WEBVTT - Listener Questions Volume #2 0:00:05.960 --> 0:00:10.000 So I absolutely love talking about the tiniest little particles, 0:00:10.119 --> 0:00:12.399 the hearts of black holes, and how we could be 0:00:12.480 --> 0:00:14.200 misunderstanding like all of it. 0:00:14.720 --> 0:00:18.800 And I love talking about parasites, teeny tiny little wasps 0:00:18.880 --> 0:00:22.600 and dung beetles. But judging from my husband's face at 0:00:22.600 --> 0:00:26.200 the dinner table, it's possible that not everyone shares exactly 0:00:26.239 --> 0:00:26.960 my interests. 0:00:27.320 --> 0:00:30.400 So what do you want to hear about for the podcast? 0:00:30.440 --> 0:00:33.080 We usually pick topics that excite us and we think 0:00:33.120 --> 0:00:35.600 you'll enjoy, but you know we both have our weird 0:00:35.680 --> 0:00:38.720 quirks and preferences, so we want to hear from you. 0:00:38.960 --> 0:00:42.000 We'd love to answer questions you have about the universe, 0:00:42.040 --> 0:00:46.200 what you think is extraordinary and interesting and needs more explanation. 0:00:46.600 --> 0:00:49.479 Sometimes we turn your idea into a whole episode. Sometimes 0:00:49.479 --> 0:00:52.280 we give you a fifteen minute answer during a listener 0:00:52.400 --> 0:00:53.280 question session. 0:00:53.640 --> 0:00:55.720 And the questions you send us will help us more 0:00:55.840 --> 0:00:59.480 generally to gauge our audience's interests, which help us pick 0:00:59.560 --> 0:01:01.040 additional topics for the future. 0:01:01.160 --> 0:01:03.680 So please don't be shy I send us your questions. 0:01:03.720 --> 0:01:05.880 We want to hear from you. We want this podcast 0:01:05.920 --> 0:01:08.880 to be about what you are curious about, and today 0:01:08.880 --> 0:01:13.200 we're tackling three fantastic, hilarious, amazing questions send to us 0:01:13.319 --> 0:01:16.440 by listeners just like you, And if you want. 0:01:16.280 --> 0:01:18.160 To be on the next show, you can email us 0:01:18.200 --> 0:01:20.680 at Questions at Daniel and Kelly dot org. 0:01:20.840 --> 0:01:22.400 Your science podcast fame. 0:01:22.440 --> 0:01:28.399 Awaits Welcome to Daniel and Kelly's Extraordinary Universe. 0:01:42.040 --> 0:01:45.199 Hi. I'm Daniel, I'm a particle of physicist and I've 0:01:45.319 --> 0:01:47.080 never run out of questions. 0:01:47.280 --> 0:01:47.480 Hi. 0:01:47.800 --> 0:01:51.000 I'm Kelly Wiener Smith And every question I ask pleads 0:01:51.000 --> 0:01:52.080 to even more questions. 0:01:52.360 --> 0:01:53.360 Why is that? Do you think? 0:01:53.720 --> 0:01:56.120 Because we know so little about everything? I think at 0:01:56.160 --> 0:01:57.000 the end of the day. 0:01:57.520 --> 0:02:00.760 See, we even have questions about questions, there's never an 0:02:00.880 --> 0:02:01.320 end to them. 0:02:01.520 --> 0:02:04.280 So my question for you today, Daniel, is when you 0:02:04.320 --> 0:02:07.040 were working on a PhD, did you get a satisfying 0:02:07.080 --> 0:02:08.360 answer to your big question? 0:02:10.200 --> 0:02:12.880 You're really going to ask me that that's so embarrassing. 0:02:13.639 --> 0:02:16.840 You know. I did a PhD which was pretty technical. 0:02:17.080 --> 0:02:21.240 I was measuring how often two top quarks are made 0:02:21.440 --> 0:02:24.120 and decay in a very specific way. And it was 0:02:24.200 --> 0:02:26.760 only when I was writing up my thesis five years 0:02:26.800 --> 0:02:29.560 into the project that I did enough reading of the 0:02:29.639 --> 0:02:32.760 literature to understand, like, hey, is this interesting at all? 0:02:32.919 --> 0:02:36.120 And how am I contributing to the scientific conversation? And 0:02:36.160 --> 0:02:39.200 that's when I learned I basically wasn't. Oh no, So 0:02:39.680 --> 0:02:40.160 what did. 0:02:40.000 --> 0:02:41.840 You publish it? Anyway? I guess at that point you 0:02:41.880 --> 0:02:42.160 have to. 0:02:42.520 --> 0:02:44.440 Yeah, absolutely, you have to. And you know that's just 0:02:44.480 --> 0:02:47.560 part of the process, because when you start graduate school, 0:02:47.560 --> 0:02:49.320 you're like a science baby. I mean, you have your 0:02:49.440 --> 0:02:52.480 inspiration for why you want to study particles, but you 0:02:52.480 --> 0:02:54.640 don't know what the interesting questions are and what we 0:02:54.639 --> 0:02:56.919 could actually learn in a reasonable amount of time. So 0:02:57.280 --> 0:02:59.520 you rely on senior people the guide you and help 0:02:59.520 --> 0:03:01.840 you pick a time topic and get started on it. 0:03:02.280 --> 0:03:04.720 And so it was only when I finished my thesis 0:03:04.720 --> 0:03:06.680 that I feel like I knew enough to know what 0:03:06.800 --> 0:03:08.160 was interesting and what wasn't. 0:03:08.639 --> 0:03:10.239 Oh man, that's frustrating. 0:03:10.440 --> 0:03:12.640 I always tell the students that I work with, do 0:03:12.639 --> 0:03:13.720 you feel like you've read enough? 0:03:13.919 --> 0:03:14.840 Yeah? You haven't? 0:03:14.960 --> 0:03:16.920 Keep reading, go back and read, and they're like, no, no, 0:03:16.919 --> 0:03:19.399 I'm good. I'm like, oh, you're good, read twice as much. 0:03:19.800 --> 0:03:20.600 Are not good? Yet? 0:03:20.639 --> 0:03:22.760 You just need to keep reading. That solves a lot 0:03:22.760 --> 0:03:24.639 of problems. But man, it's hard to know when to stop. 0:03:24.800 --> 0:03:29.160 And that's why your book has such a lengthy bibliography. 0:03:29.320 --> 0:03:31.120 At least I practice what I preach. 0:03:31.440 --> 0:03:34.320 Yes, And how about you? Do you feel like your 0:03:34.320 --> 0:03:36.960 thesis was exciting, was compelling that you got to answer 0:03:37.000 --> 0:03:38.400 a big, fat, juicy question. 0:03:38.760 --> 0:03:42.480 I was asking whether or not this brain infecting parasite 0:03:42.640 --> 0:03:45.720 changes like some personality traits in the fish that it infects. 0:03:46.080 --> 0:03:49.280 And after like seven years it took me a really 0:03:49.280 --> 0:03:53.880 long time to get my PhD. The answer is like no. 0:03:55.960 --> 0:03:58.560 But you know, negative answers are just as important, right, 0:03:58.560 --> 0:04:01.040 you can't not publish it because the answers not exciting 0:04:01.600 --> 0:04:04.560 or not that interesting. It's important to cross things off 0:04:04.560 --> 0:04:07.400 the list. You know. I've been doing particle physics for decades. 0:04:07.440 --> 0:04:09.880 I've never discovered a new particle. Every single paper I've 0:04:09.880 --> 0:04:12.000 written is like, and we didn't find this, and we 0:04:12.040 --> 0:04:14.280 didn't find that, and we didn't find this other thing. 0:04:15.560 --> 0:04:18.200 I felt like I had designed a really good experiment, 0:04:18.279 --> 0:04:20.160 and so when I decided the answer was no, I 0:04:20.200 --> 0:04:21.520 was like, Oh, the ANSWER's really no. 0:04:21.720 --> 0:04:22.440 I feel good. 0:04:22.240 --> 0:04:24.279 About the answer being no, so yeah, no can be 0:04:24.279 --> 0:04:27.359 a satisfying answer. Also, but my PhD advisor would like 0:04:27.360 --> 0:04:28.720 me to finish publishing that paper. 0:04:28.920 --> 0:04:31.479 Wait, still are you joking, No, I mean it. 0:04:31.720 --> 0:04:32.880 Yeah. 0:04:32.960 --> 0:04:36.000 I've published a lot of side projects, and actually all 0:04:36.040 --> 0:04:39.640 of those side projects ended up becoming my dissertation. So 0:04:39.720 --> 0:04:42.560 we have had a lot of publications together, but the 0:04:42.640 --> 0:04:46.120 main project ended up being so massive and overwhelming and 0:04:46.120 --> 0:04:48.240 hard to analyze that I still haven't had a chance 0:04:48.240 --> 0:04:50.159 to write it up. But that is my twenty twenty 0:04:50.160 --> 0:04:52.400 five project, and that's why I wrote a bunch of 0:04:52.400 --> 0:04:55.240 my other collaborators to say, I'm not doing anything else 0:04:55.279 --> 0:04:55.680 this year. 0:04:56.040 --> 0:04:57.800 I'm finally going to publish my PhD. 0:04:58.080 --> 0:05:00.000 Was it also your twenty twenty project and your twenty 0:05:00.040 --> 0:05:05.640 fifteen projects? Yeah? Science takes a while, people, Science takes 0:05:05.680 --> 0:05:06.360 a while. 0:05:06.360 --> 0:05:09.800 It does, unfortunately, But you know what doesn't take a 0:05:09.839 --> 0:05:11.720 while sending an email to. 0:05:11.680 --> 0:05:12.080 You and me. 0:05:12.400 --> 0:05:15.960 That's right, and our amazing listeners have done that. And 0:05:16.000 --> 0:05:19.400 we have three fantastic questions today, all of them sort 0:05:19.400 --> 0:05:21.719 of more Daniel centric, but we've got a lot of 0:05:21.800 --> 0:05:26.480 Kelly centric questions queued up for our next Audience Questions episode. 0:05:26.839 --> 0:05:29.640 But should we jump into our first audience question today? 0:05:30.080 --> 0:05:32.200 Absolutely, let's do it. And as a reminder, we're going 0:05:32.279 --> 0:05:34.000 to be answering this question from a listener and then 0:05:34.080 --> 0:05:36.520 reaching out to the listener to give us a grade 0:05:36.560 --> 0:05:39.120 to see did we answer your question or did we 0:05:39.200 --> 0:05:43.400 just confuse even more or leave you unsatisfied with Nobody 0:05:43.400 --> 0:05:46.640 knows the answer, which is usually the way things turn out. 0:05:47.560 --> 0:05:50.120 But at least that's a real answer. So here we go. 0:05:50.920 --> 0:05:53.400 I have a question about the presence of super massive 0:05:53.400 --> 0:05:57.279 black holes in our galaxy. So my understanding is, we 0:05:57.360 --> 0:06:00.360 have evidence that a number of smaller galaxies have merged 0:06:00.360 --> 0:06:03.240 with the Milky Way in the past, right, and pretty 0:06:03.279 --> 0:06:07.160 much all galaxies have super massive black holes at their center, right, 0:06:08.040 --> 0:06:11.840 So what happened with those other black holes when they 0:06:12.040 --> 0:06:15.039 entered our galaxy? Unless it was a direct hit, they 0:06:15.080 --> 0:06:18.520 wouldn't have merged with our black hole immediately, right? So 0:06:18.560 --> 0:06:22.000 how long did this merger take? And in the interim 0:06:22.160 --> 0:06:24.839 it seems like there could have been just several super 0:06:24.880 --> 0:06:28.200 massive black holes flying through our galaxy circling the center. 0:06:28.720 --> 0:06:31.880 Do we have evidence of that happening? It seems like 0:06:31.920 --> 0:06:34.200 they must have left quite a path of destruction through 0:06:34.200 --> 0:06:37.040 the Milky Way. If not, is it strange that we 0:06:37.080 --> 0:06:40.279 can't find evidence of this? And could any still be 0:06:40.320 --> 0:06:41.159 out there right now? 0:06:41.640 --> 0:06:42.080 Wow? 0:06:42.279 --> 0:06:46.280 This is a super interesting and super informed question. Where 0:06:46.279 --> 0:06:48.960 do we start here, Daniel, Maybe we start with what 0:06:49.240 --> 0:06:51.760 happens when galaxies merge, because this was all sort of 0:06:51.800 --> 0:06:52.240 a new to me. 0:06:52.800 --> 0:06:56.039 Yeah, this is a really fascinating question, basically wondering like, 0:06:56.600 --> 0:06:58.839 why don't we see a bunch of black holes zooming 0:06:58.839 --> 0:07:00.640 around the center of the galaxy. Why does it seem 0:07:00.720 --> 0:07:03.039 like there's only one in the center of the Milky Way. 0:07:03.640 --> 0:07:06.440 Chris is a pretty sophisticated understanding of how galaxies merge, 0:07:06.440 --> 0:07:08.600 and that's suggests to him like there should be a 0:07:08.600 --> 0:07:10.600 bunch of black holes. And that's my favorite kind of 0:07:10.680 --> 0:07:14.400 question when you hear a listener having internalized something about 0:07:14.400 --> 0:07:17.520 physics and then drawing some conclusion, comparing that to the 0:07:17.600 --> 0:07:19.760 understanding and being like, wait, some thing's not fitting here. 0:07:19.840 --> 0:07:22.880 What am I missing? Because that's the essential process of science, 0:07:22.960 --> 0:07:26.080 right build that model compared to the data, update it. 0:07:26.080 --> 0:07:28.520 It's wonderful to see it happening in real time. So yeah, 0:07:28.560 --> 0:07:30.960 I agree we should start by reminding the listeners, at 0:07:31.040 --> 0:07:33.320 least who might not know as much as Chris does 0:07:33.400 --> 0:07:35.160 about how galaxies come together. 0:07:35.520 --> 0:07:37.600 Based on what you just said, I just want to 0:07:37.640 --> 0:07:40.640 confirm is it actually the case that every galaxy has 0:07:41.080 --> 0:07:43.840 a black hole at the middle, because I hadn't realized that. 0:07:44.000 --> 0:07:45.920 But we've seen a lot of galaxy, so we should 0:07:46.240 --> 0:07:48.120 know if that's a consistent thing or not. 0:07:48.320 --> 0:07:51.040 So that's a great question. We don't have a definitive 0:07:51.040 --> 0:07:53.480 answer because we can't look at every galaxy in the universe. 0:07:53.520 --> 0:07:56.760 But every single galaxy we've looked at has a supermassive 0:07:56.760 --> 0:08:00.120 black hole at the center, or we can explain where 0:08:00.120 --> 0:08:02.040 it went, like it got kicked out, or there's a 0:08:02.080 --> 0:08:05.880 collision or something. So there's very strong evidence that every 0:08:05.920 --> 0:08:08.760 galaxy has a super massive black hole, but it's not 0:08:08.840 --> 0:08:11.520 something we understand. If we try to model the formation 0:08:11.600 --> 0:08:14.040 of those black holes are the centers of galaxies, The 0:08:14.160 --> 0:08:16.720 models don't describe the data, like we can't get our 0:08:16.760 --> 0:08:18.680 black holes to be as big in the models as 0:08:18.680 --> 0:08:21.520 we see in reality, like they're huge black holes of 0:08:21.600 --> 0:08:24.240 the center of galaxies only a billion years after the 0:08:24.320 --> 0:08:26.680 universe forms. We have no idea how you make such 0:08:26.680 --> 0:08:29.240 a big black hole so quickly. So there's a lot 0:08:29.280 --> 0:08:32.200 we still don't understand about super massive black holes. For sure. 0:08:32.400 --> 0:08:34.719 Do we know why there's a super massive black hole 0:08:34.760 --> 0:08:36.959 at the center of every galaxy does that make sense. 0:08:37.360 --> 0:08:39.560 We don't know why they're so big, but it makes 0:08:39.600 --> 0:08:42.080 sense that. You know, galaxies are big pools of stuff, 0:08:42.080 --> 0:08:44.360 and stuff pulls on itself and falls towards the center, 0:08:44.800 --> 0:08:46.840 and eventually, if you get stuff dense enough, you're going 0:08:46.920 --> 0:08:49.000 to get a black hole. So it makes sense to 0:08:49.040 --> 0:08:50.920 have a black hole at the center of every galaxy. 0:08:50.960 --> 0:08:53.880 It's the densest point, and you cross that threshold, you 0:08:53.880 --> 0:08:54.520 get black holes. 0:08:54.559 --> 0:08:57.600 So yeah, okay, all right, So then let's back up 0:08:57.600 --> 0:08:59.360 to what happens when galaxies. 0:08:58.920 --> 0:09:01.760 Merg Yeah, because Chris is asking why we don't see 0:09:01.880 --> 0:09:04.600 multiple black holes at the center of the Milky Way 0:09:04.679 --> 0:09:08.040 from multiple galaxies merging, and this touches on the whole 0:09:08.040 --> 0:09:10.720 story of how galaxies form. We think that all the 0:09:10.720 --> 0:09:13.320 galaxies we see today are made up of a bunch 0:09:13.320 --> 0:09:16.920 of little baby galaxies that came together to make big galaxies. 0:09:17.440 --> 0:09:19.880 So we don't think big galaxies were formed all at 0:09:19.920 --> 0:09:23.200 once into some huge gravitational collapse in the early universe. 0:09:23.600 --> 0:09:25.800 We think that a bunch of little galaxies were made 0:09:26.040 --> 0:09:29.000 and then those galaxies come together to make bigger galaxies. 0:09:29.040 --> 0:09:32.600 It's like a hierarchical bottom up formation rather than just 0:09:32.640 --> 0:09:34.680 like a single formation of a big galaxy. 0:09:35.320 --> 0:09:37.800 Is it easy to explain why we think it started 0:09:37.840 --> 0:09:40.480 with little galaxies coming together as opposed to just lots 0:09:40.520 --> 0:09:41.720 of big galaxies forming. 0:09:41.920 --> 0:09:43.800 For a long time, there were both of those theories, 0:09:43.880 --> 0:09:45.840 the sort of top down and the bottom up approach. 0:09:46.440 --> 0:09:48.600 But you can tell the difference in the models, like 0:09:48.840 --> 0:09:51.280 the age of the stars and the formation and the 0:09:51.320 --> 0:09:53.880 structure of the galaxies are different if you start from 0:09:53.920 --> 0:09:57.040 little ones which then build up together to make big ones. 0:09:57.280 --> 0:09:59.240 And we can see evidence for this, for example, in 0:09:59.320 --> 0:10:02.000 our Milky Way, and surrounding the Milky Way, we see 0:10:02.000 --> 0:10:04.640 a bunch of little galaxies we call them dwarf galaxies 0:10:04.960 --> 0:10:07.280 that are not fully incorporated, that are sort of in 0:10:07.320 --> 0:10:11.240 the gravitational grasp of the Milky Way but not completely eaten. 0:10:11.320 --> 0:10:12.920 So we see a lot of evidence for this theory 0:10:12.960 --> 0:10:15.280 that galaxies are formed sort of bottom up. 0:10:15.480 --> 0:10:18.000 All right, So galaxies are formed bottom up. They all 0:10:18.120 --> 0:10:21.679 have super massive black holes at the center. I think 0:10:21.720 --> 0:10:25.079 we did talk in another episode about how sometimes galaxies merge, 0:10:25.160 --> 0:10:27.240 and this is one way the Earth we could all 0:10:27.280 --> 0:10:28.760 be in trouble if we got too close and we 0:10:28.840 --> 0:10:31.720 merged with another system that's coming back to me now. 0:10:31.840 --> 0:10:34.240 And so these supermassive black holes at the center. Just 0:10:34.280 --> 0:10:37.440 to remind folks, these are not little normal stellar black 0:10:37.480 --> 0:10:40.120 holes like a black hole that you think about from 0:10:40.120 --> 0:10:42.480 a collapsing star, Like a star burns up all of 0:10:42.520 --> 0:10:44.959 its gas and then it can no longer resist gravity 0:10:44.960 --> 0:10:47.480 and eventually collapses and forms a black hole. That's the 0:10:47.520 --> 0:10:50.120 kind of thing we expect to be like ten solar 0:10:50.160 --> 0:10:52.840 masses ten times the mass of our sun. Maybe a 0:10:52.880 --> 0:10:55.800 super massive black hole is something that's like ten thousand, 0:10:56.240 --> 0:10:59.480 or a million, or a billion times the mass of 0:10:59.520 --> 0:11:03.960 our Sun. So like really extraordinarily massive objects that are 0:11:03.960 --> 0:11:06.480 out there at the center of these galaxies. Even these 0:11:06.559 --> 0:11:09.520 dwarf galaxies have them up to like fifty thousand times 0:11:09.520 --> 0:11:10.480 the mass of our Sun. 0:11:10.800 --> 0:11:14.920 So if we know that dying suns cause black holes, 0:11:15.520 --> 0:11:18.560 how do we get super massive black holes. Is it 0:11:18.600 --> 0:11:20.720 like a dying sun party, like they all get together 0:11:20.760 --> 0:11:22.160 to see the sunset or something. 0:11:23.600 --> 0:11:25.440 We don't know the answer to that. Like, if you 0:11:25.600 --> 0:11:27.480 design a model, you say I'm going to use all 0:11:27.480 --> 0:11:29.880 the known physics we have and the gravity, and you 0:11:29.960 --> 0:11:32.600 create these galaxies, you get black holes at the center, 0:11:32.679 --> 0:11:34.800 But they don't get this big, like, they don't get 0:11:34.800 --> 0:11:37.160 as big as we see them out there in the universe. 0:11:37.600 --> 0:11:40.280 So they get massive, and we even call them super massive, 0:11:40.320 --> 0:11:42.480 but they don't get as big as we see so 0:11:42.520 --> 0:11:45.280 we don't understand exactly how they form. There's lots of 0:11:45.320 --> 0:11:48.040 crazy theories. One theory is that black holes may have 0:11:48.040 --> 0:11:51.480 formed much much earlier, they called primordial black holes, before 0:11:51.559 --> 0:11:54.480 even there was matter, when the universe was still cooling 0:11:54.520 --> 0:11:57.440 and coalescing. Instead of making protons, maybe it made a 0:11:57.440 --> 0:11:59.920 bunch of black holes. So the black holes are much 0:12:00.080 --> 0:12:02.560 older than we think, and they've been forming matter for 0:12:02.600 --> 0:12:05.160 a long time. Nobody's ever seen one of these primordial 0:12:05.200 --> 0:12:07.440 black holes, you know. There's a lot of ideas for 0:12:07.559 --> 0:12:10.240 how these black holes could have gotten so massive. But 0:12:10.280 --> 0:12:13.079 for Chris's question, the point is all of these galaxies 0:12:13.080 --> 0:12:15.480 come with a super massive black hole. So what happens 0:12:15.480 --> 0:12:17.800 to the black hole during the merger right when two 0:12:17.800 --> 0:12:20.480 galaxies come together make a bigger galaxy, to the black 0:12:20.480 --> 0:12:23.040 holes always combine? How long does that take? Why don't 0:12:23.080 --> 0:12:25.760 we see black holes in our milky way? This is 0:12:25.800 --> 0:12:29.840 super fascinating because black holes are really awesome objects and 0:12:29.880 --> 0:12:32.640 they're really massive, and the short version of the story 0:12:32.760 --> 0:12:35.319 is that we think galaxies come together and then black 0:12:35.320 --> 0:12:38.440 holes merge. We think that super massive black holes can 0:12:38.520 --> 0:12:41.120 merge into bigger black holes just the same way like 0:12:41.480 --> 0:12:44.760 two stars that are binary stars both collapse to black holes. 0:12:44.880 --> 0:12:48.320 They can combine into a bigger black hole, and we've 0:12:48.360 --> 0:12:51.680 seen evidence of the smaller black hole collapse in merger. 0:12:51.920 --> 0:12:54.839 That's where the famous gravitational waves are from. They're from 0:12:54.880 --> 0:12:57.760 two black holes orbiting each other, going faster and faster 0:12:57.800 --> 0:13:00.240 and faster as they coalesce into a bigger black hole. 0:13:00.800 --> 0:13:04.760 So we've seen gravitational waves from stellar mass black holes. 0:13:05.040 --> 0:13:07.800 And then last year we saw a lot of evidence 0:13:07.840 --> 0:13:12.080 a little bit less direct for gravitational radiation from super 0:13:12.120 --> 0:13:17.079 massive black hole mergers, which we think correspond to galaxy mergers. 0:13:17.480 --> 0:13:20.640 Super massive black holes at the hearts of galaxies coming together, 0:13:21.000 --> 0:13:24.880 swirling around each other, generating gravitational radiation, and then mentionally 0:13:24.920 --> 0:13:28.160 collapsing into a super duper massive black hole. 0:13:28.960 --> 0:13:33.160 Is this a possible explanation for why super massive black 0:13:33.160 --> 0:13:36.040 holes are bigger than theory predicts or has this already 0:13:36.080 --> 0:13:37.720 been explored? 0:13:37.760 --> 0:13:38.439 Like are they bigger? 0:13:38.480 --> 0:13:40.480 Because actually you're just looking at one and it was 0:13:40.600 --> 0:13:43.360 three that came together, or that doesn't explain it. 0:13:43.480 --> 0:13:45.760 No, that doesn't explain it. We include that in our model, 0:13:45.760 --> 0:13:48.600 and it can't describe the black holes that we see 0:13:48.640 --> 0:13:52.120 out there, not something else, some other process that's juicing 0:13:52.160 --> 0:13:54.199 them up. You know, there was this paper last year 0:13:54.240 --> 0:13:56.679 about how black holes could be causing dark energy, and 0:13:56.720 --> 0:13:59.560 this is correlation between the acceleration of the universe and 0:13:59.600 --> 0:14:02.440 the side the super massive black holes. But people don't 0:14:02.440 --> 0:14:05.400 really know if that's anything or nothing. There are papers 0:14:05.520 --> 0:14:08.320 examining like the size of the bulge in the galaxy 0:14:08.400 --> 0:14:10.840 and the size of the black hole. Those seem to 0:14:10.840 --> 0:14:13.520 be correlated, which suggests that it's not just something local, 0:14:13.559 --> 0:14:17.240 it's a bigger process across the galaxy. It's very active 0:14:17.280 --> 0:14:19.080 area of research, and in a few years I think 0:14:19.080 --> 0:14:21.360 we'll know a lot more because we're gathering a lot 0:14:21.400 --> 0:14:24.320 more data about super massive black hole mergers from these 0:14:24.320 --> 0:14:28.000 pulsar timing arrays. You use the whole galaxy basically as 0:14:28.040 --> 0:14:31.000 a gravitational wave detector by looking at how the gravitational 0:14:31.040 --> 0:14:35.440 waves ripple across pulsars. It's really super interesting. One of 0:14:35.480 --> 0:14:37.680 the most fascinating things to me is that we actually 0:14:37.760 --> 0:14:43.280 don't understand how these supermassive black holes merge. Like theoretically, 0:14:43.280 --> 0:14:46.440 it's a little complicated when they get really close together. 0:14:46.760 --> 0:14:48.720 I mean, when they get really close together, I guess 0:14:48.760 --> 0:14:50.840 I would just assume that they like attract each other 0:14:50.880 --> 0:14:53.000 and just like pull each other into each other. 0:14:53.160 --> 0:14:54.040 Or is that too simple? 0:14:54.160 --> 0:14:56.360 No, you're exactly right. And if they're heading right towards 0:14:56.360 --> 0:14:58.640 each other, boom, they just suck into each other. But 0:14:58.720 --> 0:15:02.080 remember they're moving asked already, and if they're not exactly 0:15:02.120 --> 0:15:05.640 angled at each other, they're gonna end up orbiting each other. Right, 0:15:05.680 --> 0:15:09.280 there's gonna be angular momentum. They're spinning around each other. Basically, 0:15:09.320 --> 0:15:11.800 if one black hole passes by the other one instead 0:15:11.800 --> 0:15:14.360 of hit directly hitting it, it's gonna swing around and 0:15:14.360 --> 0:15:16.400 the two are gonna end up orbiting each other. Now, 0:15:16.440 --> 0:15:18.360 if those black holes are surrounded by a bunch of 0:15:18.360 --> 0:15:21.600 other stars, then they're gonna lose energy and they're gonna 0:15:21.600 --> 0:15:24.200 fall towards each other. And you might be thinking, well, 0:15:24.240 --> 0:15:27.680 what about the gravitational radiation is not gonna sap the 0:15:27.720 --> 0:15:30.440 black hole's rotational energy so that they end up falling 0:15:30.480 --> 0:15:34.400 towards each other. Yeah, that's true. That happens, but that's 0:15:34.400 --> 0:15:36.360 not a lot of energy. It's not fast enough to 0:15:36.440 --> 0:15:39.880 explain how they actually fall together. What they need is 0:15:39.920 --> 0:15:43.680 the friction, the tugging from stars and gas and dust 0:15:43.720 --> 0:15:46.800 to slow them down and help them fall in. Gravitational 0:15:46.840 --> 0:15:49.880 waves are not enough. But when they get really close 0:15:49.920 --> 0:15:52.280 and there's no other stars and it's just two black 0:15:52.280 --> 0:15:56.480 holes orbiting each other, we don't understand why they eventually collapse. 0:15:56.520 --> 0:15:59.160 We think that's a stable situation, like two black holes 0:15:59.280 --> 0:16:01.520 orbiting each other with out any stars to slow them 0:16:01.520 --> 0:16:03.600 down or whatever, they should do that for a long 0:16:03.640 --> 0:16:07.320 long time, we don't really understand why they close that 0:16:07.480 --> 0:16:10.600 final gap. We know that it happens because we've seen 0:16:10.640 --> 0:16:14.480 evidence gravitational waves from those mergers, but theoretically it doesn't 0:16:14.560 --> 0:16:17.240 quite make sense. It's called the final parsec problem. It's 0:16:17.280 --> 0:16:20.000 still an open question right now in physics. 0:16:20.240 --> 0:16:22.320 And I'm assuming that we don't have a lot of 0:16:22.360 --> 0:16:26.120 these instances where you have two black holes orbiting each 0:16:26.120 --> 0:16:28.160 other that you can look at to try to get data, 0:16:28.200 --> 0:16:30.440 because that's probably a pretty rare thing to see. 0:16:30.560 --> 0:16:32.760 It is hard to see because super massive black holes 0:16:32.760 --> 0:16:36.160 are in galaxies far far away, and it's very difficult 0:16:36.160 --> 0:16:38.720 to see these things and observe them, and the timescale 0:16:38.720 --> 0:16:41.360 of these things is very, very long, so we have 0:16:41.480 --> 0:16:45.480 not yet detected individuals supermassive black hole mergers. What we've 0:16:45.520 --> 0:16:49.280 detected with these gravitational wave observatories that span the galaxy 0:16:49.600 --> 0:16:52.360 is like a general hum from lots and lots of them, 0:16:52.360 --> 0:16:54.400 so we know that it's happening. But if we can 0:16:54.440 --> 0:16:57.120 get data from an individual and you're absolutely right, and 0:16:57.200 --> 0:17:00.120 track like what's happening over those last few seconds, we 0:17:00.160 --> 0:17:03.200 could learn a lot about how these things collapse. And 0:17:03.240 --> 0:17:05.560 so it's something we haven't understood. But still now to 0:17:05.560 --> 0:17:07.399 answer Chris's question, now that we have sort of the 0:17:07.400 --> 0:17:09.919 background on like how these galaxies merge and how the 0:17:09.960 --> 0:17:13.280 black holes mysteriously merge, even though don't quite understand it, 0:17:13.720 --> 0:17:16.480 Chris is basically asking, if the Milky Ways made up 0:17:16.520 --> 0:17:19.679 of all these galaxies, and those galaxies have black holes 0:17:19.720 --> 0:17:21.600 and they merged, why don't we see a bunch of 0:17:21.640 --> 0:17:24.080 black holes at the center of the galaxy instead of 0:17:24.160 --> 0:17:27.159 just one right, And the answer is that the Milky 0:17:27.160 --> 0:17:30.080 Way hasn't had a big collision recently for some reason. 0:17:30.080 --> 0:17:32.639 The Milky Way is pretty smooth and chill. There hasn't 0:17:32.640 --> 0:17:35.080 been a lot of activity. So if we had recently, 0:17:35.119 --> 0:17:37.160 in the last you know, a few hundred million years, 0:17:37.200 --> 0:17:40.359 collided with a big Mama galaxy, then yes, we probably 0:17:40.400 --> 0:17:43.080 would have two supermassive black holes at the center swirling 0:17:43.080 --> 0:17:45.399 around each other and we could watch it happen and 0:17:45.440 --> 0:17:48.760 maybe learn something about this final parsec problem. But we're 0:17:48.800 --> 0:17:52.119 sort of lucky, I guess, in that over the last 0:17:52.119 --> 0:17:55.760 few billion years we haven't had as many collisions, which 0:17:55.760 --> 0:17:57.800 is probably one reason why we're not as big. Like 0:17:57.840 --> 0:18:01.080 if you look at Andrama, the nearby galaxy much bigger 0:18:01.080 --> 0:18:04.040 than the Milky Way, it's a big Mama galaxy and 0:18:04.359 --> 0:18:06.520 pretty soon at you in a few billion years, we 0:18:06.560 --> 0:18:08.680 are going to collide with it and form some super 0:18:08.760 --> 0:18:11.679 duper galaxy. But we're I guess a little bit quieter 0:18:11.800 --> 0:18:13.800 and a little bit smaller, and that's the reason we 0:18:13.840 --> 0:18:17.200 don't have surviving multiple super massive black holes at the center. 0:18:17.480 --> 0:18:19.520 And just to be clear, the physicist in you would 0:18:19.560 --> 0:18:22.280 really like to be around when our galaxy merges with 0:18:22.320 --> 0:18:25.919 another m H but Kelly and her children would not 0:18:25.960 --> 0:18:27.480 want to be around because that could be a very 0:18:27.560 --> 0:18:28.320 chaotic time. 0:18:28.400 --> 0:18:28.920 Is that right? 0:18:29.160 --> 0:18:31.959 That would be a very chaotic time. Yeah, exactly. You know, 0:18:32.000 --> 0:18:33.959 even though it would be far away, like the collision 0:18:33.960 --> 0:18:37.640