Latest / Daniel and Kelly’s Extraordinary Universe / What can we learn from dwarf galaxies?

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What can we learn from dwarf galaxies? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Daniel, what's your favorite thing about looking up at the stars?
0:12
Speaker 1: You mean, other than the hot coco? Did you always
0:14
Speaker 1: drink hot coco when you look at the stars? Do
0:16
Speaker 1: you have like a peplold in response? There? Can you
0:19
Speaker 1: see stars if you're not holding hot coco? I've never tried.
0:22
Speaker 1: It might steam up your glasses. No, But I mean
0:24
Speaker 1: like about the actual stars, not not what you're drinking
0:27
Speaker 1: when you look at them. I don't know. I love
0:29
Speaker 1: how big everything is up there, the stars, the galaxies,
0:33
Speaker 1: all of us, just so overwhelmingly huge. But aren't you
0:37
Speaker 1: a little bit biased about that? What do you mean?
0:39
Speaker 1: I mean you're only seeing the big stuff when you
0:41
Speaker 1: look up at the sky. There's plenty of little cute
0:44
Speaker 1: stuff on those stars or on those planets. Oh yeah,
0:47
Speaker 1: that's true, I suppose, But it doesn't change my mind.
0:49
Speaker 1: You still like big stuff. I like my universe the
0:52
Speaker 1: way I like my hot coco. Big and dark him
1:11
Speaker 1: or handy cartoonists and the creator of PhD comics. Hi,
1:14
Speaker 1: I'm Daniel. I'm a particle businessist and a professor at
1:17
Speaker 1: uc Herbhine, and I don't really drink that much hot coco.
1:21
Speaker 1: But does that mean you don't look at the stars
1:22
Speaker 1: very much. It does, unfortunately mean I don't look at
1:25
Speaker 1: the stars very much. Basically, it's because I don't do
1:27
Speaker 1: as much camping as I used to, and camping was
1:29
Speaker 1: my number one way to see the stars and also
1:32
Speaker 1: to drink hot cocoa. You know you can do all
1:34
Speaker 1: those three things independently. What that's not true. You can't
1:38
Speaker 1: just make hot coco at home in your living room
1:41
Speaker 1: or look at the stars. Next, you're telling me you
1:43
Speaker 1: can like make s'mores over your range. You could even
1:46
Speaker 1: do it on the microwave. What you have under those
1:49
Speaker 1: super smart microwaves? Did you got for free? I think
1:53
Speaker 1: that would cause offense to the fundamental nature of space
1:55
Speaker 1: and time making smores in the microwave. Yes, you'd be
1:58
Speaker 1: blacklisted by the Boy and Girls Couts. But anyways, Welcome
2:02
Speaker 1: to our podcast Daniel and Jorge Explain the Universe, a
2:05
Speaker 1: production of iHeartRadio in which we take a long, deep
2:08
Speaker 1: sip of this sweet, sweet universe, trying to appreciate all
2:12
Speaker 1: of its incredible flavors and colors and mysteries. We look
2:17
Speaker 1: out into the cosmos and we wonder why things are
2:20
Speaker 1: the way they are, why they look the way they do.
2:22
Speaker 1: And if it's possible to explain all of it, to
2:25
Speaker 1: understand the swirling and the dancing and the frothing and
2:28
Speaker 1: all the twoing and frowing that's happening up there in
2:31
Speaker 1: the night sky, and to explain all of it to you,
2:35
Speaker 1: that's right. We'd give you some more of this amazing universe,
2:38
Speaker 1: all the hot stuff, all the cold stuff, all of
2:41
Speaker 1: the chocolate stuff, and even all of the vanilla stuff.
2:43
Speaker 1: That's also pretty interesting. Did you say even all of
2:46
Speaker 1: the vanilla stuff, Like vanilla is an afterthought? I thought
2:49
Speaker 1: you were a great defender of vanilla as an actual flavor.
2:51
Speaker 1: I am a big defender. It's my favorite flavor. That's
2:54
Speaker 1: like saying your favorite color is white, dude, it is.
2:56
Speaker 1: Actually I love nothing more than a black page. The
3:01
Speaker 1: more white I can put into my drawings, the less
3:03
Speaker 1: work I have to do. A white page is usually
3:06
Speaker 1: the enemy of creative types. But I'm glad that it
3:08
Speaker 1: inspires you. But it's true that there's a lot of
3:11
Speaker 1: stuff out there to enjoy and to experience, of all
3:13
Speaker 1: different flavors and all different sizes. Sometimes people focus on
3:18
Speaker 1: the biggest, craziest, most extreme stuff in the universe, but
3:21
Speaker 1: there's a whole scale of things happening out there, tiny
3:24
Speaker 1: little gas clouds all the way up to supermassive galaxies.
3:28
Speaker 1: That's right, All of the big stuff in the universe
3:30
Speaker 1: usually gets all the big headlines. People mostly pay attention
3:34
Speaker 1: to supermassive black holes or giant superstars that are millions
3:38
Speaker 1: of times bigger than our sun. But sometimes it's the
3:40
Speaker 1: little stuff that can tell you a lot about the
3:43
Speaker 1: big ideas in the universe. Because remember that we don't
3:46
Speaker 1: get to control what happens in the universe. If we
3:48
Speaker 1: want to learn the way the universe works, we just
3:51
Speaker 1: got to sit back and watch the experiments that nature
3:54
Speaker 1: has arranged for us. We don't get to say what
3:57
Speaker 1: happens if you shoot two black holes together. We just
3:59
Speaker 1: have to look to see if somebody has already smashed
4:02
Speaker 1: them together. And so, because we are beggars, we don't
4:05
Speaker 1: get to be choosers, and that means that we need
4:07
Speaker 1: to make the most of everything that's out there. We
4:10
Speaker 1: need to think about what we can learn from the
4:12
Speaker 1: big stuff and also what we can learn from the
4:14
Speaker 1: little stuff, because everything out there in the universe has
4:17
Speaker 1: something to teach us, and there is a lot to
4:19
Speaker 1: be taught out there in the universe, a lot of
4:22
Speaker 1: amazing things big and small, and so today we're going
4:25
Speaker 1: to focus on one type of thing out there in
4:27
Speaker 1: the universe then maybe doesn't get as much attention as
4:30
Speaker 1: some of the big stuff, so to be on the program,
4:32
Speaker 1: we'll be asking the question what are dwarf galaxies? I
4:42
Speaker 1: love they We're going to get to talk about dwarf
4:44
Speaker 1: galaxies today because they are some of the most fascinating
4:46
Speaker 1: and interesting and reviewing aspects of the universe. They have
4:51
Speaker 1: so much to teach us about what's going on and
4:54
Speaker 1: where everything came from. Yeah, they're pretty exciting and pretty awesome,
4:58
Speaker 1: and so as usual, we were wondering how many people
5:00
Speaker 1: out there had thought about dwarf galaxies or know what
5:03
Speaker 1: they are. So thank you very much to everybody who
5:05
Speaker 1: answers these questions for the podcast. We love hearing your thoughts,
5:09
Speaker 1: as does everybody else. And if you are out there
5:12
Speaker 1: and have been listening to podcast for a while and
5:14
Speaker 1: would like to share your voice for everybody else, please
5:17
Speaker 1: don't be shy right to us two questions at daniel
5:19
Speaker 1: an Horgay dot com. So think about it for a second.
5:22
Speaker 1: What do you think our dwarf galaxies. Here's what people
5:26
Speaker 1: had to say. My guess is they're just smaller galaxies,
5:28
Speaker 1: smaller collections of stars that have not yet been swallowed
5:32
Speaker 1: up by a big galaxy. I would imagine at all
5:35
Speaker 1: galaxies kind of start out that way and grow and
5:39
Speaker 1: merge and until they become big, beautiful spirals like the
5:43
Speaker 1: Milky Way. Dwarf galaxies are like those little mini galaxies,
5:47
Speaker 1: and they can be like satellite galaxies to galaxies like
5:51
Speaker 1: the Milky Way, just a tiny little galaxies, not that big.
5:55
Speaker 1: I don't know. Maybe a dwarf galaxy is a galaxy
5:59
Speaker 1: with not enough mass to be considered a galaxy, like
6:02
Speaker 1: what happened to Pluto. I don't know. I'm guessing land
6:06
Speaker 1: or galaxies, as the name suggests, are smaller galaxies. I
6:11
Speaker 1: guess that by the name, dwarf galaxies have a lot
6:15
Speaker 1: less stars and planets and other stuff. But I don't
6:19
Speaker 1: know how smaller it has to be to be considered
6:22
Speaker 1: a dwarf galaxy. The term dwarf galaxies kind of reminds
6:27
Speaker 1: me of the galaxies that are like globular clusters, so
6:34
Speaker 1: or it might just be as it says in the name.
6:36
Speaker 1: They're just smaller galaxies, maybe much less stars, maybe a
6:43
Speaker 1: different shape, maybe maybe less dark matter keeping them together.
6:52
Speaker 1: I don't believe there probably won't be any black hole
6:56
Speaker 1: in the center, but there might be, I don't know.
6:59
Speaker 1: All right, straightforward answers here, everyone said they're just a galaxies,
7:03
Speaker 1: but smaller. It's like a dwarf serving of ice cream
7:07
Speaker 1: or a dwarf cup of cocoa. Oh yeah, that is
7:10
Speaker 1: that a new diet perhaps little servings of everything. I
7:13
Speaker 1: think that's maybe the oldest diet. Well that's a thing
7:15
Speaker 1: on the internet, right, there are all these videos of
7:17
Speaker 1: people making like little, tiny, like lego sized foods. Really
7:22
Speaker 1: like instead of having a saying which you just have
7:24
Speaker 1: like a tiny little sandwich. Yeah, there's this whole genre
7:27
Speaker 1: of YouTube videos they make like tiny food. Oh but
7:29
Speaker 1: that's not for eating, right, that's just for like being silly.
7:33
Speaker 1: Nobody's sitting down to tuck into like a tiny roast chicken,
7:36
Speaker 1: are they. Well maybe they could, they could, I don't know.
7:39
Speaker 1: They usually cut the videos after they make the food.
7:41
Speaker 1: I do like those tiny kitchen videos. Those are really fun.
7:44
Speaker 1: All right, Well, let's dig into it, Daniel, what is
7:47
Speaker 1: a dwarf galaxy. So everybody was basically right, Dwarf galaxies
7:51
Speaker 1: are a little cute galaxies. Because it turns out that
7:54
Speaker 1: galaxies come in all sorts of sizes. We tend to
7:58
Speaker 1: think about galaxies in term of ones like our own
8:01
Speaker 1: the Milky Way that has hundreds of billions of stars,
8:06
Speaker 1: Like galaxies that are much much bigger than the Milky Way,
8:08
Speaker 1: all the way down to galaxies that are very very
8:11
Speaker 1: small things that you probably wouldn't even call a galaxy.
8:15
Speaker 1: Maybe let's put things into perspective, but like, how big
8:17
Speaker 1: is our galaxy? What are the size ranges that qualify
8:21
Speaker 1: a galaxy is a dwarf galaxy? So our galaxy has
8:24
Speaker 1: somewhere around two hundred to four hundred billion stars. That's
8:29
Speaker 1: a really difficult number to wrap your mind around. Two
8:31
Speaker 1: hundred like a billion times two hundred exactly. There are
8:35
Speaker 1: more stars in the galaxy than people on Earth. Right,
8:39
Speaker 1: It's incredible, like every single person on Earth could have
8:42
Speaker 1: like pointier soul stars just for themselves in the Milky Way.
8:46
Speaker 1: It's really an incredible number of stars out there, hold
8:49
Speaker 1: them firing and burning with planets around them. Lots of
8:52
Speaker 1: Earth like planets. It's really hard to sort of like
8:55
Speaker 1: get the whole scope of the galaxy in your mind.
8:57
Speaker 1: But that's the size of our galaxy, a few hundred
9:01
Speaker 1: billion stars. You'd be like Oprah. You'd be giving up
9:04
Speaker 1: stars to everyone. You get a star, and you get
9:06
Speaker 1: a star, You're all stars. That's right. Donate to the
9:09
Speaker 1: podcast and I will give you a star in return. Now,
9:13
Speaker 1: do you offer free home delivery for that? Or do
9:15
Speaker 1: you have to pay for shipping? See that's how they
9:17
Speaker 1: get you the shipping. It's the free star, but it's
9:20
Speaker 1: gonna cost you ten trillion dollars to deliver it to
9:23
Speaker 1: your house and also the life of very human on Earth.
9:26
Speaker 1: M Yeah, And in this case, it's not just the shipping,
9:28
Speaker 1: it's the handling, right, because that's particularly tricky when you're
9:31
Speaker 1: dealing with something several thousand degrees kelvin. But no, I
9:35
Speaker 1: will email you a plaque of ownership of your star
9:37
Speaker 1: if you donate to the podcast. Oh boy, I feel
9:39
Speaker 1: like you just made a serious offer. Let's see if
9:42
Speaker 1: we get any takers. But our galaxy, as big as
9:45
Speaker 1: it is, is not even the biggest galaxy out there.
9:49
Speaker 1: How big do galaxies get like Andromeda. How big is Andromeda?
9:53
Speaker 1: Andromeda has more than a trillion stars in it. It's
9:56
Speaker 1: about five times as big as the Milky Way, like
9:59
Speaker 1: totally dwarfs us in terms of galaxies, And there are
10:03
Speaker 1: other galaxies out there that are even bigger. WHOA, what's
10:06
Speaker 1: the biggest galaxy that we know of? Or what's the
10:08
Speaker 1: biggest galaxy that Google knows of? So the biggest galaxy
10:12
Speaker 1: that we know of is about a billion light years away.
10:14
Speaker 1: It's called I See one one oh one, and there's
10:18
Speaker 1: a lot of uncertainty, but the current estimate is that
10:21
Speaker 1: it has the mass of about one hundred trillion stars,
10:25
Speaker 1: so like a hundred times more stars than Andromeda. Whoa,
10:29
Speaker 1: which is already five times bigger than us, So it's
10:31
Speaker 1: like five hundred times bigger than us in terms of mass. Yeah,
10:35
Speaker 1: there's some nuances there because there's a big variation in
10:38
Speaker 1: the masses of stars. Actually, more stars are smaller than
10:41
Speaker 1: the mass of our sun. Remember, the most common kind
10:44
Speaker 1: of star out there is a red dwarf, which is
10:46
Speaker 1: smaller than the kind of star that we have. So
10:49
Speaker 1: if you're just measuring the mass in terms of like
10:51
Speaker 1: our solar masses, that's going to underestimate the number of
10:55
Speaker 1: stars that are out there in that galaxy, so it
10:57
Speaker 1: may even be more. This is just like a really
11:00
Speaker 1: shocking number, hundreds of trillions of stars. You know. For comparison,
11:04
Speaker 1: there's like a few trillion trees on Earth, So that
11:07
Speaker 1: means that like every tree on Earth could have like
11:10
Speaker 1: twenty stars in that mega galaxy. WHOA, Well, I'm not
11:14
Speaker 1: sure trees are collecting stars these days, but you're welcome
11:19
Speaker 1: to assign a star for every tree in the galaxy.
11:23
Speaker 1: Any tree that donates to the podcast, I will email
11:25
Speaker 1: them a certificate of ownership. They technic they kind of
11:28
Speaker 1: do already because I print out the outline every single
11:32
Speaker 1: time on paper. Wow, which means you're sacrificing trees for
11:35
Speaker 1: the podcast. Yeah. I like to think they donated for
11:38
Speaker 1: the good of the of knowledge, But I guess maybe
11:42
Speaker 1: a question is like, is there an upper limit to
11:44
Speaker 1: the size of a galaxy or can galaxies just be
11:47
Speaker 1: infinitely big? And if there's a limit, what causes that limit?
11:50
Speaker 1: Is it something about the conditions at the beginning of
11:52
Speaker 1: the universe. There's no technical limit to the size of
11:55
Speaker 1: a galaxy. Galaxies just form and get bigger and bigger.
11:59
Speaker 1: That's fundamental the history of the universe is that galaxy
12:02
Speaker 1: started out basically a small clumps of stars, which then
12:06
Speaker 1: merge with other clumps of stars, and so you get
12:08
Speaker 1: this like hierarchical formation, this merging of mergers of mergers,
12:13
Speaker 1: and so there's no reason why you can't just like
12:16
Speaker 1: keep clumping galaxies together, and they are going to keep
12:18
Speaker 1: clumping together. Really, the only thing that limits the size
12:21
Speaker 1: of the galaxy is the fact that the universe is expanding,
12:24
Speaker 1: and that expansion is accelerating, so it's increasing the distances
12:28
Speaker 1: between galaxies, so it sort of like keeps the galaxy
12:32
Speaker 1: separated a little bit and prevents them from colliding all
12:35
Speaker 1: into one huge mega galaxy. So it's a bit of
12:38
Speaker 1: a race against time, right because recently the universes started
12:43
Speaker 1: accelerating right in terms of its expansion, So maybe we
12:46
Speaker 1: have seen the biggest galaxies that will ever form. Some
12:48
Speaker 1: cosmologists think that we live at the time of the
12:51
Speaker 1: biggest structures in the universe because of the accelerating expansion
12:55
Speaker 1: of the universe, then size of structures cannot grow anymore
12:59
Speaker 1: because so much space is being created between existing galaxies,
13:03
Speaker 1: and so like we have galaxies, and we have clusters
13:05
Speaker 1: of galaxies that are mostly held together by gravity. Then
13:08
Speaker 1: we have superclusters which are sort of on the edge
13:10
Speaker 1: of whether gravity can hold them together or dark energy
13:14
Speaker 1: will rip them apart. And so it might be that
13:16
Speaker 1: like our cluster of galaxies eventually collapses into one big galaxy,
13:21
Speaker 1: maybe even our supercluster collapses into a super galaxy. But
13:25
Speaker 1: the stuff and other superclusters, probably dark energy will keep
13:29
Speaker 1: us from ever merging with them. So we might get
13:31
Speaker 1: future bigger galaxies, but we won't ever get like bigger
13:34
Speaker 1: blobs of stuff. We might have reached sort of like
13:37
Speaker 1: peak size of blob or like at the end of purity,
13:43
Speaker 1: it's all downhill after that, stuff just starts falling apart
13:47
Speaker 1: after that. Yeah, hopefully let's get to party as much
13:50
Speaker 1: as we can right now. But I guess it also
13:52
Speaker 1: depends on what dark energy is going to do in
13:54
Speaker 1: the future, right Isn't it a possibility that dark energy
13:56
Speaker 1: will reverse and it will cause everything to start contract
14:00
Speaker 1: and then we'll very basically at the entire universe is
14:02
Speaker 1: going to collapse into a clump and then it'll be
14:06
Speaker 1: like one giant galaxy. Basically, it certainly does depend on that.
14:09
Speaker 1: The scenario we just outlined assumes that dark energy continues
14:13
Speaker 1: the way that it has that's constant in space, and
14:16
Speaker 1: that as space gets bigger, you add more dark energy.
14:20
Speaker 1: So dark energy is an increasing fraction of the energy
14:23
Speaker 1: density of the universe, which just further accelerates the expansion.
14:27
Speaker 1: If you just extrapolate that out naively, then yeah, you
14:30
Speaker 1: get the scenario we just outlined. But as you say,
14:32
Speaker 1: we don't really understand dark energy where it comes from.
14:35
Speaker 1: What is this source of potential energy that's accelerating the
14:38
Speaker 1: expansion of the universe. Could it change? And in fact
14:41
Speaker 1: it might, right because we don't know the underlying mechanism
14:44
Speaker 1: that creates it. It could be that there's some complicated
14:47
Speaker 1: dynamics there that change with time and give us a
14:50
Speaker 1: different future. Like it could just all turn off suddenly
14:53
Speaker 1: and then we have a big crunch where everything collapses down,
14:56
Speaker 1: as you say, into one big superstructure, one megaga. But
15:01
Speaker 1: we're not here today to talk about the super big galaxies.
15:04
Speaker 1: They get enough attention. Let's turn our mental eyes down
15:07
Speaker 1: to the other end of the spectrum. Yep, yep, we're
15:10
Speaker 1: talking about dwarf galaxies, and like you said, it's the
15:13
Speaker 1: case that all galaxies started out as dwarf galaxies, right,
15:16
Speaker 1: Like at the beginning of the universe, everything was spread out,
15:20
Speaker 1: but then these things started to clump together, and so
15:23
Speaker 1: everything started with small galaxies. Yeah, everything started with these
15:26
Speaker 1: little fluctuations due to quantum mechanics, a little bit that
15:29
Speaker 1: was more dense over here, a little bit that was
15:31
Speaker 1: less dense over there, and then gravity did its work
15:34
Speaker 1: and pulled that stuff together and made little clumps of
15:37
Speaker 1: gas which then turned into stars. And that's how you
15:40
Speaker 1: got the first galaxies. So there was like a size
15:43
Speaker 1: of those clumps that formed the first galaxies. And you know,
15:46
Speaker 1: some of those have merged into bigger galaxies, and some
15:49
Speaker 1: of them have not, and some of them are more
15:50
Speaker 1: recent and haven't yet merged into other galaxies. So at
15:54
Speaker 1: the small end of the scale are those little mini
15:57
Speaker 1: galaxies that have not merged or not merged. As many times,
16:00
Speaker 1: I wonder if there's like an average size galaxy at
16:03
Speaker 1: the beginning of the universe, do you know what I mean? Like,
16:06
Speaker 1: the universe presumably was kind of the same everywhere, and
16:09
Speaker 1: there's a certain density of stuff, which means that on average,
16:13
Speaker 1: there was probably like like every galaxy was almost the
16:16
Speaker 1: same size, right, some small size. Yeah, And we can
16:19
Speaker 1: actually see this in the cosmic microwave background radiation. We
16:22
Speaker 1: can see this pattern of overdensity and under density, and
16:25
Speaker 1: we can use that size actually to measure like the
16:28
Speaker 1: expansion rate of the universe. We have a whole podcast
16:31
Speaker 1: episode about like measuring the curvature of space and the
16:34
Speaker 1: history of it, and you can see those kind of
16:36
Speaker 1: things expand from an early characteristic quantum fluctuation size lown
16:41
Speaker 1: up into something macroscopic, which, as you say, then determines
16:46
Speaker 1: basically the size of these initial clumps. Yeah. But again
16:49
Speaker 1: it's quantum base, right, So it's totally random. So there
16:51
Speaker 1: could have been maybe a spot in the universe but
16:54
Speaker 1: that had a big fluctuation which maybe would have made
16:56
Speaker 1: a big galaxy out there at the beginning of time. Yeah,
16:59
Speaker 1: it random, you're right, and so it's less likely, but
17:02
Speaker 1: it's possible to get a larger gravitational collapse an early
17:05
Speaker 1: galaxy that started out big. But there's also a typical
17:08
Speaker 1: characteristic size where galaxies start, and so that's on the
17:13
Speaker 1: little end, and so these dwarf galaxies are basically on
17:16
Speaker 1: that smaller end of little gravitational clumps that formed little
17:20
Speaker 1: stellar neighborhoods. And so right now we have these galaxies
17:24
Speaker 1: and giant structures of galaxies. But it used to be
17:27
Speaker 1: the case, maybe at the beginning of the universe, where
17:30
Speaker 1: like the entire universe was just kind of evenly distributed
17:33
Speaker 1: with tiny little galaxies. Yeah, and these galaxies get to
17:36
Speaker 1: be pretty small, like remember the Milky Ways, hundreds of
17:40
Speaker 1: billions of stars. Dwarf galaxies can go all the way
17:44
Speaker 1: down to like hundreds or thousands of stars, all the
17:48
Speaker 1: way up to like several billion stars. So there's an
17:51
Speaker 1: enormous spectrum of size there, from really just a handful
17:54
Speaker 1: of stars all the way up to billions of stars. Mm. Interesting.
17:58
Speaker 1: All right, let's get more into actual dwarf galaxies and
18:01
Speaker 1: what they can tell us about dark matter and the
18:03
Speaker 1: rest of how the universe form. But first let's take
18:07
Speaker 1: a quick break. All right, we're talking about dwarf galaxies,
18:22
Speaker 1: and we talked a little bit about how basically dwarf
18:24
Speaker 1: galaxies were the og galaxies in the universe, right like,
18:28
Speaker 1: at the beginning of time, every galaxy was a dwarf back. Yeah,
18:31
Speaker 1: there may have been some larger galaxies formed randomly, as
18:34
Speaker 1: you said, But the original galaxies, yeah, we're all dwarf galaxies,
18:38
Speaker 1: that's how it all began, and they usually kind of
18:42
Speaker 1: have a fuzzy shape to them, right, They don't have
18:44
Speaker 1: maybe this nice spiral shape or form that the Milky
18:48
Speaker 1: Way has. It's actually interesting and really subtle point there,
18:51
Speaker 1: because if you have an initial clump of stuff that
18:53
Speaker 1: collapses under gravity, it tends to form a disk, and
18:57
Speaker 1: it forms a disc because it's spinning, and it's spinning
18:59
Speaker 1: like around some particular axis. Gravity can squeeze it down
19:02
Speaker 1: sort of along that axis, but on the plane perpendicular
19:06
Speaker 1: to it, it can't squeeze it down as much because
19:08
Speaker 1: it's still spinning and it retains that angular momentum. So
19:11
Speaker 1: if you have just like an initial spinning blob of stuff,
19:13
Speaker 1: it tends to form a disc. Now, when dwarf galaxies
19:16
Speaker 1: merge together to make bigger galaxies, then you have like
19:19
Speaker 1: disc spinning in lots of different directions, and you end
19:21
Speaker 1: up with like more ellipsoid galaxies which eventually later then
19:25
Speaker 1: also collapse into like some big overall disc, which is
19:29
Speaker 1: why like the Milky Way is mostly a disc. All right. Well,
19:33
Speaker 1: then like how many. I guess that question is like
19:35
Speaker 1: how many dwarf galaxies do you need to come together
19:38
Speaker 1: to make a galaxy like the Milkyway, Because you're saying
19:40
Speaker 1: the Milky Way probably formed out of dwarf galaxies coming together, right,
19:43
Speaker 1: I'm just wondering how many it takes. Yeah, I mean
19:46
Speaker 1: if dwarf galaxies start out as a few thousand stars, right,
19:50
Speaker 1: and the Milky Way has a few hundred billion stars,
19:54
Speaker 1: then that means that the Milky Way might be like
19:57
Speaker 1: a million dwarf galaxies all smooth together into one big galaxy.
20:02
Speaker 1: But you said the range is between like a dwarf
20:04
Speaker 1: galaxy is between a thousand and several billion. Yeah, Well,
20:07
Speaker 1: you know, this is one of those sort of artificial
20:09
Speaker 1: distinctions in astronomy, like what do you call a galaxy
20:12
Speaker 1: and what do you call a dwarf galaxy. There's this
20:14
Speaker 1: threshold of a few Above a few billion or a
20:17
Speaker 1: few tens of billions of stars, it's called a galaxy,
20:21
Speaker 1: and below that it's called a dwarf galaxy. For example,
20:24
Speaker 1: the large Magellanic cloud is orbiting the Milky Way and
20:27
Speaker 1: it has like thirty billion stars in it. Some people
20:30
Speaker 1: call it a dwarf galaxy. Some people say, no, no,
20:32
Speaker 1: it's its own galaxy, and so that's a bit of
20:35
Speaker 1: an artificial distinction. But if you want to go like
20:36
Speaker 1: all the way back to the og galaxies out of
20:39
Speaker 1: which everything was built, then those are all going to
20:41
Speaker 1: start out pretty small. So if those are like a
20:44
Speaker 1: few thousand stars, then it's going to take millions of
20:46
Speaker 1: those to make a milky way. I feel like, if
20:50
Speaker 1: you have a thousand stars, maybe you shouldn't be called
20:52
Speaker 1: a galaxy, you know, that's such a that's more like
20:56
Speaker 1: a I don't know, like a star neighborhood or something
20:59
Speaker 1: star clump associated stars. That's the bias, right, that's us
21:02
Speaker 1: looking at our neighborhood and observing other galaxies. But something
21:06
Speaker 1: we learn as we develop better tools is to see
21:09
Speaker 1: fainter stuff, is to discover the stuff that is not
21:12
Speaker 1: as easy to spot. And the whole history of science
21:15
Speaker 1: is us drawing big conclusions from the stuff we first
21:18
Speaker 1: see and then discovering, oh, that wasn't representative. It turns
21:21
Speaker 1: out we need to revise our whole picture of how
21:24
Speaker 1: things work. And so we've been seeing the biggest, brightest,
21:27
Speaker 1: most exciting galaxies, but there the whole spectrum of other
21:30
Speaker 1: kind of stuff out there, whether you want to call
21:31
Speaker 1: it a galaxy or mini galaxy or galaxy no or
21:35
Speaker 1: dwarf galaxy. You know, that's just the name. You mean, Like,
21:38
Speaker 1: there could be aliens out there in one of these
21:40
Speaker 1: megan galaxies looking at us and saying, that's not a
21:43
Speaker 1: real galaxy. It only has four hundred billion stars. That's
21:47
Speaker 1: nothing exactly. Remember if we demote other galaxies that they
21:50
Speaker 1: might come for us. Yeah, but you're saying so, you're
21:52
Speaker 1: saying that our galaxy, the Milky Way, it probably is
21:55
Speaker 1: made up of hundreds of these original dwarf galaxies that
21:59
Speaker 1: the universe started with. Hundreds or thousands or maybe even
22:02
Speaker 1: millions of dwarf galaxies have been smooshed together. Like the
22:06
Speaker 1: stars that are in the Milky Way did not all
22:09
Speaker 1: start in the same part of the universe. They all
22:12
Speaker 1: came together after they already formed clumps of stars. So
22:16
Speaker 1: all the stars in the Milky Way did not form
22:17
Speaker 1: out of the same big gas cloud. You had like
22:20
Speaker 1: millions of different gas clouds that made millions of little
22:23
Speaker 1: pockets of stars which then formed together later into a
22:27
Speaker 1: bigger galaxy. You mean they were all sort of clumped
22:30
Speaker 1: together initially maybe is that what you're saying? But then
22:33
Speaker 1: within that giant cloud, little galaxies form that then eventually
22:38
Speaker 1: clumped together. Well, I mean they clumped together eventually, the
22:40
Speaker 1: same way that for example, Andromeda and the Milky Way
22:43
Speaker 1: will eventually merge in a few billion years. Gravity is
22:47
Speaker 1: inexorably pulling us together and we will form some big
22:50
Speaker 1: combined galaxy. I don't know what you call it, like
22:52
Speaker 1: the Andromeda Way or Milky Andromeda or something Vanilla Andromeda.
22:58
Speaker 1: I vote for vanilla and drama in tribute to the
23:00
Speaker 1: greatest flavor. Right. Sounds good? And then you can ask like, well,
23:04
Speaker 1: you know, did the Milky waan Andromeda? Did they form
23:07
Speaker 1: together out of the same big clump. Well, their gravitational
23:09
Speaker 1: future is secure that they will eventually be together, but
23:12
Speaker 1: really they formed separately and then came together. And that
23:15
Speaker 1: same idea applies to all the dwarf galaxies that formed
23:18
Speaker 1: the Milky Way and the dwarf galaxies that formed Andromeda.
23:21
Speaker 1: They sort of formed separately and then later came together
23:24
Speaker 1: to make bigger galaxies. So then has enough time gone
23:28
Speaker 1: by to explain how our gas they form out of
23:30
Speaker 1: maybe millions of little galaxies like I know, that's a
23:33
Speaker 1: big mystery with black holes. Right, Yeah, that's a great question.
23:37
Speaker 1: And that's actually one of the great triumphs of dark
23:39
Speaker 1: matter is that when we do simulations of our universe
23:42
Speaker 1: and we say, here's so much dark matter there was,
23:44
Speaker 1: and here's some quantum fluctuations, and then we just like
23:47
Speaker 1: run the clock forward, we can actually reproduce the large
23:51
Speaker 1: scale structure of the universe, formation of the big galaxies
23:55
Speaker 1: that we see. And actually the bigger galaxies we see
23:57
Speaker 1: do appear in our simulations. But as we'll talk about
24:00
Speaker 1: later in the podcast, the dwarf galaxies, we don't really
24:02
Speaker 1: understand why there aren't more of them. So we do
24:05
Speaker 1: understand some of it, but not all of it. Interesting,
24:08
Speaker 1: are there still dwarf galaxies merging into our Milky Way
24:11
Speaker 1: galaxy or within our Milky Way galaxy? Or are we
24:13
Speaker 1: pretty much like just one big unified family right now?
24:17
Speaker 1: There are so many dwarf galaxies still out there right now,
24:19
Speaker 1: A bunch of them are orbiting the Milky Way, right
24:22
Speaker 1: which means eventually they might get slurped up by the
24:25
Speaker 1: Milky Way. Wait, what we have like a galaxy system?
24:28
Speaker 1: Oh yeah, like we have our galaxy, and we have
24:30
Speaker 1: little galaxies orbiting around this. Yeah, we have satellite galaxies, right,
24:35
Speaker 1: little dwarf galaxies orbiting the Milky Way, trapped by our
24:39
Speaker 1: gravity and eventually they'll gets slurped up. WHOA, how many
24:42
Speaker 1: satellite galaxies do we have? That's an interesting and complicated question.
24:45
Speaker 1: We have something around a couple dozen satellite galaxies that
24:49
Speaker 1: we've discovered, and one of the big questions about the
24:52
Speaker 1: research right now is why don't we have more. So
24:56
Speaker 1: if you run these simulations, they suggest that you should
24:59
Speaker 1: get ga taxies about the size of the Milky Way,
25:01
Speaker 1: and we do, and that all makes sense, but they
25:04
Speaker 1: also suggest that the Milky Way should have a lot
25:06
Speaker 1: more dwarf galaxy satellites. There should be like five hundred
25:11
Speaker 1: of them orbiting the Milky Way, but we only see
25:13
Speaker 1: a couple dozen. And that's one of the things people
25:15
Speaker 1: are still confused about. And that's why dwarf galaxies are
25:18
Speaker 1: so interesting, because they're one of the things that remain
25:21
Speaker 1: not well understood interesting. So you're saying that, like, we
25:25
Speaker 1: run a simulation of the universe based on what we
25:27
Speaker 1: know and then explains the big stuff out there, like
25:30
Speaker 1: the galaxy superclusters and the bubbles and the walls of superclusters.
25:35
Speaker 1: But it doesn't match what we see kind of at
25:38
Speaker 1: the local level around us, around our galaxy. Yeah, exactly.
25:41
Speaker 1: It suggests that if you're going to have big galaxies
25:44
Speaker 1: that comes out of formations of a bunch of little ones,
25:46
Speaker 1: but not all the little ones should get slurped up
25:49
Speaker 1: into the big ones, that you should have lots and
25:51
Speaker 1: lots of little galaxies still left over orbiting the bigger galaxies.
25:55
Speaker 1: But when we look out into the night sky, we
25:57
Speaker 1: just don't see them like we look for them, try
26:00
Speaker 1: to spot them. We've seen some of them, but we
26:02
Speaker 1: don't see as many as we expect. It sounds like
26:04
Speaker 1: there's something wrong with the simulation, not necessarily with the universe.
26:09
Speaker 1: You know, the universe has to follow our program man. Yeah,
26:13
Speaker 1: that's what I'm saying. I don't think the universe cares. No,
26:16
Speaker 1: it's not that the universe has done something wrong and
26:18
Speaker 1: needs to be chastised or something. This is just the
26:21
Speaker 1: process we have. We think we understand the rules that
26:23
Speaker 1: control how things happen, and so then we do a
26:26
Speaker 1: bunch of simulations to say, what do the rules predict
26:28
Speaker 1: and if they predict something we don't see, that means
26:31
Speaker 1: obviously something is wrong with the simulation, but the question
26:34
Speaker 1: is what or the other thing is maybe something is
26:37
Speaker 1: wrong with what we're seeing, like maybe we're just not
26:39
Speaker 1: seeing everything that's out there. Dwarf galaxies are tricky to
26:43
Speaker 1: spot because they're small. They only have hundred thousands or
26:46
Speaker 1: maybe millions of stars in them, so they are much
26:49
Speaker 1: fainter than other galaxies, which make them more challenging to spot.
26:54
Speaker 1: So we were expecting from the simulations to see about
26:56
Speaker 1: five hundred dwarf galaxies orbiting the Milky Way, but we've
26:59
Speaker 1: only seen about twelve. And you're saying, like, I wonder
27:03
Speaker 1: if you could maybe even see them from our point
27:05
Speaker 1: of view, right, Like they're so small, maybe to us
27:07
Speaker 1: they just look like a little cluster of stars, not
27:10
Speaker 1: necessarily a whole other galaxy. It is complicated by the
27:13
Speaker 1: fact that we are inside the Milky Way, which makes
27:15
Speaker 1: it harder to see out of the Milky Way because
27:17
Speaker 1: there's so many stars and gas and dust in between.
27:20
Speaker 1: They have taken that into account, like how many galaxies
27:22
Speaker 1: should we have seen from our point of view that
27:26
Speaker 1: they have factored in something that they're not sure about
27:29
Speaker 1: has to do with the dark matter in these dwarf galaxies. Like,
27:32
Speaker 1: we also suspect, and I want to dig into this
27:34
Speaker 1: in a minute, that these dwarf galaxies are much heavier
27:37
Speaker 1: in dark matter than in normal matter. A typical galaxy
27:41
Speaker 1: is about eighty five percent dark matter fifteen percent normal matter.
27:45
Speaker 1: The Milky Way is a bit above that, like ninety
27:48
Speaker 1: percent dark matter ten percent normal matter. But these dwarf
27:52
Speaker 1: galaxies might be overwhelmingly dark matter. They might have a
27:55
Speaker 1: lot more dark matter in them than normal matter, which
27:58
Speaker 1: of course make them harder to spot. Now, this mystery
28:02
Speaker 1: about not seeing enough dwarf galaxies around the Milky Way,
28:05
Speaker 1: is that also true for other galaxies? Like if you
28:07
Speaker 1: look at the Andromeda galaxy, do you also see less
28:11
Speaker 1: or fewer dwarf galaxies than you think you would? Yeah,
28:15
Speaker 1: it's a problem everywhere. It's harder to study for more
28:17
Speaker 1: distant galaxies because they aren't more distant, and these galaxies
28:21
Speaker 1: are small. So you know, our observations of dwarf galaxies
28:25
Speaker 1: around Andromeda are not even as good as our observations
28:28
Speaker 1: of dwarf galaxies around the Milky Way, which are already
28:31
Speaker 1: very challenging to see. So the Milky Way is sort
28:34
Speaker 1: of like the best laboratory for studying this. But yeah,
28:36
Speaker 1: we see similar stuff in Andromeda. Beyond that, it's just
28:39
Speaker 1: too difficult to study. I guess it's kind of like
28:42
Speaker 1: trying to detect the wisps of smoke around, like a
28:45
Speaker 1: giant cloud of smoke. Right, that's kind of what these
28:48
Speaker 1: galaxies look like from far exactly, and it's not always
28:50
Speaker 1: easy to tell, like where is the edge of a galaxy?
28:53
Speaker 1: And is that the count is a dwarf galaxy or
28:55
Speaker 1: is it already falling into the main galaxy right against
28:59
Speaker 1: all sorts of distant Oh, I see that's the real mystery.
29:02
Speaker 1: I just change how you call them, then done. You
29:05
Speaker 1: can check off that box. No, it doesn't matter what
29:08
Speaker 1: you call them, because there's just a disagreement about the
29:10
Speaker 1: distribution of stars in our simulations and what we see
29:14
Speaker 1: out there in the universe. But a lot of astronomers
29:17
Speaker 1: think that probably this will be resolved if we improve
29:20
Speaker 1: our abilities to discover these dwarf galaxies. For example, recently
29:24
Speaker 1: they found eight new Milky Way dwarf galaxies that they
29:27
Speaker 1: hadn't spotted before because they are ultra faint because they
29:30
Speaker 1: are more than ninety nine point nine percent dark matter.
29:34
Speaker 1: They're basically dark matter galaxies with a little sprinkling of
29:37
Speaker 1: stars in them. WHOA wait, I feel like now you're
29:41
Speaker 1: getting into the definition of a galaxy itself. Like are
29:44
Speaker 1: you saying, like a bunch of dark matter with a
29:47
Speaker 1: few stars in it, that's a galaxy. Stick, that's a
29:51
Speaker 1: galaxy according to astronomers. Yeah, it has the mass, right,
29:54
Speaker 1: it has stars in it, so yeah, they call that
29:56
Speaker 1: a galaxy. I guess maybe the definition then is just
29:59
Speaker 1: like a stuff out there in space that's maybe separate
30:02
Speaker 1: from other clubs of stuff. Yeah, But then you get
30:05
Speaker 1: in the question like, what do you call a globular cluster?
30:07
Speaker 1: Why is that not a dwarf galaxy? Why is it
30:10
Speaker 1: a cluster? Exactly right, That's what I would That's why
30:12
Speaker 1: I'm confused. Now, Well, welcome the club. Astronomy is a
30:16
Speaker 1: disaster when it comes to naming things. And that comes
30:18
Speaker 1: from a particle physicist, and I know that we have
30:20
Speaker 1: no high ground when it comes to naming things. Yeah,
30:23
Speaker 1: I guess it's hard to name things in general, right,
30:26
Speaker 1: It's hard to name your kids. I can only imagine
30:28
Speaker 1: naming the entire universe. Well, the real challenge here is
30:31
Speaker 1: that a lot of this is historical. You know, we
30:33
Speaker 1: didn't always understand the connections between things. We saw stuff
30:36
Speaker 1: in the sky, we gave it different names. Later we realized, oh,
30:39
Speaker 1: this is really another kind of that. You know, even
30:41
Speaker 1: if you just look in our solar system, you know,
30:43
Speaker 1: we have like comets and asteroids, and then we have
30:45
Speaker 1: like centaurs, which are sort of like between comets and asteroids.
30:50
Speaker 1: We have planets, and we have moons, and like, you know,
30:52
Speaker 1: the distinctions between these things are fuzzy. What's really going
30:55
Speaker 1: on is that you have a whole spectrum of stuff
30:57
Speaker 1: out there, from big to small and every thing in between.
31:01
Speaker 1: So the distinctions between things are sort of artificial labels
31:04
Speaker 1: that we are just putting on stuff because what we
31:06
Speaker 1: historically saw first, what we sort of originally called things.
31:10
Speaker 1: The truth is that there's a smooth spectrum of all
31:13
Speaker 1: sorts of stuff out there. Sounds like you just need
31:15
Speaker 1: to call everything stuff, like a lot of galaxy. It's
31:19
Speaker 1: just stuff. That's not a black hole, it's just stuff.
31:22
Speaker 1: If I usually change your name from physicists to stuffists,
31:25
Speaker 1: stuff is this, yeah, exactly, I'm just you can be stuffy.
31:28
Speaker 1: Stuff is this? Yeah, I'm just trying to stuff as
31:29
Speaker 1: much knowledge in my mind about stuff. Basically, you know,
31:32
Speaker 1: it's different from like biology. Cats and dogs really are
31:35
Speaker 1: different things. There's not an entire spectrum of every creature
31:38
Speaker 1: between a cat and a dog. That doesn't exist. But
31:41
Speaker 1: I think out there in the universe there really is
31:43
Speaker 1: like every kind of thing between every other kind of thing.
31:46
Speaker 1: So there's a whole spectrum of stuff out there is
31:48
Speaker 1: just waiting to be discovered. Interesting. All right, Well, let's
31:52
Speaker 1: get a little bit deeper into this connection between dark
31:56
Speaker 1: matter and dwarf galaxies and how maybe dwarf galaxies can
31:59
Speaker 1: help us understand or finally figure out what dark matter is.
32:03
Speaker 1: But first let's take another quick break. All right, we're
32:18
Speaker 1: talking about dwarf galaxies. And it's pretty interesting that what
32:23
Speaker 1: you said earlier that like a clump of dark matter,
32:25
Speaker 1: which is a few sprinkles of stars, you would still
32:27
Speaker 1: call that a galaxy. I would still call that a galaxy.
32:31
Speaker 1: I mean, think about where that came from. Originally, you
32:34
Speaker 1: had a clump of stuff in the very early universe,
32:37
Speaker 1: a tiny little bit denser than everything else. Mostly that
32:40
Speaker 1: means the dark matter because it was more dark matter
32:43
Speaker 1: than everything else that dark matter makes like a little
32:45
Speaker 1: we call it a gravitational well. Everything likes to roll
32:48
Speaker 1: downhill towards lower gravitational potential. Gravity gathers stuff together, and
32:54
Speaker 1: so every little gravitational well gathered together a blob of
32:57
Speaker 1: dark matter and a blob of normal matter you know, gas, etc.
33:01
Speaker 1: And that led to star formation. And so it's because
33:04
Speaker 1: of dark matter that gas clumped together and made the
33:07
Speaker 1: first stars in the early universe. And so every sort
33:10
Speaker 1: of like original og clump there. I guess we call
33:13
Speaker 1: a dwarf galaxy. I see, Okay, I guess it's kind
33:16
Speaker 1: of also like our galaxies mostly dark matter too, Like
33:19
Speaker 1: the Milky Way is mostly dark matter with a few
33:22
Speaker 1: sprinkles of stars, like by mass, where the Milky Ways
33:25
Speaker 1: with fifteen percent Yeah, exactly. On average, the universe is
33:28
Speaker 1: about eighty percent dark matter in terms of mass, and
33:32
Speaker 1: so everything out there is mostly dark matter with a
33:35
Speaker 1: sprinkling of stars. Wait, are you saying the Milky Way
33:37
Speaker 1: should actually be called the milk chocolate the way. It's
33:40
Speaker 1: more like the hot Cocoa Way, right, It's really a
33:43
Speaker 1: river of dark deliciousness with a few sprinkles of marshmallows,
33:46
Speaker 1: like the stars are the marshmallows on top of the
33:48
Speaker 1: dark matter hot coco give means more. But what's fascinating
33:52
Speaker 1: is that these dwarf galaxies have much more dark matter
33:56
Speaker 1: than typical Like they can be up to ninety nine
33:58
Speaker 1: point ninety nine percent dark matter. Right, All dwarf galaxies
34:02
Speaker 1: are just these last few that we found. Most dwarf
34:04
Speaker 1: galaxies are overwhelmingly dark matter. There's are a few that
34:08
Speaker 1: are like satellites of the Milky Way that have had
34:10
Speaker 1: their dark matter stripped out of them, but the great
34:12
Speaker 1: majority of them are overwhelmingly dark matter. It's just sort
34:15
Speaker 1: of like the size of that clump of stuff tends
34:18
Speaker 1: to have fewer stars. Really, why is that if you
34:21
Speaker 1: have a smaller clump of stuff, you have less gravity
34:24
Speaker 1: sort of holding those initial stars together because stars are
34:28
Speaker 1: sort of poison to other stars. Like, what happens when
34:31
Speaker 1: you form stars is you get a bunch of radiations
34:33
Speaker 1: shooting out from that star, and that tends to heat
34:36
Speaker 1: up and blow out all the gas that you need
34:38
Speaker 1: to make stars. So remember to make a star, you
34:41
Speaker 1: need a blob of cold gas. The gas can't be
34:43
Speaker 1: like moving around too fast or gravity which is super
34:46
Speaker 1: weak won't have a chance to suck it together. So
34:49
Speaker 1: as soon as you start forming stars, then those stars
34:52
Speaker 1: like push out all the other gas. And then as
34:54
Speaker 1: soon as you have the first supernova, it basically blows
34:57
Speaker 1: out all the gas from a dwarf galaxy. But if
35:00
Speaker 1: you have a big enough clump, then they can retain
35:03
Speaker 1: that gas anyway. Right, So as you're sort of serving
35:06
Speaker 1: of gravity, you get smaller, you get too small to
35:09
Speaker 1: sort of overcome these supernova and these other effects that
35:13
Speaker 1: are killing your star formation. Oh I see, because I
35:16
Speaker 1: guess when a star explodes in a supernova, the dark
35:19
Speaker 1: matter doesn't care, right, Like a star will explode, but
35:23
Speaker 1: the dark messines it doesn't interact with dark matter, and
35:26
Speaker 1: the dark matter doesn't care, but it will blow out
35:28
Speaker 1: all the other star stuff that's in that Meni galaxy.
35:31
Speaker 1: And that's why if you're small, then you'll most likely
35:34
Speaker 1: blow out all of your star stuff, but you'll keep
35:37
Speaker 1: your dark matter stuff. So it's like you're super concentrating
35:40
Speaker 1: the dark matter, you're purifying, distilling it. There you go, yeah, distilling.
35:45
Speaker 1: So the dwarf galaxies that are still around. They're the
35:48
Speaker 1: ones with overwhelmingly dark matter and very very few stars
35:51
Speaker 1: in them. They had like one initial round of star
35:54
Speaker 1: formation and then they basically poison the well. So they're
35:57
Speaker 1: also super fascinating from that point of view because they're
35:59
Speaker 1: like fossils of star formation. They didn't have like many
36:03
Speaker 1: many cycles like that, sort of like a window into
36:05
Speaker 1: the much earlier part of the universe. But also they
36:09
Speaker 1: are these very cool blobs of dark matter. And you know,
36:12
Speaker 1: dark matter a continuing source of mystery and consternation for
36:16
Speaker 1: a physicists, and these are really awesome laboratories to study
36:20
Speaker 1: dark matter. But I guess you can't really see this
36:23
Speaker 1: dark matter, right, you're just inferring that it's there, or
36:25
Speaker 1: that this clump of stars has ninety nine point whatever
36:29
Speaker 1: amount of dark matter. You're just seeing a little bit
36:32
Speaker 1: of stars that are clumped together and spending more than
36:35
Speaker 1: they should, and so you're inferring that there's a bunch
36:37
Speaker 1: of dark matter there. Yeah, we're not seeing this dark
36:40
Speaker 1: matter like directly using gravitational lensing for example. I mean
36:43
Speaker 1: a few cases we can, but mostly we're inferring that
36:46
Speaker 1: these clumps of stars have a lot of dark matter.
36:49
Speaker 1: Based on the motion of the stars, which is originally
36:52
Speaker 1: how we discover dark matter. We saw that stars are
36:55
Speaker 1: moving really really fast, but that there's not enough stuff
36:58
Speaker 1: in the galaxy to hold them together if they're moving
37:01
Speaker 1: that fast, and which you can do if you look
37:03
Speaker 1: at the velocity of stars, how fast they're moving around
37:06
Speaker 1: the center of a galaxy is you can tell how
37:08
Speaker 1: much gravity does there have to be to keep that
37:11
Speaker 1: star at that distance from the center of that galaxy.
37:14
Speaker 1: And that gives you like a map of the gravity
37:16
Speaker 1: of that galaxy, which you can turn into a map
37:19
Speaker 1: of the mass of the galaxy. And so you can say,
37:21
Speaker 1: based on the spinning stars that I see, where is
37:24
Speaker 1: the mass in that galaxy? And that tells you where
37:27
Speaker 1: the dark matter is in that galaxy. So like a
37:29
Speaker 1: few tracers in a galaxy will tell you basically where
37:33
Speaker 1: the invisible mass is. What about our milkway, like what's
37:38
Speaker 1: our percentage of dark matter to regular stars? So the
37:41
Speaker 1: Milky way is a little bit more dark matter than
37:44
Speaker 1: the rest of the universe. We're like ninety percent dark
37:47
Speaker 1: matter and ten percent other stuff, whereas the rest of
37:50
Speaker 1: the universe is about eighty percent dark matter. But it
37:53
Speaker 1: also varies with distance from the center of the galaxy.
37:57
Speaker 1: Like where we are where the Sun is relative to
38:00
Speaker 1: enter the galaxy. Everything between us and the center is
38:02
Speaker 1: about fifty fifty dark matter and other kinds of matter,
38:05
Speaker 1: whereas if you go further out then it starts to
38:08
Speaker 1: be overwhelmingly dark matter. And remember that the dark matter
38:11
Speaker 1: halo for the Milky Way is much bigger than the
38:13
Speaker 1: distribution of stars that goes out much much further, so
38:17
Speaker 1: the stars peter arout and at some point it's only
38:19
Speaker 1: dark matter. I guess anytime you're in between stars, you're
38:22
Speaker 1: basically sitting in dark matter, right, Yeah, Well, we don't
38:25
Speaker 1: really know the sort of fine scale structure of dark matter.
38:28
Speaker 1: We have these very coarse probes from like how stars move,
38:31
Speaker 1: and we have stellar streams. Were actually the whole podcast
38:34
Speaker 1: episode about like trying to see the fine scale structure
38:37
Speaker 1: of dark matter within the galaxy. It's really hard, and
38:39
Speaker 1: the bottom line reason is that gravity is just super weak,
38:42
Speaker 1: and so in order to measure where the dark matter is,
38:44
Speaker 1: you need really big blobs of it, which means we
38:46
Speaker 1: can't see small blobs of it. But we can look
38:49
Speaker 1: at these dwarf galaxies and trace the motion of their
38:52
Speaker 1: stars and use that to figure out where the dark
38:55
Speaker 1: matter is in those galaxies and how much of it
38:58
Speaker 1: there is. Well, it's interesting that our Milky Way galaxy
39:01
Speaker 1: has kind of like a higher concentration of dark matter
39:04
Speaker 1: than the rest of the other the universe in general
39:08
Speaker 1: and other other galaxies as well. Are we a higher
39:10
Speaker 1: concentration of dark matter than like Andromeda. We do have
39:13
Speaker 1: board dark matter on average and Andromeda. Andromeda is a
39:16
Speaker 1: bigger galaxy, and so it's a smaller chance to like
39:19
Speaker 1: fluctuate up to have more dark matter than a smaller
39:23
Speaker 1: galaxy like the Milky Way. But these smaller galaxies, like
39:25
Speaker 1: the dwarf ones, they're really fun ways to study dark
39:28
Speaker 1: matter because what one thing we can do, for example,
39:31
Speaker 1: is we can look to see whether the dark matter
39:33
Speaker 1: in these dwarf galaxies is banging into itself and giving
39:37
Speaker 1: off some sort of like telltale signature. Particle physicists particular
39:42
Speaker 1: of like pointing their telescopes at these dwarf galaxies to
39:45
Speaker 1: try to see signals from the dark matter. Oh, I
39:48
Speaker 1: see what you're saying. Like we can use dwarf galaxies
39:51
Speaker 1: as kind of like a way to know where there's
39:54
Speaker 1: a lot of dark matter out there in the emptiness
39:56
Speaker 1: of space. Like if you see a dwarf galaxy, then
39:58
Speaker 1: that gives you a target. Point your telescope too, and say, okay,
40:01
Speaker 1: I know for sure there's a lot of dark matter
40:04
Speaker 1: in this one spot. It's the dark matter doing anything
40:07
Speaker 1: interesting that might tell us a little bit about what
40:10
Speaker 1: it is exactly. And one particularly interesting thing that people
40:13
Speaker 1: hope dark matter will do is that two dark matter particles,
40:17
Speaker 1: whatever they are, we don't know what they are, might
40:19
Speaker 1: smash into each other and they might annihilate, might turn
40:22
Speaker 1: into something else, and occasionally that will involve turning into photons.
40:28
Speaker 1: So normally we think of dark matter as dark not
40:30
Speaker 1: creating any photons, but there are some theories where it
40:33
Speaker 1: has some kind of interaction which eventually can turn into photons.
40:37
Speaker 1: And so you see this like characteristic flash of gamma rays.
40:41
Speaker 1: Problem is the universe filled with gamma rays. All sorts
40:44
Speaker 1: of other stuff generates gamma raise. So one thing you
40:46
Speaker 1: can do is point your telescope at the center of
40:48
Speaker 1: the galaxy where you expect there to be a lot
40:50
Speaker 1: of dark matter and look for gamma raise. But you
40:52
Speaker 1: like swamped in gamma rays from other stuff. Dwarf galaxies
40:56
Speaker 1: have very little other stuff. They're mostly dark matter. So
41:00
Speaker 1: if you point your telescope at the heart of these
41:02
Speaker 1: dark matter galaxies, these dwarf galaxies, and you see gamma
41:05
Speaker 1: rays there, then you can be more certain that it
41:08
Speaker 1: comes from dark matter. We haven't seen any there's nothing
41:11
Speaker 1: unusual emanating from the hearts of these dwarf galaxies. But
41:14
Speaker 1: they've given us some really powerful limits telling us what
41:17
Speaker 1: dark matter doesn't do. Wait, are you saying that dark
41:19
Speaker 1: matter it might be actually shining and might a mid light?
41:24
Speaker 1: Would you have to change the name then, from dark
41:26
Speaker 1: matter to like dim matter darkish matter. There's so many
41:31
Speaker 1: theories of dark matter that you can't even really describe
41:33
Speaker 1: all of them, and so many ways to look for
41:35
Speaker 1: dark matter. You know, people complain to me sometimes like
41:38
Speaker 1: you guys are still looking for dark matter. You haven'
41:40
Speaker 1: found it? When are you going to give up? The
41:41
Speaker 1: problem is that there's so many ways that dark matter
41:43
Speaker 1: could be discovered, and so many different ideas for what
41:45
Speaker 1: it could look like Because we know so little about
41:48
Speaker 1: it that we've got to try lots of different ways,
41:50
Speaker 1: and in some of those theories, Yeah, dark matter can
41:52
Speaker 1: annihilate and turn into photons. So yeah, what is still
41:56
Speaker 1: be called dark matter? I look forward to having that
41:58
Speaker 1: argument with you when we collect our Will Prize for
42:00
Speaker 1: discovering dark matter. Well, if dark matter doesn't midlight, it's
42:03
Speaker 1: gonna be kind of dim and it's gonna be a
42:06
Speaker 1: dark ish and it's gonna be sort of red shifted,
42:08
Speaker 1: right because these galaxies are probably moving away from us,
42:11
Speaker 1: which means that you could technically call it chocolate. And
42:16
Speaker 1: if it's red shifted, it should be like rose chocolate matter, right,
42:19
Speaker 1: Is that a thing? Is rose chocolate a thing? Yeah? Absolutely,
42:22
Speaker 1: they invented it recently. He had dark chocolate, milk chocolate,
42:25
Speaker 1: white chocolate, and now rose chocolate. It's a whole new process.
42:29
Speaker 1: M Well, there you go. Physicists are inventing new things
42:33
Speaker 1: all the time. That was definitely not a physics invention.
42:36
Speaker 1: I think it was Nestlie that came out with it.
42:38
Speaker 1: But we can do more than just look for dark
42:40
Speaker 1: matter annihilating with itself. We can also study in detail
42:43
Speaker 1: the distribution of dark matter, like where in these dwarf
42:46
Speaker 1: galaxies did did dark matter end up? And does it
42:49
Speaker 1: agree with our simulations and our calculations because we can
42:53
Speaker 1: tell not just how much dark matter there is, but
42:55
Speaker 1: also like is it mostly at the core, is it
42:58
Speaker 1: really clumped, is it smooth spread out? This kind of stuff,
43:01
Speaker 1: and what we see is that it does not agree
43:04
Speaker 1: with what we predict. That our simulations get it wrong.
43:07
Speaker 1: How can we tell how it's distributed. If it's invisible,
43:10
Speaker 1: it's invisible, but it affects the motion of the stars.
43:13
Speaker 1: And so if, for example, you have all the dark
43:15
Speaker 1: matter at the very very center, then the stars closer
43:18
Speaker 1: to the center will be going really really fast. If
43:20
Speaker 1: the dark matter is more spread out, then the stars
43:22
Speaker 1: closer to the center are not as affected by all
43:24
Speaker 1: that dark matter. So by looking at how the velocity
43:27
Speaker 1: of the stars changes as you get further from the center,
43:30
Speaker 1: we can make a map of where in the galaxy
43:33
Speaker 1: that dark matter is. Is it all clumped in the center,
43:35
Speaker 1: is it more spread out? And when we do that
43:38
Speaker 1: we see weird stuff that we don't understand. What I mean,
43:41
Speaker 1: weird stuff. So our simulations predict that you should have
43:44
Speaker 1: like a really hard core of dark matter, that yeah,
43:46
Speaker 1: you have a big fluffy halo, but the density should
43:48
Speaker 1: rise really rapidly as you get towards the center, and
43:51
Speaker 1: what we see in our telescopes is not the same thing.
43:54
Speaker 1: We see like a flatter distribution. It doesn't get as
43:56
Speaker 1: peaky towards the core. The density of dark matter at
43:59
Speaker 1: the very part of these dwarf galaxies is lower than
44:02
Speaker 1: what we expect in astronomy. This is called as the
44:05
Speaker 1: core versus cusp problem. Simulations predict a sharp cusp in
44:09
Speaker 1: the density, but what we see is more like a
44:11
Speaker 1: flat core. They're fuzzier than you expected. But isn't that
44:14
Speaker 1: just kind of a matter of time, Like, over time
44:17
Speaker 1: it should clump together towards the center, right, because that's
44:20
Speaker 1: what dark matter does. It is, and we factor that
44:22
Speaker 1: time into our simulations, and the predictions just disagree with
44:25
Speaker 1: what we expect to see at a universe of this age. Yeah,
44:28
Speaker 1: so yeah, over time it will tend to clump more
44:31
Speaker 1: and more and more. But it hasn't clumped as much
44:33
Speaker 1: as we expected. What could it be? What could be
44:36
Speaker 1: the explanation? Well, there's lots of really fun ideas. This
44:39
Speaker 1: is a big crack and sort of the success of
44:41
Speaker 1: dark matter and explaining the large structure of the universe.
44:43
Speaker 1: And some people think it's a good argument for Mond
44:46
Speaker 1: one of these alternative theories. It says, you know, dark
44:48
Speaker 1: matter doesn't even exist at all. It's just that we've
44:51
Speaker 1: misunderstood gravity, and the gravity at different distance scales and
44:55
Speaker 1: the different accelerations works differently than we expected, and the
44:58
Speaker 1: whole dark matter thing is mistake. And it's true that
45:01
Speaker 1: dark matter does not do a good job of explaining
45:03
Speaker 1: what we see in these dwarf galaxies. It's like a
45:05
Speaker 1: big open problem for dark matter, and Mond does a
45:09
Speaker 1: good job of explaining what we see in these galaxies,
45:12
Speaker 1: and so that's a bit of a puzzle, right. Mind
45:14
Speaker 1: also fails to explain lots of other stuff in the universe,
45:16
Speaker 1: lots of reasons why we think dark matter is a
45:19
Speaker 1: better sort of overall picture than MOND, But this is
45:23
Speaker 1: one place where Mond does better than dark matter. What
45:26
Speaker 1: are some of these ideas then that maybe dark matter
45:28
Speaker 1: does have some strange interaction with itself, or maybe there's
45:32
Speaker 1: like a dark matter sun in the middle of that
45:34
Speaker 1: galaxy blowing out some of the dark matter stuff like that. Yeah,
45:38
Speaker 1: one really interesting clue is that there's actually a lot
45:40
Speaker 1: of variation, Like they're not as cuspies you expect. But
45:44
Speaker 1: also these cores is a lot of diversity of these cores,
45:47
Speaker 1: so you see lots of different sort of shapes, and
45:49
Speaker 1: people wonder like, why would you get so many different
45:51
Speaker 1: shape if the only thing that's happening here is gravity.
45:53
Speaker 1: Gravity is pretty simple. It's not as complicated as like
45:56
Speaker 1: baryonic physics, you know, with photons and protons and electromaticism.
46:00
Speaker 1: It's very complicated. Dark matter should create simpler structures. And
46:04
Speaker 1: so one idea is just what you suggested, that maybe
46:07
Speaker 1: dark matter has some complicated self interaction that we don't
46:10
Speaker 1: know about that's creating interesting sorts of structures in the
46:13
Speaker 1: hearts of these galaxies that we just can't see because
46:16
Speaker 1: it's all made out of dark matter. So it's sort
46:19
Speaker 1: of like the cutting edge of current research is to
46:21
Speaker 1: try to understand what's going on at the hearts of
46:23
Speaker 1: these dwarf galaxies. What is dark matter doing right? Right?
46:27
Speaker 1: It could be boring like rose chocolate bars for all
46:31
Speaker 1: you know, right, huge cups of rose chocolate cosmic hot
46:34
Speaker 1: coco could just be out there waiting for us to
46:37
Speaker 1: sip them. But then if you're out there sipping them,
46:39
Speaker 1: you're also looking at the stars, but you're inside of
46:41
Speaker 1: the stars. Kind oh, my gosh, I don't even know
46:43
Speaker 1: what to do. I'd have to be camping at the
46:45
Speaker 1: same time. Yeah, camping in space, space camping. That's absolutely
46:49
Speaker 1: the title of my new science fiction TV series that
46:52
Speaker 1: I'm pitching to Netflix. There you go. Well, I think
46:54
Speaker 1: they already have space camp but maybe you can get
46:58
Speaker 1: away with trademarking. This is why we have lawyers. They'll
47:04
Speaker 1: figure it out. Yeah, they'll figure it out, all right. Well,
47:07
Speaker 1: another interesting journey into a corner of the universe that
47:11
Speaker 1: maybe a lot of people don't pay attention to, but
47:13
Speaker 1: that could actually reveal a lot about how things work.
47:16
Speaker 1: Dwarf galaxies. And remember that as we develop better and
47:19
Speaker 1: more powerful technological eyeballs to look out into the universe,
47:22
Speaker 1: we see fainter stuff and smaller stuff, which might hold
47:26
Speaker 1: some of the answers to some of the enduring mysteries
47:29
Speaker 1: we've been puzzling over for a long time. So the
47:31
Speaker 1: next time you're out there camping or not, or looking
47:35
Speaker 1: at the stars or not, or drinking hot chocolate or not,
47:39
Speaker 1: you can do those three things independently. Think about the
47:42
Speaker 1: little structures of the universe out there and how they
47:44
Speaker 1: maybe have special properties that can really kind of reveal
47:48
Speaker 1: some of the more interesting inner workings of the universe.
47:51
Speaker 1: I have one last question for you before we sign
47:53
Speaker 1: off for him. Do you prefer a cup of hot
47:54
Speaker 1: cocoa or hot vanilla? Hot vanilla? You mean like pure
47:58
Speaker 1: vanilla extract? I don't know. You said nila is your
48:00
Speaker 1: favorite flavor, better than chocolate. So what's a delicious vanilla
48:03
Speaker 1: beverage you enjoy on a camping trip? Oh? Boy, yeah,
48:07
Speaker 1: just warm milk. I think it's just called warm milk.
48:13
Speaker 1: Somebody invented that too, man. Yeah, yeah, vanilla milkshake. I'll
48:17
Speaker 1: take that camping any day. All right. Well, we hope
48:19
Speaker 1: you enjoyed that. Thanks for joining us, See you next time.
48:30
Speaker 1: Thanks for listening, and remember that Daniel and Jorge explain
48:33
Speaker 1: the Universe is a production of iHeartRadio. Or more podcast
48:37
Speaker 1: from my heart Radio. Visit the iHeartRadio app, Apple Podcasts,
48:41
Speaker 1: or wherever you listen to your favorite shows.