Speaker 1: Hey, Daniel, you like dark chocolate, right, and you hate
Speaker 1: white chocolate.
Speaker 2: It's more than just liking it, It's a way of life.
Speaker 3: Man.
Speaker 1: WHOA, that's a lot writing on a flavor. But I
Speaker 1: wonder does the shape of a chocolate matter to you?
Speaker 2: Hmm? You mean, like if it's a chocolate chip or
Speaker 2: a chocolate bar or something else.
Speaker 1: Yeah, I'm trying to figure out how picky you are.
Speaker 2: Well, you know, it is really fun to make chocolate
Speaker 2: have all sorts of weird shapes, but I think it
Speaker 2: all tastes the same. What if it's pear shape, as
Speaker 2: long as it's not a disaster fruit and chocolate is
Speaker 2: a delicious combination.
Speaker 1: What if it's shaped like white chocolate.
Speaker 2: Like, chocolate isn't the shape, man?
Speaker 1: What if it's shaped like a galaxy?
Speaker 2: Ooh, that sounds delicious.
Speaker 1: Or what if it's the size of a galaxy?
Speaker 2: Sounds like I have my work cut out from it.
Speaker 1: Hi am Hore, my cartoonist and the author of Oliver's
Speaker 1: Great Big Universe.
Speaker 2: Hi. I'm Daniel. I'm a particle physicist and a professor
Speaker 2: at UC Irvine, and I've never run out of my
Speaker 2: taste for dark chocolate.
Speaker 1: I wonder if your dislike of white chocolate is just
Speaker 1: context based.
Speaker 2: You mean, like it's a bad childhood memory.
Speaker 1: Yeah, No, well I mean more like situational. You know, like,
Speaker 1: what if you're in a dessert not a dessert, Well,
Speaker 1: maybe it could be a desert island. But what if
Speaker 1: it's also deserted, but the only dessert available or anything
Speaker 1: to eat is white chocolate? Would you starve or would
Speaker 1: you eat it?
Speaker 2: I would eat it, but as I did, I would
Speaker 2: understand how much better it would have been if it
Speaker 2: was dark chocolate.
Speaker 1: I see, you'd be complaining the whole time.
Speaker 2: He I'd be the only one there, So who's to
Speaker 2: complain to?
Speaker 1: Hey, you could complain to the white chocolate. I guess
Speaker 1: could paint a face on it, kind of like.
Speaker 2: Wilson, complaining makes everything better.
Speaker 1: That it does. But anyways, welcome to our pot. Daniel
Speaker 1: and Jorge explain the Universe, a production of iHeartRadio.
Speaker 2: In which we do our best to enjoy all of
Speaker 2: the flavors of the universe. The electronic, the muonic, the
Speaker 2: tawonic flavors, the ups, the downs, the charms, the bottoms,
Speaker 2: the tops, everything in the universe that has a flavor
Speaker 2: and everything that can be explained. We take a bite
Speaker 2: out of all of it and explain everything to you.
Speaker 1: Wait wait, wait, you just said you take a bite
Speaker 1: out of white chocolate and enjoy it.
Speaker 2: I'm confused on adviceive Council. I'm going to pass on
Speaker 2: answering that question.
Speaker 1: But aren't you curious what makes white chocolate different than
Speaker 1: dark chocolate?
Speaker 2: Yeah, it's the lack of chocolate.
Speaker 1: No, it has chocolate as coco butter.
Speaker 2: Coco butter is chocolate the way like butter by itself
Speaker 2: is a whole meal. You know, it's there to accentuate
Speaker 2: the flavors.
Speaker 1: Obviously, you haven't been to Texas with the eat of
Speaker 1: fright butter, which is where I am right now.
Speaker 2: Yeah, exactly so. Not a big fan of deep fried
Speaker 2: butter or white chocolate. To put those two things in
Speaker 2: the same category.
Speaker 1: They probably have the same number of calories.
Speaker 2: To be honest, have you tried deep fried white chocolate?
Speaker 1: Ooh, that might be a different state. Sounds like more
Speaker 1: of an Arkansas thing.
Speaker 2: Maybe keep traveling and report back.
Speaker 1: That's right, I'm going a mission to try all the
Speaker 1: freight of fats. But anyways, we do like to wet
Speaker 1: our appetite and satisfy our appetite for the universe, our
Speaker 1: curiosity for how things work out there in the cosmos.
Speaker 1: Why are things the way they are, why are they
Speaker 1: shaped like the way they are, and why do they
Speaker 1: taste the way they do?
Speaker 2: Because it's more than just the colors in the night sky,
Speaker 2: the bright twinkling lights, the reds, the greens, everything else
Speaker 2: that's up there. It's also the structure in the night
Speaker 2: sky that tells us a story about the history of
Speaker 2: the universe and where the universe is headed.
Speaker 1: It's right because things in the universe aren't all the same.
Speaker 1: Some things are shaped differently than others. They look different,
Speaker 1: they have a different form, and it all reflects back
Speaker 1: on how it all came together.
Speaker 2: All the structure in the universe was inevitably put together
Speaker 2: by gravity as it pulls things together in battles, angular momentum,
Speaker 2: and other forces, and the shapes that we end up
Speaker 2: with and how they change over time tell us about
Speaker 2: how those forces work together and what the history of
Speaker 2: the universe is. If you peer out in the night
Speaker 2: sky beyond the stars, you see all these little smudges.
Speaker 2: Those smudges are distant galaxies and each one has its
Speaker 2: own shape that tells a story about how it got there.
Speaker 1: And so the podcast will we tackling the question what
Speaker 1: are the possible shapes of galaxies? Now, Daniel, is this
Speaker 1: like the shape? What it looks like? Or how much
Speaker 1: do galaxies exercise? Like? Are you a fit galaxy? Are
Speaker 1: you a buff galaxy? Are you a little flabby around
Speaker 1: the edges?
Speaker 2: I'm not selling a galaxy workout video, and this is
Speaker 2: not some sort of cosmic drift. No, we are not
Speaker 2: judging the shapes. We are just observing and trying to
Speaker 2: understand how they got there.
Speaker 1: Doing Galaxies have names like p X thirty nine. Isn't
Speaker 1: that also the name of some workout.
Speaker 2: Program it is? Now, yeah, we're panding that and we're
Speaker 2: making a cosmic workout program exactly.
Speaker 1: That's right. Yes, it's the milky way.
Speaker 2: You gets fit, like the whirlpool galaxy. I don't know
Speaker 2: how that works.
Speaker 1: Does it depend on how much dark chocolate the galaxy
Speaker 1: has eaten?
Speaker 2: Collapsing into a huge bar of dark chocolate is the
Speaker 2: eventual end of every galaxy.
Speaker 1: The dream state for all physicists.
Speaker 2: But it is fascinating to look up at the night
Speaker 2: sky and to see all these different shapes. Some of
Speaker 2: them are ellipses, some of them are blobs, some of
Speaker 2: them are stretched out. There's even one that looks like
Speaker 2: a question mark. Almost every possible shape you can imagine
Speaker 2: is up there somewhere in the night sky. And there
Speaker 2: are so many galaxies in the universe that it makes
Speaker 2: astronomers wonder how they all got that way. It makes
Speaker 2: them want to invent crazy illogical names for the various categories.
Speaker 2: There's a lot of rich signs to do in the
Speaker 2: shapes of galaxies.
Speaker 1: Well, that's kind of a new concept, maybe for a
Speaker 1: lot of people, because you know, we all grew up
Speaker 1: looking at pictures of galaxies and they all kind of
Speaker 1: the same, right, they look like little swirls.
Speaker 2: I mean, if you've only looked at a few pictures,
Speaker 2: they might all look the same. But as soon as
Speaker 2: you look at a handful or a dozen or so,
Speaker 2: you start to notice there's a lot of weird shapes
Speaker 2: out there. Some of them have more arms, fewer arms,
Speaker 2: some of them have no arms at all. There's a
Speaker 2: lot of weird stuff in the universe.
Speaker 1: M Is it sort of like cloud watching, Like you
Speaker 1: look out into the sky and you look at the
Speaker 1: clouds and they're all different shapes, like pie shaped or
Speaker 1: you know, a butterfly shape.
Speaker 2: Yeah, exactly. And if you understand the dynamics of water
Speaker 2: droplet formation and air currents, you can understand why certain
Speaker 2: clouds look the way they do. They tell you a
Speaker 2: story about what's happening up there, what the forces are
Speaker 2: that are doing battle. And it's the same for galaxies.
Speaker 2: There's enormous cosmic forces pushing on these things and pulling
Speaker 2: on these things, and the shapes reveal exactly what happened.
Speaker 1: How much dark chocolate it eight.
Speaker 2: How much it's been subscribing toges new workout video.
Speaker 1: That's right, how many spins it's been doing well? As usual,
Speaker 1: we were wondering how many people out there had thought
Speaker 1: about this question of what shape galaxies can be, and
Speaker 1: so as usual, Daniel went out there into the internet
Speaker 1: to ask people what are the possible shapes galaxies can take.
Speaker 2: I'm grateful as always to our group of volunteers, and
Speaker 2: if you would like to join them to contribute your
Speaker 2: voice to the podcast, please don't be shy right to
Speaker 2: us to questions at Danielanjorge dot com. Everybody's welcome.
Speaker 1: So think about it for a second. What kinds of
Speaker 1: shapes have you seen in galaxies? Here's what people had
Speaker 1: to say.
Speaker 4: There's spiral galaxies or barred spirals like ours. I don't know,
Speaker 4: maybe there's just bars. There's irregular ones that were disturbed
Speaker 4: by gliding with other galaxies haven't settled down yet. I
Speaker 4: think there's blobs or spherical shape galaxies, and I hope
Speaker 4: there's a galaxy shape like Mickey.
Speaker 2: Mouse somewhere out there.
Speaker 5: I think they're most often some kind of circular shape,
Speaker 5: given that they're rotating around the black hole that's usually
Speaker 5: at the center of the galaxy. I think the Milky
Speaker 5: Way is considered a spiral galaxy, but I would guess
Speaker 5: he can probably have most any shape that's possible that
Speaker 5: could form around a center of man No.
Speaker 3: I did used to take part in Zooniverse, so I
Speaker 3: know that you can have spiral shape galaxies, and they
Speaker 3: can have different numbers of arms, and they can also
Speaker 3: have a bar feature or not across the center. Then
Speaker 3: you also get s elliptical galaxies, which when they're sort
Speaker 3: of close to the plane it's called lenticular galaxies. And
Speaker 3: then you can have globular clusters. Now may be other
Speaker 3: galaxy shapes as well, but they're the main types that
Speaker 3: I remember.
Speaker 1: All right. I feel like they quickly spiral out of control.
Speaker 2: There are a lot of ellipses there. As people were.
Speaker 1: Thinking, Yeah, they just kept going around and around in circles.
Speaker 2: I don't know if there is a Mickey mouse shaped galaxy,
Speaker 2: but if the universe is infinite, then I guess somewhere
Speaker 2: there has to be one.
Speaker 1: Well, I wonder if there are like three galaxies kind
Speaker 1: of crashing into each other right before they do, they
Speaker 1: do look like a maybe a Mickey mouse shape.
Speaker 2: Well, you know, if you google Mickey mouse galaxy, you
Speaker 2: don't get mostly scientific images.
Speaker 1: Yeah. Or I wonder if you look far enough or
Speaker 1: long enough at galaxy shapes, if you'll eventually run into
Speaker 1: one that's inappropriate. We're not safe for work.
Speaker 2: Not safe for the universe, safe for astronomy. Probably. It's
Speaker 2: sort of like looking at clouds. You can stare at
Speaker 2: a galaxy and imagine a creative interpretation.
Speaker 1: Interesting, I see what you're saying. Maybe it reveals more
Speaker 1: about your inner space than outer space.
Speaker 2: Yeah, exactly, It's like a roar shark test.
Speaker 1: Yeah, if you have a dark mind or a white
Speaker 1: chocolate mind.
Speaker 2: A white chocolate mind is like a brain that's been
Speaker 2: battered and fried.
Speaker 1: Oh my gosh. Well, anyways, maybe we should start at
Speaker 1: the beginning here, you know, if we're going to talk
Speaker 1: about the shape of galaxies, like how do galaxies form
Speaker 1: in the first place, and what might determine their shape?
Speaker 2: Yeah. I think people usually think about the universe in
Speaker 2: terms of stars, but to me, it's much more natural
Speaker 2: to think about the universe in terms of galaxies. It's
Speaker 2: like the basic building block of the universe. You look
Speaker 2: at into deep space and it's mostly filled with galaxies
Speaker 2: scattered everywhere. You can argue about whether those galaxies come
Speaker 2: together to make larger structure and whether the internal structure
Speaker 2: of those galaxies is more important, But to me, galaxies
Speaker 2: are like the basic building block of the universe. So yeah,
Speaker 2: it's important to figure out like why do we have galaxies,
Speaker 2: Why are they typically this size? Why does the universe
Speaker 2: do this kind of thing?
Speaker 1: I see, Galaxies are sort of like maybe the atom
Speaker 1: for you, Like, you know, it's made out of things
Speaker 1: that are smaller, but you know, to understand most of
Speaker 1: what we see around us in chemistry and materials and
Speaker 1: things like that, you can just sort of think about
Speaker 1: the atomic structure.
Speaker 2: Yeah, to me, it's always really fascinating the size of
Speaker 2: things that emerge. You know, we don't know if there's
Speaker 2: the smallest thing in the universe, but it's fascinating that,
Speaker 2: Like the atom is a certain size, right, and planets
Speaker 2: are a certain size, and stars are a certain size.
Speaker 2: Galaxies also are a certain size, and if you poke
Speaker 2: into the physics behind them, how they came together, and
Speaker 2: then you learn something about what the universe likes to do,
Speaker 2: which somehow maybe bubbles up from the tiniest particles, though
Speaker 2: that's not a process that we understand.
Speaker 1: You mean, like galaxies don't vary that much in size, right,
Speaker 1: Like you don't see a tiny, tiny galaxy and humongas
Speaker 1: you know, superstructure spanning galaxies. They mostly all fall within
Speaker 1: a certain range, just like planets all sort of fall
Speaker 1: within a certain range.
Speaker 2: Yeah, there is a very wide range of size of galaxies,
Speaker 2: but it doesn't extend down to like the size of cats.
Speaker 2: You don't have like galaxies the size of cats, and
Speaker 2: you don't have galaxies the size of superclusters exactly. So
Speaker 2: there's a certain like size of galaxy that the universe
Speaker 2: likes to make and not much much much bigger and
Speaker 2: not much much much smaller, And that tells you something
Speaker 2: about the balance of the forces.
Speaker 1: Sort of like planets too. I guess you can have
Speaker 1: small planets, but you can't have like a Solar system
Speaker 1: sized planet.
Speaker 2: Yeah, if you had something like that, it would just
Speaker 2: collapse into a star, right. And in the end, it
Speaker 2: all comes back to the same original story of like,
Speaker 2: why do we have any structure at all? Why is
Speaker 2: in the universe just like smoothly filled with particles. Why
Speaker 2: do things clump together? And that dates back all the
Speaker 2: way to the very beginning of little patches where things
Speaker 2: were denser and little patches where things were less dense.
Speaker 2: We think there were quantum fluctuations in the early universe
Speaker 2: as particles formed out of this pre particle goo, this
Speaker 2: very hot and dense stuff that we don't understand very well.
Speaker 2: You've got little fluctuations that were more dense here and
Speaker 2: less dense there, and those were the seeds that gravity
Speaker 2: latched onto that started pulling things together to make things
Speaker 2: more and more dense. Because the denser you are, the
Speaker 2: more you have gravity and then you can pull on things,
Speaker 2: which leads to a runaway effect where things get more
Speaker 2: and more dense.
Speaker 1: So I guess you need these fluctuations to even start something, right,
Speaker 1: because if everything in the universe was evenly spaced, then
Speaker 1: you would feel the same pool of gravity in all
Speaker 1: directions and nothing would ever clump together exactly.
Speaker 2: So the quantum fluctuations get you started, and then they
Speaker 2: get blown up by inflation. Right, the universe expanded super
Speaker 2: duper rapidly in the first few moments that we understand,
Speaker 2: and those grew these little fluctuations from quantum size something
Speaker 2: you could never see to macroscopic fluctuations, things big enough
Speaker 2: for like gravity to really grab a hold of and
Speaker 2: start to seed structure. And you have these fluctuations in
Speaker 2: the dark matter as well as in the normal matter.
Speaker 2: And it's really these fluctuations that determine everything. These quantum fluctuations,
Speaker 2: blown up to a specific size, create pols of dark matter,
Speaker 2: which then create galaxies.
Speaker 1: Now, these quantum fluctuations, these are quantum fluctuations of what
Speaker 1: the matter or the space itself.
Speaker 2: I think most fundamentally they are quantum fluctuations in the fields. Right,
Speaker 2: we don't really know what happens before we have fields.
Speaker 2: But you can think about the fields before you can
Speaker 2: think about the particles, because as the fields are cooling,
Speaker 2: it starts to make sense to talk about individual particles.
Speaker 2: Before that, it's more like you're talking about waves in
Speaker 2: the ocean rather than droplets. But as things cool down
Speaker 2: and get less dense than you get particles. So it's
Speaker 2: those quantum fluctuations in those initial fields that give you
Speaker 2: a little bit more energy here, a little bit less
Speaker 2: energy there, and that eventually turns into more particles here
Speaker 2: and fewer particles there.
Speaker 1: Because I guess the fields don't scale with the growth
Speaker 1: of the universe, do they. They kind of stay at
Speaker 1: the same sea scale. So when the universe was a
Speaker 1: lot smaller, the fluctuations in those fields were huge in
Speaker 1: comparison to the size of the universe.
Speaker 2: Mm hmm exactly. And then as the universe expands, that
Speaker 2: energy just gets dilute, right, Everything gets colder and less dense.
Speaker 1: And smaller by comparison, I guess.
Speaker 2: Right, yeah, and smaller by comparison. And we talked in
Speaker 2: a recent episode about how different slices of the universe
Speaker 2: pie evolve over time. You have the radiation slice, which
Speaker 2: gets more dilute but also gets red shifted, so its
Speaker 2: energy actually goes away faster. As the universe expands, you
Speaker 2: have the matter portion, where the energy is constant, but
Speaker 2: because space is expanding, it gets more and more dilute.
Speaker 2: Then you have the dark energy fraction, which doesn't get
Speaker 2: diluted as the universe expands, and so its overall energy
Speaker 2: fraction increases.
Speaker 1: But I guess getting back to galaxies, So how did
Speaker 1: these quantum fluctuations then result in galaxies?
Speaker 2: So these quantum fluctuations give you a little bit more
Speaker 2: matter here and a little bit less matter there. And
Speaker 2: in the very early universe, you had dark matter and
Speaker 2: you had normal matter, and you had photons, and these
Speaker 2: things are all sort of sloshing around, and the photons
Speaker 2: are pressing on the normal matter, the dark matter is
Speaker 2: pulling things back in, and you had this actual ringing
Speaker 2: of the early universe. It would be called these baryon
Speaker 2: acoustic oscillations, sort of like the sound of the early universe.
Speaker 2: The pressure waves in that initial plasma was slashing around,
Speaker 2: and a big component of that is the dark matter
Speaker 2: that's pulling things together. At some moment that the universe
Speaker 2: expands enough and cools enough that that goes from being
Speaker 2: a plasma to being a neutral gas. Like the protons
Speaker 2: and the electrons find each other so they can no
Speaker 2: longer be pushed by the photons, so that sort of
Speaker 2: freezes the structure into place, and you get places where
Speaker 2: you had more dark matter and more normal matter, and
Speaker 2: that's where you ended up with galaxies today.
Speaker 1: In the spots that had more dark matter and regular matter.
Speaker 2: So some of those spots have more dark matter, some
Speaker 2: of the spots have less dark matter but more normal
Speaker 2: matter because they got pushed by the photons. And if
Speaker 2: you look out into the universe, you can actually see
Speaker 2: these spots. We have clusters of galaxies that formed where
Speaker 2: the dark matter was denser, and then you have these
Speaker 2: rings of galaxies that formed where the normal matter was denser.
Speaker 2: Actually see these bubbles from the early universe. It's sort
Speaker 2: of incredible. But basically, you had places with more matter
Speaker 2: and that means more gravity and that pulls all the
Speaker 2: gas together and that's what allows you to create stars.
Speaker 2: And galaxies are basically just huge pools of gas with
Speaker 2: stars forming inside them.
Speaker 1: So that's kind of what a galaxy is, or was
Speaker 1: initially was just a cloud of gas, and at the beginning,
Speaker 1: I imagine it was just kind of a homogeneous, you know,
Speaker 1: blobby kind of cloud of gas, no structure or shape
Speaker 1: at all, or maybe just kind of like a blobby shape.
Speaker 2: A big blob of gas that's pulling together and collapsing.
Speaker 2: And initially it's almost all hydrogen. It's like a tiny
Speaker 2: little bit of helium also made in the Big Bang,
Speaker 2: but almost all hydrogen. And then you get these things
Speaker 2: collapsing into stars, and those groups of stars then form galaxies.
Speaker 2: But you still have also lots of gas in there,
Speaker 2: so you have stars embedded in huge clouds of gas,
Speaker 2: and together those things have formed galaxies.
Speaker 1: All right. That sounds like when galaxies start to get
Speaker 1: into shape and started to become something. And so let's
Speaker 1: dig deeper into that. What are some of the new
Speaker 1: and old ideas about how galaxies form? And then let's
Speaker 1: figure out if they've been exercising. First, let's take a
Speaker 1: quick break. All right, we're talking about the shapes of galaxies.
Speaker 1: What shapes can they be? Can they be square? Can
Speaker 1: they look like a cube? Can they look like Mickey mouse?
Speaker 1: Inquiring minds one to know?
Speaker 2: Well, one thing we can see initially is that there
Speaker 2: are different sizes of galaxies. There are smaller galaxies out there,
Speaker 2: there are bigger galaxies out there. You know, our galaxy
Speaker 2: has a few one hundred billion stars, but there are
Speaker 2: galaxies out there with trillions of stars and dwarf galaxies
Speaker 2: with only like tens of thousands or hundreds of thousands
Speaker 2: of stars. So there's a pretty big range of galaxies.
Speaker 1: But then I guess what determined these sizes the size
Speaker 1: of the galaxy. Is it just like how much gas
Speaker 1: happened to pull together because of these quantum fluctuations. Isn't
Speaker 1: there like a limit to what these quantum fluctuations look like.
Speaker 2: That was sort of the original idea that big galaxies
Speaker 2: were born big and little galaxies were born little, and
Speaker 2: it just depended on like the scoop of stuff that
Speaker 2: you got. And in that scenario, like large galaxies would
Speaker 2: form all at once. You know, you have this huge collapse,
Speaker 2: this monolithic collapse of the gas down into huge galaxy
Speaker 2: making stars until it was all used up. But these days,
Speaker 2: the newer idea is that galaxies don't vary that much
Speaker 2: in size when they're formed. That basically only makes small
Speaker 2: galaxies initially, and then the bigger galaxies are made from
Speaker 2: mergers of other galaxies.
Speaker 1: That's the new idea of how galaxies form. It's like
Speaker 1: they were all made a kind of like lego blocks,
Speaker 1: and then the lego blocks started to assemble into bigger
Speaker 1: galaxies exactly.
Speaker 2: And this newer idea comes from seeing more examples. You know,
Speaker 2: initially we could basically only see either nearby galaxy or
Speaker 2: very bright older galaxies that were further away. But now
Speaker 2: that we have new exceptional tools like James Webb and
Speaker 2: even Hubble, we can see further back in time and
Speaker 2: we can see more examples of smaller galaxies that were
Speaker 2: further away. So we can see those small galaxies forming.
Speaker 1: But isn't it kind of a mystery how you go
Speaker 1: from the smaller galaxies to the bigger galaxies or is
Speaker 1: it all just like random collisions out there in space.
Speaker 2: I think there are definitely still open questions, but there's
Speaker 2: also a lot of it that we do understand. Basically,
Speaker 2: it's gravity you form these little galaxies, and then those
Speaker 2: galaxies come together because if they're close enough together, gravity
Speaker 2: will pull them together. Space is expanding between them. Dark
Speaker 2: energy is fighting it, but gravity wins at small distances
Speaker 2: and eventually will pull those things together, the way the
Speaker 2: Milky Way and Andromeda are getting pulled together overcoming the
Speaker 2: power of dark energy.
Speaker 1: So then I guess as we look out into space
Speaker 1: and back into time, that's basically the movie that plays
Speaker 1: out for you. As you look out into the cosmos,
Speaker 1: you see a bunch of little galaxies, and as you
Speaker 1: fast forward in time, they you can sort of see
Speaker 1: them merge together to form the galaxies that are closer
Speaker 1: to us, which are more recent.
Speaker 2: Exactly, And even our galaxy is the product of many,
Speaker 2: many mergers. We think that our galaxy is the combination
Speaker 2: of lots and lots of smaller galaxies which came together
Speaker 2: to make the Milky Way, sort of like Voltron or
Speaker 2: Power Rangers or whatever.
Speaker 1: I don't think power Rangers merge there, Daniel, Oh.
Speaker 2: No, they don't come together and make one super power Ranger.
Speaker 1: No, I don't think.
Speaker 2: So what is that Pokemon or am I thinking.
Speaker 1: Of I think you're thinking of Voltron?
Speaker 2: Yes, not even know what Vultron is, so I couldn't
Speaker 2: be thinking of Voltron. Is it teenage mutan? Ninja? Turtles?
Speaker 2: Did they come together?
Speaker 1: It's g I Joe, it's what it is Ji Barbie.
Speaker 1: My t Ijo emerged with Barbie, and that's how you
Speaker 1: get the Milky Way.
Speaker 2: Now you're just spreading misinformation about pop culture and about science.
Speaker 2: You giving me too much work to do here, man.
Speaker 1: Yes, that's how we lost the election. But anyways, as
Speaker 1: getting back to the original question, which is about the
Speaker 1: shape of galaxies, You've given us kind of a general
Speaker 1: picture of where galaxies come from. But what the term
Speaker 1: is their shape, like, what the term is whether they're
Speaker 1: spiral or blobby or mickey mouse shape.
Speaker 2: So let's start with the spiral ones because those are
Speaker 2: sort of the most natural and the simplest ones. And
Speaker 2: when small galaxies form, they tend to be spiral galaxies.
Speaker 2: And that's why spiral galaxies are the most common type
Speaker 2: of galaxy in the universe. And the reason you get
Speaker 2: a spiral is that this initial blob of gas is spinning, right,
Speaker 2: Everything in the universe is spinning, and that spin can't
Speaker 2: go away. We can serve angular momentum in the universe,
Speaker 2: which means if something is spinning, then to stop it
Speaker 2: spinning you have to apply some torque to it. You
Speaker 2: if you like spin it the other direction. But an
Speaker 2: isolated object like in space you started spinning, is just
Speaker 2: going to spin forever. Something else from the outside would
Speaker 2: have to come and push on it in order for
Speaker 2: it to stop spinning.
Speaker 1: I wonder if, maybe for listeners we should explain that
Speaker 1: this idea of just a generic blob of guys out
Speaker 1: there in space, that it has actually a spin direction,
Speaker 1: because you might imagine like something that big and that
Speaker 1: sort of random, it like all the particles are actually
Speaker 1: kind of flying all directions all the time, not necessarily
Speaker 1: in a particular direction, but overall it sort of has
Speaker 1: to have a preference for a general spin direction, right.
Speaker 2: Yeah, And this can be a little tricky to get
Speaker 2: your mind around. You might think, well, there's lots of
Speaker 2: particles out there, why don't they all just average out
Speaker 2: to no spin? And so think about it in terms
Speaker 2: of like every individual particle, you know, draw a line
Speaker 2: through like the center of mass of a bunch of particles.
Speaker 2: Each particle is contributing to the spin of the overall
Speaker 2: object in some way. If it's flying to the left,
Speaker 2: then effectively it's spinning it one way. If it's flying
Speaker 2: to the right, it's effectively spinning it. The other way. So,
Speaker 2: now add up all those little pushes basically from all
Speaker 2: those particles, and ask yourself, does it add up to zero? Well,
Speaker 2: what are the chances that adds up to exactly zero?
Speaker 2: That's like saying I'm going to flip a coin a
Speaker 2: billion times? What are the odds I'm going to get
Speaker 2: exactly half a billion heads and exactly half a billion tails.
Speaker 2: Basically that's impossible. So while it's possible for some object
Speaker 2: out there to have zero total spin, it's very unlikely.
Speaker 2: The most common thing is for it to have some
Speaker 2: small amount of overall spin.
Speaker 1: It's sort of like I wonder if like you can
Speaker 1: think about the shape of the blob, like it would
Speaker 1: be almost impossible for this blob of gas to be
Speaker 1: like perfectly spherical, like most likely it has a little
Speaker 1: bit of an oblongness in one direction, and so that
Speaker 1: maybe tells you that the galaxy leans wider in this direction.
Speaker 1: I think maybe you can think about the spinning of
Speaker 1: it is the same way. It's like that all the
Speaker 1: particles are moving in all directions, but overall it's seat
Speaker 1: of maybe spinning a little bit more in a particular direction.
Speaker 2: Yeah, the distance from the center plays a big role
Speaker 2: because the anc momentum varies with distance, So you're right.
Speaker 2: The fact that it's randomly distributed in distance is also
Speaker 2: makes it pretty hard to imagine that they would be
Speaker 2: perfectly balanced. So you just like carve out a random
Speaker 2: chunk of gas from the early universe. Overall, it's very
Speaker 2: unlikely for it to be perfectly balanced in spin, so
Speaker 2: that means it has some overall spin even if it's tiny. Now,
Speaker 2: collapse that gas with gravity, and that tiny overall spin
Speaker 2: becomes a pretty fast spin. The way if you're like
Speaker 2: figure skating and you pull your arms in, you spin
Speaker 2: faster and faster because the same angular momentum over shorter
Speaker 2: distances requires a higher velocity of spin. So now this big,
Speaker 2: slowly spinning blob of gas has become a denser, more
Speaker 2: quickly spinning blob of gas.
Speaker 1: Right, It's sort of like when you flush the toilet.
Speaker 1: Initially things are spinning slowly, but then as they flush
Speaker 1: down the center it, things are spinning really fast.
Speaker 2: I love how you always go for the toilet analogy.
Speaker 2: That really crystallizes it in my mind.
Speaker 1: I'm all about the dark humor. So then it's spinning.
Speaker 1: You have this big cloud of gas. It's collapsing because
Speaker 1: of gravity. Maybe it's kind of squeezes into a pancake first, right,
Speaker 1: because the gravity that not in the direction of the
Speaker 1: spin tends to just flatten this big cloud first, right.
Speaker 2: Exactly, The spin makes it collapse into a pancake instead
Speaker 2: of just into a point right along the plane of
Speaker 2: the spin. Basically, angular momentum needs to stick around and
Speaker 2: so the same way that like the Earth doesn't collapse
Speaker 2: into the Sun because of our orbital angular momentum around
Speaker 2: the Sun, the gas turns into a big swirling orbit
Speaker 2: around the center of the galaxy, the same way like
Speaker 2: a black hole has an accretion disk around it for
Speaker 2: all the same reasons. So it sort of collapses into
Speaker 2: a disc, and that's when the stars start to form.
Speaker 2: When the gas gets dense enough, stars begin to form.
Speaker 2: So it's not like you have a bunch of gas
Speaker 2: which forms stars and then the stars collapse into a disc.
Speaker 2: It's the gas collapsing into a disc that allows the
Speaker 2: stars to form. They form in that disk.
Speaker 1: Okay, So now is that why most galaxies are flat
Speaker 1: sort of like a you know, and you don't get
Speaker 1: spherical galaxies or do you get spherical galaxies.
Speaker 2: You can get elliptical galaxies which include some spheres, and
Speaker 2: there are also globular clusters out there. But these galaxies,
Speaker 2: the spiral galaxies, that's why they are flat. They're flat
Speaker 2: because the stars form in that disc which is shaped
Speaker 2: by gravity and anglar momentum sort of playing against each other.
Speaker 2: So here you can see two totally different things in
Speaker 2: the universe, gravity and angular momentum fighting each other on
Speaker 2: these vast cosmic scales and determining the structure of most
Speaker 2: of these galaxies. All these spiral galaxies are basically a
Speaker 2: balance between these two things, angler momentum and gravity.
Speaker 1: Okay, so we had a cloud. It's flattened to a pancake,
Speaker 1: and now what to turn into a spiral? Who flushed
Speaker 1: the toilet?
Speaker 2: So it's still spinning. It's got to keep spinning. That's
Speaker 2: why it's a pancake. And then you get these arms
Speaker 2: that form. And a lot of people imagine that galactic
Speaker 2: arms are like your arms that you spinning around. Your
Speaker 2: arms are like a collection of mass, and as your
Speaker 2: arms spin, that mass moves. But in the case of galaxies,
Speaker 2: these arms are not structural. It's not the same stars
Speaker 2: in the arm and the whole time, the arms are
Speaker 2: actually density waves in this pancake. So some star get
Speaker 2: closer together and then further apart, and closer together and
Speaker 2: further apart. It's more like a wave passing through a stadium.
Speaker 2: Those people aren't running in a wave. It's just a
Speaker 2: wave moving through the stationary crowd.
Speaker 1: Yeah, we had a whole episode about that. I remember.
Speaker 1: It's sort of like a wave in traffic, Like you
Speaker 1: were stuck in the highway. There's sort of these ways
Speaker 1: that go from the back to the front or the
Speaker 1: front to the back, where you get these cars kind
Speaker 1: of clustering together for a while, but then they spread
Speaker 1: out after a while, right, sort of like a traffic
Speaker 1: jam almost.
Speaker 2: Yeah, it's sort of like a traffic jam. And it
Speaker 2: explains why galaxies aren't like really really tightly wound. If
Speaker 2: you stick your arms out and then you spin, your
Speaker 2: arms tend to sort of like lag behind you. Or
Speaker 2: if you had like a ribbon and you were spinning,
Speaker 2: you would end up winding it around yourself. And so
Speaker 2: people wondered for a while when they thought that these
Speaker 2: arms really were structural, why galaxies weren't all like wound
Speaker 2: up like a ball of yarn. So this explains why
Speaker 2: they aren't because they're actually just density waves. But you
Speaker 2: do see a big range of tightness, like you see
Speaker 2: some with looser wines and some with tighter wines. It's
Speaker 2: really interesting to see like the variety.
Speaker 1: By one, you mean, like the spiral. Some spirals are
Speaker 1: more spirally than others.
Speaker 2: Yes, some are looser and some are tighter. They're all spirals,
Speaker 2: but some are looser and some are tighter. And sometimes
Speaker 2: you see multiple arms, right, But a listener question about
Speaker 2: a galaxy with like three arms and why you sometimes
Speaker 2: have four arms or two arms. These are density waves
Speaker 2: that come out of the perturbations of the initial gas
Speaker 2: cloud as it's spinning, and so you can get different
Speaker 2: numbers of arms. You also typically get like a big
Speaker 2: central bulge. So that's the shape of these spiral galaxies.
Speaker 2: And they spin for a long time. And they think
Speaker 2: that eventually spiral galaxies will merge with other spiral galaxies.
Speaker 2: But they don't have to write. Sometimes the spiral galaxy
Speaker 2: is happy by itself and they can just sort of
Speaker 2: live out its life. And the future of these spiral
Speaker 2: galaxies is that eventually these density waves dissipate and you
Speaker 2: get just sort of like a smooth pancake galaxy.
Speaker 1: Wait, what so it starts out smooth, then you get
Speaker 1: these density waves and give give it a spiral shape,
Speaker 1: and then eventually after why all the spirals flatten out too.
Speaker 2: Yeah. I wouldn't say that it starts out smooth. I
Speaker 2: mean the density waves come from something in that galaxy
Speaker 2: that was clumpy that seeds the density wave. But eventually
Speaker 2: interaction between these stars, the pushes and the pulls and
Speaker 2: the friction, et cetera, will smooth these things out and
Speaker 2: they will dissipate. You get these things called lenticular galaxies,
Speaker 2: which have no relationship to lentils at all. To my
Speaker 2: wife's great disappointment, It just means that they're basically smooth.
Speaker 1: But I guess maybe we're just saying, is that maybe
Speaker 1: we've been imagining this original cloud of gas that started
Speaker 1: the galaxy as being perfectly smooth, but maybe it wasn't right.
Speaker 1: Like maybe this cloud of gas was lopsided, or maybe
Speaker 1: it was denser in one direction, and then those weird
Speaker 1: shapes of the gas then gave you these weird arms distributions.
Speaker 2: Yeah, it definitely was not smooth, right, The reason this
Speaker 2: cloud of gas formed in on some other cloud is
Speaker 2: because it was denser. It formed around some core that
Speaker 2: was a little bit denser that pulled it together, and
Speaker 2: there were other sort of like mini cores within it,
Speaker 2: you know, other little seeds of gravity. So it definitely
Speaker 2: didn't start out as a perfectly smooth structure at all,
Speaker 2: and so that plays out and forms these density waves.
Speaker 2: But because the interaction, things eventually spread out and it
Speaker 2: gets smoothed out.
Speaker 1: So that's the future of the bilky Way galaxy too. Eventually,
Speaker 1: we're just going to We're just going to be a
Speaker 1: pancake if we.
Speaker 2: Were left to our own devices. But because Andromeda is
Speaker 2: going to slam into us, that's going to change our shape.
Speaker 2: And whether we form a new spiral galaxy as a
Speaker 2: merger or whether we end up an elliptical galaxy depends
Speaker 2: a little bit on how much gas we have left
Speaker 2: when it.
Speaker 1: Happens, all right. So that's how spiral galaxies get formed.
Speaker 1: And so they talk about some of the other shapes
Speaker 1: that galaxies can take, including Daniel's minky mouse galaxy. So
Speaker 1: let's talk about that. But first let's take another quick break,
Speaker 1: all right, we're talking about the shape of galaxy sees
Speaker 1: sponsored by Disney. No, the check didn't come through, sponsored
Speaker 1: by Warner Brothers. Let's talk about bugs, bunny shape galaxies.
Speaker 2: You want all these children's entertainment companies to be responsible
Speaker 2: for the not safer astronomy shapes of galaxies.
Speaker 1: Well, I'm sure we can censor those out now.
Speaker 2: We are censoring the nice sky.
Speaker 1: Oh my gosh, I feel like the nice sky sensors itself.
Speaker 1: Why is it so hard to see?
Speaker 2: I know most of the universe has already censored. Maybe
Speaker 2: dark matter is hidden for us for a reason.
Speaker 1: That's right. It's it's like the universe using a black marker.
Speaker 2: It's not dark matter, it's bleeved matter.
Speaker 1: That's right. Maybe it's not safe for humans.
Speaker 2: It's redacted matter.
Speaker 1: Yeah, we can't be trusted with its secrets.
Speaker 2: If you only knew what the universe was hiding.
Speaker 1: Oh my goodness. You know you can get in trouble
Speaker 1: for divology classified information. Have you heard?
Speaker 2: I have not.
Speaker 1: I want to watch out for that. All right, So
Speaker 1: let's talk about some of the other shapes that galaxies
Speaker 1: can be. We talked about spiral shapes. That's kind of
Speaker 1: maybe the traditional shape of a galaxy that most people
Speaker 1: think about, but galaxies can have other shapes.
Speaker 2: Yeah, spiral galaxies are the most common in the universe,
Speaker 2: but the biggest galaxies are elliptical galaxies. These are often
Speaker 2: found in like the rich central regions of galaxy clusters,
Speaker 2: and they are usually the result of lots of spiral
Speaker 2: galaxies merging. And these elliptical galaxies are not nearly as
Speaker 2: pretty to look at. Like a spiral has features, you
Speaker 2: can see it. It's like a disc, there's arms in it.
Speaker 2: Sometimes elliptical galaxies basically just a big blob. You know,
Speaker 2: it's smooth, there's almost no features in it. It's just
Speaker 2: a bunch of stars.
Speaker 1: Well maybe that's pretty to some people.
Speaker 2: I'm not saying it's not esthetic, but it's just a
Speaker 2: bit of a blob.
Speaker 1: Are you trying to shape shame some galaxies out there?
Speaker 2: I'm just creating categories, man, that's all I'm doing. An
Speaker 2: important feature of elliptical galaxies is that they don't have
Speaker 2: a lot of star formation going on, and so why
Speaker 2: they're elliptical galaxies?
Speaker 1: Now, hold on, what do you mean by elliptical, Like
Speaker 1: it's shaped like an ellipses, but Is it flat or
Speaker 1: is it Are you saying it's more shaped like a football?
Speaker 1: What is this shape? Exactly?
Speaker 2: It's more like a big watermelon, you know. And an
Speaker 2: ellipse in general includes spheres, right, It's just sort of
Speaker 2: like a more general phrase the same way that like
Speaker 2: a circle technically is an ellipse. It just has its
Speaker 2: two axes equal. So an elliptical galaxy is just like
Speaker 2: a big watermelon shaped galaxy. It might be longer in
Speaker 2: one direction or another.
Speaker 1: So it's like a blob, like a submarine shape.
Speaker 2: Blob, Yeah, exactly, like it's a big submarine floating through space.
Speaker 2: It's not flat like a pancake.
Speaker 1: And that's the overall shape of it. Is it like
Speaker 1: denser in the middle? Is it just all all the
Speaker 1: stars evenly distributed? Does it have like a shell? Paint
Speaker 1: the picture for us?
Speaker 2: So, elliptical galaxies definitely do have a core where things
Speaker 2: are denser, and then they peter out near the edge.
Speaker 2: But essentially there's not that much else to talk about.
Speaker 2: They're roughly ellipsoidal, and they have a bunch of stars
Speaker 2: in them, and I think maybe the other most interesting
Speaker 2: thing about them is that they don't have a lot
Speaker 2: of gas basically mostly stars, which means that you're not
Speaker 2: having a lot more stars being formed. Right. It's the
Speaker 2: gas that forms the stars, and in a lot of
Speaker 2: galaxies you continuously have more stars being formed, But elliptical
Speaker 2: galaxies are almost always quenched, which means no new stars
Speaker 2: are being formed.
Speaker 1: And are the stars in them also really old?
Speaker 2: Right?
Speaker 1: If it's not forming new stars in all of its
Speaker 1: stars must.
Speaker 2: Be old exactly, which affects the color of the galaxies
Speaker 2: as well. Because stars that are really big turn out
Speaker 2: to be really hot, which makes them blue, and those
Speaker 2: kinds of stars don't burn for very long. The colder stars,
Speaker 2: the smaller stars, are redder, and those tend to be
Speaker 2: the ones that burn for billions and billions of years.
Speaker 2: So if you look at a galaxy and you see
Speaker 2: only red stars, that means there are no new stars
Speaker 2: being formed there. There's only the long lived short people
Speaker 2: who are left. And so these elliptical galaxies don't have
Speaker 2: new stars being formed, which makes them redder than other galaxies.
Speaker 1: So all the blue stars basically burn themselves out and
Speaker 1: are maybe just floating there but you can't see them.
Speaker 2: Yeah, exactly, they have their stellar remnants, but they're no
Speaker 2: longer burning. And that's basically why this is an elliptical galaxy.
Speaker 2: I mean, imagine two spiral galaxies forming. If they don't
Speaker 2: have a lot of gas left, then what happens. They're
Speaker 2: mostly just stars. And then those two spiral galaxies merge,
Speaker 2: and now you have two planes. You have one plane
Speaker 2: of rotation from each galaxy, and now they've mixed, so
Speaker 2: you have some stars moving along one plane, some stars
Speaker 2: moving along another plane. Now throw in another spiral galaxy,
Speaker 2: and another and another. Eventually you have lots of different
Speaker 2: planes of rotation, and what do you get. You get
Speaker 2: an ellipse. So you add a bunch of spiral galaxies
Speaker 2: together without a whole lot of gas to make new stars,
Speaker 2: then you just get a big ellipse.
Speaker 1: It's like you're just joining different pancakes at different angles,
Speaker 1: and then you push it all together and you just
Speaker 1: get a giant cloud of stars exactly.
Speaker 2: And that might make you think, well, then every single
Speaker 2: galaxy that's merged should be an ellipse, right, because you
Speaker 2: get these spirals, and then you add spirals together, you
Speaker 2: should get ellipses. How can you still have really big
Speaker 2: spiral galaxies? Like the Milky Way or Andromeda. And the
Speaker 2: answer is the gas. When the two spiral galaxies merge,
Speaker 2: if there's still a lot of gas in the original spirals,
Speaker 2: then that gas interacts and collapses again, forming a new spiral.
Speaker 2: And that's how you get a big spiral galaxy. The
Speaker 2: gas from the original ones smashes into each other, forming
Speaker 2: new stars in a new disk.
Speaker 1: Right. But I guess maybe the question is like, why
Speaker 1: don't elliptical galaxies eventually collapse into a pancake too? Like,
Speaker 1: wouldn't they also have, you know, an overall spin, even
Speaker 1: if you're adding different mini galaxies, but didn't it all
Speaker 1: have an overall spin? Wouldn't over time it also collapse
Speaker 1: into a pancake and then maybe also into a spiral.
Speaker 2: It might eventually, but because there's very little gas in
Speaker 2: those galaxies, is almost no friction, and so it's really
Speaker 2: hard for those stars to interact with each other. You know,
Speaker 2: they're basically really isolated from each other except for gravity.
Speaker 1: What do you mean by let low friction? How does
Speaker 1: that plan into a cloud of gas form into a pancake.
Speaker 2: It's very hard for these stars to exchange energy in
Speaker 2: any way. Think about how things can come things collapse
Speaker 2: because they bounce off each other. If everything just stayed
Speaker 2: in its original orbit, nothing would ever collapse. Your gas
Speaker 2: cloud never would have formed a pancake. In order to
Speaker 2: collapse down to a pancake, they have to somehow bounce
Speaker 2: off each other and exchange energy. That's why, for example,
Speaker 2: dark matter doesn't collapse into a pancake because it has
Speaker 2: no interactions other than gravity. It just stays in a
Speaker 2: big spherical halo.
Speaker 1: So even though it's drawn to the center, when they
Speaker 1: get to the center, they just miss each other and
Speaker 1: keep going.
Speaker 2: Yeah, exactly. But if there's some gas there to sort
Speaker 2: of slow the stars down and exchange energy, then things
Speaker 2: can collapse. But elliptical galaxies have almost no gas, and
Speaker 2: so the stars basically ignore each other unless they come
Speaker 2: really close and some gravitational interaction can slow them down.
Speaker 2: So I think like eventually elliptical galaxies will flatten out
Speaker 2: for all the same reasons we've been talking about, but
Speaker 2: because gravity is so weak compared to the other forces,
Speaker 2: it's going to take much much longer then if you
Speaker 2: actually have a lot of gas in there to facilitate
Speaker 2: that kind of interaction.
Speaker 1: But as we're looking back into time with like the
Speaker 1: James Web telescope gig do we see evidence of that
Speaker 1: like in the distant past? Is it mostly all pancakes
Speaker 1: or are there still a lot of elliptical galaxy.
Speaker 2: In the distant past? We can see that these pancakes
Speaker 2: are the ones that are formed. Like, you don't form
Speaker 2: elliptical galaxies initially, you form little spirals, and then if
Speaker 2: those spirals use up most of their gas and have
Speaker 2: quenched and then merge, then you see ellipticals being formed.
Speaker 2: So the only way to make an elliptical galaxy is
Speaker 2: to basically use up the gas in the spiral galaxies
Speaker 2: initially and then merge them, and then they're sort of
Speaker 2: frozen in their original planes.
Speaker 1: So I guess maybe what you're saying, is it not
Speaker 1: enough time has passed made for these elliptical galaxies to
Speaker 1: flatten out, to basically see everything flatten out.
Speaker 2: Exactly in the far far future. Elliptical galaxies, if left
Speaker 2: to their own devices, will eventually flatten out because of gravity.
Speaker 2: But spiral galaxies are flattened because the gas, because the
Speaker 2: gas has a lot more interactions than the stars.
Speaker 1: All right, So then that's the elliptical galaxies, what other
Speaker 1: shapes can galaxies be?
Speaker 2: So there's another category called irregular galaxies, and these are
Speaker 2: ones that are basically not elliptical and not spiral. So
Speaker 2: astronomers are like, hmmm, let's make a bucket for other stuff.
Speaker 2: And irregular galaxies can be like almost any shape. You
Speaker 2: see stuff long and thin, you see stuff spread out,
Speaker 2: you see stuff in a question mark shape. There's a
Speaker 2: huge number of these also, but almost every single time
Speaker 2: it's a transient shape. It's because something has been like perturbed.
Speaker 2: Two galaxies have smashed into each other or passed really
Speaker 2: close to each other and torn themselves apart and haven't
Speaker 2: yet settled into some new stable shape, probably elliptical or spiral.
Speaker 2: So it's sort of like an intermediate state for galaxies
Speaker 2: that are interacting.
Speaker 1: I thought you mean a regular like a toilet reference.
Speaker 2: Again, these should have more fiber of these galaxies, I mean,
Speaker 2: really take care of yourselves.
Speaker 1: Yeah, puts a men abuse with that dark chocolate.
Speaker 2: Maybe dark matter is the fiber of the universe that
Speaker 2: really is making things.
Speaker 1: Regular, all right, So you're saying that in paint the
Speaker 1: picture for us. Again, these are just like we shapes
Speaker 1: out there of galaxies like they look like an L
Speaker 1: shaped or like a maybe like a Mickey mouse.
Speaker 2: Yeah, if you just google like irregular galaxies, you can
Speaker 2: see all sorts of crazy stuff and it's basically the
Speaker 2: results of collisions, so it can be a mess. Just
Speaker 2: like if you look at simulations of what's gonna happen
Speaker 2: when Andromeda in the Milky Way collide. In the beginning,
Speaker 2: it doesn't really have any shape at all. It's just
Speaker 2: like a huge spray stars this way and stars that way,
Speaker 2: and then eventually it settles down into a new shape.
Speaker 2: But in the intermediate shape, it just depends on the
Speaker 2: angles and the sizes and how they hit. You can
Speaker 2: get basically any shape you like.
Speaker 1: And you say, most of these irregular galaxies are because
Speaker 1: of collisions of other galaxies, But can you form an
Speaker 1: irregular shape galaxy from scratch?
Speaker 2: Cool question. I think the answer is no, because you
Speaker 2: don't get star formation in a spiral galaxy until the
Speaker 2: gas collapses, right, So it's not like you can form
Speaker 2: a bunch of stars in a random place. The stars
Speaker 2: don't really form until the gas is already collapsed into
Speaker 2: a disc. Really, and so I don't think you can
Speaker 2: form in a regular galaxy from scratch. I think it's
Speaker 2: the combination of other galaxies coming together sort of chaotically.
Speaker 1: All right, So then does that cover all the shapes
Speaker 1: galaxies can be.
Speaker 2: It doesn't. There's one really cool, very strange, spectacular shape
Speaker 2: of galaxy that's very very rare. It's called a ring galaxy.
Speaker 1: WHOA, Like it's shaped like a hoop.
Speaker 2: It's really cool. It has like a central core, like
Speaker 2: a blob in the middle, and then there's a big gap,
Speaker 2: and then surrounding it is a whole ring of stars.
Speaker 1: So it's flat.
Speaker 2: It's flat, yeah, exactly, So it's flat pancake, but instead
Speaker 2: of being like a full disc, it's got a core
Speaker 2: and then like a ring, so it's sort of like
Speaker 2: a bicycle wheel. You have like the tire and then
Speaker 2: you have the central hub and there's a huge gap
Speaker 2: in between.
Speaker 1: Sort of like a Saturn galaxy.
Speaker 2: Yeah, exactly, like a Saturn galaxy. And these are really fascinating.
Speaker 2: The center is red, so like they're older stars, and
Speaker 2: the ring tends to be blue, so they're really beautiful
Speaker 2: to look at. WHOA and patriotic, Yeah, I guess they're French.
Speaker 2: They're Dutch and they're American red.
Speaker 1: Right that all of that. Yes, it's multinational. How do
Speaker 1: these galaxies form?
Speaker 2: So this was a real mystery for a long time.
Speaker 2: We didn't even see one of these until like nineteen fifty.
Speaker 2: They're so rare, and I think that these things are
Speaker 2: formed in a really lucky, spectacular collision. Basically, when one
Speaker 2: galaxy passes right through the center of the other one,
Speaker 2: it creates this ring from the shock wave of dense
Speaker 2: gas that's rushing out of that collision.
Speaker 1: You mean like two spiral galaxies or two elliptical galaxies
Speaker 1: just totally just head on crash into each other.
Speaker 2: Yeah, exactly. You have like some galaxy punched right through
Speaker 2: the exact center of another gas rich spiral galaxy. It'll
Speaker 2: create this shock wave in that gas which will create stars.
Speaker 2: And that's why the ring tends to be blue, because
Speaker 2: it tends to be big, fat, young hot stars that
Speaker 2: tend to burn bright. Whoa no judgment?
Speaker 1: Is it's safe for work? Does it safe for work?
Speaker 1: The broadcast?
Speaker 2: I mean hot in a technical temperature sense.
Speaker 1: Right, Well, you just got really excited there.
Speaker 2: I'm excited to see star formation, right. Star formation is
Speaker 2: so exciting. It's like the thing that makes the universe bright.
Speaker 2: It's the reason we can see things in the universe
Speaker 2: is because stars form. It's kind of a miracle almost,
Speaker 2: And so these collisions create a whole ring of new
Speaker 2: stars that are sort of moving out away from the galaxy.
Speaker 1: So that the main stars crash into each other and
Speaker 1: the collision kind of exploded all the gas to the
Speaker 1: outer edge and that's where these new stars are forming.
Speaker 1: But why did it stay in a flat shape?
Speaker 2: Well, the original disc essentially was flat, right, and so
Speaker 2: what happened was created a pressure wave in that flat disc.
Speaker 2: There isn't gas in those other directions to compress. It's
Speaker 2: sort of the same reason that like a ripple moves
Speaker 2: along the surface of the water, you slap the water
Speaker 2: and you get rings on the surface. You don't get
Speaker 2: rings of water like moving up also, and that's sort
Speaker 2: of where the gas is.
Speaker 1: I see. It's like you had a giant disc flat
Speaker 1: pancake and you sort of poked the middle of it
Speaker 1: and it sent the ripple along the pancake exactly.
Speaker 2: And that's what we're seeing. We're like in the middle
Speaker 2: of watching this. So this is a pretty spectacular hypothesis.
Speaker 2: And people thought well, if this is true, then we
Speaker 2: should see like galaxies literally on top of each other,
Speaker 2: and also we should be able to like identify the
Speaker 2: galaxy that caused that ripple. And now we've seen enough
Speaker 2: of these things that you can actually spot that we
Speaker 2: have pictures of ring galaxies where you can tell which
Speaker 2: galaxy has just passed through it, like you know, recently
Speaker 2: on galactic timescales, and we've even seen one where the
Speaker 2: galaxy is in the process of punching right through the
Speaker 2: middle of the other galaxy.
Speaker 1: Well, it's interesting that this is happening not just in
Speaker 1: one place, but like all over the universe.
Speaker 2: Yeah, everywhere. And it turns out that's what the question
Speaker 2: mark galaxy is. It looks kind of like a question
Speaker 2: mark because we're seeing one galaxy which is a spiral,
Speaker 2: and then there's another galaxy which is on edge so
Speaker 2: it looks like a line, and it's passing right through
Speaker 2: the middle of it. So you get this combination of
Speaker 2: two galaxies forming a question mark, and in a million
Speaker 2: years or so, the one that's being hit is going
Speaker 2: to turn into a ring galaxy.
Speaker 1: Wait, wait, how does how does a question mark form.
Speaker 2: Save one which is a disc and you can sort
Speaker 2: of see the arms of it, and that's sort of
Speaker 2: the round part of the question mark. This is so
Speaker 2: difficult to do over audio. And then the line part
Speaker 2: of the question mark is another galaxy, but we're only
Speaker 2: seeing it on edge, so it looks like a line
Speaker 2: instead of a circle. So instead of looking like a
Speaker 2: figure eight, it looks like a figure eight, but one
Speaker 2: of them has been twisted down, so it's like a
Speaker 2: circle and a line combined.
Speaker 1: Complicated, Yes, it's complicated. I think we're a galaxy question mark.
Speaker 2: I think we're supposed to merge into something question mark.
Speaker 1: I don't know. Yeah, maybe it just.
Speaker 2: Goes to show you there's questions everywhere in the universe
Speaker 2: literally literally.
Speaker 1: Yeah, all right, Well, what does this all tell us about,
Speaker 1: like the Bilky Way and why we're here and is
Speaker 1: it weird that we're here or are we a pretty
Speaker 1: typical galaxy?
Speaker 2: So we're a pretty typical galaxy. We're not one of
Speaker 2: the biggest galaxies, we're not one of the smallest galaxies.
Speaker 2: We have one of the most common types of galaxies
Speaker 2: in the universe. But it also tells us that we
Speaker 2: contain multitudes. You know that the Milky Way has lots
Speaker 2: of little baby galaxies inside of it. Some of the
Speaker 2: reasons we have stars that are not in the disc
Speaker 2: that like orbit above the disc or whatever, are from
Speaker 2: those collisions, stars that survive those collisions of galaxies and
Speaker 2: are still hanging out orbiting in their original galactic plane.
Speaker 2: And when we look at the distribution of galaxies, all
Speaker 2: the different shapes, it forces us to tell this story,
Speaker 2: to explain everything we see, and to play detective and
Speaker 2: to understand, like what happened in the early universe, how
Speaker 2: did we get here from the big blob of gas
Speaker 2: from the Big Bang? And it helps us unravel, you know,
Speaker 2: the whole history of the universe and also to think
Speaker 2: about its future.
Speaker 1: But it sort of seems like in terms of shape,
Speaker 1: there's really only one shape, which is the sort of
Speaker 1: like the spiral, and then the other shapes you get
Speaker 1: them by combining spirals together, so it's more like a
Speaker 1: sequential category of galaxies.
Speaker 2: Yeah, to use your analogy, it's like the spirals are
Speaker 2: atoms and everything else is like a molecule built out
Speaker 2: of those atoms.
Speaker 1: And those other shapes only sort of happen if two galaxies.
Speaker 2: Collide, exactly a cloud of gas will form a spiral
Speaker 2: galaxy if left on its own, and the other ones
Speaker 2: need combinations of spiral galaxies.
Speaker 1: And it also sounds sort of like the future is
Speaker 1: a little bit unknown, right, like we're maybe not sure
Speaker 1: what eventual shape things are going to take in the future.
Speaker 2: Yeah, our galaxy and will collide with Andromeda, and whether
Speaker 2: we form a new spiral galaxy along that plane depends
Speaker 2: how much gas is left. We know that Andromeda is
Speaker 2: already starting to quench, and we think that the Milky
Speaker 2: Way is quenching, which might mean that we don't have
Speaker 2: enough gas to make a new spiral galaxy. It might
Speaker 2: mean we end up with a big elliptical blob.
Speaker 1: Or we win end up with a galaxy.
Speaker 2: Maybe from some point of view, just before Andromeda plummets
Speaker 2: into the heart of the Milky Way, you might be
Speaker 2: able to make us do a question.
Speaker 1: Mark. Well, here's the question, Daniel. If our galls she's
Speaker 1: called the Milky Way and there's chocolate in our galaxy,
Speaker 1: isn't all chocolate then milk chocolate?
Speaker 2: No, you're ruining chocolate for me, man, I'm going to
Speaker 2: have to look forward to importing chocolate from Andromeda.
Speaker 1: There you go. Should have just said no way man.
Speaker 1: All right, well, an interesting view into the cosmos and
Speaker 1: all the different things that can happen out there, and
Speaker 1: another interesting reminder that the universe is still evolving, still changing.
Speaker 1: Things are colliding, things are changing shapes, things are asking
Speaker 1: questions of themselves. It's an ever changing universe.
Speaker 2: And the past is contained in the present. If we
Speaker 2: can dig into it deep enough and think hard about
Speaker 2: the rules at play, we can figure out what happened
Speaker 2: in the universe.
Speaker 1: That's right, sort of like how the white chocolate contains
Speaker 1: cocoa butter, which is technically makes.
Speaker 2: It chocolate and you should only eat it at state
Speaker 2: fairs deep.
Speaker 1: Fried, that's right, or in a desert island.
Speaker 2: Only crack open in case of emergency.
Speaker 1: All right, well, we hope you enjoyed that. Thanks for
Speaker 1: joining us. See you next time.
Speaker 2: For more science and curiosity, come find us on social
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