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How many generations of stars will there be? · Daniel and Kelly’s Extraordinary Universe

0:01
Speaker 1: Hey, Jorhan Daniel here, and we want to tell you
0:03
Speaker 1: about our new book. It's called Frequently Asked Questions about
0:07
Speaker 1: the Universe because you have questions about the universe, and
0:09
Speaker 1: so we decided to write a book all about them.
0:12
Speaker 1: We talk about your questions, we give some answers, we
0:14
Speaker 1: make a bunch of silly jokes as usual, and we
0:17
Speaker 1: tackle all kinds of questions, including what happens if I
0:20
Speaker 1: fall into a black hole? Or is there another version
0:22
Speaker 1: of you out there that's right? Like usual, we tackle
0:25
Speaker 1: the deepest, darkest, biggest, craziest questions about this incredible cosmos.
0:29
Speaker 1: If you want to support the podcast, please get the
0:31
Speaker 1: book and get a copy, not just for yourself, but
0:34
Speaker 1: you know, for your nieces and nephews, cousins, friends, parents, dogs, hamsters,
0:39
Speaker 1: and for the aliens. So get your copy of Frequently
0:42
Speaker 1: Asked Questions about the Universe is available for pre order now,
0:46
Speaker 1: coming out November two. You can find more details at
0:49
Speaker 1: the book's website, Universe f a Q dot com. Thanks
0:53
Speaker 1: for your support, and if you have a hamster that
0:55
Speaker 1: can read, please let us know. We'd love to have
0:57
Speaker 1: them on the podcast. Hey Daniel, how far back do
1:11
Speaker 1: you know? Your family story. Oh you mean like where
1:13
Speaker 1: my family comes from? Yeah, you know, like how many
1:15
Speaker 1: generations back do you know? Well? I actually met my
1:18
Speaker 1: great grandfather when I was a kid, and I know
1:21
Speaker 1: some family history back a couple more generations than that,
1:24
Speaker 1: So I guess that makes like four or five generations.
1:27
Speaker 1: How about you. That's pretty good. I actually have only
1:30
Speaker 1: met my grandparents through to the four of them. But
1:33
Speaker 1: then it gets a little fuzzy. You know, they're all immigrants,
1:35
Speaker 1: and we know at least one future generation, I mean
1:37
Speaker 1: our kids. Yes, children are the future, and hopefully there
1:40
Speaker 1: are enough future generations that one day we become fuzzy memories. Well,
1:44
Speaker 1: I'm not sure if I will have great grandkids, but
1:46
Speaker 1: if I do, I'm sure they'll remember us, right, they
1:48
Speaker 1: can always listen to this podcast. If nothing else, they'll
1:51
Speaker 1: remember us as a cautionary tale, assuming they care. Hi
2:09
Speaker 1: am or hammy cartoonist and the creator of PhD comics. Hi.
2:12
Speaker 1: I'm Daniel. I'm a particle physicist, but I'm the first
2:16
Speaker 1: person in my family to get a PhD. You're the
2:19
Speaker 1: first doctor or the first academic doctor. I'm definitely the
2:22
Speaker 1: first doctor of any kind in my direct line. Though
2:25
Speaker 1: there is another Daniel Whiteson out there somewhere who I
2:29
Speaker 1: think has a degree. Interesting, it's like your long loss twin,
2:33
Speaker 1: maybe another version of the multiverse version of you. There's
2:36
Speaker 1: another Daniel whites In which is a distant cousin of
2:38
Speaker 1: mine who's an excellent artist and lives in London. Actually
2:42
Speaker 1: you should switch places. Sounds like he has a coulder life.
2:45
Speaker 1: I'm pretty happy with my situation. Thanks very much. Do
2:48
Speaker 1: you think you'll be the last PhD in your family?
2:51
Speaker 1: I don't know. My brother got a PhD, but that
2:53
Speaker 1: might be it. I'm not sure which direction my kids
2:55
Speaker 1: are headed. But anyways, welcome to our podcast. Daniel and
2:58
Speaker 1: Jorge explained the university but that of I Heart Radio,
3:01
Speaker 1: in which we sum up the knowledge and the thinking
3:03
Speaker 1: of many, many generations of deep thinkers and scientists and
3:07
Speaker 1: philosophers and explorers who are trying their hardest to understand
3:11
Speaker 1: this incredible, beautiful universe that we find ourselves in. We
3:14
Speaker 1: talk about everything that we know about science, things that
3:17
Speaker 1: we don't know about science, the way the universe works,
3:19
Speaker 1: and the way the universe definitely doesn't work. We talk
3:21
Speaker 1: about the latest results of the craziest thought experiments and
3:25
Speaker 1: everything in between, and throwing a few banana jokes to
3:28
Speaker 1: keep you awake and hopefully not to slip you up.
3:30
Speaker 1: But it is a pretty big universe, pretty amazing, and
3:33
Speaker 1: science has discovered a lot about it. We know a
3:36
Speaker 1: lot about how the universe started, how it's evolved, and
3:39
Speaker 1: what explains everything we see today, and a big job
3:42
Speaker 1: of science is also to think about the future and
3:45
Speaker 1: what's going to happen to this crazy cosmos. That's right,
3:48
Speaker 1: because one thing we know about the universe for sure
3:50
Speaker 1: is that it's not static. It's not just hanging out
3:53
Speaker 1: like this forever. It's evolving. It's not quite alive, but
3:57
Speaker 1: it's definitely developing and changing and has different modes to it. Yeah,
4:01
Speaker 1: the universe hasn't always been the way it is right now,
4:04
Speaker 1: and it's not going to be the same wave in
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Speaker 1: the future. It's it's always changing, evolving and growing, hopefully
4:10
Speaker 1: getting more mature. Do you think the universe is getting
4:12
Speaker 1: more mature. I'm not sure it's getting better behaved, but
4:15
Speaker 1: it's definitely getting older. It's still getting into trouble. You
4:19
Speaker 1: thinking the universe that learns its lessons, I'm not sure
4:23
Speaker 1: who's teaching the universe anything. But I think it's fun
4:25
Speaker 1: to realize that the universe seems sort of static on
4:29
Speaker 1: our time scale, like the universe is not going to
4:31
Speaker 1: look any different the day you die than the day
4:34
Speaker 1: you are born, but that these processes are happening on
4:37
Speaker 1: a much much longer time scale, and that if you
4:40
Speaker 1: look at the universe over like millions of years or
4:42
Speaker 1: billions of years, it's very much dynamic. It's changing, it's growing,
4:46
Speaker 1: it's evolving. It's gonna look very different in five billion
4:49
Speaker 1: years than it does today. Yeah, or not even billions
4:51
Speaker 1: of years, Like millions of years, I mean, the Earth
4:54
Speaker 1: looked a lot different. That even our Solar system look
4:56
Speaker 1: pretty different, right, and even a few million or hundreds
4:59
Speaker 1: of millions of years. Yeah, that's something we're learning about.
5:01
Speaker 1: You know, the planets are doing a dance where they're
5:03
Speaker 1: moving in and they're moving out, and we think maybe
5:05
Speaker 1: Jupiter spent some time near the Sun and then Saturn
5:08
Speaker 1: swooped in and saved it and pulled it back out
5:10
Speaker 1: to the colder parts of the Solar system where it
5:13
Speaker 1: can't survive. So there's definitely a lot of stuff going on.
5:15
Speaker 1: If you look at the Solar system or our galaxy
5:17
Speaker 1: on like a super time lapse, you would think it
5:20
Speaker 1: was crazy. Yeah, it's a big action movie. But only
5:23
Speaker 1: if you hit the fast forward button a couple of
5:26
Speaker 1: times and then don't forget to rewind it before you
5:29
Speaker 1: return the tape. Just you know, be kind. Hopefully some
5:32
Speaker 1: people out there get that joke. Probably not if you're
5:34
Speaker 1: under thirty or thirty five, you would get that at least,
5:39
Speaker 1: I guess maybe what's the equivalent now you have to
5:41
Speaker 1: take it off your Netflix queue. Maybe the courtesy to
5:44
Speaker 1: not to nobody. But yeah, it's a big, beautiful universe,
5:47
Speaker 1: and we often wonder what's going to happen in the future,
5:51
Speaker 1: and in particular to the things we see around us,
5:53
Speaker 1: you can think about the sort of age and cycle
5:56
Speaker 1: of the stuff around us. Not just the planets are
5:58
Speaker 1: spinning around the Sun, but the solar is to itself
6:00
Speaker 1: is moving around the galaxy. It takes like two hundred
6:04
Speaker 1: and fifty million years to do one loop around the
6:08
Speaker 1: center of the galaxy for the Sun to orbit the
6:10
Speaker 1: center of the galaxy and came back to where it started.
6:13
Speaker 1: So from that point of view, you know, the galaxy
6:15
Speaker 1: itself is not that old, like it hasn't done that
6:18
Speaker 1: many spins. It's like, you know, thirty to forty galactic
6:22
Speaker 1: years old, it's still searching for itself. Maybe it still
6:26
Speaker 1: hasn't figured out what it wants to do with it
6:28
Speaker 1: that the rest of its life. It's like running through
6:30
Speaker 1: cosmic fields towards the Andromeda Galaxy. There's gonna be a
6:33
Speaker 1: very dramatic moment there where they both learn who they
6:36
Speaker 1: really are. They're going to find themselves. You're going to
6:39
Speaker 1: become one with the cosmos and with each other exactly.
6:42
Speaker 1: And then within those galaxies there's stuff happening. Stars are
6:46
Speaker 1: being born, stars are dying and exploding, is all sorts
6:49
Speaker 1: of crazy stuff. Yes, stars are probably the thing that
6:52
Speaker 1: people most noticed or think about even when they think
6:54
Speaker 1: about space and the entire universe, and it's a big
6:57
Speaker 1: part of the universe. There are a lot of stars
6:58
Speaker 1: out there, and we kind of have to ask what's
7:01
Speaker 1: going to happen to all those stars eventually in the
7:05
Speaker 1: near future and forever perhaps, Yeah, because stars do not
7:08
Speaker 1: live forever. Some of them last millions of years, some
7:11
Speaker 1: billions of years, some potentially trillions of years. But there
7:14
Speaker 1: are stars that formed and burned and died even before
7:17
Speaker 1: our solar system came to be, the things that you
7:20
Speaker 1: and I are made out of, and then our solar
7:22
Speaker 1: system are built out of our remnants of ancient stars
7:26
Speaker 1: which shine through the universe and no longer exist. So
7:29
Speaker 1: we can look into the past and think about, like,
7:31
Speaker 1: how many generations of stars have there been so far
7:35
Speaker 1: that burned and died before we even came to being. Yeah,
7:38
Speaker 1: it's kind of like people, you know, we humans have
7:41
Speaker 1: generations that come and go, and each time that they're
7:43
Speaker 1: a little bit different, hopefully. And if we're made of
7:46
Speaker 1: star dust, then by analogy, are you made out of grandparents?
7:48
Speaker 1: Doesn't Yeah? Yeah, So there have been a lot of
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Speaker 1: generations of stars since the beginning of the universe, and
7:55
Speaker 1: so today we'll be tackling the question how many generations
8:02
Speaker 1: of stars will there be? I guess, Daniel, that number
8:07
Speaker 1: could be finite. Is that the idea like, maybe there
8:10
Speaker 1: aren't that many generations of stars that can happen, or
8:12
Speaker 1: is that number infinite? Perhaps? Yeah, exactly, That's what we're
8:15
Speaker 1: gonna dig into. There's a lot of different ideas about
8:17
Speaker 1: the future of the universe and how this might happen.
8:20
Speaker 1: A lot of things we still don't even really understand
8:23
Speaker 1: about the conditions for star formation where it's happening universe,
8:27
Speaker 1: where it's not happening in the universe, and all that's
8:29
Speaker 1: going to come together to give us a picture for
8:31
Speaker 1: how many times stars can burn and then explode and reform. Yeah,
8:36
Speaker 1: I guess it's interesting that what you said earlier is
8:38
Speaker 1: that maybe a lot of people don't realize that stars
8:41
Speaker 1: kind of have a lifespan, right, Like, you know, your
8:44
Speaker 1: the Sun is not going to be there forever. It
8:46
Speaker 1: wasn't always there since the beginning of time. It came
8:48
Speaker 1: about at some point in the in the past, and
8:50
Speaker 1: it's not going to be there forever into the future,
8:53
Speaker 1: and in its place, maybe there will be another star exactly.
8:56
Speaker 1: The Sun came around sort of late in the universe,
8:58
Speaker 1: and universe four billion years old. The Sun is only
9:01
Speaker 1: like four and a half billion years old, So there
9:04
Speaker 1: was nine or so billion years of stuff happening in
9:07
Speaker 1: the universe before our sun even existed, Right, that's a
9:11
Speaker 1: lot of time for stuff to happen. Stars formed and died,
9:14
Speaker 1: and then our star formed from the leftover bits of
9:18
Speaker 1: other stars and also you know, untouched material from the
9:21
Speaker 1: Big Bang and our son will not last forever. It's
9:24
Speaker 1: only got a five more billion years or so, And
9:27
Speaker 1: so it's a fun question to think about, like how
9:29
Speaker 1: many times can you gather stuff together to make stars,
9:32
Speaker 1: burn it, blow it up again, and then repeat. Can
9:35
Speaker 1: you do that forever? Or is there some fundamental limit
9:38
Speaker 1: to how many times the universe can get right? Yeah?
9:41
Speaker 1: And if we run out of generations of stars, well,
9:43
Speaker 1: that does that mean the universe will be dark forever
9:46
Speaker 1: at the end of light of sunny days in the universe.
9:48
Speaker 1: That's a dim weather forecast. Man, you know, it's a
9:51
Speaker 1: cloudy future, zero percent chance of radiation forever the sunblocks.
9:55
Speaker 1: That's that's a positive. Don't invest in sunscreen companies people,
9:59
Speaker 1: at least not in the billion year bond market. But anyways,
10:03
Speaker 1: we're wondering how many people out there have thought about
10:05
Speaker 1: this idea of solar or star generations and how many
10:08
Speaker 1: there will be in the future. So it's usual Daniel
10:11
Speaker 1: went out there and ask people how many generations or
10:14
Speaker 1: stars do you think there will be? And as always,
10:17
Speaker 1: I am deeply grateful to those of you who are
10:19
Speaker 1: willing to answer these crazy questions online. If you'd like
10:22
Speaker 1: to hear your voice speculating on difficult physics questions on
10:26
Speaker 1: the podcast. Please write to us new questions at Daniel
10:29
Speaker 1: and Jorge dot com. Here's what people had to say.
10:32
Speaker 1: I think I heard somewhere there's been three generations of stars.
10:36
Speaker 1: So if we're supposed to the universe is supposed to
10:39
Speaker 1: last for billions of years more, at least four or
10:43
Speaker 1: five more, let's say, Um, possibly, and I'm limited amount
10:48
Speaker 1: of generations. We don't really know what's going to happen
10:51
Speaker 1: in the future exactly. Um, you might, you're smarter than me,
10:55
Speaker 1: but um, yeah, I don't know. I don't know. It
10:58
Speaker 1: depends on the time, depends if the time is infinite,
11:02
Speaker 1: I don't know. Probably they can be a lot, a
11:06
Speaker 1: lot of generations eleven, Okay, how many generations of stars
11:16
Speaker 1: will there be? I think so, I know that we've
11:20
Speaker 1: got the original and then we've got the next generation. Um,
11:25
Speaker 1: I'm gonna say we're going to have all the generations
11:28
Speaker 1: of stars. I have no idea. Well, we're in the
11:32
Speaker 1: third generations of star at the moment, even though this
11:36
Speaker 1: generation is called population one. I bet Jorge has something
11:40
Speaker 1: fun to say about that naming logic, But I'm not
11:43
Speaker 1: sure how much of the matter in the universe has
11:46
Speaker 1: now been used to create stars. So let's say it's
11:48
Speaker 1: ten percent. Sure it is, but let's say ten percent,
11:52
Speaker 1: and we are three generations into the universe, so then
11:56
Speaker 1: ten times as many, let's say thirty generations. I've thought
12:00
Speaker 1: about this because we know how long the universe is
12:04
Speaker 1: gonna last and how long it's gonna be dense enough
12:07
Speaker 1: for new star formation. Our son is like four billion
12:11
Speaker 1: years old in the universe is like fourteen, so maybe
12:15
Speaker 1: there's been two or three generations there, and Son's got
12:19
Speaker 1: another four billion years left and it's kind of an
12:22
Speaker 1: average star. So maybe that's we're just on the second
12:25
Speaker 1: generation right now, so maybe ten more generations. It's my
12:30
Speaker 1: best guess. Five billion seems like a good number of
12:35
Speaker 1: star generations. I mean, if we're taking the average life
12:38
Speaker 1: spent at a star to be somewhere around five billion years,
12:44
Speaker 1: and you know, at some point, you know, all the
12:46
Speaker 1: stars exploding, our decaying that we're going to kind of
12:49
Speaker 1: reach a point where gas and dust is to spread
12:52
Speaker 1: out to create more stars. Yeah, we're gonna reach a plateau.
12:55
Speaker 1: So I'm just gonna get five billion years, I guess
12:59
Speaker 1: infinite until the universe ends because and you can't really
13:05
Speaker 1: count them because different stars generations and at different times,
13:09
Speaker 1: because the lickspans of stars is so different. All right,
13:12
Speaker 1: So a lot of guessing. I mean, everyone seemed to
13:15
Speaker 1: have sort of an idea. Maybe they're like three infinite.
13:20
Speaker 1: I like that as a guess. That's a good guess.
13:23
Speaker 1: They said that sounds like a good number, Like, why
13:25
Speaker 1: not like a good number? Yeah, next time they asked
13:27
Speaker 1: me if i'd like a raise, I'll say, yeah, you
13:29
Speaker 1: know what, five billion seems like a good number. Pennies
13:32
Speaker 1: or nano dollars or something. All Right, So that's a
13:37
Speaker 1: pretty interesting question. How many generations of stars will there be?
13:40
Speaker 1: Are we gonna have stars until the end of time
13:43
Speaker 1: or are we going to run out of fuel or
13:45
Speaker 1: ability to form these stars eventually in the future. Start
13:49
Speaker 1: us off, Daniel, I guess how do you define a
13:51
Speaker 1: generation of a star? And how did those kind of
13:54
Speaker 1: come about? Yeah, it's a good question. How do you
13:56
Speaker 1: even define a generation of a star? It's actually not
13:59
Speaker 1: that easy to like crisply say what generation of stars
14:03
Speaker 1: in because every star is made out of a bunch
14:05
Speaker 1: of material that just happened to be around and some
14:07
Speaker 1: of it could be like leftover pristine material from the
14:10
Speaker 1: Big Bang, and other bits could have been in other stars.
14:14
Speaker 1: But I think it's important to understand this sort of
14:16
Speaker 1: process of how stars are formed and then burn and
14:19
Speaker 1: then die, so we can think about how often that
14:22
Speaker 1: can happen um And so you know, the way that
14:24
Speaker 1: stars form is that you have these big clumps of
14:27
Speaker 1: gas and dust, these things like these giant molecular clouds.
14:32
Speaker 1: And I think the thing that people might not realize
14:34
Speaker 1: is that for stars to form, you need cold stuff
14:38
Speaker 1: because what you need is gravity to pull this stuff together. Remember,
14:42
Speaker 1: the stars are a delicate balancing app between gravity is
14:44
Speaker 1: trying to pull things together to make it more dense,
14:47
Speaker 1: and pressure that's like resisting being compacted too much. But
14:50
Speaker 1: gravity is really weak. So to get a star to form,
14:53
Speaker 1: you need like a really pretty cold, pretty huge clump
14:57
Speaker 1: of stuff near each other and it gathers together to
15:00
Speaker 1: form a star and reach that critical density where fusion
15:03
Speaker 1: can start. So you need to start with something like
15:05
Speaker 1: ten to twenty degrees kelvin m m. And it has
15:09
Speaker 1: to be cold because if it's too hot, it won't
15:11
Speaker 1: clump together, like it'll just kind of keep missing itself
15:15
Speaker 1: and it won't compress. Yeah, because if it's too hot,
15:18
Speaker 1: that means that the particles are moving around too fast,
15:20
Speaker 1: and so gravity just can't slow them down exactly. So
15:24
Speaker 1: they need to be like basically motionless so that gravity
15:27
Speaker 1: can gently tug on them and pull them together into
15:30
Speaker 1: a star. Maybe it's too hot, it just won't happen, right,
15:33
Speaker 1: And we've talked about in another episodes about how you
15:36
Speaker 1: need like a certain minimum amount of stuff, right, like
15:39
Speaker 1: more than a jupiter's worth of stuff. And also it's
15:42
Speaker 1: about kind of the kind of stuff it is, right like,
15:45
Speaker 1: the only certain kinds of stuff will clump and form
15:48
Speaker 1: into start. Yeah, in order to get fusion going, you
15:50
Speaker 1: need like at least like eighty times the massive Jupiter.
15:54
Speaker 1: You can get clumps forming that are smaller than that,
15:56
Speaker 1: they just won't necessarily start fusion. But typically these cloud
16:00
Speaker 1: it's where stars are formed, or like a thousand light
16:02
Speaker 1: years long, and they have a huge amount of material
16:05
Speaker 1: like thousands two million times the mass of our sun,
16:09
Speaker 1: and inside that you have like denser regions, which astronomers
16:12
Speaker 1: referred to by the technical word clumps, and then inside
16:15
Speaker 1: that are like slightly denser regions they call cores, and
16:18
Speaker 1: that's usually where stars are actually formed, but it's not
16:21
Speaker 1: something we understand in great detail, you know, like what
16:24
Speaker 1: actually makes those cores, what triggers them to collapse into
16:27
Speaker 1: a star or some people think like and nearby supernova
16:30
Speaker 1: has to come through and the shock wave there can
16:32
Speaker 1: trigger the collapse to make the star. But you're right.
16:35
Speaker 1: You can also be a variety of material. But you know,
16:37
Speaker 1: when the Big Bang happened, it made mostly hydrogen, and
16:40
Speaker 1: so most of the stuff in the universe is still hydrogen.
16:43
Speaker 1: There's a little bit of helium also, and so most
16:46
Speaker 1: of the stars in the universe are made of mostly
16:48
Speaker 1: hydrogen and helium. And then there's heavier stuff, right, And
16:52
Speaker 1: it's important that it's hydrogen and or helium because those
16:55
Speaker 1: are sort of the lightest elements, right, And so to
16:57
Speaker 1: make a proper star, you need fusee in and so
17:00
Speaker 1: it's easier to sort of merge together the lighter elements
17:03
Speaker 1: than it is to merge together like the heavy elements.
17:06
Speaker 1: That's right. To fuse hydrogen, you need a lower temperature
17:09
Speaker 1: than you do to fuse helium, which is a lower
17:11
Speaker 1: temperature than you need to fuse lithium. Etcetera, etcetera. So
17:14
Speaker 1: if you want to start a sun, you better start
17:16
Speaker 1: with a lot of hydrogen and something I think it's
17:18
Speaker 1: funny is that astronomers referred to anything that's not hydrogen
17:22
Speaker 1: or helium as a metal, by which I think they
17:25
Speaker 1: just mean like, oh, this is a serious heavy element.
17:27
Speaker 1: But you know, like chemists or like oxygen is not
17:30
Speaker 1: a metal. You know, carbon is not a metal, but
17:32
Speaker 1: according to astronomers, it's helium, hydrogen or metals. It's like
17:36
Speaker 1: there's only three elements of the periodic table for astronomers, hydrogen, helium,
17:41
Speaker 1: and metal. That's it. It's sort of like musical taste,
17:45
Speaker 1: like someone who's really into classical music thinks anything not
17:48
Speaker 1: classicals like heavy metal inten that's right e either Mozart
17:52
Speaker 1: or it's hip hop exactly. Yeah, So you need a
17:55
Speaker 1: lot of hydrogen and helium, which is good because the
17:57
Speaker 1: universe started with a whole bunch of hydrogen and lium, right,
18:01
Speaker 1: But you can also make it like if I have
18:03
Speaker 1: a whole bunch of oxygen, can I make a star
18:05
Speaker 1: out of just oxygen? You could make a star out
18:07
Speaker 1: of just oxygen, and if you had enough of it
18:10
Speaker 1: and it was cold enough and near enough to itself,
18:13
Speaker 1: then it could pull itself together with gravity, and you
18:16
Speaker 1: could even you know, get oxygen fusion happening to make
18:19
Speaker 1: heavy your stuff. That certainly is possible. Could that happen naturally?
18:23
Speaker 1: It wouldn't happen naturally because the amount of oxygen in
18:26
Speaker 1: the universe is tiny compared to the other stuff in
18:29
Speaker 1: the universe. So, you know, most of the stuff in
18:31
Speaker 1: the universe still hydrogen. You know, we've been burning stars
18:34
Speaker 1: for billions of years to make quote unquote metals like oxygen,
18:38
Speaker 1: but we haven't made that much progress. You know, it's
18:40
Speaker 1: still overwhelmingly hydrogen. So you make a random star, it's
18:44
Speaker 1: gonna be mostly hydrogen helium. Now, the like fraction of
18:48
Speaker 1: metals in stars has been increasing as the universe goes up,
18:51
Speaker 1: just because there's more of that stuff around. But to
18:54
Speaker 1: get like a star sized blob of oxygen by itself,
18:57
Speaker 1: that's never gonna happen. Well, I mean, I guess in
19:00
Speaker 1: infinite universe somewhere it's happening, right, Or like we could
19:03
Speaker 1: maybe engineering maybe somehow. That sounds like a fun project.
19:08
Speaker 1: Let's make an oxygen Why do you do that? What
19:11
Speaker 1: are you doing this? Weekend. Oh, I got some you know,
19:13
Speaker 1: house projects going and make an oxygen star. Yeah, clean
19:17
Speaker 1: mic bathroom, and also make a star. All right, So
19:20
Speaker 1: then that's kind of how the stars form, and I
19:22
Speaker 1: think we've talked in other episodes about kind of what
19:25
Speaker 1: happens then, right, like, eventually all of that hydrogen and
19:27
Speaker 1: helium merges into heavier elements, and those merging two even
19:32
Speaker 1: heavier elements, and at some point the star burns out
19:35
Speaker 1: or kind of implodes. Right, there's a couple of possibility therapy.
19:39
Speaker 1: As fusion happens, it creates heavier elements, and those heavier
19:42
Speaker 1: elements are then fuel for the next round of fusion,
19:45
Speaker 1: which are fuel for the next round of fusion. But
19:47
Speaker 1: at some point it stops. When you get up to
19:49
Speaker 1: iron and iron can't fuse and create energy. If you
19:53
Speaker 1: fuse iron and iron, you actually lose energy, and so
19:56
Speaker 1: that cools down the star, and so it's sort of
19:59
Speaker 1: like it creates I should eventually it snuffs the star out,
20:02
Speaker 1: and so the star is no longer able to resist
20:06
Speaker 1: the gravitational forces because it's not producing enough radiation pressure
20:10
Speaker 1: to resist that collapse. And then depending on the mass
20:13
Speaker 1: of the star, either you know, just like cools down
20:15
Speaker 1: into a white dwarf, or maybe it goes supernova and
20:18
Speaker 1: blows its material out, or maybe it goes supernova and
20:21
Speaker 1: the core becomes a black hole. Depends on exactly how
20:24
Speaker 1: much stuff you started from. But yeah, eventually stars do
20:27
Speaker 1: fizzle out, right, So the star is born, it lives,
20:31
Speaker 1: and it dies, and that's one generation of star. And
20:34
Speaker 1: then how it the next generation of star form? Then
20:36
Speaker 1: if it just snuffs out, or if it turns into
20:38
Speaker 1: a black hole, because it doesn't capture all of the
20:41
Speaker 1: materials into the star and sort of hold onto them forever.
20:44
Speaker 1: Even in the scenario where you create a black hole,
20:46
Speaker 1: a large part of the material of the original star
20:49
Speaker 1: is blown out into the universe. Like our son for example,
20:52
Speaker 1: it won't go supernova and it won't go into a
20:54
Speaker 1: black hole, but still it's going to have this big
20:57
Speaker 1: red giant phase when it's burning helium and it puffs
21:00
Speaker 1: up to be really really huge, and a lot of
21:02
Speaker 1: the material gets really dispersed, and then it blows that
21:06
Speaker 1: stuff out into the universe. So when you end up
21:08
Speaker 1: with like a core that's left over from a star
21:11
Speaker 1: doesn't have all the material at the star, some of
21:13
Speaker 1: the stuff from the star is blown out into the universe,
21:16
Speaker 1: and then you can get remixed into the basic ingredients
21:19
Speaker 1: of hydrogen helium to form the next stars. So that's
21:22
Speaker 1: how you can sort of recycle material that's made in
21:25
Speaker 1: a star into other future stars or planets or people. Oh,
21:29
Speaker 1: I see, it's like when a star dies, most of
21:32
Speaker 1: its materials go out back into space, like you compost
21:35
Speaker 1: it kind of, you know, you don't throw it on
21:37
Speaker 1: in the trash, you know, it doesn't all get buried
21:39
Speaker 1: in a coffin, is put bike into the soil. Yes,
21:43
Speaker 1: some of it is sort of lost to black holes
21:46
Speaker 1: or maybe to a white dwarf that eventually will cool
21:48
Speaker 1: into a black dwarf and can't really be used again.
21:50
Speaker 1: But a lot of it is tossed back out there
21:53
Speaker 1: as fodder or ingredients for the next generation of stars,
21:56
Speaker 1: which will have a higher metal percentage than the previous generation,
21:59
Speaker 1: just because this star has now made more metals out
22:02
Speaker 1: of the wrong ingredients. Right, they'll be heavier metal, more extreme.
22:06
Speaker 1: But I guess you know, one question I have is, like,
22:09
Speaker 1: you know, stars are so far apart, like do you
22:11
Speaker 1: actually get mixing of like you know, left or star
22:14
Speaker 1: and stuff from one star mixing with left door stuff
22:16
Speaker 1: from another star, or is it mostly like it all
22:18
Speaker 1: stays within the same you know, recycling area. Stars are
22:23
Speaker 1: far apart, but you know they tend to be made
22:25
Speaker 1: in clumps. So you have like stellar nurseries, these big
22:28
Speaker 1: gas clouds where stars are made, and those gas clouds
22:31
Speaker 1: are collected both from the interstellar medium and the intergalactic
22:36
Speaker 1: medium and also from old stars. So along a long
22:39
Speaker 1: time scale, this stuff really does move around and gather,
22:43
Speaker 1: and so stuff doesn't just like stay in one place.
22:45
Speaker 1: There are flows and ebbs and currents of all of
22:48
Speaker 1: this stuff. All right, Well, so that's one generation of
22:51
Speaker 1: a star, and so you can have multiple generations as
22:54
Speaker 1: the stars and the stuff goes out and it comes
22:56
Speaker 1: back in. And so let's talk about how many generations
22:59
Speaker 1: there have been of stars in the universe, and then
23:02
Speaker 1: let's talk about what the future holds. But first let's
23:05
Speaker 1: take a quick break. Al Right, how many star generations
23:21
Speaker 1: have there been and will there be in the universe? Thaniel,
23:24
Speaker 1: we talked about one generation of a star, and we
23:27
Speaker 1: know that if a star eventually dies and all this
23:29
Speaker 1: stuff kind of goes out into space and then it
23:32
Speaker 1: maybe gets combined, and then that stuff then by gravity,
23:36
Speaker 1: I guess it cools off and then comes together again,
23:39
Speaker 1: and then maybe it ignites and then creates a new
23:42
Speaker 1: generation of a star. But eventually that star will die.
23:47
Speaker 1: So and this happens over I guess millions of years
23:49
Speaker 1: or billions of years. It depends a lot on the
23:52
Speaker 1: size of the star. So a larger star will burn
23:55
Speaker 1: hotter because it's core has a lot more pressure on it,
23:58
Speaker 1: so it's temperature is higher. It burns through its material
24:01
Speaker 1: much much faster. So the bigger the star, the shorter
24:04
Speaker 1: its lifespan. Like the stars a few hundred times the
24:07
Speaker 1: mass of the Sun, it might only live like two
24:10
Speaker 1: to five million years. If a star is really really small,
24:14
Speaker 1: like much smaller than the mass of the Sun, like
24:16
Speaker 1: right on the threshold, it might burn for a trillion years,
24:19
Speaker 1: whereas our star, you know, the Sun is going to
24:22
Speaker 1: burn for about ten billion years. So the serving size
24:26
Speaker 1: you get at the very beginning totally determines how long
24:28
Speaker 1: you will burn for. Interesting, it's sort of like rock stars.
24:32
Speaker 1: Some of them, you know, flame out after a one album,
24:35
Speaker 1: and some of them have a long and nice career.
24:39
Speaker 1: I guess Bob Dylan is very low mass, right, because
24:42
Speaker 1: he's like on album fifty. Yeah, and whereas you know,
24:45
Speaker 1: Rick Astly was a supernova. But so you're telling me
24:48
Speaker 1: that each generation of a star, there's sort of no
24:51
Speaker 1: fixed time period. Like in human years, you can think
24:53
Speaker 1: of a generation as being roughly, I don't know, thirty
24:57
Speaker 1: forty years, but in a star it could be like
24:59
Speaker 1: one year or hundred years. Yeah, but it is a
25:01
Speaker 1: sort of similar to humans, right. Some humans live a
25:04
Speaker 1: long time and have kids in their nineties, like Charlie Chaplin.
25:07
Speaker 1: Some people have kids when they're teenagers, and so over
25:10
Speaker 1: fifty years you might have like three generations. It's sort
25:13
Speaker 1: of similar with stars. And that's why I was saying earlier,
25:15
Speaker 1: it's not exactly clear, you know, to say like which
25:17
Speaker 1: generation a star is in, because if I have material
25:20
Speaker 1: from all sorts of sources, including two generation stars or
25:23
Speaker 1: three generation stars, or even pristine material left over from
25:27
Speaker 1: the Big Bang. So it's tricky, but you can sort
25:29
Speaker 1: of organize roughly into a few generations when we look
25:34
Speaker 1: back into the cosmic history, you mean, sort of like
25:36
Speaker 1: the average or maybe just looking at like our son,
25:39
Speaker 1: we know how many generations it's at yeah, Well, we
25:42
Speaker 1: don't know actually how many generations the history of our
25:44
Speaker 1: son features, because in theory, you could have a series
25:48
Speaker 1: of really really massive stars hundreds and hundreds of times
25:52
Speaker 1: the mass of the Sun that die and burnout and
25:55
Speaker 1: die and burnout and dying burnout. You could have, you know,
25:58
Speaker 1: material that's been in a hundred of those stars that's
26:00
Speaker 1: around there in the universe right now. So we don't
26:03
Speaker 1: actually know for any given piece of material how many
26:05
Speaker 1: stars it's been in. What we can do is look
26:08
Speaker 1: at the stars we see in our galaxy and in
26:11
Speaker 1: other galaxies, and we notice something interesting. We noticed sort
26:14
Speaker 1: of like two rough populations of stars. Stars that seem
26:18
Speaker 1: to be sort of a lot older and have less
26:21
Speaker 1: medals in them, and then start the tend to be
26:23
Speaker 1: younger and bluer and hotter and have more medals in them.
26:26
Speaker 1: But then each of those would be in a sort
26:28
Speaker 1: of different generation, right, Like some of them might be
26:31
Speaker 1: you know, a hundred ten generation and someone might be,
26:35
Speaker 1: you know, fifteen or five. That's right. But the interesting
26:38
Speaker 1: thing about these two populations, so we have like the
26:41
Speaker 1: older ones and the younger ones, the older ones we
26:44
Speaker 1: call population two stars, is that they all seem to
26:47
Speaker 1: be really really old. They all seem to have formed
26:50
Speaker 1: like eleven, twelve, thirteen billion years ago and to still
26:54
Speaker 1: be around. So those stars probably are a second generation
26:58
Speaker 1: stars at most because they formed very very early on
27:02
Speaker 1: in the universe and they're still around. So that limits
27:04
Speaker 1: like how many generations of stars there could be before them.
27:08
Speaker 1: The other population of stars we see, what we call
27:10
Speaker 1: population one. They're still forming today. Oh, I see, you're
27:14
Speaker 1: sort of categorizing what do you see out there in
27:16
Speaker 1: the universe. You're not categorizing by generation. You just sort
27:19
Speaker 1: of looking out there and categorizing by age, Like, Wow,
27:23
Speaker 1: does over there look pretty young, so they must be
27:26
Speaker 1: later generation, but these over here look really old, so
27:29
Speaker 1: they must be kind of like one of the O
27:30
Speaker 1: G generation. Yeah. It's just like looking at humans and
27:33
Speaker 1: you're like, well, this bunch of people all are similar
27:36
Speaker 1: and come from a similar era and act the same way.
27:38
Speaker 1: So we'll call them boomers, right, and these folks will
27:41
Speaker 1: call gen z ers. And you know, there's not a
27:43
Speaker 1: crisp delineation between generations between millennials and gen xers and whatever.
27:48
Speaker 1: But it's sort of a rough rule of thumb, especially
27:51
Speaker 1: when we look out there we notice, just like we
27:53
Speaker 1: noticed in human populations, these sort of clusters of stars
27:56
Speaker 1: that have similar properties. All right, So then you can
27:59
Speaker 1: categorize kind of age out there by what we see
28:03
Speaker 1: right now, and so step us through what are the
28:04
Speaker 1: different populations. So what we've seen are these two populations
28:08
Speaker 1: population one in population too. And you know these are
28:11
Speaker 1: historical names given by a German astronomer back in the
28:14
Speaker 1: forties when he was looking at these stars and he
28:16
Speaker 1: saw that a bunch of them were bluer stars and
28:19
Speaker 1: these were tend to be like in the galactic disc,
28:21
Speaker 1: right far from the center, and that closer to the
28:24
Speaker 1: center you had more red stars. So we called them
28:27
Speaker 1: population one in population two. He didn't understand at the
28:29
Speaker 1: time what it meant that population two stars were probably
28:32
Speaker 1: much much older. In population one stars were more recent,
28:36
Speaker 1: But we know that now and it makes sort of
28:38
Speaker 1: sense because you know, as stars live in the galaxy,
28:42
Speaker 1: they tend to slow down in their orbit and sort
28:45
Speaker 1: of fall towards the center. So the center of the
28:48
Speaker 1: galaxies mostly these older stars that formed, like you know, eleven, twelve,
28:53
Speaker 1: thirteen billion years ago, and they have less metals in
28:56
Speaker 1: them than the other stars because they were formed in
28:59
Speaker 1: the time when the verse had less metal in it,
29:01
Speaker 1: it was more hydrogen. So those are the population two stars.
29:04
Speaker 1: They tend to be like making up the bulge of
29:07
Speaker 1: the galaxy. And then also they're in these weird globular
29:10
Speaker 1: clusters that sort of orbit the galaxy that we had
29:13
Speaker 1: a whole fun podcast episode about. I guess maybe a
29:15
Speaker 1: question is how do we know how old they are?
29:17
Speaker 1: And how do we know how much metal is in them?
29:20
Speaker 1: Like is it from like the spectrum of the light
29:22
Speaker 1: that comes from them or the distance? Like how do
29:25
Speaker 1: we know their age from how far they are? Or
29:28
Speaker 1: like how can we tell their age? And is that
29:29
Speaker 1: polite to ask? That's a little tricky their age. What
29:33
Speaker 1: you can do is you can look at the color
29:34
Speaker 1: of the star. Stars tend to be bluer when they're
29:37
Speaker 1: younger because bluer means hotter, and so hotter stars don't
29:42
Speaker 1: last as long, they don't live as long, and so
29:45
Speaker 1: if you see a star that's blue, that means it
29:47
Speaker 1: must be younger because they just don't have that long
29:50
Speaker 1: a life cycle. Like if you see a cat, you
29:52
Speaker 1: know that cat is not a hundred years old because
29:54
Speaker 1: there just aren't any hundred year old cats. So if
29:56
Speaker 1: you see blue stars, you know that they tend to
29:58
Speaker 1: be younger. Red stars are either old stars or they
30:03
Speaker 1: might be smaller stars. And so it's not exactly clear
30:06
Speaker 1: always when you look at a star's color to tell
30:09
Speaker 1: its age. But what we do see is that population
30:12
Speaker 1: one stars tend to have a lot of blue stars
30:14
Speaker 1: in them, which means that they're young, whereas in the
30:16
Speaker 1: bulge there aren't very many blue stars. So let's suggests
30:19
Speaker 1: that there aren't many young stars there, and most of
30:21
Speaker 1: those are pretty old. Oh I see, Wait, you're grouping
30:24
Speaker 1: them by location or by how old you think they are? Well, both,
30:27
Speaker 1: and there's a correlation there, right. The stars in the
30:29
Speaker 1: center tend to be reader and older, and the stars
30:33
Speaker 1: in the disc tend to be bluer and younger. All right,
30:36
Speaker 1: So then I guess you can assume that the younger
30:38
Speaker 1: stars are maybe a later generation, right because they were
30:42
Speaker 1: born more recently, whereas the older stars they might be
30:46
Speaker 1: even one of the original generations, right, because if you're
30:48
Speaker 1: saying they're fourteen billion years old, that's when the universe started. Yeah,
30:51
Speaker 1: we don't think that they're part of the original generation.
30:54
Speaker 1: They are like you know, eleven to thirteen billion years old,
30:57
Speaker 1: so we think they formed, like you know, a billion
30:59
Speaker 1: years after the start of the universe. He also asked
31:02
Speaker 1: about how we can tell what they're made at it.
31:03
Speaker 1: That's another clue. When we look at the spectrum from
31:06
Speaker 1: the stars, how they're glowing, we can tell what's inside
31:09
Speaker 1: the star because different elements glow at different temperatures. They
31:13
Speaker 1: tend to like get excited at different energy levels, so
31:16
Speaker 1: they have like a characteristic fingerprint. So just as you said,
31:18
Speaker 1: we can look at the spectrum of light that tells us, like,
31:21
Speaker 1: you know, how much light in there at this frequency
31:23
Speaker 1: and how much of that frequency tells you exactly the
31:26
Speaker 1: composition of the star. And what we see is that
31:28
Speaker 1: these stars tend to have a lot less metal in
31:31
Speaker 1: them than the stars that are forming today, like even
31:33
Speaker 1: our sun. So these population two stars can have like
31:37
Speaker 1: a hundreds or thousands as much iron in them, for example,
31:41
Speaker 1: as our sun. So that also suggests that they were
31:44
Speaker 1: formed earlier in the universe when the universe had less
31:47
Speaker 1: metal in it. Oh, I see right, because as the
31:49
Speaker 1: as the star progresses through its life, it makes metals, right,
31:53
Speaker 1: But then if it's been alive for that long or
31:55
Speaker 1: burning for that long, wouldn't it have made a lot
31:57
Speaker 1: of metals, But by now it makes metals, but you know,
31:59
Speaker 1: not that much. And that's when a star burns. It's
32:02
Speaker 1: mostly burning helium and hydrogen. It doesn't convert all of
32:05
Speaker 1: that into iron, for example. But the fast burning ones
32:08
Speaker 1: do create metals more quickly, I guess, or at east
32:13
Speaker 1: generation burns and is born, then you sort of increment
32:17
Speaker 1: in metalicity, but not every star makes it all the
32:20
Speaker 1: way up to iron. Like, you need enough stuff in
32:23
Speaker 1: the star to create the conditions so you can get
32:26
Speaker 1: hot enough so you can fuse the stuff to make iron.
32:29
Speaker 1: Some stars stop after making helium or lithium or carbon
32:32
Speaker 1: or neon or whatever, depending on how much mass they
32:35
Speaker 1: have in the temperature that they achieve. All right, so
32:37
Speaker 1: then what does that tell us about how many generations
32:39
Speaker 1: there have been in the universe? Since we know that
32:42
Speaker 1: you know, the older stars are only a few generations
32:44
Speaker 1: in but do we know how many generations the younger
32:47
Speaker 1: stars are or what generation they're in. Yeah, we're not sure,
32:51
Speaker 1: but the current thinking is that there are roughly three generations.
32:55
Speaker 1: So these stars we call population one. These younger stars
32:58
Speaker 1: like our sun that are out around the disc, including
33:01
Speaker 1: stars that are just forming and stars that are a
33:03
Speaker 1: few billion years old. These are the ones with a
33:05
Speaker 1: lot of metals in them, like they start with like
33:07
Speaker 1: one to four percent of them are made out of metal.
33:10
Speaker 1: So that's population one. And then the population to the
33:12
Speaker 1: one sort of in the bulge of the galaxy, the
33:15
Speaker 1: older ones. We call those population two. And we think
33:18
Speaker 1: that there was a population before that, that very early
33:21
Speaker 1: on in the universe, before any of the stars that
33:23
Speaker 1: are burning today were formed, that there was an initial
33:26
Speaker 1: star forming phase, but that all those stars are gone.
33:29
Speaker 1: Now that those stars didn't last very long, just a
33:32
Speaker 1: few million years, maybe tens or hundreds of millions of years,
33:35
Speaker 1: but that those are all gone, and we call those
33:37
Speaker 1: population three stars. So we've never actually seen one because
33:41
Speaker 1: they're so old, they would be very very distant and
33:43
Speaker 1: so very hard to make out. So that's sort of
33:46
Speaker 1: the rough timelines. Population three stars were the first in
33:48
Speaker 1: population too, and now today we're making population one stars.
33:52
Speaker 1: I feel like you picked the opposite order, like the
33:55
Speaker 1: higher than the number of population the first in order
33:59
Speaker 1: of time. I know, because the next generation of stars
34:01
Speaker 1: gonna be what population zero zero and then minus one.
34:04
Speaker 1: I think you named yourself until corner there. Physicist, I
34:07
Speaker 1: think we certainly did. It's sort of like you know,
34:09
Speaker 1: deciding the charge of the electron, like whoops, that was
34:12
Speaker 1: not the best choice. But I don't think at the
34:15
Speaker 1: time we really understood the context is sort of the
34:18
Speaker 1: historical sweep of all of this stuff, or we definitely
34:20
Speaker 1: would have named it something else. All Right, So there
34:22
Speaker 1: was an original generation of stars. But those stars you're
34:26
Speaker 1: saying they're all gone because I guess in the early
34:29
Speaker 1: universe things were sort of like hot and volatile, and
34:32
Speaker 1: so all those stars burned out pretty quickly. Yeah, we
34:34
Speaker 1: think that those stars were really big. The very very
34:37
Speaker 1: first stars were like hundreds of millions of times the
34:40
Speaker 1: mass of the Sun. It was harder to make smaller
34:43
Speaker 1: stars early on because there wasn't as much metal, so
34:46
Speaker 1: it's difficult to get like a big blob of stuff
34:48
Speaker 1: too cool. Like if you have some metal that can
34:51
Speaker 1: sede a core to gather stuff together, it's like a
34:54
Speaker 1: heavier spot. But if you just have a big cloud
34:56
Speaker 1: of gaseous hydrogen, it's harder to get like a small
34:59
Speaker 1: clump to other. So these first stars were probably like
35:02
Speaker 1: hundreds of times the mass of the Sun and then
35:05
Speaker 1: burning for only like a few million years and dying
35:08
Speaker 1: at supernova after making a little bit of you know
35:11
Speaker 1: what astronomers would call medals. But again, we haven't seen those,
35:14
Speaker 1: so they're they're hypothetical. Like we've seen really really distant galaxies,
35:18
Speaker 1: some of the first galaxies that ever formed, but we
35:20
Speaker 1: can't resolve the stars in those galaxies, so we can't
35:24
Speaker 1: say we've ever seen a population three star. Interesting that
35:27
Speaker 1: they're only sort of in our imagination or in our
35:30
Speaker 1: I guess theories about where the second population of stars
35:33
Speaker 1: came from. Yeah, it's like the oral history of your family, right,
35:37
Speaker 1: maybe you don't have any pictures of great great great
35:39
Speaker 1: grandma Janine or whatever, but maybe your family knows something
35:43
Speaker 1: about what she liked for breakfast and that she was
35:45
Speaker 1: a rock star. Maybe it was very bright back in
35:48
Speaker 1: Lithuania or whatever. So then that first generation burned out
35:52
Speaker 1: and that gives the population to which are redder but
35:56
Speaker 1: a little bit cooler. And in that population, some of
35:58
Speaker 1: that population burned out, and that where the population one
36:02
Speaker 1: that we see now and like our son comes from,
36:05
Speaker 1: but our son, right, it has a mix of stuff
36:07
Speaker 1: in it. It has some stuff, certainly from population two
36:11
Speaker 1: stars that burned out, probably some stuff from population three stars,
36:14
Speaker 1: but also it has a lot of stuff that hasn't
36:16
Speaker 1: done anything since the Big Bang. Because our son is
36:20
Speaker 1: seventy hydrogen and twenty percent helium, so it's only like
36:24
Speaker 1: one to two percent metals. Most of the stuff in
36:28
Speaker 1: our sun is basically on its first act since the
36:31
Speaker 1: Big Bang happened. But we still think it's a third
36:33
Speaker 1: generation star. Yeah, because it has stuff in it that
36:36
Speaker 1: was created from other suns like that one to two
36:39
Speaker 1: percent that really changes what a star is. And that
36:42
Speaker 1: stuff was made by other suns. And you know, like
36:45
Speaker 1: most of the Earth is that kind of stuff, Like
36:47
Speaker 1: most of the Earth is not hydrogen or helium. Right,
36:49
Speaker 1: So basically everything on our planet came from the death
36:53
Speaker 1: of a star, whereas the Sun is mostly pristine. Stuff
36:56
Speaker 1: from the Big Bang still got a lot to go
36:58
Speaker 1: on and ply more generations. And so I guess the
37:02
Speaker 1: question is how good is that stuff in the Sun,
37:04
Speaker 1: Like it's good for one more generation or a billion
37:08
Speaker 1: more generations? What will the future hold? So let's get
37:11
Speaker 1: into that, But first let's take another quick break. Al Right,
37:26
Speaker 1: how many generations, so stars will there be in the future.
37:29
Speaker 1: We know that our son is sort of like the
37:31
Speaker 1: third generation star in the universe's history, and so the
37:35
Speaker 1: question is is this like the beginning of the history
37:37
Speaker 1: of stars or you know, or do we only have
37:40
Speaker 1: a few more generations left. Yeah, it's really fun to
37:43
Speaker 1: think about what the future might look like, and you
37:46
Speaker 1: have to like think deep, deep into the future of
37:48
Speaker 1: the universe. And I think there's sort of two big questions.
37:51
Speaker 1: You know. One is like, if you had perfect conditions
37:55
Speaker 1: for making stars, so that you could always gather the
37:57
Speaker 1: hygien together and healing together to burn it, how long
38:00
Speaker 1: would it take to burn all that fuel and convert
38:03
Speaker 1: it all to iron for example? You know, that's one question,
38:07
Speaker 1: But the reality is that the universe is not a
38:09
Speaker 1: perfect laboratory form. Making starts. You need very specific conditions.
38:14
Speaker 1: So I think we should also think about, like how
38:16
Speaker 1: long the universe will be conducive to star making. You
38:18
Speaker 1: might have the ingredients you need to make stars unburned hydrogen,
38:22
Speaker 1: but that doesn't necessarily mean that you're gonna be making stars. Well,
38:25
Speaker 1: let's think about it. Maybe just our star, Like what's
38:28
Speaker 1: gonna happen to our start. We know, we talked about
38:30
Speaker 1: how it's going to burn out and sort of blow up,
38:32
Speaker 1: get big and then cool down eventually. But and then
38:35
Speaker 1: do you think another star will take its place eventually? Well,
38:37
Speaker 1: our star is probably going to turn into a white dwarf, right,
38:40
Speaker 1: which is just like a hot lump of stuff. No
38:43
Speaker 1: longer fusion is happening, but it's still really hot and
38:45
Speaker 1: so it's glowing, which is why it's called a white dwarf.
38:48
Speaker 1: And white dwarfs are stable, like, we don't think they
38:51
Speaker 1: really do anything else. They just sit there and gradually
38:54
Speaker 1: cool off until they become a black dwarf, and that
38:57
Speaker 1: could take, you know, trillions of years. We don't think
38:59
Speaker 1: there are any black dwarfs in the universe right now.
39:01
Speaker 1: There's a bunch of white dwarfs sitting there glowing hot,
39:04
Speaker 1: but none of them have had enough time to cool
39:06
Speaker 1: the black dwarfs. But that doesn't mean that our sun
39:09
Speaker 1: won't contribute to the next generation of stars because the
39:12
Speaker 1: white dwarf doesn't take all the material from the Sun.
39:15
Speaker 1: There's a lot of the material from the Sun that
39:17
Speaker 1: will get blown out into maybe a new planetary disk
39:20
Speaker 1: for that white dwarf or just out into the interstellar
39:23
Speaker 1: medium and contribute to another generation of stars. So our
39:27
Speaker 1: star it's going to become a white dwarf and then
39:30
Speaker 1: blow out its stuff out into space, which then is
39:32
Speaker 1: gonna maybe combined with the hydrogen helium from other stars
39:37
Speaker 1: that burned out and then make other stars. Yeah, and
39:40
Speaker 1: this happens because the sun before it burns out, before
39:43
Speaker 1: it stops fusing, it gets really really big, and the
39:45
Speaker 1: outer shells tend to get blown out while the inner
39:48
Speaker 1: part collapses. So it seese outer layers of the star
39:51
Speaker 1: they're gonna get blown out and they can definitely contribute
39:53
Speaker 1: to future stars or a planet. There could be aliens
39:56
Speaker 1: ten billion years from now that are eating their cereal
39:59
Speaker 1: and thinking, wow, this could have been another star billions
40:02
Speaker 1: of years ago, and they would be right. I see,
40:04
Speaker 1: when you're eating your cereal, you you are maybe? I
40:07
Speaker 1: mean everything is made in the chorus stars, right, and
40:10
Speaker 1: anything about hydrogen and yeah, unless you're eating hydrogen for breakfast,
40:14
Speaker 1: what you're eating was made in a star. Interesting, not recommended,
40:18
Speaker 1: but not as filling or it is I guess pretty
40:21
Speaker 1: filling hydrogen the cereal Oh the humanity, Oh, I see,
40:25
Speaker 1: so it's not like a star blows up and then
40:27
Speaker 1: in its place and you star forms. It's like you
40:30
Speaker 1: need this kind of like mixing between the spaces of stars, right, Yeah,
40:34
Speaker 1: it's more like you know, when a tree dies and
40:36
Speaker 1: it gives its nutrients back into the ground. You don't
40:38
Speaker 1: automatically just get a new trine exactly the same spot.
40:41
Speaker 1: It just provides nutrients for a future plant to gobble
40:45
Speaker 1: up and to build something else. So you're saying one
40:47
Speaker 1: scenario is that this keeps happening for a long time.
40:51
Speaker 1: You know, you get more generations of star but eventually,
40:54
Speaker 1: like all of the hydrogen and helium in the universe
40:56
Speaker 1: is going to have been consumed, maybe could be by
41:00
Speaker 1: stars and turn into heavier metals. Yeah, I don't think
41:03
Speaker 1: that's likely to actually happen in our universe, and we
41:06
Speaker 1: can talk about why it'd be difficult to arrange that.
41:09
Speaker 1: But in theory, if you engineer the universe to be
41:12
Speaker 1: a perfect star making laboratory, then yeah, you could eventually
41:16
Speaker 1: burn all the fuel. Like it's one direction. Or we're
41:18
Speaker 1: not making more hydrogen, right, We're just decreasing the amount
41:21
Speaker 1: of hydrogen in the universe as years go by. It's
41:24
Speaker 1: not an unrenewable resource, right right, yeah, because I guess
41:28
Speaker 1: you can fuse things together, but it's kind of hard.
41:31
Speaker 1: Once you made all this iron, eventually it's hard to
41:35
Speaker 1: like turn it back into hydrogen. Yeah, these things are stable,
41:38
Speaker 1: Like if you go far enough and you make uranium
41:40
Speaker 1: and then that stuff is unstable, it'll break down, but
41:43
Speaker 1: it'll break down into something else stable. It's not gonna
41:45
Speaker 1: go all the way back down to hydrogen. Helium is
41:47
Speaker 1: pretty stable, doesn't split spontaneously into hydrogen. So yeah, hydrogen
41:51
Speaker 1: is not a renewable resource. Like you know, we got
41:54
Speaker 1: a lot of it. It's gonna take a long time
41:56
Speaker 1: to burn through all of it. But as the years
41:58
Speaker 1: go on, the hydrogen for action of the universe is dropping.
42:01
Speaker 1: So like, if you made a whole universe made out
42:03
Speaker 1: of iron, it wouldn't do anything, like you would just
42:06
Speaker 1: sit there. It depends on the distribution, but it probably
42:08
Speaker 1: would form a lot of black holes. And that's pretty
42:10
Speaker 1: dense stuff. So you know, if you had like a
42:13
Speaker 1: solar sized blob of iron, it will collapse into a
42:16
Speaker 1: black hole. All right. So then I guess technically, if
42:19
Speaker 1: you were to engineer the universe, how like how many
42:21
Speaker 1: generations of stars. Do you think we could get in
42:23
Speaker 1: It's hard to know. And I asked them aster physicists
42:26
Speaker 1: this question, and they were all just like, WHOA such
42:29
Speaker 1: a big number. I can't even imagine, um, you know,
42:32
Speaker 1: hygrogenive depletion. I got some estimates between a hundred trillion
42:37
Speaker 1: and tend to the one hundred years to deplete all
42:40
Speaker 1: the hydrogen in the universe years. But how much is
42:43
Speaker 1: that in generations? Well, it depends, right. Stars can burn
42:47
Speaker 1: for maybe ten billion years or a trillion years, depending
42:50
Speaker 1: on their mass, or they could even burn short amounts
42:54
Speaker 1: of time if you have more massive stars. We don't
42:56
Speaker 1: really see a lot of really really massive stars. But
42:59
Speaker 1: so if you say, for example, the average length of
43:01
Speaker 1: a lifespan of the stars maybe ten billion years, then
43:05
Speaker 1: that's still a lot of generations, right Then a trillion
43:08
Speaker 1: years has a hundred generations in it. A hundred trillion years, right,
43:12
Speaker 1: it's ten thousand generations in it. If it's even longer
43:16
Speaker 1: time spans, and we're talking thousands and thousands of generations.
43:19
Speaker 1: So from that point of view, like we're on generation three,
43:22
Speaker 1: we're really just getting started. I would have thought that
43:24
Speaker 1: you can maybe just computed from the fact that, for example,
43:27
Speaker 1: we're on our son isn't the generation three, and it
43:30
Speaker 1: already has one of other stuff. So wouldn't each generation
43:35
Speaker 1: sort of take up another one to two percent of
43:37
Speaker 1: the hydrogen and helium. Yeah, that's a good question. I
43:39
Speaker 1: don't think this stuff that gets thrown out in the
43:41
Speaker 1: universe is an equal sampling of the stuff that the
43:44
Speaker 1: star made. Like the stuff in the core is the
43:46
Speaker 1: stuff that's most likely to get kept into the white Dwarf, right,
43:49
Speaker 1: So the heavy stuff is less likely to get distributed
43:52
Speaker 1: out into the universe. So the next generation of star
43:55
Speaker 1: is not going to have like all of the iron
43:57
Speaker 1: that was made in the previous generation. Most of that
43:59
Speaker 1: stuff is gonna end up either in the black hole
44:01
Speaker 1: or the white dwarf or the neutron star that's left over.
44:04
Speaker 1: But I guess if you're engineering it though, like you,
44:07
Speaker 1: I'm gonna burn my son. My son is gonna burn
44:09
Speaker 1: until it has one or two percent of other stuff.
44:11
Speaker 1: Then I'm gonna throughout all that one or two percent
44:14
Speaker 1: of stuff and take all the hygiene and healing and
44:16
Speaker 1: make an e star eventually. That's how I'm gonna run
44:19
Speaker 1: out right, Because I'm gonna be losing each generation. Yeah,
44:22
Speaker 1: if you're optimal about it, then I suppose you could
44:24
Speaker 1: spend one generation burning about a percent or so of
44:28
Speaker 1: the stuff in the universe, in which case maybe we
44:30
Speaker 1: would run out at some point right through a hundred
44:33
Speaker 1: generations maybe. Yeah. So it depends a lot on how
44:35
Speaker 1: this stuff is distributed and how you organize it, and
44:38
Speaker 1: the mass of the stars that you are making, how
44:40
Speaker 1: long it takes for these things to happen. But yes,
44:42
Speaker 1: somewhere between hundreds or thousands of generations of stars. Wow,
44:47
Speaker 1: and then that's it, no more stars. And then that's it,
44:50
Speaker 1: no more stars exactly. And in that scenario, the universe
44:54
Speaker 1: is dark, you know, it's just like populated by a
44:57
Speaker 1: bunch of white dwarfs that are slowly who link to
45:00
Speaker 1: black dwarfs, and it's basically not generating any light. And
45:04
Speaker 1: that's just like the ideal you know, horehy magical engineering
45:07
Speaker 1: scenario where you are able to extract all the hygiene
45:10
Speaker 1: and helium you're saying like that, in real life, the
45:12
Speaker 1: physics of like for me and you start are actually
45:15
Speaker 1: much harder exactly. But before we leave that, I want
45:17
Speaker 1: to throw out one thing which is that in that
45:20
Speaker 1: future really dark universe, there won't be any stars made,
45:23
Speaker 1: but occasionally you might get a bright flash of light
45:26
Speaker 1: because white dwarfs can actually create light, like if two
45:29
Speaker 1: of them come together, they can combine and give you
45:33
Speaker 1: like a type one a supernova. This is very special
45:36
Speaker 1: kind of supernova, and so for a few weeks it
45:38
Speaker 1: can like brighten up the neighborhood it's in before dimming again.
45:42
Speaker 1: So the deep deep far future would be mostly dark
45:45
Speaker 1: with these like occasional few week long bursts of light.
45:48
Speaker 1: And then again this is still like the optimal scenario, right,
45:51
Speaker 1: so it could be a hundred to a thousand generations
45:53
Speaker 1: of starts optimally, but really it could be a lot less. Really,
45:57
Speaker 1: it could be a lot less. And when you look
45:59
Speaker 1: around in the orse, you notice something, which is that
46:02
Speaker 1: the rate of star formation in the universe is dropping,
46:06
Speaker 1: Like we used to be making more stars sort of
46:09
Speaker 1: per year a billion years ago than we are now,
46:12
Speaker 1: Like the rate of new star creation is falling in
46:15
Speaker 1: our universe. So meaning what would you put the estimate
46:18
Speaker 1: of the number of generations ever add like would it
46:22
Speaker 1: be It might be less than a hundred, then it
46:24
Speaker 1: might be less than a hundred. Absolutely, it might be
46:26
Speaker 1: less than twenty. You know, a lot of it depends
46:29
Speaker 1: on what's going to happen with dark energy. In order
46:31
Speaker 1: to form stars, what you need is a bunch of
46:33
Speaker 1: stuff near each other, like these cold gas clumps near
46:37
Speaker 1: each other. But what dark energy is doing is that
46:39
Speaker 1: it's pulling galaxies away from each other, and so that
46:43
Speaker 1: makes it harder for like gas to clump together to
46:46
Speaker 1: fall into these galaxies and create new stars. And what
46:50
Speaker 1: we see around us is that there are lots of
46:52
Speaker 1: dead galaxies, galaxies with lots of material in them, but
46:55
Speaker 1: there's just no more stars being formed. That's kind of sad.
47:00
Speaker 1: I guess they're like graveyard galaxies, nothing but embers. Yeah,
47:03
Speaker 1: because they don't have any like more gas falling into
47:06
Speaker 1: them to stimulate star formation. And also sometimes in the
47:10
Speaker 1: center of these galaxies, the black hole that's formed these
47:13
Speaker 1: supermassive black hole can be emitting so much energy that
47:16
Speaker 1: basically heats up those gas clouds so that they don't
47:19
Speaker 1: form stars because remember these gas clouds have to be cold.
47:23
Speaker 1: So you can get in these configurations where you have
47:25
Speaker 1: this huge amount of mass stuck in a galaxy but
47:27
Speaker 1: no light being created no stars being formed, and that's
47:31
Speaker 1: not something we understand very well. It's called star quenching.
47:34
Speaker 1: It's a really active area of research. But it might
47:36
Speaker 1: be that every galaxy is headed in that direction. It
47:39
Speaker 1: might just be a few more generations before all these
47:42
Speaker 1: galaxies sort of die and stop forming stars. And then
47:46
Speaker 1: what's going to happen after that? Like want the black
47:48
Speaker 1: hole eventually cooled down? And what want things cool down
47:51
Speaker 1: for that galaxy and maybe stars could kick back up again.
47:54
Speaker 1: We don't know. We don't think those black holes will
47:56
Speaker 1: cool down. We think they're just keep absorbing stuff. You know,
47:58
Speaker 1: stars will keep falling into them. They'll get it bigger
48:01
Speaker 1: and bigger. Some stars might get thrown out of those galaxies.
48:05
Speaker 1: Right the way that stars fall into the black holes,
48:07
Speaker 1: that they're basically like sort of bumping against each other,
48:09
Speaker 1: not physically bumping, but like exchanging kinetic energy. One of
48:13
Speaker 1: them slows down, the other one speeds up. So you'll
48:15
Speaker 1: throw some stars out of the galaxies into intergalactic space.
48:18
Speaker 1: And then these galaxies will just become bigger and bigger
48:21
Speaker 1: black holes. And if dark energy takes over, then you'll
48:24
Speaker 1: have these black holes separated by larger and larger distances,
48:27
Speaker 1: and so that's the future of the universe is these
48:30
Speaker 1: galaxies collapsing into ever distant black holes. So it sounds
48:34
Speaker 1: like the answer then too, the question of how many
48:36
Speaker 1: generations of stars will there be is maybe not that many,
48:39
Speaker 1: maybe only less than twenty to go before the whole
48:42
Speaker 1: universe is completely dark. Yeah, and it all depends on
48:45
Speaker 1: what happens with dark energy. Like if dark energy decides, hey,
48:48
Speaker 1: we're done with this expansion, let's turn everything around and
48:51
Speaker 1: bring galaxies together. Remember, we just don't understand dark energy
48:55
Speaker 1: at all. We have no mechanism to explain what it's doing,
48:58
Speaker 1: which means we can't predict its future. And it might,
49:01
Speaker 1: for example, turn around and bring everything back together, which
49:04
Speaker 1: could stimulate whole new periods of star formation, you know,
49:07
Speaker 1: before the universe is squeezed back down into a new
49:10
Speaker 1: big crunch. So, really, are ignorance of the number of
49:13
Speaker 1: future generations comes from our ignorance of the overall fate
49:17
Speaker 1: of the future of the universe. So I guess the
49:18
Speaker 1: lesson is a don't invest in sunscreen, maybe invest in
49:22
Speaker 1: flashlight batteries or anti dark energy devices. I guess if
49:26
Speaker 1: you know you're saying that if dark energy reverses or
49:29
Speaker 1: goes away, then then you might get possibly more stars
49:32
Speaker 1: in the future, but right before the universe crunches down,
49:35
Speaker 1: So it's it's not that useful. Nobody be a bright ending.
49:38
Speaker 1: We'll go out with a bang, with a flash, We'll
49:40
Speaker 1: be our goodbye tour. Alright, Well, I think that answers
49:43
Speaker 1: the question. It kind of makes you appreciate the sun
49:46
Speaker 1: right now, like it could be maybe only in the
49:49
Speaker 1: middle of its like universal lifespan of stars. That's right.
49:53
Speaker 1: We don't know how many times this magical thing will happen,
49:56
Speaker 1: that this blob of gas and dust and a little
49:58
Speaker 1: bit of heavier stuff will collapse into this incredible right
50:03
Speaker 1: ball of heat that's capable of burning and burning and
50:06
Speaker 1: burning so stably that life has a chance to evolve
50:09
Speaker 1: on the service of planets near it. We don't know
50:12
Speaker 1: how many more times that will happen, so we should
50:14
Speaker 1: definitely cherish this one experience. Yeah, that that means that,
50:17
Speaker 1: like you said, it's the only reason life exists at all,
50:19
Speaker 1: So you know, maybe the universe won't get them any
50:22
Speaker 1: chances in the future to make more life. That's right,
50:25
Speaker 1: So we better figure out space travel before that happens,
50:29
Speaker 1: and better flashlight technology as well. All right, well, we
50:32
Speaker 1: hope you enjoyed dad, Thanks for joining us, see you
50:36
Speaker 1: next time. Thanks for listening, and remember that Daniel and
50:46
Speaker 1: Jorge explain the Universe is a production of I Heart
50:49
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50:56
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