We’ve Been Wrong About Black Holes

[00:00:00]Every galaxy has a super massive black hole at the center. In some cases, [music] they could be up to a billion times heavier than the sun. We think that the galaxy and the super massive black hole at the center are very closely linked. So, we see a lot [music] of very clear correlations between how heavy the black hole is and how heavy the [music] galaxy is in its stars, in the amount of stars it has towards the center of [music] the galaxy, but then also like how the stars are moving. What are the processes that [music] could be happening inside the galaxy itself to take material from nice stable orbits around the very center and actually send [music] it tumbling towards the middle?

[00:00:35]By growing the black hole, you can almost kill the galaxy.

[00:00:44]Hi, Dr. Becky Smith. Thank you so much for welcoming us into your beautiful office in the University of Oxford.

[00:00:51]We're here today to talk about black holes, which I think everyone is fascinated by. Black holes in of themselves are incredibly mysterious.

[00:00:59]So, what is a black hole? What's going on in the interior of a black [laughter] hole?

[00:01:03]>> I guess we don't really know.

[00:01:05]>> So, we define it as the thing inside the event horizon, that radius around the black hole, this like sphere of unknowing >> stuff, right? We don't get any information from, we don't get any light from. So the black hole is everything inside the event horizon, but we have no idea what that looks like.

[00:01:24]I mean, I like to say that black holes have been terribly named because I think they give people a massive misconception of what they are. People imagine a hole, you know, something like that is nothing in space when in fact they are quite literally mountains of matter that we can't see. like dark star might be a better word for it because especially when you think about how they're formed from when a star runs out of fuel and goes supernova, you take the core of the star that you know has been turned from hydrogen into helium by nuclear fusion and then through the supernova probably converts helium into heavier things like carbon, oxygen, nitrogen all the way up to iron and then there's no process that it can resist gravity crushing it down anymore. So you've taken something that's made of all the elements of the periodic table >> and [clears throat] you've crushed it until you can't see it.

[00:02:12]>> Which is why I think dark star might be a a better, you know, word for it. And we can't say, you know, okay, this black hole is made of this much hydrogen versus this much iron or whatever. All of that information is lost when the black hole is formed.

[00:02:24]>> They only have really like three simple properties or at least like three things that capture what they are.

[00:02:29]>> Exactly. Yeah. Like mass and and spin and charge. That's that's it basically.

[00:02:34]That's all we could know about a black hole. And you specialize in possibly the most charismatic form of black hole, which are these super massive black holes. So, it seems like every galaxy has a super massive black hole at its center. And a lot of the properties of that galaxy depend on the super massive black hole. What's going on there?

[00:02:51]>> Yeah, [laughter] it's a big question and it's one we've spent, you know, decades trying to figure out as well. Like we say it so casually now, like every galaxy has a super massive black hole at the center. It's based on, you know, years worth of of research to get to this point. So, we think that the galaxy and the super massive black hole at the center are very closely linked. So, we see a lot of very clear correlations between how heavy the black hole is and how heavy the galaxy is in its stars, in the amount of stars it has towards the center of the galaxy, but then also like how the stars are moving as well. Like if they're very ordered rotation, then we think that the black hole isn't quite as heavy. But if they're very scrambled, then we think the black hole is a is going to be a lot heavier. So there's a very tight correlation there. And so what we think is happening between a black hole and a galaxy is that the two are what we say co-evolving together, like growing up together, you know, hand in hand. And one of the big mechanisms that we think affects galaxies over their lifetimes is if they merge together with another galaxy. And this we think can grow both the galaxy and the black hole together and how they co-evolve together.

[00:04:01]>> So you know if you think about galaxies and how they form and you see these galaxies with these beautiful spiral structures they're these really nice like flat disc galaxies. They're almost kind of like a blown up version of the solar system, right? You've got the black hole at the center and you've got everything just nicely orbiting around the center. All the stars making these beautiful spiral patterns. If two of those galaxies merge together, all of that gets scrambled up. So no two stars will ever like collide in a galaxy merger just because of how big space is.

[00:04:33]Like the nearest star to the sun is four light years away. So if we think about in terms of like what that would look like if the two actually merged and collided, most of the time the stars just passed by each other.

[00:04:44]>> But what happens is that there's a lot of scrambling in all of that process as well. So you redistribute a lot of the angular momentum so that the spin in the galaxy and you take things from nice ordered orbits and you send stuff tumbling towards the center. So that reshapes the galaxy but it can also grow the black hole as well. And then maybe even the two super massive black holes in the center will merge as well. And so this is how we end up with this really nice tight correlation between black hole and galaxy or at least that's how we thought we ended up with these really nice tight correlations. That was like the leading hypothesis for decades and it definitely does happen. It's definitely how a lot of black holes do grow but we don't think it's the entire picture now.

[00:05:27]>> So tell us what made us rethink our picture of what is going on.

[00:05:31]>> Yeah. So it's a lot of the work that I've been doing is um how black holes grow when a galaxy has been left alone for its entire life when it hasn't merged with something else. when it stays this beautiful nice flat disc of a spiral and is left to its own devices.

[00:05:47]Essentially, we looked at the super massive black holes in the centers of these galaxies to work out how massive are they because the assumption was if they've never merged with another galaxy, the super massive black hole should be on the smaller side. When I say smaller, I don't mean size smaller necessarily. I mean like the mass of it is smaller. So for a super massive black hole, you're talking more like a million times the mass of the sun as opposed to a billion times the mass of the sun, which is what we find. Yeah. In one of these galaxies that has merged together.

[00:06:17]>> So what we look for in the galaxy is that pristine sort of spiral shape that tells us that it has been left alone.

[00:06:24]>> If the galaxy had had a merger and all of that scrambling had taken place, then you would expect a galaxy to have what we call a central bulge. So essentially like you have a sphere of stars in the center where everything is orbiting the center but it's not on like a nice flat plane like >> it's a little bit chaotic different directions.

[00:06:44]>> Exactly. Yeah. All different planes.

[00:06:45]Kind of like a beehive, you know, just like everything is is going round but it's all it's all very chaotic. And if you have enough merges, eventually like you completely destroy the the spiral disc shape entirely and you end up with something that is just an entire sphere of stars, you know, that's just held up by the fact that everything is just very chaotic.

[00:07:04]>> So the shape of the galaxy really encodes like its history. So by looking for these nice >> pure disc galaxies, we're like, okay, that's not had a merger. Therefore, the black hole has never been able to grow thanks to a merger either. Mhm.

[00:07:19]>> So we went out and measured the super massive black hole masses in these kind of galaxies and found they weren't on the lighter side like expected. In some cases they could be up to a billion times heavier than the sun.

[00:07:33]>> And so they were much larger than expected. They didn't lie on the nice correlation either that we see between galaxies and black holes. They were above it. They had heavier black holes than you would expect for the galaxy properties. So there was clearly something going on here in these isolated galaxies.

[00:07:51]>> And then our friends who run simulations of the universe as well. And you know they literally go from start with a big clump of hydrogen gas. What do you get out of it if you put all the laws of physics in?

[00:08:03]>> They actually sort of tracked okay where is the material that's ending up in the black holes coming from? M >> and they found that in about 35% of the time of the cases >> it was coming from a merger event. So either from the fact that you you scramble everything up, you send gas tumbling towards the center which eventually ends up in the black hole and grows the black hole >> or it's the fact that two two black holes have merged. It's like a combination of those things. 35% of the time it comes from merges. And that was like an upper limit in some other simulations that weren't like we didn't directly collaborate with. they find that it's like 15%. You know, it's lower.

[00:08:42]>> So, basically, at least 65% of the time, it seems like it's something else that's growing black holes. Something else is feeding these black holes. So, they get super massive.

[00:08:54]>> We've discussed, you know, a couple numbers here, a million times the mass of the sun to a billion. How big can these black holes actually get?

[00:09:02]>> Yeah, that's a big question in sort of like research. So there's a lot of people who model like the black holes themselves and have found that they think there might be a limit to at least a black hole that we can see which always throws people when I say that because people are like well black holes famously [laughter] are black you know they they don't have light that they emit right we can't really see them necessarily >> because of the fact that the gravity is so strong that we can't get any information or light from them everything gets trapped there but we can actually see the material around a black hole.

[00:09:35]>> So because the gravity is so strong, any material that is close enough by will end up in what we call an accretion disc.

[00:09:42]>> So it's a disc of material that is spiraling around the black hole that will eventually grow the black hole in mass and will get trapped there. And we can see that >> because it's moving so fast that material because of how strong the black hole's gravity is. It heats up.

[00:09:55]>> Yeah. And some of our viewers might have seen that really famous image of Sagittarius a star where like it's just a glowing ring and in the center is that's the black hole.

[00:10:03]>> Exactly. Yes. So that's really really close in. You can see that glowing ring.

[00:10:06]But these accretion discs sometimes can span much much larger than that. So our black hole in the center of the Milky Way not very active at all. Not really growing that fast at all, which is possibly the reason that we might all be here in the first place is is is for that. But if we had a very active black hole, it could have galaxywide consequences. But it it's it's the accretion discs around them glow very very brightly. It's how we see black holes. It's how they were first discovered. So we discovered what we call quaazars back sort of like in the late 20th century sort of like 70s I think ' 80s and they were originally dubbed quazars because it was a port monto of quasi stellar objects >> something that sort of looked like a star >> but wasn't a star you know they were really bright pimp pimp pricks of light and it was only thanks to the launch of the Hubble Space Telescope that they resolved the galaxies around these very bright pimp pricks of light and those pimp pricks of light are essentially >> the material around the super massive black hole. So it's growing glowing so so brightly that we can see it and out outshines you know entire galaxies of stars >> and some some of that light to my knowledge comes from the black hole ejecting or just having very very energetic almost burps of gas as well.

[00:11:19]>> Yeah, that can sometimes happen as well.

[00:11:20]So if you put too much material in the regions around a black hole, the pressure can sort of grow because I like to remind people black holes they aren't just endless hoovers. They can't just like take everything, right, that you throw at them because the material is almost fighting to get down into the black hole. It has to collide to lose energy enough that it, you know, isn't just orbiting the black hole. It actually is spiraling and will eventually make it in. So, if you throw a lot of material into that one very what is quite small region because black holes are so dense, right? they're very compact, you can increase the pressure so much that you end up with this burp, this releasing of energy uh in the form of either, you know, hydrogen gas and radiation making it back out into space.

[00:12:03]And so this is what I was alluding to before when I said that black holes can have these huge consequences on their galaxies because these burps can either be sort of like almost like a wind. You can imagine it outwards from the black hole or sometimes if you have very strong magnetic fields, you can end up with them in in jets that are ejected like up and out from sort of like the pole of the spin of the black hole. It doesn't come from the black hole itself because nothing can escape a black hole.

[00:12:25]It comes from the regions around it. Um, and that material as well can if it impacts with the material in the galaxy can heat up that material or it can even pick it up and eject it out of the galaxy entirely. And that's the material that the galaxy would use to make new stars. So the black hole by by growing the black hole you can almost kill the galaxy >> which is like an insane thing when you think about the scales involved here because >> if the galaxy was you know the size of a grain of sand >> the black hole would be smaller than an atom but the jets it can give off would be like extend across your entire palm.

[00:13:02]>> Yeah. So the fact that like something so yes heavy but tiny you know something that can fit you know within the scale of the solar system but is a million to a billion times heavier than the sun >> has then an impact across hundreds of thousands of light years.

[00:13:17]>> Yeah. A huge galaxy and honestly like even though it's super m like a lot of mass compared to the galaxy it inhabits also not that much mass.

[00:13:25]>> Yeah. Yeah. Like less than 1% of the entire galaxy's mass. Right. And it's very intriguing when people think about the super massive black hole in the center of the galaxy. I think they do picture sort of like a solar system model, right? Where you have the sun in the center and you have the planets going around. You have the black hole in the center. You have all the stars in the galaxy going around. But actually, because the black hole in terms of like the the mass of a galaxy is so small, you know, it's it's a small percentage.

[00:13:50]If you took the black hole out of the center of the galaxy, the galaxy would be absolutely fine. It would carry on as is. Whereas if you took the sun from the solar system or the solar system, it would be chaos, right? Everything would would fly off in different directions.

[00:14:03]So it's a very different setup to the solar system, even though I think that's how people picture it in their heads. So it seems like understanding these super massive black holes is almost like understanding like the fate of of the galaxy eventually. Um and so can you tell us a little bit about the two types of galaxies we see that's to my knowledge just like this one type of galaxy which forms a lot of stars super active and this other one where galaxies are kind of done with with forming stars they're kind of more static uh they're almost like this is almost like the two stages of life for a galaxy >> and it's really intrinsically tied to um this idea of what shape the galaxy is as well. So we have a lot of star forming galaxies and we have a lot of dead galaxies. We also have a lot of spiral galaxies and we have a lot of what we call elliptical galaxies which are those sort of spheres of stars that I was talking about before. And so a spiral galaxy tends to be the thing that if you have a star forming galaxy it's most likely to be spiral. So roughly um like I think it's something like 70% of spiral galaxies are forming stars and 30% of them are not. Whereas for elliptical galaxies, these big spheres of stars about 90% of them are dead and only 10% of them are forming stars.

[00:15:17]>> So the question is how do you end up with that mix in the universe?

[00:15:21]>> And so there are like questions about what processes are responsible for stopping forming stars >> and what processes are responsible for transforming the shape. So one we might expect is a merger of a galaxy again, but merger of two galaxies again might transform the shape, but also again in that scrambling process might heat up the gas that you would otherwise use to make more stars in the future because you need cold gas to make new stars.

[00:15:46]>> Unintuitive. Yeah.

[00:15:47]>> Yeah. Unintuitive because you think heat up the gas, make a really hot star, but actually you need it very cold so that essentially gravity can start to pull on that gas. You need it sort of the gas to be very non-energetic. You need to be very calm so that gravity can clump it together to make it dense enough to form a star. The gas is very very hot, has too much energy, the molecules are quite literally bouncing off the walls, you know, holes in space, but you know what I mean. Um, and so therefore, the gravity can't take an effect to clump it together to make it dense enough to form a star.

[00:16:16]>> So merges could be one of those things, but also the black hole, right? And this is kind of what your thesis touched on, which is like there's these kind of two stages of of a galaxy's life and then a very like sparssely populated kind of third category in the middle. Um where it seems to be kind of that transition from one to the other. So tell us just like the fate of a galaxy does it transition very quickly from one to the other uh and what role do black holes play in that?

[00:16:42]>> Yeah. Yeah. So we think it's all again to do with the shape of the galaxy. So we think spiral galaxies if they make that transition to stopping forming their stars that seems to happen quite slowly.

[00:16:52]>> So a very slow sort of like transition period through to being sort of what we call red and dead.

[00:16:58]>> So star forming galaxies tend to be very blue in color because lots of hot stars are forming. Non-star forming galaxies tend to be very red in color because it's kind of like the dying embers of a fire, right? People always get confused by that, right? that blue is hot and red is not because that's not what taps have been telling us our entire lives. But you think of it kind of like um like a a Bunson burner. Yeah. Like a Bunson burner or the flame on your hob is a lot hotter, right, than a dying embers kind of fire flame which is a lot redder. Um and so spiral galaxies you think make this transition from blue to red, from star forming to not very slowly. Whereas these elliptical galaxies we think make that transition very quickly, transforming their shape very quickly at the same time. But sometimes also we think maybe they can rejuvenate their star formation again if you have like a big influx of everything cools down and you can get it re-triggering star formation or if you have some outside sort of like in infall of gas maybe like a a very small galaxy sort of you know pops in like a pebble into a pond or something can reinvigorate star formation too. So we think galaxies aren't just moving from blue to red.

[00:18:01]Maybe there's some movement from red to blue as well. Mhm.

[00:18:04]>> But one of the processes that we think can trigger this killing of a galaxy is the growth of the black hole and is like the these outflows and these jets.

[00:18:12]There's big arguments about whether do they just kill galaxies. These big black hole burps like is that the only thing they do or can they also trigger more star formation because if you put out this shock wave into the galaxy that can shock gas and clump [clears throat] it together and so you could end up with stars forming along where the shock has traveled as well. So there's a lot of sort of like evidence that both can happen. It's just trying to work out what happens most often and what's the the most dominant effect.

[00:18:39]>> Yeah. And it seems like a really prevalent question that's kind of the through line of all these all these different open questions >> is how do you grow a black hole? What are the different mechanisms you could possibly feed a black hole? Uh and so walk us through just like time to grow a black hole in a box. How do we how do we feed it best?

[00:18:56]>> Yeah. Yeah, I mean that's basically what my research is on right now is if it's not mergers growing super massive black holes or it can happen but if it's not all the time >> what processes are responsible? So if we think okay we've got an isolated galaxy there's obviously no external influences going on. So what are the processes that could be happening inside the galaxy itself to take material from nice stable orbits around the very center and actually send it tumbling towards the middle. So we think the spiral arms might uh play some sort of role acting as sort of like funnels for gas to travel down. You also see some galaxies with what we call a bar structure through the middle. So it's like this long straight structure that then the spiral arms come out of the ends of. And so we think the bar might also act as a funnel.

[00:19:43]>> But then also one idea is that galaxies could actually take in material from um what we call the cosmic web. So it's the structure that connects galaxies essentially across the universe. If you plot the positions of galaxies out that you find when you look out with our telescopes with these big surveys and sort of make that plot in three dimensions and just keep zooming out, you'll see this structure of the universe emerge, which is kind of like a sponge. Yeah, >> you've got lots of galaxies all clumped together at nodes and then they're connected by these like filaments between them and then you have big voids in the middle of all that.

[00:20:20]>> There seems to be gas that could also flow along that too and we see this big structure popping out when we simulate the universe forming as well.

[00:20:28]>> And so if this gas does flow along these filaments that connects all these galaxies, you could have gas coming into the galaxy that way that could feed the black hole. Mhm.

[00:20:36]>> So, there's lots of different ideas for what could be going on, but we just don't know which one it actually is. Uh how efficient these processes are. If one, you know, perhaps there's some ideas that the the bar in a galaxy might be the thing that can push the most material into the center. That's what simulations suggest, but we don't know that yet from observations. So, it's like which one's going on? Which one's the most dominant? How efficient are all these processes? We just and and is the are these processes dominant across all of the time in the universe? Because one might be dominant now as we look at the universe around us. But in the more distant universe in the past cuz light takes time to travel to us. So as we see things more distant, we're seeing them as they were billions of years ago.

[00:21:21]>> You know, in the past were different processes dominating instead.

[00:21:25]>> There's so many open questions like that that we're just actively working on trying to solve.

[00:21:29]>> Yeah. And before I ask you how, you know, what kind of evidence do we need to gather before we can actually settle these questions, what's the actual importance of of nailing this down? Like why does it matter >> how a black hole got so big or whether or not it could have gotten got gained most of its mass early on in the universe? What's the actual impact of settling questions?

[00:21:50]>> Why do we care? Basically, yeah.

[00:21:51][laughter] >> Um, I mean, the black hole is just a key component of understanding galaxy evolution as a whole. how galaxies have evolved to go from the early universe to today which then ties into cosmology which is how the universe as a whole has evolved from what it was you know billions of years ago to what we see today so in that sense it's like one very important piece of the whole puzzle >> I guess you could then ask why care about astrophysics and cosmology at all in the first anything >> yeah exactly and I mean for me I just think humans are naturally curious and discovery is so important and it ties into all of that.

[00:22:29]>> For those that don't think that's important, um this kind of blue sky research where you're asking these big questions directly does affect society eventually down the line. So for example, astrophysics research has led to first of all digital cameras.

[00:22:45]>> Astronomers needed a better way to record how much light is hitting, you know, they originally had photographic plates and like film, right? And it was just like it it is bright compared to this, right? there was no way of measuring it very analytically and so they invented digital detectors that could record this much light has hit this pixel versus this pixel and the Hubble Space Telescope was one of the first things that really had the you know early what we call CCDs like charge couple devices which were this much light in this pixel versus not and now we all have them in our pockets right in in our phones every day right so that's directly come out of astronomers being like I need to record how bright this thing is >> and then radio astronomy has produced usable Wi-Fi basically Wi-Fi radio astronomy. So if you think about the fact that your Wi-Fi router sits in your house and just pings out a signal that bounces off every wall, window to get weaker and weaker and weaker so that by the time it reaches your phone or your laptop, it's the slowest internet possible, right?

[00:23:44]>> But radio astronomy had the same problem. They need really big telescopes to detect the really long wavelengths of light from astronomy that are like, you know, over meters, 10 meters, 100 meters long. And so they, what they do instead of building one giant telescope is they use lots of little detectors and combine them all into one telescope. So you've got weak signals from lots of little places that need combining into one strong signal. So they developed that algorithm that people were like, "Oh, we could actually use that to make Wi-Fi good." And so now we all have good Wi-Fi as well. And then you think about the fact that you know with the likes of the launch of the James Websp space telescope for example or you know any telescope to be honest that we get images from that we have to be like we need to understand how to process this image to remove all the sources of noise to pull together like from radio astronomy different sources of information from from ether different telescopes all that kind of image analysis directly then leads into things like medical imaging as well. So a lot of the algorithms that were developed to process astronomy images are now used in medical imaging as well. So it just there's so many things that then lead to you know various different things that are advantageous to society. And I think the thing that's happening now in astronomy that leads into my work is there is a radio telescope for example um the SKA that's currently being built to again help understand these black hole burps. It's just one thing that they're going to look at, but there's so many different areas of astronomy they're going to focus on. It's going to take data so fast that we're not going to be able to get the data off the [snorts] like data server quick enough >> to be able to study it faster than it's actually taking the data. Mhm.

[00:25:27]>> So you then get into a point where people astronomers are now going to be pushing for okay can we have better like data access you know sort of like bandwidths and things like that to make that quicker better data transfer speeds and then that's going to then again impact on data transfer around the world whether that is for news or communications or you know even sort of like things like banking and stuff like that you know you can imagine a future where that's improved because of again because of radio astronomy.

[00:25:52]>> Yeah. and we're entering kind of that era of just like huge huge volumes of data coming in from these telescopes. So one thing you know I'm super compelled by is like the huge impacts that James Web specifically has made on our understanding of just the universe. So are there any surprising observations that James Web has made on your field of research?

[00:26:12]>> Yeah, definitely. So one fun thing that appeared well there was I guess two for my area of research specifically. The first one was that there were far more of these disc galaxies at greater distances than we ever thought. So earlier in the universe's history than we ever thought. So the early universe would have been very chaotic, you know, lots more mergers and it we thought it took a really long time like a couple of billion years before everything started to calm down and settle into these nice ordered rotation like disc galaxies. We thought everything would be really irregular before that. And then JC just kept being like, "Oh, there's some more disc galaxies at this distance. Oh, and another one like even further and more and more and more even further away." So that was very exciting to to sort of think about, okay, >> maybe sort of those two shapes that we're used to seeing nearby, maybe that sort of like sequence popped out earlier than we thought in the universe history.

[00:27:06]And then it also found more massive black holes earlier in the universe's history than we'd expect too because of that issue of the fact that you can't throw that much material at a black hole and it just grow. There is like a limit to how fast it can grow because of that release of pressure that needs to happen.

[00:27:22]>> And so there's a set amount of time, right, that you need to be able to grow a super massive black hole to become super massive. If the only thing that can form a black hole that we know of anyway is like a supernova, >> which forms something like 10 times heavier than the sun, there's a set amount of time that you need to go from 10 times heavier than the sun to at least a million times heavier than the sun.

[00:27:41]>> And yet we were seeing a million times heavier than the sun black holes way earlier than that time frame.

[00:27:47]>> You know, sort of like 800 million years into the universe's lifetime, right?

[00:27:50]Which is a very short amount of time. So now people are saying maybe there's another way you can form a black hole in the early universe then. like maybe you can take a clump of gas and just directly collapse it back down >> into a black hole skipping star and supernova and everything that you need.

[00:28:05]>> So that was very very intriguing for me because I'm like well I'm looking at different ways of growing black holes that might be more efficient if you have lots of discs and a does lots of discs in the early universe and black holes are more massive than we think. So that's been very fun. Um, and then outside of my field as well with the JBT, it's been the the little red dots discovery has been like something that's been one of those ones that like >> red dots. Yeah.

[00:28:27]>> Yeah. It's really grabbed a lot of people to be like, "What what are they?

[00:28:31]They're weird." You know, they're these things that people went looking for. So, people were actively looking for growing black holes in JWST data, but specifically they were looking at spectra. So when you take the light from a galaxy and you you split it into its rainbow of light essentially and you make a graph, >> what colors do we see? Yeah.

[00:28:51]>> Yeah. Exactly. You make a graph of what colors of light, what wavelengths of light do we see? And usually from a galaxy, we get lots of very clear spikes of light that come from specific elements. So hydrogen or oxygen and silicon, they all glow at a very specific color or wavelength. When you have a black hole there and you've got hydrogen spiraling around the black hole, you don't just have a very sharp specific color because the color gets red shifted and blue shifted. It gets Doppler shifted as it moves towards and away from you. So that sharp spike gets smeared out in a graph.

[00:29:22]>> Yeah. It's kind of just like how an ambulance moves towards you kind of hear it almost like different frequencies even though really it's just emitting one frequency gets like really high pitched and then low pitched. Yeah.

[00:29:32]>> Yeah. So a high pitch light is a blue light and a low pitch light is is a red light essentially. So we see that same change in in sort of pitch but it's in wavelength of of in color.

[00:29:41]>> And so we look for these sort of like broadened emission lines in spectra. And so people went looking for those found a bunch and we're like okay these must be growing super massive black holes. Hey, what do they look like?

[00:29:52]>> Oh they're weird little red dots. like there doesn't seem to be like what we'd expect is it's actually like the images behind you at the moment actually which is where you see the galaxy and then a bright point of light in in the middle >> where you that's the light from the black hole and then the galaxy is around it >> when we're looking at the little red dot is that the black hole is that the galaxy >> we're not sure so then people went to look for well can we find more red dots in JST images and they found >> loads of them like way more than we were expecting and then we're like well these must be growing super massive black holes too. But then they got the spectra for the images they found and they didn't always have these broadened emission lines. So it's been a real fun sort of like who done it almost, you know, to be like what actually are we seeing? And lots more evidence that's been gathered. There's this weird sort of shape they have to their spectrum as well where they have this like Vshape where there's like more blue light and more red light but not as much in the middle which is weird. That's not what you'd expect from a black hole or a galaxy really. So, we think dust might be uh at play here. So, like heavier elements in the universe that block a lot of light, but also very dense gas as well. One of the leading ideas now is that they're in like a really like dense cocoon of gas, the black holes, and the red dot is essentially that dense gas that's reprocessing all of the the light from the accretion disc around the black hole.

[00:31:13]>> Yeah, that's super interesting. One thing that I think I've noticed throughout this interview, which is that, you know, like black holes, we think that they're black, but we mostly see them as like really bright points of light, and that's the main way that we detect them. Is it possible that there are like these ultra ultra massive black holes that we just like cannot see?

[00:31:32]>> I mean, there's a lot of black holes that we can't see. So, there's like I think we think 10% of super massive black holes are active right now and are growing and therefore we can actually see the points of light around them. And it's only when they have these accretion discs around them that we can actually understand their properties as well. So it's through those we can measure the mass and then measure the rate they're growing at and things like that. But there is a question of whether as black holes get more massive whether we'll they sort of like wink out and they can't have these accretion discs anymore. So there's a couple of different sort of radi you can draw around black holes. The most famous is like the event horizon, right? That's the point of no return. That's when the gravity is so strong that you'd have to be traveling at the speed of light to be able to escape it.

[00:32:17]>> The next one out that you can draw is what's called the innermost stable circular orbit. So that's when you can actually have something on an orbit around the black hole. Any closer to the black hole, you're not going to be able to orbit it. You you're just going to spiral in and get lost. So that marks sort of like the inner edge really of sort of the accretion disc. tends to push a little bit further out for various different reasons, but that's kind of like the edge of where you can have something around the black hole is the accretion disc. The next radius out that you draw though is what's called the self-gravitational radius.

[00:32:47]>> And that's the reason that we have a galaxy of stars at all [laughter] because at that radius essentially if you have like a cloud of gas, >> that cloud of gas is more attracted to itself by gravity than it is to the black hole. The self gravitational radius, right? And so that means a clump of gas can form a star that ends up in orbit around the black hole rather than just slowly eventually falling towards the black hole. So it's why we have a galaxy of stars in the first place because that radius exists.

[00:33:18]>> But what's interesting to think is what happens when the innermost stable circular orbit pushes past the self-gravitational radius. That happens as a black hole grows. So as a black hole gets heavier and heavier >> the event horizon pushes out >> but the innermost stable circular orbit pushes out.

[00:33:36]>> Really the self gravitational radius doesn't push out as fast. So you can end up in a situation where >> one eclipse is the other.

[00:33:42]>> One eclipse is the other. You no longer can actually get an accretion disc forming around the black hole because they're just going to form stars instead.

[00:33:49]>> So no accretion disc means a no growth of the black hole >> and b it doesn't light up so that we can see it. Mhm. And so it's really interesting to think is there like what point does that crossover between those two things happen.

[00:34:02]>> And it does depend on a number of things especially like if you've got a black hole that's spinning as opposed to just like static.

[00:34:09]>> So it if it's spinning it can push it out a little bit. So you can get heavier and heavier black holes. But we think the top limit is around about 100 billion times heavier than the sun. Mhm.

[00:34:17]>> We found a black hole that's around 60 billion times heavier than the sun, which if it was not spinning, we wouldn't be able to see, but we think all black holes are spinning because >> whatever, you know, all the gas that's gone in to form them was spinning. So, you can't really shake the spin. So it's interesting to think whether that black hole which is called to 618 is like reaching the sort of limit of how how heavy black holes can grow >> through this accretion disc process.

[00:34:47]>> Interesting.

[00:34:48]>> Like there's nothing stopping you like throwing it like directly down into the black hole and it would obviously grow with it. But the main way we think they grow through these accretion discs is no longer possible for something that big.

[00:34:58]>> And then it would, you know, wink out.

[00:34:59]We wouldn't be able to see it either.

[00:35:01]like they could be all be out there in the centers of galaxies and we just don't know because we can't measure their masses and know that they're that heavy.

[00:35:06]>> It's wild. Yeah. And so just like you know you specialize in super massive black holes, but are there like tell us about the the zoo of black holes that also exist?

[00:35:15]>> Yeah, cuz they're super massive. Yes.

[00:35:17]But there's also what we call stellar mass black holes. So these are the black holes that form after supernova >> around about 10 times heavier than the sun cuz it's massive stars that end up collapsing to form black holes. Like the sun won't form a black hole when it dies. It'll form a black hole's baby brother. It's called a white dwarf. Um which is just a star that's essentially made of like you know very very dense uh helium like packed down essentially where it's electrons as tightly packed as they can go.

[00:35:45]>> And so that's what's like resisting gravity. Um, and so you can have stellar mass black holes, you can have super massive black holes. We find a load of each of those, but it's like what about in the middle [laughter] what we call intermediate mass black holes. Something say like 10,000 times heavier than the sun or 100,000 times heavier than the sun.

[00:36:04]>> We don't really find anything interesting >> in that region, right? It's called the mass gap >> because there really is just like a gap of things that we don't find from around about 100 or so times heavier than the sun up to a million times heavier than the sun. And there's lots of different, you know, sort of ideas of why that might be. There's just not a formation mechanism in there to make something that heavy. That maybe a lot of the growth of super massive black holes happened early in the universe. Hence, they all sped through that phase very quickly. And now today, we've been left with, you know, just the super massive things.

[00:36:35]>> It's hard because we'd like to be able to see if we can find them in the early universe, but the smaller the black hole, the less it lights up the material around it. So it's fainter and so we don't spot them and so it gets very difficult to sort of try and figure out what's actually going on in that mass gap. And that's definitely one of the big unknowns around black holes still.

[00:36:54]>> Yeah. And correct me if I'm wrong, but there's also like a a kind of type of black hole I've heard of, which is a a primordial black hole.

[00:37:01]>> A primordial black hole. Yeah. Oh, I love primordial black holes. They're very cool. So this is a hypothetical type of black hole. So we don't really have like evidence that they actually exist. But the idea is that >> in the very early universe when you know we just had this what we call like a soup of matter, right? It was just like there was just atoms and they weren't really doing much except just sort of like clumping together and uncclumping and clumping and under gravity and things like that. The idea is that the universe might have been so dense then that you could have had matter clumping together that would sp like spontaneously clumping that would then give you a density enough so much that you would form a black hole that it would be so dense that light couldn't escape. And so there's the idea that the early universe did that to the point where it would have formed so many of them that they just pervade the entire universe and would, you know, be anywhere from, you know, like micro kilograms all the way up to maybe even earth mass in some cases.

[00:38:00]>> So it's fun to think about whether they could do that >> and could pervade the universe in that way. There's some ideas that maybe that's what dark matter is made of.

[00:38:09]>> A lot of people like developing that idea. There's some pieces of evidence that fit that. There's some pieces of evidence that that don't fit that idea at all. So, you know, it's kind of trying to figure out what's going on.

[00:38:19]>> But it's exciting to think that they might exist. There are some clues from what we call surveys where you know they're sort of surveying stars in the galaxy and they're looking at the brightness of those stars and the brightness of the one star might have just like really strangely like flared in brightness for a very short space of time like micros secondsonds like yes stars vary in brightness naturally you know there are sort of like pulsations and there are planets that pass in front of them that cause them to dip in brightness >> but this one has sort of been like lensed like the brightness has sort of artificially just been lensed like something's passed in front of it that we can't see >> which people suggest might be primordial black holes which would be really fun you know to sort of prove them in that way um that they do exist but for now they still remain hypothetical >> but they're kind of hard to spot because not only do you know can can black holes grow but they can also slowly I guess like evaporate as well >> they can yeah so again this is another hypothetical idea um evaporation of black holes this is what Stephen Hawking worked on in his lifetime was this idea of hawking radiation >> which is that the only way that a black hole can dissipate over time is by losing energy. So E= MC² is what Einstein told us energy and mass are equivalent. So if you've got mass locked in a black hole, it is trapped there forever unless >> Hawking radiation is real.

[00:39:43]>> So it's a weird one because it gets down into like quantum physics. But essentially at the event horizon what can happen is the mass of the black hole can produce like two quantum particles spontaneously one of which ends up back in the black hole but the other one escapes >> as gamma radiation and stuff as well. It could perhaps do that. So you do radiate energy away >> and therefore reduce the mass of the black hole.

[00:40:07]>> Yeah.

[00:40:07]>> But the rate that that happens at is so incredibly slow.

[00:40:10]>> It's just a weak signal that we can't really ever directly observe it.

[00:40:14]>> Exactly. Yeah. So people are hoping maybe to detect the gammaray radiation from Hawking radiation if they can. And if there is a big collection of primordial black holes perhaps at the center of the galaxy or something, we might be able to see that signal.

[00:40:26]>> Mhm.

[00:40:27]>> There's a lot of work maybe going into it, but it's such a faint signal that a lot of people don't have hope that we'd ever be even be able to detect it.

[00:40:33]>> Unless we somehow learn how to grow a black hole in a lab, >> which I don't think we will do. Uh but maybe we could have one nearby. There's an idea that maybe this Have you heard of planet 9? that might be out there.

[00:40:46]Yeah. So, obviously people say planet 9, is it Pluto? Sadly, no. [laughter] Uh Pluto got demoted nearly 20 years ago now. I think 20 years ago this year.

[00:40:53]>> Uh and so the idea is that there is still something at the edge of the solar system though that could be influencing the orbits of some of the objects out on the edge of the solar system. Um and people have been searching for this planet that we might have missed >> for a very long time and not found anything.

[00:41:11]>> It's nice to think that like we're in the solar system. We've we've seen like light years away, but we still don't really know our own neighborhood all that well.

[00:41:18]>> Exactly. Yeah. Finding things that don't glow. Very difficult. It turns [laughter] out you have to look in like infrared cuz you know objects have some sort of like inherent thermal energy that they'll radiate but infrared gets very very faint. So it's very very difficult. So there are some people suggested because we haven't found anything. What if planet 9 is actually a primordial black hole [laughter] around about 10 times heavier than Earth, but because it's a black hole would be squashed down into the size of a tennis ball.

[00:41:44]>> And so if that actually is the case, and it's a big if, >> then that might be a test bed for Hawking radiation, for detecting gamma rays from it. If if it is actually radiating and hawking radiation, maybe we could even send a probe to it to test it as well and test our ideas around the gravity around black holes. That would be very cool. But obviously it's a big if of whether there even is a planet 9 out there and that's what's causing this like shephering of uh orbits of these objects in the edge of the solar system in the first place and if that even is the primordial [snorts] black hole.

[00:42:14]>> I like how >> Yeah. [laughter] I like how there's like different mysteries and someone just goes, "Oh, what if it's a primordial black hole?"

[00:42:20]>> Yeah. And so we touched on dark matter and we were talking I guess like just before this interview that people sometimes get a little bit skeptical when when you raise dark matter mostly because there's a lot of unknowns. We don't really know what dark matter is or consists of. Um, so tell us just like how do we know that dark matter is a thing?

[00:42:37]>> Yeah. Yeah. It's understandable because when I say like, oh, dark matter is matter, but it just it doesn't interact with light.

[00:42:44]>> So, it doesn't absorb light. It doesn't emit light. It doesn't radiate light in any way. What that means in terms of physics is that it doesn't interact with the electromagnetic force. And there are a number of different like fundamental forces in physics. Gravity is one, electromagnetism, strong force, weak force. Those are things that like bind atoms together and uh govern radioactivity for example.

[00:43:07]>> So basically when you're saying it doesn't interact with light, that sounds very weird so that we can't see it, but really all we're saying is it just doesn't interact with one of those forces in the same way that some elements aren't radioactive. So don't interact with the weak force which governs radioactivity.

[00:43:21]>> So that's one of the things that sort of helps people understand, okay, right, it's not that weird necessarily. But also, if you're still struggling with this idea, like I like to say we don't we can't see the wind.

[00:43:31]>> Yeah.

[00:43:31]>> But we still know it's windy because trees move.

[00:43:33]>> Yeah.

[00:43:34]>> Right. That is how a lot of our evidence of dark matter like that's where a lot of it comes from. So we see for example >> that galaxies and galaxy clusters can act as big lenses. So Einstein said in his theory of general relativity that if you have a massive object, it curves space itself. And objects moving on that curved space is what gives you the effects of gravity essentially. And so when we have like a a big galaxy or a big galaxy cluster curving space in front of galaxies in the background, instead of seeing galaxies as they actually look like, the light travels on that curved space to us and we see them all warped.

[00:44:12]>> Yeah. And from the amount of warping, you can work out, okay, how heavy is the thing that's doing the warping, the big galaxy or galaxy cluster. And when you do that calculation using Einstein's theory of general relativity, you get a mass way more than we can see in stars.

[00:44:29]You go, okay, well, there's gas and there's dust and there's black holes and there's planets and there's things that don't glow. Fine. You take into account all of that and it's still way more matter than we can actually see. Like five to 10 times more matter than we can actually see and account for there.

[00:44:41]>> Mhm. Yeah.

[00:44:42]>> So that's one big piece of evidence for dark matter. The other big piece of evidence is when we simulate the universe and we put all our known laws of physics into a computer >> and we say go and we see what comes out of it. If there isn't dark matter there, galaxies don't form in the way that we see around us today. You need this what we call cold dark matter there to make galaxies form. Mhm.

[00:45:05]>> So those are like two of the big pieces, but there's lots of other, you know, pieces of evidence that are out there as well that we have for this idea of dark matter.

[00:45:12]>> Really, all of it rests on whether you believe Einstein's theory of general relativity is the best theory of gravity that we have. So there's a lot of people that are working on alternate theories of gravity >> that essentially like okay well if we change gravity then those calculations that we do for how much mass is there doing the warping of the background galaxies or when we put those laws of gravity into a big simulation we do end up end up with like you know the galaxies we see today can we do an alternate theory of gravity >> that does make sense >> and I think this is a disconnect that happens between you know this like scientists and the public is they assume, you know, that we're wedded to this idea of dark matter definitely existing.

[00:45:54]>> But in actual fact, there's a lot of scientists working on getting rid of it from our models if we can.

[00:46:00]>> But they haven't been able to find anything better than Einstein's theory of general relativity, which is why we still come back to it.

[00:46:05]>> But also this idea of, you know, we get new evidence and new observations all the time. So we do have to change our our theories. So maybe in the future it will be that, you know, dark matter was a placeholder for something else that we just didn't understand.

[00:46:16]>> Yeah. If we figure something like that out, I think scientists would absolutely celebrate rather than be like, you know, like, ah, damn, dark matter [laughter] was wrong. They'd be like, oh, wow, we've learned this thing. Never mind dark matter. You know, and I think that's what's interesting as well when you know the history of dark matter research. Like I like to say it was the the most begrudgingly like accepted theory in all of physics. You know, it took 20 or 30 years for people to be like, "No, actually, I think this is a thing." People were [laughter] like, "Surely not. That can't be like, you know, 10 times as much like dark matter that we can't see than normal mass. That can't be a thing. But yet, just the evidence just kept piling and piling up until it became undeniable. At least if you believe Einstein's theory of general relativity, which that's the best theory of gravity we seem to have. All evidence points to yes, it is.

[00:47:02]>> So, it's just up to us to figure out what's going on if we Yeah. believe that.

[00:47:07]>> Yeah. And it seems like lots of people who are working on like these absolutely huge questions all get drawn to black holes because they're almost like these extreme test beds where we can start to think about the convergence of say quantum mechanics and gravity. So tell us a little bit about just like black holes how can they help us understand just like these edges of physics. Yeah, it's I mean they push everything to the extreme and it's the extreme where you start to break things like in the classic example of like you know we thought Newton's theory of gravity was everything in terms of our theory of gravity and it's only when you start to get into heavier objects like the sun for example and Mercury's orbit you see that it doesn't fit Newton's predictions for what Mercury's orbit should be that you realize oh you need Einstein's theory because that actually takes into account the fact that when you start to get heavier objects things change >> maybe by probing now around black holes, right? Going to the real extreme of you you've literally curved space as much as you possibly can. You got the heaviest gravity is where then we can really test and try and see if we can break Einstein's theory of general relativity in the way that we broke Newton's theory of of gravity.

[00:48:10]>> Mh.

[00:48:11]>> And like you know things like um for example the event horizon telescope that took that first image of the black hole that you were talking about before. We have one from Messia 87's black hole. We have now from our own super massive black hole at the center of the Milky Way Sagittarius Aar. We have these images. They're not just images, right?

[00:48:28]They're also observations. They're data where we can test gravity itself and say, is Einstein's theory of general relativity giving us the right prediction for what this material that is producing this glow of this radio light that's been detected? Is that giving us what we would predict with is the general activity, or is it giving us something completely different that perhaps another theory of gravity can better explain? And all signs point to Einstein was right at the minute.

[00:48:53][laughter] But we'll see. Yeah. And it's by probing that that maybe we'll get a breakthrough in quantum gravity as well. It's one of the the big things of physics is the fact that we have this theory of quantum physics, but it's very separate from Einstein's theory of general relativity.

[00:49:08]And we need them really to be together.

[00:49:11]We need them to be able to almost like talk to each other to explain maybe black holes, but also like what happened in the very first sort of fractions of a second of the universe as well. There's so many unanswered questions that we could get at >> if we had a theory of quantum gravity.

[00:49:26]So, a lot of people working on that as well.

[00:49:28]>> Yeah. And so, tell us just like what's the state of play in terms of like the evidence that we have now? What can we discern from the kind of data that we're drawing from telescopes and detectors right now? And what are like the detectors like on the horizon that we can look forward to and what will they be able to tell us?

[00:49:43]>> Yeah. Okay. So, like the big questions we're asking now. So there's a lot of big things in terms of black hole growth like you know what processes are responsible how efficient are they then we're asking how do like can you form a super massive black hole in a different way these are the kind of questions that we're answering now with the likes of the James web space telescope with what we call IFU data as well which integral field unit which is where you take an image of the galaxy at every single wavelength or you can think of it as like a spectrum at every single pixel it's so much data it's so beautiful it's my favorite kind of data [laughter] to get and to get your hands on and to work with. So, we're answering those kind of questions now. But I think with the advent of things like the Reuben Observatory, which has literally just come online and started taking data, which is a huge survey telescope, so it's been built in Chile.

[00:50:34]>> Mhm.

[00:50:34]>> And um it'll essentially every three nights >> take a new image of the entire sky that it can see from Chile.

[00:50:42]>> Um which is amazing. So basically anytime anything changes or moves or flares in brightness we will get you know a new sort of data point on that.

[00:50:50]So when we're studying black hole growth you know >> that accretion disc is not like a static object. It's moving. It's changing.

[00:50:57]There's more material coming in all the time. So it's always varying in brightness. So the fact that we're going to have like variability data for all of the growing black holes that we know of is going to be amazing and I can't wait for it.

[00:51:10]>> Yeah. basically like the transition from like film photographs to to video.

[00:51:15]>> Yeah, exactly. [laughter] Exactly that.

[00:51:16]We have video for like a few you know grown black holes and a few stellar mass black holes in in in the Milky Way but now you know to have it for anything that you can spot in the sky.

[00:51:26]>> So excited for that. Uh and then in terms of like resolving galaxy shapes which is very important to me as well because I need the shape of the galaxy that encodes the history to know what the galaxy's been through. We then have like the Uklid space telescope that's just been launched by issa for example and it started its survey of the sky as well.

[00:51:44]>> It's kind of like imagine the Hubble ultra deep field >> but for the entire sky. That's the kind of data we're going to get with Uklid.

[00:51:50]So we're going to be able to resolve and change you know things that look fuzzy from the ground into these crystal clear structures and be able to tell you know is it spiral? Does it have the the sort of the the bulge in the middle or not?

[00:52:02]You know that kind of those kind of questions.

[00:52:04]>> Yeah. And get stunning photographs along the way.

[00:52:06]>> Yeah. Exactly.

[00:52:07]>> And I think one of the perks of being an astrophysicist is that you get to go to some pretty stunning locations. So tell us like have you ever gone to these like pristine night sky locations?

[00:52:18]>> Yeah, definitely. It's definitely one of the perks of the job and the fact that we have to build telescopes away from light pollution and high up so that you're like above all like the humidity and the turbulence and everything in the air. And so it tends to be in farong places like Hawaii and the Canary Islands and Australia. So yeah, I've been to uh the summit of Mount Aaya, which is so incredible. Although it's so high up there, it's like 4,000 mters that you you tend to have some sort of like, you know, lowle altitude sickness in the way that like your body conserves oxygen. So it takes oxygen away from your eyes. So you almost get out and you're like, "Oh, it's not actually that cool this guy." And then someone's like, "Take a hit of oxygen," you know, kind of thing. And you you take a hit and it's like, "Wow." Everything just like pops out and appears, which is incredible. One of my favorite night skies is actually from the Palmer in the Canary Islands. We have telescopes on the top of the mountain there as well.

[00:53:09]That's incredible because that's only like 2,000 meters. So, you really have like this incredible night sky stretched out ahead of you. And the setup up there is very very cool too cuz now there's enough telescopes on the mountain that they've built like um you know like a little hotel that all the astronomers stay on during the day when they sleep you know and then they work at night kind of thing. But one of the telescopes I worked on was the Isaac Newton telescope, which is like a UK owned telescope up there, which was built back in the 70s. And so when they built it, that hotel thing just didn't exist. So they uh built like obviously sort of like astronomer quarters under the telescope, under the control room. So it has like, you know, a bed and a kitchen and a library and everything you would need to live up on top of the mountain.

[00:53:48]And also the bathrooms, which are still the bathrooms that you use if you observe at the telescope overnight from the control room. The thing is they don't like you to turn on any lights in the rooms because like you could have light leakage that could affect your observations or could affect any anybody else on the mountain using the other telescopes that could affect their observations. And so you're like basically walking through this like abandoned 70s what feels like an underground bunker [laughter] in the darkness trying to use the L in the middle of the night at like 2:00 a.m.

[00:54:21]while you're observing. um which you know you can almost like hear the cinemas worth of people watching a horror film like screaming at you to turn on the light while you're doing it.

[00:54:30]Right. It's um >> forget back rooms. This is like the new setting for like a horror movie.

[00:54:35]>> Yeah, exactly. Like you're very aware of it and you're very like [laughter] I'm very aware as like the small female.

[00:54:41]I'll probably die first in the horror movie as well, right? So I'm always like [laughter] But uh it feel it feels worth it when you get your scientific data, you know? So yeah. And on top of just go getting to go to all these like cool locations doing like world changing science, you you also run a YouTube channel.

[00:54:57]>> Yeah. Um, so I just love communicating science with people. I love chatting with people about science and I'm very aware that like the research that I do and that I absolutely love to do and that I've made my, you know, life and career around it is funded by the taxpayer, you know. And in the same way that I love to hear what marine biologists are doing because I'm obsessed with dolphins and whale sharks, [laughter] I think, well, there are other people that love space and astronomy in the same way that want to hear about what we're up to. And so, if there are people that want to chat science with me, I'll happily chat science, you know, and and so when I was going through my PhD, I was doing a lot of, you know, uh, public lectures and things like this and engaging with the public on like open days and things. And then one of my first jobs out of my PhD was up at the University of Nottingham. It was a research fellowship. It was 90% research, but it was also 10% of my time was making videos for their existing YouTube channel. It was called 60 Symbols. Sure, there are people watching now that remember watching a 60 Symbols video. Um, there was a producer that would turn up with a camera and just be like, go film and have a chat about something cool.

[00:56:03]>> And I fell in love with that idea of just yeah, chatting about whatever you found really interesting that was going on. And when I left that position to come here to Oxford, I couldn't be on the channel anymore because it was Nottingham's channel and that was fine.

[00:56:16]But the producer Brady Haran, who runs Number File, Computer File, 60 Symbols, all of these amazing channels, he was like, "You could do it, you know, just just film yourself and cut out the things you don't want and cover those cuts with some images of galaxies and and you'll be fine and you'll figure it out." And I I really did just figure it out. I like to joke that I did another PhD just in in video editing, you know, and video production. And the first videos on my channel are blurry and bad audio, you know, and like the editing is really basic. But it was really fun when a video topic that I've made that I was like, "This is really cool. We're chatting about it in, you know, the like the department now like people would connect with and find and the algorithm would push out as well, you know, and it would reach more people and the channel grew and I'm just really pleased that there are just so many people that seem to love space as much as I do." Yeah, it does help you. You study possibly the coolest things in space.

[00:57:12]>> Yeah, [laughter] I think yeah, people don't just love space as much as I do, but they're as intrigued by black holes as much as I am as well.

[00:57:18]>> And so, final question. Of course, you study black hole formation and growth as well as its relationship with I guess the fate of every galaxy. So, I think people are going to be interested.

[00:57:29]>> Can you foresee the fate of our own galaxy?

[00:57:32]>> Ooh, yeah. So, that's an interesting one. Um so in terms of the Milky Way's black hole and the Milky Way as a whole I guess um the biggest thing coming up I guess is the merger with our closest neighbor Andromeda or M31 as it's sometimes known it's around about 2 and a half million light years away currently but in around 5 billion years or so the Milky Way and Andromeda will merge and collide. So it comes back to that idea of okay we're going to scramble up that nice beautiful spiral shape of the Milky Way that we have currently and the spiral shape of Andromeda. Will we form an entire sphere of stars, you know, one of these sort of elliptical galaxies by the end? We don't know. It depends on how what the angle they come in at and whether other galaxies nearby will also play a role.

[00:58:16]Um how many passes they might make cuz they sort of slosh together as well.

[00:58:20]>> And so in terms of the black hole, it will probably grow a lot bigger in that process. It probably merge with Andromeda's super massive black hole at the center of that as well. Grow a lot bigger. might end up burping, which could be a big deal as well because when these black holes burp, you know, they put a lot of radiation out through the galaxy that could ripple through. So, not only do we have to think, okay, well, where's the sun and the solar system going to end up in all of this sloshing and redistributing around, but will it get impacted by this high energy radiation that's burped up by the accretion disc around the black hole as well?

[00:58:49]>> Like I alluded to this before, it could be the reason that we're all here right now >> is because the fact that the Milky Way's black hole isn't that big. It's not had one of these big periods of activity in the nearistant past when life has been evolving on Earth >> and therefore that's the reason that we're all here because we haven't been disrupted by one of these big black hole burps.

[00:59:10]>> Yeah. We're one of those pristine ones that have been left alone for the most part.

[00:59:13]>> Exactly.

[00:59:14]>> Yeah. Well, that was a fascinating conversation. Thank you so much for speaking with me. And if you enjoyed my conversation with Dr. Becky as much as I did, you can consider going to her YouTube channel, learning so much more about the universe. Or if you haven't had enough questions today, check out our montage where we unpack mysteries of reality. Thanks for watching.