Daniel and Jorge Explain the UniverseDaniel and Jorge explore the enduring mystery of how much heavy metal sits in our Sun.
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Look, I get it.
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Hey, hooray, how's your dad band going?
Uh?
Pretty good? Yeah, we're getting better. It's a lot of fun, didn't you? Guys have some clever name sort of We call ourselves the Grateful Dads.
And is that the kind of music you play? Psychedelic sixties rock or are you more like alternative or metal?
We play a little bit of everything you know, Eighties music, nineties rock, some Marvin Gaye, some Pink Floyd, a little bit of.
All right, So then the physicist in me wants to know how metal are you guys?
I would say we're Les and Iron Maiden, maybe more than the Doobie Brothers.
That sounds like it leaves a lot of uncertainty.
That's for sure. We always try to rocket. Hi. I'm horam and Cartoonez and the author of Oliver's Great Big Universe.
Hi. I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I like music with all different kinds of metal.
You mean, like the instruments or like the genre.
The genre? You know, a little heavy metal, little light metal? Is light metal even a thing?
Mmm? I think some of these heavy metal groups have saw songs. Does that still count as metal?
I'm not even going to weigh in on that.
Yeah, we don't want to anger those metal people. They're pretty intense. But anyways, Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we attempt to understand everything in the universe, from the tiny quantum particles to the amazing shiny metals that make up our universe. We want to know how everything in the universe functions we want to know what its smallest bits are and how they come together to explain everything in our amazing, crazy, delicious and bonkers universe.
That's right, because the universe is made out of all kinds of things, and in this podcast we'd like to explore all of it and to figure out what it's all made out of, how it's all put together, and what makes things the way they are.
How you can go from quantum particles to dad bands in passive or marching bands in New Mexico, the only kind of band I've ever been in.
And did you play metal or did you play a metal instrument?
Not even I played the totally unhearable instrument, the clarinet. Oh, you can only hear the clarinet in the marching band if you're literally in the middle of the clarinet section. Otherwise it's just trumpets.
But the clarinet is made out of metal, isn't it? Or is that one of the woodwinds.
It's a woodwind, though there are metal bits of course to operate the holes.
And what kind of music did you guys play?
Oh? You know, we played marching band versions of all your greatest.
Hits, including metal songs.
Including metal songs. Absolutely, there's a marching band version of every song you love and we ruin it.
Well, maybe you should start a band with physicists.
What would we call it?
I don't know what would you call it?
Maybe some Higgs Boson reference. We make everything heavy.
How about you too have mass?
That's pretty good?
Or how about the clash of particles?
All right, now, I just need some musical talents that I'm all set.
How about the doov Boson brothers?
All right? I think we're good on band names.
But yeah, it is interesting to think about all the things that the stuff in the universe is made out of, right, it.
Is really interesting. It's fascinating to understand how all that stuff got made and how it comes together to make our universe, because even the tiniest little bits of metal here and there are required, absolutely essential for the universe to operate the way that it does.
Yeah, Because the universe, I guess, is made out of all kinds of things, gases, solids, liquids, metals, non metals, acids, bases, There's all kinds of ways that you can categorize the stuff that stuff is made out of, right.
Yeah, absolutely, And though it's all made out of the same fundamental bits. You take quarks and you mix them together to make protons and neutrons, you add electrons. Those few little ingredients can make all kinds of things out there in the universe, with all kinds of different behaviors. Some of them conduct electricity, some of them don't. Some of them are strong, some of them are brittle, some of them are soft, Some of them interact, and some of them don't. It's incredible the variety of stuff you can make with just a few basic bits.
Some of the stuff is soft rock, some of it is classical physics, some of it is heavy metals.
Literally, with the same instruments, you can make any kind of.
Music, and with the same kinds of particles, you can make everything that you see out there in the universe, all the different kinds of stuff out there. And sometimes it's kind of surprising all the different kinds of things that we're made out of, right, Like, we're not just made out of carbon and the basic building blocks, but there's a bunch of weird things that it turns out are sort of essential to our living. Right. Our bodies need copper.
Yeah, and oxygen, for example, and all sorts of bits to take advantage of the clever tricks of chemistry to communicate information along our nerves. To capture oxygen in our red blood cells, you need all sorts of elements. So it's wonderful that these things exist out there in the universe, that they've been somehow manufactured through physics in order to shape our existence.
Now, some of us have more or less metal inside of us, right, I mean, I grew up in the eighties and so my teeth are full of metals, all kinds of metals in there. Absolutely got some lead grills.
And some of us probably played with mercury as a kid, and so we have more or less mercury in us.
Yeah, did you play with mercury? I play with mercury all the time, which probably maybe explains a lot.
That's why you're in a heavy metal band now, Yeah.
Yeah, that's why I'm so mercuriers. But yeah, it kind of makes you wonder what else the stuff out there in the universe is made out of. You know, even our planet I'm sure is mostly iron and rocks and silica. But the stuff out there in space, what is that made out of?
Yeah, most of the stuff in the solar system is not us or even the Earth. An overwhelming fraction of the Solar system is basically just the Sun. And of course the Sun is crucial to life on Earth and the operation of the Solar system. So it's in our interest to understand, like, hey, what's in the sun, because that affects how long it's gonna last and how it behaves.
And so today on the podcast, we'll be tackling the question how much metal is in the sun, not how much metal is the sun?
How metal is the sun? If it had a dad band, what would it.
Play well, would probably play a lot of songs about the Sun. You know, here comes the Sun, you are my Sunshine.
It's opening has to be here comes the Sun. Absolutely, that's its walk on music. For sure, that's their theme music.
Who would the son be in a band with Jupiter, I guess or other sons?
It might outshine Jupiter, yeah, yeah.
Or maybe it's a solo act. Can you be a solo metal act?
Probably you'd have to because nobody wants to be in the Sun's shadow.
I think if you're next to the Sun, you're definitely not in the shadow.
I know. I love how that joke makes no.
Sense I'm trying to save it there. But no, you know, I'm finding the loss of physics here, Daniel.
No, I was going for maximum nonsense.
M right, right, was on purpose. There's very metal of you. If he has shouted it out, it would be even more metal.
This is a really fascinating topic to me because I love mysteries in our own neighborhood. You know, we wonder about what's going on at the edge of the universe or the beginning of time. But gosh darn it, we haven't even figured out what our own solar system is made out of.
We live in it, but we don't know kind of what's in it, what's it all made out of. But it's kind of an interesting question because you're particularly asking how much metal is in the sun, not like what is the sun made out of? Because I guess most of the sun is just one thing, right.
Yeah, the Sun is mostly hydrogen and a little bit of helium, and what you call the rest is kind of up for debate. I cringe to inform you that it depends on your definition of metal, because in astronomy, metal is anything but hydrogen or helium.
Right. I was going to mention that, like what exactly do you mean by metal? Because the metal means different things to different people, right, yeah, exactly, I feel like to us or to the everyday person, a metal is something that shiny and hard conducts electricity. Now is that wrong?
No, it's totally reasonable to think metals are things that are metallic that have those properties, right, And that's how chemists, for example, use the word metal. But astronomers think about things differently.
Wait wait, wait, so is there an official definition of metal by chemists that's different than the definition of metals by physicists.
Well, by astronomers in particular, because the condensed matter physicists would agree with the chemists because they're sort of almost on the chemistry side of physics. But astronomers, Wow, that's their own community, and you know, they got their issues with naming stuff. There's fights about everything.
M Okay. So then if we're asking how much metal is in the sun, what are we asking like how much non helium and hydrogen is in the sun? Or are we asking how much metallic shining stuff is in the sun?
Well, I want to know everything about what's in the sun, like how much iron is there anyway? And where did it come? From how could iron get into the sun? But we don't even know very well the answer to the more basic question, which is how much non hydrogen and helium is there in the sun? How much astronomy metal is in the sun?
Oh okay, so we're really asking the question how much of the sun is not hydrogen or helium?
Yeah? Exactly?
Can we ask later how much of the sun is the shiny metallic stuff?
I mean, you're very mercurious, so you're allowed to ask anything.
A mercurious What you said mercurious?
Yeah?
Is that like a merman, but like a curious merman?
Well, you know, I guess you can be bi curious, you can be mercurious. You know, I don't know what that means. I'll let you figure that out. You just want to dive into everything?
Yeah, I want to know it all, but only for a short amount of time. But anyways, how much metal is in the sun? That's an interesting question. How did you come up with this question?
Well? I was reading some paper is about the mysteries of how much metal is in the sun. I thought it was fascinating that we still don't know the answer to this pretty basic question that influences like the most important thing in our neighborhood.
Mmm.
Interesting, And I think also like what's in the sun sort of affects the kind of light that we get from the sun, right, Like you can tell what kinds of things are inside of a star by looking at its light.
And it has really cosmic consequences because we use the Sun to calibrate our understanding of what's in the rest of the universe, and the amount of metal in stars controls their fate, like whether they'll collapse into a black hole or not, and also how likely they are to have planets around them. And so if we revise our understanding of what's in the sun, it could change our understanding of what's out there in the universe, how long it will last, and the likelihood that there could be aliens. So yeah, in the end, it always connects to aliens.
Where did that come from? Is this just a big excuse to talk about aliens again?
That's what this whole podcast is. Are you just figuring that out?
Yeah, a little bit. Yeah, that we were explaining the universe.
It's just a fun for talking about aliens.
I see, this is all just deployed to what prepares us subconsciously for the imminent arrival of aliens or the big reveal that you are an alien.
No comment.
Yeah, that's very suspicious, all right. So, as usual, we were wondering how many people out there had thought about this question and about the amount of metal in the sun.
Thanks very much to everybody who answers these questions. I love hearing your thoughts on the question of the day, so please don't be shy. If you would like to contribute, write to me two questions at Danielanjorge dot com and I'll get you on the air.
So think about it for a second. How much metal do you think is in the sun. Here's what people have to say.
I think the heavier elements only come out during supernovas, and so I would have to say no metal in the sun.
I think that nineteen nine percent of the solar systems metals allocated in the Sun itself. But with regards to the makeup of the Sun, I think that only about eight percent.
Of it is metal.
The rest of it is gas.
Most it is fine, I want to guess, not very much right now, like less than one percent. But as the Sun grows older, maybe the amount of metal in the core will increase until the mass becomes so great that the light cannot escape, and then the sun will turn black.
If we measured that diameter of the outer core, I would assume that the metal is like less than like ten percent of like the diameter with But I feel like it's a trick question because don't cosmologists say anything above helium as a metal, so this might be a true question. I'm going to go ninety eight percent metal.
The Sun is totally metal, but I think if we're talking about actual composition, there is not all that much. I'm going to guess that the Sun has a little bit of metal, like maybe one or two percent of its total composition, but that's actually considered a lot compared to other stars, and that the stars that came before the Sun had even less metal.
All Right, I like the person who said the sun is totally metal.
The sun has a good attitude. I think that's what he means.
Yeah, well it is pretty hot, I guess intense.
Yeah, it's just not back down. Yeah, it just keeps rocking on and on.
Yeah, and it eventually burns up. So that kind of fits the heavy metal rock star trope.
Flaming out as a pretty metal thing to do.
Yeah, all right, well, Daniel, maybe start with the basics. How does a star even get metal in it? Because, as we all know, stars are made out of hydrogen, helium or hydrogen initially, right, all stars, or at least the original stars were made out of hydrogen.
Yeah, it's a cool question. Stars can get metal in them in two ways. One is that they can be formed with metal in them. Stars come from a collapse of a big cloud of like gas and dust and other bits. So there's metal in the neighborhood. When the star collapses, then that metal will become part of the star. But that depends, as you were alluding to, on what's what's been made? Has something else out there made metal? And the only way that we know to make metal is in the hearts of stars. So the second way that stars can get metal in them is they can make metal. They confuse hydrogen and helium together to make heavier stuff, producing metal.
I meaning like when a star was formed and it gathered all the gas to become a star, maybe there were metals floating around where all this stuff was and that's how metal got inside the star. But were the first stars made out of pure hydrogen or did the universe makes the metal at the Big Bang?
Yeah, great question. So about a millions of a second after the sort of primordial goo, things were expanding and cooling, and you got quarks forming into protons and neutrons, and protons are hydrogen. So basically the first thing that was made was hydrogen. Because protons form, then you have a few minutes in which the conditions are ripe for fusion for those protons to bang together and make heavier stuff, And so that's when helium was made. But you only had like three minutes where the universe was in the right conditions to make anything heavier. So you had huge amounts of hydrogen, made a little bit of helium, but almost nothing else. Basically, after the Big Bang, you had vast quantities of hydrogen, trace amounts of helium, and almost nothing else. Basically, no metal was around after the Big Bang.
Although I hear you saying almost, does that mean that there was a little bit of the heavier metals in the universe right after the Big Bang before stars got made.
It's impossible to say that there was none. But it's very hard to make those heavier elements without the density and the time. Using helium together makes something very unstable. If you just start with two helium nuclei, you really need three together to get the carbon, and that's much harder to do without the density that you have in stars and the time to fuse them. So it's possible you made a little tiny bit of carbon after the Big Bang, but it's overwhelmingly hydrogen, a little bit of helium and maybe tiny negligible amounts of carbon m.
So the universe, I guess, was pretty pure hydrogen and helium, and then those started to make stars, and that's when the first metals really came into the universe exactly.
So those first stars were basically metal free, just huge clouds of hydrogen with a little bit of helium in them, and they produced the first metals. Right. They didn't start with really any metal in them at all, but these were huge stars. It turns out if you form stars without any metal in them, you got much bigger globs. And those stars are really big, so they burn really hot and they burn really fast, so they don't last for very long, and then when they die, they spray their metals out into the universe to see the next stars.
Right, And some of them burn and explode and collapse without having used up all of the hydrogen and helium.
Right, Oh, yes, absolutely, stars do not burn all of their hydrogen helium before they end their lives.
So like when those first stars exploded, how much of them was still hydrogen and helium and how much of the heavier metals had they eight?
Yeah, that's a cool question. We can answer that by looking at how much metal is in the next generation of stars, because those little bits of metal are excellent seeds for the next stars. Like, metal is heavier than non metal, it has more protons, and it has more mass. It's denser, so it's more likely to form a seed of another star start that gravitational collapse. So the next generation of stars, the stars we call population two, these are still really really low metal. It's like less than a tenth of one percent of those stars is metal, so it's still overwhelmingly hydrogen and helium even in the second generation of stars.
Whoa so maybe painted picture. So those first stars burned, they collapse, they exploded, and then all that stuff re collapsed again.
Yeah, exactly, but it didn't happen that quickly. Helium floats around for like hundreds of millions of years before the first stars are born. There this period in the early universe called the dark ages, before there was any light in the universe, just these dark clouds of hydrogen and helium. And then those first stars burn for like just a few million years. The larger the star is, the shorter it's life, So those didn't burn for very long. But then the next generation they're a little smaller and they can burn for a very very long time.
Why were they smaller.
The more metal you have in the universe, the more likely it is that a big cloud of gas is going to break up into multiple stars rather than collapsing into one megastar, because you have all these different places for it to seed. Remember that for a star to form, you need sort of special conditions. You need a big cloud of gas, but you need to also be cold enough so that it can collapse, and you need some like gravitational seed to get that runaway effect going. And so if you have a variety of different densities, you're more likely to have smaller clumps than bigger clumps, and those smaller stars tend to burn colder and then they last longer.
So if you have a giant cloud of hydrogen, it doesn't break up as much. It just hangs around until it all condenses into a giant star exactly.
And people might be imagining like that one cloud makes one star, but it's more likely that a huge cloud makes multiple stars all simultaneously. And if that cloud has more metal in it, then you have more seeds for those stars, so you end up with more smaller stars rather than fewer megastars like you did in the first batch.
Okay, so then that's the second generation of stars, right.
Yeah, exactly, And those stars were formed like thirteen fourteen billion years ago, but they burn a long time because they're small, they're redder, they're colder stars. So we can still see some of those stars around in the universe, especially in globular clusters.
Like around us or only far away or further back in time.
They're also in the heart of our galaxy, so population two stars are all around.
Did that generation of stars then they eventually explode and make the next generation of stars?
That definitely happened. It's a little bit misleading to think about these as generations in a sort of crisp sense. It's not like all that first generation died and then there's only the second generation, and there's only the third generation. Every star is formed from remnants of multiple stars, and some of them might have gone through one, two, three, four generations, maybe even more. It depends on the size of those stars. So this categorization is very rough. It's not super precise. It's not like all the stars are in sync. But the latest generation of stars, which are called population one stars formed more recently in the universe, when there's been more time to make metal in the universe. So these we call high metallicity stars, which means they have like between one and four percent metal.
Wait, wait, wait, the third generation of stars is called population one.
Yeah, that's exactly right. Population one are the ones made most recently. Population two is the previous generation. Population three is still somewhat theoretical first generation of stars. And I know the naming system is ridiculous, and I will defend it even for a moment.
What generation is our sun?
Our son we think is a population one star, so it's part of the most recent generation.
All right, Well, then let's get to the question of how much matall is in our star, the Sun, and whether it rocks or not. So let's dig into that But first, let's take a quick break.
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All right, we're asking the question how much metal is in the sun, and by metal we mean elements that are not hydrogen or helium.
Yeah, exactly. We want to know how much oxygen, carbon, neon, hydrogen, sulfur, iron, all that stuff all added up. That's even like the first most basic question you want to know, like how much of that heavier stuff is in the sun. And then of course we want to know the proportions also, But we first need to nail down the initial question.
Well, why do you think astronomers call everything not hydrogen and helium? Metals because they couldn't come up with another name, or is there rationale there? Like I would think metals maybe in chemistry has the connotation that it conducts electricity or is shining. So what's the astronomer's excuse.
Well, I think there is this division between hydrogen helium, of which there's so much in the universe, and everything else, and so you really need another category. I don't know if metal was the right way to describe it, but there definitely are two different categories. There really is hydrogen helium and all the other stuff in the universe.
So it's more of a name just given by population or abundancy.
Also, this is the stuff produced by Star, so it's sort of like the output of Star. It doesn't have to do as much with like the chemical properties or the behaviors or the appearance the way it does in chemistry. It's more about the abundance in the universe and how it was made.
All right, So then the latest generation of Star has about one point four to four percent metals, Yeah.
Exactly, And so there's a variation there, like depending on where you were when you were formed, and also whether you can make metals inside you. There's a pretty big spread, and how much metal there is in stars. On the other hand, most stars still hydrogen helium. Like, we've been burning hydrogen for fourteen billion years. We've hardly made a dent in the fraction of the universe that is hydrogen.
You mean our star or in the universe in general.
The universe in general, you know, the universe is still mostly hydrogen. Like ninety two percent of the universe right now is hydrogen.
So like our star right now is burning hydrogen. Were you saying, like the amount of hydrogen it's burning or fusing together is super tiny tiny.
I'm saying, we've been burning for fourteen billion years and we've hardly made a dent. Yeah, stars are the universe's mechanism for like turning light stuff like hydrogen into heavier stuff. And you might think, wow, we've been burning for a long time. We must have plowed through it all. But there's still vast, vast quantities of hydrogen out there.
Now, Why is that just because there's so much hydrogen and helium in the sun, But really the part is fusing, it's only at the very tiny center of it. Or why isn't it burning up faster?
The reason you suggest, it is totally accurate. Like fusion happens mostly at the core where things are dense and things are hot, at least in the initial stages. Then when the core of the sun fills with ash or fills with heavier metals than the sun confused, then the fusion moves outwards. But also remember fusion is hard. Even if you have an enormous pile of hydrogen you squeeze it to the right pressure and density and temperature, it's not like all the hydrogen is instantly just going to fuse into helium. You need a lot of hydrogen and a lot of time to get any fusion happening. So it's a very low probability thing, which is why you need an enormous pile a very high temperature, high density gas to get any event to happen.
All right, So then that's kind of the general picture. But what about our sun? How much of our sun is still hydrogen and helium and how much of it is badly named metals.
So about twenty years ago we thought we had this settled. We had studied the sun and looked at the light that comes from the sun, the spectrum of it, like how much red light is there, how much green light, how much blue light, and use that to try to figure out what was in the sun, And we thought we had it nailed down. We thought the answer was about one point eight percent metal.
Meaning like if you look at the light from the sun, the spectrum of the light from the sun sort of can tell you what the Sun is made out of, or we thought it could.
Yeah, exactly. The Sun is really fascinating because, on one hand, a lot of the light comes from just the Sun being hot. Everything out there in the universe that's made of charged particles will glow based on its temperature, and the hotter things are, the higher energy to photons it will be released. So a lot of the light from the Sun is what we call just black body radiation, something hot giving off light the way like I give off light and you give off light. We don't give off light in the visible spectrum the way the Sun does, because we're not white hot the way the Sun is. But that's where a lot of the light from the Sun comes from.
Where does the other light come from?
The other light comes from specific atoms in the sun emitting light or absorbing that light. So I feel like an oxygen atom in the atmosphere of the Sun, and it gets hot, its electrons jump up a couple of energy levels, then they jump down, they relax, and they emit a photon, and that photon it's very specific energy. It corresponds to the difference in the energy levels of that electron around the oxygen atom. Every atom out there can emit an absorb light in very specific wavelengths. So if you look at the spectrum from the Sun, this says overall black body radiation. Then these spikes where certain atoms are emitting light that correspond to their energy levels and their dips where other atoms are absorbing light that's produced by the Sun at the energy levels that they can do it. So you look at all those wiggles in the spectrum and you can tell what's in the sun, or.
At least it seems like we thought we could. So we did that for our sun, and we thought it had a certain amount of metals in it. But then what happened.
So people thought, Okay, that's cool, one point eight percent, that makes total sense. But then people thought, well, let's cross check it. Let's see if we can measure what's in the sun using another technique and come up with the same answer. Another way to figure out what's in the sun is to watch it boil, is to like look for waves in the surface of the sun, because that tells you like how thick the sun is, the viscosity of the sun, which depends on what's in there, what's sort of mucking around?
Wait, what what do you mean, Like as you look at the surface of the Sun, you see it churning. It's like super hot plasma, right mm hmm, And the way the plasma churns tells you how goopy it is.
Yeah, they call it helio seismology, and it's sort of similar to the way you can use earthquakes to understand what the Earth is made out of. Like an earthquake shake the earth, and then that shaking travels through the Earth and it reflects at boundaries. Like that's how we know where that boundary is between various layers of the Earth. We can also deduce things about like what's there because how it bounces and reflects depends on the relative density of things at those layers. So just by measuring earthquakes at the surface, you can get a pretty good picture for what's in the earth. In the same way we can look at ripples on the surface of the sun helio seismology, they call it. To get a picture for what's in the sun.
We don't have earthquake measuring devices on the sun. How do we know the shaking of the surface of the sun.
So we don't need a complete picture of what's in the sun. But we can watch waves move across the surface of the sun. You know, we have a lot of telescopes that can look at the Sun and they can see the behavior and the churning on the surface, and there's a lot of stuff going on there. But we only need a sort of rough picture of what's in the sun because it turns out this one very particular thing that's controlled by the metals that we're trying to get a sense of. It's a balance between two processes that are trying to move the heat out of the sun. The sun has sort of two parts to it. It's like the outermost part and the innermost part. And the innermost part a lot of heat is being created it's radiating out, so that radiation comes out from the core and hits the outer part of the sun. But that outer part can be kind of opaque because of like oxygen or heavy elements can absorb those photons, so that means that that energy can't be radiated out from the core of the Sun. Instead, you need to get that energy out using another method we call convection, basically just like hot stuff rising up the way it does in a pot of water. So there's sort of two parts to the Sun, one where photons can bring the energy out and the other where you have to rely on convection. Then there's a boundary between these two regions, and that depends a lot on how much oxygen is there in the Sun, and that's what we're trying to measure with this helio seismology. We're trying to figure out like where's the threshold between these two parts of the inside of the sun.
And we do this by just looking at the flow that you can see in the picture of the sun. Or do we have like an X ray way to look inside the sun.
No, we have no X ray. Unfortunately, it's just effectively sound waves in the sun. Right of course, nobody's hearing these things. When we say sound waves, we just mean pressure waves moving through the sun. But just the same way that earthquakes make effectively sound waves through the Earth, and you can listen to the Earth ringing just by seeing the Earth shake. If we watch the surface of the Sun, we don't have like instruments on the surface that measure the actual shaking, but you can see these ripples in the plasma on the surface. You can effectively see sound moving through the Sun and bouncing back. And this boundary between the two parts of the Sun, one that's opaque to photons and one that isn't shows up as like a glitch in the sound waves. It changes how those sound waves move through the Sun.
Well, wait, are you saying there's sort of like two kinds of sun surfaces.
Yeah, there's like a surface within the surface, the same way that like the Earth has multiple layers to it, you know, mantle and the outer core and the inner core, et cetera. The Sun also has these regions, and there's this boundary they think it's like seventy ish percent of the solar radius. Within that photons can like fly free and you have this radiative transfer where photons can move heat out from the center. The outer part is more opake and photons can't really get through it. It's the only way to get heat out from the Sun. There is more like convection, like hot gas rising up.
But then what are you basically saying that looking at these soundwaves tells us a different number for what the Sun is made out of exactly.
Looking at the sound waves tells us something about where this balance is between the two different parts of the Sun, and that depends on how much metal is in the Sun. Because the metallicity of the Sun controls whether it's opaque or transparent. You have more oxygen, more carbon, more neon. That makes the Sun more opaque, which changes how far the photons can get. So if we can use sound waves on the surface of the Sun figure out where is this transition within the Sun between opaque and transparent to these photons, then we could figure out how much metal is in the Sun because the metallicity controls where that transition is.
But then why do metals make the sun more apake.
These heavy elements like oxygen, they like to absorb these photons.
Like more than hydrogen.
Yeah, more than hydrogen. You know, every atom likes to absorb photons of a certain energy, and so the kinds of energy that tend to be produced in fusion tend to also be the kind that oxygen likes to gobble up, for example. So if you do all these calculations, you figure out, well, where is this threshold, where's the sun become opaque inside of it? And what does that mean about the amount of metal inside the sun? You get a different number. So from helio seismology, from these sound waves, we get the number one point eight percent. Whereas we look at the spectrum of light from the sun, we got the number one point three percent. So we thought, oh, this would be a great way to cross check and to just make sure we understand what's in the sun. And then it turns out, oops, the numbers don't agree.
Now is that do you think maybe because looking at the spectrum of the sun only kind maybe tells you what's in the surface as the sun.
It is possible, but they've accounted for that. They have models for where these things are distributed in the sun and how much they would radiate. So there are definitely questions there and things people are trying to drill down on, but they do think they've accounted for that.
But the second one of the ways seems a little a bit more circumspect. I guess or more indirect than actually just looking at the light from the sun.
It does in the end, we're always just getting information from far away and using that to try to infer what's going on and what's happening here is something I love in science. It's like, well, let's cross check our understanding by seeing if we could do this two different ways, making different assumptions, or probing our model in different ways to see whether it breaks. And this kind of detailed work has led to crazy discoveries in the past. You know, when we, for example, predicted how many neutrinos would be coming from the Sun versus how many newtrinos we saw from the sun, and we saw a huge difference. That led to understanding neutrino oscillations and neutrino masses. So not every way is going to be as precise, but it's important different ways to cross check each other and to try to get some hints about what's really going on inside the sun.
Well, it sounds like we've measured how much metal is in the sun in two different ways and they disagree by a pretty big amount, And so let's get into what the difference means, who's right, who's wrong, and how metal is the sun. So let's stick into that, But first, let's take another quick break.
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All right, we're asking how much metal is in the sun, and it sounds like we have two answers. One way, by looking at the light from the sun to els is that it's one point three percent non hydrogen and helium. But looking at the flow of the plasma and how the sound waste travel across the service of the Sun, that tells us that maybe the sun is one point eight percent non hydrogen and helium. So who's right and who's wrong.
We don't know yet, But we have a third answer. People came up with yet another way to try to figure out how much metal is in the sun, just asking the sun. Nobody thought of that. Oh my gosh. You know, if the Sun really isn't a rock band, it's gonna love doing interviews. But this third way actually does use neutrinos, because fusion at the heart of the sun produces vast, vast quantities of neutrinos, these tiny, little ghostly particles that are everwhere, but we can't feel them. Because they only have weak interactions. They have no electric charge, they have no strong force charge. They're very difficult to spot. But we have technologies neutrino eyeballs we've invented to be able to pick out a few of these neutrinos. We can also measure the energy of those neutrinos. And the neutrinos are produced by fusion in the sun, and how much metal you have in the sun affects the rate at which that fusion happens and also affects the energy of the neutrinos that's produced. We're trying to fuse protons and protons together. If there's a bunch of heavy metal around that actually interferes with the fusion, makes it less likely, it makes it more important to have higher energy on those protons, et cetera. So the neutrino energy spectrum you expect depends on how much metal is in the sun, but it's a bit of a weak effect. It's not a very strong way to measure this quantity.
Well, also, what do you compare it to, like, how do you know what the right amount of neutrinos should be for a certain amount of metals?
Yeah, great question. We have a really detailed model of the fusion and how it produces neutrinos, and that's been the subject of decades of study. And of course first there were big mysteries. We predicted a huge amount of neutrinos, we only saw a third of them. Later we discovered that's because those neutrinos are changing into a another kind of neutrino as they travel through space. Check out our episode on neutrino oscillation if you want to understand that more. But yeah, there are definitely uncertainties there. These are models we have of how the diffusion is happening and how the neutrinos are being created, So we don't have an absolute calibration of that either. We just have these calculations we've done that predict the spectrum. And then those calculations depend also on the metal. So you tweak the metals up, you get one spectrum. You tweak the metals down, you get another spectrum. So we can tweak the amount of metals we put into these calculations to match what we see, and then we think, well, that's the most likely value of the metal in the sun.
So then what does this neutrino method say about the metals in the sun.
So unfortunately this method isn't super precise. It slightly favors the higher metal scenario, so like one point eight percent, but it can't rule out the one point three percent. It's just sort of more like a hint. It's a little bit of a vote towards heavy metals.
So then we have three competing methods and they all say something slightly different. How are we going to figure out which.
We're going to dig in and question all of our assumptions, understand where we might have overlooked something. We're going to do more experiments, collect more data, these neutrino experiments. Specifically, this is sort of like the first run, the first gasp of the data. As that runs longer and longer, a little bit more and more precise and maybe sharpen our understanding. But this is really crucial that we figure this out because the Sun is sort of like our yardstick for the rest of the universe. For other stars, we have no hope. But like looking at sound waves on the surface, we can only look at the light from those stars, and we compare the light from those stars to the light we get from the Sun, and we use that to infer what's in them. Our whole estimate for what's out there in the universe is based on what's in the sun. If we were wrong about what's in the sun, then we were wrong about the whole universe.
Well, unless it turns out that these other ways to measure what's in the sun are wrong, and maybe the one that you can't apply to other stars is right.
Yeah, absolutely, it could be or it could be that we don't understand what's inside the sun and how this all works, and they're wrong. Either way, we'd love to understand better what's in the sun because it helps us understand what's out there in the universe. It also really helps us understand the fate of all of those stars. Even though the stars are mostly not metal, those metals can really influence whether those stars have planets around them, how long those stars will live, and how they will die.
Ooh wait, what's the connection between the metals in the star and their planets?
I knew you wanted to talk about aliens.
Right, No, no, I just ask about the planets. I had to say anything about aliens. Don't project your alien fetish on me.
Man, Who do you think is living on those planets.
Man, nobody maybe alg plants, heavy metal bands. Nobody said anything about aliens Daniels.
All right, well I'm about to okay, get ready. Well, the more metal there is in the initial cloud that forms that solar system, the more metal there's going to be for making planets, And the more metal there is, the more likely you are to seed something that's not just the star. You have this huge collapsing cloud. Why doesn't it all just become a star? If some little seed near the star can form fast enough to make its own little gravitational well, it can gather up a bunch of stuff and get into orbit and avoid collapsing into the star. Do that you need a little density seed. And so stars with more metal in them tend to have more planets around them as well, rocky planets and giant planets.
We think, or we know this for sure, like we measured this out there.
We've measured this out there because we've seen planets around other stars, and so we've seen this correlation. Stars whose light indicates more metal in them also tend to have more planets around them.
So there's a correlation between metlicity and number of planets.
Potentially, no that's something we've measured. Of course, we have a bias view of all the planets out there. We can't see all the kinds of planets. We're not great at seeing some kinds of planets. We can only see planets under certain conditions, et cetera, et cetera. So this is sort of an initial thing, but it's a correlation that we've noticed and also one that makes sense. Right, it fits in with our model for householders systems form.
All right, well, I guess how are we going to figure out what's in our sun?
Then?
Is there going to be a conclusive proof at some point? Like are we going to be able to maybe dip into the sun and get a scoop of it?
That would be awesome. We were thinking about sending your band over to visit the sun. Are you guys available? Who's your agent?
Well, it depends how much are you paying and.
What's the budget.
Will there be green eminems in the green room?
I thought it was brown Eminem's in the green room?
Well, I mean, I think the whole point is that we get to choose what kind of amms are in the waiting room.
All right, we'll work on the budget, but it's not something that we are likely to figure out directly. It's always going to be a game of improving our models, comparing the model's predictions to what we see out there in the universe, and then seeing if we get it to tell a coherence story.
Could we send something into the sun, like have something fall into the Sun and acid falls and gets destroyed and maybe tells us what's in the.
Sun potentially with some technological advances. As I know, you know, our recent Parkers solar probe got pretty close to the Sun but almost got toasted. It's very difficult to even get that close to the Sun, and it was nowhere near being able to actually sample something. On the other hand, we're sort of already in the Sun in one sense, because where is the edge of the Sun. The Sun starts out very dense and like gets more and more dilute. Then it's got this huge extended corona and the wind. So we're already sort of sampling stuff from the Sun. So it's possible that like the solar wind itself might have clues we can use to figure out what's in the Sun. The energy of those particles could potentially be sensitive to the metallicity of the Sun.
Well, it's kind of interesting that, like, we only have one star close to us to be able to run these experiments and verify our models of what goes on in any star, and so we're sort of hoping that our sun is not super atypical or weird.
Yeah, exactly, And we know that our star is unusual in some sense. It's more massive than your typical star. Most of the stars out there are red dwarfs, but it's also in the sort of unusually good position to sample the average kind of stuff in the Milky Way. We're like halfway from the Milky Way center to the edge of the disc of stars, and most stars out there in the universe are in big galaxies like the Milky Way. So the Sun is sort of a scoop of typical material, we think. So understanding what's in the Sun will really help us understand what's in the universe.
And how heavy metal aliens might be. Isn't that the whole point of this episode, Daniel.
Yes, exactly. We were just working up to that one joke the whole time, all right.
Well, another example of how there are still big mytories even in our own heart of the Solar system, the Sun, we sort of don't really know what it's actually made out of, and even though it's so close, we can actually go in there and figure it out ourselves directly. We have to find all these clever ways to infer what's inside the Sun, and.
These basic questions about what's in our own backyard affect the whole universe. They tell us what's likely to be out there in the universe and also how it all will end. Stars with more metal in them are more likely to form neutron stars rather than black holes, and so the fate of all those stars we see up there in the night sky could depend on these measurements of what's in our backyard.
We hope you enjoyed that. Thanks for joining us. See you next tent.
For more science and curiosity, come find us on social media where we answer questions and post videos. We're on Twitter, Discord, Instant, and now TikTok. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth. You're probably not thinking about the iron mental impact, but the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's last sustainability to learn more.
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