Daniel and Jorge Explain the UniverseDaniel and Jorge turn their eyes to the center of the galactic action and give us a sense for where we are.
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Hey, hoorge, does the town you live in have a real center, like a downtown?
It does.
Yeah, it has a little kind of town square where everyone hangs out. There's also downtown LA which is about ten minutes away.
And does anybody ever go to downtown La? Is it like a destination? Kind of?
Sometimes we just went to like a science festival there, but not typically it's pretty rare.
I guess it's also like the center of traffic in LA. Yeah. What about Irvine? Irvine has a new center. It's just one hundred percent pure sprawl.
It's all edges.
It's all parking lots and shopping centers.
So if you find yourself in the middle of a parking lot all of a sudden, you might be totally lost.
It's actually the law in Irvine that everything is legally required to be exactly identically bland, even the people. We're all beige down here because of the sunshine in.
More ways than one.
Hi, I'm Poorhammy cartoonist and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle physicist and a professor. You see Irvine, and I've learned to distinguish. Fifty shades of beige.
Sounds like a fan fiction version of fifty Shades of Gray, but less seeny.
Totally safe for work. Now. When we moved into our house in Irvine, real story, they gave us a set of options of the colors and at the top it said color makes a world of difference, and then there were four shades of beige you could choose from.
Wow, that's a lot of options of beage. So you can't paint your house green if you wanted to.
No, we are restricted from painting our house various colors. We actually once did paint our garage crazy rainbow stripes, and we got a stern letter.
Mmm, what happens if you don't change it?
They repainted for you, and then they send you the bill.
The city will send them a painter to your house. It sounds very nineteen eighty fourge.
That's why all the exciting stuff that's happening in Irvine is happening inside people's houses.
Oh, fifty shades of hidden beage.
But anyways, welcome to our podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we tried to illuminate all the amazing shades of meaning and nuance in the universe. We go all the way from black holes to white dwarfs and everything in between. The incredible color and ferocity of the processes in the universe, the indensity and the screaming jets from the centers of galaxies, it's the very quiet outer edges of stellar clusters. We talk about all of it. We dig into every little bit of it. We touch on our curiosity to understand the universe around us, and we explain all of it to you.
That's right, because it is a pretty colorful universe, and we try to paint the whole rainbow of knowledge that humans have managed to figure out over millennium about this amazing universe that we live in, which is not all concentrated in one place, but it's also not all evenly distributed across the universe.
Yeah, that's right. And we look at the world around us in all sorts of crazy colors, reds and greens and blues. But when we look out into the wider universe. We can use other frequencies of light, frequencies that don't even have color, all the way down from the radio waves up to a gamma rays. Light that wiggles super duper fast, and light that wiggles much much slower.
I just had this interesting conversation recently where I learned that magenta is not really a color.
Do you know that it's just a word? What is magenta exactly?
It's not really Well, I guess it's not really a frequency of color. It's like a color we see when you combine certain frequencies in your head.
Oh, I see, there's no single frequency of light that if you shoot it at an eyeballer person will experience magenta.
Yeah. Or I think related? Is color pink? Like there's no color pink.
Isn't that true? Then for white? Also, you can't have like a white laser because white is every frequency together.
Mmm.
Interesting? Yeah, I guess, well white was never a color?
What white is not a color? Wow? This has quickly become a philosophy of color. Podcast Is black not a color? Either? Right?
I don't know.
Is it is the lack of light a color? I don't know. I think color is just something you experience in your mind anyway, It's not a property of the photons. Right, Infrared photons and gamma ray photons don't have any colors, so either do photons that stimulate a green response in your mind. The green is just in your head, man, So is magenta, so is black, is white? Color is just an experience. So beige is also just in your head. Nothing to complain about. No, Now you run the beige within me. Ah, that's beage is my fault. You are beige inside and out, Daniel, Oh my god, for all this time I thought I'd escape the beige. Noess, But you're right.
Irvine has gone into you. It's seeped into your pores, and you're Europe.
I'm beige through and through, that's what you're saying.
But anyways, and there are a lot of colors out there in the universe, but it's not all evenly disturbied. Like if you look out into the night sky, you don't see it just all light. There are patches of not light and patches of intense light.
Yeah, as we build these technological eyeballs that can see photons of various colors. When we look out and use it to build a map of what's out there in the universe. Where are all the other stars in the universe, How do they cluster together? What's going on around the corner? Are we in the boring part of the universe or are we at the hopping city center?
Yeah?
Where are the happening places in the universe? To be On the podcast, we'll be taggling the question what does the center of the galaxy look like? And more important, what does it smell like? And the thing is smells in space.
There are smells in space, absolutely, because there's lots of fascinating organic molecules out there. Remember that whole episode we did about the smells of space astronauts coming in from spacewalks and reporting that their suits smelled like barbecue.
Mm, so you're saying it's space malls like death.
No, space smells like lunch.
Space smells like you're never going to breathe again if you actually smell space.
Yeah, that's right. And it's interesting that the galaxy has a center. You know, the Solar System has the center, the Earth has a center, the galaxy has a center. But then on a broader scale, we don't think the universe has a center, and it's interesting to me as a sort of human reaction. It's sort of our way of categorizing stuff, So is that we look for the center of things. Lots of write in and ask about where is the center of the universe, Like it's an important thing to understand where the center of something is.
Yeah, I guess it's sort of a way to orient yourself and know where you are relative to other things. Like if you know where the center of town is, and you'd sort of know where you are, But if it was a whole ingenious population of buildings, then it'd be easy to get lost or feel lost at least.
Yeah, that's why I still get lost in an her behind. I think because there is no way to orient yourself. But I think also there's a sense of origin, right, there's the feeling that like the most important things are happening at the center, or the processes that drive the formation of whatever it is you're talking about the Earth or the solar system or the galaxy are determined by the stuff happening at the center. It's not usually the case that the outer edges are controlling the structure of the interior. Usually it's the opposite.
Well, unless you're California, in which case, you know, Sacramento is the capital of the state.
Oh, maybe it's the political capital, but it's definitely not the center of the action, that's for sure. Yeah, it is interesting.
Everything kind of has the center, and I guess it has to do with gravity, right, Like, gravity is basically one of the biggest laws in the universe, and it sort of dictates the structure of everything, right, the structure of Earth. If we didn't have gravity, Earth would just be a cloud of dust. And if it wasn't for gravity, the Solar System would just be a cloud of dust and gas. It's kind of because of gravity. Gravity is very centralized.
Yeah, and that's one of my favorite weird facts about the universe that even though gravity is the weakest force out there by like ten to the thirty two, you know, it's so much weaker than all the other forces, in the end, it wins, right. It's the only force that can't be neutralized. It can't be balanced by opposite charges. There's only positive masses and attractive gravity, at least on small scales if we're going to ignore dark energy for a while, And so it clusters things together and it wins the race. It's patient, and it takes forever because gravity is so weak, but eventually it dominates the whole structure of the universe. As you say, the reason we have solar systems and galaxies and the whole larger structure the universe is because of gravity. It's in charge of organizing the universe.
You think, if we didn't have gravity, we would still be around, Like, could life have formed without gravity?
Life would definitely not have formed without gravity. Without gravity, we wouldn't have stars. Right. Gravity is what pulled together those clouds of gas and dust into dense packets, which started fusion, which made chemical elements that we use for life. And without gravity, the universe would be smoother, right, Those little extra blobs of over density would never have turned into very hot and dense stars.
M But could life have formed anyways in some kind of primordial you know, galactic gas.
Perhaps so, though it would be very very different from any life. We imagine just after the Big Bang and before stars formed, we had only hydrogen and very very trace amounts of anything else, a little bit of helium and the tiniest bit of heavier stuff, and it'd be pretty hard to form life out of just that kind of simple, basic elements. It's so much harder to build complicated structures like the ones that our life is based on. But it doesn't mean it's impossible. It just means life as we know it is probably impossible.
Mmmm.
You're saying, without gravity, the universe would.
Be page exactly. Gravity makes things colorful.
But it is an interesting question. What does the center of the galaxy look like? I guess we can see the center of the galaxy from Earth, right, I mean, we're in the galaxy. We should be able to sort of know where the center is.
Well, we can look in the direction of the center of the galaxy, but the same way that you can't always, like see downtown from your house in the burbs, there's often stuff in the way. Right, you can't see around the trees and the other buildings. The center of the galaxy is actually kind of obscured by all the gas, the dust, and the crazy stuff that's going on between us and it, so it's not that easy to see. Mmmm.
Well, as usual, we were wondering how many people out there had wondered what the center of the galaxy looks like and thought about what's in there.
So thanks very much to everybody who answers these questions for this fun segment of the podcast. If you'd like to hear your voice, please don't be shy. Every week somebody writes in and says that after two years of listening they're finally ready to put their hat in the ring. So let that be you and write to me at questions at Danielandjorge dot com.
So think about it for a second. What do you think the center of the galaxy looks like? Here's what people had to say.
I think if you were to take radio static and change it to visual light, it would look like that.
In terms of radio waves, I think in the middle of the galaxy, I think there would be a lot of radio waves, except if the black hole in the middle absorbs them all.
I feel like it be harder to see things.
I don't know, maybe the radio waves get blocked by a lot of gas or you know, the space space things.
I think the center of the galaxy is in a turmoil, so it's sending out radiation on all wavelengths. So I would guess that if we look at the center of the galaxy in the radio spectrum, we should see like a big bright spot.
All right, A lot of people seem to be talking about radio, like, is there radio in the center of the galaxy?
They're tuned in their station to listen to the center of the galaxy.
Be cool to be a galactic DJ. Sounds like a cool job.
Sounds pretty intense. But they're on the right track because when we look at the center of the galaxy in the visual light, it's not very easy to see anything, but radio waves from the center of the galaxy can get here. So radio is actually the best way to see the center of the galaxy.
Interesting, and what kind of music do they play in the center of the galaxy? Mostly fuzz, golden oldies, page oldies. We're asking the deep questions today. What music does the Milky Way like?
Of course we can't hear the most modern Milky Way music. We hear stuff that was sent to us twenty six thousand years ago, so it's definitely oldies, though I don't even know how gold it is.
Well, let's start with the basics, Daniel, take us on a trip. What does it mean for the galaxy to have a center?
So people have been trying to figure this out for several hundred years, people look up at the night sky and see the stars and then wonder, like, where is the sun in our neighborhood. Is it just a bunch of stars sprinkle out through the universe. Is there a collection of stuff? Is there one spot that's more interesting than another. So for the last couple hundred years, people have been building these star maps and trying to gain a sense of where we are. I remember, it was only like one hundred years ago that we realized that we were in a galaxy. That's when Hubble noticed that some of the smudges that are up there in the sky that look just like clouds of gas and dust, are actually super duper far away. They're actually outside of our galaxy. That's when we first realized that we have a galaxy, this blob of stars, and that there are other galaxies out there, so that our galaxy is just one of many. And people have continued making maps of the stars so try to get a picture of what our galaxy looks like, which is complicated because of course we're inside the galaxy, so we can't like ever de outside and see what it looks like. We can only map it from the inside, which is a challenge.
Yeah, It's interesting to think about what people thought about before we knew there were other galaxies, right, Like, are there scientific papers from that time or people writing about it. Did we think that we were in like a cloud of stars or just an infinite space filled with stars? What was the general thinking about what the rest of the universe looked like before we knew there were other galaxies.
Yeah, it's a great question. The first sort of maps were from like the late seventeen hundreds, A kind named Herschel sort of drew all the stars that you could see and mad like the first map of these stars try to orient where the sun was, and we just really couldn't see very far, so we didn't have a sense for what was going on beyond that, and people imagined that all of space was just filled with stars that just sort of like hung out there. But then people noticed this, like, oh, there's this disk in the middle right where the stars get denser. So as our ability to see things got better, we were able to notice more and more that there was a pattern things got denser in one direction, and so like in the early nineteen hundreds, we have more detailed catalogs that show us that the stars are not just sprinkled out through the whole universe, but that there's sort of a flat disc structure.
And this all came about because of photography, I think, right, like if you just look with your naked eye at the night sky, you see some stars, but it's only when you sort of have a photography setup and you can expose a sheet of paper or photo paper for a long time do you get to sort of see really what's out there.
Right, Yeah, the name of the game is capturing more light, and you can do that by longer exposure. And you can also do that by having a larger aperture. So building telescopes with larger light gathering capacities is also key. If you're going to gather light over time, you need to also track the objects. It doesn't make a smear in your photograph, but both of those things are crucial. Gathering light over time and having a larger aperture that lets you see dimmer things which are further away things, which lets you expand the sort of mental map in your mind of where we are, what our cosmic neighborhood is.
And I guess before we would look at the Milky Way, like the Milky Way you can't see with your naked eye on a super clear night, right, if you are in the middle of nowhere, you can see sort of a white streak across the sky. Did people think that that was just like some sort of galactic cloud or did they have an intuition like, oh, my goodness, there's tons of stars in that strip.
Well, once we identified other galaxies, we could study them, and that gave us a lot of clues about the nature of our galaxy. The same way that like, once you look at other planets, you notice, oh boy, those are around Probably our planet is round two really solidifies the idea that planets are spears, right when you can see other planets being spears. So when we could study, for example, Andromeda, because we had telescopes, we could see, oh, look, that looks like a big flat disk with all these spiral arms. That's a very strong clue that maybe our galaxy looks like that also. And then you could look up at the night sky you can see the pattern of stars, so you can fit it into that shape. And in fact, our galaxy looks a lot like Andromeda. I mean it's smaller, but it has roughly the same shape. It's a big elliptical swirl with the central blob and a few arms that spiral out.
So those two things sort of came about at the same time, Like, we noticed that in this direction there's a whole bunch more stars, and also, hey, we're our galaxy, so maybe this direction is where the center of the galaxy is.
Yeah, that kind of understanding really crystallized in the early nineteen hundreds, and now we have a pretty good map of the galaxy. Recently, there's a spacecraft called Gaya which is doing a super precise map of billions of stars to give us a very accurate picture of our galactic neighborhood. And let's ask all sorts of really fun interesting questions. But we now know that we live like sort of halfway out from the center of the galaxy along one of these spiral arms.
Yeah, break down what we know about the Milky Way. So it's like a cluster of stars, but it's sort of flat shape, right, It sort of looks like a disc, but it's not a perfect disc because it's sort of organized in terms of streaks or swirls.
Right, Yeah, it's not even a perfectly flat disc. Remember, we did an episode about how the milky way itself. It's a little bit twisted. It's sort of like a hat where it's like tilted up on one side and tilted down on the other side, maybe because of recent mergers or gravitational interactions with other galaxies.
Wait, like a horse saddle kind of.
Yeah, sort of, it's like tilted up on one side and tilts it down on the other side.
Whoa we have like a cowboy milky way.
Yeah, exactly. It's got a little flare to it. So that's the disc. It's mostly a disc, but there's a little bit of a tweak to it. But then, as you say, the disc itself is not perfectly smooth. We have these arms. So there's like a central bulge, a big blob in the center of stars, and then that's surrounded by a central bar. It's like long bar of stars, which is itself embedded in the nuclear bulge, which is like circular blob at the very center of the galaxy.
Wait, what do you mean like a bar Like two arms that shoot straight out from the center.
Yeah, they're not really called arms. They're sort of short compared to what we call the galactic arms themselves. But yeah, it's two lines that shoot out from the center, and it's embedded inside this larger nuclear bulge. So we have this central bar and a nuclear.
Bulge sort of like if you took a pen and stabbed it through an orange. That's kind of what it.
Looks, I guess, so I think of it more like a half closed eye, you know, has like a slit through it.
All right.
So then so we're about halfway out from the center to the edge.
Yeah, this central bloble sort of looks like an eye winking at you. And then you have these arms that shoot out from it. And so the Milky Way has four of these arms. They start at this nuclear bulge, either the orange or the eyeboledgever you prefer, and then they streak out they swirl around the center. And so there's four of these arms, and we actually live on a spur that comes off of one of those arms. We don't even live on one of those arms.
WHOA, we're like in the suburb of the suburb exactly.
It's called the Orion spur. So when you're camping and it's very dark and you look up at the night sky and you see this white streak that we call the Milky Way, which you're looking at is the next arm over. You're looking towards the center of the galaxy and you looking at the next arm.
Well, you're sort of looking at all of it, aren't you, Like, isn't some of that also the center of the galaxy coming through and hitting your eyeballs?
Well, you're looking through everything, of course, and so you're seeing nearby stars that are in our arm. Those are the stars you see, and then you also see sort of the outer edge of the next arm. But these arms have gas and dust in them, and so it's hard to see all the way through them. Some of the light from the center also does make it through, but this gas and dust is really good at obscuring the light behind it, so it's very difficult to see all the way through it. So none of the light that hits your eyeball really is coming from the center of the galaxy. It's in the direction of the center of the galaxy. But you're seeing the stuff that's between us and.
The center mostly, right, I mean, there might be some light that's coming through, Yes.
There might be some, but visible light is really really quenched by the galactic dust.
All right, Well, I guess that begs the question what is going on there in the center of the galaxy? What can we see? And most important, at least for me, is how do we know this? If we're in the Milky Way galaxy, how do we know what the milk away galaxy looks like? So let's get into that, but first let's take a quick break.
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All right, we're talking about the center of the galaxy and how it's a lot more exciting there. Are you suffering from some sort of galacticfomo fear of missing out?
No, I'm pretty happy here on Earth. The galactic center is kind of a crazy place, Lots of pulsing, lots of radiation, not a place that I would survive very long.
But if you're in Irvine, that means you're in sort of like the suburb of the suburb of the suburb of the suburb of the galaxy.
Yeah, it turns out it's a pretty nice place to raise kids, so I'm not too.
Really happy it's a super suburb.
Yeah. So we turn out to be about twenty six thousand light years away from the center of the galaxy. The whole galaxy is like one hundred thousand light years across, so we're like halfway between the center and like sort of the outskirts, the last visible stars.
And so how do you define what the center of the galaxy is?
Like?
Is there a limit, does it get super dense all of a sudden as you go towards the center. Is there like a ball in the middle of stars? Or is it pretty fuzzy.
So there's a few ways to define it. One way is the geometrical center, to say, like, here's the whole Milky Way, what's literally at the center. And that's like taking the United States and saying, Okay, Kansas is the center of the United States. It's literally in the middle. A more sensible way to define it is the gravitational center to add up all the stuff in the Milky Way and wait its location by its gravity and find like the center of mass of the Milky Way, like the point around which everything is spinning, which might be different than the geographical location. In principle, it could be different. If the Milky Way was asymmetric somehow, then it could be different. We think in our case that those two things mostly line up because the density profile of the Milky Way is that it's densest at the center and mostly symmetric as it goes out. Then there's the definition of the center of the galaxy. And astronomers have just like picked a spot it's called Sagittarius A and it's a radio emitter, and said, we define this to be the center of the galaxy. It's like the coordinate system. That's a little arbitrary. You could put it anywhere, but everybody has to agree on an exact location, and so that's where they put it.
Wait, wait, there's a star in the middle of the galaxy that we can make out and see.
Well, there's a radio source, right, And when people started to look up at the night sky and realize that we could look at the night sky in other wavelengths than just visible light. They started to build radio telescopes to listen to radio waves from space. They noticed a very bright source of radio waves coming from the direction of the center of the galaxy. So that's what we call Sagittarius A. It's a bright radio source, and that's where we put the center of the galaxy. So it's not a star, it's a radio source.
I guess we'll dig into what it actually is. Maybe step us through what is at the center then? Is it like a cluster stars. There's a big black hole there too.
Right, So there is a big black hole and that's what's generating all those radio emissions. Sagittarius A star is the black hole at Sagittarius A, which is the radio emitter, and so there's a huge black hole there almost five million solar masses. That's the densest part of the galaxy. But the whole blob near the center is very very dense with stars. There's like ten million stars in the sort of central cubic parsec mber parsek is around three light years.
Wait, there's ten million stars per cubic parsk near the center.
Yeah, exactly, So that's about a million stars per cubic light year.
How dense is that? Like, if we were there, would we just be toast? Would it be super bright? Could you survive? Could there be like an Earth there? Or would it just be too intense?
It would be really intense. The density around here is much much lower. It's like three or four light years to the nearest star, so the density around here is like less than one star per cubic parsec. There it's ten million stars per cubic parsec, so it's much more intense. The light and the other forms of radiation are crazy in the center of the galaxy. It's hard to imagine lifelike hours thriving or surviving even in the middle of the galaxy.
Well, it'd be super bright, but I wonder, a there's still I mean there are still stars there, so there must be solar systems right and planets there is just be super bright.
Everywhere you look.
There are definitely stars there, and we can see some of them, like there's this star S two that we see orbiting the central black hole, and by watching it move we can tell how massive that black hole is. Are there solar systems there? Is harder to answer because the crazy intense environment is not very conducive to stable orbits. Remember, if another star comes near our solar system, it could disrupt Earth's orbit or Jupiter's orbit and we could lose a planet. So in an environment where there are so many stars jostling around each other, it's probably a lot harder to hold onto planets.
So maybe can you paint a picture like how close are these solar systems together? Like if you were in a solar system like ours, how close would the next solar system be, like several solar systems away or right next door? Or are they all sort of bunched together or what's going on?
Yeah, the density of stars is literally ten million times as dense as it is here. Ten million times denser means stars aren't on apur average two hundred times closer together. So instead of having a few light years between stars, the average distance between stars is like two percent of a light year, which is like twenty five times the radius of Pluto's orbit. So other stars are not like literally next door, but they're much closer than around here, where the next star over is like five thousand Pluto orbits, So there'd be a lot more stars, a lot brighter, Like there would be no darkness on a planet orbiting one of those stars because the night sky would be so bright with stars that would be so close. I remember, when stars get closer, they get brighter fast because the brightness goes as the distance squared. So if a star gets ten times closer, it's one hundred times brighter.
Well, I guess it's all relative, right, Like if you were sunglasses, Yeah, it might look just.
Like it here. Yeah, but the stars there are also different from the stars here because it's not a very good place to make stars because it's so crazy and there's so much radiation. And remember that to make stars you need like cold gas that can very gradually get pulled together by gravity. So most of the stars in the center of the galaxy are old stars because it's not a star forming region. So you have these really old, small red stars, so they're dimmer and they're redder. But there's a lot of them.
I mean, like they were formed outside of the center and then they all congregated in the middle because of gravity.
Yeah, or they were formed when the center wasn't as crazy during early days of the Milky Way. Remember the Milky Way is almost as old as the universe. It's like thirteen billion years old, and some of the stars in the center might be about as old as the Milky Way itself. Stars that are small can burn for billions and billions of years. We think our star is going to burn for about ten billion, but our star is a little bit heavier than the typical star. Most stars, like red dwarfs, could burn for much longer and may have been around at the very formation of the galaxy, So those stars could predate the galaxy having like an active center, you know, just the way you can have like an old building in the center of downtown with all these skyscrapers built around it.
But of course here in La all the stars live in Beverly Hills and up in the Hollywood.
Hills, and some in Pasadena.
Know, the big podcast stars all live in South Pasadena, all right. So that's the center of the galaxy. There's a big black hole there and it's chalk full of stars. I guess my biggest question is, like how do we know all of these things? Like how can you tell what's there or what the structure the whole galaxy looks like. If we're in the middle of it, you know, like you can't take a selfie. We haven't taken a selfie. How do we know about all these structures, like the arms and the orion spur, Like, how do we know all of this, you know, sort of detailed structure if we're in the middle of it.
Yeah, great question. For most of the stuff that's not at the center of the galaxy, we still can see it. We can see through our spur to other spurs. We can figure out where those stars are. But a lot of it is obscured by the gas and the dust, especially in the direction of the center of the Milky Way, and so visible light just doesn't work. Like I get a sense for how little we can see the center of the galaxy. If you sent a trillion photons to us from the center of the galaxy, one of them would survive. So it's like a dipping by a factor of a trillion from all of this gas and dust in the visible spectrum. But there are other frequencies of light that are better at getting through that gas and dust that we can use to see what's going on in the rest of the galaxy.
Mm, Like, certain light waves don't get stopped by gas and dust. Those atoms out there floating just ignore the light.
Right exactly. We just did an episode on transparency, and we talked all about how different frequencies of light interact with matter differently. So visible light goes through our atmosphere, which is why we can see stuff, but UV light is often blocked by the stuff in our atmosphere, so the atmosphere is partially opaque to UV light. So different frequencies of light interact with objects differently. Some things are transparent in some frequencies and opaque in other frequencies. And so cosmic dust, which is basically just like little tiny rocks, tiny little bits of old planets and the hearts of stars that blew up and got spread out. Those things are good at interacting with high frequency light because they're so small. But low frequency light, radio waves and infrared, it's big enough that it basically doesn't see them, just passes right through them.
Big enough in the sense that like the atoms that are floating out there can't do anything with that light, right.
Yeah. The general rule of thumb is if you're seeing something in light, you can't really see stuff that's smaller than the wavelength of light that you are using. And so if you use very long wavelength light, it basically ignores everything that's smaller than its wavelength. So long wavelength light is really good at getting through clouds of tiny little particles. So that's why radio waves and infrared can get through this stuff, whereas UV light and visible light, which has shorter wavelengths, can't really get through this dust.
It's literally like having X ray vision of the galaxy. Like if you could see in the X ray yet X ray glasses, you could see the center of the galaxy more clearly.
And in general, that's why it's so powerful to have telescopes that can see in different frequencies, because some parts of the galaxy are like really bright in X rays and dim in the visible, so you need X ray telescopes to see them. Other parts of the galaxy you can only see in radio and infrared because of this reddening from the cosmic dust, so you got to have those infrared telescopes. James Web, for example, is an infrared telescope. It's really good at looking at the center of the galaxy and this kind of stuff.
All right, I guess I see how you can see the center of the galaxy using X ray vision, But I guess my question is, like, how do you know the structure of the Milky Way from the point of view where we are now, Like, how do you not has these arms? Can you actually see those arms from this point of view? But then it all looks sort of like a fuzzy streak, Like if you look at a frisbee from the side, you can't tell what it looks like from the side.
Yeah, A crucial thing are distance measurements. So you need to know how far away things are. You look at an individual star out in space, you want to know how far away it is. That lets you build a three D map of the galaxy. So rather than just having everything like pasted on a celestial sphere and not knowing where things actually are, if you can say this star is really far away, this one is really close, it lets you build a three D map of everything and from that you can build up the structure and so to know the distance of these stars, we need things like cephids and parallax and all sorts of other tricks that we've talked about before to figure out how far away each star is. And that's one of the things this Guya satellite is really good at it does parallax on all these stars and understands their location and also their velocity, which is super cool. So we built up sort of a three D map of the galaxy, and of course we have better information about the side of the galaxy that we're in and the spur that we are in, so it gets fuzzier as you get to the other side of the galaxy. And just as an example, almost all of the exoplanets that we discovered are in a little spot on our side of the galaxy. We can't do exoplanet research on the other side of the Guy galaxy because we can't see through the center of the galaxy to that other side as well, So we know a lot more about our neighborhood on our side of the galaxy than the rest of it.
I see you sort of use stereovision to try to get a three D view from our point of view. But this three D idea, the parallax only works for close by things, right, does it actually work to see how far something is on the other side of the galaxy.
Parallax is most powerful for close by things, but we have this distance ladders. We have parallax for close by stuff and then we have cephids, the variable stars for more distant things on the other side of the galaxy. These are stars where their period of variability when they get bright and dim and brightened dim is connected to their true brightness, and so by noticing how they get bright and dim and the period of that, we can figure out how right they actually are, and therefore we can tell how far away they are, So you can use sephids to understand how far away things are on the other side of the galaxy.
Aren't those pretty rare?
Though? Those are pretty rare, But the galaxy is huge, so we have found several thousands of fids. I think more than thirty three hundred last time I checked, But we still have some of those. So we can use those together with parallax to get a kind of a picture. But it's not perfect, and it's especially bad in the direction of the center of the galaxy because the center tends to redden things because of the dust. Dust only lets redder light through lower frequency light through, and so we don't always know like, oh, is that actually a dimmer star or is it just reddened by all the dust? So, like one thing, people argue about it is like how far away is the center of the galaxy exactly? And there's all these measurements, some of which disagree with each other about exactly how far away it is. It's really a challenge to measure the distance to the center of the galaxy, right.
That's kind of what I'm trying to get at, which is that, you know, we see all these illustrations of what the Milky Way looks like online and in books, like, hey, this is what the milk Away looks like, but we really don't know what the Milky Way looks like. And I'm just kind of wondering, like, what does the picture of what we actually know look like. Maybe we have some sense of structure around us, but then for the rest of the galaxy, like the other arms on the other side, how many sephids do we actually know are there? And what is that the map of the data actually looks like.
I think we do know roughly the shape of the Milky Way. I mean, we know those other spurs and the guy A satellite and the sephiz do paint that picture for us. It's definitely fuzzier on the other side of the galaxy than it is here. And we don't have like the crystal picture we'd love to have if you were like out on top of the galaxy and just took a picture from it. So we're definitely limited as we go to the other side of the galaxy. But these illustrations you see about the shape of the galaxy, those are pretty right on. I mean, we don't have every single star in those arms on the other side the way we do on our spur, or even in the neighboring spur, but we're pretty sure about the shape of the milky Way. All right, let's get back to the center of the galaxy. But first let's take a quick break. When you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt, you're probably not thinking about the environmental impact of each and every bite. But the people in the dairy industry are us. Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty. 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. Take water, for example, most dairy farms reuse water up to four times. The same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is US Dairy tackling greenhouse gases? Many farms use anaerobic digestors that turn the methane from maneure into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love with less of an impact. Visit usdairy dot com slash sustainability to learn more.
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Today.
We're back and we're thinking about how to actually see the center of the galaxy. So there was recently a really cool image of the center of the galaxy taken by a radio telescope. This is an array of telescopes in South Africa. It's called Meerkat, and radio is still the best way to see the center of the galaxy because of course it's the longest wave length, and so it gets through the gas and the dust and it gives us this awesome picture of what's going on. It's like morphology shows us the shapes of stuff in the center of the galaxy, as if we could like X ray through all that gas and dust. So the Meerkat radio telescope is basically an array eight by eight of these sixty four antennas spread across five miles of desert in South Africa, and they put out a paper recently with this incredible picture of the center of the galaxy.
Now, now these are not telescopes like maybe we think of when we hear the word telescope. That they don't have lenses, that they don't look like it too. They look more like giant dishes, right, like the kind you see in the movie Contact.
Yeah, that's right. It's an array of dishes, and so each one looks like a satellite dish. You might be using it to pro wat your favorite sports team on, but you have an array of them spread across the desert. You'd love, of course, is just to have like a five mile wide dish to gather all that information. You can't afford to build that. But it's better to have sixty four separate dishes that have greater distance between them than to have one big dish that's in the end smaller. You in effect have a larger aperture.
So they like having tapas for dinner instead of it dish.
That's right, And you can get more information by having these dishes like further.
Apart, like a sampler plate of appetizer.
As the information washes across your you can tell which direction it came from. You can do interferometry to get all sorts of useful information. So it's almost as good as having a single telescope that's like actually five miles wide. So yeah, it doesn't look like a traditional telescope. There's nobody like peering through a lens and seeing the center of the galaxy. They get this data, which again is not even visible light, it's radio waves, and they process it and they convert it into something that you can see with your eyes, and so there's this wavelength shifting, right. You would never see this image yourself. It comes in light that your eyeballs can't see. But we do all this computing and we crunch the numbers and we figure out where are the bright sources of radio. So if you google this image from meercap, what you're looking at is where there are intense radio sources and where there's less intense radio.
Sources, and it's sort of focused to the center of the galaxy. That's kind of the idea, right, That's why you're having so far apart is that you can sort of triangulate and be confident that what you're seeing is coming from the center and it's not just some artifact that's in between.
And you can see at the very heart of this image is Sagittarius, a star. We know this is a really big black hole there, and we know it generates a lot of radio waves from the gas that's swirling around it, and it's the brightest thing in radio. So it's at the very center. It's very small, it's very bright. So that's super cool because it shows you, like, wow, the center of the galaxy really does have this very intense core and then spread around it is the beginning of the galactic disc.
No, the black hole is sucking stuff in, but the stuff that's falling into it, that's the stuff that's really bright.
That's right. We don't see anything from the black hole itself. Right, the black hole is the black hole. We're not seeing hawking radiation or anything. Black hole we think is totally black. But the stuff that's swirling around it and falling in that is accelerating and giving off radiation. We can only see it in the radio because everything else is blocked.
Cool.
So we have this picture from the center of the galaxy. You can look it up. It's called meer Cat And what do we learn from it?
So the black hole is no surprise, but there's a bunch of other cool features. You can see these blobs from the beginning of the galactic disc, and it's sort of cool that it's tilted. But they've plotted in these celestial coordinates, which is declination versus right ascension, which is just sort of like a grit around the Earth that uses the north and the south poles, and so it's tilted pretty hard in those angles, and it shows you like the angle of the Earth relative to the angle of the disk of the galaxy. Right the north pole of the Earth is not aligned with the north pole of the galaxy, like the equator is not aligned with the galactic disk. It's actually quite tilted. So that's sort of cool. That orients you, right, It shows you that're like, whoa, we're kind of leaning.
Over, we're leaning into the galaxy. But I guess, is there any reason to expect that they would be aligned or it?
Is?
It kind of random?
It's kind of random. I mean, the Earth is kind of aligned with the spin of the Sun and the disk of the Solar System, though of course there's a tilt there. But the spin of our Sun is not necessarily aligned with the spin of the galaxy, right, because all the stars basically have random directions. It just comes from the spin of the blob of gas and dust that formed our Solar system. But it just helps orient you and show you that, like our north pole is not like the galactic north pole.
Mmmm, sort of like our north pole is not the Sun's north pole you were saying. It just kind of gives us a sense of which where we're actually going.
Yeah, And even though it makes no sense, it gives me a little bit of vertigo because I feel like I'm standing here on the Earth, and I'm like, whoa, I'm leaning over, and everybody in the center of the galaxy looking at us is like, whoa, those guys are leaning over. And I mean it makes no sense obviously, but it sort of gives me this sense of vertigo.
Yeah, I mean, everyone knows South Pasadena is the true north pole with the galaxy, and so I feel it just fine.
Right, yeah, well that's the north pole of the podcast universe also. But you also see these other really cool features. Some of my favorite features are super nova remnants, So a bunch of stars that used to be near the center of the galaxy and then blew up. You can see their clouds. You can see these like puffs from the super nova that are left over from these stars having exploded.
Where did those come from?
Those just came from stars that lived and burned and then died. And then the other really fascinating thing are these filaments above and below the disk of the galaxy. Are these shooting lines sort of like the galaxy has these hairs or something, and they stretch for like hundreds of light years you mean, like sort of like geysers or just as structures of stars. Well, we don't really understand what they are exactly. But they don't just shoot up and down from the black hole. They're shooting like up and down from the whole disc. So in this picture you could see like dozens of these things. There are these streaks up and down above and below the disc, these huge filaments. And we've known about these for a few decades that we've only ever seen a few of them. People think that they're like maybe these weird magnetized tubes of gas that funnel high energy particles and then those particles are emitting in the radio because they're getting accelerated by the magnetic field. But nobody has any theory for like why these things exist. When we found them a few decades ago, it was a pretty big surprise to see these like hairs sticking up and down from the the top and bottom of the galaxy.
MM just sort of like tornadoes.
Kind of sounds like, yeah, exactly, they're like magnetic particle tornadoes. And so there's some clue there about like the turbulence at the center of the galaxy. Maybe the stars are interacting somehow with their magnetic fields and the larger galactic magnetic field. We don't really know, but one thing that's really cool about this picture is that it's the first time we have like enough of these things to start to do like statistics, to say like how often are they here, or are they connected to stars or whatever. So it's the first picture that really gives us enough detail to start to understand the crazy dynamics at the heart of the galaxy.
Hmm.
And I guess that's important because you know, understanding what's happening in the center of the galaxy tells us a bit about how galaxies form right and where they're going exactly.
And we also know that the galaxy center is very different from the rest of the galaxy. Like we can think about star formation out here in the suburbs and understand it, but star formation in the center of the galaxy is very, very different. And because the conditions are different, and anytime you have different conditions, you have an opportunity to learn something new because maybe your theory for star formation works, but maybe it doesn't right and maybe there's something else happening. For example, they recently discovered a blob of like one hundred very new stars very close to the center of the galaxy. Again, we don't think that the center of the galaxy is a good place to form stars because of all the crazy intense radiation that heats up the gas. And yet they found this blob of like one hundred very massive, very short lived stars. They don't understand how those formed. Something else is going on that we don't understand. People think maybe there are like these clusters of metals that pull gas together, but nobody can understand why these stars exist. They call it the paradox of youth. And how do we see these stars? Do they emit a lot of radio ways too. Stars actually don't emit in the radio, so we can't see them that way, But stars do emit in the infrared, and so infrared telescopes can see into the center of the galley, things like James Webb. That's how, for example, we can follow these stars that orbit very close to the black hole. We can't see their visible light, it's blocked by all the dust, but we can see them in the infrared.
To me, it's just sort of like a pocket of inactivity that maybe let you have these stars.
It could be, but there's a lot of stuff to learn about what's going on in the center of the galaxy. We'd also really like to understand the center of the galaxy because it's where most of the dark matter is. Dark matter is actually most of the mass of the galaxy. Eighty or ninety percent of masses of galaxies are in dark matter, and a lot of that is clustered towards the center. So people who want to understand, like what is the dark matter have all pointed their telescopes towards the center of the galaxy to see if they can observe dark matter doing something weird, like smashing into itself and giving off flashes of light that we might be able to detect.
We don't know what it is what dark matter is, but we know there's a higher density of it in the center of the galaxy. Even though we can't actually see.
It exactly, we know there's more of it in the center of the galaxy. Just by I understanding the velocity of stars how they swirl around in the galaxy, it gives us like a mass profile. It tells us where the mass in the galaxy is. Because it's showing us where the gravity is. We could figure that out by how fast stars are rotating a different radii, And so we know there's a lot of dark matter in the center of the galaxy. So people have pointed special telescopes at the center of the galaxy to try to pick up signatures from that dark matter. And about five years ago, actually people saw these weird bumps, these very high energy gamma rays coming from the center of the galaxy that had to be super bright to get through all the gas and dust, but still they were making it to Earth and people were wondering, like, is this a sign of dark matter or is there something else going on at the center of the galaxy. It's hard to know if it's dark matter. If you're not sure what else could be emitting radiation to the center of the galaxy. So basically understanding what's at the center of the galaxy gives us an opportunity to learn a lot more different kinds of physics, to do all sorts of tests to look for dark matter, to understand star formation. It's just like a really cool laboratory because the conditions are so weird and different and intense.
And I guess it's the closest galactic center to us, right, I mean, we can see other galaxies, but maybe we can't see it as much detail as we can.
The center of our galaxy.
Yeah, it's both good and bad. It's very close, as you say, so we can trace out stellar motion near the black hole, but also it's obscured by gas and dust. So in some ways we can see the centers of other galaxies more clearly, even though they're further away, because we don't have to look through their galactic disk. So it's both studying our galactic center and other galaxies. Galactic centers can teach us different kinds of things.
All right, well, then, I guess maybe to summarize, what are some of the big questions we have about the center of the galaxy.
So we don't understand a lot about the center of the galaxy, like what is in there? Are there a bunch of pulsars giving us weird blips and bleachs that might be dark matter? We don't understand like why is there a bar in the center of the galaxy. Why isn't it just like a blob with arms. Some galaxies have bars, other galaxies don't have bars. We don't really understand like how that forms. We don't know if stars are still being made in the center of the galaxy, and that's something we really like to understand how star formation happens, why it stops. We don't understand these filaments, these weird magnetic particle tornadoes, what they mean, what they tell us about the magnetic fields of the stars, If there are supernervous down there that are driving it. It's basically a big cloud of mystery.
Yeah, and you forgot the biggest question of them all. Is the center of the galaxy bait or is it kind of a spicy green?
How late do the dance club stay open in the center of the galaxy?
Yeah?
How big are the parking lots that you can get lost in down there?
Are there good food trucks at two am?
All right?
Well, the next time you look up at the night sky, think about where you are in the galaxy and which way is it tilted? Where are all the exciting things happening in the milky Way?
Is it near you?
Or is it all happening downtown? And when you think about the broader context, try not to fall over from vertigo. When you realize that we'd tilted relative to the Sun. Who's tilted relatives to the galaxy? Who's just one of billions of galaxies floating out in space?
You hope you enjoyed that. Thanks for joining us, See you next time.
Thanks for listening, and remember that. Daniel and Jorge Explain the Universe is a production of iHeartRadio. 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. How is us dairy tackling greenhouse gases? Many farms use anaerobic digestors to turn the methane from an are 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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