Episode 134: Transcript
Episode: 134: The State of the Galaxy
Transcription by Keffy
Annalee: [00:00:00] Charlie Jane, do you remember when this happened?
Star Trek Clip: [00:00:06] How soon until we reach the galactic barrier?
Coming out of warp now, Captain.
So that's the edge of the galaxy. Is it wrong that I think that's pretty damn cool?
Frontiers are always cool, Mr. Reese.
If only we could enjoy it.
Charlie Jane: [00:00:30] Why yeah, I mean... Who doesn't love the barrier around the galaxy in Star Trek? I think it's just an excuse for them to like all shake in their seats and have lightning come out of the control panels. It goes right back to like the first ever episode with Captain Kirk where no man has gone before. It's just everything in Star Trek has to be dramatic. So of course, leaving the galaxy is like super dramatic.
Annalee: [00:00:53] And you know, Star Trek has always treated the galactic barrier as something kind of magical. Like, I guess in the original series it had psychic energy and it could like interact with humans who had psionic potential.
Charlie Jane: [00:01:09] Turns you into a god.
Annalee: [00:01:09] Yeah, I mean, just like Barclay, for those who remember. I guess in some of the novels, it's made of unknown matter or unknown forces. And then, of course, in Discovery, it's made of this bonkers thing that they just invented where it's like giant bubbles that they have to go through that make weird noises.
Charlie Jane: [00:01:32] Yeah, I mean, there's actually an episode of Original Series where there's the aliens from the Andromeda galaxy who turn people into soap crystals. And in that episode Spock explains the galactic barrier’s made out of negative energy and that—
Annalee: [00:01:49] Negative energy, right.
Charlie Jane: [00:01:48] Just, you know, negative. That's all.
Annalee: [00:01:52] If you’re feeling negative. Basically it's just made of, like, bad vibes.
Charlie Jane: [00:01:56] It's a bummer. It's the bummer around the galaxy, basically.
Annalee: [00:02:01] And it's all very scientific.
Charlie Jane: [00:02:04] Mm-hmm.
Annalee: [00:02:04] And on that note, you're listening to Our Opinions Are Correct, a podcast about science fiction, science, and black holes so vast and powerful they juggle stars like they were ping pong balls.
[00:02:17] I'm Annalee Newitz. I'm a science journalist who writes science fiction, and my latest novel is called The Terraformers.
Charlie Jane: [00:02:23] I'm Charlie Jane Anders. I'm a science fiction writer who thinks a lot about science, and my latest novel is Promises Stronger Than Darkness, and I'm also writing the comic New Mutants: Lethal Legion.
Annalee: [00:02:35] Today, we are delivering the State of the Galaxy address. We're going to be talking about how humans figured out that we're living in a galaxy and how science fiction represents other galaxies. But most importantly, we're going to be talking about the latest scientific hypotheses about galaxies with the incredible Molly Peeples.
[00:02:55] She's an astronomer with the Space Telescope Science Institute and Johns Hopkins University, and she studies where galaxies come from and what they're actually made of. Also, on our mini episode next week, we'll be talking about an incredible expedition that I went on during my summer vacation earlier this year. It involves estuaries, nitrogen, and a mass spectrometer.
Charlie Jane: [00:03:18] Ooh.
Annalee: [00:03:18] I know.
Charlie Jane: [00:03:20] Yeah. And speaking of mini episodes, did you know that this podcast is entirely independent and it's funded by you, our listeners, through Patreon. That's right. If you become a patron, you are making this podcast happen and you know, you get mini episodes every other week in between our regular episodes and you get access to our Discord channel where we're just hanging out all the time and spouting off like our views on everything in the news and everything else. Think about it all of that could be yours for just a few bucks a month. Anything you give us goes right back into making our opinions even more correct.
[00:03:54] So, find us at Patreon.com/ouropinionsarecorrect. Okay, let's get into the galaxy.
[00:04:03] [OOAC theme plays. Science fictiony synth noises over an energetic, jazzy drum line.]
Charlie Jane: [00:04:36] So, Annalee, it feels like we've always known that there was a thing called galaxies around us, but of course that's not true. How did we first discover galaxies and figure out what they actually are?
Annalee: [00:04:46] Yeah, the whole history of this is kind of a situation where people saw things and didn't really understand what they were. So, we kind of knew about the Milky Way starting thousands of years ago, but people just didn't know really what it was. They just thought literally it was a bunch of milk in the sky at some point. And the word galaxy is actually from the Greek for circle of milk. So we've always kind of had this idea that it was out there.
[00:05:14] It really gets started in terms of knowing that it's full of stars in the Middle Ages in the Islamic world. And there's this Persian astronomer in the 900s named Abd al-Rahman al-Sufi. And he worked as an astronomer in the royal court in what is now Iran. And in 964, so over a thousand years ago, he published a book called The Book of the Constellations of the Fixed Stars.
[00:05:42] And this was a dramatic scientific update on observations that Ptolemy had made in the early first millennium. Ptolemy was this famous Hellenic astronomer who identified 48 constellations. And al-Sufi comes in and is like, look, we really know a lot more about this now. We're going to update it.
[00:06:02] So, The Book of the Constellations of the Fixed Stars is a compendium of all the constellations that were known, and it included for the first time this cloudy object. And there's little known about what it is, and he just records it as a cloudy object, and now we know that it was the Andromeda Galaxy.
[00:06:22] And this becomes kind of a theme, like, people keep seeing Andromeda and saying there's this weird cloudy object out there, we're not sure what it is. They don't realize that it's literally thousands, millions of stars.
[00:06:34] So, many astronomers in the Islamic world are building on al-Sufi's work over the next couple of centuries. They're writing in Arabic because that was the lingua franca of science at that time, because all of the great work on astronomy and math were being done in the Islamic world. And there are just a bunch of astronomers doing things like using parallax to figure out that the Milky Way is incredibly far away from Earth. And they start hypothesizing that the Milky Way... is probably made up of a bunch of stars, but no one can see clearly enough to find out.
Charlie Jane: [00:07:07] Yeah, I mean, it's just, it's, I feel like again and again we find out that while Europe was kind of stuck in this sort of dark ages of indulgences and superstition, the Islamic world was just rushing forward with scientific advancements and huge innovations in mathematics, especially. And that was really where all the action was happening for hundreds of years.
Annalee: [00:07:31] That’s right. And while I was researching, I found this really interesting story from the 14th century about a Syrian legal scholar and imam who's known as Ibn al-Qayyim, and he wrote this book whose title is sometimes translated as Key to the Blissful Abode or Key to Happiness, and you can find excerpts from the book all over the place because it's such a big book that people will kind of take out chunks of it. But it's basically a massive treatise on science and religion, and there's a long section in it about why superstition is terrible and how astrology is total bunk.
[00:08:12] And to bolster his argument, Ibn al-Qayyim points out that the constellations can't possibly influence us because the Milky Way is so full of stars that it's not really proper to reduce them to their constellations. And plus, he adds, we don't know enough about the stars and their positions to even make claims about what a constellation is or isn't.
[00:08:36] And what's interesting about this is that he's not an astronomer. He's more like a cultural critic who's just read a lot about the latest science and really believes in being immersed in science as a way of being a good person. And he's aware that there's tons of stars out there, more than we can perceive. And what that shows is that it was so widely accepted at that time that the Milky Way was basically a galaxy that even this guy who's not even a scientist is able to very emphatically fight back against superstition using this widely understood knowledge. And I have to say that part of the thing about the story that I love is that 14th century Damascus, people were mad about astrology and how astrology was like leading the masses astay.
Charlie Jane: [00:09:26] Yeah. And you know, I mean, you only have to look up at the night sky on a night without a lot of light pollution and you can see that there's just so many stars out there and you have to wonder what's holding them together. Why are there so many stars out there? If we want to believe in this simplistic, like we're the center of the universe view, which a lot of people did at the time.
[00:09:44] So then what happened?
Annalee: [00:09:44] Okay. So, then things start heating up and some science starts moving over to Europe. And in the late 18th century, there's a big development when a French astronomer named Charles Messier tries his own hand at creating something like al-Sufi's Book of the Constellations of the Fixed Stars.
[00:10:06] So, Messier goes on top of a hotel in Paris and is able to use his 4 inch refracting telescope, which would have been really badass at the time, to look for new objects that he wants to catalog. So he can add to general knowledge about constellations, but also just about objects in the sky. So, he's not really looking at constellations anymore. He's looking for new weird stuff.
[00:10:31] So in 1781, he publishes a list of those objects, which people still use today. It's called the Messier Catalogue. There are about 110 objects in the catalog, some of which were added actually after Messier died, which is a whole other thing, but 40 of those objects are galaxies.
[00:10:50] And when Messier saw them, just like when al-Sufi saw Andromeda, He just sees these cloudy things, and this was a period of time when people already knew about nebulas, so they knew there were these cloudy objects called nebulas, so he misidentifies these 40 galaxies as nebulas. He also sees star clusters, which are just really densely packed regions of stars. These are called globular clusters now. He also thinks those are nebulas, because again, they just look fuzzy on his telescope.
[00:11:25] So, the Messier Catalogue, like I said, it's still used now by amateur astronomers like me. And it's kind of like how bird watchers look for certain birds. When you start out as an amateur astronomer, you try to find all these different Messier objects because they're really easy to see, even if you have a pretty low grade telescope, and each object is called M dash whatever number. Andromeda is M-31, people still call it M-31, it's my favorite. It’s the closest galaxy to us, so it's hard not to love it. Eventually it's going to actually slam into the Milky Way, but not while we're still around, that'll take billions of years.
[00:12:03] But I think, again, the important thing is that Messier sees all these galaxies, but he doesn't know that they're galaxies. He just thought they were weird things inside the Milky Way.
Charlie Jane: [00:12:12] Wow, when I think about 40 galaxies, it just reminds me of that guy who used to walk around downtown San Francisco with a big sign saying 12 galaxies. Impeach Clinton. And like eventually Impeach Bush and then Impeach Madison and Jefferson. And he had this whole, very complicated site about like 12 galaxies and how there was exitronic radiation influencing our political system. And you know, what would he even do with 40 galaxies?
Annalee: [00:12:36] I don't even know. I know he obviously hadn't even seen the Messier Catalogue, even though it's over 200 years old at this point.
Charlie Jane: [00:12:44] So okay, so you have Messier and people like that thinking these are just nebulas or weird smudges. When did people first realize that these were actual galaxies?
Annalee: [00:12:53] Yeah, so amazingly, it's not until the early 20th century, which is amazingly recent given that people had actually been seeing these things for at least 2, 000 years.
[00:13:05] So the guy who's credited with finally identifying a galaxy outside of the Milky Way is Edwin Hubble. He was an American astronomer and he basically managed to get some time on the world's largest telescope in 1919. That was the Hooker telescope, well named, on Mount Wilson, which is near Los Angeles.
[00:13:31] And this was a telescope that was used in lots and lots of discoveries at that time. And it's kind of funny because Hubble gets all this credit. But he didn't actually discover galaxies beyond the Milky Way. People had been observing them for centuries, like I said. So, what he did have was access to this really powerful telescope and he knew about the recent discovery of a Harvard astronomer, named Henrietta Leavitt, and she had figured out a thing called a standard candle.
[00:14:02] In this case, the standard candle was a Cepheid variable star. So, okay, what is a standard candle? You're probably wondering. Sounds great, right? Standard candle could be a great emo band. So, a standard candle is any type of star whose brightness is consistent no matter where it is, and Cepheid variable stars are like that. You always know how bright they're going to be no matter where you find them. They're just a very regular kind of variable star. And it's perfect for measuring distances because if the standard candle is dim, we know it's further away than a standard candle that's bright. So, we can use that star to tell us am I looking at a really distant object? Am I looking at something really close up? And so, Leavitt had been observing these Cepheid variable stars and realized, oh my god, these are great standard candles. Their brightness is totally predictable.
Charlie Jane: [00:15:00] So now I have to ask, where's the Leavitt space telescope? Like, why doesn't she get a freaking space telescope?
Annalee: [00:15:06] Yeah, good question. So, there was a movement to try to name the Webb telescope after Henrietta Leavitt, but that did not work. But there is a telescope that is named after her. It's in Texas and it is a telescope for doing major surveys of the sky. So, it's kind of honoring what she was good at. But yeah, she didn't get the big acknowledgement. She got the kind of footnote.
Charlie Jane: [00:15:35] And it's not a space telescope. I mean, come on.
Annalee: [00:15:37] I know. I really wish that there was a bit more acknowledgement because she's really the person whose research allowed us to discover galaxies. Yeah. So, Hubble uses Leavitt's discoveries. He has it in the forefront of his mind. And then he basically just aims the Hooker telescope at some of Messier's spiral nebulas, right? Because remember, he thinks they're nebulas. So, lots of people, including Hubble, had suspected that these were probably galaxies, but they didn’t have a way of proving it. But, luckily, he found some of Leavitt's Cepheid variable stars, those standard candles, in M31. Remember, my favorite, Messier object, the Andromeda Galaxy, which at the time was known as the Andromeda Spiral Nebula. But what he found was that those standard candles were dim enough that it became completely obvious that Andromeda was not inside the Milky Way. It was way further away. And it was frickin’ packed with stars.
[00:15:37] So, it's obvious that we've got a bunch of stars. They're not inside our galaxy. They're somewhere else. And so, this is just mind blowing. And Hubble is so excited that instead of going the standard scientific route and like giving a paper at a symposium and publishing a scientific paper, he goes right to The New York Times and he's like, Dudes, I totally found this thing.
[00:17:05] So, in 1924, there's a huge splash in the media where he announces this discovery. And I have no idea if he credited Leavitt or not. But he gets all the glory.
Charlie Jane: [00:17:16] So, you say that people had already theorized that these things that we thought were nebulas might be galaxies, but how did we come up with the idea that there was such a thing as a galaxy. That the stars aren't just like equally spread across the universe.
Annalee: [00:17:29] I mean, that's really because of Hubble's announcement, using Leavitt's standard candles. So, people knew that there were tons of stars spread out everywhere and they assumed that the earth and our star were kind of nestled in like a giant milky way. And everything was inside. So, it was believed basically until Hubble's announcement, it was believed that there was one galaxy and we were in it.
Charlie Jane: [00:17:57] Oh, okay. So now we have the Hubble Space Telescope, named after Edwin Hubble. And what has it told us about galaxies that we didn't already know?
Annalee: [00:18:08] So, it's told us a bunch of stuff, but the really big deal from the Hubble telescope came in 1995 when Scientists who've been working on the telescope for about 16 years knitted together a bunch of images they'd taken that were the deepest images of the universe that had ever been produced.
[00:18:27] And they put all those images together in a mosaic, which was called the Hubble Deep Field Image. It showed about a quarter of a billion galaxies. And the image was gorgeous. Like, you can see it online. I personally remember when it came out. It's just incredible because you can just visualize all of these stars and it was astonishing because you realize as you look at it, that galaxies aren't all spirals. They come in a ton of shapes and sizes and colors, and suddenly the universe looked a lot bigger and weirder than it ever had.
Charlie Jane: [00:19:07] Yeah, it's interesting because, I mean, obviously we've had science fiction for decades where there's like, a galaxy involved, like Star Wars, it's a, a galaxy far, far away. But in the ‘90s, around the time you get that deep field image, you suddenly have a lot of science fiction that deals with, like, galaxy spanning civilizations. Iain M. Banks, Vernor Vinge, are writing about, like, huge civilizations that are galaxy wide. And suddenly you have this really concrete vision of what the next step in human history civilization could be after we spread out among the stars. Maybe we spread out through the whole galaxy, maybe a bunch of galaxies.
Annalee: [00:19:45] Yeah. I was thinking that the Hubble Deep Field Image was kind of like the blue marble image taken of earth back in 1972, which was the first time that a lot of people had ever seen earth from a distance in this gorgeous color. And it was just a radical change in perspective. It really shifted how people looked at our place in the universe.
Charlie Jane: [00:20:08] Yeah. And it's interesting that we still don't see that much science fiction featuring other galaxies in relation to our own. And, obviously Star Trek has the Galactic Barrier. It has in intruders from Andromeda. I guess, Star Wars in the expanded universe had invaders from another galaxy called the Yuuzhan Vong.
[00:20:31] But, you know, in general, there's not a lot of our galaxy, the Milky Way, in relation to other galaxies. And the thing that's interesting in Star Trek is that there's sort of this suggestion that the physical laws of the universe might change when you leave our galaxy, which is really interesting and something I'd love to see more science fiction deal with.
Annalee: [00:20:45] Yeah, I almost feel like that's a trope that other galaxies would have different physics or different physical laws. But then I think back on Star Wars where, it's set in a galaxy far, far away. And I feel like that's a science fictional way of saying basically once upon a time. It lets us know that we're in this radically different place where anything could happen.
[00:21:10] Similarly, uh, Stargate: Atlantis is set mostly in the Perseus galaxy, and that's where the lost city of Atlantis is. So again, it feels fantastical. It's very once upon a time.
Charlie Jane: [00:21:21] Yeah, and one of our all time favorite TV shows, the sadly canceled too soon, Vagrant Queen, takes place in a distant galaxy and someone from Earth is like flung into this other galaxy and has to kind of make his way in this very different world.
[00:21:37] Again, there's that license of like, we're no longer in the Milky Way galaxy so things can get super, super weird.
Annalee: [00:21:43] Yeah. I feel like when we deal with other galaxies in science fiction, it's either that kind of fairy tale idea, like somewhere far away where anything could happen. Or it's like it's a distant frontier and it might be completely bonkers scientifically.
[00:22:03] And we never really talk about galaxies as just an ordinary part of the universe. But after the break, we're going to remedy that. We're going to talk to astronomer Molly Peeples, who studies the way real galaxies actually behave.
[00:22:17] OOAC session break music, a quick little synth bwoop bwoo.
Annalee: [00:22:22] Now we're joined by Molly Peeples, who is an Aura Associate Astronomer at the Space Telescope Science Institute and a Research Scientist at Johns Hopkins University who studies the evolution of galaxies, as well as the physics of how galaxies interact with the circumgalactic medium, which is all the stuff that surrounds galaxies like dust and wayward stars and mini galaxies.
[00:22:44] We are so glad to have you here to weigh in on the state of the galaxy. Welcome, Molly.
Molly: [00:22:49] Hello.
Annalee: [00:22:51] So, I wanted to just start by giving people a really concrete picture of what we think galaxies look like and what they're made of. I think we have a lot of ideas and we've seen images from, you know, the Hubble Deep Field, but when we're talking about a galaxy, what is it beyond just a bunch of stars?
Molly: [00:23:11] Yeah. So, I like to think of galaxies as, the main thing they do is they convert cosmic gas into stars. And so, at their heart, they've got a lot of gravity, primarily from dark matter. And this attracts a lot of the gas, the cosmic web from the outskirts of the universe. And that gas as it cools and condenses, it gets dense enough to start forming stars. And then once those stars blow up, they will create all of the elements that we know and love, such as oxygen, carbon, nitrogen, iron, those things that make up life that are not just hydrogen and helium. And as those stars will up, they'll expel that material back into the gas inside the galaxy and outside of the galaxy itself and some of that gas will then continue to cool and condense and form new future stars. So that’s most of what galaxies are doing, it's just turning gas into stars, many stars at a time.
Annalee: [00:24:16] It sounds like an awesome job.
Charlie Jane: [00:24:19] So, we were joking about like how Star Trek has this barrier around the galaxy, which is made out of negative energy. Uh, but what actually does surround our galaxy and what is the circu-galactic medium, and what's it made out of?
Molly: [00:24:30] Yeah, so the circumgalactic medium is basically the stuff that, roughly speaking, is gravitationally bound to the galaxy, but it is not necessarily what we think of when we look at a galaxy and we see something that's full of stars. The area that all of the gas that's flowing into the galaxy has to pass through to get to, it's the region that all of the gas, that is being blown up out of stars is going back out into. It's a pretty dynamic place, but it's also huge.
[00:25:04] I think one of the things that's really unappreciated and that I definitely try to not think of on a daily basis because it's kind of mind breaking, um, is just how big galaxies are. So, for example, if our own Milky Way galaxy was about the size of a city, you know, maybe, 10, 20 miles in size, the nearest galaxy would be hundreds of miles away with basically no other metropolitan areas in the in between. And that area would be then filled with what we call the circumgalactic medium.
Annalee: [00:25:39] I always wonder, like, when you talk about the circumgalactic medium, say, just around the Milky Way. I think of the Milky Way as being kind of a flat disc, a flat circle, if you will. But does the circumgalactic medium mean that actually I should really be thinking of the galaxy as more like a sphere, or is a sphere the wrong shape, also?
Molly: [00:25:58] Sphere is not wrong. I like to think of it as kind of the full ecosystem. It's really easy when we look at some of these pictures from telescopes to be like, okay, here's an edge to the galaxy.
[00:26:12] And in some sense, there is, but in another sense, it's sort of fuzzy and it kind of peters out and just gets, you know, more and more rural as you go out. There are also stars and the circumgalactic medium. So then we call the stellar halo instead of the gaseous halo. But they're just much more diffuse and few and far between than they are in the actual plane of a galaxy, like the Milky Way
Charlie Jane: [00:26:40] So, I know that you've been working on a project called FOGGIE, figuring out gas and galaxies in Enzo. And part of that, you've produced some incredible simulations of galaxies interacting with each other. And there's one that shows a Milky Way-like galaxy evolving over billions of years. And it's just so exciting and action packed and full of galaxies smashing into each other.
[00:27:02] And so can you talk about like, what goes into that movie and where you get the data to create it and what we're actually seeing when we look at that film.
Molly: [00:27:08] So the FOGGIE project is a bunch of simulations. So fake universes in boxes, that we've evolved with the Enzo code, hence the E, Enzo in FOGGIE.
[00:27:23] And part of the Figuring Out Gas and Galaxies In Enzo is that the great thing about these fake universes is that unlike our own real universe, we can actually go in and pick apart everything and find out what's really going on and then compare that to what we would look at if we were observing it with a real telescope.
[00:27:42] So, the way that I ran these simulations, these simulations were all run on NASA's Pleiades supercomputer and took several years to run. So, it's not a small undertaking to do one of these.
Annalee: [00:27:53] Amazing.
Molly: [00:27:53] We started with initial conditions, basically by observations of the cosmic microwave background, astronomers have gotten a pretty good idea of what the statistical fluctuations in density in the universe are. And we just evolve that forward with time with models for estimating how… We know how gravity works. We basically know how fluid dynamics works following that gas through time. We put in prescriptions for, okay, if the gas gets this dense, we're going to let it form some stars and then those stars are going to have material go back into their environs. One of the people I work with likes to say that if you were going to have a perfectly accurate model of the universe, it'd have to be the size of the universe. So, we do have to make some approximations.
[00:28:45] So, yeah, what you're seeing in these movies is what we think the formation and evolution of a galaxy, like Charlie said, like our own Milky Way, would actually look like.
[00:28:56] And definitely one of misconceptions when you look at some of these, many observations of galaxies is that galaxies are these staid, very long lasting things that kind of look the same way for a long time. But that's only because human lifetimes are very, very short compared to the many billions of years that it takes to build a galaxy.
[00:29:19] And one of the ways the galaxies grow is by colliding with other galaxies. And that's a lot of what you see going on and a lot of these movies and what's happening there is the galaxies are so big with so much space in between the stars that when two galaxies collide the stars don't actually collide with one other. The here's so much empty space, they're just kind of whooshing past one another and interacting gravitationally.
[00:29:47] But the gas that comes in with both galaxies, that gas will come in and shock in a big train wreck and often then form extra stars that then you can see some of these movies will blow up pretty soon and, you know, expel much more gas out, into their environs. And that's a lot of what you're seeing going on in some of these.
Annalee: [00:30:07] It really is cool. We'll link to it in the show notes. Like, I love just watching giant galaxies smash into each other. It's basically science fiction. Like you, I mean, it's highly accurate science fiction. You've created a simulated universe. It's so awesome.
So, okay. Do we know what happens two galaxies smash into each other? Each of those galaxies, well, most galaxies have a giant black hole at their center, right? So, what happens to those two black holes? Do they fight? Do they become friends?
Molly: [00:30:39] That's a great question. The short answer is that they probably eventually end up merging. The longer it is… We don't really know in detail how that happens. That gravity is going to do its thing and they're going to eventually end up settling down at the center of the newly formed galaxy and, you know, going around one another pretty fast and continuing to eat up the gas at the center there, the details of how they do that final last merge is still an area of open active research, both in trying to, like, get observations to what's going on there and an understanding from a theoretical point of view.
[00:31:23] But, there's no reason to expect that they don't eventually merge. But the details of how it happens, we don’t really understand yet.
Charlie Jane: [00:31:30] We used to sort of think that the Milky Way was this, like, at least I used to see images of the Milky Way as this perfect spiral with lots of like arms going off in all directions. And now the latest research suggests that it's a barred spiral with like a bar across and we have fewer arms than we thought since we're viewing it from one vantage point from edge on and it just looks like a big line across the sky. How actually do we figure out what our galaxy looks like from a distance kind of, from outside of it?
Molly: [00:31:59] Yeah, that's a really good question. Because in some ways our own Milky Way is the easiest galaxy to observe because it's the closest.
Annalee: [00:32:08] We're in it!
Molly: [00:32:09] Because we’re in it. So, there are a lot of galaxies that are spiral galaxies that have bars. So, if we do have a strong bar or a weak bar at the center of the galaxy, that's not unusual. And oftentimes galaxies that used to have a bar will no longer, and then it'll come and go. So that’s not surprising that we probably do have a bit of a bar at the center of the galaxy. The way that people go about studying what the actual structure of the Milky Way might look like is, the short answer is very painstakingly. What you have to do is actually find a good sample of stars, both between us in the center of the galaxy and then further out. And try to measure their distances, which is notoriously the most difficult thing to do in astronomy is measure the distance to something and try to measure its velocity, both relative to us and on the sky to try to map out a full orbit and then piece all of those together to try to figure out what a full dynamical model might be.
[00:33:11] And, yeah, it's definitely an active thing where people are like, well, we think if we connect to these dots, we'll have a spiral arm and other people like, actually. I think we might just be saying that because those are the brightest things and we haven't looked over here. So, it's definitely an active piece of research to try to figure out exactly what the spiral arm structure of our Milky Way might look like if viewed from the outside.
Annalee: [00:33:36] Right, so it's kind of just right now it seems likely that it has a bar, but we can't actually go measure that and say like, all right, we saw the bar.
Molly: [00:33:44] Yeah, I think the idea that the Milky Way is a bar galaxy is pretty much as a much firmer idea right now than the details about exactly how many spiral arms we have in which stars may or may not be in the spiral arms.
Annalee: [00:34:01] Cool. All right. So we definitely have a bar. This is not the kind of bar where you can go get a whiskey, but you know, it's still pretty cool.
[00:34:08] I was wondering if there's like a normal way that galaxies form and like a norm for how they look, or are they all just super different?
Molly: [00:34:18] Yes and no. Yeah, so in some ways, galaxies like our Milky Way are kind of the most normal. We're a pretty normal mass, in a pretty normal environment, and we've had a pretty normal history to the extent that there is a whole area where people will compare, our own Milky Way, which we can again, study in lots of detail to other galaxies, and there's a lot of hair pulling, of like, oh, my God, what if the Milky Way is not actually perfectly normal?
[00:34:48] And as with humans, everybody's normal until you look at them a little bit closely, and then nobody is normal whatsoever.
Annalee: [00:34:54] Yeah.
Molly: [00:34:54] But galaxies that tend to be smaller than the Milky Way tend to have formed their stars in a much more stochastic way. So, they might have formed a little bit and then kind of stopped and then formed some more and then kind of stopped.
They have morphologies and shapes and kinematics that oftentimes are much more of an irregular mess than the nice spiral disk that we get out of the Milky Way.
Annalee: [00:35:20] So, they look sort of like a blob or like…
Molly: [00:35:23] Yeah, just a lot more disordered and they may not have as much rotation in them as, you know, like a nice frisbee disc like the Milky Way. And then galaxies that are more massive than the Milky Way, oftentimes they got more massive because they formed a lot of their stars really early on, or they've merged with a lot of other galaxies and mostly they've kind of stopped forming stars.
[00:35:52] So, they tend to be much more of the colors of older stars, much redder instead of bluer, and they look very smooth on the sky. They have much less gas because they’ve basically converted all their gas into stars at this point, but, you know, there are exceptions to all of those rules. There are galaxies that are much more massive than the Milky Way.They're still very happily forming stars very, very quickly. There are small dwarfy galaxies, especially near the Milky Way that no longer are forming stars. And part of this is thought because when they enter the circumgalactic medium of the Milky Way, well, the Milky Way is taking all of the gas out in order to form its own stars. And so those tiny things aren't able to get more gas to form more stars themselves.
[00:36:38] And of course, galaxies way back in the day, billions of years ago, were on different parts of these trajectories and generally looked like much more trainwrecks than the nice orderly things that we've seen today.
Annalee: [00:36:50] Trainwreck galaxies. So, the, the Magellanic Clouds that are in orbit around our galaxy, those are examples of the tiny kinds of galaxies that all of their gas is being suctioned off by the Milky Way.
Molly: [00:37:02] Yes, the Magellanic Clouds are examples of what are called dwarf irregular galaxies, meaning they are smaller and they have this irregular morphology, that are kind of blobby looking. They are still forming stars.
Annalee: [00:37:15] Oh, okay, cool. Good job.
Molly: [00:37:16] Yeah, but the ones that are… Those are ones that are like 1/5th to 1/10th the size of the Milky Way. It’s the ones that are much smaller that generally have stopped forming stars.
Charlie Jane: [00:37:30] So, when did galaxies first evolve and when we're looking at really distant galaxies, are we just seeing, you know, we're seeing the light obviously from a long time in the past. So, what can we deduce about how those galaxies are behaving now?
Molly: [00:37:43] Yeah, so. Galaxies, I mean, this part, both of those questions get into like, what is the definition of a galaxy? So one of the things with the recently launched JWST is it's going to be able to see, because it can see in infrared light, it can see galaxies that were forming much longer ago that it just had their light shift from the the normal visible wavelengths that we can see with our eyes to these much redder wavelengths and definitely one of the big science cases there is being able to look at the first galaxies.
[00:38:21] And it happened pretty soon after the Big Bang, only about a few hundred million years. And, again, the time scales here are crazy because pretty soon is a few hundred million years. So, about 13 billion years ago is when these things were thought to first form and we're seeing evidence of definitely very small, very young galaxies.
[00:38:42] But people will argue. They're like, well, that's not really a galaxy. That's just a star cluster. And it's like, but if it started converting gas into stars in the presence of a lot of gravity like that's probably a baby galaxy instead of just a star cluster.
[00:39:02] So, I like to think that, yes, JWST is starting to see some of the first galaxies, and potentially some of the first stars, or at least some of the first supernovae, hopefully.
Annalee: [00:39:11] I love that people are debating, like, is it a cluster or is it a galaxy?
Charlie Jane: [00:39:16] Is it the presence of a black hole at the center that like people think makes it not a galaxy but rather a star cluster?
Molly: [00:39:24] Um, I think if the presence of a black hole was detected, that would definitely actually make people think it's more of a galaxy because it's got more going on. I think when you're always looking at things on the edge that you're not going to be able to get more information about for a while, it's easy to argue about the definitions.
[00:39:45] The other question that you asked about, you know, what are the galaxies that we see from a really long time ago, because it's taken so long for their light to get here. What would they look like today? How do we know what they look like today? This gets into, like, in my mind, I always go straight to like, what is time, anyhow? What is now? Right? Because in some sense, it's taken 13 billion years for that light to get to us. That is what's happening now. Now is 13 billion years ago, is 10 billion years ago because it, you know, it's taken that much time to get to us.
[00:40:22] In another sense, right? Like, those galaxies have gone and done their thing and 13 billion years after we observe them, they probably look a lot like the galaxies that are much closer to us right now. I mean, one of the ones that starts getting into some of the, you know, thinking about sci fi implications is the Andromeda galaxy, which is our closest big galaxy, very similar to the Milky Way. This is the furthest away object you can see, uh, with the naked eye.
[00:40:54] If you go to the southern hemisphere on a really dark night, it's a really faint, fuzzy blob that you can see. That’s how, like, super close it is, right? But it's two and a half million light years away. Two and a half million years ago was about when the Homo genus was starting to evolve, right?
[00:41:14] Like, way, way, way, pre humans, right? This was a really long time ago as far as like our brains are able to think about. But we definitely think of that as, oh, that's a nearby neighbor. Like that definitely is very much present day, right?
Annalee: [00:41:31] So, I guess what you're saying is that the aliens that are coming to meet us from the Andromeda galaxy might be coming from millions of years ago. Hmm.
Molly: [00:41:42] Yeah.
Annalee: [00:41:42] So, I wanted to ask you, like, on that note, a sort of a sci-fi question. Which is, so we were talking earlier about how one of the tropes in science fiction about other galaxies is that there might be different physical laws. Like, if you go out of our galaxy, suddenly physical laws change, and maybe in a different galaxy, they'd have, I don't know, physics would be different. Is that possible or is that just silly?
Molly: [00:42:08] I would say it's not possible, but it's also not silly.
Annalee: [00:42:14] Okay, so somewhere in between on the scale of silly to possible.
Molly: [00:42:19] I think some of these, right? Like you get into what is the point of science fiction? What is the point of speculative fiction anyhow, right? And if the answer is to try to teach people about the way space can really be, then maybe things like, yes, faster than light travel is possible is like, not a great way to go. But if the answer is like, to think about, different scaffoldings to try to understand the human experience, then a few tooth fairies of like, okay, you can travel really fast or, you know, wormholes can exist or within this region, you can go this speed, but not this speed. I think that kind of stuff, you know, can provide a really interesting structure to try to put some of these more human stories on top of. But from the purely, you know, speculative what is possible, we have no reason to believe that it's possible and all observations to… When physicists think about how could the laws of physics change, we think about things like, okay, the laws are fixed, but, like, maybe it's possible for the individual constants to change. Like, the proportion of what is the speed of light relative to the gravitational constant relative to the mass of the electron, like, if those tweaked a very small amount. Would we be able to tell what effects would it have? And those are the sorts of things you can also measure. And every measurement that's been done to very high precision to try to place constraints on those elsewhere in the universe have basically shown, yes, everything is the same.
[00:44:18] But once you start going, you know, possible multiverse, right? Like we can only observe what's in the observable universe, right? And again, that's the stuff that's causally connected. That's is close enough to us that light has had time to get from that stuff to us. That maybe the initial primordial soup that didn't expand to become our own observable universe, maybe some other little pocket has slightly different things.
[00:44:45] But, I'm personally of the belief that if the laws of physics were different, we would definitely not have life as we understand it now. That everything's so precarious to get us to have evolved in the first place that I think if you tweaked any little bit of it, it would be, whatever the definition of life would be would be completely different.
Annalee: [00:45:05]
Charlie Jane: [00:45:05] That's great So what are you looking forward to next in our exploration of other galaxies? Is there something that you're excited to see from the James Webb Space Telescope or some of the other telescopes that we're gonna find out soon?
Molly: [00:45:16] Yes, I think JWST, by being able to see better into the infrared than we've ever seen before, it's gonna be really nice to see some of these young baby galaxies with the same fidelity that we can see a lot of the more local galaxies and really to kind of be able to compare things at the same scales. And also just what we're going to be able to see into star forming regions in local galaxies. This is going to be really exciting. And then other telescopes, the one that I'm super excited about is, the astronomical community is working on what's currently being called the Habitable Worlds Observatory. And this is a concept for launch in about 20 years. Basically think the Hubble Space Telescope but instead of being 2. 4 meters, maybe 8 to 10 meters in diameter.
Annalee: [00:46:06] Wow.
Charlie Jane: [00:46:06] Wow. That's amazing.
Molly: [00:46:08] Yeah. And so instead of having to observe, for example, the circumgalactic medium by looking at shadows against bright background light sources, looking at, this is where the name FOGGIE came from, cosmic fog, like that. We'd actually be able to see it in emission, see the actual photons coming from it directly, which will be really, really exciting. And I think completely change how we understand galaxies.
Annalee: [00:46:32] I hope they're going to name this telescope the Henrietta Leavitt telescope. We've been like, we've been jonesing for her to have like a badass space telescope.
Molly: [00:46:40] Yeah, it's uh, I Personally think it's unlikely that any space telescopes are going to get named after humans for a while because it turns out all humans are flawed if you look at them too closely.
Annalee: [00:46:52] Good point. But I still think she should get one before we stop.
Molly: [00:46:56] There are a lot of women who should definitely get stuff named after them. But the upcoming Nancy Grace Roman telescope is one I'm definitely excited about in that in that regard.
Annalee: [00:47:08] All right. Well, thank you so much for joining us and telling us all about the state of the galaxy as we know it. And can people find out more about your work online?
Molly: [00:47:18] Yeah. So, the two places to go is you can find me, at my website, molly.science. And you can find out more about the FOGGIE project, including being able to download some of our movies and link to our YouTube channel at FOGGIE.science. That's F-O-G-G-I-E.science. Very purposely misspelled so it can be searched for on the internet.
Annalee: [00:47:42] Nice. Good, good forward thinking. All right. Thanks so much for joining us.
Molly: [00:47:46] Thank you.
[00:47:50] OOAC session break music, a quick little synth bwoop bwoo.
Annalee: [00:47:50] You've been listening to Our Opinions Are Correct. Thank you so much for making it all the way to the end of this episode. And thank you to our amazing producer, editor, and all-around whiz, Veronica Simonetti. Thanks to Chris Palmer and Katya Lopez-Nichols for the music, which is brand new music. I hope you noticed, it's really great.
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Both: [00:48:36] Bye.
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