WEBVTT - What can we learn from dwarf galaxies? 0:00:08.680 --> 0:00:11.880 Daniel, what's your favorite thing about looking up at the stars? 0:00:12.280 --> 0:00:14.560 You mean, other than the hot coco? Did you always 0:00:14.600 --> 0:00:16.560 drink hot coco when you look at the stars? Do 0:00:16.640 --> 0:00:19.360 you have like a peplold in response? There? Can you 0:00:19.400 --> 0:00:22.080 see stars if you're not holding hot coco? I've never tried. 0:00:22.280 --> 0:00:24.840 It might steam up your glasses. No, But I mean 0:00:24.880 --> 0:00:27.840 like about the actual stars, not not what you're drinking 0:00:27.840 --> 0:00:29.639 when you look at them. I don't know. I love 0:00:29.760 --> 0:00:33.680 how big everything is up there, the stars, the galaxies, 0:00:33.880 --> 0:00:37.680 all of us, just so overwhelmingly huge. But aren't you 0:00:37.720 --> 0:00:39.879 a little bit biased about that? What do you mean? 0:00:39.920 --> 0:00:41.440 I mean you're only seeing the big stuff when you 0:00:41.440 --> 0:00:44.159 look up at the sky. There's plenty of little cute 0:00:44.240 --> 0:00:47.200 stuff on those stars or on those planets. Oh yeah, 0:00:47.240 --> 0:00:49.520 that's true, I suppose, But it doesn't change my mind. 0:00:49.680 --> 0:00:52.240 You still like big stuff. I like my universe the 0:00:52.280 --> 0:01:11.080 way I like my hot coco. Big and dark him 0:01:11.240 --> 0:01:14.039 or handy cartoonists and the creator of PhD comics. Hi, 0:01:14.200 --> 0:01:17.200 I'm Daniel. I'm a particle businessist and a professor at 0:01:17.360 --> 0:01:20.839 uc Herbhine, and I don't really drink that much hot coco. 0:01:21.080 --> 0:01:22.840 But does that mean you don't look at the stars 0:01:22.920 --> 0:01:25.200 very much. It does, unfortunately mean I don't look at 0:01:25.240 --> 0:01:27.160 the stars very much. Basically, it's because I don't do 0:01:27.200 --> 0:01:29.560 as much camping as I used to, and camping was 0:01:29.600 --> 0:01:32.000 my number one way to see the stars and also 0:01:32.160 --> 0:01:34.160 to drink hot cocoa. You know you can do all 0:01:34.160 --> 0:01:38.080 those three things independently. What that's not true. You can't 0:01:38.120 --> 0:01:40.600 just make hot coco at home in your living room 0:01:41.520 --> 0:01:43.480 or look at the stars. Next, you're telling me you 0:01:43.480 --> 0:01:46.440 can like make s'mores over your range. You could even 0:01:46.440 --> 0:01:49.560 do it on the microwave. What you have under those 0:01:49.640 --> 0:01:53.400 super smart microwaves? Did you got for free? I think 0:01:53.400 --> 0:01:55.680 that would cause offense to the fundamental nature of space 0:01:55.680 --> 0:01:58.640 and time making smores in the microwave. Yes, you'd be 0:01:58.760 --> 0:02:02.560 blacklisted by the Boy and Girls Couts. But anyways, Welcome 0:02:02.600 --> 0:02:05.080 to our podcast Daniel and Jorge Explain the Universe, a 0:02:05.160 --> 0:02:08.520 production of iHeartRadio in which we take a long, deep 0:02:08.600 --> 0:02:12.760 sip of this sweet, sweet universe, trying to appreciate all 0:02:12.760 --> 0:02:17.160 of its incredible flavors and colors and mysteries. We look 0:02:17.200 --> 0:02:20.160 out into the cosmos and we wonder why things are 0:02:20.280 --> 0:02:22.720 the way they are, why they look the way they do. 0:02:22.840 --> 0:02:25.640 And if it's possible to explain all of it, to 0:02:25.800 --> 0:02:28.760 understand the swirling and the dancing and the frothing and 0:02:28.800 --> 0:02:31.639 all the twoing and frowing that's happening up there in 0:02:31.680 --> 0:02:34.760 the night sky, and to explain all of it to you, 0:02:35.040 --> 0:02:38.240 that's right. We'd give you some more of this amazing universe, 0:02:38.320 --> 0:02:41.080 all the hot stuff, all the cold stuff, all of 0:02:41.080 --> 0:02:43.560 the chocolate stuff, and even all of the vanilla stuff. 0:02:43.560 --> 0:02:46.440 That's also pretty interesting. Did you say even all of 0:02:46.440 --> 0:02:49.040 the vanilla stuff, Like vanilla is an afterthought? I thought 0:02:49.040 --> 0:02:51.600 you were a great defender of vanilla as an actual flavor. 0:02:51.760 --> 0:02:54.079 I am a big defender. It's my favorite flavor. That's 0:02:54.120 --> 0:02:56.360 like saying your favorite color is white, dude, it is. 0:02:56.400 --> 0:03:01.680 Actually I love nothing more than a black page. The 0:03:01.760 --> 0:03:03.880 more white I can put into my drawings, the less 0:03:03.880 --> 0:03:06.400 work I have to do. A white page is usually 0:03:06.440 --> 0:03:08.680 the enemy of creative types. But I'm glad that it 0:03:08.720 --> 0:03:11.160 inspires you. But it's true that there's a lot of 0:03:11.160 --> 0:03:13.880 stuff out there to enjoy and to experience, of all 0:03:13.919 --> 0:03:18.120 different flavors and all different sizes. Sometimes people focus on 0:03:18.160 --> 0:03:21.560 the biggest, craziest, most extreme stuff in the universe, but 0:03:21.639 --> 0:03:24.600 there's a whole scale of things happening out there, tiny 0:03:24.639 --> 0:03:28.600 little gas clouds all the way up to supermassive galaxies. 0:03:28.960 --> 0:03:30.880 That's right, All of the big stuff in the universe 0:03:30.960 --> 0:03:34.040 usually gets all the big headlines. People mostly pay attention 0:03:34.080 --> 0:03:38.200 to supermassive black holes or giant superstars that are millions 0:03:38.240 --> 0:03:40.280 of times bigger than our sun. But sometimes it's the 0:03:40.320 --> 0:03:42.720 little stuff that can tell you a lot about the 0:03:43.000 --> 0:03:46.160 big ideas in the universe. Because remember that we don't 0:03:46.200 --> 0:03:48.680 get to control what happens in the universe. If we 0:03:48.720 --> 0:03:51.240 want to learn the way the universe works, we just 0:03:51.320 --> 0:03:54.320 got to sit back and watch the experiments that nature 0:03:54.400 --> 0:03:56.920 has arranged for us. We don't get to say what 0:03:57.040 --> 0:03:59.440 happens if you shoot two black holes together. We just 0:03:59.480 --> 0:04:02.560 have to look to see if somebody has already smashed 0:04:02.560 --> 0:04:05.480 them together. And so, because we are beggars, we don't 0:04:05.480 --> 0:04:07.480 get to be choosers, and that means that we need 0:04:07.520 --> 0:04:10.280 to make the most of everything that's out there. We 0:04:10.320 --> 0:04:11.960 need to think about what we can learn from the 0:04:12.040 --> 0:04:14.520 big stuff and also what we can learn from the 0:04:14.640 --> 0:04:17.400 little stuff, because everything out there in the universe has 0:04:17.440 --> 0:04:19.640 something to teach us, and there is a lot to 0:04:19.680 --> 0:04:22.240 be taught out there in the universe, a lot of 0:04:22.279 --> 0:04:25.560 amazing things big and small, and so today we're going 0:04:25.640 --> 0:04:27.720 to focus on one type of thing out there in 0:04:27.760 --> 0:04:30.240 the universe then maybe doesn't get as much attention as 0:04:30.440 --> 0:04:32.920 some of the big stuff, so to be on the program, 0:04:32.920 --> 0:04:42.200 we'll be asking the question what are dwarf galaxies? I 0:04:42.360 --> 0:04:44.040 love they We're going to get to talk about dwarf 0:04:44.080 --> 0:04:46.840 galaxies today because they are some of the most fascinating 0:04:46.920 --> 0:04:51.000 and interesting and reviewing aspects of the universe. They have 0:04:51.120 --> 0:04:54.080 so much to teach us about what's going on and 0:04:54.120 --> 0:04:57.600 where everything came from. Yeah, they're pretty exciting and pretty awesome, 0:04:58.120 --> 0:05:00.560 and so as usual, we were wondering how many people 0:05:00.560 --> 0:05:03.240 out there had thought about dwarf galaxies or know what 0:05:03.320 --> 0:05:05.760 they are. So thank you very much to everybody who 0:05:05.800 --> 0:05:09.400 answers these questions for the podcast. We love hearing your thoughts, 0:05:09.440 --> 0:05:12.279 as does everybody else. And if you are out there 0:05:12.320 --> 0:05:14.320 and have been listening to podcast for a while and 0:05:14.320 --> 0:05:17.159 would like to share your voice for everybody else, please 0:05:17.200 --> 0:05:19.720 don't be shy right to us two questions at daniel 0:05:19.720 --> 0:05:22.120 an Horgay dot com. So think about it for a second. 0:05:22.240 --> 0:05:26.080 What do you think our dwarf galaxies. Here's what people 0:05:26.120 --> 0:05:28.760 had to say. My guess is they're just smaller galaxies, 0:05:28.800 --> 0:05:32.760 smaller collections of stars that have not yet been swallowed 0:05:32.839 --> 0:05:35.920 up by a big galaxy. I would imagine at all 0:05:35.960 --> 0:05:39.279 galaxies kind of start out that way and grow and 0:05:39.400 --> 0:05:43.760 merge and until they become big, beautiful spirals like the 0:05:43.800 --> 0:05:47.800 Milky Way. Dwarf galaxies are like those little mini galaxies, 0:05:47.800 --> 0:05:51.760 and they can be like satellite galaxies to galaxies like 0:05:51.800 --> 0:05:55.400 the Milky Way, just a tiny little galaxies, not that big. 0:05:55.600 --> 0:05:58.920 I don't know. Maybe a dwarf galaxy is a galaxy 0:05:59.000 --> 0:06:02.320 with not enough mass to be considered a galaxy, like 0:06:02.880 --> 0:06:06.320 what happened to Pluto. I don't know. I'm guessing land 0:06:06.520 --> 0:06:11.280 or galaxies, as the name suggests, are smaller galaxies. I 0:06:11.320 --> 0:06:14.920 guess that by the name, dwarf galaxies have a lot 0:06:15.000 --> 0:06:19.440 less stars and planets and other stuff. But I don't 0:06:19.480 --> 0:06:22.400 know how smaller it has to be to be considered 0:06:22.520 --> 0:06:27.600 a dwarf galaxy. The term dwarf galaxies kind of reminds 0:06:27.640 --> 0:06:33.000 me of the galaxies that are like globular clusters, so 0:06:34.080 --> 0:06:36.280 or it might just be as it says in the name. 0:06:36.360 --> 0:06:43.719 They're just smaller galaxies, maybe much less stars, maybe a 0:06:43.720 --> 0:06:49.920 different shape, maybe maybe less dark matter keeping them together. 0:06:52.480 --> 0:06:56.160 I don't believe there probably won't be any black hole 0:06:56.200 --> 0:06:59.040 in the center, but there might be, I don't know. 0:06:59.279 --> 0:07:03.680 All right, straightforward answers here, everyone said they're just a galaxies, 0:07:03.720 --> 0:07:06.880 but smaller. It's like a dwarf serving of ice cream 0:07:07.000 --> 0:07:10.000 or a dwarf cup of cocoa. Oh yeah, that is 0:07:10.000 --> 0:07:13.520 that a new diet perhaps little servings of everything. I 0:07:13.560 --> 0:07:15.800 think that's maybe the oldest diet. Well that's a thing 0:07:15.800 --> 0:07:17.640 on the internet, right, there are all these videos of 0:07:17.760 --> 0:07:22.800 people making like little, tiny, like lego sized foods. Really 0:07:22.840 --> 0:07:24.400 like instead of having a saying which you just have 0:07:24.440 --> 0:07:27.200 like a tiny little sandwich. Yeah, there's this whole genre 0:07:27.240 --> 0:07:29.680 of YouTube videos they make like tiny food. Oh but 0:07:29.760 --> 0:07:33.040 that's not for eating, right, that's just for like being silly. 0:07:33.560 --> 0:07:36.240 Nobody's sitting down to tuck into like a tiny roast chicken, 0:07:36.280 --> 0:07:38.680 are they. Well maybe they could, they could, I don't know. 0:07:39.520 --> 0:07:41.640 They usually cut the videos after they make the food. 0:07:41.840 --> 0:07:44.520 I do like those tiny kitchen videos. Those are really fun. 0:07:44.800 --> 0:07:47.360 All right, Well, let's dig into it, Daniel, what is 0:07:47.360 --> 0:07:51.080 a dwarf galaxy. So everybody was basically right, Dwarf galaxies 0:07:51.120 --> 0:07:54.160 are a little cute galaxies. Because it turns out that 0:07:54.320 --> 0:07:58.160 galaxies come in all sorts of sizes. We tend to 0:07:58.200 --> 0:08:01.400 think about galaxies in term of ones like our own 0:08:01.520 --> 0:08:05.640 the Milky Way that has hundreds of billions of stars, 0:08:06.080 --> 0:08:08.720 Like galaxies that are much much bigger than the Milky Way, 0:08:08.800 --> 0:08:11.600 all the way down to galaxies that are very very 0:08:11.640 --> 0:08:15.080 small things that you probably wouldn't even call a galaxy. 0:08:15.280 --> 0:08:17.720 Maybe let's put things into perspective, but like, how big 0:08:17.840 --> 0:08:21.400 is our galaxy? What are the size ranges that qualify 0:08:21.440 --> 0:08:24.160 a galaxy is a dwarf galaxy? So our galaxy has 0:08:24.320 --> 0:08:29.160 somewhere around two hundred to four hundred billion stars. That's 0:08:29.160 --> 0:08:31.840 a really difficult number to wrap your mind around. Two 0:08:31.960 --> 0:08:35.200 hundred like a billion times two hundred exactly. There are 0:08:35.240 --> 0:08:39.320 more stars in the galaxy than people on Earth. Right, 0:08:39.440 --> 0:08:42.440 It's incredible, like every single person on Earth could have 0:08:42.480 --> 0:08:46.040 like pointier soul stars just for themselves in the Milky Way. 0:08:46.480 --> 0:08:49.640 It's really an incredible number of stars out there, hold 0:08:49.679 --> 0:08:52.440 them firing and burning with planets around them. Lots of 0:08:52.480 --> 0:08:55.000 Earth like planets. It's really hard to sort of like 0:08:55.280 --> 0:08:57.839 get the whole scope of the galaxy in your mind. 0:08:57.960 --> 0:09:01.080 But that's the size of our galaxy, a few hundred 0:09:01.280 --> 0:09:04.120 billion stars. You'd be like Oprah. You'd be giving up 0:09:04.160 --> 0:09:06.400 stars to everyone. You get a star, and you get 0:09:06.400 --> 0:09:09.840 a star, You're all stars. That's right. Donate to the 0:09:09.880 --> 0:09:12.959 podcast and I will give you a star in return. Now, 0:09:13.000 --> 0:09:15.840 do you offer free home delivery for that? Or do 0:09:15.880 --> 0:09:17.440 you have to pay for shipping? See that's how they 0:09:17.480 --> 0:09:20.839 get you the shipping. It's the free star, but it's 0:09:20.880 --> 0:09:23.640 gonna cost you ten trillion dollars to deliver it to 0:09:23.679 --> 0:09:26.360 your house and also the life of very human on Earth. 0:09:26.440 --> 0:09:28.560 M Yeah, And in this case, it's not just the shipping, 0:09:28.720 --> 0:09:31.839 it's the handling, right, because that's particularly tricky when you're 0:09:31.840 --> 0:09:35.040 dealing with something several thousand degrees kelvin. But no, I 0:09:35.040 --> 0:09:37.320 will email you a plaque of ownership of your star 0:09:37.400 --> 0:09:39.720 if you donate to the podcast. Oh boy, I feel 0:09:39.760 --> 0:09:42.640 like you just made a serious offer. Let's see if 0:09:42.640 --> 0:09:45.760 we get any takers. But our galaxy, as big as 0:09:45.800 --> 0:09:48.520 it is, is not even the biggest galaxy out there. 0:09:49.240 --> 0:09:53.000 How big do galaxies get like Andromeda. How big is Andromeda? 0:09:53.080 --> 0:09:56.240 Andromeda has more than a trillion stars in it. It's 0:09:56.280 --> 0:09:59.280 about five times as big as the Milky Way, like 0:09:59.400 --> 0:10:03.400 totally dwarfs us in terms of galaxies, And there are 0:10:03.400 --> 0:10:06.520 other galaxies out there that are even bigger. WHOA, what's 0:10:06.559 --> 0:10:08.960 the biggest galaxy that we know of? Or what's the 0:10:08.960 --> 0:10:12.120 biggest galaxy that Google knows of? So the biggest galaxy 0:10:12.200 --> 0:10:14.800 that we know of is about a billion light years away. 0:10:14.880 --> 0:10:18.880 It's called I See one one oh one, and there's 0:10:18.880 --> 0:10:21.480 a lot of uncertainty, but the current estimate is that 0:10:21.520 --> 0:10:24.960 it has the mass of about one hundred trillion stars, 0:10:25.320 --> 0:10:29.400 so like a hundred times more stars than Andromeda. Whoa, 0:10:29.600 --> 0:10:31.960 which is already five times bigger than us, So it's 0:10:31.960 --> 0:10:35.440 like five hundred times bigger than us in terms of mass. Yeah, 0:10:35.440 --> 0:10:38.040 there's some nuances there because there's a big variation in 0:10:38.080 --> 0:10:41.800 the masses of stars. Actually, more stars are smaller than 0:10:41.840 --> 0:10:44.760 the mass of our sun. Remember, the most common kind 0:10:44.760 --> 0:10:46.800 of star out there is a red dwarf, which is 0:10:46.840 --> 0:10:49.280 smaller than the kind of star that we have. So 0:10:49.320 --> 0:10:51.520 if you're just measuring the mass in terms of like 0:10:51.800 --> 0:10:55.360 our solar masses, that's going to underestimate the number of 0:10:55.440 --> 0:10:57.920 stars that are out there in that galaxy, so it 0:10:57.920 --> 0:11:00.560 may even be more. This is just like a really 0:11:00.559 --> 0:11:04.239 shocking number, hundreds of trillions of stars. You know. For comparison, 0:11:04.559 --> 0:11:07.920 there's like a few trillion trees on Earth, So that 0:11:07.960 --> 0:11:10.720 means that like every tree on Earth could have like 0:11:10.840 --> 0:11:14.439 twenty stars in that mega galaxy. WHOA, Well, I'm not 0:11:14.559 --> 0:11:19.280 sure trees are collecting stars these days, but you're welcome 0:11:19.320 --> 0:11:23.000 to assign a star for every tree in the galaxy. 0:11:23.040 --> 0:11:25.360 Any tree that donates to the podcast, I will email 0:11:25.400 --> 0:11:28.679 them a certificate of ownership. They technic they kind of 0:11:28.720 --> 0:11:32.120 do already because I print out the outline every single 0:11:32.160 --> 0:11:35.400 time on paper. Wow, which means you're sacrificing trees for 0:11:35.400 --> 0:11:38.319 the podcast. Yeah. I like to think they donated for 0:11:38.440 --> 0:11:42.080 the good of the of knowledge, But I guess maybe 0:11:42.120 --> 0:11:44.000 a question is like, is there an upper limit to 0:11:44.040 --> 0:11:46.680 the size of a galaxy or can galaxies just be 0:11:47.040 --> 0:11:50.280 infinitely big? And if there's a limit, what causes that limit? 0:11:50.480 --> 0:11:52.640 Is it something about the conditions at the beginning of 0:11:52.679 --> 0:11:55.160 the universe. There's no technical limit to the size of 0:11:55.160 --> 0:11:58.920 a galaxy. Galaxies just form and get bigger and bigger. 0:11:59.240 --> 0:12:02.280 That's fundamental the history of the universe is that galaxy 0:12:02.400 --> 0:12:05.920 started out basically a small clumps of stars, which then 0:12:06.040 --> 0:12:08.800 merge with other clumps of stars, and so you get 0:12:08.840 --> 0:12:13.360 this like hierarchical formation, this merging of mergers of mergers, 0:12:13.480 --> 0:12:16.000 and so there's no reason why you can't just like 0:12:16.280 --> 0:12:18.760 keep clumping galaxies together, and they are going to keep 0:12:18.800 --> 0:12:21.920 clumping together. Really, the only thing that limits the size 0:12:21.920 --> 0:12:24.800 of the galaxy is the fact that the universe is expanding, 0:12:24.880 --> 0:12:28.840 and that expansion is accelerating, so it's increasing the distances 0:12:28.880 --> 0:12:31.880 between galaxies, so it sort of like keeps the galaxy 0:12:32.000 --> 0:12:35.320 separated a little bit and prevents them from colliding all 0:12:35.400 --> 0:12:38.720 into one huge mega galaxy. So it's a bit of 0:12:38.720 --> 0:12:42.959 a race against time, right because recently the universes started 0:12:43.120 --> 0:12:46.120 accelerating right in terms of its expansion, So maybe we 0:12:46.240 --> 0:12:48.760 have seen the biggest galaxies that will ever form. Some 0:12:48.800 --> 0:12:51.320 cosmologists think that we live at the time of the 0:12:51.360 --> 0:12:55.800 biggest structures in the universe because of the accelerating expansion 0:12:55.800 --> 0:12:59.200 of the universe, then size of structures cannot grow anymore 0:12:59.360 --> 0:13:02.920 because so much space is being created between existing galaxies, 0:13:03.240 --> 0:13:05.880 and so like we have galaxies, and we have clusters 0:13:05.880 --> 0:13:08.560 of galaxies that are mostly held together by gravity. Then 0:13:08.600 --> 0:13:10.960 we have superclusters which are sort of on the edge 0:13:10.960 --> 0:13:14.040 of whether gravity can hold them together or dark energy 0:13:14.120 --> 0:13:16.400 will rip them apart. And so it might be that 0:13:16.520 --> 0:13:20.680 like our cluster of galaxies eventually collapses into one big galaxy, 0:13:21.120 --> 0:13:25.600 maybe even our supercluster collapses into a super galaxy. But 0:13:25.760 --> 0:13:29.079 the stuff and other superclusters, probably dark energy will keep 0:13:29.160 --> 0:13:31.640 us from ever merging with them. So we might get 0:13:31.720 --> 0:13:34.840 future bigger galaxies, but we won't ever get like bigger 0:13:34.840 --> 0:13:37.560 blobs of stuff. We might have reached sort of like 0:13:37.760 --> 0:13:42.680 peak size of blob or like at the end of purity, 0:13:43.480 --> 0:13:47.200 it's all downhill after that, stuff just starts falling apart 0:13:47.240 --> 0:13:50.400 after that. Yeah, hopefully let's get to party as much 0:13:50.400 --> 0:13:52.040 as we can right now. But I guess it also 0:13:52.040 --> 0:13:54.160 depends on what dark energy is going to do in 0:13:54.160 --> 0:13:56.679 the future, right Isn't it a possibility that dark energy 0:13:56.720 --> 0:13:59.920 will reverse and it will cause everything to start contract 0:14:00.200 --> 0:14:02.920 and then we'll very basically at the entire universe is 0:14:02.920 --> 0:14:06.160 going to collapse into a clump and then it'll be 0:14:06.200 --> 0:14:09.319 like one giant galaxy. Basically, it certainly does depend on that. 0:14:09.480 --> 0:14:13.319 The scenario we just outlined assumes that dark energy continues 0:14:13.440 --> 0:14:16.840 the way that it has that's constant in space, and 0:14:16.880 --> 0:14:20.080 that as space gets bigger, you add more dark energy. 0:14:20.160 --> 0:14:23.600 So dark energy is an increasing fraction of the energy 0:14:23.640 --> 0:14:27.239 density of the universe, which just further accelerates the expansion. 0:14:27.440 --> 0:14:30.280 If you just extrapolate that out naively, then yeah, you 0:14:30.320 --> 0:14:32.760 get the scenario we just outlined. But as you say, 0:14:32.800 --> 0:14:35.400 we don't really understand dark energy where it comes from. 0:14:35.680 --> 0:14:38.400 What is this source of potential energy that's accelerating the 0:14:38.440 --> 0:14:40.960 expansion of the universe. Could it change? And in fact 0:14:41.080 --> 0:14:44.400 it might, right because we don't know the underlying mechanism 0:14:44.640 --> 0:14:47.520 that creates it. It could be that there's some complicated 0:14:47.560 --> 0:14:50.320 dynamics there that change with time and give us a 0:14:50.320 --> 0:14:53.080 different future. Like it could just all turn off suddenly 0:14:53.400 --> 0:14:56.000 and then we have a big crunch where everything collapses down, 0:14:56.040 --> 0:15:01.760 as you say, into one big superstructure, one megaga. But 0:15:01.880 --> 0:15:04.600 we're not here today to talk about the super big galaxies. 0:15:04.600 --> 0:15:07.560 They get enough attention. Let's turn our mental eyes down 0:15:07.600 --> 0:15:10.560 to the other end of the spectrum. Yep, yep, we're 0:15:10.600 --> 0:15:13.040 talking about dwarf galaxies, and like you said, it's the 0:15:13.080 --> 0:15:16.560 case that all galaxies started out as dwarf galaxies, right, 0:15:16.600 --> 0:15:20.240 Like at the beginning of the universe, everything was spread out, 0:15:20.240 --> 0:15:23.120 but then these things started to clump together, and so 0:15:23.200 --> 0:15:26.480 everything started with small galaxies. Yeah, everything started with these 0:15:26.600 --> 0:15:29.760 little fluctuations due to quantum mechanics, a little bit that 0:15:29.880 --> 0:15:31.560 was more dense over here, a little bit that was 0:15:31.640 --> 0:15:34.320 less dense over there, and then gravity did its work 0:15:34.320 --> 0:15:37.800 and pulled that stuff together and made little clumps of 0:15:37.840 --> 0:15:40.360 gas which then turned into stars. And that's how you 0:15:40.400 --> 0:15:43.400 got the first galaxies. So there was like a size 0:15:43.480 --> 0:15:46.440 of those clumps that formed the first galaxies. And you know, 0:15:46.520 --> 0:15:48.960 some of those have merged into bigger galaxies, and some 0:15:49.040 --> 0:15:50.560 of them have not, and some of them are more 0:15:50.600 --> 0:15:54.360 recent and haven't yet merged into other galaxies. So at 0:15:54.360 --> 0:15:57.080 the small end of the scale are those little mini 0:15:57.120 --> 0:16:00.560 galaxies that have not merged or not merged. As many times, 0:16:00.720 --> 0:16:03.720 I wonder if there's like an average size galaxy at 0:16:03.720 --> 0:16:06.280 the beginning of the universe, do you know what I mean? Like, 0:16:06.440 --> 0:16:09.960 the universe presumably was kind of the same everywhere, and 0:16:09.920 --> 0:16:13.480 there's a certain density of stuff, which means that on average, 0:16:13.520 --> 0:16:16.560 there was probably like like every galaxy was almost the 0:16:16.600 --> 0:16:19.440 same size, right, some small size. Yeah, And we can 0:16:19.480 --> 0:16:22.680 actually see this in the cosmic microwave background radiation. We 0:16:22.680 --> 0:16:25.680 can see this pattern of overdensity and under density, and 0:16:25.720 --> 0:16:28.320 we can use that size actually to measure like the 0:16:28.400 --> 0:16:31.520 expansion rate of the universe. We have a whole podcast 0:16:31.560 --> 0:16:34.760 episode about like measuring the curvature of space and the 0:16:34.800 --> 0:16:36.960 history of it, and you can see those kind of 0:16:36.960 --> 0:16:41.800 things expand from an early characteristic quantum fluctuation size lown 0:16:41.920 --> 0:16:45.760 up into something macroscopic, which, as you say, then determines 0:16:46.080 --> 0:16:49.160 basically the size of these initial clumps. Yeah. But again 0:16:49.200 --> 0:16:51.920 it's quantum base, right, So it's totally random. So there 0:16:51.920 --> 0:16:53.920 could have been maybe a spot in the universe but 0:16:54.000 --> 0:16:56.920 that had a big fluctuation which maybe would have made 0:16:56.960 --> 0:16:59.680 a big galaxy out there at the beginning of time. Yeah, 0:16:59.720 --> 0:17:02.320 it random, you're right, and so it's less likely, but 0:17:02.360 --> 0:17:05.680 it's possible to get a larger gravitational collapse an early 0:17:05.720 --> 0:17:08.760 galaxy that started out big. But there's also a typical 0:17:08.840 --> 0:17:13.840 characteristic size where galaxies start, and so that's on the 0:17:13.880 --> 0:17:16.680 little end, and so these dwarf galaxies are basically on 0:17:16.680 --> 0:17:20.600 that smaller end of little gravitational clumps that formed little 0:17:20.600 --> 0:17:24.760 stellar neighborhoods. And so right now we have these galaxies 0:17:24.760 --> 0:17:27.200 and giant structures of galaxies. But it used to be 0:17:27.280 --> 0:17:29.720 the case, maybe at the beginning of the universe, where 0:17:30.080 --> 0:17:33.600 like the entire universe was just kind of evenly distributed 0:17:33.640 --> 0:17:36.760 with tiny little galaxies. Yeah, and these galaxies get to 0:17:36.800 --> 0:17:40.520 be pretty small, like remember the Milky Ways, hundreds of 0:17:40.720 --> 0:17:44.600 billions of stars. Dwarf galaxies can go all the way 0:17:44.640 --> 0:17:48.200 down to like hundreds or thousands of stars, all the 0:17:48.240 --> 0:17:51.119 way up to like several billion stars. So there's an 0:17:51.280 --> 0:17:54.520 enormous spectrum of size there, from really just a handful 0:17:54.560 --> 0:17:58.400 of stars all the way up to billions of stars. Mm. Interesting. 0:17:58.440 --> 0:18:01.320 All right, let's get more into actual dwarf galaxies and 0:18:01.560 --> 0:18:03.720 what they can tell us about dark matter and the 0:18:03.880 --> 0:18:06.960 rest of how the universe form. But first let's take 0:18:07.000 --> 0:18:22.200 a quick break. All right, we're talking about dwarf galaxies, 0:18:22.280 --> 0:18:24.680 and we talked a little bit about how basically dwarf 0:18:24.720 --> 0:18:28.120 galaxies were the og galaxies in the universe, right like, 0:18:28.400 --> 0:18:31.920 at the beginning of time, every galaxy was a dwarf back. Yeah, 0:18:31.920 --> 0:18:34.840 there may have been some larger galaxies formed randomly, as 0:18:34.880 --> 0:18:38.439 you said, But the original galaxies, yeah, we're all dwarf galaxies, 0:18:38.480 --> 0:18:42.119 that's how it all began, and they usually kind of 0:18:42.160 --> 0:18:44.239 have a fuzzy shape to them, right, They don't have 0:18:44.280 --> 0:18:48.080 maybe this nice spiral shape or form that the Milky 0:18:48.080 --> 0:18:50.960 Way has. It's actually interesting and really subtle point there, 0:18:51.040 --> 0:18:53.800 because if you have an initial clump of stuff that 0:18:53.920 --> 0:18:57.399 collapses under gravity, it tends to form a disk, and 0:18:57.440 --> 0:18:59.639 it forms a disc because it's spinning, and it's spinning 0:18:59.680 --> 0:19:02.840 like around some particular axis. Gravity can squeeze it down 0:19:02.840 --> 0:19:06.160 sort of along that axis, but on the plane perpendicular 0:19:06.160 --> 0:19:08.280 to it, it can't squeeze it down as much because 0:19:08.280 --> 0:19:11.399 it's still spinning and it retains that angular momentum. So 0:19:11.440 --> 0:19:13.680 if you have just like an initial spinning blob of stuff, 0:19:13.720 --> 0:19:16.560 it tends to form a disc. Now, when dwarf galaxies 0:19:16.560 --> 0:19:18.919 merge together to make bigger galaxies, then you have like 0:19:19.000 --> 0:19:21.359 disc spinning in lots of different directions, and you end 0:19:21.440 --> 0:19:25.480 up with like more ellipsoid galaxies which eventually later then 0:19:25.520 --> 0:19:29.080 also collapse into like some big overall disc, which is 0:19:29.080 --> 0:19:33.160 why like the Milky Way is mostly a disc. All right. Well, 0:19:33.160 --> 0:19:35.439 then like how many. I guess that question is like 0:19:35.440 --> 0:19:38.119 how many dwarf galaxies do you need to come together 0:19:38.440 --> 0:19:40.840 to make a galaxy like the Milkyway, Because you're saying 0:19:40.840 --> 0:19:43.760 the Milky Way probably formed out of dwarf galaxies coming together, right, 0:19:43.840 --> 0:19:46.159 I'm just wondering how many it takes. Yeah, I mean 0:19:46.200 --> 0:19:50.320 if dwarf galaxies start out as a few thousand stars, right, 0:19:50.320 --> 0:19:54.440 and the Milky Way has a few hundred billion stars, 0:19:54.840 --> 0:19:57.320 then that means that the Milky Way might be like 0:19:57.440 --> 0:20:01.920 a million dwarf galaxies all smooth together into one big galaxy. 0:20:02.000 --> 0:20:04.240 But you said the range is between like a dwarf 0:20:04.280 --> 0:20:07.640 galaxy is between a thousand and several billion. Yeah, Well, 0:20:07.680 --> 0:20:09.679 you know, this is one of those sort of artificial 0:20:09.680 --> 0:20:12.640 distinctions in astronomy, like what do you call a galaxy 0:20:12.680 --> 0:20:14.479 and what do you call a dwarf galaxy. There's this 0:20:14.560 --> 0:20:17.440 threshold of a few Above a few billion or a 0:20:17.480 --> 0:20:20.960 few tens of billions of stars, it's called a galaxy, 0:20:21.200 --> 0:20:23.960 and below that it's called a dwarf galaxy. For example, 0:20:24.080 --> 0:20:27.600 the large Magellanic cloud is orbiting the Milky Way and 0:20:27.600 --> 0:20:30.400 it has like thirty billion stars in it. Some people 0:20:30.440 --> 0:20:32.600 call it a dwarf galaxy. Some people say, no, no, 0:20:32.720 --> 0:20:35.000 it's its own galaxy, and so that's a bit of 0:20:35.000 --> 0:20:36.760 an artificial distinction. But if you want to go like 0:20:36.840 --> 0:20:39.560 all the way back to the og galaxies out of 0:20:39.600 --> 0:20:41.720 which everything was built, then those are all going to 0:20:41.760 --> 0:20:44.359 start out pretty small. So if those are like a 0:20:44.400 --> 0:20:46.720 few thousand stars, then it's going to take millions of 0:20:46.760 --> 0:20:50.200 those to make a milky way. I feel like, if 0:20:50.240 --> 0:20:52.640 you have a thousand stars, maybe you shouldn't be called 0:20:52.640 --> 0:20:56.159 a galaxy, you know, that's such a that's more like 0:20:56.200 --> 0:20:58.600 a I don't know, like a star neighborhood or something 0:20:59.040 --> 0:21:02.520 star clump associated stars. That's the bias, right, that's us 0:21:02.600 --> 0:21:06.560 looking at our neighborhood and observing other galaxies. But something 0:21:06.600 --> 0:21:09.640 we learn as we develop better tools is to see 0:21:09.720 --> 0:21:12.040 fainter stuff, is to discover the stuff that is not 0:21:12.200 --> 0:21:14.960 as easy to spot. And the whole history of science 0:21:15.359 --> 0:21:18.439 is us drawing big conclusions from the stuff we first 0:21:18.480 --> 0:21:21.800 see and then discovering, oh, that wasn't representative. It turns 0:21:21.800 --> 0:21:24.160 out we need to revise our whole picture of how 0:21:24.200 --> 0:21:27.080 things work. And so we've been seeing the biggest, brightest, 0:21:27.119 --> 0:21:30.160 most exciting galaxies, but there the whole spectrum of other 0:21:30.240 --> 0:21:31.760