1 00:00:00,740 --> 00:00:16,610 Okay. Okay. 2 00:00:16,620 --> 00:00:24,329 So, yes, today I'm going to talk to you all good on Sandiford about the spaghetti ification of stars by supermassive black holes, 3 00:00:24,330 --> 00:00:28,980 which I think is basically the most extreme event in the observable universe. 4 00:00:29,100 --> 00:00:33,990 Okay. So what we're going to talk about today, we'll start with a tour of the Galactic Centre. 5 00:00:34,410 --> 00:00:36,690 Okay. Which is an interesting object in itself. 6 00:00:37,970 --> 00:00:42,980 I'll explain what on earth I mean by the phrase spaghetti ification, how we ended up with this ridiculous time. 7 00:00:44,340 --> 00:00:48,450 How we may observe spaghetti fide stars in the observable universe. 8 00:00:49,320 --> 00:00:52,700 And then the rest of the talk about what can we learn from these systems? Okay. 9 00:00:53,780 --> 00:00:56,870 So let's take a step back. We're not going as far back as for George. 10 00:00:56,870 --> 00:01:00,860 This is talk, but a little bit further out in Francesco's talk. Okay, let's think about the galaxy. 11 00:01:01,040 --> 00:01:04,280 Okay. So this is the Milky Way. We live here. 12 00:01:04,580 --> 00:01:09,530 Roughly halfway out. Okay. But we're going to focus instead on a central region. 13 00:01:09,740 --> 00:01:16,850 Okay. And as you can already tell from this slide, the key difference between here and here is the density of the stellar environment. 14 00:01:17,420 --> 00:01:22,370 Okay. If I go outside, I look at the night sky. I do see plenty of stars if I'm not in the centre of the city. 15 00:01:23,510 --> 00:01:26,840 But in the study in the Galactic Centre we get a very different picture. 16 00:01:26,880 --> 00:01:32,420 Okay. And if I went to look at the night sky, it would be truly stunning. The density is orders and orders of magnitude higher. 17 00:01:33,420 --> 00:01:36,749 Okay. So let's actually zoom in on the centre of our own galaxy. Okay. 18 00:01:36,750 --> 00:01:40,020 So this is an image of our own galactic centre by shuttle itself. 19 00:01:40,710 --> 00:01:48,330 So, yes, it's an extremely dense environment. And also that the stars are clustered around the very centre which is inside this box. 20 00:01:49,500 --> 00:01:53,490 So we'll zoom in again. We can start to resolve individual stars. 21 00:01:53,500 --> 00:01:59,970 Now we see again incredible density, some quite bright objects, but we're still clustering right around the centre. 22 00:02:00,660 --> 00:02:06,740 So we zoom in once more. Okay. And we can see the now famous star cluster. 23 00:02:07,160 --> 00:02:10,880 Whether or not these are actually famous depends on how much astrophysics you keep up with. 24 00:02:11,120 --> 00:02:18,410 These won a Nobel Prize a couple of years ago. Okay. And so the star clusters are a group of stars at the very centre of our galaxy. 25 00:02:18,650 --> 00:02:24,020 There's 30 or 40 of them. And this ring here is one light month across. 26 00:02:24,220 --> 00:02:27,530 Okay, so that's the distance. Light can travel in a month. 27 00:02:28,310 --> 00:02:33,320 So for reference for scale, the nearest stellar neighbour to the sun is four light years away. 28 00:02:33,920 --> 00:02:38,900 So this distance is 1/50 of the gap between the star and its nearest neighbour. 29 00:02:39,110 --> 00:02:44,490 And we have 30 or 40 stars. So that's the difference. So we can keep zooming in. 30 00:02:44,970 --> 00:02:49,550 You know, it's what we do in astronomy. Okay. And we can. So this is the Nobel Prize winning work. 31 00:02:49,950 --> 00:02:54,330 You can just watch the Galactic Centre and you can watch the stars evolve through time. 32 00:02:54,450 --> 00:02:55,410 You can follow them around. 33 00:02:56,320 --> 00:03:03,490 Case of particularly interesting is, for example, this yellow star where we see it completes an entire orbits of 20 or so years. 34 00:03:04,040 --> 00:03:07,710 Okay. Now you will see the first obvious thing. 35 00:03:07,720 --> 00:03:13,800 All of these orbits are centred on this white star. Hey, this is a terrible use of a marker for this object. 36 00:03:14,540 --> 00:03:20,610 And if we observe this point of an optical telescope, we see nothing. 37 00:03:21,070 --> 00:03:26,430 There's no emission from the. But there's clearly an object there. Everything is orbiting around this point. 38 00:03:27,060 --> 00:03:28,740 We know Newton's laws of gravity. 39 00:03:28,740 --> 00:03:34,950 So we can basically weigh this object, we can measure the mass, and it comes out at a few million times the mass of the sun. 40 00:03:35,850 --> 00:03:40,980 So it's an incredibly massive object. Okay. Then you can say, okay, well, my yellow star didn't hit anything. 41 00:03:41,640 --> 00:03:44,459 So that gives me an upper bound for the size of this object. 42 00:03:44,460 --> 00:03:50,070 And combining the two measurements, you get a density and you infer that rather than a white star, this is a black hole. 43 00:03:50,580 --> 00:03:55,020 Okay. This is a supermassive black hole. There's no other objects in the universe that can be distance. 44 00:03:56,120 --> 00:04:03,710 We now believe that the centre of all large galaxies is a black hole and is tightly correlated with the properties of the galaxy themselves. 45 00:04:04,670 --> 00:04:08,840 Okay. So as I said, as 2020, Nobel Prize for black holes keep winning Nobel Prizes. 46 00:04:08,840 --> 00:04:15,800 So it's quite nice. So this rather than looking particularly at the black hole, let's look at these orbits themselves. 47 00:04:15,920 --> 00:04:20,960 Okay. Now, one of the very interesting things you see is that they appear to come really quite close to one another. 48 00:04:21,770 --> 00:04:25,819 Okay. Now, this is a two dimensional projection of three dimensional orbits. 49 00:04:25,820 --> 00:04:28,820 Okay. So this is an exaggeration. They're not necessarily quite so close. 50 00:04:29,300 --> 00:04:32,900 But let's think about some of the implications of this dense orbital neighbourhood. 51 00:04:33,590 --> 00:04:36,650 Okay. So now we're going to make graphics from paint. 52 00:04:37,400 --> 00:04:42,320 We have a black hole in the centre and I have a star going on a purple orbit is perfectly happy going around. 53 00:04:42,350 --> 00:04:45,690 It will do that. Whether. Let's introduce a second stop. 54 00:04:46,590 --> 00:04:49,980 Okay. My Blue Star, if I run time forward. Okay. 55 00:04:50,190 --> 00:04:53,790 I can imagine in principle that my two stars can get pretty close to one another. 56 00:04:54,360 --> 00:04:57,360 And if they do, they will interact gravitationally. 57 00:04:57,900 --> 00:04:59,910 Okay. And they'll be a force between the two objects. 58 00:05:00,270 --> 00:05:06,000 This force will give a kick to my Purple Star, change its momentum, but it will also change its orbit. 59 00:05:06,780 --> 00:05:10,830 Okay. And then if I run the time forward again, I can imagine, at least in principle, 60 00:05:11,160 --> 00:05:16,680 I can random shuffle the occasional star arbitrarily close to the black hole. 61 00:05:16,680 --> 00:05:21,620 Innocent. And then I have a big ball of gas, and I've thrown it at a black hole. 62 00:05:21,630 --> 00:05:25,010 All sorts of colour. Okay. Okay. 63 00:05:25,020 --> 00:05:27,890 So we can measure the density of the Galactic Centre. 64 00:05:27,900 --> 00:05:31,800 We know a little bit about the orbits of individual stars, so you can ask, well, how likely is this? 65 00:05:32,910 --> 00:05:37,230 So my tenuous link to Francesco's talk is not very OC. 66 00:05:37,530 --> 00:05:45,690 So if I sits and I watch the centre of the Milky Way for a whole year, there's a one in 10,000 chance roughly that this happens. 67 00:05:46,770 --> 00:05:51,570 So it's unlikely to happen tomorrow in the Milky Way. But the key is this is per galaxy per year. 68 00:05:52,350 --> 00:05:56,790 So one way of waiting to see one of these is to wait a long time. That's not the most efficient way. 69 00:05:57,210 --> 00:06:00,810 There are many, many millions and billions of galaxies in the observable universe. 70 00:06:01,320 --> 00:06:01,710 Okay. 71 00:06:01,830 --> 00:06:10,050 So while it's extremely unlikely in any one galaxy, it's very likely that today, somewhere in the observable universe, one of the events is going. 72 00:06:12,000 --> 00:06:17,580 And there's a little shout out for Oxford. This calculation was first properly done by John McGowan is in the ferry the Pope. 73 00:06:18,630 --> 00:06:24,480 Okay. So I hope I convince you that in principle I can imagine throwing a star at a black hole. 74 00:06:24,480 --> 00:06:30,300 So let's think about some of the implications of this. So I have a star that's perfectly happy, and then I introduce a black hole. 75 00:06:30,980 --> 00:06:35,250 Well, what happens? Well, we have a force of gravity between the two objects, as is Newton's laws. 76 00:06:35,620 --> 00:06:42,640 Gee, I want them to overall squared. And the leading order effect of a gravitational force is just to put my star on an orbit. 77 00:06:43,570 --> 00:06:49,690 It's very simple. Hey, that's not what we're interested in. What we're interested in is something called the tidal force. 78 00:06:50,440 --> 00:06:54,310 So the tidal forces. The difference in the gravitational force across an object. 79 00:06:54,640 --> 00:06:59,230 You know, we like simplifications in physics, but the sun is not a point particle. 80 00:06:59,740 --> 00:07:02,380 It has some finite size, which I'm going to call bigger. 81 00:07:03,690 --> 00:07:09,840 And that tells us that the blobs of the star on this side of the black hole, well, they're closer to the black hole. 82 00:07:09,990 --> 00:07:17,280 So they'll feel a larger gravitational force. And the points in the middle and the tidal force is simply the difference in the two forces. 83 00:07:18,290 --> 00:07:19,970 So I can calculate that very simply. 84 00:07:20,450 --> 00:07:27,730 I find I write down for each blob which will have mass delta and the force on that object, minus the force on that object. 85 00:07:27,740 --> 00:07:31,310 And the only difference between the two is the difference in the distances to the black hole. 86 00:07:32,090 --> 00:07:36,790 Okay. So we want to understand the properties of the tidal force. 87 00:07:36,800 --> 00:07:40,060 So we'll do a little bit of algebra so I can satirise this. 88 00:07:40,840 --> 00:07:45,980 I have one minus the radius of the star itself, divided by the distance to the black hole. 89 00:07:46,320 --> 00:07:50,750 Now, we're going to assume this is a small number of wise. I'll be inside the black hole and that's less interesting. 90 00:07:51,290 --> 00:07:54,589 Okay. So I have one minus a small number to the minus two. 91 00:07:54,590 --> 00:08:03,260 And if you remember your total expansions from undergraduate, that's the same as one plus 2x1 minus x minus two, and I can simplify. 92 00:08:03,830 --> 00:08:10,070 And so the tidal force has the following properties. If I increase the mass of the black hole, I get a larger tidal force. 93 00:08:11,810 --> 00:08:14,870 Stars of larger radii are easier to distort. 94 00:08:14,870 --> 00:08:18,290 Tidal, okay, because there's a greater distance between the sides. 95 00:08:18,290 --> 00:08:23,329 My star and the force grows as one over r cubed so very far away from the black hole. 96 00:08:23,330 --> 00:08:27,620 I don't have to worry about tidal effects, but if I get closer and closer, this grows very quickly. 97 00:08:28,250 --> 00:08:34,680 Okay. And also importantly, there's a minus sign. Which tells me that relative to the blob in the centre, 98 00:08:35,370 --> 00:08:40,710 the blob on the outside this side wants to go is a greater acceleration towards the black hole. 99 00:08:40,860 --> 00:08:47,920 So wants to move that. Okay. So if I repeat this calculation for the blob on the far side, okay, this is all relative. 100 00:08:47,940 --> 00:08:53,370 Of course, everything wants to go this way, but relative to the blob in the centre, it wants to move further out. 101 00:08:53,640 --> 00:08:56,110 And that's because it's far away. Right. 102 00:08:56,830 --> 00:09:02,800 And if I repeat the calculation for these two points here, I find that they want to go in ones that might be slightly less obvious, 103 00:09:03,430 --> 00:09:08,740 but you can draw a sort of false triangle and you see the radial components between these two blobs will be the same. 104 00:09:09,130 --> 00:09:12,250 But there's this horizontal component. Okay, which is going to cancel. 105 00:09:13,530 --> 00:09:17,960 So from these four points, I can see what happens if I take a bowl of gas and I put it in a black hole. 106 00:09:18,120 --> 00:09:25,170 Okay. It's distorted slightly. Okay. So this is precisely the reason we get to high tides and too low tides a day on the earth. 107 00:09:25,710 --> 00:09:28,850 Okay. But we're not interested in small effects to the moon. 108 00:09:28,860 --> 00:09:36,890 We're interested in taking this to its logical extreme. So I'm going to get an extremely dense object, and I'm going to put it in this store. 109 00:09:37,950 --> 00:09:41,830 Okay. And you can see what happens. I really stretch out my star. 110 00:09:42,510 --> 00:09:47,459 Okay. And if I ramp up the density some more, you know, I stretch it out some more. 111 00:09:47,460 --> 00:09:52,200 And then if I get an unimaginably dense object, you know, I can see what's happening. 112 00:09:52,320 --> 00:09:56,070 Okay, so this is the logical extreme. Okay. And this is my stellar spaghetti. 113 00:09:56,610 --> 00:10:00,300 So this is, you know, it's long and thin and yellow. It looks like spaghetti. 114 00:10:00,330 --> 00:10:02,490 This is where this spaghetti ification term came. 115 00:10:03,700 --> 00:10:09,130 So when I was actually preparing these slides, my office meant told me it should be spaghetti because there's only one of them. 116 00:10:09,580 --> 00:10:16,600 But the the important fact is that for the supermassive black holes in the centre of galaxies, this can actually completely destroy the star. 117 00:10:17,590 --> 00:10:22,469 Okay. Now, to see that, take a sort of average effective tidal force. 118 00:10:22,470 --> 00:10:26,290 So add it up over the whole star, you see. Okay. It grows through the black hole mass. 119 00:10:26,530 --> 00:10:32,780 The mass of the star, the red the star. And it goes like one overachieved. Well, what's holding the staff together? 120 00:10:32,790 --> 00:10:36,740 The staff is being held together precisely by gravity. So it's Newton's law again. 121 00:10:36,770 --> 00:10:42,379 GM want them to overall squared, but it's the same mass. It's the mass of a star twice divided by the radius to start. 122 00:10:42,380 --> 00:10:45,050 This is a rough holding the start to get. 123 00:10:45,830 --> 00:10:51,900 Now, if I make my tidal force larger than the force holding the star together, well, then I no longer effectively have a star. 124 00:10:51,920 --> 00:10:55,010 I have a completely unbound set of gas. 125 00:10:56,190 --> 00:11:00,330 I'd like to solve this equation for a special radius called the tidal radius, which this happens. 126 00:11:01,430 --> 00:11:03,010 And then I'm going to do something unpleasant. 127 00:11:03,020 --> 00:11:07,040 I'm going to take the sun and I'm going to throw it at the supermassive black hole in the centre of the galaxy. 128 00:11:07,040 --> 00:11:12,680 And I find, well how big is this number? And it's 70 million kilometres, but it's just a number. 129 00:11:13,370 --> 00:11:16,490 But the important fact is, is that it's bigger than the black hole itself. 130 00:11:16,790 --> 00:11:23,450 So the black hole in the centre is 3 million kilometres. So this complete disruption of the star happens outside of the black hole. 131 00:11:23,900 --> 00:11:27,530 And if this happens outside of a black hole, in principle, I can see it. Okay. 132 00:11:27,540 --> 00:11:30,890 Light from this event will escape. We can observe. Okay. 133 00:11:31,880 --> 00:11:37,310 Now, this is kind of a classic astrophysics. Lots of APR equals two ignored factors of two. 134 00:11:37,610 --> 00:11:39,830 So you might ask, is this really possible? 135 00:11:40,160 --> 00:11:46,340 So an alternative approach to solving this problem is to take a ball of gas in a computer and process a black hole and see what happens. 136 00:11:46,940 --> 00:11:50,510 So that's what Bonura Atoll did in 2015. Okay. 137 00:11:50,540 --> 00:11:57,140 And so the the white again, the black hole is white and you throw a star in and it goes apart. 138 00:11:57,170 --> 00:12:02,270 Okay. At earlier time, you get a sort of nice spaghetti shape, but eventually it's completely torn apart. 139 00:12:03,260 --> 00:12:11,330 Stream stream interactions. It's a bit of a mess, but eventually if we wait long enough, it's going to start to settle down. 140 00:12:14,050 --> 00:12:17,860 Okay. And the reason it settles down is simply conservation of angry moments. 141 00:12:18,580 --> 00:12:22,800 I took a star on some orbits and my favourite and I can't get rid of that angular momentum. 142 00:12:23,020 --> 00:12:24,400 All I can do is redistribute it. 143 00:12:24,730 --> 00:12:32,820 So she ends up with a ring and this is the ring with radius of the circular orbit with the same arguments and as the star I threw in an. 144 00:12:33,910 --> 00:12:37,630 Okay. Now, just to be safe, we should throw another star in on a different orbit. 145 00:12:38,120 --> 00:12:44,140 Okay. And you see. Okay. The early time behaviour is quite sensitively dependent on the star I pick and the orbits I pick. 146 00:12:44,740 --> 00:12:51,640 But after a couple of orbits round, we're going to mangle the star and we will eventually end up with another round. 147 00:12:53,310 --> 00:12:58,010 Okay. Okay. Now, so I said, you know, late time. 148 00:12:58,020 --> 00:13:04,430 So it's important to get a scale of the time here. So from the start of the simulation to this point, here was 22 Earth hours. 149 00:13:05,000 --> 00:13:09,520 Okay, so what a day for the people around the store either. 150 00:13:09,640 --> 00:13:13,720 But, you know, this is this is a relatively rapid. Again. 151 00:13:13,790 --> 00:13:16,910 And the interesting point is, okay, then I have a ring of gas around the black hole. 152 00:13:17,180 --> 00:13:21,620 This will evolve. It could get very hot. And I could potentially emit light that I could observe. 153 00:13:22,400 --> 00:13:26,560 Okay. We've got to remember that these are rare events. 154 00:13:26,950 --> 00:13:32,140 So it's not going to be in our galaxy, it's going to be in another galaxy. And of a galaxy is a very far away. 155 00:13:32,900 --> 00:13:38,500 Okay. So while in principle it's possible to observe these, we need to ask if in practice it's also possible. 156 00:13:39,420 --> 00:13:43,290 Okay. So to answer that question, we have to go, well, how bright is a tidal disruption event? 157 00:13:44,190 --> 00:13:48,570 So we need to answer this question. We start with. How bright is the star? 158 00:13:49,460 --> 00:13:53,000 While a star is effectively an engine for turning mass into light. 159 00:13:53,570 --> 00:14:02,510 Okay, so it has some energy budget. He's got some energy budget and see squid as that's it's an energy this engine has to work with. 160 00:14:03,490 --> 00:14:09,110 And in terms this is a photon of some efficiency and this efficiency is set by the nuclear reactions in the stars. 161 00:14:09,140 --> 00:14:13,330 Cool. And it does this over some time, the entire lifetime of the store. 162 00:14:13,570 --> 00:14:17,530 Okay. So this is a rough and ready approximation of the luminosity of a star. 163 00:14:17,570 --> 00:14:20,920 Okay. I have some total budget and I radiator over my whole lifetime. 164 00:14:22,400 --> 00:14:24,610 Well, if you think about it, a TDI, 165 00:14:24,620 --> 00:14:30,680 so I'm going to start calling them TDs for total disruption events because spaghetti ification is a bit of a mouthful. 166 00:14:31,400 --> 00:14:35,930 So a TD has the same energy budget rather than nuclear reactions. 167 00:14:35,930 --> 00:14:40,490 I'm shredding a star and I'm throwing it into a black hole, but I still have m.c squared to work with. 168 00:14:42,090 --> 00:14:47,220 There's going to be a different efficiency and efficiency associated with the accretion process and there's going to be a different time. 169 00:14:49,070 --> 00:14:53,840 So to get a rough and ready idea for how bright a TD will be, you take the luminosity of a star, 170 00:14:53,870 --> 00:14:57,140 you divide these two equations, assume the efficiencies are roughly the same, 171 00:14:58,010 --> 00:15:01,729 and you get an amplification of the luminosity the star by a factor of ratio of 172 00:15:01,730 --> 00:15:06,880 the time the star lives four divided by the time in which the two can happen. 173 00:15:08,230 --> 00:15:12,190 And this is a big number. This is about 10 billion. The sun will live for 10 billion years. 174 00:15:12,730 --> 00:15:16,900 And when all said and done, it takes roughly a year to shred the star and throw it into the black. 175 00:15:18,850 --> 00:15:24,520 Now, this is a very big number in the case of the luminosity of the entire Milky Way galaxy is roughly 10 billion solar luminosity. 176 00:15:25,270 --> 00:15:31,480 So what we're talking about here is taking all of the light from this galaxy and putting it as a single point source right at the centre. 177 00:15:32,500 --> 00:15:35,680 Okay. Now, if one of these events ever did happen in the Milky Way. 178 00:15:36,130 --> 00:15:42,380 Would be truly phenomenal. Okay, so from our perspective, halfway out, this object would have 30 times the brightness of the full moon. 179 00:15:42,880 --> 00:15:46,210 Can you be able to see it in the day? People probably lose their minds. 180 00:15:46,240 --> 00:15:51,340 It would be it would be fantastic for funding, if nothing else. Okay. 181 00:15:51,730 --> 00:15:57,010 And so. Okay, now we understand that, you know, in principle, these can happen and we can observe them at cosmological distances. 182 00:15:57,670 --> 00:16:00,730 Okay. So in practice, how do we go about doing this rare event? 183 00:16:01,420 --> 00:16:04,780 Well, we sit, we watch the whole sky and we wait. 184 00:16:05,480 --> 00:16:08,890 Okay. It's it's actually it's a very effective technique, actually. 185 00:16:09,340 --> 00:16:14,530 So there's whole groups of astronomers out there, and they take a picture of the whole sky each night and then they compare on any two months. 186 00:16:14,710 --> 00:16:20,290 Okay. Now, the group with the best appreciation of branding is the assassin collaboration. 187 00:16:21,370 --> 00:16:26,380 Okay, so this is the All-sky Automated Survey for Supernova. 188 00:16:27,100 --> 00:16:30,750 Okay. It shows astronomers love for forcing acronyms. Okay. 189 00:16:30,760 --> 00:16:35,829 And so what assassin do is they have a whole bunch of telescopes dotted around the earth and they take 190 00:16:35,830 --> 00:16:41,680 an image of the whole sky and they know precisely where everything was yesterday and how bright it was. 191 00:16:42,550 --> 00:16:49,090 And if in today's image, suddenly something's twice as bright, that means that a tidal disruption event may have happened. 192 00:16:49,480 --> 00:16:54,430 Okay. That principally interested in finding supernova, which is another way of blowing up the star. 193 00:16:55,510 --> 00:17:01,270 And so. But occasionally, for basically every one supernova they find, they're going to find one of these tidal disruption event. 194 00:17:01,780 --> 00:17:03,400 And they let everyone know. Okay. 195 00:17:05,170 --> 00:17:13,690 So these objects were first theorised in the late seventies, early eighties, but it was wasn't until the 20 tens when we started to get solid data. 196 00:17:14,330 --> 00:17:17,979 Okay. There's now about 30 of these objects. Okay. 197 00:17:17,980 --> 00:17:19,940 So we can start to do population studies. 198 00:17:19,960 --> 00:17:25,960 There's going to be hopefully tens of thousands by the end of the 2030s because we've got some new telescope service coming online. 199 00:17:27,010 --> 00:17:33,700 Okay. I'm going to tell you about two of them today. I'm going to tell you about Assassin 14 and I an assassin 15 now. 200 00:17:34,210 --> 00:17:37,980 Okay. So the naming convention is discovered by assassin. 201 00:17:37,990 --> 00:17:43,270 We always named things after ourselves in astronomy. And it was found in 2014. 202 00:17:43,330 --> 00:17:48,100 That's the 14 an assassin. Start with 14 A and they count up. 203 00:17:48,670 --> 00:17:53,890 So Ali, was the 321st objects found by assassin in 2014. 204 00:17:54,910 --> 00:17:59,740 Okay. So this was a hugely exciting event. It was actually very nearby in cosmological terms. 205 00:17:59,980 --> 00:18:03,130 So everyone turned the telescopes and followed up. 206 00:18:03,340 --> 00:18:06,940 Okay. And what do we do when we get brightness versus time? 207 00:18:07,420 --> 00:18:10,660 Okay, that's all we're going to get in astrophysics. That's all we ever have to work with. 208 00:18:11,260 --> 00:18:16,870 So some groups pointed in actually telescope. This was actually done over in Oxford astrophysics. 209 00:18:16,870 --> 00:18:19,240 So so that's a nice sort of connection. 210 00:18:19,750 --> 00:18:27,710 I mean, the telescopes in space, but the people we were using it were sort of a groups appointed, say a U.V. telescope, optical telescope. 211 00:18:27,730 --> 00:18:30,800 So so we have a huge amount of data. Okay. 212 00:18:32,180 --> 00:18:38,780 There's also Assassin 15 LH So if I'd given this talk yesterday, I would have said this was the brightest one of these ever. 213 00:18:39,590 --> 00:18:43,400 And then another one blew up yesterday, too, which is even brighter. 214 00:18:44,190 --> 00:18:48,110 But. But Assassin 50 LH went off in 2015. It was phenomenally bright. 215 00:18:48,470 --> 00:18:53,060 So all sorts of groups followed up. So we have infrared data, we have optical data. 216 00:18:53,060 --> 00:19:03,500 We have easy data. We're not struggling for data. The problem is, if we run our simulation, we can probe this sort of time scale, the powerful gap. 217 00:19:03,770 --> 00:19:07,340 Okay, so if we're really lucky, we may be able to explain one data point. 218 00:19:08,370 --> 00:19:12,360 Okay. So the problem is, how do we go from this ring? 219 00:19:13,140 --> 00:19:18,120 Okay. Which we know is roughly the endpoint of our simulation. How do we go from this ring to this data? 220 00:19:18,810 --> 00:19:25,080 Okay. So that's the question. And that's what I spent my Ph.D. doing, is trying to work out what's this popular? 221 00:19:26,320 --> 00:19:33,240 Okay. So to understand these systems, we need to do fluid dynamics in general relativity. 222 00:19:33,370 --> 00:19:36,620 Okay, we have a ring of gas. Okay. 223 00:19:36,630 --> 00:19:39,930 It's a fluid. It's going to move. It's dynamics. 224 00:19:40,110 --> 00:19:43,140 And there's a black hole in the middle. We're playing with general relativity. 225 00:19:43,710 --> 00:19:48,480 Now, this is slightly tricky because I was told to produce some slides for a second year undergrad audience. 226 00:19:48,840 --> 00:19:54,390 This is a third year course, and I don't think they taught this in anything other than the maths departments or quite recently. 227 00:19:55,020 --> 00:19:58,560 But this is the Saturday morning of theoretical physics. You know, we're going to do it anyway. 228 00:20:01,500 --> 00:20:06,190 Okay. We're physicists. We give physicists. Okay. So what we're going to do is we're going to conserve mass. 229 00:20:06,240 --> 00:20:09,630 Okay. The only way mass can change my system is if it ends up in the black hole. 230 00:20:10,810 --> 00:20:13,990 Well, conserve angular momentum. Exactly the same principle. 231 00:20:14,680 --> 00:20:20,080 We'll conserve energy and then we'll see what we get. Okay, so so that's that's the process. 232 00:20:22,060 --> 00:20:28,780 Okay. So so you've probably heard in popular media the film Interstellar perhaps about accretion disks. 233 00:20:29,170 --> 00:20:34,149 Okay. So these are the sorts of systems we describing here. So imagine you have a fluid, okay? 234 00:20:34,150 --> 00:20:41,260 And it's a roughly two dimensional structure. It has radial behaviour and it's some useful behaviour but it's very thin. 235 00:20:42,730 --> 00:20:48,219 So my flow has some high take, it has some density rho, it's moving radially. 236 00:20:48,220 --> 00:20:51,370 We've lost you and the distance off in the black hole. 237 00:20:51,880 --> 00:21:00,070 Okay, now mass conservation tells me if I draw a purple box in the flow, I cannot create or destroy mass in that box. 238 00:21:00,610 --> 00:21:03,999 Okay. So if I wait some time in the mass, in my box changes. 239 00:21:04,000 --> 00:21:08,740 That tells me mass is either left the box or entered the box. It's a very simple principle. 240 00:21:09,340 --> 00:21:12,820 In the language of general relativity, we have a partial differential equation. 241 00:21:13,180 --> 00:21:17,740 Okay. So drove it. T is how does my massive my box change over time. 242 00:21:18,400 --> 00:21:25,120 And the second time tells me how does mass flow in and out of my box? If I add them up, I, of course, have to get zero. 243 00:21:25,450 --> 00:21:31,780 Okay. So there's an additional factor, which I'm going to call the interstellar term. 244 00:21:32,080 --> 00:21:38,260 Okay. So if anyone's seen the film Interstellar, you know, the an astronaut leaves Earth, goes to a black hole, 245 00:21:38,260 --> 00:21:43,960 spends a few hours there in his frame, and then comes home where 40 years have passed and his daughter hates him. 246 00:21:44,560 --> 00:21:52,610 Okay. Now, so we have to be very careful in general relativity when we say something like day to normal physics problems. 247 00:21:52,960 --> 00:21:57,010 But it is fine. We can all agree. Maybe not in cosmology, but we can all agree what we mean. 248 00:21:57,490 --> 00:22:01,600 But we're interested in the rate of change of this disk with respect to time on earth. 249 00:22:01,750 --> 00:22:06,880 That's what we measure. That's our data. Okay. But from the fluids perspective, that can be a very different time. 250 00:22:07,660 --> 00:22:11,350 Okay. So this tells me the connection between the two clocks in the system. 251 00:22:11,680 --> 00:22:15,070 Okay. And it's in a textbook. You can look at it. Okay. 252 00:22:15,670 --> 00:22:20,639 So this is the this is the procedure. So then we move on to energy and then some conservation. 253 00:22:20,640 --> 00:22:24,030 Okay. So this fluid is is orbiting in a ring. It's moving very quickly. 254 00:22:24,030 --> 00:22:28,950 It has an event. And again, I cannot create or destroy and condense them in my system. 255 00:22:30,320 --> 00:22:33,410 So I wrote all the ways in which all the ways in which angular momentum can change. 256 00:22:33,650 --> 00:22:37,610 And this one's a little bit more intimidating. But again, we can understand each of the terms. 257 00:22:38,420 --> 00:22:43,170 So the terms in the square bucket, square brackets tell me I have a box. 258 00:22:43,230 --> 00:22:45,050 I am still thinking about my post box. 259 00:22:45,800 --> 00:22:51,860 If the mass in this box changes and that mass had angular momentum, then the angry momentum of the box has changed. 260 00:22:52,580 --> 00:22:57,810 Okay. So kind of trivial to. The second term describes. 261 00:22:58,080 --> 00:23:03,120 Okay, well, what if I had two boxes next to each other and fluid leaves this box and moves into this box. 262 00:23:03,390 --> 00:23:06,270 But this box has a different angle and then some profile. 263 00:23:06,750 --> 00:23:12,330 If you imagine moving from one circular orbit onto a second circular orbit, there's orbits have different time movements. 264 00:23:13,050 --> 00:23:16,620 So this term, in effect describes the fluid moving between these two states. 265 00:23:18,400 --> 00:23:25,450 Okay. Now, this third term is a little bit more complicated, and my supervisor will hate me for using the word friction here. 266 00:23:25,870 --> 00:23:30,940 Okay. You may ask, well, why? Why does the fluid want to go into the black hole at all? 267 00:23:31,330 --> 00:23:34,930 The earth is on an orbit circle, but it's basically a ring. 268 00:23:35,290 --> 00:23:39,060 It doesn't charge headfirst at the sun. Okay. So why would my fluid do any different? 269 00:23:39,980 --> 00:23:43,520 Well, the difference between the fluid and the earth is that there are neighbouring elements in the 270 00:23:43,520 --> 00:23:48,500 flow and they can rub off against each other and there's friction between layers in the flow. 271 00:23:49,190 --> 00:23:57,440 We in reality this is turbulence, it's so much more complicated process, but for our purposes you can model it as a friction or a viscosity. 272 00:23:58,160 --> 00:24:02,930 Fluid elements rub past each other. Energy is dissipated and angular momentum is moved around. 273 00:24:04,000 --> 00:24:07,360 Okay. This actually drive secretion accretion. Without this, there is no accretion. 274 00:24:08,860 --> 00:24:17,050 And this is a final term which tells me, okay, imagine I emit light out of the top of my desk while light travels carries momentum as well as energy. 275 00:24:17,230 --> 00:24:20,560 And these are very bright objects. So that can appreciably change the flow. 276 00:24:21,460 --> 00:24:24,580 Okay. So energy conservation, we're nearly there. 277 00:24:25,190 --> 00:24:29,200 Okay, so this tells me, okay, I have fluid, it's in a box, I move it around. 278 00:24:29,560 --> 00:24:32,020 I can't just do that or create and change energy. 279 00:24:32,530 --> 00:24:39,640 So energy conservation tells me that all of the energy change in my box is dumped into heat, which is then radiated out the top of my box. 280 00:24:39,820 --> 00:24:43,810 Okay, that's where the light. And this tells me the temperature of my desk. 281 00:24:45,220 --> 00:24:47,170 Okay. So then you just do everything at once. 282 00:24:47,530 --> 00:24:53,560 You confirm you conserve all free quantities and you combine and you get a set of equations which are right here. 283 00:24:53,950 --> 00:25:00,040 Okay. And it's a diffusion equation. So what you find is that my ring is going to diffuse out and I'm going to end up with a disk. 284 00:25:00,900 --> 00:25:08,070 Okay. It looks pretty complicated, but the key point is if I write down a ring of material and put a black hole in the middle, 285 00:25:08,250 --> 00:25:11,700 all I have to do is solve this equation, and I can do that on a computer. 286 00:25:12,120 --> 00:25:15,270 And this is sort of the algorithm for solving these problems. Okay. 287 00:25:15,900 --> 00:25:20,490 I evolve the density forward. I use energy conservation to work out the temperature. 288 00:25:21,330 --> 00:25:24,840 And from the temperature, I remember Planck's law of radiation. 289 00:25:25,050 --> 00:25:32,010 And so I can get the brightness as a function of frequency. So every last bit of my disk has some temperature, it's got some brightness. 290 00:25:32,970 --> 00:25:37,200 I add it all up and I can compare to my telescope. So this is a procedure. 291 00:25:38,350 --> 00:25:43,480 Okay. So let's see what happens. Okay. This is time is zero. 292 00:25:43,840 --> 00:25:47,170 There's a black hole over on this side, which I've added thing. 293 00:25:47,410 --> 00:25:51,850 So any fluid that passes this black line will go since the black hole it's got. 294 00:25:52,690 --> 00:25:55,960 This is my ring at an initial time. Okay. 295 00:25:56,560 --> 00:25:59,860 And we're just going to press go and solve the equation and see what happens. 296 00:26:00,040 --> 00:26:04,250 Okay. You have to watch quite closely early times because it moves quickly. Okay. 297 00:26:04,430 --> 00:26:07,560 So what happens is that my fluid rushes in, okay? 298 00:26:08,080 --> 00:26:12,800 The the friction in effects moves material around, and it wants to go towards the black hole. 299 00:26:13,040 --> 00:26:16,670 So the fluid rushes in and my temperature goes up. Okay. 300 00:26:17,390 --> 00:26:24,080 But then I lose material into the black hole, so the density drops, I have less energy available and my temperature starts to come down. 301 00:26:25,550 --> 00:26:29,770 So this besides quite easy to understand. Now you might wonder what's going on here. 302 00:26:30,070 --> 00:26:33,340 Okay. Well, a lot of my food appears to be running away from the black hole. 303 00:26:33,460 --> 00:26:37,030 What's going on here? Okay, so that's angular momentum conservation. 304 00:26:37,510 --> 00:26:43,360 Okay. I can't just move material in. We have this picture of an accretion flow is just material diving towards a black hole. 305 00:26:43,570 --> 00:26:47,410 But actually, to conserve total momentum, I need to move a lot of my fluid outwards. 306 00:26:48,500 --> 00:26:53,240 Okay. All right. So this, you know, you might think this is the end. 307 00:26:53,570 --> 00:27:00,830 Okay. Can we compare to the telescope now? Unfortunately there's this extra effect switch morphing start to go wrong when 308 00:27:00,830 --> 00:27:04,340 there's a black hole in the sensor and we return to the film Interstellar. 309 00:27:06,430 --> 00:27:09,669 So if you've seen this film Interstellar or basically any black hole in pop culture, 310 00:27:09,670 --> 00:27:15,550 you'll probably see this strange, glowing, three dimensional UFO type shape surrounding it. 311 00:27:15,830 --> 00:27:21,100 Okay. This doesn't look anything like my two dimensional flat desk that I've been describing. 312 00:27:21,230 --> 00:27:26,590 So so what's what's the difference here? Okay. And the difference is an effect called gravitational lensing. 313 00:27:26,650 --> 00:27:32,620 So this is a purely optical effect. The physical system is a black hole in a 2D structure. 314 00:27:32,830 --> 00:27:40,090 But if I look at the system, you know, I'm effectively measuring photons and where they've come from and I observe a warped structure. 315 00:27:40,480 --> 00:27:48,250 Okay. So this is, you know, the bending of light raised by a by a gravitational field is one of the classical tests of general relativity. 316 00:27:48,620 --> 00:27:54,430 Okay. And the you know, the stars this famous Eddington expedition moved ever so slightly. 317 00:27:55,060 --> 00:28:00,280 Now, if you throw a light ray, it's a black hole. You can get much more substantial deviations in the flow. 318 00:28:00,670 --> 00:28:04,180 Okay. So we call this the pub orbit. 319 00:28:04,900 --> 00:28:10,030 Okay. So you've got a photon on its way home. It stops off for one, and then it's instead. 320 00:28:11,320 --> 00:28:16,180 Okay, so this pub orbits like they're highly, highly warped things. 321 00:28:16,210 --> 00:28:22,090 Okay. Now, just as a note of caution, as any undergrads will tell you, pub orbits are very dangerous. 322 00:28:22,780 --> 00:28:29,310 And that's because they're chaotic. Now, if I start arbitrarily close to a pub of it, I stop off for one. 323 00:28:29,730 --> 00:28:33,260 I can actually end up at any point in the universe. Right. 324 00:28:34,290 --> 00:28:37,410 Okay. So you got to be very careful here. Okay. 325 00:28:37,590 --> 00:28:41,100 And so this is warping. It's this it's just the bending of light rays. 326 00:28:41,250 --> 00:28:46,920 And so my 2D structure, which is physically remains physically two D is observed to be warped. 327 00:28:46,920 --> 00:28:51,240 Okay. And I get this classic UFO shape. And the UFO shape comes because. 328 00:28:52,250 --> 00:28:56,550 Oh, my laser pointer seems to go. The photons behind the black hole. 329 00:28:58,600 --> 00:29:01,810 Emitted a needle bent over the top effectively. 330 00:29:02,200 --> 00:29:07,389 And so I can actually see them when in a naive Newtonian gravity, they'll be absorbed by the black hole. 331 00:29:07,390 --> 00:29:10,570 And so I can see light that appears to come from behind the black hole. 332 00:29:10,630 --> 00:29:15,720 And that's the warp. Okay. Really the one last effect. 333 00:29:15,760 --> 00:29:20,090 Okay. And for this last effect, I want you to imagine that I have a lime green accretion disk. 334 00:29:20,780 --> 00:29:24,680 Okay. It's not a particularly realistic physical model, but it highlights an important point, 335 00:29:25,400 --> 00:29:29,360 and that is that the fluid in this system is rushing around at nearly the speed of light. 336 00:29:29,690 --> 00:29:38,960 Okay, so let's imagine it's orbiting counterclockwise, which means that this blob of fluid is moving directly at an incredibly high velocity, 337 00:29:39,590 --> 00:29:42,560 and this blob of fluid is moving away from it at an incredibly high velocity. 338 00:29:43,480 --> 00:29:48,130 Now if an ambulance charges towards you in the street, the side at the frequency of the siren goes up. 339 00:29:48,280 --> 00:29:51,460 And then as it charges away from you, it goes down. And that's called the Doppler shift. 340 00:29:52,090 --> 00:29:58,570 Okay. Now, what doesn't happen with an ambulance is the blue flashing light doesn't go ultraviolet and that infrared as it travels away. 341 00:29:58,960 --> 00:30:03,010 And that's simply because ambulances don't travel close to the speed of light. 342 00:30:03,280 --> 00:30:07,719 Okay. Whereas, you know, they travel roughly close to the speed of sound. 343 00:30:07,720 --> 00:30:09,040 And that's why sound waves are changed. 344 00:30:10,030 --> 00:30:15,370 But if you can show that for the fluid on the very inner edge, the circular orbit can be half the speed of light. 345 00:30:15,550 --> 00:30:20,410 Okay. So we're going to get not just warping but strong shifting in the radiation. 346 00:30:21,070 --> 00:30:27,580 Okay. And I bother to do an actually accurate lime green accretion flow as observed from Earth. 347 00:30:27,730 --> 00:30:30,940 Okay. And you see that on this side, which is rushing towards you. 348 00:30:31,690 --> 00:30:36,880 The Doppler shift is so strong that actually ends up ultraviolet and you won't be able to see it, but it might give you cancer. 349 00:30:38,020 --> 00:30:43,570 This side over here would end up blue, perpendicular to my line of sight. 350 00:30:43,600 --> 00:30:47,710 There is no relative velocity of the source and I recover my lime green. 351 00:30:48,550 --> 00:30:53,110 Hello. And on this side, it's rushing away from me. And I get red and then infrared. 352 00:30:53,530 --> 00:30:57,850 Okay. So they actually deliberately kept this out of the film, Interstellar. 353 00:30:57,910 --> 00:31:00,940 They calculated it properly. You know, kit form was on the film. 354 00:31:01,360 --> 00:31:06,460 They calculated it properly, but then it looks rubbish. Like you just see a tiny corner of the mission. 355 00:31:06,550 --> 00:31:09,790 Okay. These are boosted as well. So it's much brighter. 356 00:31:09,940 --> 00:31:15,550 And black holes look boring. So? So they took it out. Okay, so now we're ready to go. 357 00:31:16,030 --> 00:31:20,320 Okay. We have a ring of material. We press go. 358 00:31:20,620 --> 00:31:25,299 We fold the temperature through in time. Every last bit of my disk has a temperature. 359 00:31:25,300 --> 00:31:31,720 It emits some light. And then we we understand that we have to take the image of this flow with a special sort of camera, 360 00:31:32,080 --> 00:31:34,230 which takes into effect the warping in the shifting. 361 00:31:35,280 --> 00:31:40,950 And what that allows us to do is calculate the brightness as a function of frequency at a given snapshot. 362 00:31:41,640 --> 00:31:44,700 And this is great because this is exactly what we compared to our telescope. 363 00:31:45,340 --> 00:31:51,059 So she pointed an X-ray telescope. What you can really see is here a few points, a TV telescope. 364 00:31:51,060 --> 00:31:54,600 What you really see is this little band here. Okay. So we see what happens. 365 00:31:56,400 --> 00:32:02,460 Okay. So we see that as we press go, the fluid rushes in and it gets to high temperatures. 366 00:32:02,970 --> 00:32:10,290 That means that my spectra, my blue curve moves up to higher energies because hotter objects emit more higher energy photons. 367 00:32:10,840 --> 00:32:18,980 Okay. But as the schools, even though it it cools only a little bit, the change as observed by an X-ray telescope will be quite strong. 368 00:32:20,360 --> 00:32:26,630 And that's because it's in the V tail. So it's exponentially sensitive to the peak of the distribution. 369 00:32:27,350 --> 00:32:32,450 Okay. So we have a clear theoretical prediction. X-ray light curves of these events should decay away rapidly. 370 00:32:33,630 --> 00:32:39,840 Over in the U.S., we get a very different story. Sure, it goes up again to early times, but then it just sort of sits there. 371 00:32:40,140 --> 00:32:44,820 It sits there for two years. This will run up to a thousand days and basically nothing happens. 372 00:32:45,870 --> 00:32:49,470 Okay. And we have two competing effects here. My whole system is cooling. 373 00:32:49,680 --> 00:32:55,440 I'm losing material and I'm cooling. If I take a black body and I call it, I make it less bright. 374 00:32:57,210 --> 00:33:02,250 So that's what's going on up here. But I'm also spreading. I'm conserving increments. 375 00:33:02,250 --> 00:33:08,280 And so my area is getting bigger. Now, if I take a black body of constant temperature and I make this area bigger, it's brightness goes up. 376 00:33:09,240 --> 00:33:14,250 And so these two effects completely cancel out in the evening. So we have another theoretical prediction. 377 00:33:15,150 --> 00:33:18,990 Okay. So does it work? Well, I probably won't be giving this talk if it didn't work. 378 00:33:19,890 --> 00:33:27,050 So sweet. And presto. And compared to the X-ray data collected over in this department and we see, okay, 379 00:33:27,120 --> 00:33:31,620 the blue curve is the theoretical prediction and the orange is the observed data. 380 00:33:31,830 --> 00:33:39,900 There are various gaps when the thing went behind the sun and you can say, okay, we're clearly modelling that the average trend of the data will. 381 00:33:40,880 --> 00:33:48,080 The real world is is messy. It's not a nice little two dimensional simple model occurs, but we're clearly modelling the trend. 382 00:33:49,590 --> 00:33:55,440 Okay. So what about the other data? This may be a disappointing slide. 383 00:33:56,490 --> 00:34:00,660 Okay. So a day, 200 onwards. Okay, we're doing a very good job. 384 00:34:00,990 --> 00:34:02,760 Fantastic. But what on earth is going on here? 385 00:34:03,390 --> 00:34:11,190 Okay, now, these are strange astronomy units where bigger numbers are less bright and this is a factor of 100. 386 00:34:11,910 --> 00:34:15,450 So effectively, we're a factor of 102 early times. So what's going on? 387 00:34:16,790 --> 00:34:20,120 Well, we learned from this that this early time admission is not coming from the disk. 388 00:34:20,210 --> 00:34:24,050 Actually, there's no way you can force a disk model to do this sort of behaviour. 389 00:34:24,440 --> 00:34:28,070 It doesn't want to change it. You've. It's the wrong part of the spectrum. 390 00:34:29,060 --> 00:34:34,790 So what does it. It depends which of my colleagues you ask effectively as this is. 391 00:34:34,790 --> 00:34:42,020 This is one of the big open questions. Okay. It's a real shame because it's really easy to observe, but we don't really have a good model for it. 392 00:34:43,370 --> 00:34:50,479 There are lots of plausible theories. I'm going to tell you about my personal favourite and to go back to the one I actually believe. 393 00:34:50,480 --> 00:34:57,640 It's true. It's not just my favourite. If we press go on a simulation, my spaghetti goes once round the black hole. 394 00:34:58,030 --> 00:35:04,990 Absolutely fine. But then on the second time on the flight, call, the front of the spaghetti smashes into the back of the spaghetti. 395 00:35:06,080 --> 00:35:11,510 Okay. This is a extremely high velocity collision of a gas. 396 00:35:13,040 --> 00:35:14,510 So he's probably going to shock. 397 00:35:15,030 --> 00:35:19,700 I tell you, there's going to be a collision is going to heat my gas and it's going to give off a whole bunch of light. 398 00:35:20,720 --> 00:35:26,080 And the reason we we like this particular interpretation is it has a set of very nice properties. 399 00:35:26,090 --> 00:35:33,430 Okay. It's going to be very bright. But but it's also going to decay away very quickly, because eventually I end up with my ring, okay. 400 00:35:33,440 --> 00:35:39,710 Within 22 hours or a couple of days. And then I no longer have these intersections between the ends of my spaghetti. 401 00:35:40,280 --> 00:35:43,670 Okay. So it should go away very quickly. Okay. 402 00:35:43,880 --> 00:35:47,690 So if we just add in by hand the sort of exponentially decaying components. 403 00:35:48,650 --> 00:35:54,469 We see that the sum of the two, we only basically need one extra component that's decaying away very quickly, 404 00:35:54,470 --> 00:35:58,610 and then we can have a nice description of the entire entire evolution. 405 00:35:59,410 --> 00:36:01,630 Okay. So this is really cool. 406 00:36:01,900 --> 00:36:08,770 Okay, this is really cool because they have a model which reproduces the data, but not just that we have to put physical parameters into the model. 407 00:36:08,840 --> 00:36:14,470 Okay, we start with a black hole and a ring of material so we can actually use these effectively as scales of the system. 408 00:36:14,800 --> 00:36:17,080 We can weigh the black hole in the middle. Okay. 409 00:36:17,590 --> 00:36:23,260 And so for assessing 14 alloy, we find that the mass of the black hole has to be very similar to the one at the centre of our own galaxy. 410 00:36:23,890 --> 00:36:30,680 Around 2 million solar masses. And I know that I had to put about 5% of a solar mass into my ring in the storm. 411 00:36:31,460 --> 00:36:34,760 Okay. So this could be a powerful technique to learn more about these systems. 412 00:36:36,320 --> 00:36:37,549 So does it work? So. 413 00:36:37,550 --> 00:36:45,750 So does it work on more sources so we can go to the formerly record holder, 15 Al Hage And this is a real difficult test case for the theory. 414 00:36:45,800 --> 00:36:52,070 Okay. We've got nine different bands at different parts of the spectrum, and we've only got four free parameters in the model. 415 00:36:53,040 --> 00:36:56,129 Okay. So we press go and you can see, okay, again, 416 00:36:56,130 --> 00:37:04,500 we find this rapidly decaying for air component at early times and then it looks like it's all going to go wrong. 417 00:37:04,500 --> 00:37:08,729 But then the disk shown by these purple dashed lines and each figure starts to 418 00:37:08,730 --> 00:37:14,730 kick in and the disk component nicely explains each of the bumps and wiggles, 419 00:37:14,730 --> 00:37:17,100 which we see in every single component. Okay. 420 00:37:17,430 --> 00:37:24,600 So it's there's pronounced rises in luminosity up in the easy and just a gentle kink in the light curve in the infrared. 421 00:37:25,140 --> 00:37:30,480 But every single light curve shows some deviation from the early time behaviour at roughly 100 days. 422 00:37:31,110 --> 00:37:39,090 And this is when, this is when the disk component is kicking in. And then beyond that we nicely describe within the turbulent fluctuations all the. 423 00:37:41,280 --> 00:37:46,600 And The reason assassin 15 LH was such a bright object is that the black hole at the centre was a real beast. 424 00:37:46,770 --> 00:37:50,080 Okay, this had a billion solar masses. Okay. 425 00:37:50,150 --> 00:37:55,310 So it's very difficult to imagine. And it was about 0.1 Solomon. 426 00:37:57,100 --> 00:38:02,200 Okay. So this is really cool because what we've developed is effectively a set of weighing scales of black holes in the universe. 427 00:38:02,500 --> 00:38:06,070 We sit around, we wait for a black for one of these events to happen. 428 00:38:06,370 --> 00:38:11,740 We follow up with multi wavelength telescopes, we fit in the data and we can just measure the mass of the black hole. 429 00:38:12,490 --> 00:38:19,570 We can look at the galaxy and we can see how big the galaxy and we can start to contribute to these these plots that astronomers love to make, 430 00:38:19,690 --> 00:38:23,110 which is actually hence why we're in this case. 431 00:38:23,110 --> 00:38:26,910 Why is the mass of the black hole an x is the mass accounts like? 432 00:38:27,290 --> 00:38:30,549 And one of the problems of doing this in conventional methods is that there's 433 00:38:30,550 --> 00:38:34,960 a real systematic bias and there's a systematic bias towards big black holes. 434 00:38:35,410 --> 00:38:39,850 Big black holes are effectively easier to see because they have a larger effect on their surroundings. 435 00:38:39,970 --> 00:38:44,110 Okay, so we have one down here. So the Milky Way black hole is here. 436 00:38:44,560 --> 00:38:47,620 Okay, so and there's lots more small galaxies. 437 00:38:48,250 --> 00:38:51,560 So N30 two just happens to be nearby so we can resolve this problem. 438 00:38:52,000 --> 00:38:56,890 Okay. But there's this big gap which is on physical. It's a systematic bias and we can now fill that in. 439 00:38:57,460 --> 00:39:04,450 Okay, so we take all these TDs. I said there's 30 of them so far, and each of these Red Stars is one of these systems and we see that, 440 00:39:04,450 --> 00:39:08,200 okay, we can fill in the gap and this is the blue points are just these points. 441 00:39:09,580 --> 00:39:13,070 And so this is very exciting. Okay. So thank you very much. 442 00:39:13,100 --> 00:39:20,060 So in today's talk, I told you this specification occurs due to the extreme tidal forces near to black holes. 443 00:39:20,660 --> 00:39:25,190 Stellar spaghetti ification produces emission observable at cosmological distances. 444 00:39:25,550 --> 00:39:29,540 And understanding these events allows us to weigh supermassive black holes. 445 00:39:30,050 --> 00:39:30,710 Thank you very much.