WEBVTT - Why do some galaxies have bars? 0:00:08.240 --> 0:00:10.920 Hey, Daniel, remember a few weeks ago when you insulted 0:00:10.960 --> 0:00:13.200 America's favorite chocolate bar hershees. 0:00:14.520 --> 0:00:17.760 How could I forget? I got some strong emails about 0:00:17.760 --> 0:00:18.360 that comment. 0:00:18.680 --> 0:00:21.560 Oh yeah, did you get us barred from the airwaves? 0:00:21.920 --> 0:00:23.799 No? But I think I might have to raise the 0:00:23.800 --> 0:00:25.200 bar in terms of my comments. 0:00:25.520 --> 0:00:27.360 You mean we're not already at the bottom. 0:00:27.200 --> 0:00:28.920 We're scraping the bottom of the bar roll. 0:00:30.120 --> 0:00:32.760 Yeah, it sounds like you need to spend less time 0:00:32.800 --> 0:00:35.599 in bars drinking away your chocolate sorrows. 0:00:35.840 --> 0:00:37.640 I'll have a chocolate TEENI please. 0:00:37.440 --> 0:00:54.760 Sure give it a shot. Hi am Hori, my cartoonist 0:00:54.760 --> 0:00:57.320 and the author of Oliver's Great Big Universe. Hi. 0:00:57.440 --> 0:01:00.200 I'm Daniel. I'm a particle physicist and a professor at 0:01:00.280 --> 0:01:03.240 U SEE Irvine, and I do have strong opinions about chocolate. 0:01:03.280 --> 0:01:05.319 Do you have opinions about strong chocolate? Or do you 0:01:05.280 --> 0:01:06.720 have strong opinions about chocolate? 0:01:06.800 --> 0:01:10.119 Yes? And yes, it's. 0:01:10.080 --> 0:01:13.440 Because you're really passionate about chocolate. It gives you a 0:01:13.480 --> 0:01:14.080 lot of comfort. 0:01:14.280 --> 0:01:16.040 I feel like, if you're gonna eat chocolate, then you 0:01:16.040 --> 0:01:18.240 should eat chocolate that you like. But you know, people 0:01:18.319 --> 0:01:20.480 prefer lots of different kinds of chocolate. I don't mean 0:01:20.520 --> 0:01:23.000 to judge people who like Hershey's. You know, all the 0:01:23.040 --> 0:01:25.200 power to them if that's what they want. It's everywhere. 0:01:25.240 --> 0:01:26.720 I feel like you're maybe being a bit of a 0:01:26.800 --> 0:01:27.520 chocolate snob. 0:01:27.760 --> 0:01:29.280 I mean, are you being a snob to know what 0:01:29.360 --> 0:01:31.880 you like and know what you don't like. I don't 0:01:31.880 --> 0:01:34.360 want to insult anybody else's preferences to anybody who is 0:01:34.360 --> 0:01:38.520 offended by me calling Hershey's chocolate garbage, I do apologize. 0:01:38.720 --> 0:01:40.679 That sounds like a non apology, Daniel. 0:01:41.160 --> 0:01:46.240 It did sound like an apology. I agree, But it 0:01:46.280 --> 0:01:47.840 sounded like I was trying, didn't it. 0:01:47.920 --> 0:01:49.880 I don't think that counts these days. I think you 0:01:49.880 --> 0:01:53.880 could raise your bar in terms of apologies to the masses. 0:01:54.000 --> 0:01:56.280 Well, I'll say this, I enjoy chocolate. I hope everybody 0:01:56.280 --> 0:02:00.240 else out there enjoys chocolate, whatever flavor or variety they prefer. Yeah, 0:02:00.280 --> 0:02:00.680 there you go. 0:02:00.880 --> 0:02:03.520 But anyways, welcome to our podcast Daniel and Jorge Explain 0:02:03.560 --> 0:02:06.520 the Universe, a production of iHeartRadio. 0:02:06.000 --> 0:02:08.880 In which we whip up a delicious concoction of everything 0:02:08.919 --> 0:02:11.799 that's out there in the universe, all the dark energy, 0:02:11.840 --> 0:02:14.840 all the dark matter, all the dark ideas that describe 0:02:14.880 --> 0:02:17.800 how the universe actually works, what it's made out of, 0:02:17.800 --> 0:02:20.800 and how it came to be. We melt it all down, 0:02:20.960 --> 0:02:23.320 form it into squares, and ship it to you over 0:02:23.360 --> 0:02:24.040 the airwaves. 0:02:24.200 --> 0:02:26.400 That's right. We try to lower the bar of science 0:02:26.440 --> 0:02:29.679 and make it accessible to everyone out there. We try 0:02:29.680 --> 0:02:32.600 to make it silky and smooth and delicious and easy 0:02:32.639 --> 0:02:33.320 to go down. 0:02:33.240 --> 0:02:36.680 Because wondering about how the universe works is something everybody does, 0:02:36.720 --> 0:02:39.000 and everybody should have access to what we know and 0:02:39.040 --> 0:02:41.959 what we don't know about the universe. Thinking like a 0:02:42.000 --> 0:02:45.760 physicist is not something only professional physicists can do. It's 0:02:45.760 --> 0:02:48.720 something everybody can do and should do about how the 0:02:48.720 --> 0:02:51.240 world works. And we're here to walk you through that. 0:02:51.280 --> 0:02:53.239 It's right because we all live in the universe. We're 0:02:53.280 --> 0:02:56.239 all members of the universe, and we can all wonder 0:02:56.240 --> 0:02:58.320 about how it all works, how it's all put together, 0:02:58.680 --> 0:03:00.760 and why things are the way they are. 0:03:01.400 --> 0:03:03.320 Do you have like a membership card for the universe? 0:03:03.360 --> 0:03:04.040 I don't have one. 0:03:04.240 --> 0:03:06.000 Oh oh uh, awkward? 0:03:06.720 --> 0:03:07.200 Awkward. 0:03:08.560 --> 0:03:10.360 Maybe you just got lost in the mail, Daniel. I'm 0:03:10.400 --> 0:03:15.040 sure that's what happened. Sure you are invited. 0:03:15.200 --> 0:03:18.240 Maybe it's part of the Hershey's Cabal. That's secretly organizing 0:03:18.240 --> 0:03:18.840 the whole universe. 0:03:18.880 --> 0:03:21.640 Oh you've been you've been blacklisted or dark chocolate listed. 0:03:21.919 --> 0:03:23.000 Yeah, milk chocolated. 0:03:23.160 --> 0:03:28.520 That's what you get for insulting hours that be accessible 0:03:28.560 --> 0:03:30.800 chocolate to the masses. Yeah, but you can still come 0:03:30.840 --> 0:03:31.400 to the universe. 0:03:31.440 --> 0:03:33.079 I guess, all right, thank you, you give. 0:03:32.960 --> 0:03:38.280 Be somebody's plus one. Just don't invite physicist, maybe because 0:03:38.280 --> 0:03:40.880 there they'll prefer to be on the outside of the 0:03:40.960 --> 0:03:42.240 universe looking in. 0:03:42.720 --> 0:03:44.520 No. I love being the part of the universe that's 0:03:44.560 --> 0:03:48.400 looking at itself, right. That's what makes the questions so important. 0:03:48.720 --> 0:03:51.280 That we're not outside the universe studying it like some 0:03:51.320 --> 0:03:54.839 weird objects. It's part of our context, our lives. It's 0:03:54.880 --> 0:03:58.320 our existence that we're trying to understand. Physics is sometimes 0:03:58.360 --> 0:04:00.880 sold is like bigger than human But to me, it's 0:04:00.920 --> 0:04:04.680 the fundamental question of humanity, answering the deepest questions about 0:04:04.680 --> 0:04:05.600 our own existence. 0:04:05.880 --> 0:04:09.040 Is it sold as bigger as humanities? Where is that listed? 0:04:10.240 --> 0:04:12.760 That's how it was sold to me. I guess, so 0:04:12.840 --> 0:04:15.520 maybe I shouldn't generalize from any equals one. But one 0:04:15.560 --> 0:04:18.760 reason I got into physics originally was that it seemed 0:04:18.800 --> 0:04:22.200 like the questions were universal, They weren't limited to things 0:04:22.200 --> 0:04:25.000 happening on Earth. You know, you study biology, and you 0:04:25.040 --> 0:04:28.200 know it's fascinating and important, but it might be very 0:04:28.200 --> 0:04:29.480 different on other planets. 0:04:30.040 --> 0:04:35.200 Maybe that's why you're not invited, Daniel. You think you're 0:04:35.240 --> 0:04:36.280 bigger than the rest of us. 0:04:36.360 --> 0:04:38.440 I think some of the pelophysics is that it does 0:04:38.520 --> 0:04:41.120 seem to be universal, though of course we don't know, 0:04:41.240 --> 0:04:43.599 and that's a question we can only answer in the 0:04:43.600 --> 0:04:45.120 future when we meet aliens. 0:04:45.839 --> 0:04:48.360 I guess it does sort of tap into that sense 0:04:48.400 --> 0:04:51.200 of the cosmos, the grand pictures that we all kind 0:04:51.200 --> 0:04:53.400 of have inside of us. And it is pretty amazing 0:04:53.440 --> 0:04:56.360 what we've been able to understand and study and come 0:04:56.400 --> 0:04:58.640 to terms with in terms of where we are in 0:04:58.720 --> 0:05:01.960 the universe, within our Solar System, within our galaxy, within 0:05:02.000 --> 0:05:05.960 our supercluster of galaxies, within the observable universe. It's pretty 0:05:06.000 --> 0:05:08.200 amazing that we can see so much structure out there 0:05:08.360 --> 0:05:10.440 just by looking out to the night sky. 0:05:10.640 --> 0:05:13.160 Yeah, it's amazing what we know about the universe, never 0:05:13.240 --> 0:05:17.239 having left our tiny little neighborhood. Everything we know about 0:05:17.240 --> 0:05:20.080 the structure of galaxies and superclusters and all that stuff 0:05:20.320 --> 0:05:22.560 is based just on the few photons that happen to 0:05:22.640 --> 0:05:25.679 hit Earth from those distant locations. It would be incredible 0:05:25.760 --> 0:05:27.480 to get in a warp ship and like actually visit 0:05:27.520 --> 0:05:30.200 some of these places and learn more about what's actually 0:05:30.200 --> 0:05:32.760 going on there right now. But we can do a 0:05:32.800 --> 0:05:36.040 pretty impressive job even from here. But of course, there 0:05:36.040 --> 0:05:39.760 are still lots of unanswered questions about how solar systems form, 0:05:40.120 --> 0:05:42.480 what planets there are in our Solar system, what planets 0:05:42.480 --> 0:05:45.480 there have been in our Solar system, and larger questions 0:05:45.520 --> 0:05:48.839 about galaxies, why they exist, how they form, and why 0:05:48.920 --> 0:05:50.520 they take their weird shapes. 0:05:50.839 --> 0:05:53.359 That's right, because we're orbiting around our Sun, and the 0:05:53.400 --> 0:05:56.200 Sun is orbiting in a galaxy, which is a huge 0:05:56.240 --> 0:06:00.040 cluster of stars. There are one hundred billion stars in 0:06:00.040 --> 0:06:03.160 the Milky Way galaxy. But how these galaxies get form 0:06:03.360 --> 0:06:05.640 is kind of a still up in the air, right. 0:06:05.760 --> 0:06:08.279 It is, And it's an important question because galaxies are 0:06:08.360 --> 0:06:11.480 kind of the basic building block of the universe. They're 0:06:11.520 --> 0:06:13.560 like the atoms of the universe from which you can 0:06:13.600 --> 0:06:17.000 put together structures and superstructures and all sorts of other stuff. 0:06:17.120 --> 0:06:20.240 It's incredible that like galaxies actually exist and they tend 0:06:20.240 --> 0:06:23.000 to be a certain size so it's an important thing 0:06:23.040 --> 0:06:26.040 to understand, like why are universe features galaxies? How they 0:06:26.040 --> 0:06:29.039 come to be, how long they will continue to be 0:06:29.160 --> 0:06:30.880 the basic building block of the universe? 0:06:31.160 --> 0:06:34.120 Yeah, and why do they have some strange features? And 0:06:34.160 --> 0:06:36.279 so today on the podcast we'll be asking the question 0:06:41.600 --> 0:06:46.679 why do some galaxies have bars? Are these like drinking bars? 0:06:46.720 --> 0:06:49.080 Like our galaxy has a bar, can go and get 0:06:49.080 --> 0:06:49.560 a drink. 0:06:49.720 --> 0:06:51.800 There's definitely bars in our galaxy, right, I've been to 0:06:51.839 --> 0:06:54.000 some of them. So that's a question we can definitively 0:06:54.080 --> 0:06:55.280 answer today on the podcast. 0:06:55.640 --> 0:06:57.760 They seem to be closer around Earth at least all 0:06:57.760 --> 0:07:00.200 the bars we know are on Earth. Is that kind 0:07:00.200 --> 0:07:05.280 of a physics question or is a biology question? 0:07:05.480 --> 0:07:08.640 Well? I think there's some history of drinking alcohol in space, right. 0:07:09.000 --> 0:07:11.320 I think Zach and Kelly's new book has some stories 0:07:11.360 --> 0:07:14.480 about astronauts who have smuggled things up to the ISS, 0:07:14.760 --> 0:07:17.560 So perhaps there is an unofficial bar off Earth as well. 0:07:19.440 --> 0:07:22.000 I wonder if anyone has tried a like brew beer 0:07:22.320 --> 0:07:23.360 on the space station. 0:07:24.120 --> 0:07:28.720 Space moonshine, either purpose or by accident. The Moon does 0:07:28.760 --> 0:07:30.680 shine more brightly in space, so maybe it's easier to 0:07:30.680 --> 0:07:33.600 make moonshine m there you go. Yeah, And so of 0:07:33.640 --> 0:07:36.800 course we don't know if aliens enjoy relaxing in bars 0:07:36.920 --> 0:07:39.600 or whether they like Hershey's chocolate in their chocolate tenies. 0:07:40.040 --> 0:07:42.360 But today we're not talking about places to drink. We're 0:07:42.360 --> 0:07:45.560 talking about the structures at the centers of galaxies. 0:07:46.400 --> 0:07:48.560 I see. So when you say a galaxy bar, it's 0:07:48.600 --> 0:07:52.520 not like a like a buffet bar or a beer bar. 0:07:53.000 --> 0:07:55.160 It's more like a destructor. Is a structure in a 0:07:55.200 --> 0:07:58.560 galaxy that looks like a bar or a structures multiple ones. 0:07:58.680 --> 0:08:00.920 Yeah, there's a kind of galaxy out there called a 0:08:01.080 --> 0:08:04.720 barred galaxy, but not every galaxy has this kind of 0:08:04.760 --> 0:08:07.120 bar at the center, and so it's an open question 0:08:07.360 --> 0:08:09.560 about why some galaxies have bars. 0:08:09.960 --> 0:08:11.880 Well, as usually, we were wondering how many people out 0:08:11.920 --> 0:08:15.360 there had thought about galaxy bars and why some galaxies 0:08:15.360 --> 0:08:18.440 have them, why some don't? Are they over twenty one? 0:08:18.680 --> 0:08:20.520 Can you get your favorite drinks in them? And so 0:08:20.640 --> 0:08:22.520 Daniel went out there into the internet to find out 0:08:22.720 --> 0:08:24.680 what people think about this question. 0:08:24.840 --> 0:08:28.000 And whether you like salad bars or chocolate bars or 0:08:28.040 --> 0:08:30.520 any other kind of bar, You are welcome to participate 0:08:30.560 --> 0:08:32.640 in this segment of the podcast. Just write to meet 0:08:32.679 --> 0:08:36.040 you questions at Danielandjorge dot com and I'll set you up. 0:08:36.120 --> 0:08:37.520 So think about it for a second. Why do you 0:08:37.559 --> 0:08:41.400 think some galaxies have bars? Here's what peop glad to say. 0:08:42.040 --> 0:08:45.559 So I didn't know galaxies had bars in the center. 0:08:46.400 --> 0:08:50.680 So I'm going to say maybe it has it because 0:08:51.440 --> 0:08:55.920 gravity is aliding them in a special way, but can't 0:08:55.920 --> 0:08:59.480 be made into sphere because of the black holes gravity. 0:09:00.960 --> 0:09:05.040 I think planets don't share orbits because the center of 0:09:05.080 --> 0:09:09.440 gravity would have to be absolutely stationary or it would 0:09:09.480 --> 0:09:13.320 oscillate and shake itself out of sync. I think that 0:09:13.400 --> 0:09:18.160 the bars in the center of galaxies are there to 0:09:18.200 --> 0:09:22.040 give people somewhere to go. But like if women's clothes 0:09:22.080 --> 0:09:25.679 shops have bars, they have somewhere for men to go 0:09:25.760 --> 0:09:28.120 instead of trying to look interested. 0:09:28.559 --> 0:09:31.720 I expect that galaxies have bars at their centers because 0:09:31.760 --> 0:09:33.520 you're going to need a place to kill some time 0:09:33.559 --> 0:09:36.840 and have have a beer if your interstellar flight is delayed. 0:09:37.120 --> 0:09:40.800 I have no idea what does a bar in the 0:09:40.880 --> 0:09:41.920 center of abilitum? 0:09:42.960 --> 0:09:46.319 All right, some fun ideas here, some of them a 0:09:46.400 --> 0:09:47.520 little bit inappropriate. 0:09:47.559 --> 0:09:51.080 Perhaps I think this might be the highest fraction of 0:09:51.200 --> 0:09:54.320 joke answers we've ever gotten, which means people really just 0:09:54.360 --> 0:09:56.240 don't know anything about bars and galaxies. 0:10:00.000 --> 0:10:03.000 Maybe they're just a barring and not knowing anything about them. 0:10:03.679 --> 0:10:05.600 Or maybe they'd already spent too much time at a 0:10:05.600 --> 0:10:07.400 bar when they got these questions and they were in 0:10:07.480 --> 0:10:08.040 silly mood. 0:10:08.280 --> 0:10:11.240 Oh there you go. Yeah, maybe you shouldn't send these 0:10:11.320 --> 0:10:12.920 questions up during happy. 0:10:12.720 --> 0:10:16.280 Hours Monday morning nine am. Is that what happy hour is? 0:10:17.160 --> 0:10:22.280 Yeah? Depends on how much you led your job, I guess. 0:10:22.240 --> 0:10:24.000 And where you are in the world. Right, we have 0:10:24.080 --> 0:10:25.920 listeners all over the world. 0:10:26.200 --> 0:10:29.760 Yeah, we are a global podcast. All right, Well, Daniel, 0:10:30.040 --> 0:10:32.360 maybe step us through this. What exactly do you mean 0:10:32.840 --> 0:10:34.400 by a galaxy bar? 0:10:35.200 --> 0:10:39.719 So, galaxy bars are features of one particular kind of galaxy, 0:10:40.200 --> 0:10:42.560 and galaxies, it turns out, can have all sorts of 0:10:42.600 --> 0:10:45.600 different shapes in them. Galaxies, of course, are clusters of 0:10:45.640 --> 0:10:48.400 stars and they can be very very small, from dwarf 0:10:48.440 --> 0:10:52.520 galaxies that have thousands of stars to super mega galaxies 0:10:52.520 --> 0:10:55.360 that have billions and billions of stars. But we tend 0:10:55.440 --> 0:10:57.320 to notice some features in them. And you know, the 0:10:57.360 --> 0:11:00.440 beginning of any science is basically just bought it, just 0:11:00.480 --> 0:11:03.400 like look at it. Categorize it, sort it, see what 0:11:03.520 --> 0:11:07.360 patterns emerge. And very early on when people were studying galaxies, 0:11:07.400 --> 0:11:09.920 they noticed that they could have different structures, even things 0:11:09.960 --> 0:11:12.840 we could see here from Earth with limited telescopes. 0:11:13.200 --> 0:11:15.560 Right, And we've talked a little bit about before the 0:11:15.600 --> 0:11:18.319 different shapes that galaxies can have, right, And they can 0:11:18.360 --> 0:11:20.800 be sort of like a blob like a football, or 0:11:20.800 --> 0:11:23.760 maybe like a spiral, or maybe just like a pancake. 0:11:23.880 --> 0:11:26.760 Right, yeah, exactly. And there are regular galaxies that are 0:11:26.760 --> 0:11:30.040 probably in the process of merging between two galaxies. There 0:11:30.080 --> 0:11:32.240 is a galaxy out there that looks like a question mark, 0:11:32.280 --> 0:11:35.480 for example. But the most common galaxy out there is 0:11:35.520 --> 0:11:36.760 a spiral galaxy. 0:11:37.240 --> 0:11:39.800 How common is it and is it like fifty? 0:11:40.400 --> 0:11:43.280 It's somewhere around two thirds of all the galaxies that 0:11:43.320 --> 0:11:46.720 we have studied, our spiral galaxies. And there's a reason 0:11:46.720 --> 0:11:48.120 for that. And we went into all of that in 0:11:48.160 --> 0:11:51.760 our recent podcast about the various shapes that galaxies can have. 0:11:52.360 --> 0:11:56.200 But basically, galaxies form from huge blobs of gas which 0:11:56.280 --> 0:11:59.160 spin and collapse and then form a disc. And that 0:11:59.240 --> 0:12:02.640 dense disc gas tends to form those stars, and the 0:12:02.640 --> 0:12:05.560 spinning of the galaxy turns that disc into a spiral. 0:12:06.240 --> 0:12:08.640 That's kind of like the default shape of a galaxy, right, 0:12:09.120 --> 0:12:11.280 But then you can get other shapes, as we talked about, 0:12:11.280 --> 0:12:13.920 when they merge with each other, other galaxies or they 0:12:13.960 --> 0:12:16.240 crash into other galaxies. 0:12:15.840 --> 0:12:18.240 Right exactly. So a spiral galaxy is like the basic 0:12:18.280 --> 0:12:20.600 building block of the universe in that sense, it's the 0:12:20.600 --> 0:12:23.599 most important one to understand because the other ones, ellipticals 0:12:23.600 --> 0:12:26.760 and irregulars are all made out of spiral galaxies. And 0:12:27.120 --> 0:12:29.719 also our galaxy is a spiral galaxy. So if we're 0:12:29.720 --> 0:12:32.160 going to understand like the context of our lives, let's 0:12:32.160 --> 0:12:32.720 begin at. 0:12:32.600 --> 0:12:35.600 Home, right, And I guess maybe just to paint the 0:12:35.640 --> 0:12:38.280 picture for folks, by a spiral, it sort of looks 0:12:38.320 --> 0:12:41.880 like a like a toilet flushing, right, Like, It's not 0:12:42.000 --> 0:12:44.680 like one like they're tracing out a spiral with a 0:12:44.720 --> 0:12:48.000 pen and a paper. It's more like a swirl that's 0:12:48.240 --> 0:12:49.560 kind of converging in the middle. 0:12:49.800 --> 0:12:52.200 Yeah, And the spiral galaxy usually has several arms. They 0:12:52.200 --> 0:12:54.680 can have two, sometimes they have three. There are galaxies 0:12:54.720 --> 0:12:57.040 out there with four arms. Each one is like a 0:12:57.040 --> 0:13:00.000 spiral that usually goes like one time around. The galaxy 0:13:00.040 --> 0:13:02.600 starts from the center and then comes out, So it's 0:13:02.640 --> 0:13:04.440 sort of more like a pinwheel. 0:13:04.000 --> 0:13:06.240 Right, So that gives you the image of the spiral galaxy. 0:13:06.679 --> 0:13:09.520 And so that's the basic shape of most galaxies out there. 0:13:09.559 --> 0:13:11.600 But you say, you're saying some of them have a 0:13:11.640 --> 0:13:13.400 bar through them or on them. 0:13:13.360 --> 0:13:15.840 At the center. Some galaxies don't have bars. The spiral 0:13:15.920 --> 0:13:18.160 arms just start at the very center. But a good 0:13:18.160 --> 0:13:21.120 fraction galaxy is the center of them. Isn't part of 0:13:21.120 --> 0:13:23.640 the spiral arm. It's a separate thing. It's like a bar. 0:13:24.160 --> 0:13:27.280 Like the Milky Way galaxy has this big blob of 0:13:27.440 --> 0:13:29.640 stars and gas and dust at the center of it, 0:13:29.679 --> 0:13:32.520 which forms this big bar and the spiral arm that 0:13:32.559 --> 0:13:35.360 comes out of each end of the bar. So the 0:13:35.360 --> 0:13:37.600 spirals don't go to the very center of the galaxy. 0:13:37.640 --> 0:13:39.320 They start at the edges of this bar. 0:13:39.800 --> 0:13:42.719 WHOA, wait, wait, wait too, you're saying our Milky Way 0:13:42.760 --> 0:13:43.560 galaxy is a bar. 0:13:44.160 --> 0:13:45.880 Yes, we live in a bar galaxy. 0:13:46.160 --> 0:13:49.400 Whoa is it a milk chocolate bar? Since we're the 0:13:49.440 --> 0:13:49.920 Milky Way. 0:13:50.920 --> 0:13:52.679 Now I'm afraid to answer because I don't want to 0:13:52.720 --> 0:13:55.600 anger the Hershey universe cabal that's in charge of everything. 0:13:55.800 --> 0:13:59.920 Yeah, what if the Milky Way is a hercheese product. 0:14:00.240 --> 0:14:02.040 This is why it's so important for science to be 0:14:02.200 --> 0:14:04.480 free of this kind of oppression. People should feel free 0:14:04.520 --> 0:14:06.400 to speak their minds on chocolate, right. 0:14:06.400 --> 0:14:10.200 Well, people shouldn't disparage other people if theyread chocolate. I 0:14:10.200 --> 0:14:14.240 think that is maybe the most important part of your yeah, 0:14:14.320 --> 0:14:16.880 se point take. But our Milky Way is a bar? 0:14:16.960 --> 0:14:20.480 Are you saying so? Like our spirals, the arms of 0:14:20.520 --> 0:14:25.480 our galaxy don't spiral into a single blob in the middle. 0:14:25.560 --> 0:14:27.360 It's they spiral into a bar. 0:14:27.720 --> 0:14:30.720 That's right. Our galaxy is two major arms, and then 0:14:30.760 --> 0:14:33.400 there's some spurs that come off of them, and each 0:14:33.560 --> 0:14:36.200 arm comes from a different side of the bar. So 0:14:36.240 --> 0:14:38.840 the two major spirals that make the Milky Way galaxy, 0:14:39.080 --> 0:14:41.800 they don't actually meet at the center. They come to 0:14:41.880 --> 0:14:44.400 different sides of this bar that's at the core of 0:14:44.440 --> 0:14:45.080 the galaxy. 0:14:45.160 --> 0:14:47.840 Interesting, the picture I'm getting is sort of like I 0:14:47.880 --> 0:14:50.480 don't know if you've seen those like Hawaiian fire dancers 0:14:50.720 --> 0:14:52.800 where they have a stick and at each end of 0:14:52.800 --> 0:14:56.040 the stick it's on fire and so then they spin it. 0:14:56.200 --> 0:14:58.560 That's kind of sort of what's the picture that we 0:14:58.640 --> 0:15:01.360 get of the Milky Way galaxy? Isn't it like there's 0:15:01.400 --> 0:15:03.560 a bar and from the each end of the bar 0:15:03.960 --> 0:15:06.120 you get these swirls that spiral out. 0:15:06.320 --> 0:15:08.560 Well, I am not fancy enough to take vacations to Hawaii. 0:15:08.680 --> 0:15:11.240 Tend to spend my money on chocolate instead. But it 0:15:11.320 --> 0:15:12.040 sounds accurate. 0:15:12.400 --> 0:15:14.920 You know that you can get chocolate in Hawaii. In fact, 0:15:14.960 --> 0:15:18.120 it's kind of known for they're kind of known for 0:15:18.160 --> 0:15:18.960 having good chocolate. 0:15:19.760 --> 0:15:23.040 Macademian that chocolate here, I come, there you go. But yeah, 0:15:23.040 --> 0:15:25.240 that sounds accurate. Wow. Or if you imagine like a 0:15:25.240 --> 0:15:28.520 baton twirler at a football game and ribbons at the 0:15:28.600 --> 0:15:31.400 end of the baton. If he or she spins the baton, 0:15:31.480 --> 0:15:34.600 then the ribbons spiral around it. But the ribbons, of course, 0:15:34.600 --> 0:15:36.480 don't meet at the very center. They come from the 0:15:36.600 --> 0:15:37.320 edges of the bed. 0:15:38.400 --> 0:15:41.160 Now, this is an interesting idea just because to me 0:15:41.240 --> 0:15:43.560 and I wonder if to a lot of our listeners 0:15:43.600 --> 0:15:46.080 this is kind of news. Right, Like most of the 0:15:46.080 --> 0:15:48.040 time that you see a picture or a drawing of 0:15:48.080 --> 0:15:50.160 the milk Away Galaxy, they don't it doesn't have the 0:15:50.280 --> 0:15:53.280 bar in the middle, right like the famous isn't the 0:15:53.320 --> 0:15:55.880 famous image of like you are here? Or it points 0:15:55.880 --> 0:15:57.800 to a point in the Milk Away. Of a drawing 0:15:57.840 --> 0:16:00.080 of the milk Away that one doesn't have a bar, 0:16:00.200 --> 0:16:00.720 I don't think. 0:16:00.920 --> 0:16:02.520 Yeah, that's a good point. I'm not sure if that 0:16:02.600 --> 0:16:06.040 image is scientifically vetted. It also really doesn't have big 0:16:06.120 --> 0:16:09.280 distinct arms the way you might expect, But a more 0:16:09.320 --> 0:16:12.880 scientifically accurate picture of the Milky Way shows the specific 0:16:13.040 --> 0:16:15.520 arms and the bar. The bar is not like a 0:16:15.640 --> 0:16:19.440 very rigid rod. It's a bit of a blob also to. 0:16:19.440 --> 0:16:22.760 Me now of stars, like a just an elongated cluster 0:16:22.840 --> 0:16:23.400 of stars. 0:16:23.720 --> 0:16:26.160 Yeah, it's stars, and it's gas and it's dust like 0:16:26.200 --> 0:16:28.520 the rest of the galaxy. But you know, this is 0:16:28.680 --> 0:16:32.560 us imposing order on a huge swirling mass of stuff. 0:16:32.920 --> 0:16:34.760 So part of this, of course, is just the impression 0:16:34.840 --> 0:16:38.160 we make, how our brains filter the full details of 0:16:38.400 --> 0:16:40.360 the buzzing chaos of reality. 0:16:41.360 --> 0:16:43.240 All right, Well, so then the Milkway has a bar. 0:16:43.720 --> 0:16:46.880 Lots of galaxies maybe have bars in the middle of them, 0:16:47.000 --> 0:16:49.320 and so the question is why do they have bars, 0:16:50.160 --> 0:16:51.960 What's going on there in the middle of the galaxy? 0:16:52.360 --> 0:16:55.840 And can you play galactic limbo with that bar? And 0:16:55.880 --> 0:16:58.800 so let's get to these deep and profound questions. But 0:16:58.880 --> 0:17:14.399 first let's take a quick all right, we're talking about 0:17:14.480 --> 0:17:16.720 the Milky Way galaxy and the fact that it has 0:17:16.720 --> 0:17:19.600 a bar of stars in the middle. The swirls of 0:17:19.640 --> 0:17:22.480 the galaxy don't converge to a round blob in the middle. 0:17:22.520 --> 0:17:25.240 They converse to kind of like a rod of stars. Right. 0:17:26.000 --> 0:17:27.679 Yeah, it might be more accurate to call it like 0:17:27.680 --> 0:17:30.520 a football because it's a little wider in the center 0:17:30.640 --> 0:17:32.959 than it is at the edges. But yeah, there's sort 0:17:32.960 --> 0:17:33.640 of a long. 0:17:33.440 --> 0:17:37.760 But it's not a bar. Why don't we just call 0:17:37.800 --> 0:17:38.719 them football galaxy? 0:17:38.840 --> 0:17:44.240 Football galaxy? That sounds great. I am done defending the 0:17:44.320 --> 0:17:46.360 naming schemes of astronomy. 0:17:47.640 --> 0:17:50.720 Because it's indefensible, because you just can't do it. 0:17:50.800 --> 0:17:52.960 Sorry, astronomers, you have no champion in me anymore. 0:17:53.040 --> 0:17:55.760 Oh boy, you're throwing the astronomers under the bus. 0:17:56.119 --> 0:17:57.120 No, I'm just throwing. 0:18:00.440 --> 0:18:02.200 Naming peculiarities. 0:18:02.440 --> 0:18:04.879 Oh, it certainly does. And nobody's ever asked me my 0:18:04.960 --> 0:18:06.959 opinion when they make up these names. 0:18:07.160 --> 0:18:09.560 Okay, So the Milky Way has a bar or football 0:18:09.680 --> 0:18:11.440 kind of in the middle, which is weird, right, because 0:18:11.440 --> 0:18:14.800 you would expect a galaxy to be sort of, you know, 0:18:14.920 --> 0:18:16.119 round and symmetric, right. 0:18:16.119 --> 0:18:18.399 You would kind of expect it. And that's exactly why 0:18:18.440 --> 0:18:21.320 we are really interested in these questions like what structures 0:18:21.400 --> 0:18:24.480 form in the universe. The answer to that question reveals 0:18:24.560 --> 0:18:28.080 the forces at play. Like wire galaxies created in the 0:18:28.119 --> 0:18:31.440 first place, Well, there's gravity, why don't they just collapse 0:18:31.480 --> 0:18:34.560 into a central ball, while there's angular momentum that turns 0:18:34.560 --> 0:18:37.320 them into disks? Why do the arms form at all? 0:18:37.560 --> 0:18:39.960 Well, maybe a question we can ask here is like 0:18:40.119 --> 0:18:42.919 what percentage of galaxies are barred galaxies? Like, is the 0:18:42.920 --> 0:18:45.480 Milky Way super weird that it has a bar? Or 0:18:45.600 --> 0:18:48.560 is it like most spiral galaxies have bars or some 0:18:48.600 --> 0:18:49.680 of them or fifty to fifty. 0:18:49.880 --> 0:18:52.639 That's a really interesting question, and the answer depends on 0:18:52.680 --> 0:18:55.560 the mass of the galaxy in a super weird way 0:18:56.200 --> 0:18:58.600 for galaxies about the mass of the Milky Way, like 0:18:58.720 --> 0:19:02.920 billions and billions of solar masses. It's around two thirds 0:19:02.960 --> 0:19:07.280 of spiral galaxies that have bars. The more massive the galaxy, 0:19:07.440 --> 0:19:10.240 the smaller the fraction of the spirals have bars. And 0:19:10.440 --> 0:19:14.159 also the less massive the galaxy, the smaller fraction have bars. 0:19:14.640 --> 0:19:16.719 So there is this like sweet spot in the middle 0:19:16.880 --> 0:19:19.800 where galaxies are more likely to have bars. And if 0:19:19.840 --> 0:19:22.639 you move away from that lower mass or higher mass, 0:19:23.000 --> 0:19:25.920 then the fraction that have bars decreases. 0:19:25.880 --> 0:19:28.639 M interesting, So it depends on the size and mass 0:19:28.640 --> 0:19:31.000 of the galaxy. But maybe let's take a back to 0:19:31.040 --> 0:19:33.119 the basics, because it sounds like there's a lot of 0:19:33.520 --> 0:19:36.640 physics lying on here, as you might expect from our podcasts, 0:19:37.000 --> 0:19:41.040 But so what's going on at the center? Like how 0:19:41.080 --> 0:19:43.359 can this bar still be there after all these billions 0:19:43.359 --> 0:19:43.800 of years? 0:19:43.920 --> 0:19:47.199 It all comes from asymmetries like little over densities. If 0:19:47.240 --> 0:19:49.919 you start from a galaxy that was perfectly smooth, like 0:19:50.000 --> 0:19:52.919 all the matter was evenly distributed, or like you had 0:19:52.920 --> 0:19:55.880 a cluster of stars that were perfectly distributed in circles 0:19:55.880 --> 0:19:59.240 on perfectly circular orbits, then it wouldn't form a bar. 0:20:00.040 --> 0:20:02.320 You tweak it a little bit, like one little spot 0:20:02.359 --> 0:20:05.240 has more density than another spot, then that spot's going 0:20:05.280 --> 0:20:07.440 to have more gravity and it's going to attract more 0:20:07.480 --> 0:20:10.919 stars to it, and so you get these density waves 0:20:10.960 --> 0:20:14.679 forming inside the galaxy. So the same process that forms 0:20:14.720 --> 0:20:17.639 the arms, theives density waves of the arms that we 0:20:17.680 --> 0:20:20.960 describe as like traffic passing through a freeway, can also 0:20:21.080 --> 0:20:24.199 form density structures in the center of the galaxy and 0:20:24.240 --> 0:20:25.880 in this case, they form bars. 0:20:26.560 --> 0:20:28.880 Well, yeah, I remember we spent a whole episode talking 0:20:28.880 --> 0:20:32.560 about this idea of density waves in a galaxy. It's 0:20:32.560 --> 0:20:34.640 not like the arm of a galaxy what you see 0:20:34.640 --> 0:20:37.320 as a soirl like, it doesn't rotate around the galaxy. 0:20:37.800 --> 0:20:40.840 It's more like a ripple through a whole bunch of stars. 0:20:41.119 --> 0:20:43.600 Exactly. It's more like a ripple. It's like people doing 0:20:43.640 --> 0:20:46.960 the wave in a football stadium. They're not moving sidewaves, 0:20:46.960 --> 0:20:50.080 but the wave itself is moving, right, And so the 0:20:50.119 --> 0:20:53.560 galaxy arms are waves in the density of stars, and 0:20:53.600 --> 0:20:56.399 the bar is the same way. The bar is like 0:20:56.440 --> 0:20:59.560 a density wave. So it's a structure that forms, but 0:20:59.640 --> 0:21:02.320 it moves through the stars. It doesn't move at the 0:21:02.320 --> 0:21:05.960 same speed the stars are moving around the galaxy. It 0:21:06.000 --> 0:21:07.760 can move faster, it can move slower. 0:21:08.160 --> 0:21:09.760 Wait, what do you mean the bar? Does a bar 0:21:09.920 --> 0:21:13.720 rotate and bar devastates moving like, which direction is the 0:21:13.760 --> 0:21:14.240 bar moving? 0:21:14.480 --> 0:21:17.600 The bar rotates the same direction as the galaxy and 0:21:17.640 --> 0:21:18.680 it definitely rotates. 0:21:18.840 --> 0:21:20.720 Oh, kind of like the arms and a clock. 0:21:21.119 --> 0:21:22.960 Kind of like the arms and a clock, and also 0:21:23.119 --> 0:21:26.200 like the arms of the galaxy. Right, because the arms 0:21:26.240 --> 0:21:30.679 are density waves, they move relative to the stars, So 0:21:30.760 --> 0:21:32.600 one star might be in the density wave and then 0:21:32.640 --> 0:21:35.159 they'll get passed by the density wave which moves on. 0:21:35.640 --> 0:21:38.960 WHOA are there like videos online about this? That would 0:21:39.000 --> 0:21:39.840 be cool to see. 0:21:39.680 --> 0:21:42.080 You mean, like actual footage of bars rotating, not. 0:21:42.280 --> 0:21:43.639 Like a simulation or something. 0:21:43.720 --> 0:21:45.440 Yeah, I would love to see that, but the time 0:21:45.480 --> 0:21:47.960 scales are ridiculous, Like the Milky Way takes two hundred 0:21:47.960 --> 0:21:51.600 and fifty million years to rotate, So there's no chance 0:21:51.640 --> 0:21:54.800 for like, watch a galaxy rotate unless you're gonna set 0:21:54.840 --> 0:21:56.560 it your camera for tens of millions of years. 0:21:56.600 --> 0:21:58.120 So wait, how do we know it's rotating. 0:21:58.560 --> 0:22:00.840 Well, we build up a model of how galaxy works 0:22:00.880 --> 0:22:03.639 that includes angular momentum, and you need those components that 0:22:03.760 --> 0:22:07.080 rotation to explain what we see. If they weren't rotating, 0:22:07.200 --> 0:22:09.920 there's no anglar momentum, and these things would collapse a 0:22:09.960 --> 0:22:12.119 lot faster. A lot of galaxies and a lot of these 0:22:12.119 --> 0:22:15.440 structures are supported by angular momentum. Like, where else would 0:22:15.440 --> 0:22:17.840 the spiral arms come from if it wasn't spinning. 0:22:18.320 --> 0:22:18.760 I don't know. 0:22:19.160 --> 0:22:21.440 Yeah, So we do a lot of simulations to try 0:22:21.440 --> 0:22:23.480 to explain the galaxies we see. We said, well, we 0:22:23.480 --> 0:22:25.480 think we understand all the forces at play. We put 0:22:25.480 --> 0:22:27.320 it in the computer, we press the button, it goes, 0:22:27.320 --> 0:22:29.359 and we see what comes out of the simulation. Then 0:22:29.400 --> 0:22:32.200 we compare that to what we see in the sky. Interesting, 0:22:32.320 --> 0:22:34.639 that's what we do to try to explain what's happening 0:22:34.720 --> 0:22:37.000 or try to gain some understanding of the forces at work. 0:22:37.160 --> 0:22:40.800 Wow, so nobody's ever actually seen a galaxy swirling. We 0:22:40.960 --> 0:22:44.840 just think it does. I mean, it's the most likely 0:22:44.960 --> 0:22:47.960 or obvious explanation, but still it's a fact that we 0:22:48.040 --> 0:22:51.440 haven't seen a galaxy swirl. Like, we've only seen a 0:22:51.480 --> 0:22:53.840 photograph of it. It's like you've only seen a photograph 0:22:54.280 --> 0:22:57.159 where Merry go round. Ever, like you've never seen a 0:22:57.160 --> 0:22:58.280 mirror go around move. 0:23:00.000 --> 0:23:02.480 Well, that's true when we've only even known about other 0:23:02.560 --> 0:23:05.760 galaxies for like one hundred years. It was Hubble who 0:23:05.760 --> 0:23:08.920 saw these little smudges in the sky and deduced their 0:23:09.000 --> 0:23:13.920 distance from analyzing special stars in them, the sephids, whose brightness, 0:23:13.920 --> 0:23:17.439 of course is famously connected to their pulsing frequency. And 0:23:17.480 --> 0:23:19.680 he's the one that understood that these things were outside 0:23:19.800 --> 0:23:23.280 our galaxy. So we only known that other galaxies exist 0:23:23.400 --> 0:23:26.119 for like one hundred years and had good enough telescopes 0:23:26.160 --> 0:23:29.560 to like resolve their structure for a few decades, which 0:23:29.600 --> 0:23:32.680 is basically no time at all relative to their actual emotion. 0:23:33.160 --> 0:23:36.240 So yeah, we're studying galaxies basically frozen in time. 0:23:36.720 --> 0:23:40.439 Well that's interesting. Now you're saying that about two thirds 0:23:40.440 --> 0:23:43.160 of galaxies have a bar in the middle of them, 0:23:43.400 --> 0:23:46.560 and this bar is rotating and rippling through the center 0:23:47.119 --> 0:23:50.040 of the galaxy. Like what's the mechanism for making these bars? 0:23:50.160 --> 0:23:52.240 Like why not? Why a bar shape? Why not a 0:23:52.320 --> 0:23:55.240 star shape or a banana shape. 0:23:56.359 --> 0:23:58.159 I would love to see a banana shape at the 0:23:58.200 --> 0:24:01.240 center of galaxy and probably some galaxy out there that 0:24:01.320 --> 0:24:03.960 has that, because there's so many galaxies out there and 0:24:04.000 --> 0:24:05.840 so many of them are doing weird things. 0:24:06.000 --> 0:24:08.760 I guess if you think about a galaxy, is banana shape, 0:24:08.800 --> 0:24:10.760 Like each arm is like a banana. So it's like 0:24:10.800 --> 0:24:13.680 if you take if you take several bananas and arrange 0:24:13.720 --> 0:24:16.840 them in a star shape, you would get a spiral galaxy. 0:24:16.920 --> 0:24:19.120 Right, Yeah, that's true. That's a message from the universe 0:24:19.480 --> 0:24:21.040 that bananas are important, and you. 0:24:21.000 --> 0:24:23.800 Start with them in chocolate this they're galactic. 0:24:25.160 --> 0:24:28.000 And that's why we sell frozen chocolate covered bananas here 0:24:28.040 --> 0:24:28.920 in Orange County. 0:24:29.040 --> 0:24:31.800 That is the purpose of the universe, isn't it? Is 0:24:31.800 --> 0:24:39.840 it deep fried too? Why not fried chocolate covered bananas? 0:24:41.040 --> 0:24:43.160 I think I've had that at a restaurant, actually. 0:24:43.040 --> 0:24:45.960 But you asked a great question that wasn't about dessert, 0:24:46.000 --> 0:24:48.800 which is why do some galaxies have bars? Why do 0:24:48.840 --> 0:24:51.560 they form bar shapes and not other things? And the 0:24:51.560 --> 0:24:54.400 answer is that we're not sure, Like we don't understand 0:24:54.440 --> 0:24:57.920 why some galaxies form bars and some don't. We don't 0:24:58.080 --> 0:25:02.240 totally understand the mechanism for the formation itself. Like we've 0:25:02.240 --> 0:25:05.560 seen this happen in simulation sometimes and it comes out 0:25:05.600 --> 0:25:07.960 of instabilities. You put a bunch of stars a little 0:25:07.960 --> 0:25:10.200 bit closer to each other, they tend to form these 0:25:10.240 --> 0:25:13.840 density waves. And what's happening here at the center is 0:25:13.840 --> 0:25:16.680 that the stars are no longer totally in a circular orbit. 0:25:17.040 --> 0:25:19.840 The bar like twists the orbits so that some stars are 0:25:19.840 --> 0:25:23.639 moving more on radial orbits passing close through the center 0:25:23.720 --> 0:25:24.480 of the galaxy. 0:25:24.720 --> 0:25:27.359 What do you mean, radar like more oval shape orbits? 0:25:27.520 --> 0:25:30.080 Yeah, more oval shape, So they're not equally distributed around 0:25:30.080 --> 0:25:32.879 the center of the galaxy. They're like passing back and forth. 0:25:33.200 --> 0:25:36.280 Oh interesting, I guess maybe it's sort of rare or 0:25:36.400 --> 0:25:38.560 sort of a coincid is that you would have circular 0:25:38.720 --> 0:25:40.639 orbit orbits, right Like, if I throw a rock at 0:25:40.640 --> 0:25:42.840 the Sun right now, it would not necessarily go in 0:25:42.880 --> 0:25:45.399 a round orbit. It might maybe more likely go in 0:25:45.440 --> 0:25:46.760 an oval shape orbit. 0:25:46.960 --> 0:25:49.280 Yeah, there's lots of possible solutions, and a circle is 0:25:49.280 --> 0:25:51.800 like a special case of it. And also to maintain 0:25:51.880 --> 0:25:55.399 a circular orbit requires resisting the tugs and the pulls 0:25:55.400 --> 0:25:58.560 of everything else around you. Remember that you're not orbiting 0:25:58.560 --> 0:26:01.159 by yourself. The Earth is being on by Jupiter, and 0:26:01.240 --> 0:26:03.440 Jupiter is being pulled on by everything else. That's one 0:26:03.440 --> 0:26:06.399 of the reasons why our orbits are eccentric. So the 0:26:06.400 --> 0:26:09.800 more complicated dynamics you have, the more lack of symmetry, 0:26:09.960 --> 0:26:12.280 the more these things are getting pulled by other stuff, 0:26:12.400 --> 0:26:14.480 the more they're going to fall out of perfectly circular 0:26:14.560 --> 0:26:18.800 orbits and clump together in other kinds of orbits. 0:26:18.359 --> 0:26:20.600 So that you're saying, the stuff at the center of 0:26:20.640 --> 0:26:23.840 our milk away galaxy is not necessarily going around in 0:26:23.840 --> 0:26:26.400 a circle, it's maybe going in an oval shape around 0:26:26.400 --> 0:26:29.679 the center. But then how does that explain the ripple 0:26:29.840 --> 0:26:32.520 that is the bar or all of these things going 0:26:32.560 --> 0:26:33.800 in an oval in sync. 0:26:34.119 --> 0:26:37.000 Yes, the bar itself is like a denser region which 0:26:37.080 --> 0:26:40.960 passes through the center of the galaxy, and it influences 0:26:41.000 --> 0:26:43.800 other stuff. So gas near the center of the galaxy, 0:26:43.840 --> 0:26:47.320 for example, moves at faster speeds than gas further out, 0:26:47.480 --> 0:26:49.479 So the gas can catch up to the bar and 0:26:49.560 --> 0:26:52.120 pass through it. But then the bar is stronger gravity 0:26:52.200 --> 0:26:55.320 slows it down, so the material tends to lose some energy. 0:26:56.000 --> 0:26:58.800 This actually ends up funneling a bunch more gas towards 0:26:58.840 --> 0:27:01.879 the center of the galaxy and can create new stars 0:27:02.080 --> 0:27:03.040 right there in the bar. 0:27:03.200 --> 0:27:06.280 But then, I guess, like making the bar is so common, 0:27:06.480 --> 0:27:09.280 you're seeing about two thirds of galaxies, spiral galaxies have 0:27:09.320 --> 0:27:11.600 a bar in them. Why don't we see that effect 0:27:11.680 --> 0:27:14.840 like in other places, like when I flushed the toilet, 0:27:15.000 --> 0:27:17.640 or you know, in our Solar system. Even we don't 0:27:17.640 --> 0:27:19.520 have a bar in our solar system. I guess we 0:27:19.560 --> 0:27:23.000 don't have spiral arms in our Solar system either, Like 0:27:23.240 --> 0:27:25.800 you know, things coalesced into the planets, although we do 0:27:25.880 --> 0:27:26.800 have an asteroid built. 0:27:27.560 --> 0:27:29.639 I think it comes down to the balance of all 0:27:29.680 --> 0:27:31.600 the things at play. You know, we have gravity in 0:27:31.640 --> 0:27:33.720 the Solar System, and of course in the galaxy. But 0:27:33.760 --> 0:27:36.040 the galaxy is a lot more friction. You know, there's 0:27:36.160 --> 0:27:38.760 gas and there's dust. This stuff is interacting much more 0:27:38.800 --> 0:27:41.040 than things in the Solar system. So there's a lot 0:27:41.040 --> 0:27:44.120 more transfer of energy between the stuff in the galaxy 0:27:44.160 --> 0:27:46.520 than there is in the Solar system. Solar systems like 0:27:46.520 --> 0:27:48.639 a cleaned up little galaxy. There's not nearly as much 0:27:48.680 --> 0:27:51.200 stuff between the planets as there is between the stars. 0:27:51.240 --> 0:27:54.040 In the galaxy. There's a lot more of this exchange 0:27:54.040 --> 0:27:57.080 of energy and friction and stuff bumping into other stuff 0:27:57.400 --> 0:28:00.439 in the galaxy, which can give you more interesting complex 0:28:00.640 --> 0:28:04.320 basically turbulent structure. And we don't know how long these 0:28:04.359 --> 0:28:07.320 bars last. There's some theories that say these bars will 0:28:07.400 --> 0:28:09.919 last forever, and we see some galaxies that have had 0:28:10.000 --> 0:28:12.920 their bars for like ten billion years. There are other 0:28:12.960 --> 0:28:15.800 theories that the bars could be oscillatory, like maybe the 0:28:15.800 --> 0:28:18.240 bar forms, but then the formation of the bar tends 0:28:18.280 --> 0:28:20.439 to destroy the bar, and then another bar forms a 0:28:20.480 --> 0:28:23.120 billion years later. So it could be that every galaxy 0:28:23.200 --> 0:28:25.359 goes through phases where it has a bar and doesn't 0:28:25.359 --> 0:28:28.000 have a bar. These are really open questions in the 0:28:28.000 --> 0:28:29.240 study of galaxy formation. 0:28:29.600 --> 0:28:33.200 Mmmm, it's doing like pull ups or something on a bar, 0:28:34.359 --> 0:28:37.800 going back and forth. But this is an interesting idea 0:28:37.840 --> 0:28:40.200 that it maybe depends on time. Like you're saying, they 0:28:40.240 --> 0:28:43.160 can come in and out. What do you see when 0:28:43.200 --> 0:28:44.960 you look at the galaxies out there in the universe, Like, 0:28:45.040 --> 0:28:49.920 don't can't we see them across different ages and times? Yeah? 0:28:50.000 --> 0:28:52.960 Do we see that the older galaxies have more bars 0:28:53.040 --> 0:28:55.240 or younger galaxies have more bars? What do we see? 0:28:55.400 --> 0:28:57.320 Yeah, so we're not sure. We have a lot of 0:28:57.360 --> 0:28:59.640 different clues that sort of point us in different directions. Like, 0:28:59.680 --> 0:29:03.160 on one hand, we see some galaxies with really really 0:29:03.200 --> 0:29:06.160 old bars. I was reading a paper about a galaxy 0:29:06.360 --> 0:29:09.080 we're looking at ten billion years in the past, and 0:29:09.120 --> 0:29:11.640 we can see the formation of a bar back then. 0:29:12.040 --> 0:29:14.880 So that's just like some bars formed really early in 0:29:14.960 --> 0:29:17.920 the universe and may have lasted a really long time. 0:29:18.280 --> 0:29:20.760 Of course, you can't see the same galaxy over time. 0:29:21.160 --> 0:29:21.960 Yeah, how do we know? 0:29:22.280 --> 0:29:25.080 We don't know necessarily how long a bar lasts when 0:29:25.120 --> 0:29:27.840 it's formed. But in this one particular galaxy, they could 0:29:27.840 --> 0:29:31.400 see evidence of the bar over about ten billion years 0:29:31.680 --> 0:29:34.400 because they could see how the bar had disrupted the 0:29:34.440 --> 0:29:37.840 structure of the galaxy. So it's a little speculative, but 0:29:38.120 --> 0:29:40.520 they think that that bar lasted for about ten billion 0:29:40.560 --> 0:29:43.520 years in that galaxy because of how it like shepherded 0:29:43.800 --> 0:29:46.920 the stars and influence the gas to create new stars. 0:29:47.240 --> 0:29:49.719 So it's not everybody that believes that paper, but that 0:29:49.760 --> 0:29:52.880 one paper argues that there are galaxies with really long 0:29:53.000 --> 0:29:53.680 lived bars. 0:29:54.960 --> 0:29:56.239 And then I guess, how do you know that they 0:29:56.280 --> 0:29:56.920 can go away? 0:29:57.120 --> 0:30:00.640 Yeah, another great question. That's again from simulation. We see 0:30:00.680 --> 0:30:04.240 in some simulations that a bar can like drive gas 0:30:04.280 --> 0:30:06.840 inwards towards the center of the galaxy. It's an over 0:30:06.880 --> 0:30:09.480 density and so it pulls stuff in and that can 0:30:09.560 --> 0:30:13.160 disrupt the motion of stars through the galactic core. So, 0:30:13.200 --> 0:30:16.080 like the formation of the bar could create gravity which 0:30:16.160 --> 0:30:19.920 pulls in more gas, which ends up disrupting the bar itself. 0:30:20.480 --> 0:30:22.280 So we don't know. And this is the kind of 0:30:22.280 --> 0:30:25.800 thing we study in simulations, and these simulations are never perfect, right, 0:30:25.800 --> 0:30:28.640 You can't include everything in the galaxy in your simulation, 0:30:28.760 --> 0:30:31.960 every tiny particle. It would take forever. So whenever they 0:30:31.960 --> 0:30:35.120 do these simulations, they're always making approximations. Well, let's leave 0:30:35.120 --> 0:30:37.240 out the dark matter, or let's ignore this effect. Or 0:30:37.400 --> 0:30:39.880 something to make it tractable. And so you've got lots 0:30:39.880 --> 0:30:42.640 of different simulations with sort of different answers, and people 0:30:42.680 --> 0:30:45.120 are still exploring this, like right now, nobody really knows 0:30:45.120 --> 0:30:46.360 the answers to these questions. 0:30:46.440 --> 0:30:49.600 So when you simulate it, you add a little asymmetry 0:30:49.720 --> 0:30:52.760 or like an offset to the distribution of the stars, 0:30:52.800 --> 0:30:54.680 and then you get a bar. And then what you 0:30:54.680 --> 0:30:57.120 see in the simulation is that sometimes the bar disappears 0:30:57.120 --> 0:31:00.000 after a while exactly, and then maybe it comes back 0:31:00.120 --> 0:31:01.240 later mm hmm. 0:31:01.680 --> 0:31:04.520 And there's some other hints from the simulations. Some suggest 0:31:04.720 --> 0:31:07.960 that it depends on the thickness of the disk. Like 0:31:07.960 --> 0:31:11.080 our galaxies mostly flat, but it's not a totally thin disk. 0:31:11.480 --> 0:31:14.120 It's not like it's a paper thin, right, There's a 0:31:14.200 --> 0:31:17.320 width to the galaxy, and some galaxies have thinner disks 0:31:17.360 --> 0:31:20.400 and some galaxies have thicker discs, And some of these 0:31:20.400 --> 0:31:24.240 stimulations suggest that galaxies with thinner discs are more likely 0:31:24.320 --> 0:31:27.600 to have bars than galaxies with thicker discs in them. 0:31:27.840 --> 0:31:28.840 WHOA why would they be? 0:31:29.160 --> 0:31:31.720 I think it has to do with basically the gravitational 0:31:31.840 --> 0:31:35.160 environment in which a disruption forms, Like if there's a 0:31:35.200 --> 0:31:38.720 lot of other gravity happening anyway, then the small over 0:31:38.760 --> 0:31:41.640 density is less likely to cause a big pile up 0:31:41.720 --> 0:31:44.120 in the galactic spin. Like, for example, you had a 0:31:44.160 --> 0:31:46.880 huge amount of dark matter in your galaxy and then 0:31:46.880 --> 0:31:49.440 the gravity of the galaxy is mostly dominated by that 0:31:49.560 --> 0:31:51.560 dark matter. In the same way, if you have lots 0:31:51.560 --> 0:31:53.720 of other stars like above and below where the over 0:31:53.760 --> 0:31:56.080 density forms, then those stars are going to tend to 0:31:56.120 --> 0:31:59.400 smooth stuff out because of their gravity. A thicker disc 0:31:59.480 --> 0:32:02.280 might prevent a little over density from turning into a 0:32:02.280 --> 0:32:02.720 big bar. 0:32:03.000 --> 0:32:05.360 Interesting, it's like a two D effect, like it only 0:32:05.400 --> 0:32:06.720 happens in thin sheets. 0:32:06.960 --> 0:32:11.160 Yeah, it could be. Another study suggested that mergers can 0:32:11.200 --> 0:32:14.880 destroy bars. Remember, spiral galaxies merge and form sometimes new 0:32:14.920 --> 0:32:18.960 spiral galaxies, sometimes elliptical galaxies, And it could be that 0:32:19.080 --> 0:32:21.520 bars are destroyed in these mergers, and then the new 0:32:21.560 --> 0:32:24.560 galaxy doesn't necessarily have a bar. It depends on the 0:32:24.560 --> 0:32:28.480 instability and the formation of the stars in that new galaxy. WHOA, 0:32:29.040 --> 0:32:31.200 but there's another really interesting clue. And to answer a 0:32:31.240 --> 0:32:33.840 question you asked a few minutes ago about whether bars 0:32:33.880 --> 0:32:36.800 form more recently or not, we find that it also 0:32:36.920 --> 0:32:39.720 depends on the mass of the galaxy. So a lot 0:32:39.760 --> 0:32:42.280 of the bars tend to have formed more recently in 0:32:42.520 --> 0:32:45.840 lower mass galaxies. So it might be that lower mass 0:32:45.880 --> 0:32:48.960 galaxies take longer to form stars and then take longer 0:32:48.960 --> 0:32:51.600 to form bars. So most of the bars that are 0:32:51.640 --> 0:32:53.880 forming in the universe today we think are in the 0:32:53.960 --> 0:32:57.080 lower mass galaxies. They might not just have had time 0:32:57.160 --> 0:32:58.720 to make a bar until now. 0:32:59.240 --> 0:33:02.840 So you need like time and mass and flatness to 0:33:02.880 --> 0:33:03.520 make a bar. 0:33:03.520 --> 0:33:06.800 And some sort of seed, right, some gravitational over density. 0:33:07.280 --> 0:33:09.760 I think it's really fascinating that basically all the structure 0:33:09.800 --> 0:33:13.280 in the universe comes from one place being heavier than another. 0:33:13.680 --> 0:33:16.280 When the universe began, if it was totally smooth, nothing 0:33:16.280 --> 0:33:18.960 would have happened because all the gravity would have been balanced. 0:33:19.360 --> 0:33:22.760 Basically everything that happened in the universe is because of 0:33:22.840 --> 0:33:24.280 gravitational imbalances. 0:33:24.480 --> 0:33:27.160 M yeah, I definitely happen, and I definitely have a 0:33:27.360 --> 0:33:32.680 mass imbalance in certain parts of my body. Gravity. Yeah, 0:33:32.720 --> 0:33:37.680 it's all good. I'm blaeing the chocolate bars. So then, 0:33:37.720 --> 0:33:40.080 but then, how does the mass of the galaxy affect 0:33:40.120 --> 0:33:43.080 these bars? Like why would having more mass or less 0:33:43.120 --> 0:33:45.160 mass affect the bar formation? 0:33:45.520 --> 0:33:49.320 Because structure formation takes time, right, Gravity is very very weak, 0:33:49.640 --> 0:33:52.760 and it takes time for gravity to overwhelm these other things. 0:33:52.800 --> 0:33:55.600 It takes time for gravity to pull stars together, it 0:33:55.640 --> 0:33:58.520 takes time for those stars to then influence each other. 0:33:58.840 --> 0:34:01.520 So all these things take time, and lower mass galaxies 0:34:01.560 --> 0:34:03.720 have less gravity, so it just takes them longer to 0:34:03.760 --> 0:34:06.880 sort of come together and form these things. And structure 0:34:06.920 --> 0:34:10.479 is sort of hierarchical, right, it's bottom up. You build 0:34:10.520 --> 0:34:13.000 the stars, the stars build a galaxy, You build a 0:34:13.040 --> 0:34:15.719 structure on that, and then you build structures on those structures. 0:34:16.120 --> 0:34:18.640 The barred spiral galaxy is sort of like the pinnacle 0:34:18.680 --> 0:34:22.200 of universal structure. It's like the most complex organized thing 0:34:22.239 --> 0:34:23.640 the universe has made so far. 0:34:25.239 --> 0:34:27.279 Well, it definitely sounds like we've raised the bar here 0:34:27.320 --> 0:34:29.920 in terms of galactic mysteries. It seems like this is 0:34:29.960 --> 0:34:32.000 still a question for many scientists, and in fact, it 0:34:32.120 --> 0:34:36.200 might even have interesting consequences for our conception of dark 0:34:36.239 --> 0:34:39.560 matter and how they influence the formation of these galaxies. 0:34:40.200 --> 0:34:43.520 So let's dig into those dark matters. But first, let's 0:34:43.600 --> 0:34:59.920 take another quick break. Right, we're talking about galactic bars now, Daniels, 0:35:00.000 --> 0:35:03.520 this is where single stars go to meet other single stars. 0:35:05.520 --> 0:35:08.000 This is where molecular clouds hang out hoping to one 0:35:08.040 --> 0:35:08.880 day make stars. 0:35:09.600 --> 0:35:11.880 They're like celebrity bars. You see a lot of stars 0:35:11.880 --> 0:35:13.680 in them. 0:35:13.880 --> 0:35:15.400 This is where stars are born. Baby. 0:35:15.640 --> 0:35:18.480 All right, Well, we talked about how we're not quite 0:35:18.520 --> 0:35:21.160 one hundred percent sure why some galaxies are bars. It 0:35:21.200 --> 0:35:24.200 seems like it's just a matter of the physics, like 0:35:24.239 --> 0:35:27.319 the weirdness of how stars and the gravity interact and 0:35:27.360 --> 0:35:30.719 form ripples in a cluster of stars. But there is 0:35:30.760 --> 0:35:33.680 sort of another component to it, which is dark matter. Right. 0:35:33.800 --> 0:35:36.440 Dark matter plays a big role in how galaxies form, 0:35:37.200 --> 0:35:40.560 how fast they form, what shapes they have, and so 0:35:40.640 --> 0:35:42.719 what do these bars tell us about dark matter? 0:35:42.880 --> 0:35:46.160 Yeah, you're exactly right. And remember that the stars themselves 0:35:46.200 --> 0:35:49.000 are just like tracers that tell you where most of 0:35:49.040 --> 0:35:52.759 the mass is in the universe. So most of the dynamics, 0:35:52.760 --> 0:35:56.000 the gravitational forces, are hidden from us. We live in 0:35:56.000 --> 0:35:58.360 a dark universe where we only see a tiny, little 0:35:58.360 --> 0:36:01.720 fraction of what's going on out there. So by studying 0:36:01.719 --> 0:36:03.920 the motion of the gas and the dust and the stars, 0:36:03.960 --> 0:36:06.040 we could try to get a glimpse for what's going 0:36:06.080 --> 0:36:09.080 on sort of behind the curtain. What the fuller picture 0:36:09.200 --> 0:36:11.960 of the universe is, and you're absolutely right that dark 0:36:12.000 --> 0:36:14.799 matter controls the formation of the galaxies. We wouldn't have 0:36:14.880 --> 0:36:17.560 galaxies this early in the universe if it wasn't for 0:36:17.719 --> 0:36:20.640 dark matter. Eighty percent of the matter in the universe 0:36:20.880 --> 0:36:23.319 is dark matter, but more like ninety percent of the 0:36:23.360 --> 0:36:27.280 matter in galaxies is dark matter. So galaxies are basically 0:36:27.440 --> 0:36:30.960 mostly dark matter. And because dark matter feels gravity, it 0:36:31.000 --> 0:36:35.160 has a huge influence on gravitational turbulence, like the formation 0:36:35.360 --> 0:36:36.000 of bars. 0:36:36.040 --> 0:36:39.279 Absolutely so, all this time that we've been talking about 0:36:39.280 --> 0:36:41.600 the mass of a galaxy, I thought we were talking 0:36:41.640 --> 0:36:44.040 about the stars, But are we also talking about the 0:36:44.160 --> 0:36:45.640 mass due to dark matter. 0:36:45.760 --> 0:36:47.880 Yeah, we're talking about the total mass, not just the 0:36:47.960 --> 0:36:49.360 visible mass of the galaxy. 0:36:50.000 --> 0:36:52.520 Or are they pretty correlated, like the more stars you 0:36:52.560 --> 0:36:55.359 see in a galaxy, the more dark matter it has. 0:36:56.040 --> 0:36:58.800 Yeah, great question. We did a podcast recently about the 0:36:58.880 --> 0:37:02.799 variation of dark man matter in galaxies. Most galaxies have 0:37:02.960 --> 0:37:06.160 around ninety percent of their mass is dark matter, but 0:37:06.200 --> 0:37:08.320 there is a variation. There's some that are like ninety 0:37:08.400 --> 0:37:11.360 nine percent dark matter and some that have almost none 0:37:11.520 --> 0:37:14.480 or maybe zero dark matter. It tells a really fun 0:37:14.520 --> 0:37:16.840 story about the history of galaxies and how they form 0:37:16.880 --> 0:37:19.239 and merge and might even strip each other of dark 0:37:19.280 --> 0:37:22.279 matter on the whole. There's a reasonable correlation, and like 0:37:22.400 --> 0:37:26.120 ninety percent of a galaxy's mass is invisible ninety percent 0:37:26.600 --> 0:37:27.440 ninety percent. 0:37:27.560 --> 0:37:31.200 Yeah, but isn't like the proportion of the universe something 0:37:31.239 --> 0:37:33.439 like five to one dark matter to normal matter. 0:37:33.560 --> 0:37:36.319 Yeah, so galaxies tend to have more dark matter than 0:37:36.400 --> 0:37:37.400 most of the universe. 0:37:38.200 --> 0:37:39.879 Why is that? Is it just because there's a lot 0:37:39.880 --> 0:37:42.719 of like stars and does kind of in between galaxies 0:37:42.719 --> 0:37:43.120 out there. 0:37:43.239 --> 0:37:45.880 It's because dark matter is really responsible for the formation 0:37:45.960 --> 0:37:48.960 of galaxies, and once a galaxy forms, it's hard for 0:37:49.000 --> 0:37:51.480 it to lose its dark matter, but it's possible for 0:37:51.520 --> 0:37:53.640 it to lose its gas and its dust and even 0:37:53.719 --> 0:37:56.319 its stars. There's all sorts of processes that tend to 0:37:56.320 --> 0:37:59.560 blow out gas and dust from a galaxy, you know, 0:38:00.000 --> 0:38:03.319 supernova or radiation from the central black hole. All these 0:38:03.320 --> 0:38:06.120 things can push normal matter out of a galaxy, but 0:38:06.160 --> 0:38:09.200 they don't affect its dark matter. So the dark matter 0:38:09.239 --> 0:38:11.960 is sort of there in the background, forming the gravitational 0:38:11.960 --> 0:38:14.759 structure on which the rest of the universe lives, and 0:38:14.800 --> 0:38:17.640 it's much less influenced by everything else that happens to 0:38:17.719 --> 0:38:18.479 the normal matter. 0:38:19.000 --> 0:38:21.800 Okay, so if our galaxy is ninety percent dark matter, 0:38:22.160 --> 0:38:24.960 I would think that was like the most powerful thing. 0:38:25.080 --> 0:38:27.759 That term is the shape with a galaxy. So does 0:38:27.800 --> 0:38:31.279 that mean that the dark matter in our galaxy is 0:38:31.320 --> 0:38:33.799 also in a spiral shape and maybe also has a 0:38:33.840 --> 0:38:35.720 bar of dark matter in the middle. 0:38:35.840 --> 0:38:37.960 Yeah, great question. We don't know the answer to that 0:38:38.040 --> 0:38:40.680 because we don't know the distribution of dark matter in 0:38:40.719 --> 0:38:43.760 the galaxy with a lot of precision. We know roughly 0:38:43.800 --> 0:38:46.000 that it's denser in the core and then it's spread 0:38:46.000 --> 0:38:49.040 out like a big halo. But we also know something 0:38:49.080 --> 0:38:50.920 about the physics of dark matter, like we know that 0:38:51.040 --> 0:38:54.560 dark matter doesn't feel friction with other dark matter the 0:38:54.640 --> 0:38:57.160 way normal matter does. Like two clouds of gas that 0:38:57.200 --> 0:39:00.640 pass through each other will exchange energy them will tend 0:39:00.640 --> 0:39:03.160 to fall towards the center for example. These kinds of 0:39:03.280 --> 0:39:05.920 energy exchanges just don't happen for dark matter because dark 0:39:05.960 --> 0:39:09.160 matter passes right through itself. It only feels gravity, and 0:39:09.160 --> 0:39:11.920 gravity is not strong enough for those kinds of exchanges. 0:39:12.239 --> 0:39:15.440 So the complex structures you see forming in normal matter 0:39:15.520 --> 0:39:18.120 don't always happen in dark matter. That's why we think 0:39:18.200 --> 0:39:21.040 dark matter is sort of a bigger, fluffier halo than 0:39:21.040 --> 0:39:23.200 the more compact visible matter in the galaxy. 0:39:24.200 --> 0:39:27.439 The shape of the regular stars is mostly due to gravity, right, 0:39:27.480 --> 0:39:30.360 and dark matter feels gravity with itself, doesn't it. 0:39:30.120 --> 0:39:33.719 It's mostly due to gravity, but also crucially relies on 0:39:34.080 --> 0:39:37.680 losing energy. Like if stuff is just swirling around gravitationally, 0:39:37.880 --> 0:39:40.880 it won't collapse nearly as easily if it's not sticky, 0:39:40.880 --> 0:39:43.480 if it just passes right through itself. When things are 0:39:43.560 --> 0:39:46.600 orbiting a black hole, for example, they could orbit there forever, 0:39:46.840 --> 0:39:48.600 but they're much more likely to fall in if they 0:39:48.640 --> 0:39:51.200 exchange some energy, so one of them gives up energy 0:39:51.239 --> 0:39:53.520 to another one rather than passing right through. 0:39:53.880 --> 0:39:56.400 You mean, like if the stuff swirling around crashes with 0:39:56.480 --> 0:39:59.560 itself or like bumps into itself and it's going to 0:39:59.640 --> 0:40:00.400 lose some energy. 0:40:00.880 --> 0:40:03.040 Yeah, So things are just much more stable if there's 0:40:03.080 --> 0:40:07.200 no interactions other than gravity. The other interactions, they tend 0:40:07.239 --> 0:40:09.680 to exchange energy and then stuff can fall into the 0:40:09.719 --> 0:40:12.480 center to make stars or to make galaxies, or to 0:40:12.480 --> 0:40:15.080 make arms, this kind of stuff. But the truth is 0:40:15.120 --> 0:40:17.360 we don't really know what structure there is to the 0:40:17.440 --> 0:40:19.440 dark matter. We don't have a lot of great probes 0:40:19.719 --> 0:40:22.840 for exactly where the dark matter is throughout the galaxy. 0:40:23.480 --> 0:40:25.360 It could be a dark chocolate bar in the middle. 0:40:25.480 --> 0:40:28.720 It could be just like a moose spread out throughout 0:40:28.719 --> 0:40:29.880 the whole galaxy. 0:40:30.400 --> 0:40:32.560 It could be We're getting better and better techniques to 0:40:32.640 --> 0:40:35.560 map where the dark matter is in the galaxy, but 0:40:35.600 --> 0:40:38.000 we don't have a very accurate picture. But you know, 0:40:38.120 --> 0:40:41.160 simple models of the physics of dark matter tell us 0:40:41.160 --> 0:40:43.480 how it should be distributed, though we don't know if 0:40:43.520 --> 0:40:45.080 those models are accurate, of course. 0:40:45.640 --> 0:40:48.360 But then in all these simulations you're talking about where 0:40:48.360 --> 0:40:50.920 we are finding out all these things about the bars, 0:40:51.320 --> 0:40:54.120 do they include dark matter in those simulations? And kauds 0:40:54.120 --> 0:40:55.520 of assumptions do you have to make there? 0:40:55.760 --> 0:40:58.080 They do include dark matter, and they treat dark matter 0:40:58.120 --> 0:41:01.640 as like a collisionless fluid, like they're in the backdrop 0:41:01.680 --> 0:41:05.320 of providing more gravity. And the dark matter does definitely 0:41:05.360 --> 0:41:08.799 influence the formation of bars in these simulations. The more 0:41:08.920 --> 0:41:12.040 dark matter you have, the less often you get a bar, 0:41:12.440 --> 0:41:15.040 even when you have some sort of like gravitational instability 0:41:15.120 --> 0:41:17.240 or over density in the visible matter. 0:41:17.520 --> 0:41:20.920 So does dark matter help the bars or prevent the bars? 0:41:21.000 --> 0:41:24.040 It prevents the bars from forming. So the more dark 0:41:24.080 --> 0:41:26.480 matter you have, the more it tends to smooth out 0:41:26.560 --> 0:41:29.080 the gravity of the disc, just like having a thicker 0:41:29.120 --> 0:41:31.120 disc right, as you were saying earlier, sort of like 0:41:31.120 --> 0:41:34.280 a two D effect. The more three d R galaxy becomes, 0:41:34.280 --> 0:41:36.880 the less susceptible it is to these effects. In the 0:41:36.920 --> 0:41:40.480 same way dark matter basically reduces the effect of gravity 0:41:40.480 --> 0:41:44.160 of the visible matter provides this like background gravity pulling 0:41:44.200 --> 0:41:45.360 on everything. 0:41:45.400 --> 0:41:48.560 I see, like it evens out the strength of gravity 0:41:48.640 --> 0:41:51.400 in the galaxy. Right, because you think dark matter is 0:41:51.440 --> 0:41:54.480 distributed spread all over the place, the more significant that is, 0:41:54.520 --> 0:41:58.880 the more generally speaking, gravity is in that galaxy exactly. 0:41:59.000 --> 0:42:01.200 And so if you have no dark matter, do you 0:42:01.239 --> 0:42:01.920 always get a bar? 0:42:02.080 --> 0:42:05.160 Nothing happens every time in simulation, but the proportion definitely 0:42:05.160 --> 0:42:07.799 goes up if you have no dark matter. But we 0:42:07.840 --> 0:42:10.080 don't expect that to happen in the universe very often, 0:42:10.320 --> 0:42:12.560 as we talked about recently on the podcast. We don't 0:42:12.600 --> 0:42:15.480 think galaxies can form without dark matter, though they might 0:42:15.560 --> 0:42:18.640 later be stripped of their dark matter in some collisions, 0:42:19.080 --> 0:42:21.239 But then collisions are also going to destroy a bar. 0:42:22.120 --> 0:42:25.400 So is the bar kind of a sign of how 0:42:25.480 --> 0:42:27.319 much dark matter there is in a galaxy, then. 0:42:27.320 --> 0:42:30.080 Yes, exactly. And people have used bars to try to 0:42:30.160 --> 0:42:33.319 measure the dark matter fraction in galaxies. Like if you 0:42:33.320 --> 0:42:35.200 look up at the night sky and you measure the 0:42:35.200 --> 0:42:38.120 fraction of galaxies that have bars in them, that tells 0:42:38.120 --> 0:42:40.239 you something about how much dark matter there can be 0:42:40.280 --> 0:42:42.960 in those galaxies, because if there's a lot of dark 0:42:43.000 --> 0:42:45.960 matter in all those galaxies, they wouldn't have bars, And 0:42:46.000 --> 0:42:48.200 if there was less dark matter in those galaxies, more 0:42:48.239 --> 0:42:50.600 of them would have bars. So we can actually use 0:42:50.680 --> 0:42:53.120 the bars as a way to like indirectly estimate the 0:42:53.200 --> 0:42:55.799 dark matter fraction of the universe in a way that's 0:42:55.840 --> 0:42:58.520 separate from the galactic rotation speed or any of the 0:42:58.640 --> 0:42:59.320 other probes. 0:43:00.160 --> 0:43:02.880 Like the bar sets the bar for dark matter. 0:43:05.040 --> 0:43:07.799 Yeah, it raises the bar on our understanding. 0:43:07.480 --> 0:43:09.680 Our precision to measure dark matter. 0:43:10.280 --> 0:43:13.200 Yeah, this is not a very precise measurement because we 0:43:13.239 --> 0:43:15.239 don't have that many galaxies where we can measure this 0:43:15.360 --> 0:43:17.920 kind of thing. But it's consistent with everything else we 0:43:18.000 --> 0:43:20.920 know about dark matter. So the fraction of galaxies with 0:43:21.000 --> 0:43:24.239 bars is consistent with our understanding that eighty percent of 0:43:24.280 --> 0:43:26.439 the matter in the universe is dark matter, and something 0:43:26.480 --> 0:43:29.960 like ninety percent of the matter in galaxies is dark matter. 0:43:31.520 --> 0:43:35.240 And then what percentage is Hershey's chocolate versus snob chocolate. 0:43:36.840 --> 0:43:40.640 I see, now you're disparaging people's choice chocolate. It goes 0:43:40.680 --> 0:43:47.600 both ways. I'm all right, I can take it. If 0:43:47.600 --> 0:43:49.279 I can dish it out, I can take it. That's fair. 0:43:49.640 --> 0:43:52.520 I'm sure that Hershey's dominates the chocolate market, but I'm 0:43:52.560 --> 0:43:55.320 glad that there are now a variety of chocolate offerings 0:43:55.320 --> 0:43:56.160 for people to enjoy. 0:43:56.520 --> 0:43:59.480 All right. Well, another interesting feature of our galaxy and 0:43:59.560 --> 0:44:01.800 of our u universe the way physics works to create 0:44:01.840 --> 0:44:04.600 these weird characteristics of the things we see out there, 0:44:04.640 --> 0:44:07.799 which then kind of reveal what things are made of 0:44:07.880 --> 0:44:11.080 and how things work in the grand cosmic scale things. 0:44:11.200 --> 0:44:13.360 Absolutely, and it's just part of the game we're playing, 0:44:13.400 --> 0:44:15.759 looking out at the night sky and out deep into 0:44:15.800 --> 0:44:18.000 the universe to try to get a handle on what's 0:44:18.080 --> 0:44:21.640 going on out there, what structures form, why do they form, 0:44:21.719 --> 0:44:24.239 and what do they reveal about the flash of titanic 0:44:24.280 --> 0:44:26.439 forces that's happening underneath it all. 0:44:26.920 --> 0:44:28.640 It sounds like these bars are giving us a good 0:44:28.680 --> 0:44:33.600 handle on galaxy formation and dark matter content of the Universe. 0:44:34.760 --> 0:44:36.480 I'm going to go hit the lunch bar after this. 0:44:37.400 --> 0:44:42.600 Yeah, just don't hit the dessert bar too hard. It 0:44:42.600 --> 0:44:44.879 depends on the kind of chocolate ban Yeah, that's right. 0:44:44.920 --> 0:44:46.240 The brand apparently. 0:44:48.520 --> 0:44:51.120 Love all you and love all your chocolate choices. Keep 0:44:51.239 --> 0:44:54.600 chomping on bars. That sounds really credible, Daniel. I'm working 0:44:54.600 --> 0:44:55.960 on it, man, I'm working on it all right. 0:44:56.000 --> 0:44:58.239 Well, we hope you enjoyed that. Thanks for joining us. 0:44:58.840 --> 0:44:59.600 See you next time. 0:45:04.120 --> 0:45:07.320 For more science and curiosity, come find us on social media, 0:45:07.400 --> 0:45:11.920 where we answer questions and post videos. We're on Twitter, Discorg, Insta, 0:45:12.040 --> 0:45:15.760 and now TikTok. Thanks for listening, and remember that Daniel 0:45:15.800 --> 0:45:19.240 and Jorge Explain the Universe is a production of iHeartRadio. 0:45:19.520 --> 0:45:24.640 For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, 0:45:24.800 --> 0:45:27.160 or wherever you listen to your favorite shows.