Daniel and Jorge Explain the UniverseDaniel and Jorge talk about whether its possible to have stars made out of bosons!
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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 bourbon kind, or the other kind of gas, any kind of gas, like kind of 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 starman out of laughing gas.
That would be pretty funny.
I am more handmade cartoonist and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle physicist and I'm no kind of star, but I but you're a gas I try to make people laugh.
Well. Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we try to gass 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 hypotheesis.
Well, fortunately we have better ways of exploring the universe than just faith. We have science, and science encourages us to think creative, but then ask ourselves questions like, hmmm, how do we know that's true? And how could we approve 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 into the universe with a new kind of telescope and we see something totally weird that 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 no 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, is 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. The 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 dwarfs 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 weirder, stranger kinds of stars we haven't even scratched the surface of.
Yeah, so is this the weirdest star? Daniel epis in our Extreme series?
This is the most hypotheticalist star.
I see, I see the most imaginative star. Maybe the most bunkers is the 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, 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 of button when they discovered the Higgs boson.
Right, That would be me. Yes, I'm a star of 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 and front of you, and so yeah, sometimes you actually get to press a button.
Yeah, did you press any buttons? 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 to the large Hadron collider when they first turned it on, very early on. It was two thousand and eight, 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 controller room that you have to hit in the case of an emergency. And I'd 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 one hundred percent of 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 with tea.
But yeah, we're asking the 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.
Thermo dynamic 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 surgeons 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 bolk 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 two questions at Danielanjorge dot com.
All right, well here's what people had to say.
No idea, God, the clowns of the star.
Do you know there's bosons and fermions. Those are two types of particles. I think one adds up to a different charge than the other. It so maybe a Boson star is just a start, just completely made out of bosons. That's my best guess.
I thought we were done with boson. We have found a Figgs boson then, and that's it. Moving on no O 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 to give off a lot of bosons, and I'm gonna have to back up a few podcasts 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?
A lot? Actually a lot. You can tell me 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 fifteen seconds. So thanks everybody for your great ideas.
Yeah, well there are a lot of good ideas here. Some people are saying there are 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 meetings, and the meetings 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 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 of 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 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 on 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 and can either spin one half up or spin one half down. So fermions all have these half integer spin 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, your a 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 and 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 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't fill up a room with 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. We've done really interesting experiments that we talked about in the podcast, like the bos 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, and then is a star made out of bosons or that gives off the bosons.
Yeah, a boson star is a star made out of bosons. 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 are like the most famous kind of boson. But think about it's sort of how hard it is to make a star. You can't just make a star add 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's 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. Though. In most stars you have fusion and gravity imbalance, and other stars that aren't burning, like white dwarfs, you have other weirder stuff happening. But then 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, yeah, 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, and 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 all together 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 got a huge pile I love 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?
I mean, I 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.
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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 get a bunch of bosons together? Like, do they have masks? Would gravity bring them together? Or do you need to capture them somehow or you know, lure them with big shoes and red noses? How do we bring them together.
Really comically sized cookies? I think, And that just pulled the ball in. No, that's a fair question. You know. 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?
It?
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's outward pressure. So I have gravity. You need to have these objects having some appreciable mass, right, You need to have gravity 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 of a handle to pull it together.
Right. Well, But isn't in 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, That has to be a balance or 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 masks.
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. They got to scratch them off. We also need a particle that's stable. We don't want our Boson star to decay instantaneous 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 quarks 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 Hig star, and also a W star or a Z star. W's and zs are the bosons associated with the weak nuclear force, and they're also very massive, and they decay very quickly. Z's decay into a pair of quarks. W's dek 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, a particle made out of just glue, 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 particle, which boson particle could we used 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 we're 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 axion is, And by folks, I mean including myself.
Well, an axion is named after a detergent because it was thought up by Frank Wilcheck and he was doing his grocery shopping while he was thinking about the and there's a detergent called axion. He thought, ooh, that's a cool name. So the axion particle is one that was thought 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 have been charged think a little more broadly, dig deeper into that bag of hypothetical particles to find other things. And the idea that the axion 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 it must have 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 ament 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 are a boson and they have a little bit of mass and they are stable.
Hey did I tell you that Frank will Chick retweeted me the other day or mentioned being a tweet.
I didn't know that. I didn't even know he tweeted it. Yeah.
I felt like an action star my cell 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 bunch together by gravity.
Yeah, that's the requirements to be the dark matter, right. You need to have mass otherwise you're not explaining 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 axions 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've talked on this podcast before about the definition of a star versus a planet, and a star is defined to be something that has fusion happening at its core. Here though, unfortunately we're gonna 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? That if you get a whole bunch of axions together, then gravity would keep them in a ball of axions like a sphere of axioms. But 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 and the electron, the gravitational force between them is basically zero, but should compared to the other forces. But if you have a lot of axions near each other, then yeah, you're gonna have a lot of mass and that will make a gravitationally bound system. And so you could get a huge sorting 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? Right? Remember, a star is to have two conditions. 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 holes 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 dwarfs 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 repel each other, or protons or you know.
Balls of dirty or neutrons.
Yeah, I like to make a planet, but bosons they can't 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're exactly right that the reason a neutron star and a white dwarf don't collapse into a black hole is because of the fermi 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. Right, 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 you have too 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 charge 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 axions.
If I have two photo in the same spot, don't they just become a bigger photon or are they still technically two photon?
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 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 axions might repel each other and then form that outward pressure to keep the axion 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.
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All right, 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 or may not exist. I feel like we're stacking imaginaries here. Do imaginary concepts exclude each other? Daniel, do they add up? We're so confused. Can they merge?
These bunkers concepts are all bosons, so we can have an infinite number of bunkersness.
I see, they don't exclude each other, so you can just stack them.
Infinitely exactly until we get a boso star.
All right, Well, let's say that the axion does exist, and let's say that you could somewhere out there and get them all together enough to make some sort of axion object. It still doesn't tell me how that makes it a star, Like, why isn't wouldn't be called an axion planet or an axion you know?
Ball, Well, if you were around when they were deciding on the name of these things, then that would have been a good idea axion 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 using 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 that is it In physics. There are no standards for being a star. Anyone can be a star. It's like our society today. If you need an Instagram.
Account, yeah, or famous parents. Yeah, being a physicist is easy, snow, 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, he.
Said, yeah, exactly, as you trying 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 action planet ball 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 have a similar sort of structure too, black holes, right, or a more massive black hole then 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. 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 the it's the uncertainty the principle that keeps them kind of from collapsing. Can you have an uncertainty principle the size of a planet, like that's a big ball of un.
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 riding 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 inn photons also be stacked like that. Does the unsertainty 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 of 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 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, So 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 are 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, right, there's no fusion happening 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 being seeing a big lens in the sky. It would look a lot like dark matter.
Right.
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, Like like if I have a bunch of axions there and I shoot a laser beam into it, would laser beam just shoot right through it. It wouldn't interact with the with the axions.
If you shot a laser beam into a Boson star, then no, nothing would happen. It would go right through because photons and axions don't interact with each other. For some theories of axions. There are other versions of axions where the photons and axions 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 Bosone 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 be really really really small, you could also make Boson stars and it's 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 galaxy. Yeah, exactly, an accion star could help gather bananas.
Exactly the way stars tell us where dark matter is, bananas tell us where bonon stars are.
Perfect analogy and that would be super weird because you'd see a banana, but it would have like the mass of a black hole. Yeah, exactly, like the most powerful banana in the universe.
And it would attract other bananas.
And monkeys also and whoorhes 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 disc. And a Boson star might also get an accretion disc, and it might have radiation from that accretion disk. 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 disk of 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 actons or bosons? Like you could throw bozzons 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 image that black hole and we saw the shadow of the black hole, we saw the back of the event horizon in 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 w 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 of 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 papers talking about, like exactly how to look for gravitational waves that come from boson star collisions rather than black hole collisions.
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 think 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, out of 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 axiom 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 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, when 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 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. I mean, you got the people thinking in the back of the room, going what about this other weird thing? And sometimes those ideas are right. I'm really glad that in science were 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 were just thinking about what could be out there in the universe. So if you are a budding astronomer or astrophysicists and you're thinking 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're all imaginary back of the conference room rumors.
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 listen, and remember that. Daniel and Jorge Explain the Universe is a production of iHeartRadio. Or more podcasts from iHeartRadio visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth. You're probably not thinking about the environmental impact, but the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is us dairy tackling greenhouse gases? Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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