter is, bananas tell us where both stars are.

Perfect analogy. And that would be super real because you'd see a banana, but it would have like the mass of a black hole. Yeah, exactly. It'd be like the most powerful banana in the universe. And it would attract other bananas. And monkeys also. or his maybe. Yeah. And you would also get other gravitational effects like it might have matter swirling

around it the same way that black holes do. If you have nearby gas, it would get pulled in by the gravitational field, but it doesn't always collapse in, right? Not everything near a black hole automatically falls in because it's spinning. So some things instead of falling in, gather into this accretion disk. And a boson star might also get an accretion disc. And it might have radiation from that accretion disc. And the way that we detect black holes normally is we see like gravitational influence and an accretion disc and like signals from that accretion disc of the incredible gravitational stress. Those are also the signals of a boson star. So how could we tell the difference or is it even possible that black holes are made out of axions or bosons? Like you could

throw bosons into a black hole and it would grow too, right? Yeah, you can throw anything into a black hole and you can make a black hole out of anything. So it's possible that black holes have a lot of bosons or axions in them, certainly. How could you tell the difference between a black hole and a boson star? You'd have to look really directly at it because a boson star doesn't have an event horizon. So for example, when we directly imaged that black hole and we saw the shadow of the black hole, we saw the back of the event horizon and the front of it inside the accretion disk, that's pretty clearly not a boson star because there's a black spot in the middle.

But if you looked at one of these things directly and you didn't see the black spot, if you saw gas all the way through it, then you think, oh, that's probably a boson star. All right. Well, then how could we see these hypothetical boson stars if they exist? There are two ways. One is direct imaging of them, right? Just look at black hole candidates and see if you can see the event horizon. If you can't, then it might be a boson star. There's another way, which is maybe easier because directly imaging black holes is hard. You know, we've been working on it for a long time and only done it for one. and that's it looking at the gravitational waves. Gravitational waves are generated from spinning black holes or from things moving around black holes like neutron stars and stuff like that.

So because there's a slightly different structure in the field because bosons have a different distribution than like a singularity, the heart of a black hole is a slightly different pattern in the gravitational waves. So you might be able to detect the difference. There's some recent paper is talking about like exactly how to look for gravitational waves that come from boson star collisions rather than black hole collision. So this is an imaginary event featuring two imaginary objects made out of an imaginary particle. Made out of a lot of imaginary particles, yes, exactly.

I feel like now we're going deeper into the rabbit hole here. We're being incepted to like level four. And there's even level five inception there, which is like, how do these things get made in the first place? even if axions are real, even if all the laws of physics work the way we talk about so that if you put axions in the same place, they would make a boson star, are there conditions in our universe for that to happen? Should it arise? So it's not like easy to imagine how you would make that many axions. Really, you got to go all the way back to the big bang and say, maybe during the big bang there was some crazy fluctuation and these things got made primordially and like before most particles were made. where maybe even early black holes were made, that you got these weird collections of bosons created quantum mechanically during the Big Bang, and those are the seeds of current boson stars. Because I guess you can't think of any circumstances right now in our universe

in which you could get that many bosons. That's right, yeah. And then maybe, Daniel, we're just imaginary, imagining these imaginary things. My brain feels like it's filled with bananas sometimes. Which might be imaginary themselves if they weren't so delicious. Good thing, physics is so easy, right? All right, well, so that's a boson star, and that's pretty interesting. And now, are there people looking for these right now?

Is this something that people are taking seriously, or is it still kind of in the back of the conference room there? It's definitely in the back of the conference room, but there are also some people taking it very seriously, which is sort of the way in physics. You got like the mainstream stuff people are working on, and then you got the people thinking in the back of the room going, hmm, what about this other weird thing? And sometimes those ideas are right. I'm really glad that in science we're open to all sorts of crazy ideas. And there are definitely people dedicated to this topic, you know, running detailed

simulations of what boson stars would look like and trying to understand like the plasma loops that might form around them and how you would see those signals and gravitational wave detectors of the future. So it's definitely something people are thinking about. And how many of those can you fit into a clown car? Or how many of them are willing to get into one for the sake of physics? That's philosophy. That's philosophy.

man. That's not science. I see. That's the other imaginary science. Or maybe it's psychology. I don't know. All right. Well, it's always interesting to think about what could be out there in the universe, you know? Like we have all these rules. And if you sort of think about those rules enough, you sort of come up with these weird things that may or may not exist. Yeah. And it could be that we are in the era before the discovery of boson stars when people are just thinking about what could be out there in the universe. So if you are a budding astronomer or astrophysicist And you're thinking, hmm, the universe has all been discovered.

There is still plenty of crazy stuff out there for you to find. Yeah, because at some point even things like black holes in dark matter, they were all imaginary back of the conference room rumors, right? Absolutely. These are now just Nobel Prizes waiting to be won. Well, we hope you enjoyed that. And the next time you look out into the star, think about what you're not seeing that could be out there,

sucking bananas and turning them into smoothies. Thanks for joining us. 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. Every case that is a cold case that has DNA right now in a backlog will be identified in our lifetime. On the new podcast, America's Crime Lab, every case has a story to tell. And the DNA holds the truth. He never thought he was going to get caught. And I just looked at my computer screen. I was just like, gotcha. This technology's already solving so many cases. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation, you're not going to choose an adaptive strategy, which is more effortful to use, unless you think there's a good outcome. Avoidance is easier. Ignoring is easier. Denials is easier. Complex problem solving. takes effort. Listen to the psychology podcast on the IHeart radio app, Apple Podcasts, or wherever you get your podcasts. Hi, it's Honey German, and I'm back with season two of my podcast. Grazias, come again.

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