Daniel and Jorge Explain the UniverseHow do we know the shape of our galaxy, since we're stuck in the middle of it?
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Hey Daniel, you're often saying that things in space are beautiful.
Yeah, you know. I never look at a telescope image and think yuck. I love the swirls of galaxies, I love the explosions of stars.
It's all gorgeous, but one makes it beautiful. Is it the symmetry?
No, I think it's beautiful just to see the power of physics and action at a grand scale.
So would you still think something in space was beautiful if it was a little off?
Why did you do something? Or hey, is there something I should know about?
I mean, I'm not saying I had anything to do with it, but you know, maybe just be open minded about the shape of things in space.
Fortunately, I love galaxies and stars of all shapes and sizes.
I am Warham, a cartoonist and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle physicist, and I do really think the universe is beautiful.
There's a lot to appreciate out there, right. It's big and amazing and quite sparkly spaces.
It is, And it makes me wonder why do we find our universe beautiful? Are we lucky that we just ended up in the universe that we find beautiful or is it sort of predetermined that any universe we would find ourselves in we would appreciate Somehow.
Do you think it's that there's an evolutionary advantage to finding the universe beautiful? Like, you know, maybe there were some early humans who hated the universe, but you know, they didn't make it because they got depressed about living in something they didn't like.
Yeah, I would like to think that there's an evolutionary advantage to joy, but I'm not a biologist, so it's too far out of my bailey wick mm.
But welcome to our podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we marvel at the beauty of the universe and try to unravel its inner meaning. We look at everything around us and ask why is it that way? Why isn't it this other way? What does it mean that it swirls this way and bends that way and twists this other direction. We look everywhere in the universe and we never stop asking why.
Because there is a lot out there for us to observe and explore and appreciate. And that's a very interesting word, isn't it, Daniel, to appreciate the universe and space and everything in it.
Absolutely. And one thing I love when we look at like Hubble images is seeing the dynamics. When you imagine that things out there in space are fixed their static you're just sort of looking at a picture, but When you see these images from Hubble, you see flows, you see like explosions, you see gas clouds smashing into each other. Of course, it's on the millions of years timescale, so you're seeing one image of it. But even just from that one image, you can tell their stuff going on.
So do you think of being faster, Like if you hit the fast forward button, you'd be like, wow, now that's beautiful.
Well, I would like to hit the fast forward button and see what happens to the university, but answer a lot of really fun questions. But I think there's also a lot of beauty in taking some process that's dynamic, that's violent, and then just freezing it. It's like looking at our water drop hitting a surface and seeing those little mini droplets in the ring come out. It captures something about the physics that's happening in a way I just find beautiful.
Mmmm. So lately you've been talking to an artist right about this idea of beauty in the universe.
Yeah, that's right. We have some listeners who are scientists, and listeners who are engineers, and also listeners who are ritists and artists and cartoonists, and of all stripes, and one of them called me up recently and asked me what I thought about the meaning of life and beauty in the universe, and we had a really fascinating conversation.
Wow, would you have to say about the meaning of life beauty in the universe? Sounds like a big question and the title of our next movie starring Julia Robbers life Beauty the Universe.
Well, I think I said something like, scientists try to uncover beauty in the universe and artists try to create it.
Wow, but are artists part of the universe?
Yeah, and I guess that makes all artists beautiful.
I would agree with that, especially cartoonists.
Yes. Absolutely. But she also asked me a really fascinating question. We were like just about to get off the phone, and she said, hold on a second, I have a question, a science question view have always been curious about.
Do you think a lot of people have such a question that they've always wanted to ask in case they ever talked to a physicist.
I don't know. I hope. So I think everybody should be prepared. If you end up on an airplane flight next to a physicist, you should be ready. You should have that question in your pocket.
But that is a pretty great question. But how do we know what the shape of the Milky Way? Galaxy here?
Yeah, that was her question. She said, we're inside the Milky Way, so how is it that we can see pictures of the Milky Way? Or more generally, how do we know the shape of the Milky Way if we're stuck in the middle of it? Right?
Because I guess we don't have the equivalent of a galactic mirror, right, we can't take a selfie. So how do you know, like what your nose looks like? Right? If you never had a mirror, how would you know what your nose looks like?
Yeah, we need like a super long selfie stick, you know, put a hubble on the edge of a stick that's like one hundred thousand light years long to take a picture of the Milky Way. That would take for a long long time.
So today we'll be answering this question from one of our listeners. So today on the program, we'll be asking the question, how do we know the shape of the Milky Way? And Daniel, it turns out it has a very surprising shape, doesn't it.
It does have a weird shape. I think a lot of people have an idea for what the Milky Way looks like. But I was actually surprised when I dug into this to discover it's not quite the shape that everybody expected.
You know, you just made me realize that most basically any picture we've ever seen of the milk Way was probably an artist's rendition.
Oh, I know, don't even get me started on artists in astronomy. It's crazy. The renditions are the artists probably both. But almost anytime you see a new result in astronomy usually comes with some image, and that image is not usually data. It's usually like some artist rendition of how this might look, which includes huge amounts of like just invented stuff that's totally speculation, and you can't disentangle like what we know what it's actually real from what like the artists just thought of at three am when they were doodling on their computer.
Right, they should publish the data, right, Like just show a bunch of numbers, Yeah, at the top of the article. Yeah, I'm sure click on that.
Well, I think the data itself is fascinating. Think about the picture of the black hole. That's fascinating to see an actual picture of an actual black hole. The zillions of artistic images of black holes. But there's only one truth, and we want to know the truth, not just like what's some artist imagined. Imagine if in particle physics we just like published artists impressions of data from the collision, you know, instead of actual, we would get tossed out of science.
That's what you said, Daniel, The artist do capture truth.
I think they create beauty. I don't know if it's always true. It's not always true that they succeed. All right, all right, well this is an interesting question. How do you know what the shape of the milky Way is if you are standing in the middle of it and or at least off to a little bit of a corner of it. So, as usual, Daniel went out there into the wilds of the Internet to ask people if they knew how we know the shape of the milk Way. And so, if you'd like to participate in future baseless speculation without research on topics of the day, please write to us. And also if you have a question for a physicist you've never had a chance to ask, please write to us to questions at Danielandjorge dot com. We love our listener emails, and we really do respond to every single one.
We should change the name of the podcast Daniel to baseless speculation. I think that's implied already in physics or in our podcast Dangel and Jorge, so it must include baseless speculation. Yeah, so think about it for a second. Do you know how we know the shape of the Milkway? What would you answer? Was what people had to say.
I believe our galaxy is relatively flat. So I assume if you ham a telescope through the galaxy and then raise it above or below the plane of our galaxy, you could see there's nothing there. So the natural conclusion is that the galaxy is rather flat.
I would guess that the way we know the shape of our galaxy is by using all the telescopes that we have, such as Hobble, and looking at the whole range of radiation from UV to visible lights to X and gamma rays and making up an image of our galaxy.
I think it is, you know, by scientists and astronomers looking at distant stars in our own galaxy and trying to map the distance. And we also can observe the band of light in the clear dark sky which looks like, you know, a straight line. And also more importantly, I think we have observed distant galaxies and then we can see that most galaxies are spiral.
I'm assuming that it's mostly just from you know, the telescope images and knowing where the large sources of mass in our galaxy are, and performing models and looking at gravity to figure out what kind of shape its best.
That's a tough one. I'm honestly not really one hundred percent sure. I do know, just like from an energy perspective, I believe the shape is you know, saddle, and I think it has to do with offsetting energy.
I don't know many clever people figuring out how stars move around the center of the galaxy, and that's that gives us a clue of how everything is organized around us.
All Right, people had some pretty good ideas here. Nobody said I don't know, or that sounds impossible, right.
Well, I think people know that we've mostly figured it out, and so they imagine there must be a way to do it.
Oh. Interesting, they just assume we figured it out.
Many clever people.
Yeah, I guess nobody assumed that all this time physicists have been making stuff up.
It's just been an artist impression. This entire time, this entire time.
Yeah, Actually, the Milky Way looks like a or an X.
It's a top hat.
It looks like a glass of milk. Actually, yeah, So that's an interesting question because we are in the middle of the galaxy, right or you know, a little bit off to the side, but we're not like very far away from it, so we don't have a view of it, so it's kind of hard to tell. I mean, when you look out, you see a cloud of stars.
Yeah, when you look out, you just see a cloud of stars. And that's why it took us actually a long time to figure out the shape of the Milky Way. It's something we've only recently understood, even like at its broadest scale. You know, like people thousands of years ago didn't understand the shape of the Milky Way. It's a modern idea that the Milky Way is this spiral disk.
I guess it'd be like, you know, trying to guess what the shape of the Pacific Ocean is if you're a fish, it'd be kind of hard.
Do you think fish wonder about that?
I don't think they want to know, you know, I bet.
Fish artists are constantly drawing images of the shape of the Pacific Ocean that are just totally baseless speculation for.
Their news articles. Yeah, and I'm sure the fishes have a.
Real problem with that, I know on their fish casts.
Yeah. So it's a pretty interesting question, and I guess we figured it out. Until the question is how do we figure out what is the shape of the Milky Way galaxy? So Daniel's step us through what is kind of a history of this? When did we realize we are in a galaxy?
First of all, those are two actually fascinating but different questions. Like people have looked up at the night sky and seen this band, this thing we call the Milky win the night sky, this band of light that looks like spilled milk that people have seen obviously for thousands of years. For that you only need eyeballs, And people have been wondering like what is that? You know, And it was only like around the time of Galileo, when we had telescopes that people realized it wasn't just some sort of gas or some sort of fire in the sky, but it was actually made of zillions of tiny little stars. So that idea there is only a few hundred years old.
Wow, So how did Galileo figure it out? I mean, when you look at the milk away with a telescope, you can actually see the individual dots, or you just see a concentration of dots kind of in that area.
Well both. I mean, it gets denser in some regions and it's dimmer in other regions. But you can look at the edges of it and you can see that that cloud is really just made up of lots of tiny little dots. And of course, the more powerful of your telescope, the more you can resolve the denser and denser regions.
But at that time, I'm guessing Galileo didn't know we were in a galaxy or what a galaxy was, right, Like, he probably just thought there's a there's a weird concentration of stars along this line.
Yeah, we didn't even have the idea of a galaxy. We just thought, well, there was just a universe and it was filled with stars, and the whole idea of that stars were clumped into galaxies. These little like island universes they called them, originally came about only about one hundred years ago, when people started measuring the distances to these other faint little smudges like, you have the big Milky Way, right, this huge spilled milk in the sky, and people understood, oh, that's just a bunch of stars. But then people also saw these little smudges that couldn't quite resolve, that looked like distant gas clouds, and they thought, oh, these are other just you know, gas clouds that are fairly nearby. I mean, it wasn't until about one hundred years ago that they realized that those were entire different galaxies that were so far away. And that's sort of the origin of this idea that we are a cluster of stars gathered together into this little island in space.
Right. What year was that?
That was in about nineteen twenty. That was the year of the Great Debate in astronomy, when there were folks arguing that the Milky Way basically was the whole universe and those little smudges were just gas clouds in the Milky Way, and other folks arguing that the Milky Way was just a little island and those smudges were other distant galaxies. So even in nineteen twenty, there was a huge debate about that.
And that's around the time when we started to kind of get a sense of the shape of the Milky Way, right.
Yeah, exactly, because the whole idea, the basic concept for how you build a map for something you're inside of, is that you need to measure the distances to the things you're seeing. If you're just looking at the night sky and you seeing a bunch of pinpricks, you can't tell the difference between lots of different shapes. Is everything far away and really bright? Is everything close by and not that bright? Are some things far and something's close. It's really hard to tell if you don't know the distances. So you have to build basically a three D map to everything you're seeing from the inside. And that started to happen only when we develop better techniques for measuring the distances to stars.
Right, Because from where we are, all stars look like little pinpoints, right, It's not like stars that are closer to us actually look like a circle. Everything is so far away that everything looks like a pinpoint. Basically.
Yeah, the only things that you can actually resolve in the telescope are planets and things in our solar system. Everything else is so far away that it looks just like a point. Remember, the nearest star is more than four light years away, So there's no way you're going to see the difference between like the left side of the star and the right side of the star, and you can't resolve it. And even if you could, that wouldn't tell you necessarily how far away it was because you wouldn't have any recognizable features on it to give you a sense of scale, So you still wouldn't know is it close by and pretty small or really far away and huge. And that was actually the question about these nebula. I mean, with a neebla, you can see the left and the right side of it, these smudges, and people were wondering are they close by and pretty big or really far away and incredibly enormous. And that was one argument actually against the idea that these nebula were other galaxies. People thought, if there are other galaxies, they must be just like unfathomly far away and really really big. So, yeah, you definitely need some sort of system to measure the distance to these things, because you can't just look at a star and tell how far away it is.
Yeah, okay, so then how did we start to get a sense of the shape of the Milky Way? Did we just start looking out into this swirl and it gave us somehow a sense of the shape of it.
Yeah, it dates back, you know, more than one hundred years. People just sort of started looking at stars and trying to get a map. And the way you can tell the distance to nearby stars. He's using something called parallax, which means you look at the star when we're on one side of the sun, and then again when we are on the other side of the sun. That it gives you a sense based on how much it moves in the sky how far away it is. It's sort of like putting your finger at arm's length and then looking at it through your left eye or your right eye. You can see that it changes, and then as your finger gets closer and closer, it makes it bigger and bigger difference. So by how much your view changes as you look from one eye to the other, you can tell how far away something is. It's binocular vision, right, So that was the first idea to use parallax to measure the distance to fairly nearby stars.
Wow, and how well does that work?
It works pretty well for stars up to you know, ten twenty fifty light years maybe, But there's a problem in that it only really lets you see pretty nearby stars, stars that are bright enough, and stars that can penetrate like the interstellar fog of the gas and the dust. So the first ideas we had of the shape of the Milky Way where oh, it's basically a blob and we're in the middle of it, because that's what happens when you're standing in a fog. Like imagine you're in a crowd of people in a fog. You look around, you think, oh, I'm at the center of this crowd, right, but everybody thinks that because they have a limited vision.
Crowd could look like a hot dog or a top hat. Right.
You never know, Yeah, you'd never know. And so what we had to do is develop a way to see further away stars, to see out to the edges of the Milky Way, to find something really bright that we could calibrate, that we could figure out how far away it is, and that let us get a sense for the shape of the Milky Way.
All right, let's get into how we finally crackice method for measuring the shape of the galaxy and what the shape actually is. But first let's take a quick break.
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All right, we're asking the question, how do we know the shape of the Milky Way and Daniels? So so far we have one method for telling how far stars are, but it doesn't get us far enough. So how do we know what the shape of the blob of stars that we're in looks like?
So we take advantage of some really weird, really lucky stars. It's almost like somebody has sprinkled these stars out there precisely to allow us to measure the distance to them. It's amazing how perfectly they work for exactly this purpose.
So it has to do something with a special kind of star.
There's a special kind of star. Now a normal star burns at the same brightness all the time, and so you can't tell the difference between it being really far away and super bright or it being close up and fairly dim. But there's another kind of star, a variable star whose brightness changes week to week and month to month. These are called cephids, and they're first discovered by a famous female astronomer, Henrietta Levitt, And so on the timescale like days or months, they get brighter and then they get dimmer, and they get brighter and then they get dimmer.
Right, And that tells us a little bit about where it is the frequency or is it more like we know that these stars are all about the same size.
They're not all about the same size. But there's a really key relationship. There's a connection between how quickly they change, like the period between going from brightest to dimmest. There's a close connection between that time and the brightness of the star, the actual brightness of the star. And so while you can't measure how bright the star would be if you were standing right next to it, you can measure how long it takes to go from it to brightest to its dimmest. And what they discovered when they that nearby sephids ones that they could measure the distance to using other techniques. Was that there was this incredible relationship, this very clean relationship. So if you measured the period, you could extract the luminosity. If you knew how long it took to go from bright to dim and back, you could then calculate how bright it actually was.
Oh, I see, that's pretty clever. It's like we and I guess we use parallaxes, is what they would use to sort of calibrate all this, Like the using parallax, we figured out that close by cephids are brighter when they blank faster or something like that.
That's right. We use the close by ones, the ones where we could measure their brightness and their actual distance using parallax. And we figured out that there's this relationship between the period and the luminosity. And if you know the actual brightness of a star and you can measure the brightness here on Earth, then you could tell how far away it is, because everything goes by one over R squared, Like the further you are away from the star, the dimmer it will be. But that's something that's very simple and easy to understand. You're twice as far away, it'll be four times as dim, you're ten times as far away, it'll be one hundred times as dim. So if you know the actual brightness, you know the brightness that you measure here, you can figure out how far away from it you must be, right.
That's pretty clever. And so that's our main methods for getting the shape of the galaxy, Like just going by these stars.
That's our main method. Yeah, these sefid stars really are the key, and we can see them because they're super dup or bright. Like some of these stars are like ten thousand times brighter than the Sun, so they can penetrate through those clouds of gas and dust and you can see them even on the other side of the Milky Way.
Well, sometimes there are ten thousand times brighter. Sometimes they're dimmer.
On a good dead they're so bright that you can see them in other galaxies. That was the clue that Hubble needed to understand that these nebula, these little smudges in space were super duper far away because he saw these cephids varying in other galaxies. Like you can see sephids in Andromeda, you can see them in other galaxies blinking on and off and telling us how far away.
It was really Yeah, like within this much there would be like a little pixel that turned on and off.
Yes, exactly, And that's the key that told them that these nebula were not just pretty big gas clouds inside our galaxies, but actually entire other galaxies because his distance measurements put them much further away than anything else we saw in the sky. It's like if you map the stuff around you and you find there's an edge and then there's a huge gap, and they see these other dots. That's what gives you this like island universe picture of our cosmos. It's not just a bunch of stars sprinkled through space, which with occasional clumping, but that there are these little localized blobs which we now call galaxies, these island universes.
So it's almost like somebody on purpose put a bunch of light posts all over the universe for us to see what the shape and the structures of it are.
It's really incredible. Without sephids, we would know so much less about the nature of the universe. Now recently we've developed even more powerful techniques to do sort of the same thing on a grander scale, to see deeper into the universe, and we've talked to in another podcast about the whole structure of our cosmos, the large scale structure, like where galaxies themselves are distributed. And for that we use type one A supernova, which is another space object in the same kind of category, where by watching it from far away you can tell how bright it actually is and then you can figure out how far away it must be. But cephids are sort of like the middle ground parallaxes for really close stuff. Cephids is for sort of intermediate and type one A supernova take you the furthest distance. But when it comes to mapping the Milky Way, it's really the sephids that are leading the charge, and they're sort of amazing, Like you might wonder, like why is a star blinking on and off so regularly.
Yeah, it's almost like we don't really have a picture of the real Milky Way. We just have a pare of cepid milky Way.
Yeah, they sort of map out. It's like tracers, Right, you can tell where the cephids are and then you can assume where the rest of the Milky Way is because that's something we can anchor to.
Yeah, hopefully the CEPHD galaxy looks like the regular Milky Way galaxy, right, like, hopefully there's nothing weird that makes them a different shape.
Yeah. Well, if you look at some of the most recent papers, and we'll talk about these results in a minute, mapping the shape and Milky Way to great detail, you can see that we have the most concentration of stepids nearby, because those are the ones that are easiest to see. So we know the shape of our side of the Milky Way much better than the other side of the Milky Way because we haven't seen as many sephids over there.
That's right, because we're probably in the good side of the galaxy, right, everyone has a good side, and if we're on this side, we're probably the better side.
If we're taking a selfie, we definitely want this profile to show up.
Yeah, yeah, yeah, And I guess maybe a question is why exactly are these sephids blinking so regularly?
I know it's weird, right, because our sun just burns, and it burns pretty steadily, and you know, it varies a little bit, and there's these eleven year cycles, but it doesn't just like go up and down on timescales of weeks and months. Imagine what it would be like to live at a solar system like that, where it got substantially brighter and then dimmer, and then brighter than dimmer. But there's some really interesting physics going on inside the star. It happens because these stars are mostly burning helium, and as they get hot, the helium gets ionized, gets stripped away from its electrons, and then it becomes opaque. So it's still burning on the inside, but that light is no longer leaving the star, so it absorbs its own radiation, which makes it really hot, and then it expands, which then cools it down, so then it's less ionized and less transparent, and so then it sort of collapses again until it heats up and gets more opaque and absorbs its own radiation, which fluffs it back out again. So it's incredible cycle. And it's amazing that it's so regular. You know, these stars go on and off, on and off on the timescale of weeks for millions of years.
Oh sounds like my diet.
How much helium union these days for it?
It makes me feel light, right, So that's pretty cool. So it's yeah, it's pretty red, and I wonder what it would be like to live in a solar system like that, Like, you know, you wouldn't just have seasons, you would also have potentially you know, like hot sun cold sun seasons.
Yeah, amazingly. I don't think I've ever read a science fiction novel set on a planet orbiting a sentid. That would be pretty fascinating. Somebody should write that one, or if somebody has written it, please email me and let me know because I want to read it.
Yeah, and I guess you know, we also maybe had a sense of what our galaxy could look like by looking at other galaxies, right, Like we saw these mudges, and once we got a better view of them, we saw that they mostly only fall in a couple of shapes.
Right, Yeah, it's pretty fascinating. If you look at the other galaxies, you can see a bunch of patterns, Like a lot of them are spiral galaxies like ours, where you have a heavy blow in the middle, sort of like an egg, you know, with a yolk, and then a few arms spiraling out past it. And that's pretty awesome.
Yeah, and what else?
Do you also have other kinds of galaxies like you have elliptical galaxies. This is a name we give galaxies that don't really have any interesting features, like these arms. And sometimes these are big and older galaxies with older stars in them. They're not making stars as much anymore. But you can actually also find smaller elliptical galaxies. And then there are the galaxies we call irregular galaxies. These are just like smears of stars in space. They're not like nicely organized or spinning or tight or compact in any way. And I think these are mostly galaxies that have recently had some sort of interaction, like two galaxies or colliding, and in the meantime it's a bit of a mess until gravity sort of reorganizes it back into something nice.
And neat right, need more fiber maybe that might help a.
Little less helium in their diet. And then there's another kind of galaxy called a dwarf galaxy. These galaxies are much smaller. You can have galaxies of all sorts of sizes, you know, from like three thousand to three hundred thousand light years, but these dwarf galaxies are like, you know, maybe a thousand light years across, contained just about like a billion stars. And some of these are like satellites of other galaxies, like the Milky Way has other little galaxies orbiting it. These little dwarf galaxies sort of going.
Around us, right, And how did they form? Did they form on their own, like did they make their own stars or did they just kind of group together and got kicked out of a galaxy?
Totally fascinating topic of current research. You know, we think that some of these formed on their own when the structure of the universe came to be, that these pockets of dark matter gathered together gas and dust to make galaxies. And some of those pockets were bigger and some of them were smaller, which is why you have a variation in the size of galaxies. But also galaxies are turbulent and sometimes you have collisions, and when you have collisions, you have like the main clump sticks together to make a big new galaxy, but some bits get tossed off and you end up with these little dwarf galaxies. It's sort of like the shards of galaxies after collisions. But it's not something we totally understand. And dwarf galaxies are a really fascinating area of study, especially for dark matter, because some of them have a lot of dark matter and some of them have like weird. The almost no dark matter, so it something we're still trying to understand.
Some of them have dwarf matter. Probably all right, let's get into well we actually know about the shape of the galaxy. We talked about how we can tell what the shape is, but let's talk about what it actually looks like. But first, let's take another quick break.
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All right, the shape of the galaxy, Daniel, do we have a shapely milky way? Or do we have a blobby milky way? Does it need to go in a diet?
It definitely has a blob in the middle, you know, like many of us do these days. But I think it's quite a nice shape. I like the bar in the middle and then the spirals coming out of it. I think it's really pretty gorgeous.
Well, let's describe the milky way. What do we know about the shape that isn't an artist rendition? What do you mean has a bar in the middle?
Yeah, so a spiral galaxy is not just like a point in the middle with spiral arms coming out our galaxy and like something like two thirds of spiral galaxies have a bar. It's like an elongated blob instead of a circle in the middle, and then the spiral arms come out of the edges of those bars.
Wait, what what do you mean it's a bar that's laying flat or it's like standing up on the plane of the galaxy. No, it's laying flat like a tassel, like a like a stick with some tassel.
Yeah, exactly, it's like a stick with tassels, and it's laying flat on the plane of the Milky Way. And then the spiral arms start at the edge of the bar and they spin around. Oh so we just have two arms. We actually have multiple arms. We have four major arms, two really big ones and two smaller ones, and then other little strands, so you can have multiple tassels.
Out of the edge of one side of the bar, they go off in different direction.
Yeah, they leave from sort of like different parts of the bar, then spiral out. Really gorgeous. You should spend some time looking at images of galaxies. It's beautiful and something I only recently understood about these spirals is that they're not just like a bunch of stars clumped together. They're actually a shock wave moving through the galaxy. Wait what, it's not a tassel. It's more like a wave when you move your arms through water. Yeah, there's like a shockwave of density moving through the galaxy. And as that happens, new stars are formed, and so it's like this new star forming region is sort of passing through the galaxy. I mean, the galaxy is definitely spinning, but these arms also spin relative to the galaxy. It's like one of those toys with flashing lights, where which light is lit up is moving and it gives the impression of motion. Right, the spiral arms are something like that. There are these shockwaves of gas creating new stars as they move, and so they rotate relative to the galaxy.
Oh wait, so the arms of the galaxy are not they're not streaming stars. They're not like we were spinning and you know, sort of like a the trail of a comet. Maybe you're saying it's more it's the opposite. It's like they're being created by something else.
They're being created by this shockwave that's passing through the galaxy. It's like this shockwave of density that's moving through. You know, like if you have traffic, right, somebody slams on the break in traffic, then this shockwave passes through the traffic, the shockwave of density where the cars are like all closer near to each other. And that's what's happening in the galaxy. And that's what these arms are. And when that happens, you get many more stars being formed, because you know, it's not actually that easy to make a star. You have hot gas that's all swirling around. It's not easy for gravity to condense that down because remember gravity is really weak. Things need to be sort of cold and slow moving for gravity to win, and so it needs some help. And so these shockwaves that compress the gas get things started.
WHOA, all right, that's good to know. And this shockwave is coming from the center of the galaxy, like there's some kind of event or what created this shock wave?
Yeah, that's a great question. I think it must come from the history of the galaxy formation. A lot of these spiral galaxies are formed from the collisions of smaller galaxies, so what you're seeing is sort of leftover angular momentum from those collisions that's then turned into this chak wave.
Somebody spilled a lot of milk in the Milky.
Way and they're still crying about it, all.
Right, So then what else do we know? What else have we found? And I guess what's our best measurement of the shape of the galaxy?
So there's a recent couple of papers in the last few years by this really awesome project that's been doing a careful job of trying to map the shape of the Milky Way. And the project actually has a great name. It's called the Ogel Project og l E because hey, you know, they're checking out the shape or the Milky Way, so they're sort of ogling the gag the stars exactly. They're creeping the stars though. It stands for Optical Gravitational Lensing Experiment, and it's a Polish project that's actually based in Chile, and they can search for micro lensing like these little events, these little gravitational lensing events where some object in our galaxy passes in front of something in the background and gives a little gravitational blur to it. But they can also do a really good job of looking for sephids so they have the largest catalog of sephids anybody's ever collected, and they used it to map the shape of the Milky Way.
Who did They also consider calling it the lensing Experiment with gravitational and optics, but couldn't couldn't get the copyright.
They would have been suited by Scandinavia.
Couldn't get the l E g O copyright.
No, exactly. They have to let that go, all right.
So it's maybe our best view of the galaxy because they like nobody else has looked at it with this much detail.
Yeah, they have the biggest collection. So they have twenty four hundred sephids and they they're scattered all over the galaxy, though most of them are on our side with the galaxy because it's easier to spot closer by cephids. And they've learned something kind of amazing about the shape of the Milky Way. They learned that the Milky Way is not actually flat.
What it's not like a like a cooked egg.
Yeah, it's not like a cooked egg. It's got a warp to it. So like you imagine a flat surface and there's a blob in the middle. Well, as you move away from the edge, of the milky Way, the arms tilt up, and on the other side the arms sort of tilt down. So it makes like a very gentle sort of s shape if you look at it from the side.
Or like a what he said, like a tilda, like a little squiggle. It's from the side, the galaxy looks like a squiggle.
Yes, it's sort of cool.
So I guess you could figure that out. Yeah, if you look close enough, you know, you would see that some stars are higher or lower at the tips.
Yeah, exactly, So these tips are bent, we're spinning around. We have these cool structure. We have the bar, we have the spirals. But then we also have this twist, like this literal twist in the story about the shape of the milky Way. This thing we've been trying to understand for hundreds of years now has this really interesting wrinkle to it.
Oh, and that shape is it rotating with the galaxy or is the galaxy kind of like undulating as well as it's spinning.
It's fascinating it's actually undulating. Like the galaxy takes two hundred and twenty million years for a star to go all the way around. That's like the length of a galactic year. Our sun will be back where it is today in two hundred and twenty million years. But this twist takes like six or seven hundred million years to rotate. It's moving slower than the actual stars.
Wow. So, like if you spit up of a movie of the galaxy, you would see it like rippling kind of.
Yes, exactly, And that's what I'm talking about that you're seeing as like really long term physics, sort of a frozen moment of it in time. Like the galaxy is not just a blob sitting there. It's undulating, it's rippling, it's twisting, it's torquing, right, But we're seeing just a moment of it. These incredible galactic forces that operate over like millions and billions of years. We can spot it with just these images. That's what I find really beautiful about these dynamic astronomical images.
Whether did you say torquing or torquing you see the galaxy?
I think actually that's what's going on, is that it's twirking with some other nearby galaxy.
We knew the galaxy could party so much.
I know, who knew the galaxy was not safe for work?
Yeah? All right, So but why is it tworking or warping or undulating after all this time, wouldn't it just settle into a nice disc kind of like the Solar System.
Yeah, you would think so. And if this was an ancient effect, then it would settle into a fixed shape and it would just rotate in that shape. But we think that probably what's going on is that this is something more recent, something in the last fifty or one hundred million years, not something ancient that's then been ironed out. It's something which is still happening, and so we think it's probably not something like intergalactic magnetic fields or the shape of dark matter, which are more static and not changing as much. We think probably what's going on is that it's interacting with some other galaxy.
Really what that the ripple could be our reaction to another galaxy.
Yeah, Like there could be some dwarf galaxy that's orbiting the Milky Way, or that's in the process of being absorbed by the Milky Way. Think about what happens when two objects like galaxies absorb each other. They don't just smash together and form one thing. They pass through each other first, slow down, and then come back. They sort of slosh back and forth a few times before they coalesce into one object. If you looked at that, just like one snapshot, one moment in time, you might see this kind of thing that the objects start to distort each other before they act actually a coalesce. So this could be some dwarf galaxy nearby, you know, like fifty or one hundred thousand light years away, that has already crashed through the disc of the galaxy once, creating this kind of ripple, and it's slowing down turning around to come back for another pass.
Oh, it's pretty fascinating. Yeah, it seems like the galaxy has a much more interesting shape than maybe we thought before.
Yeah, and that's because it's part of a huge dynamical system. These galaxies are all in a dance with each other. You know, they're separated by millions of light years, but they still tug on each other. And remember that our galaxy is not just sprinkled in space with other galaxies. There's a bunch of other ones nearby. We're all orbiting a common central point, and so each galaxy is like a particle of gas in this larger system, you know, and each one has like spin and bounce, and it's all story and it's you know, hit this other one and bounced off this wall and crazy stuff. So each one has a real dynamical history. They're not just like hanging out in space doing nothing.
And we are just a tiny little speck in one corner it right, Yeah, Like we're just a tiny speck in a tiny speck in a tiny speck in one of its arms.
Yeah, exactly. And we're not at the center of our milky Way, and we're not out at the edge that we are in the center when it comes to us sort of the up and down, Like we're pretty close to the galactic plane when it comes to being off or on the galactic plane, but we're not that close to the center. We're midwerk or mid twerk. Yeah. But it's good that we're not that close to the center because there's a huge amount of radiation from stuff going on in the center of the galaxy. And it's also probably good that we're not too far out from the center because there are fewer metals out there, so it'd be harder to have awesome things like steel and aluminum and all the kind of stuff we need to build our civilization. So we're in a pretty good spot.
Yeah, you don't want to be too far away from the party, but you don't want to be too close to the party either.
That's right, you want to go twerk and just the right spot.
Just like Goldilocks. All right, Well, it's overall really amazing that we can get a sense of what the shape of the galaxy. I mean, think about what huge problem it is to know what the shape of the ocean you're in or the land you're on. The fact that we can, you know, understand the universe that much and have these amazing telescopes and techniques and engineering and technology is pretty incredible that we can get a sense of our home and in our place in the galaxy.
Yeah, it really is selfies on a cosmic scale. You know, Before we had cameras, people would like look in lakes to see their reflection and wonder like, what do I look like? They knew what all their family and friends and everybody around them looked like. But it's harder to get a picture of your own body, your own face, And in the same way we wonder like what does our galaxy look like? It's weirdly more challenging to understand the shape of our own galaxy than our neighboring galaxy for just the same reasons. So it's cool that we've developed all these techniques to get a map for like our own home.
Yeah, although I think I guess technically you should call it an ugly maybe not a selfie.
That's an ogly word for it.
All right. Well, the next time you get to see some stars out there in the sky, or maybe even get a glimpse of the Milky Way, think about how much we know about it, and how we know about it, and what an incredible and maybe beautiful structure it is.
That's right, And anytime you find yourself contemplating the universe and there's something about it you just don't quite understand or are wondering about, please write to us, suggest it as a podcast, or just ask us a question. We love our listener emails, so send them on to Questions at Danielanjorge dot com.
We hope you enjoyed that, and hey, do us a favor of this week? Maybe tell your friends about the podcast or follow us on Instagram or Twitter so you can learn more about what we're up to. Thanks for joining us, See you next time.
Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeart Radio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. 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 you as dairy dot COM's Last Sustainability to learn more.
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