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