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