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How metallic is the Sun? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, or Hey, how's your dad band going?
• 0:11
  Speaker 2: Uh? Pretty good? Yeah, we're getting better. It's a lot
• 0:13
  Speaker 2: of fun, didn't you guys have some clever name, sort
• 0:16
  Speaker 2: of clever. We call ourselves the Grateful Dads.
• 0:18
  Speaker 1: And is that the kind of music you play? Psychedelic
• 0:21
  Speaker 1: sixties rock or are you more like alternative or metal?
• 0:24
  Speaker 2: We play a little bit of everything, you know, Eighties music,
• 0:27
  Speaker 2: nineties rock, some Marvin Gaye, some Pink Floyd, a little bit.
• 0:32
  Speaker 1: Of all right. So then the physicist in me wants
• 0:35
  Speaker 1: to know how metal are you guys?
• 0:37
  Speaker 2: I would say we're less and Iron Maiden, maybe more
• 0:41
  Speaker 2: than the Doobie Brothers.
• 0:45
  Speaker 1: That sounds like it leaves a lot of uncertainty.
• 0:47
  Speaker 2: That's for sure. We always try to rocket.
• 1:06
  Speaker 1: Hi.
• 1:06
  Speaker 2: I'm Horem and Cartoonez and the author of Oliver's Great
• 1:09
  Speaker 2: Big Universe.
• 1:10
  Speaker 1: Hi. I'm Daniel. I'm a particle physicist and a professor
• 1:12
  Speaker 1: at UC Irvine, and I like music with all different
• 1:15
  Speaker 1: kinds of metal.
• 1:16
  Speaker 2: You mean, like the instruments or like the genre the genre?
• 1:20
  Speaker 1: You know, A little heavy metal, little light metal? Is
• 1:22
  Speaker 1: light metal even a thing?
• 1:24
  Speaker 2: M I think some of these heavy metal groups have
• 1:27
  Speaker 2: saw songs. Does that still count as metal.
• 1:31
  Speaker 1: I'm not even going to weigh in on that.
• 1:34
  Speaker 2: Yeah, we don't want to anger those metal people. M
• 1:36
  Speaker 2: they're pretty intense. But anyways, Welcome to our podcast Daniel
• 1:39
  Speaker 2: and Jorge Explain the Universe, a production of iHeartRadio.
• 1:43
  Speaker 1: In which we attempt to understand everything in the universe,
• 1:46
  Speaker 1: from the tiny quantum particles to the amazing shiny metals
• 1:49
  Speaker 1: that make up our universe. We want to know how
• 1:52
  Speaker 1: everything in the universe functions. We want to know what
• 1:55
  Speaker 1: its smallest bits are and how they come together to
• 1:57
  Speaker 1: explain everything in our amazing, crazy, delicious and bonkers universe.
• 2:02
  Speaker 2: That's right, because the universe is made out of all
• 2:04
  Speaker 2: kinds of things, and in this podcast we'd like to
• 2:06
  Speaker 2: explore all of it and to figure out what it's
• 2:08
  Speaker 2: all made out of, how it's all put together, and
• 2:10
  Speaker 2: what makes things the way they are.
• 2:12
  Speaker 1: How you can go from quantum particles to dad bands
• 2:15
  Speaker 1: in Pasadena or marching bands in New Mexico. The only
• 2:19
  Speaker 1: kind of band I've ever been in.
• 2:22
  Speaker 2: And did you play metal or did you play a
• 2:24
  Speaker 2: metal instrument?
• 2:25
  Speaker 1: Not even I played the totally unhearable instrument, the clarinet. Oh,
• 2:29
  Speaker 1: you can only hear the clarinet in the marching band
• 2:31
  Speaker 1: if you're literally in the middle of the clarinet section.
• 2:34
  Speaker 1: Otherwise it's just trumpets.
• 2:35
  Speaker 2: But the clarinet is made out of metal, isn't it?
• 2:37
  Speaker 2: Or is that one of the woodwinds.
• 2:39
  Speaker 1: It's a woodwind, though there are metal bits of course
• 2:42
  Speaker 1: to operate the holes.
• 2:44
  Speaker 2: And what kind of music did you guys play?
• 2:45
  Speaker 1: Oh? You know, we played marching band versions of all
• 2:48
  Speaker 1: your greatest.
• 2:48
  Speaker 2: Hits, including metal songs, including metal songs.
• 2:52
  Speaker 1: Absolutely, there's a marching band version of every song you love,
• 2:56
  Speaker 1: and we ruin it.
• 3:00
  Speaker 2: Maybe you should start a band with physicists.
• 3:02
  Speaker 1: What would we call it?
• 3:03
  Speaker 2: I don't know what would you call it?
• 3:04
  Speaker 1: Maybe some Higgs Boson reference. We make everything heavy?
• 3:07
  Speaker 2: How about you too have mass?
• 3:10
  Speaker 1: That's pretty good?
• 3:12
  Speaker 2: Or how about the clash of particles?
• 3:16
  Speaker 1: All right, now, I just need some musical talents that
• 3:18
  Speaker 1: I'm all set.
• 3:21
  Speaker 2: How about the doov Boson brothers?
• 3:25
  Speaker 1: All right? I think we're good on band names.
• 3:28
  Speaker 2: But yeah, it is interesting to think about all the
• 3:30
  Speaker 2: things that the stuff in the universe is made out of, right.
• 3:32
  Speaker 1: It is really interesting. It's fascinating to understand how all
• 3:35
  Speaker 1: that stuff got made and how it comes together to
• 3:38
  Speaker 1: make our universe, because even the tiniest little bits of
• 3:41
  Speaker 1: metal here and there are required, absolutely essential for the
• 3:45
  Speaker 1: universe to operate the way that it does.
• 3:47
  Speaker 2: Yeah, Because the universe, I guess, is made out of
• 3:49
  Speaker 2: all kinds of things, gases, solids, liquids, metals, non metals, acids, bases.
• 3:54
  Speaker 2: There's all kinds of ways that you can categorize the
• 3:57
  Speaker 2: stuff that stuff is made out of, right.
• 3:59
  Speaker 1: Yeah, absolutely, And though it's all made out of the
• 4:01
  Speaker 1: same fundamental bits. You take quarks and you mix them
• 4:04
  Speaker 1: together to make protons and neutrons, you add electrons. Those
• 4:08
  Speaker 1: few little ingredients can make all kinds of things out
• 4:10
  Speaker 1: there in the universe, with all kinds of different behaviors.
• 4:13
  Speaker 1: Some of them conduct electricity, some of them don't. Some
• 4:16
  Speaker 1: of them are strong, some of them are brittle, some
• 4:18
  Speaker 1: of them are soft, some of them interact, and some
• 4:20
  Speaker 1: of them don't. It's incredible the variety of stuff you
• 4:22
  Speaker 1: can make with just a few basic bits.
• 4:25
  Speaker 2: Some of the stuff is soft rock, some of it
• 4:27
  Speaker 2: is classical physics, some of it is heavy metals.
• 4:31
  Speaker 1: Literally, with the same instruments, you can make any kind
• 4:34
  Speaker 1: of music.
• 4:34
  Speaker 2: And with the same kinds of particles. You can make
• 4:37
  Speaker 2: everything that you see out there in the universe, all
• 4:40
  Speaker 2: the different kinds of stuff out there, And sometimes it's
• 4:42
  Speaker 2: kind of surprising all the different kinds of things that
• 4:44
  Speaker 2: we're made out of, right, Like, we're not just made
• 4:46
  Speaker 2: out of carbon and the basic building blocks, but there's
• 4:49
  Speaker 2: a bunch of weird things that it turns out are
• 4:52
  Speaker 2: sort of essential to our living. Right. Our bodies need copper.
• 4:55
  Speaker 1: Yeah, and oxygen for example, and all sorts of bits
• 4:59
  Speaker 1: to take advantage of the clever tricks of chemistry to
• 5:02
  Speaker 1: communicate information along our nerves. To capture oxygen in our
• 5:06
  Speaker 1: red blood cells, you need all sorts of elements. So
• 5:09
  Speaker 1: it's wonderful that these things exist out there in the universe,
• 5:11
  Speaker 1: that they've been somehow manufactured through physics in order to
• 5:15
  Speaker 1: shape our existence.
• 5:17
  Speaker 2: Now, some of us have more or less metal inside
• 5:19
  Speaker 2: of us, right, I mean, I grew up in the eighties,
• 5:22
  Speaker 2: and so my teeth are full of metals, all kinds
• 5:27
  Speaker 2: of metals in there. Absolutely, you got some lead grills.
• 5:30
  Speaker 1: And some of us probably played with mercury as a kid,
• 5:33
  Speaker 1: and so we have more or less mercury in us.
• 5:35
  Speaker 2: Yeah, did you play with Mercury. I play with Mercury
• 5:38
  Speaker 2: all the time, which probably maybe explains a lot.
• 5:42
  Speaker 1: That's why you're in a heavy metal band now, Yeah.
• 5:44
  Speaker 2: Yeah, that's why I'm so Mercuriers. But yeah, it kind
• 5:48
  Speaker 2: of makes you wonder what else the stuff out there
• 5:51
  Speaker 2: in the universe is made out of. You know, even
• 5:53
  Speaker 2: our planet I'm sure is mostly iron and rocks and silica.
• 5:58
  Speaker 2: But the stuff out there in space, what is that
• 6:00
  Speaker 2: made out of?
• 6:01
  Speaker 1: Yeah? Most of the stuff in the Solar System is
• 6:03
  Speaker 1: not us or even the Earth. An overwhelming fraction of
• 6:07
  Speaker 1: the Solar System is basically just the Sun. And of
• 6:10
  Speaker 1: course the Sun is crucial to life on Earth and
• 6:13
  Speaker 1: the operation of the Solar system. So it's in our
• 6:16
  Speaker 1: interest to understand, like, hey, what's in the sun because
• 6:19
  Speaker 1: that affects how long it's going to last and how
• 6:21
  Speaker 1: it behaves.
• 6:22
  Speaker 2: And so today on the podcast, we'll be tackling the
• 6:24
  Speaker 2: question how much metal is in the sun, not how
• 6:33
  Speaker 2: much metal is the sun?
• 6:35
  Speaker 1: How metal is the sun? If it had a dad band,
• 6:39
  Speaker 1: what would it play?
• 6:40
  Speaker 2: Well, we probably play a lot of songs about the sun.
• 6:43
  Speaker 2: You know, here comes the Sun, you are my sunshine.
• 6:47
  Speaker 1: It's opening has to be. Here comes the Sun. Absolutely,
• 6:50
  Speaker 1: that's its walk on music. For sure, that's their theme music.
• 6:53
  Speaker 2: Who would the son being a band with Jupiter, I guess,
• 6:56
  Speaker 2: or other suns?
• 6:57
  Speaker 1: It might outshine Jupiter.
• 6:59
  Speaker 2: Yeah, or maybe it's a solo act. Can you be
• 7:03
  Speaker 2: a solo metal act?
• 7:04
  Speaker 1: Probably you'd have to because nobody wants to be in
• 7:06
  Speaker 1: the Sun's shadow.
• 7:08
  Speaker 2: I think if you're next to the Sun, you're definitely
• 7:11
  Speaker 2: not in the shadow.
• 7:13
  Speaker 1: I know. I love how that joke made no sense.
• 7:16
  Speaker 2: Yeah, I'm trying to save it there, but no, you know,
• 7:20
  Speaker 2: I'm finding the loss of physics here.
• 7:22
  Speaker 1: Daniel, No, I was going for maximum nonsense.
• 7:25
  Speaker 2: Hmm, right, right, was on purpose. There's very metal of you.
• 7:29
  Speaker 2: If he has shouted it out, it would be even
• 7:31
  Speaker 2: more metal.
• 7:33
  Speaker 1: This is a really fascinating topic to me because I
• 7:36
  Speaker 1: love mysteries in our own neighborhood. You know, we wonder
• 7:39
  Speaker 1: about what's going on at the edge of the universe
• 7:41
  Speaker 1: or the beginning of time. But gosh darn it, we
• 7:43
  Speaker 1: haven't even figured out what our own solar system is
• 7:46
  Speaker 1: made out of.
• 7:47
  Speaker 2: We live in it, but we don't know kind of
• 7:48
  Speaker 2: what's in it, what's it all made out of? But
• 7:50
  Speaker 2: it's kind of an interesting question because you're particularly asking
• 7:54
  Speaker 2: how much metal is in the sun, not like what
• 7:56
  Speaker 2: is the sun made out of? Because I guess most
• 7:59
  Speaker 2: of the sun is just one thing, right.
• 8:01
  Speaker 1: Yeah, the sun is mostly hydrogen and a little bit
• 8:04
  Speaker 1: of helium, and what you call the rest is kind
• 8:07
  Speaker 1: of up for debate. I cringe to inform you that
• 8:09
  Speaker 1: it depends on your definition of metal, because in astronomy,
• 8:14
  Speaker 1: metal is anything but hydrogen or helium.
• 8:17
  Speaker 2: Right. I was going to mention that, like, what exactly
• 8:20
  Speaker 2: do you mean by metal? Because the metal means different
• 8:22
  Speaker 2: things to different people, right, yeah, exactly. I feel like
• 8:25
  Speaker 2: to us or to the everyday person, a metal is
• 8:28
  Speaker 2: something that's shiny and hard conducts electricity. Now is that wrong?
• 8:33
  Speaker 1: No, It's totally reasonable to think metals are things that
• 8:36
  Speaker 1: are metallic that have those properties, right, And that's how chemists,
• 8:40
  Speaker 1: for example, use the word metal, But astronomers think about
• 8:44
  Speaker 1: things differently.
• 8:45
  Speaker 2: Wait wait, wait, so is there an official definition of
• 8:47
  Speaker 2: metal by chemists that's different than the definition of metals
• 8:51
  Speaker 2: by physicists.
• 8:52
  Speaker 1: Well, by astronomers in particular, because the condensed matter physicists
• 8:56
  Speaker 1: would agree with the chemists because they're sort of almost
• 8:58
  Speaker 1: on the chemistry side physics. But astronomers, Wow, that's their
• 9:02
  Speaker 1: own community, and you know they got their issues with
• 9:04
  Speaker 1: naming stuff. There's fights about everything.
• 9:06
  Speaker 2: M okay. So then if we're asking how much metal
• 9:10
  Speaker 2: is in the sun, what are we asking like how
• 9:12
  Speaker 2: much non helium and hydrogen is in the sun? Or
• 9:14
  Speaker 2: are we asking how much metallic shining stuff is in
• 9:17
  Speaker 2: the sun?
• 9:18
  Speaker 3: Well?
• 9:18
  Speaker 1: I want to know everything about what's in the sun,
• 9:20
  Speaker 1: like how much iron is there anywhere? And where did
• 9:22
  Speaker 1: it come from? How could iron get into the sun?
• 9:25
  Speaker 1: But we don't even know very well the answer to
• 9:26
  Speaker 1: the more basic question, which is how much non hydrogen
• 9:30
  Speaker 1: and helium is there in the sun? How much astronomy
• 9:32
  Speaker 1: metal is in the sun.
• 9:33
  Speaker 2: Oh okay, so we're really asking the question how much
• 9:36
  Speaker 2: of the sun is not hydrogen or helium?
• 9:38
  Speaker 1: Yeah? Exactly.
• 9:39
  Speaker 2: Can we ask later how much of the sun is
• 9:41
  Speaker 2: the shining metallic stuff.
• 9:43
  Speaker 1: I mean, you're very mercurious, so you're allowed to ask anything.
• 9:46
  Speaker 2: A mercurious said mercurious?
• 9:49
  Speaker 1: Yeah?
• 9:50
  Speaker 2: Is that like a merman? But like a curious merman?
• 9:54
  Speaker 1: Well, you know, I guess you can be bi curious,
• 9:56
  Speaker 1: you can be mercurious. You know, I don't know what
• 9:58
  Speaker 1: that means. I'll let you figure that out. You just
• 10:01
  Speaker 1: want to dive into everything.
• 10:04
  Speaker 2: Yeah, I want to know it at all, but only
• 10:06
  Speaker 2: for a short amount of time. But anyways, how much
• 10:10
  Speaker 2: metal is in the sun, that's an interesting question. How
• 10:13
  Speaker 2: did you come up with this question?
• 10:15
  Speaker 1: Well, I was reading some papers about the mysteries of
• 10:17
  Speaker 1: how much metal is in the sun. I thought it
• 10:19
  Speaker 1: was fascinating that we still don't know the answer to
• 10:22
  Speaker 1: this pretty basic question that influences like the most important
• 10:25
  Speaker 1: thing in our neighborhood.
• 10:27
  Speaker 3: Hmmm.
• 10:27
  Speaker 2: Interesting, And I think also like what's in the sun
• 10:30
  Speaker 2: sort of affects the kind of light that we get
• 10:33
  Speaker 2: from the sun, right, Like you can tell what kinds
• 10:35
  Speaker 2: of things are inside of a star by looking at
• 10:38
  Speaker 2: its light.
• 10:39
  Speaker 1: And it has really cosmic consequences because we use the
• 10:42
  Speaker 1: Sun to calibrate our understanding of what's in the rest
• 10:45
  Speaker 1: of the universe, and the amount of metal in stars
• 10:48
  Speaker 1: controls their fate, like whether they'll collapse into a black
• 10:51
  Speaker 1: hole or not, and also how likely they are to
• 10:54
  Speaker 1: have planets around them. And so if we revise our
• 10:57
  Speaker 1: understanding of what's in the sun, it could change our
• 10:59
  Speaker 1: understand of what's out there in the universe, how long
• 11:02
  Speaker 1: it will last, and the likelihood that there could be aliens.
• 11:06
  Speaker 1: So yeah, in the end, it always connects to aliens.
• 11:09
  Speaker 2: Where did that come from? Is this just a big
• 11:14
  Speaker 2: excuse to talk about aliens again?
• 11:16
  Speaker 1: That's what this whole podcast is. Are you just figuring
• 11:18
  Speaker 1: that out?
• 11:20
  Speaker 2: Yeah, a little bit. Yeah, that we were explaining the universe.
• 11:24
  Speaker 1: It's just a fun for talking about aliens.
• 11:26
  Speaker 2: I see. This is all just a ployed to what
• 11:29
  Speaker 2: prepares us subconsciously for the imminent arrival of aliens or
• 11:34
  Speaker 2: the big reveal that you are an alien?
• 11:36
  Speaker 1: No comment.
• 11:38
  Speaker 2: Yeah, that's very suspicious, all right. So, as usual, we
• 11:42
  Speaker 2: were wondering how many people out there had thought about
• 11:44
  Speaker 2: this question and about the amount of metal in the sun.
• 11:48
  Speaker 1: Thanks very much to everybody who answers these questions. I
• 11:50
  Speaker 1: love hearing your thoughts on the question of the day,
• 11:53
  Speaker 1: so please don't be shy. If you would like to contribute,
• 11:56
  Speaker 1: write to me two questions at Daniel and Jorge dot
• 11:58
  Speaker 1: com and I'll get you on the air.
• 12:00
  Speaker 2: So think about it for a second. How much metal
• 12:02
  Speaker 2: do you think is in the sun. Here's what be
• 12:04
  Speaker 2: bled to say.
• 12:05
  Speaker 1: I think the heavier elements only come out during supernova's
• 12:08
  Speaker 1: and so I would have to say no metal in
• 12:11
  Speaker 1: the Sun.
• 12:11
  Speaker 2: I think that nineteen nine percent of the Solar System's
• 12:14
  Speaker 2: metals allocated in the Sun itself. But with regards to
• 12:17
  Speaker 2: the makeup of the Sun, I think that only about
• 12:19
  Speaker 2: eight percent of it is metal. The rest of it
• 12:21
  Speaker 2: is gas.
• 12:22
  Speaker 1: Most of it is fine.
• 12:24
  Speaker 3: I want to guess not very much right now, like
• 12:27
  Speaker 3: less than one percent. But as the Sun grows older,
• 12:31
  Speaker 3: maybe the amount of metal in the core will increase
• 12:33
  Speaker 3: until the mass becomes so great that the light cannot escape,
• 12:37
  Speaker 3: and then the Sun will turn black.
• 12:39
  Speaker 4: If we measured that diameter of the outer core, I
• 12:42
  Speaker 4: would assume that the metal is like less than like
• 12:44
  Speaker 4: ten percent of like the diameter with But I feel
• 12:48
  Speaker 4: like it's a truck question because don't cosmologists say anything
• 12:51
  Speaker 4: above helium as a metal, so this might be a
• 12:53
  Speaker 4: true question. I'm going to go ninety eight percent metal.
• 12:56
  Speaker 5: The Sun is totally metal, but I think if we're
• 12:58
  Speaker 5: talking about actual companies, there's not all that much. I'm
• 13:02
  Speaker 5: going to guess that the Sun has a little bit
• 13:03
  Speaker 5: of metal, like maybe one or two percent of its
• 13:06
  Speaker 5: total composition, but that's actually considered a lot compared to
• 13:10
  Speaker 5: other stars, and that the stars that came before the
• 13:12
  Speaker 5: sun had even less metal.
• 13:14
  Speaker 2: All right, Like the person who said the sun is
• 13:16
  Speaker 2: totally metal.
• 13:20
  Speaker 1: The sun has a good attitude. I think that's what
• 13:22
  Speaker 1: he means.
• 13:23
  Speaker 2: Yeah, well it is pretty hot, I guess intense.
• 13:27
  Speaker 1: Yeah, it's just not back down. Yeah, it just keeps
• 13:31
  Speaker 1: rocking on and on.
• 13:33
  Speaker 2: Yeah, and it eventually burns up. So that kind of
• 13:36
  Speaker 2: fits the heavy metal rock star.
• 13:39
  Speaker 1: Trope, flaming out as a pretty metal thing to do.
• 13:42
  Speaker 2: Yeah, all right, well, Daniel, maybe start with the basics.
• 13:44
  Speaker 2: How does a star even get metal in it? Because,
• 13:48
  Speaker 2: as we all know, stars are made out of hydrogen,
• 13:52
  Speaker 2: helium or hydrogen initially, right, all stars, or at least
• 13:55
  Speaker 2: the original stars were made out of hydrogen.
• 13:57
  Speaker 1: Yeah, it's a cool question. Stars can get metal in
• 14:00
  Speaker 1: them in two ways. One is that they can be
• 14:02
  Speaker 1: formed with metal in them. Stars come from a collapse
• 14:05
  Speaker 1: of a big cloud of like gas and dust and
• 14:07
  Speaker 1: other bits, So there's metal in the neighborhood. When the
• 14:09
  Speaker 1: star collapses, then that metal will become part of the star.
• 14:13
  Speaker 1: But that depends, as you were alluding to, on what's
• 14:16
  Speaker 1: around what's been made? Has something else out there? Made metal,
• 14:20
  Speaker 1: And the only way that we know to make metal
• 14:22
  Speaker 1: is in the hearts of stars. So the second way
• 14:24
  Speaker 1: that stars can get metal in them is they can
• 14:26
  Speaker 1: make metal. They confuse hydrogen and helium together to make
• 14:30
  Speaker 1: heavier stuff producing metal.
• 14:32
  Speaker 2: I meaning like when a star was formed and it
• 14:34
  Speaker 2: gathered all the gas to become a star, maybe there
• 14:37
  Speaker 2: were metals floating around where all this stuff was, and
• 14:40
  Speaker 2: that's how metal got inside the star. But were the
• 14:42
  Speaker 2: first stars made out of pure hydrogen or that the
• 14:45
  Speaker 2: universe makes a metal at the Big bang?
• 14:47
  Speaker 1: Yeah, great question. So about millions of a second after
• 14:50
  Speaker 1: the sort of primordial do things were expanding and cooling,
• 14:54
  Speaker 1: and you got quarks forming into protons and neutrons and
• 14:57
  Speaker 1: protons are hydrogen, So basically the first thing that made
• 15:00
  Speaker 1: was hydrogen. Because protons form, then you have a few
• 15:04
  Speaker 1: minutes in which the conditions are ripe for fusion for
• 15:07
  Speaker 1: those protons to bang together and make heavier stuff. And
• 15:10
  Speaker 1: so that's when helium was made. But you only had
• 15:13
  Speaker 1: like three minutes where the universe was in the right
• 15:16
  Speaker 1: conditions to make anything heavier, So you had huge amounts
• 15:20
  Speaker 1: of hydrogen, made a little bit of helium, but almost
• 15:23
  Speaker 1: nothing else. Basically, after the Big Bang, you had vast
• 15:26
  Speaker 1: quantities of hydrogen, trace amounts of helium, and almost nothing else. Basically,
• 15:31
  Speaker 1: no metal was around after the Big Bang.
• 15:34
  Speaker 2: Although I hear you saying almost, does that mean that
• 15:37
  Speaker 2: there was a little bit of the heavier metals in
• 15:41
  Speaker 2: the universe right after the Big Bang before stars got made.
• 15:45
  Speaker 1: It's impossible to say that there was none, But it's
• 15:47
  Speaker 1: very hard to make those heavier elements without the density
• 15:50
  Speaker 1: and the time. Using helium together makes something very unstable.
• 15:54
  Speaker 1: If you just start with two helium nuclei, you really
• 15:56
  Speaker 1: need three together to get the carbon, and that's much
• 15:59
  Speaker 1: harder to do without the density that you have in
• 16:02
  Speaker 1: stars and the time to fuse them. So it's possible
• 16:05
  Speaker 1: you made a little tiny bit of carbon after the
• 16:07
  Speaker 1: Big Bang, but it's overwhelmingly hydrogen, a little bit of helium,
• 16:11
  Speaker 1: and maybe tiny negligible amounts of carbon mm.
• 16:16
  Speaker 2: So the universe, I guess, was pretty pure hydrogen and helium,
• 16:20
  Speaker 2: and then those started to make stars, and that's when
• 16:23
  Speaker 2: the first metals really came into the universe exactly.
• 16:26
  Speaker 1: So those first stars were basically metal free, just huge
• 16:30
  Speaker 1: clouds of hydrogen with a little bit of helium in them,
• 16:33
  Speaker 1: and they produced the first metals. Right, they didn't start
• 16:36
  Speaker 1: with really any metal in them at all, but these
• 16:39
  Speaker 1: were huge stars. Turns out, if you form stars without
• 16:42
  Speaker 1: any metal in them, you get much bigger globs. And
• 16:46
  Speaker 1: those stars are really big, so they burn really hot
• 16:48
  Speaker 1: and they burn really fast, so they don't last for
• 16:51
  Speaker 1: very long. And then when they die, they spray their
• 16:54
  Speaker 1: metals out into the universe to see the next stars.
• 16:57
  Speaker 2: Right, and some of them burn and explode and collapse
• 17:00
  Speaker 2: without having used up all of the hydrogen and helium.
• 17:03
  Speaker 1: Right, Oh, yes, absolutely, stars do not burn all of
• 17:06
  Speaker 1: their hydrogen helium before they end their lives.
• 17:09
  Speaker 2: So like when those first stars exploded, how much of
• 17:11
  Speaker 2: them was still hydrogen and helium and how much of
• 17:14
  Speaker 2: the heavier metals had they made.
• 17:16
  Speaker 1: Yeah, that's a cool question. We can answer that by
• 17:18
  Speaker 1: looking at how much metal is in the next generation
• 17:21
  Speaker 1: of stars, because those little bits of metal are excellent
• 17:24
  Speaker 1: seeds for the next stars. Like, metal is heavier than
• 17:28
  Speaker 1: non metal, it has more protons, and it is more mass,
• 17:30
  Speaker 1: it's denser, so it's more likely to form a seed
• 17:34
  Speaker 1: of another star start that gravitational collapse. So the next
• 17:37
  Speaker 1: generation of stars. The stars were called population two. These
• 17:41
  Speaker 1: are still really really low metal. It's like less than
• 17:43
  Speaker 1: a tenth of one percent of those stars is metal,
• 17:47
  Speaker 1: so it's still overwhelmingly hydrogen and helium. Even in the
• 17:51
  Speaker 1: second generation of stars whoa.
• 17:54
  Speaker 2: So maybe painted pictures. So those first stars burned, they collapse,
• 17:58
  Speaker 2: They exploded, and then all that stuff recollapsed to get.
• 18:02
  Speaker 1: Yeah, exactly, but it didn't happen that quickly. Helium floats
• 18:05
  Speaker 1: around for like hundreds of millions of years before the
• 18:08
  Speaker 1: first stars are born. There's this period in the early
• 18:10
  Speaker 1: universe called the dark Ages, before there was any light
• 18:13
  Speaker 1: in the universe, just these dark clouds of hydrogen and helium.
• 18:17
  Speaker 1: And then those first stars burn for like just a
• 18:19
  Speaker 1: few million years. The larger the star is, the shorter
• 18:22
  Speaker 1: it's life. So those didn't burn for very long. But
• 18:25
  Speaker 1: then the next generation they're a little smaller and they
• 18:28
  Speaker 1: can burn for a very very long time.
• 18:30
  Speaker 2: Why were they smaller.
• 18:31
  Speaker 1: The more metal you have in the universe, the more
• 18:33
  Speaker 1: likely it is that a big cloud of gas is
• 18:35
  Speaker 1: going to break up and do multiple stars rather than
• 18:38
  Speaker 1: collapsing into one megastar, because you have all these different
• 18:41
  Speaker 1: places for it to seed. Remember, that for a star
• 18:44
  Speaker 1: to form, you need sort of special conditions. You need
• 18:47
  Speaker 1: a big cloud of gas, but you need to also
• 18:49
  Speaker 1: be cold enough so that it can collapse, and you
• 18:51
  Speaker 1: need some like gravitational seed to get that runaway effect going.
• 18:56
  Speaker 1: And so if you have a variety of different densities,
• 18:58
  Speaker 1: you're more likely to have smaller clumps than bigger clumps.
• 19:01
  Speaker 1: And those smaller stars tend to burn colder, and then
• 19:04
  Speaker 1: they last longer.
• 19:06
  Speaker 2: So if you have a giant cloud of hydrogen, it
• 19:08
  Speaker 2: doesn't break up as much. It just hangs around until
• 19:12
  Speaker 2: it all condenses into a giant star exactly.
• 19:14
  Speaker 1: And people might be imagining like that one cloud makes
• 19:17
  Speaker 1: one star, but it's more likely that a huge cloud
• 19:20
  Speaker 1: makes multiple stars all simultaneously. And if that cloud has
• 19:24
  Speaker 1: more metal in it, then you have more seeds for
• 19:26
  Speaker 1: those stars, so you end up with more smaller stars
• 19:29
  Speaker 1: rather than fewer megastars like you did in the first batch.
• 19:33
  Speaker 2: Okay, so then that's the second generation of stars, right.
• 19:36
  Speaker 1: Yeah, exactly, And those stars were formed like thirteen fourteen
• 19:40
  Speaker 1: billion years ago, but they burn a long time because
• 19:43
  Speaker 1: they're small, they're redder, they're colder stars. So we can
• 19:46
  Speaker 1: still see some of those stars around in the universe,
• 19:49
  Speaker 1: especially in globular clusters.
• 19:51
  Speaker 2: Like around us or only far away or further back
• 19:55
  Speaker 2: in time.
• 19:55
  Speaker 1: They're also in like the heart of our galaxy. So
• 19:58
  Speaker 1: population two stars are all around.
• 20:00
  Speaker 2: Did that generation of stars then they eventually explode and
• 20:03
  Speaker 2: make the next generation of stars?
• 20:05
  Speaker 1: That definitely happened. It's a little bit misleading to think
• 20:08
  Speaker 1: about these as generations in a sort of crisp sense.
• 20:12
  Speaker 1: It's not like all that first generation died and then
• 20:14
  Speaker 1: there's only the second generation and there's only the third generation.
• 20:17
  Speaker 1: Every star is formed from remnants of multiple stars, and
• 20:20
  Speaker 1: some of them might have gone through one, two, three,
• 20:22
  Speaker 1: four generations, maybe even more. It depends on the size
• 20:26
  Speaker 1: of those stars. So this categorization is very rough. It's
• 20:29
  Speaker 1: not super precise. It's not like all the stars are
• 20:32
  Speaker 1: in sync. But the latest generation of stars, which are
• 20:35
  Speaker 1: called population one stars for more recently in the universe,
• 20:39
  Speaker 1: when there's been more time to make metal in the universe.
• 20:42
  Speaker 1: So these we call high metallicity stars, which means they
• 20:45
  Speaker 1: have like between one and four percent metal.
• 20:48
  Speaker 2: Wait wait, wait, the third generation of stars is called
• 20:50
  Speaker 2: population one.
• 20:52
  Speaker 1: Yeah, that's exactly right. Population one are the ones made
• 20:55
  Speaker 1: most recently. Population two is the previous generation. Population three
• 21:00
  Speaker 1: is still somewhat theoretical first generation of stars. And I
• 21:04
  Speaker 1: know the naming system is ridiculous, and I won't defend
• 21:06
  Speaker 1: it even for a moment.
• 21:07
  Speaker 2: What generation is our sun?
• 21:09
  Speaker 1: Our son we think is a population one star, so
• 21:11
  Speaker 1: it's part of the most recent generation.
• 21:13
  Speaker 2: All right, Well, then let's get to the question of
• 21:15
  Speaker 2: how much metal is in our star, the Sun, and
• 21:19
  Speaker 2: whether it rocks or not. So let's dig into that.
• 21:22
  Speaker 2: But first let's take a quick break. All right, we're
• 21:37
  Speaker 2: asking the question how much metal is in the Sun,
• 21:41
  Speaker 2: and by metal we mean elements that are not hydrogen
• 21:44
  Speaker 2: or helium.
• 21:44
  Speaker 1: Yeah, exactly. We want to know how much oxygen, carbon, neon, nitrogen, sulfur, iron,
• 21:49
  Speaker 1: all that stuff all added up. That's even like the
• 21:52
  Speaker 1: first most basic question you want to know, like how
• 21:54
  Speaker 1: much of that heavier stuff is in the Sun. And
• 21:56
  Speaker 1: then of course we want to know the proportions also,
• 21:59
  Speaker 1: But we first need to nail down the initial question.
• 22:01
  Speaker 2: Well, why do you think astronomers call everything not hygrogen
• 22:05
  Speaker 2: and helium metals because they couldn't come up with another name?
• 22:08
  Speaker 2: Or is there rationale there? Like I would think metals
• 22:12
  Speaker 2: maybe in chemistry has the connotation that it conducts electricity
• 22:16
  Speaker 2: or is shining. So what's the astronomer's excuse.
• 22:20
  Speaker 1: Well, I think there is this division between hydrogen helium,
• 22:23
  Speaker 1: of which there's so much in the universe, and everything else,
• 22:27
  Speaker 1: and so you really need another category. I don't know
• 22:30
  Speaker 1: if metal was the right way to describe it, but
• 22:32
  Speaker 1: there definitely are two different categories. There really is hydrogen
• 22:35
  Speaker 1: helium and all the other stuff in the universe.
• 22:37
  Speaker 2: M So it's more of a name just given by
• 22:40
  Speaker 2: population or abundancy.
• 22:43
  Speaker 1: Also, this is the stuff produced by stars, so it's
• 22:45
  Speaker 1: sort of like the output of stars. It doesn't have
• 22:48
  Speaker 1: to do as much with like the chemical properties or
• 22:50
  Speaker 1: the behaviors or the appearance the way it does in chemistry.
• 22:53
  Speaker 1: It's more about the abundance in the universe and how
• 22:56
  Speaker 1: it was made.
• 22:56
  Speaker 2: All right, So then the latest generation of star has
• 22:59
  Speaker 2: a one point four to four percent metals.
• 23:03
  Speaker 1: Yeah, exactly, And so there's a variation there, like depending
• 23:06
  Speaker 1: on where you were when you were formed, and also
• 23:08
  Speaker 1: whether you can make metals inside you. There's a pretty
• 23:12
  Speaker 1: big spread and how much metal there is in stars.
• 23:15
  Speaker 1: On the other hand, most stars still hydrogen helium. Like,
• 23:18
  Speaker 1: we've been burning hydrogen for fourteen billion years. We've hardly
• 23:22
  Speaker 1: made a dent in the fraction of the universe that
• 23:25
  Speaker 1: is hydrogen.
• 23:26
  Speaker 2: You mean our star or in the universe in general.
• 23:29
  Speaker 1: The universe in general, you know, the universe is still
• 23:33
  Speaker 1: mostly hydrogen. Like ninety two percent of the universe right
• 23:36
  Speaker 1: now is hydrogen.
• 23:37
  Speaker 2: So like our star right now is burning hydrogen. Were
• 23:40
  Speaker 2: you saying, like the amount of hydrogen it's burning or
• 23:43
  Speaker 2: fusing together is super tiny tiny.
• 23:46
  Speaker 1: I'm saying, we've been burning it for fourteen billion years
• 23:48
  Speaker 1: and we've hardly made a dent. Yeah, stars are the
• 23:50
  Speaker 1: universe's mechanism for like turning light stuff like hydrogen into
• 23:55
  Speaker 1: heavier stuff. And you might think, wow, we've been burning
• 23:57
  Speaker 1: for a long time. We must have plowed through it all.
• 23:59
  Speaker 1: But there's still vast, vast quantities of hydrogen out there.
• 24:02
  Speaker 2: Now, Why is that just because there's so much hydrogen
• 24:06
  Speaker 2: and helium in the sun. But really the part that
• 24:08
  Speaker 2: is fusing, it's only at the very tiny center of it.
• 24:11
  Speaker 2: Or why isn't it burning up faster?
• 24:14
  Speaker 1: The reason you suggest it is totally accurate. Like fusion
• 24:16
  Speaker 1: happens mostly at the core where things are dense and
• 24:19
  Speaker 1: things are hot, at least in the initial stages. Then
• 24:22
  Speaker 1: when the core of the sun fills with ash or
• 24:24
  Speaker 1: fills with heavier metals than the sun confuse, then the
• 24:27
  Speaker 1: fusion moves outwards. But also remember fusion is hard. Even
• 24:32
  Speaker 1: if you have an enormous pile of hydrogen you squeeze
• 24:34
  Speaker 1: it to the right pressure and density and temperature, it's
• 24:37
  Speaker 1: not like all the hydrogen is instantly just going to
• 24:39
  Speaker 1: fuse into helium. You need a lot of hydrogen and
• 24:42
  Speaker 1: a lot of time to get any fusion happening. So
• 24:44
  Speaker 1: it's a very low probability thing, which is why you
• 24:47
  Speaker 1: need an enormous pile a very high temperature, high density
• 24:51
  Speaker 1: gas to get any of it to happen.
• 24:53
  Speaker 2: All right, So then that's kind of the general picture.
• 24:55
  Speaker 2: But what about our sun? How much of our sun
• 24:57
  Speaker 2: is still hydrogen and helium and how much it is
• 25:00
  Speaker 2: badly named metals.
• 25:03
  Speaker 1: So about twenty years ago we thought we had this settled.
• 25:07
  Speaker 1: We had studied the sun and looked at the light
• 25:09
  Speaker 1: that comes from the sun, the spectrum of it, like
• 25:10
  Speaker 1: how much red light is there, how much green light,
• 25:12
  Speaker 1: how much blue light, and use that to try to
• 25:15
  Speaker 1: figure out what was in the sun, and we thought
• 25:17
  Speaker 1: we had it nailed down. We thought the answer was
• 25:19
  Speaker 1: about one point eight percent metal.
• 25:22
  Speaker 2: Meaning like if you look at the light from the Sun,
• 25:25
  Speaker 2: the spectrum of the light from the Sun sort of
• 25:27
  Speaker 2: can tell you what the Sun is made out of,
• 25:29
  Speaker 2: or we thought it could.
• 25:30
  Speaker 1: Yeah, exactly. The Sun is really fascinating because, on one hand,
• 25:33
  Speaker 1: a lot of the light comes from just the Sun
• 25:35
  Speaker 1: being hot. Everything out there in the universe that's made
• 25:38
  Speaker 1: of charged particles will glow based on its temperature, and
• 25:41
  Speaker 1: the hotter things are, the higher energy the photons it
• 25:44
  Speaker 1: will be released. So a lot of the light from
• 25:46
  Speaker 1: the Sun is what we call just black body radiation,
• 25:49
  Speaker 1: something hot giving off light the way like I give
• 25:51
  Speaker 1: off light and you give off light. We don't give
• 25:53
  Speaker 1: off light in the visible spectrum the way the Sun
• 25:56
  Speaker 1: does because we're not white hot the way the Sun is.
• 25:59
  Speaker 1: But that's where a lot of the light from the
• 26:00
  Speaker 1: Sun comes from.
• 26:01
  Speaker 2: Where does the other light come from.
• 26:03
  Speaker 1: The other light comes from specific atoms in the Sun
• 26:05
  Speaker 1: emitting light or absorbing that light. So I feel like
• 26:09
  Speaker 1: an oxygen atom in the atmosphere of the Sun and
• 26:11
  Speaker 1: it gets hot, its electrons jump up a couple of
• 26:14
  Speaker 1: energy levels, then they jump down, they relax, and they
• 26:16
  Speaker 1: emit a photon, and that photon it's very specific energy.
• 26:20
  Speaker 1: It corresponds to the difference in the energy levels of
• 26:24
  Speaker 1: that electron around the oxygen atom. Every atom out there
• 26:27
  Speaker 1: can emit an absorbed light in very specific wavelengths. So
• 26:31
  Speaker 1: if you look at the spectrum from the Sun, there's
• 26:33
  Speaker 1: this overall black body radiation, then these spikes where certain
• 26:37
  Speaker 1: atoms are emitting light that correspond to their energy levels
• 26:41
  Speaker 1: and their dips where other atoms are absorbing light that's
• 26:44
  Speaker 1: produced by the Sun at the energy levels that they
• 26:47
  Speaker 1: can do it. So you look at all those wiggles
• 26:49
  Speaker 1: in the spectrum and you can tell what's in the sun, or.
• 26:52
  Speaker 2: At least it seems like we thought we could. So
• 26:54
  Speaker 2: we did that for our sun, and we thought it
• 26:56
  Speaker 2: had a certain amount of metals in it. But then
• 26:58
  Speaker 2: what happened.
• 27:00
  Speaker 1: I thought, Okay, that's cool, one point eight percent. That
• 27:02
  Speaker 1: makes total sense. But then people thought, well, let's cross
• 27:04
  Speaker 1: check it. Let's see if we can measure what's in
• 27:07
  Speaker 1: the sun using another technique and come up with the
• 27:09
  Speaker 1: same answer. Another way to figure out what's in the
• 27:12
  Speaker 1: sun is to watch it boil is to like look
• 27:15
  Speaker 1: for waves in the surface of the Sun because that
• 27:18
  Speaker 1: tells you like how thick the sun is, the viscosity
• 27:21
  Speaker 1: of the Sun, which depends on what's in there, what's
• 27:24
  Speaker 1: sort of mucking around?
• 27:26
  Speaker 2: Wait, what what do you mean? Like as you look
• 27:27
  Speaker 2: at the surface of the Sun, you see it churning.
• 27:30
  Speaker 2: It's like super hot plasma, right mm hmm. And the
• 27:33
  Speaker 2: way the plasma churns tells you how goopy it is.
• 27:37
  Speaker 1: Yeah. They call it helio seismology, and it's sort of
• 27:41
  Speaker 1: similar to the way you can use earthquakes to understand
• 27:44
  Speaker 1: what the Earth is made out of. Like an earthquake
• 27:47
  Speaker 1: shakes the Earth, and then that shaking travels through the
• 27:49
  Speaker 1: Earth and it reflects at boundaries. Like that's how we
• 27:53
  Speaker 1: know where that boundary is between various layers of the Earth,
• 27:56
  Speaker 1: And we can also deduce things about like what's there
• 27:58
  Speaker 1: because how it bounces and reflects depends on the relative
• 28:01
  Speaker 1: density of things at those layers. So just by measuring
• 28:05
  Speaker 1: earthquakes at the surface, you can get a pretty good
• 28:07
  Speaker 1: picture for what's in the Earth. In the same way
• 28:10
  Speaker 1: we can look at ripples on the surface of the sun.
• 28:13
  Speaker 1: Helio seismology, they call it, to get a picture for
• 28:17
  Speaker 1: what's in the sun.
• 28:18
  Speaker 2: We don't have earthquake measuring devices on the sun. How
• 28:21
  Speaker 2: do we know the shaking of the surface of the sun.
• 28:25
  Speaker 1: So we don't need a complete picture of what's in
• 28:27
  Speaker 1: the sun. But we can watch waves move across the
• 28:29
  Speaker 1: surface of the sun. You know, we have a lot
• 28:31
  Speaker 1: of telescopes that can look at the Sun and they
• 28:33
  Speaker 1: can see the behavior and the churning on the surface,
• 28:36
  Speaker 1: and there's a lot of stuff going on there. But
• 28:38
  Speaker 1: we only need a sort of rough picture of what's
• 28:40
  Speaker 1: in the sun because it turns out this one very
• 28:42
  Speaker 1: particular thing that's controlled by the metals that we're trying
• 28:46
  Speaker 1: to get a sense of. It's a balance between two
• 28:48
  Speaker 1: processes that are trying to move the heat out of
• 28:51
  Speaker 1: the sun. The sun has sort of two parts to it.
• 28:53
  Speaker 1: It's like the outermost part and the innermost part. And
• 28:56
  Speaker 1: the innermost part a lot of heat is being created
• 28:58
  Speaker 1: it's radiating out, so that radiation comes out from the
• 29:02
  Speaker 1: core and hits the outer part of the sun. But
• 29:05
  Speaker 1: that outer part can be kind of opaque because of
• 29:07
  Speaker 1: like oxygen or heavy elements can absorb those photons. So
• 29:11
  Speaker 1: that means that that energy can't be radiated out from
• 29:14
  Speaker 1: the core of the Sun. Instead, you need to get
• 29:16
  Speaker 1: that energy out using another method we call convection, basically
• 29:20
  Speaker 1: just like hot stuff rising up the way it does
• 29:23
  Speaker 1: in a pot of water. So there's sort of two
• 29:25
  Speaker 1: parts of the Sun, one where photons can bring the
• 29:28
  Speaker 1: energy out and the other where we have to rely
• 29:30
  Speaker 1: on convection. And there's a boundary between these two regions,
• 29:33
  Speaker 1: and that depends a lot on like how much oxygen
• 29:36
  Speaker 1: is there in the Sun, and that's what we're trying
• 29:38
  Speaker 1: to measure with this helio seismology. We're trying to figure out,
• 29:41
  Speaker 1: like where's the threshold between these two parts of the
• 29:44
  Speaker 1: inside of the sun.
• 29:45
  Speaker 2: And we do this by just looking at the flow
• 29:48
  Speaker 2: that you can see in the picture of the sun.
• 29:51
  Speaker 2: Or do we have like an X ray way to
• 29:53
  Speaker 2: look inside the sun.
• 29:54
  Speaker 1: No, we have no X ray. Unfortunately, it's just effectively
• 29:57
  Speaker 1: sound waves in the sun. And of course nobody's hearing
• 30:00
  Speaker 1: these things. When we say sound waves, we just mean
• 30:02
  Speaker 1: pressure waves moving through the Sun, but just the same
• 30:05
  Speaker 1: way that earthquakes make effectively sound waves through the Earth,
• 30:08
  Speaker 1: and you can listen to the earth ringing just by
• 30:11
  Speaker 1: seeing the Earth shake. If we watch the surface of
• 30:14
  Speaker 1: the Sun, we don't have like instruments on the surface
• 30:16
  Speaker 1: that measure the actual shaking, but you can see these
• 30:19
  Speaker 1: ripples in the plasma on the surface. You can effectively
• 30:22
  Speaker 1: see sound moving through the Sun and bouncing back. And
• 30:26
  Speaker 1: this boundary between the two parts of the Sun, one
• 30:29
  Speaker 1: that's opaque to photons and one that isn't shows up
• 30:31
  Speaker 1: as like a glitch in the sound waves. It changes
• 30:34
  Speaker 1: how those sound waves move through the Sun.
• 30:37
  Speaker 2: Well, wait, are you saying there's sort of like two
• 30:39
  Speaker 2: kinds of sun surfaces.
• 30:42
  Speaker 1: Yeah, there's like a surface within the surface, the same
• 30:44
  Speaker 1: way that like the Earth has multiple layers to it.
• 30:46
  Speaker 1: You know, it's the mantle and the outer core and
• 30:48
  Speaker 1: the inner core, et cetera. The Sun also has these
• 30:51
  Speaker 1: regions and there's this boundary. They think it's like seventy
• 30:55
  Speaker 1: ish percent of the solar radius. Within that photons can
• 30:58
  Speaker 1: like fly free, and you this radiative transfer where photons
• 31:01
  Speaker 1: can move heat out from the center. The outer part
• 31:05
  Speaker 1: is more opake and photons can't really get through it.
• 31:08
  Speaker 1: It's the only way to get heat out from the Sun.
• 31:09
  Speaker 1: There is more like convection like hot gas rising up.
• 31:13
  Speaker 2: But then what are you basically saying that looking at
• 31:15
  Speaker 2: these sound waves tells us a different number for what
• 31:18
  Speaker 2: the Sun is made out of.
• 31:19
  Speaker 1: Exactly, looking at the sound waves tells us something about
• 31:22
  Speaker 1: where this balance is between the two different parts of
• 31:24
  Speaker 1: the Sun, and that depends on how much metal is
• 31:27
  Speaker 1: in the Sun, because the metallicity of the Sun controls
• 31:30
  Speaker 1: whether it's opaque or transparent. You have more oxygen, more carbon,
• 31:34
  Speaker 1: more neon. That makes the Sun more opaque, which changes
• 31:38
  Speaker 1: how far the photons can get. So if we can
• 31:41
  Speaker 1: use sound waves on the surface of the Sun figure
• 31:43
  Speaker 1: out where is this transition within the Sun between opaque
• 31:47
  Speaker 1: and transparent to these photons, then we could figure out
• 31:50
  Speaker 1: how much metal is in the Sun because the metallicity
• 31:53
  Speaker 1: controls where that transition is.
• 31:55
  Speaker 2: But then why do metals make the Sun more opake?
• 31:58
  Speaker 1: These heavy elements like oxygen, they like to absorb these
• 32:00
  Speaker 1: photons like more than hydrogen, Yeah, more than hydrogen. You know,
• 32:04
  Speaker 1: every atom likes to absorb photons of a certain energy,
• 32:07
  Speaker 1: and so the kinds of energy that tend to be
• 32:09
  Speaker 1: produced in fusion tend to also be the kind that
• 32:11
  Speaker 1: oxygen likes to gobble up. For example. So if you
• 32:15
  Speaker 1: do all these calculations, you figure out, well, where is
• 32:17
  Speaker 1: this threshold where's the sun become opaque inside of it?
• 32:20
  Speaker 1: And what does that mean about the amount of metal
• 32:22
  Speaker 1: inside the sun? You get a different number. So from
• 32:26
  Speaker 1: helio seismology, from these sound waves, we get the number
• 32:28
  Speaker 1: one point eight percent. Whereas we look at the spectrum
• 32:31
  Speaker 1: of light from the sun, we got the number one
• 32:33
  Speaker 1: point three percent. So we thought, oh, this would be
• 32:36
  Speaker 1: a great way to cross check and to just make
• 32:38
  Speaker 1: sure we understand what's in the sun. And then it
• 32:40
  Speaker 1: turns out, oops, the numbers don't agree.
• 32:43
  Speaker 2: Now is that do you think maybe because looking at
• 32:45
  Speaker 2: the spectrum of the sun only kind of maybe tells
• 32:47
  Speaker 2: you what's in the surface of the sun.
• 32:49
  Speaker 1: It is possible, but they've accounted for that. They have
• 32:51
  Speaker 1: models for where these things are distributed in the sun
• 32:54
  Speaker 1: and how much they would radiate. So there are definitely
• 32:57
  Speaker 1: questions there and things people are trying to drill down on,
• 33:00
  Speaker 1: but they do think they've accounted for that.
• 33:02
  Speaker 2: But the second one of the ways seems a little
• 33:04
  Speaker 2: a bit more circumspect, I guess, or more indirect than
• 33:08
  Speaker 2: actually just looking at the light from the sun.
• 33:11
  Speaker 1: It does in the end, we're always just getting information
• 33:14
  Speaker 1: from far away and using that to try to infer
• 33:16
  Speaker 1: what's going on, and what's happening here is something I
• 33:18
  Speaker 1: love in science. It's like, well, let's cross check our
• 33:21
  Speaker 1: understanding by seeing if we could do this two different ways,
• 33:24
  Speaker 1: making different assumptions, or probing our model in different ways
• 33:26
  Speaker 1: to see whether it breaks. And this kind of detailed
• 33:30
  Speaker 1: work has led to crazy discoveries in the past. You know,
• 33:32
  Speaker 1: when we, for example, predicted how many neutrinos would be
• 33:35
  Speaker 1: coming from the sun versus how many new trinos we
• 33:37
  Speaker 1: saw from the sun, and we saw a huge difference.
• 33:40
  Speaker 1: That led to understanding neutrino oscillations and neutrino masses. So
• 33:44
  Speaker 1: not every way is going to be as precise, but
• 33:46
  Speaker 1: it's important to have different ways to cross check each
• 33:48
  Speaker 1: other and to try to get some hints about what's
• 33:50
  Speaker 1: really going on inside the sun.
• 33:52
  Speaker 2: Well, it sounds like we've measured how much metal is
• 33:55
  Speaker 2: in the sun in two different ways and they disagree
• 33:57
  Speaker 2: by a pretty big amount, and so let's get into
• 34:00
  Speaker 2: what the difference means, who's right, who's wrong, and how
• 34:04
  Speaker 2: metal is the sun. So let's dig into that. But
• 34:06
  Speaker 2: first let's take another quick break. All right, we're asking
• 34:21
  Speaker 2: how much metal is in the sun, and it sounds
• 34:24
  Speaker 2: like we have two answers. One way, by looking at
• 34:27
  Speaker 2: the light from the sun tells us that it's one
• 34:29
  Speaker 2: point three percent non hydrogen and helium. But looking at
• 34:33
  Speaker 2: the flow of the plasma and how the sound ways
• 34:37
  Speaker 2: travel across the surface of the Sun, that tells us
• 34:39
  Speaker 2: that maybe the sun is one point eight percent non
• 34:43
  Speaker 2: hydrogen and helium. So who's right and who's wrong.
• 34:47
  Speaker 1: We don't know yet, But we have a third answer.
• 34:51
  Speaker 1: People came up with yet another way to try to
• 34:53
  Speaker 1: figure out how much.
• 34:54
  Speaker 2: Metal is in the sun, just asking the sun.
• 34:58
  Speaker 1: Nobody thought of that. Oh my god, you know, if
• 35:00
  Speaker 1: the Sun really isn't a rock band, it's gonna love
• 35:02
  Speaker 1: doing interviews. But this third way actually does use neutrinos,
• 35:06
  Speaker 1: because fusion at the heart of the Sun produces vast,
• 35:09
  Speaker 1: vast quantities of neutrinos, these tiny, little ghostly particles that
• 35:14
  Speaker 1: are everwhere, but we can't feel them because they only
• 35:16
  Speaker 1: have weak interactions. They have no electric charge, they have
• 35:19
  Speaker 1: no strong force charge. They're very difficult to spot. But
• 35:23
  Speaker 1: we have technologies neutrino eyeballs, we've invented to be able
• 35:26
  Speaker 1: to pick out a few of these neutrinos. We can
• 35:28
  Speaker 1: also measure the energy of those neutrinos. And the neutrinos
• 35:32
  Speaker 1: are produced by fusion in the sun, and how much
• 35:36
  Speaker 1: metal you have in the sun affects the rate at
• 35:38
  Speaker 1: which that fusion happens and also affects the energy of
• 35:41
  Speaker 1: the neutrinos that's produced. We're trying to fuse protons and
• 35:45
  Speaker 1: protons together. If there's a bunch of heavy metal around
• 35:48
  Speaker 1: that actually interferes with the fusion, makes it less likely,
• 35:51
  Speaker 1: it makes it more important to have higher energy on
• 35:54
  Speaker 1: those protons, etc. So the neutrino energy spectrum you expect
• 35:58
  Speaker 1: depends on how much metal in the sun, but it's
• 36:01
  Speaker 1: a bit of a weak effect. It's not a very
• 36:03
  Speaker 1: strong way to measure this quantity.
• 36:05
  Speaker 2: Well, also, what do you compare it to, like, how
• 36:07
  Speaker 2: do you know what the right amount of neutrinos should
• 36:10
  Speaker 2: be for a certain amount of metals.
• 36:12
  Speaker 1: Yeah, great question. We have a really detailed model of
• 36:15
  Speaker 1: the fusion and how it produces neutrinos, and that's been
• 36:18
  Speaker 1: the subject of decades of study, and of course, first
• 36:21
  Speaker 1: there were big mysteries we predicted a huge amount of neutrinos,
• 36:24
  Speaker 1: we only saw a third of them. Later we discovered
• 36:26
  Speaker 1: that's because those neutrinos are changing into another kind of
• 36:29
  Speaker 1: neutrino as they travel through space. Check out our episode
• 36:32
  Speaker 1: on neutrino oscillation if you want to understand that more.
• 36:35
  Speaker 1: But yeah, there are definitely uncertainties there. These are models
• 36:37
  Speaker 1: we have of how the diffusion is happening and how
• 36:40
  Speaker 1: the neutrinos are being created, So we don't have an
• 36:42
  Speaker 1: absolute calibration of that either. We just have these calculations
• 36:45
  Speaker 1: we've done that predict the spectrum, and then those calculations
• 36:49
  Speaker 1: depend also on the metal. So you tweak the metals up,
• 36:51
  Speaker 1: you get one spectrum. You tweak the metals down, you
• 36:53
  Speaker 1: get another spectrum. So we can tweak the amount of
• 36:55
  Speaker 1: metals we put into these calculations to match what we see,
• 36:58
  Speaker 1: and then we think, well, let's the most likely value
• 37:01
  Speaker 1: of the metal in the sun.
• 37:03
  Speaker 2: So then what does this neutrino method say about the
• 37:05
  Speaker 2: metals in the sun.
• 37:06
  Speaker 1: So unfortunately, this method isn't super precise. It slightly favors
• 37:10
  Speaker 1: the higher metal scenario, so like one point eight percent,
• 37:13
  Speaker 1: but it can't rule out the one point three percent.
• 37:15
  Speaker 1: It's just sort of more like a hint. It's a
• 37:18
  Speaker 1: little bit of a vote towards heavy metals.
• 37:21
  Speaker 2: So then we have three competing methods and they all
• 37:25
  Speaker 2: say something slightly different. How are we going to figure
• 37:28
  Speaker 2: out which one's right.
• 37:28
  Speaker 1: We're going to dig in and question all of our assumptions,
• 37:31
  Speaker 1: understand where we might have overlooked something. We're going to
• 37:34
  Speaker 1: do more experiments, collect more data, these neutrino experiments. Specifically,
• 37:39
  Speaker 1: this is sort of like the first run, the first
• 37:41
  Speaker 1: gasp of the data. As that runs longer and longer,
• 37:43
  Speaker 1: it little bit more and more precise and maybe sharpen
• 37:46
  Speaker 1: our understanding. But this is really crucial that we figure
• 37:49
  Speaker 1: this out because the Sun is sort of like our
• 37:51
  Speaker 1: yardstick for the rest of the universe. For other stars,
• 37:54
  Speaker 1: we have no hope. But like looking at sound waves
• 37:56
  Speaker 1: on the surface, we can only look at the light
• 37:58
  Speaker 1: from those stars. Compare the light from those stars to
• 38:01
  Speaker 1: the light we get from the Sun, and we use
• 38:03
  Speaker 1: that to infer what's in them. Our whole estimate for
• 38:06
  Speaker 1: what's out there in the universe is based on what's
• 38:09
  Speaker 1: in the sun. If we were wrong about what's in
• 38:11
  Speaker 1: the sun, then we were wrong about the whole universe.
• 38:14
  Speaker 2: Well, unless it turns out that these other ways to
• 38:16
  Speaker 2: measure what's in the sun are wrong, and maybe the
• 38:19
  Speaker 2: one that you can't apply to other stars is right.
• 38:22
  Speaker 1: Yeah, absolutely, it could be, or it could be that
• 38:25
  Speaker 1: we don't understand what's inside the sun and how this
• 38:27
  Speaker 1: all works, and they're both wrong. Either way, we'd love
• 38:30
  Speaker 1: to understand better what's in the sun because it helps
• 38:33
  Speaker 1: us understand what's out there in the universe. It also
• 38:35
  Speaker 1: really helps us understand the fate of all of those stars.
• 38:39
  Speaker 1: Even though the stars are mostly not metal, those metals
• 38:42
  Speaker 1: can really influence whether those stars have planets around them,
• 38:45
  Speaker 1: how long those stars will live, and how they will die.
• 38:48
  Speaker 2: Ooh wait, what's the connection between the metals in the
• 38:52
  Speaker 2: star and their planets?
• 38:54
  Speaker 1: I knew you wanted to talk about aliens, right.
• 38:56
  Speaker 2: No, No, I just ask about the planets. I didn't
• 38:58
  Speaker 2: say anything about aliens. Don't protect your alien fetish on me.
• 39:01
  Speaker 1: Man, Who do you think is living on those planets? Man?
• 39:06
  Speaker 2: Nobody? Maybe alg plants heavy metal bands. Nobody said anything
• 39:11
  Speaker 2: about aliens. Daniels, All right, well.
• 39:12
  Speaker 1: I'm about to okay, get ready, Well, the more metal
• 39:15
  Speaker 1: there is in the initial cloud that forms that solar system.
• 39:19
  Speaker 1: The more metal there's going to be for making planets,
• 39:22
  Speaker 1: and the more metal there is, the more likely you
• 39:23
  Speaker 1: are to seed something that's not just the star. You
• 39:27
  Speaker 1: have this huge collapse in cloud. Why doesn't it all
• 39:29
  Speaker 1: just become a star? If some little seed near the
• 39:33
  Speaker 1: star can form fast enough to make its own little
• 39:35
  Speaker 1: gravitational well, it can gather up a bunch of stuff
• 39:38
  Speaker 1: and get into orbit and avoid collapsing into the star.
• 39:41
  Speaker 1: Do that you need a little density seed. And so
• 39:44
  Speaker 1: stars with more metal in them tend to have more
• 39:47
  Speaker 1: planets around them as well, rocky planets and giant.
• 39:50
  Speaker 2: Planets, we think, or we know this for sure, Like,
• 39:53
  Speaker 2: have we measured this out there?
• 39:55
  Speaker 1: We've measured this out there because we've seen planets around
• 39:57
  Speaker 1: other stars and so we've seen this correlation. Stars whose
• 40:00
  Speaker 1: light indicates more metal in them also tend to have
• 40:04
  Speaker 1: more planets around them.
• 40:05
  Speaker 2: So there's a correlation between melicity and number of planets potentially.
• 40:10
  Speaker 1: No, that's something we've measured. Of course, we have a
• 40:12
  Speaker 1: biased view of all the planets out there. We can't
• 40:14
  Speaker 1: see all the kinds of planets. We're not great at
• 40:17
  Speaker 1: seeing some kinds of planets. We can only see planets
• 40:19
  Speaker 1: under certain conditions, et cetera, et cetera. So this is
• 40:22
  Speaker 1: sort of an initial thing, but it's a correlation that
• 40:24
  Speaker 1: we've noticed and also one that makes sense. Right, it
• 40:26
  Speaker 1: fits in with our model for householar systems form.
• 40:29
  Speaker 2: All right, Well, I guess how are we going to
• 40:31
  Speaker 2: figure out what's in our sun? Then? Is there going
• 40:33
  Speaker 2: to be a conclusive proof at some point? Like are
• 40:35
  Speaker 2: we going to be able to maybe dip into the
• 40:37
  Speaker 2: sun and get a scoop of it?
• 40:40
  Speaker 1: That would be awesome. We were thinking about sending your
• 40:42
  Speaker 1: band over to visit the sun. Are you guys available?
• 40:45
  Speaker 1: Who's your agent?
• 40:46
  Speaker 2: Well, it depends how much are you paying and what's
• 40:48
  Speaker 2: the budget. Will there be green Eminem's in the green room?
• 40:53
  Speaker 1: I thought it was brown Eminem's in the green room?
• 40:55
  Speaker 2: Well, I mean, I think the whole point is that
• 40:57
  Speaker 2: we get to choose what kind of mmms are in
• 40:58
  Speaker 2: the waiting room.
• 41:01
  Speaker 1: All right, we'll work on the budget, but this is
• 41:04
  Speaker 1: not something that we are likely to figure out directly.
• 41:07
  Speaker 1: It's always going to be a game of improving our models,
• 41:10
  Speaker 1: comparing the model's predictions to what we see out there
• 41:13
  Speaker 1: in the universe and then seeing if we get it
• 41:15
  Speaker 1: to tell a coherent story.
• 41:17
  Speaker 2: Can we send something into the sun, like have something
• 41:19
  Speaker 2: fall into the Sun, and as it falls and gets
• 41:21
  Speaker 2: destroyed and maybe tells us what's in the.
• 41:23
  Speaker 1: Sun potentially with some technological advances. As I know, you know,
• 41:27
  Speaker 1: our recent Parker solar probe got pretty close to the
• 41:30
  Speaker 1: Sun but almost got toasted. It's very difficult to even
• 41:33
  Speaker 1: get that close to the Sun, and it was nowhere
• 41:35
  Speaker 1: near being able to actually sample something. On the other hand,
• 41:39
  Speaker 1: we're sort of already in the Sun in one sense
• 41:42
  Speaker 1: because where it is the edge of the Sun, the
• 41:45
  Speaker 1: Sun starts out very dense and then gets more and
• 41:47
  Speaker 1: more dilute. Then it's got this huge extended corona and
• 41:50
  Speaker 1: the wind. So we're already sort of sampling stuff from
• 41:52
  Speaker 1: the Sun. So it's possible that like the solar wind
• 41:55
  Speaker 1: itself might have clues we can use to figure out
• 41:58
  Speaker 1: what's in the Sun. Energy of those particles could potentially
• 42:02
  Speaker 1: be sensitive to the metallicity of the Sun.
• 42:05
  Speaker 2: Well, it's kind of interesting that, like we only have
• 42:08
  Speaker 2: one star close to us, we be able to run
• 42:11
  Speaker 2: these experiments and verify our models of what goes on
• 42:14
  Speaker 2: in any star, and so we're sort of hoping that
• 42:16
  Speaker 2: our Sun is not super atypical or weird.
• 42:19
  Speaker 1: Yeah, exactly, And we know that our star is unusual
• 42:22
  Speaker 1: in some sense. It's more massive than your typical star.
• 42:25
  Speaker 1: Most of the stars out there are red dwarfs. But
• 42:27
  Speaker 1: it's also in the sort of unusually good position to
• 42:30
  Speaker 1: sample the average kind of stuff. In the Milky Way.
• 42:33
  Speaker 1: We're like halfway from the Milky Way center to the
• 42:36
  Speaker 1: edge of the disk of stars, and most stars out
• 42:39
  Speaker 1: there in the universe are in big galaxies like the
• 42:42
  Speaker 1: Milky Way, So the Sun is sort of a scoop
• 42:44
  Speaker 1: of typical material, we think, so understanding what's in the
• 42:47
  Speaker 1: Sun will really help us understand what's in the universe.
• 42:51
  Speaker 2: And how heavy metal aliens might be. Isn't that the
• 42:56
  Speaker 2: whole point of this episode, Daniel.
• 42:58
  Speaker 1: Yes, exactly. We were just working up to that one
• 43:00
  Speaker 1: joke the whole.
• 43:01
  Speaker 2: Time, all right. Well, another example of how there are
• 43:07
  Speaker 2: still big mystories. Even in our own heart of the
• 43:10
  Speaker 2: Solar system, the Sun, we sort of don't really know
• 43:14
  Speaker 2: what it's actually made out of, and even though it's
• 43:17
  Speaker 2: so close we can actually go in there and figure
• 43:20
  Speaker 2: it out ourselves directly. We have to find all these
• 43:23
  Speaker 2: clever ways to infer what's inside the sun, and.
• 43:26
  Speaker 1: These basic questions about what's in our own backyard, in fact,
• 43:30
  Speaker 1: the whole universe. They tell us what's likely to be
• 43:32
  Speaker 1: out there in the universe, and also how it all
• 43:35
  Speaker 1: will end. Stars with more metallinem are more likely to
• 43:39
  Speaker 1: form neutron stars rather than black holes, and so the
• 43:42
  Speaker 1: fate of all those stars we see up there in
• 43:44
  Speaker 1: the night sky could depend on these measurements of what's
• 43:47
  Speaker 1: in our backyard.
• 43:48
  Speaker 2: We hope you enjoyed that. Thanks for joining us, See
• 43:52
  Speaker 2: you next tent.
• 43:57
  Speaker 1: For more science and curiosity, come find us on social media,
• 44:00
  Speaker 1: where we answer questions and post videos. We're on Twitter, Discorg, Insta,
• 44:05
  Speaker 1: and now TikTok. Thanks for listening, and remember that Daniel
• 44:09
  Speaker 1: and Jorge Explain the Universe is a production of iHeartRadio.
• 44:12
  Speaker 1: For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
• 44:18
  Speaker 1: or wherever you listen to your favorite shows.