1 00:00:07,540 --> 00:00:11,440 Good afternoon, everybody. Thank you very much for coming on this. 2 00:00:11,590 --> 00:00:18,490 Not terribly pleasant afternoon and thank you for not attending the alternative event, the procession, 3 00:00:18,580 --> 00:00:24,670 the open top bus through Broad Street by Oxford United, which is starting at this very minute. 4 00:00:26,350 --> 00:00:30,129 So it's my privilege to introduce our speaker today, Professor Rob Kennicott. 5 00:00:30,130 --> 00:00:34,030 He's the premium professor in Cambridge at the Institute of Astronomy. 6 00:00:34,810 --> 00:00:39,190 And his research interests include the structure and evolution of galaxies 7 00:00:39,520 --> 00:00:43,330 and star formation in galaxies in which he's made some seminal contributions. 8 00:00:44,200 --> 00:00:49,960 In fact, he's held some of the most influential positions in contemporary astronomy for a long time. 9 00:00:50,830 --> 00:00:56,020 In the late 19th and early twenties, he was the editor in chief of the Astrophysical Journal. 10 00:00:56,020 --> 00:01:00,489 This is the principal American Journal for publishing in. 11 00:01:00,490 --> 00:01:07,300 And so the editor in chief of that journal, of course, carries a great deal of weight and not too little or amongst the community. 12 00:01:07,690 --> 00:01:12,310 He has been widely recognised for his contributions to astronomy. 13 00:01:13,180 --> 00:01:20,440 A few examples are the award of the American Astronomical Society Dannie Heineman Prize in 2007 and a share in the 14 00:01:20,440 --> 00:01:26,230 Gruber Prize in 2009 for one of the most important pieces of work that's been done with the Hubble Space Telescope, 15 00:01:26,530 --> 00:01:29,560 namely a precision measurement of the Hubble constant. 16 00:01:29,980 --> 00:01:38,320 He was made a fellow of the Royal Society in 2011. But even this work on the Hubble constant is not actually the work for which he is best known. 17 00:01:39,940 --> 00:01:45,610 He is his his most prominent piece of work is on the measurement of the empirical 18 00:01:45,610 --> 00:01:49,750 relation between the gas density and the star formation rate in galaxies, 19 00:01:49,990 --> 00:01:56,590 a relationship which is fundamental to understanding galaxy evolution and is known as the Kennicott Schmidt Law. 20 00:01:58,120 --> 00:02:05,380 It is my great pleasure to introduce Professor Rob Kennicott to deliver the 12th GMC Lecture unveiling the birth of Stars and Galaxies. 21 00:02:05,590 --> 00:02:15,920 Robert. Time to put my mark on. 22 00:02:17,500 --> 00:02:22,420 Okay. Should work. You're right. I can't tell. So thank you. 23 00:02:22,430 --> 00:02:26,530 And for all that flattery. And just let me add water. 24 00:02:26,770 --> 00:02:31,570 Despite all jokes about Cambridge and Oxford, what a tremendous honour to be here. 25 00:02:31,870 --> 00:02:35,170 And Michael, for for for making it all possible. 26 00:02:35,680 --> 00:02:41,590 So I should begin, I guess, by explaining what this unveiling is all about. 27 00:02:42,640 --> 00:02:47,540 Good. You know, astronomy proceeds in fits and starts. 28 00:02:47,980 --> 00:02:54,250 And I think if you follow astronomy mainly, you know, through the the media, the economist and so on, 29 00:02:55,090 --> 00:03:00,370 often there are breakthroughs, just moments of inspiration where we leap ahead. 30 00:03:00,670 --> 00:03:06,909 The most recent example, doubtless the detection of gravitational waves a couple of months ago, 31 00:03:06,910 --> 00:03:12,370 announcement a couple of months ago by the advanced Lego team. 32 00:03:13,330 --> 00:03:20,410 And you can think of many other examples, I'm sure. But the story I want to tell today is of a different kind. 33 00:03:20,860 --> 00:03:28,899 There are other advances in astronomy that occur where progress is almost measured, 34 00:03:28,900 --> 00:03:37,210 like the motion of the minute hand on a clock where steady progress over a period of years. 35 00:03:37,330 --> 00:03:46,720 The story I'm going to tell today, over 15 or 20 years have resulted in results that are every bit as profound. 36 00:03:47,110 --> 00:03:55,120 And the one that I'm going to talk about today is something that often in the U.S. we call the origins problem. 37 00:03:55,450 --> 00:04:00,010 It's where did everything come from? How were galaxies formed? 38 00:04:00,940 --> 00:04:07,540 When how how was the Hubble sequence of shapes and sizes and masses and galaxies? 39 00:04:07,540 --> 00:04:12,730 How did that come to be where it is? How did stars and planets form? 40 00:04:13,600 --> 00:04:23,650 Much of my research efforts since working on the distant scale has been on the problem of star formation in the universe and on the large scales. 41 00:04:24,100 --> 00:04:33,280 And part of the story I want to tell today is how, although we're making remarkable advances on every scale from woops, 42 00:04:33,280 --> 00:04:40,810 sorry, I've got to I'm going to make that mistake a few times. This is an armour, a millimetre image of dust, a forming star, 43 00:04:41,110 --> 00:04:52,660 a solar system where these rings may be protoplanets around a nearby star, just as the theories of the last decades have predicted. 44 00:04:53,440 --> 00:04:58,600 And of course, you've seen iconic images like this of stars forming in our own Milky Way. 45 00:05:00,010 --> 00:05:04,089 But there's another story to be told. It's star formation. 46 00:05:04,090 --> 00:05:10,690 When you look on the grander scales in the universe within nearby galaxies, like in 94 here, 47 00:05:11,470 --> 00:05:20,020 where each of those red blobs is a cluster of several thousand stars forming to the Hubble ultra deep field, 48 00:05:20,230 --> 00:05:26,000 where we're peering out actually the extreme deep field where we're peering back to within, you know, 49 00:05:26,140 --> 00:05:32,379 the first billion years of the age of our universe and detecting stars forming at the 50 00:05:32,380 --> 00:05:37,870 very beginning some of the first stars and galaxies to have appeared in our universe. 51 00:05:39,820 --> 00:05:49,710 And so the unveiling I'm going to talk about is actually has a literal meaning and some metaphorical meetings all rolled into one. 52 00:05:49,780 --> 00:05:53,200 It's a lot of discoveries. 53 00:05:53,500 --> 00:06:05,950 The literal story that I'll tell along the way is how the opening of a new region of electromagnetic space, infrared observations in particular, 54 00:06:05,950 --> 00:06:15,909 and submillimeter observations of galaxies from space have on an unveiled 50% of one half of the star formation that 55 00:06:15,910 --> 00:06:23,650 had previously been hidden and a 50% that includes the most violent regions of star formation in our universe. 56 00:06:23,980 --> 00:06:33,639 And then three Fig. unveilings along the way, learning about the incredible array of diversity, 57 00:06:33,640 --> 00:06:40,870 of how galaxies are transforming the raw material from stars, gas in galaxies into stars. 58 00:06:41,260 --> 00:06:47,290 How we can now reconstruct that history over cosmic time observationally. 59 00:06:47,620 --> 00:06:50,700 And to me, something I'll have the least time to talk about. 60 00:06:50,710 --> 00:06:54,970 In fact, if my talks go as usual, not much time at all. 61 00:06:55,300 --> 00:06:59,020 How a theory, a theoretical paradigm, a cold, 62 00:06:59,020 --> 00:07:08,559 dark matter based paradigm which was originally designed to explain large scale structure of cosmic filaments, 63 00:07:08,560 --> 00:07:15,130 free cosmic structure that was seed seeded by quantum fluctuations in the early universe. 64 00:07:15,430 --> 00:07:23,680 How that's the computer simulations in the state of the Earth today can reproduce not only the large scale structure of the universe, 65 00:07:23,860 --> 00:07:29,860 but also the properties of galaxies, the Hubble sequence and so on. 66 00:07:29,860 --> 00:07:34,180 They can't quite get down to planets yet, but they're working on it and they're getting there. 67 00:07:34,330 --> 00:07:38,770 And it's one theory without fine tuning that does it all. 68 00:07:39,430 --> 00:07:43,270 Now, in saying that as an introduction, my colleagues. 69 00:07:43,570 --> 00:07:50,650 Upfront would have every reason to get worried because on those four bullets, there's easily material for one hour of talk on each. 70 00:07:51,010 --> 00:07:54,880 And I know you're sort of aiming to get out of here six ish rather than nine ish. 71 00:07:55,180 --> 00:07:58,800 So am I. So and that's going to be part of the point. 72 00:07:58,810 --> 00:08:03,100 But that's the method to this, is to show you how this all goes together. 73 00:08:04,060 --> 00:08:08,110 As Roger said, I work on this problem on the large scale. 74 00:08:08,650 --> 00:08:15,280 And so in describing I'll be describing where that, you know, that relation he talked about Schmidt law comes from. 75 00:08:15,550 --> 00:08:24,490 And it turns out that although what I've done is a tiny piece of this essentially generational accomplishment that's ongoing, 76 00:08:24,790 --> 00:08:31,899 the piece I work on actually occurs at the intersection of these four threads or the cusp of all of this. 77 00:08:31,900 --> 00:08:36,440 And so in some sense, to explain the implication requires going through all of this. 78 00:08:36,440 --> 00:08:39,730 So anyway, that's the design. Let's see how it goes. 79 00:08:40,060 --> 00:08:45,250 So to begin, I'm going to at the beginning sort of speaker, 80 00:08:45,250 --> 00:08:52,120 I'll start at the sort of most general level and we'll move on to the plots that none of you will understand as we get deeper into the talk, 81 00:08:53,830 --> 00:09:00,850 even, Roger, I hope at some point. So I'll go through the context of all four of these. 82 00:09:01,600 --> 00:09:03,909 Let's begin with galaxies with a few things, 83 00:09:03,910 --> 00:09:13,060 hopefully almost all of you know about of what you're seeing as an infrared image in three colours of the nearby spiral. 84 00:09:13,210 --> 00:09:17,410 M1 or one. In Ursa major. I've chosen it. 85 00:09:17,680 --> 00:09:20,950 It's a galaxy, as you see, about 23 million light years away. 86 00:09:21,220 --> 00:09:25,330 We measured the distance as part of this Hubble project. We got the Gruber Prize for. 87 00:09:25,360 --> 00:09:34,000 So it's a pretty good number. And it is chosen because we, of course, we can't see the Milky Way from the outside yet anyway. 88 00:09:34,840 --> 00:09:40,540 But it's pretty close to what the Milky Way would probably look like if we could see it on the outside. 89 00:09:40,720 --> 00:09:50,890 So you're looking at 100 billion stars very roughly across a disk that's about 100,000 light years across. 90 00:09:50,920 --> 00:10:01,840 These are mind boggling numbers if you begin to think about it when you ask what it's made of in this case of the baryonic matter of the matter, 91 00:10:01,840 --> 00:10:07,990 we know about about two thirds is stars and about one third is gas. 92 00:10:08,650 --> 00:10:12,910 Raw material gas you think of is fuel for a future star formation. 93 00:10:12,910 --> 00:10:17,800 So this galaxy has managed to use up about two thirds of its gas tank. 94 00:10:18,520 --> 00:10:23,370 And of course, 85% is a dark matter that we don't know. 95 00:10:23,380 --> 00:10:26,860 We know we can measure how much of it is with incredible precision. 96 00:10:26,860 --> 00:10:31,330 But what it is? No, not yet. So that's another talk. 97 00:10:33,630 --> 00:10:35,470 There. I will go through this quickly. 98 00:10:35,710 --> 00:10:46,190 Again, I think, you know, just as there are about 100 billion stars in a typical large galaxy like the Milky Way or M1 or one there, 99 00:10:46,240 --> 00:10:53,770 but by coincidence, about 100 billion galaxies like that within the visible limits of the universe. 100 00:10:53,770 --> 00:10:58,839 As far back out as we can see, this is a map of those within the brightest, 101 00:10:58,840 --> 00:11:02,710 within about a billion light years, and there are thousands of galaxies there. 102 00:11:02,950 --> 00:11:09,189 And, you know, they're not arranged randomly. They are in some sort of spiderweb like filament tree structure. 103 00:11:09,190 --> 00:11:14,890 That's real. That's not your eyes. Those are not Martian canals. That that's real structure that you're seeing. 104 00:11:16,810 --> 00:11:23,530 Again, a part of the basics. And 101 Hubble that are our nomenclature. 105 00:11:23,710 --> 00:11:30,130 The old school way of describing galaxies was in terms of what's called the Hubble sequence. 106 00:11:30,880 --> 00:11:37,240 Edwin Hubble did many. He established what the nature of galaxies were, the distance to Andromeda, the first one. 107 00:11:38,110 --> 00:11:48,810 And he proposed a classification scheme that was still used today, that of elliptical galaxies, rather steroidal galaxies, 108 00:11:48,820 --> 00:11:56,950 as we'll see that are largely devoid of young stars going through the spirals and then beyond irregular galaxies. 109 00:11:57,820 --> 00:12:02,260 And what no one would be sitting somewhere here in the diagram? 110 00:12:02,890 --> 00:12:07,870 No. As I say, we can't produce such an image for our own galaxy, the Milky Way. 111 00:12:08,260 --> 00:12:17,469 But this is an artist's visualisation based on the best data that we have of roughly what it would look like a barred. 112 00:12:17,470 --> 00:12:26,560 We're certainly on the lower part of Hubble's tuning for the system, actually a very interesting system of stars in a bar. 113 00:12:27,490 --> 00:12:38,920 We are about two thirds of the way out. And one thing I didn't say in our one hour, one, if you do an age census of the stars in the spiral galaxies, 114 00:12:39,100 --> 00:12:50,230 that you can find almost a uniform range of ages from forming as we speak to stars almost as old as the universe itself, up to about 13 billion years. 115 00:12:50,440 --> 00:12:53,950 And that's the case in the Milky Way. And there are three examples. 116 00:12:53,980 --> 00:13:03,850 Our solar system has been accurately age dated for meteorites and such to about four and a half, 4.46 billion years. 117 00:13:04,570 --> 00:13:10,270 And the oldest example of a globular, a star cluster approach, 13 billion years. 118 00:13:10,510 --> 00:13:16,030 And then if you look at active nebulae, you see stars with negative ages. 119 00:13:16,030 --> 00:13:22,480 Essentially, they're in the process of forming as we speak, and it's typical of galaxies of that type. 120 00:13:23,760 --> 00:13:26,340 So that's sort of the introduction to galaxies. 121 00:13:26,700 --> 00:13:34,230 Now, before this unveiling, before we started studying the universe across the electromagnetic spectrum, 122 00:13:34,500 --> 00:13:39,430 there's a lot that you could learn simply from visible starlight. 123 00:13:39,690 --> 00:13:49,130 And so, again, from just basic introduction, here's an example of one of the nearest very active regions of star formation, the Orion Nebula. 124 00:13:49,140 --> 00:13:53,370 Most of many of you will recognise this object here. 125 00:13:53,700 --> 00:13:58,320 It's actually visible, maybe not from Oxford on a typical certainly not last night. 126 00:13:59,970 --> 00:14:03,810 It's in, I guess, officially the Sword of Orion. 127 00:14:04,110 --> 00:14:13,500 What I taught undergraduate astronomy in Minnesota. Some female students tried to convince me this was rather anatomical feature of Orion, 128 00:14:13,890 --> 00:14:18,430 and this explained why he was immortalised in the stars for a while. 129 00:14:18,450 --> 00:14:26,499 But either way, and and within this is a this is a cloud of gas that's been ionised. 130 00:14:26,500 --> 00:14:35,069 This glowing, fluorescein heated. Actually, this organisation is produced by just a so-called trapezium for very massive stars. 131 00:14:35,070 --> 00:14:41,400 30 times the mass of our sun at up in the centre and a cluster of several hundred stars. 132 00:14:41,580 --> 00:14:45,630 And that's typical of the star forming units in the Milky Way. 133 00:14:45,990 --> 00:14:55,170 Likewise, if you study, for example, with the Hubble telescope Orion at higher resolution and look very carefully around, 134 00:14:55,410 --> 00:15:00,150 you will see evidence of other interesting phenomena on smaller scale. 135 00:15:00,450 --> 00:15:08,250 These objects are called probe lids and what they are now believed to be are individual stars. 136 00:15:08,550 --> 00:15:17,700 A solar system's basically in the process and forming sometimes a front lip where you see some sort of circumstellar material, 137 00:15:17,820 --> 00:15:24,510 perhaps a disk and sometimes backlit where, you know, the essentially sitting in front of a bright light source. 138 00:15:24,810 --> 00:15:35,820 So so we we've gathered a lot of information over the last few decades on star formation in our own neighbourhood, 139 00:15:36,090 --> 00:15:49,530 in great detail in selected regions. But if you restrict yourself to the visible, you begin running up against a figurative brick wall very quickly. 140 00:15:50,550 --> 00:15:57,780 So, for example, if I wanted to make a map of all of the Orions in the Milky Way or all of the stars. 141 00:15:58,050 --> 00:16:01,860 Anything you like. You come up against this problem. 142 00:16:01,870 --> 00:16:09,440 So here is a I think, an all sky camera photograph made in the southern sky of the southern Milky Way. 143 00:16:09,450 --> 00:16:13,410 This beautiful band in the sky. Most of you are familiar with. 144 00:16:13,800 --> 00:16:20,130 But you see, of course, cutting across the stars, all of these dark bands. 145 00:16:20,340 --> 00:16:30,930 These are holes in the Milky Way. They are clouds of interstellar gas and dust particles that are blocking the light to the point that, 146 00:16:30,930 --> 00:16:34,259 in fact, even though I said the Milky Way is out of order, 147 00:16:34,260 --> 00:16:44,950 100,000 light years around in most sightlines, especially in the disk of the Milky Way, you don't see much farther than a few thousand light years. 148 00:16:45,690 --> 00:16:51,450 That, in addition to this, clumped us, there's more diffuse dust that is creating just a smog, 149 00:16:51,450 --> 00:16:56,190 basically a fog preventing us from looking at this dust. 150 00:16:57,060 --> 00:17:05,100 Interesting stuff. We just checked. Yeah, got it. It's particles roughly the size of a wavelength of light and smaller. 151 00:17:05,100 --> 00:17:12,630 Everything from nanoparticles up to, like, the soot particles. 152 00:17:12,840 --> 00:17:20,100 Smoke particles, you know, from a cigarette or so on, up to small silicate, small rocks, but micron size. 153 00:17:21,150 --> 00:17:28,410 And it in terms of concentration is incredibly concentrated in the interstellar medium. 154 00:17:28,650 --> 00:17:33,090 I don't know. Does anybody happen to know what the. If you're a coal miner, 155 00:17:33,990 --> 00:17:42,030 what the concentration in parts per million of coal dust can be in that mine before you're not allowed in without reading the equipment. 156 00:17:42,420 --> 00:17:45,810 I had to look it up. I didn't know no coal miners in the other. 157 00:17:47,010 --> 00:17:50,670 It's about at least in the U.S., it's one, one part per million. 158 00:17:51,030 --> 00:17:54,419 Any more than that, you need breathing apparatus. 159 00:17:54,420 --> 00:17:58,920 And of course, that applies to the people in the construction site, outside and and everything else. 160 00:17:59,280 --> 00:18:04,230 Interstellar space. It's one part, 410,000 parts per million. 161 00:18:04,830 --> 00:18:14,400 And of course, much more rarefied in space that the typical density of gas particles even is sort of a particle per cubic centimetre. 162 00:18:15,060 --> 00:18:21,560 So does even less than that. But you're looking through hundreds of trillions of miles of it. 163 00:18:21,570 --> 00:18:33,300 So so it's very opaque. In fact, if the air in this room had dust at 10,000 parts per million, those in the back room would not be seeing me. 164 00:18:33,600 --> 00:18:38,819 And when it condensed out, you know, it would leave far more than a little stain of dust on your shoes. 165 00:18:38,820 --> 00:18:49,800 You know, it would be you know, it would be microscopically deep. So the interstellar medium, the gas in galaxies is is very dusty. 166 00:18:50,920 --> 00:18:59,170 And that. So that has prevented us not only from making a census of, say, where the stars form or Milky Way, 167 00:18:59,320 --> 00:19:04,960 it prevents us from looking into peering into the dense disks of those individual star forming regions. 168 00:19:05,200 --> 00:19:07,330 And in other galaxies, as you'll see later, 169 00:19:07,510 --> 00:19:16,240 it blocks out the very most interesting that the star formation in the most intense and violently star forming regions in the universe. 170 00:19:18,790 --> 00:19:27,310 And again, the reason is that the size of this dust is about peaks, just very much so invisible in ultraviolet light. 171 00:19:27,790 --> 00:19:37,809 So the solution, it's easy to say, but difficult to do technologically is to observe the universe in wavelengths that are longer, 172 00:19:37,810 --> 00:19:40,760 wavelengths of light, that are longer than the dust grains. 173 00:19:40,760 --> 00:19:46,570 And then they just diffracted around or simply shine through the dust and penetrate right through. 174 00:19:47,560 --> 00:19:51,790 And so this is the infrared just mentioned anecdotally. 175 00:19:52,000 --> 00:19:57,190 Infrared radiation was discovered by William Herschel, the discoverer of the planet Uranus. 176 00:19:57,850 --> 00:19:58,720 20 years later, 177 00:19:58,930 --> 00:20:07,150 he discovered infrared radiation and measured the amount of it in the sun with a very ingenious experiment where he set up thermometers, 178 00:20:08,590 --> 00:20:17,260 used a prism to disperse sunlight and and used thermometers to show that there was heat he picked up far beyond, 179 00:20:17,890 --> 00:20:25,540 both in the red part of the solar spectrum, but then far beyond in regions where there was no light falling that you could see following on the table. 180 00:20:25,810 --> 00:20:30,760 And Herschel Space Observatory was named after him in honour of that. 181 00:20:32,140 --> 00:20:41,950 Sorry. There we go. And so the penetrating power of the infrared, even in near infrared wavelengths, is is is amazing. 182 00:20:41,950 --> 00:20:46,310 And there's just there's a terrestrial example, I think, from the 1950s. 183 00:20:46,540 --> 00:20:55,840 This is Silicon Valley a long time ago when it was an empty valley, invisible light on a hazy day. 184 00:20:56,170 --> 00:20:59,770 And and then the same time and infrared. 185 00:20:59,960 --> 00:21:03,610 Here's Orion again. Visible and infrared. 186 00:21:03,880 --> 00:21:12,100 And then quickly, here's the Milky Way. So here is the visible view, another photograph of what you see in visible light. 187 00:21:12,100 --> 00:21:17,890 When you look, try to look through the Milky Way from where we're located in the solar system. 188 00:21:18,970 --> 00:21:24,580 Centre of galaxy in this direction. And here in the near infrared is what you see. 189 00:21:24,790 --> 00:21:28,750 You penetrate the dust, the obscuration goes away, and voila. 190 00:21:29,020 --> 00:21:33,580 There's this beautiful, flat, bright, bulgy bar. 191 00:21:33,600 --> 00:21:40,350 Is the bar actually seen edge on a galaxy there? 192 00:21:40,360 --> 00:21:46,689 And in fact, if for not for the dust, I hope most of you have seen the Milky Way. 193 00:21:46,690 --> 00:21:52,839 But unless you're in a really dark site, it's you know, it usually surprises people. 194 00:21:52,840 --> 00:22:02,590 It's not an obvious thing to you. But believe me, if if that dust weren't there, there would be no doubt it would just dominate the sky. 195 00:22:03,280 --> 00:22:08,530 Very bright at night. Infrared has a second advantage, 196 00:22:08,920 --> 00:22:17,590 and that is if we go to even longer wavelengths that are still called infrared rather than a few times the wavelength of, say, red light. 197 00:22:17,800 --> 00:22:25,060 If you go two of order tens to 200 times brighter than those wavelengths. 198 00:22:25,360 --> 00:22:30,400 Then the boots, the dust glows. 199 00:22:30,820 --> 00:22:38,260 And that's just a basic property of physics that all objects in the universe emit light at some particular wavelength. 200 00:22:38,920 --> 00:22:42,520 The cooler they are, the longer the wavelength at which it glows. 201 00:22:42,850 --> 00:22:51,700 And it turns out that the dust in our galaxy or other galaxies is heated by the starlight to temperatures of anywhere 202 00:22:51,700 --> 00:22:59,560 from a few degrees above absolute zero to about 100 on average about 20 or 30 degrees centigrade above absolute zero. 203 00:22:59,830 --> 00:23:05,050 And at those wavelengths, they glow characteristically at these wavelengths. 204 00:23:05,260 --> 00:23:14,800 And by the same token, objects on the earth, which are, of course, at near 270 degrees Kelvin ish, also glow in the infrared. 205 00:23:14,890 --> 00:23:18,370 And these are just some infrared pictures, you know, hairdryer, dog, penguin. 206 00:23:19,120 --> 00:23:22,840 You can go online and find all sorts of these things. 207 00:23:24,850 --> 00:23:28,060 Now again, what I this the dust. 208 00:23:28,240 --> 00:23:40,630 This is no trivial matter. Even though that dust only makes up .000 2% of the amount of mass in the universe, if you count the dark matter, 209 00:23:40,780 --> 00:23:50,050 the dark inner resonance of the dark energy, it actually over the whole universe absorbs half of all the starlight that there is. 210 00:23:50,560 --> 00:23:57,900 And it isn't just any half, it turns out. It's it's where the dust tends to concentrate, where the stars are. 211 00:23:57,910 --> 00:24:05,290 That's the kind of Schmidt law. It's basically the there's a very tight correlation where stars form and where the gas and the dust concentrate. 212 00:24:05,530 --> 00:24:10,059 So it's year until we went to the infrared. 213 00:24:10,060 --> 00:24:18,760 We not only needed it to recover that the half of the picture we were missing, we got a completely different picture when we did it. 214 00:24:22,760 --> 00:24:25,940 Progress in this field had to wait, however, 215 00:24:25,940 --> 00:24:37,280 was technology limited that needed the development of infrared sensors and the ability to put them on cold telescopes and launch them well into space. 216 00:24:38,450 --> 00:24:41,720 The reason it doesn't work on the ground for a couple of reasons. 217 00:24:41,900 --> 00:24:47,600 For one thing, a lot of this infrared radiation doesn't penetrate the Earth's atmosphere. 218 00:24:47,840 --> 00:24:55,940 It's the greenhouse effect. And reverse greenhouse effect is the CO2 and the methane and so on, let visible light in. 219 00:24:56,270 --> 00:25:00,490 But when the earth glows, the ground gets warm and heats back. 220 00:25:00,500 --> 00:25:03,650 The heat tries to escape the infrared wavelengths. 221 00:25:03,890 --> 00:25:12,110 The atmosphere traps it. So that same trapping effect keeps infrared radiation from space, by and large, from penetrating to the ground. 222 00:25:12,410 --> 00:25:18,860 And the other problem is, since everything it room temperature glows brightly in the infrared. 223 00:25:19,010 --> 00:25:22,190 Of course, it's difficult to see the sky. 224 00:25:22,550 --> 00:25:27,080 By contrast, one of my colleagues from the University of Arizona, where I used to work, George Rekhi, 225 00:25:27,080 --> 00:25:32,760 has written a book about this, and he likens observing the sky from the ground in the infrared. 226 00:25:32,780 --> 00:25:43,520 You can try. He likens it to try to observe with a conventional telescope in broad daylight, with all of the lights on in the observatory. 227 00:25:45,440 --> 00:25:51,770 And with shining, you know, holding a blowtorch down over your detector while you're doing it. 228 00:25:52,530 --> 00:25:56,360 I actually Jorge didn't have the blowtorch prior to that, but it just is correct. 229 00:25:57,380 --> 00:26:03,560 So the way to escape all of this is to put your telescope in space. 230 00:26:03,710 --> 00:26:08,930 And there have been a series of missions, all sky surveys on the left and pointed telescopes on the right. 231 00:26:09,110 --> 00:26:15,950 This is an area in which Europe and the UK in particular have played leading roles to reveal that part. 232 00:26:17,330 --> 00:26:21,799 So when you do that that you unveil basically. 233 00:26:21,800 --> 00:26:25,190 And so just a couple of examples before we move to galaxies. 234 00:26:25,400 --> 00:26:34,490 Here again is the famous Eagle Nebula, part of a complex called M16 in Sagittarius. 235 00:26:34,790 --> 00:26:42,829 Here's the famous Hubble photo. What you see in the visible, you see this dark obscuring material which is hosting the young stars, 236 00:26:42,830 --> 00:26:46,940 but you don't see the stars themselves, observe the same region in the infrared, 237 00:26:47,240 --> 00:26:55,129 and you see that in fact, the stars themselves are forming actually at the interfaces between these fingers of molecular material, 238 00:26:55,130 --> 00:26:59,360 basically in dust and the rest of the nebula. 239 00:26:59,600 --> 00:27:08,240 And when you you can now map the entire Milky Way and make the first full inventories of star formation in the galaxy. 240 00:27:08,370 --> 00:27:18,949 I'll come back to talk about that later. One thing I won't have time to talk about today, but is a key feature of studies is that this part, 241 00:27:18,950 --> 00:27:23,240 the infrared, is also a very rich part of the electromagnetic spectrum. 242 00:27:23,570 --> 00:27:34,880 Of all the species of material that sit between stars radiate at these wavelengths ionised gas, the accretion disks around black holes. 243 00:27:35,030 --> 00:27:41,780 In this case, molecular molecules from the cold gas, atomic gas to just about any temperature. 244 00:27:42,080 --> 00:27:46,040 And even the dust grains themselves, they don't emit continuously. 245 00:27:46,040 --> 00:27:51,680 They have a band structure that can be used to trace the solid phase of the interstellar medium. 246 00:27:51,830 --> 00:27:59,000 Some of what I'll talk about the diagnostics came using some of this, but I won't have time to go through it explicitly. 247 00:27:59,420 --> 00:28:00,740 So that's the Milky Way. 248 00:28:01,550 --> 00:28:11,780 When you look at other galaxies in the infrared, depending on what wavelength you tune your telescope to, you will get very different pictures. 249 00:28:11,790 --> 00:28:16,339 This is M81, another favourite, a sort of amateur telescope project. 250 00:28:16,340 --> 00:28:19,850 Here's what it looks like in the visible. Here's an infrared composite. 251 00:28:20,990 --> 00:28:27,470 And basically at long wavelengths you're looking at different components, different species of interstellar dust. 252 00:28:27,800 --> 00:28:35,630 It is tracing in exquisite detail the distribution of cold gas, the raw, the fuel for the star formation. 253 00:28:35,840 --> 00:28:41,510 And as you go to the longer wavelengths, you begin to see you see that gas, but you're going to see concentrations. 254 00:28:41,750 --> 00:28:45,260 Each of these as are being heated by newly formed stars. 255 00:28:45,470 --> 00:28:48,560 And you can also measure the star light. 256 00:28:49,070 --> 00:28:56,360 That has been essentially the start of the forming stars, the light from them that has been blocked by the dust at other wavelengths. 257 00:28:56,960 --> 00:29:03,170 And what really the the emphasis of work in the past decade is on multi wavelength studies. 258 00:29:03,500 --> 00:29:12,350 The infrared shows the hidden star formation. But of course not all of the the star formation is blocked by dust. 259 00:29:12,710 --> 00:29:19,610 And so the way you can pick that up is by observing the same regions in either the ultraviolet. 260 00:29:20,040 --> 00:29:24,380 Part of the spectrum, just short word of visible light where young stars we met. 261 00:29:24,450 --> 00:29:30,270 Most of the mass of young stars emit most of their energy or in line sensitive to the nebulae. 262 00:29:30,280 --> 00:29:35,650 The clouds of gas like Orion, for example, the boom or alpha line in the red. 263 00:29:35,670 --> 00:29:40,830 This is a composite of both. And so any of these can be calibrated. 264 00:29:41,100 --> 00:29:45,840 You can take the brightnesses of galaxies or region subregions in any of those wavelengths, 265 00:29:46,140 --> 00:29:52,920 but by combining the obscured and the obscured get very precise measurements of the star formation rates. 266 00:29:53,010 --> 00:29:57,990 One of the things I've spent a lot of time in my career is calibrating this toolbox. 267 00:29:58,230 --> 00:30:02,700 Boring bore you to tears by showing you the details. So I won't. 268 00:30:02,970 --> 00:30:06,780 But I will show one slide for the experts. 269 00:30:07,830 --> 00:30:12,750 This just shows what these multi wavelength techniques enable you to do. 270 00:30:13,020 --> 00:30:21,000 These are plots of measuring the number of stars forming in a galaxy in terms of luminosity in different ways. 271 00:30:21,330 --> 00:30:30,840 On the top plots, it's an infrared tracer of a very one way to eight and 24 microns versus an optical tracer dust. 272 00:30:30,840 --> 00:30:32,010 Correct. At each alpha. 273 00:30:32,400 --> 00:30:41,790 And you get general before you if you only look at the dust emission and you only look at the unknown obscured, you get a general correlation. 274 00:30:42,030 --> 00:30:49,290 But the scatter is more than a factor of two and and the total scatter of our galaxy. 275 00:30:49,290 --> 00:30:53,370 Individual galaxies can deviate by over a factor of 100. 276 00:30:53,580 --> 00:30:58,620 Either either the they have they're incredibly obscured. 277 00:30:58,620 --> 00:31:02,040 So you see nothing in the visible or you can have the other extreme. 278 00:31:02,040 --> 00:31:10,290 They have no dust at all for various reasons, and the dust is missing it, whereas there are fairly straightforward schemes, 279 00:31:10,290 --> 00:31:19,620 actually linear combinations of the two, which then when you calibrate this measure, the star formation rates in different ways give you consistency. 280 00:31:19,800 --> 00:31:28,710 That's good too, less than 10%. So we've gone from factors of a few errors, down 2% to 10% or less. 281 00:31:29,460 --> 00:31:34,230 Not as good as the precision of some of the cosmological measurements or what a 282 00:31:34,230 --> 00:31:41,700 physicist in the field would consider good but superb for this sort of application. 283 00:31:41,910 --> 00:31:45,820 Real progress. So those are the tools. 284 00:31:46,240 --> 00:31:53,230 And if we start now applying these measurements to galaxies around us, what do we learn? 285 00:31:53,500 --> 00:31:56,770 So here is a Hubble tuning fork. 286 00:31:56,830 --> 00:32:02,020 Let me just make sure I've got your Hubble's tuning fork. 287 00:32:02,260 --> 00:32:09,520 But now from one of the major surveys from these, in addition to surveying the Milky Way, 288 00:32:09,520 --> 00:32:17,620 there have been a number of projects targeting nearby galaxies and distant galaxies at a range of infrared, 289 00:32:17,620 --> 00:32:27,220 visible, optical, actually radio X-ray wavelengths. This is one of them from the Spitzer Infrared Nearby Galaxies Survey project I led in the U.S. 290 00:32:27,640 --> 00:32:32,380 And the galaxies we've arranged the galaxies under a long Hubble sequence. 291 00:32:32,800 --> 00:32:39,670 And you may notice a trend here. The regulars down here, as you go left to right, galaxies here are blue. 292 00:32:39,700 --> 00:32:45,040 This blue is from starlight, actually, infrared starlight, ironically, old stars. 293 00:32:45,910 --> 00:32:49,570 Whereas on the right you see more lumpiness and more red. 294 00:32:49,780 --> 00:32:54,580 The red is 24 micron emission from active star forming regions. 295 00:32:54,790 --> 00:32:59,190 And so the first thing we learned, we saw this in the visible is the Hubble sequence. 296 00:32:59,200 --> 00:33:04,660 One of the things that defines the Hubble sequence is that it's a star forming sequence. 297 00:33:04,930 --> 00:33:12,610 Now, the one way I can illustrate that is just with the case study taking two of the galaxies closest to the Milky Way. 298 00:33:13,000 --> 00:33:16,330 On the left you should recognise some many. You should recognise these. 299 00:33:16,690 --> 00:33:18,730 On the left, the Andromeda Galaxy. 300 00:33:19,090 --> 00:33:28,720 It's the nearest large neighbour to the Milky Way, a very similar in mass to ours, about 50% more massive than the Milky Way. 301 00:33:29,110 --> 00:33:33,700 2 million, half million light years away. You can see it has a few satellite galaxies. 302 00:33:34,030 --> 00:33:38,390 On the right is is the large Magellanic Cloud. 303 00:33:38,680 --> 00:33:48,340 This is the nearest satellite of the Milky Way, much closer, 160,000 light years away. 304 00:33:48,550 --> 00:33:56,380 And much, much smaller than either Milky Way or Andromeda, about less than actually 10% of the mass of the Milky Way. 305 00:33:57,310 --> 00:34:01,549 There's two images are roughly two, two angular size. 306 00:34:01,550 --> 00:34:07,720 So Milky Way on the Andromeda enlargement closer have comparable angular size. 307 00:34:08,200 --> 00:34:11,950 You have to be in the southern hemisphere to see Magellanic Clouds. 308 00:34:12,190 --> 00:34:23,680 If I put them on the same absolute scale, here's the LMC you see, it's roughly it's actually small compared to some of the dwarf galaxy companions. 309 00:34:24,580 --> 00:34:31,120 So huge difference in number of stars, a total mass of stars formed. 310 00:34:31,450 --> 00:34:38,080 On the other hand, if I measure these galaxies in wavelengths that are sensitive to the star formation. 311 00:34:39,330 --> 00:34:43,080 This is I'm afraid it's mixed media here. 312 00:34:43,080 --> 00:34:50,180 We've got ultraviolet here for Andromeda and H alpha for LMC. 313 00:34:50,400 --> 00:34:56,580 Nevertheless, the visual impression is clear even though this galaxy is more than 15 times less massive. 314 00:34:56,790 --> 00:34:59,910 If you add up the number of stars forming today, 315 00:35:00,000 --> 00:35:10,079 they're comparable between the two galaxies that those low mass gas rich galaxies on the right hand side of 316 00:35:10,080 --> 00:35:19,650 the Hubble sequence are forming a relatively large fraction of their stars today relative to Andromeda. 317 00:35:20,880 --> 00:35:24,990 That those differences even extend down to the smaller scale. 318 00:35:25,200 --> 00:35:33,270 If you wanted a for reference, you know what would Orion if Orion were placed in a large Magellanic cloud, what it would look like? 319 00:35:33,420 --> 00:35:40,840 What would be some of these almost unresolved dots? Maybe that object there, that object there, maybe? 320 00:35:40,860 --> 00:35:43,920 Well, not that that's several Orions, but yeah. 321 00:35:43,950 --> 00:35:45,630 Look at this monster over here. 322 00:35:46,080 --> 00:35:56,990 This in the LMC, there's a region called 30 DORADUS called the Tarantula Nebula, 30 DORADUS means it's the 30th brightest star in the Constellation. 323 00:35:57,000 --> 00:36:08,430 Right? It's one like Orion. You can see this star formation region without binoculars, but this one's 160,000 light years away. 324 00:36:08,760 --> 00:36:14,460 If we zoom in in emission lines, you can see the reason for the tarantula name. 325 00:36:14,680 --> 00:36:18,690 An incredible complex of bubbles and loops. And this thing. 326 00:36:18,690 --> 00:36:22,889 Whoops, sorry. Is. Well, where's my laser? 327 00:36:22,890 --> 00:36:23,520 Laser here. 328 00:36:24,240 --> 00:36:37,980 If we zoom in on the centre, whereas the Orion Nebula was powered by four massive stars, or this one is powered by more than 2000 of those stars. 329 00:36:38,250 --> 00:36:47,610 In fact, a couple dozen stars of more than 100 solar mass times the mass of the sun we used to think is the mass limit for stars. 330 00:36:47,700 --> 00:36:52,260 And in total, over 40,000 stars, I think, forming in this region. 331 00:36:52,620 --> 00:36:58,469 And so the Hubble sequence turns out to be a sequence, not only the total number of stars, 332 00:36:58,470 --> 00:37:06,150 but also in the mass spectra of the masses of the brightest individual complexes. 333 00:37:06,450 --> 00:37:10,740 And that has implications for feedback is all talk about later. 334 00:37:12,340 --> 00:37:22,200 It's difficult in the public talk. I'll show a couple of graphs in a minute, but this diversity extends in all directions, 335 00:37:23,040 --> 00:37:31,800 just as there are galaxies which have much more star formation per given volume mass than the galaxy. 336 00:37:32,880 --> 00:37:38,940 The big one. The extremes go down thousands of times in the other direction. 337 00:37:39,210 --> 00:37:43,380 These are four examples of very low density star forming environments. 338 00:37:43,680 --> 00:37:46,950 This is an example of an early type galaxy, 339 00:37:46,950 --> 00:37:56,700 what we call a lenticular S0 galaxy that used to be called this class of Gaussian is called red and dead thought to not be forming any stars today. 340 00:37:56,940 --> 00:38:04,620 But when you look closely, often are forming very tiny amounts, but star formation still going on. 341 00:38:05,550 --> 00:38:11,130 We now know that star formation extends to the outermost edges of many galaxies. 342 00:38:11,760 --> 00:38:18,930 Here's an example of a dwarf galaxy. Even more than a factor of ten less massive than Orion, I think 100 times less. 343 00:38:19,240 --> 00:38:27,870 Oh, sorry. Ten times loss of the LMC that has a very of sporadic staffers, but it's ubiquitous. 344 00:38:28,140 --> 00:38:33,870 It's difficult to find galaxies with any gas in it that is not forming stars. 345 00:38:34,240 --> 00:38:38,550 But this particular subject is one where a lot of work has been done here. 346 00:38:39,330 --> 00:38:45,959 Both studies in the ultraviolet or the integral field spectrographs where they're 347 00:38:45,960 --> 00:38:50,910 studying galaxies were thought to be gas free and devoid of star formation. 348 00:38:51,120 --> 00:38:58,139 And what you find is typically in a third of the cases, in fact, nature is still finding a way to form stars. 349 00:38:58,140 --> 00:39:04,260 So it's a ubiquitous phenomenon, far more widespread than we had thought it was. 350 00:39:04,590 --> 00:39:09,720 It's just one example in the extreme will connect to something we'll talk about in about five, 10 minutes. 351 00:39:10,950 --> 00:39:20,400 We even see star formation in environments which by any prediction, would have been totally hostile to the formation of stars. 352 00:39:20,670 --> 00:39:30,720 This is amateur image of the Perseus cluster of galaxies, a cluster you see about a quarter of a billion light years away. 353 00:39:30,930 --> 00:39:35,220 There are a couple of hundred galaxies in this region of the cluster. 354 00:39:35,490 --> 00:39:38,400 Galaxies often congregate in these dense clusters. 355 00:39:38,900 --> 00:39:45,920 There are the most massive structures found in the universe and you probably can't see from where you sit. 356 00:39:46,250 --> 00:39:53,960 But the centre of mass of this cluster is NGC 1275, and it's got a little bit of a peculiar appearance to it. 357 00:39:54,350 --> 00:40:01,040 And if I show you, I'm afraid orientation has been flipped. But here is the galaxy imaged in H alpha. 358 00:40:01,400 --> 00:40:05,930 And if you look close up, it's, it looks like to be an elliptical galaxy, 359 00:40:06,140 --> 00:40:14,660 but it's surrounded by these filaments of ionised gas, which you will also have dust associated with them. 360 00:40:15,680 --> 00:40:22,069 This is material from what is called the cooling flow of the the dominant mass in 361 00:40:22,070 --> 00:40:30,320 these clusters is a huge cloud of hot gas temperatures of of millions of degrees, 362 00:40:30,320 --> 00:40:36,680 sometimes tens of millions of degrees, more mass in that gas than in all of the stars in these galaxies. 363 00:40:36,950 --> 00:40:45,530 And in Perseus, the gas in the centre is cooling and raining down onto the central galaxy. 364 00:40:45,980 --> 00:40:55,670 And if you imaged this in the ultraviolet with Hubble, you find a lot of behold a cluster of stars forming all over the place. 365 00:40:55,880 --> 00:41:07,970 So this, you know, what started out as a million degree gas is finding a way to cool and it's still forming stars today. 366 00:41:07,970 --> 00:41:20,160 So it's happening everywhere. You can quantify these trends in various ways, and I'll show you two ways in which we do it. 367 00:41:21,420 --> 00:41:27,870 I've been showing you Hubble sequence, but of course Hubble type is a rather non quantitative variable. 368 00:41:28,560 --> 00:41:36,990 It turns out, although the Hubble sequences, the sequence in star formation and of obviously disk structure versus spheroid and so on, 369 00:41:37,230 --> 00:41:43,050 but also turns out to be a mass sequence in the sense that the elliptical galaxies 370 00:41:43,800 --> 00:41:49,830 tend to attain masses at least ten times more massive than the brightest. 371 00:41:50,160 --> 00:41:55,920 The most massive spirals in galaxies like the Magellanic clouds tend to be less massive yet. 372 00:41:56,220 --> 00:42:04,320 So this is a measure from the Sloan Digital Sky Survey showing for a sample of about a half a million such galaxies. 373 00:42:04,680 --> 00:42:11,160 The star the rate at which stars are forming normalised to the massive stars that have already formed. 374 00:42:11,370 --> 00:42:15,959 So it's a measure, it's essentially a way to say how active taking out the size effect, 375 00:42:15,960 --> 00:42:21,840 the fact that bigger galaxies have more of everything as a logarithmic measure mass. 376 00:42:22,050 --> 00:42:28,200 Milky Way would be somewhere here, roughly here. What you see is you see these are the spiral galaxies, basically. 377 00:42:28,440 --> 00:42:37,049 And they form a tilted but rather narrow sequence, rather remarkable that when you divide out the mass, 378 00:42:37,050 --> 00:42:48,420 most spirals of the universe today are forming about the same amount of fraction of their stellar mass out of of raw material into stars. 379 00:42:48,630 --> 00:42:55,920 This is a narrow sequence that isn't fully understood, but it's a hint that there some sort of thermostat. 380 00:42:56,100 --> 00:43:00,750 There are some regulators that switch star formation on and off in galaxies. 381 00:43:00,900 --> 00:43:07,170 And here are the the nearly red and dead, elliptical and lenticular galaxies up here. 382 00:43:07,380 --> 00:43:13,110 You see, they're reforming about a hundred times fewer. So it's not zero often, but much less. 383 00:43:14,640 --> 00:43:19,590 Another way to look at it that's important for understanding the Senate law that I'll be 384 00:43:19,590 --> 00:43:25,190 introducing in a minute is just showing the star formation properties in another way. 385 00:43:25,240 --> 00:43:32,219 Oops, I keep having trouble up here is for a sample of galaxies in the nearby universe. 386 00:43:32,220 --> 00:43:39,750 Mainly normal galaxies, the distribution and the x axis of how many stars form every year. 387 00:43:40,200 --> 00:43:46,000 Purple is us. Milky Way. Well, Milky Way's forming about two solar masses. 388 00:43:46,140 --> 00:43:52,740 A star like the sun, about two such stars formed every year in the Milky Way, 389 00:43:53,100 --> 00:44:00,090 and the maximum in the local universe is about ten, ten or 15 such things. 390 00:44:00,300 --> 00:44:03,750 And then, but the rates as you go to these rendered galaxies, 391 00:44:03,750 --> 00:44:11,940 so it goes down essentially to zero to you know, well, one part of ten to the five times less than that. 392 00:44:12,360 --> 00:44:18,330 Also notice and I want to describe the sequence then there what's the vertical axis? 393 00:44:18,450 --> 00:44:28,590 It's also the star formation rate. But now I have normalised it to the the area where the projected area in which the stars form in the disk. 394 00:44:28,740 --> 00:44:31,740 So it's not per unit mass, it's per per unit area. 395 00:44:31,740 --> 00:44:37,590 I'll explain why we do that later. And you see, there's also a rather tight sequence. 396 00:44:37,740 --> 00:44:40,290 Well, first of all, there's extraordinary diversity, right? 397 00:44:40,560 --> 00:44:52,860 There's the range in star formation rate, no matter how you measure it, is over a factor of 10 million, an either axis at any one fixed absolute rate. 398 00:44:53,010 --> 00:44:58,379 The dispersion in star formation rate per unit area or vice versa is over a factor of 10,000. 399 00:44:58,380 --> 00:45:01,710 So there's, you know, there's tremendous diversity. 400 00:45:01,890 --> 00:45:10,260 But among normal galaxies, they also tend to cluster in this diagram significance that to be explained in a minute. 401 00:45:12,180 --> 00:45:15,330 Now. Here we go. So up to now, 402 00:45:15,570 --> 00:45:22,559 I've been talking about star formation along the normal Hubble sequence of the extended 403 00:45:22,560 --> 00:45:27,660 Starfleet like that in Orion like that we've been seeing in the images you saw. 404 00:45:28,140 --> 00:45:32,820 But with the advent of opening up the infrared part of the spectrum, 405 00:45:33,840 --> 00:45:43,200 we realise there's a whole second mode of star formation that had been hinted at previously but not fully understood. 406 00:45:43,680 --> 00:45:48,090 And so here's what one of the few times you can get a hint of it in the visible. 407 00:45:48,420 --> 00:45:55,440 Here's a nearby spiral NGC 1097 Spiral like the Milky Way barred spiral imaged with 408 00:45:55,440 --> 00:46:01,650 Hubble and the blow up shows that if you look in the centre of the disk of this galaxy, 409 00:46:01,830 --> 00:46:07,620 there's actually a spiral within a spiral, a very tight ring of about a thousand, 410 00:46:07,950 --> 00:46:12,990 couple thousand light years across where you have intense number of clusters of stars. 411 00:46:13,260 --> 00:46:16,920 Now, when you look at this in the visible, that looks well, that's interesting. 412 00:46:17,190 --> 00:46:25,950 But, you know, I'm not going to write home or write to nature about it because that looks like, well, maybe there's 10% excess of star formation. 413 00:46:25,950 --> 00:46:30,000 And that's what we all thought until about 15 years ago. 414 00:46:30,330 --> 00:46:36,570 But if I look in the infrared at the same galaxy, suddenly the picture changes. 415 00:46:36,780 --> 00:46:46,350 This thing only looks like a 10% perturbation because dust is actually, in this case, obscuring something that 97% of the star formation. 416 00:46:46,560 --> 00:46:53,010 And we look in the infrared, actually, this ring saturated the detector of the instrument on the satellite. 417 00:46:54,000 --> 00:47:02,370 And in fact, something like two thirds of all the star formation in the galaxy is being emitted by this very compact region. 418 00:47:02,670 --> 00:47:09,990 In the centre of just this little region alone has nearly an order of magnitude more star formation than the entire Milky Way. 419 00:47:11,340 --> 00:47:15,940 The poster child for the such galaxies. 420 00:47:15,960 --> 00:47:27,780 The nearest example of an extreme of this is a companion to M81 Ursa major M82 in this beautiful, immature white field image again. 421 00:47:28,140 --> 00:47:31,380 And you notice M82 is rather oddball. 422 00:47:33,330 --> 00:47:37,830 Hubble's classification works about 98% of the time. 423 00:47:37,830 --> 00:47:47,100 You can classify galaxies as elliptical spiral or irregular, meaning irregular with at least some semblance of uniformity. 424 00:47:47,100 --> 00:47:53,490 But this one looks more like a train wreck. Something is going on right in here. 425 00:47:53,700 --> 00:47:58,740 And so we call it peculiar, or there's a class called irregular to to explain it. 426 00:47:59,250 --> 00:48:06,180 And if you go around the sky, it's only maybe it's far even less than 1%. 427 00:48:06,480 --> 00:48:09,690 You see a whole class of galaxies back again. 428 00:48:09,690 --> 00:48:14,460 When we study these in the visible, we could see what some of these guys were unusual, 429 00:48:14,700 --> 00:48:21,570 but it's only in the infrared when suddenly we realised there was something extraordinary about them. 430 00:48:22,950 --> 00:48:28,560 Here's M82 in a closeup and it's an example of an infrared luminous starburst galaxy. 431 00:48:28,770 --> 00:48:41,160 Whereas in M81 excuse me, or Milky Way, the interstellar dust is blocking out about half of the starlight in this case when we corrected. 432 00:48:41,340 --> 00:48:46,830 So in other words, if you correct for the obscuration of the dust, you double the star formation rate. 433 00:48:47,130 --> 00:48:52,260 When you do it for m82, you increase the star formation rate by more than a factor of 100. 434 00:48:53,070 --> 00:48:56,730 Over 99% of that light is being blocked. 435 00:48:57,030 --> 00:49:01,739 And in fact, that galaxy's forming more stars than all the Milky Way and all of that stuff, 436 00:49:01,740 --> 00:49:06,960 which is coming from a tight little disk, a few hundred, well, about 1000 light years across. 437 00:49:07,290 --> 00:49:11,550 And it's a class of what are called infrared luminous or an ultra luminous galaxies. 438 00:49:11,880 --> 00:49:22,680 The most extreme examples of this one is a nondescript galaxy in the optical called ARP 220 is actually as luminous as quasars. 439 00:49:22,950 --> 00:49:28,440 It's putting out pumping out more than ten times the energy of the entire Milky Way galaxy. 440 00:49:28,620 --> 00:49:35,820 And it's being powered by and large by young stars, whereas the Milky Way is forming two stars like the sun every year. 441 00:49:36,060 --> 00:49:40,650 This one's forming about 500 solar masses per year. 442 00:49:40,860 --> 00:49:48,480 And all of that star formation is going on in a region that is 100 times smaller than the disk of the Milky Way. 443 00:49:48,690 --> 00:49:55,079 Sort of extraordinary. And in fact, objects like this one and this one are, if you work it out, 444 00:49:55,080 --> 00:50:03,870 are forming stars at the fastest rate that Mother Nature will allow the cause of the bursts. 445 00:50:04,260 --> 00:50:10,530 You can see that these all have the train wreck appearance and that in this case, appearances are. 446 00:50:10,750 --> 00:50:16,690 Do explain it. They're all the result of some sort of collision or interaction between galaxies. 447 00:50:16,960 --> 00:50:22,030 In each of these cases, two galaxies have or are merging together. 448 00:50:22,450 --> 00:50:29,650 And basically, in the case of our 222 galaxies, the mass of the Milky Way, a little bigger, have merged together. 449 00:50:29,950 --> 00:50:33,490 All of their gas is being funnelled into a little disk. 450 00:50:33,760 --> 00:50:39,010 A couple thousand. Well, several hundred light years across in that gas. 451 00:50:39,010 --> 00:50:42,190 Rather than forming stars over 13 billion years, 452 00:50:42,430 --> 00:50:50,889 it's essentially converting entirely or almost entirely to stars instantly and limited by the time 453 00:50:50,890 --> 00:50:58,360 it took to bring that gas together about a hundred thousand years with nearly 100% efficiency. 454 00:50:58,510 --> 00:51:01,810 So nature turning the dial all the way up. 455 00:51:03,640 --> 00:51:07,720 In the case of Emily, too, it's a very complicated waltz. 456 00:51:07,900 --> 00:51:11,320 It wasn't clear. It wasn't merging with M81. 457 00:51:11,530 --> 00:51:17,560 But if you image this part of the sky in cold gas, which is the fuel for the star formation, 458 00:51:17,770 --> 00:51:23,170 there you see the train wreck is there's a very complicated dance going around 459 00:51:23,410 --> 00:51:29,709 involving at least six galaxies of where clearly M82 and this is NGC 30, 460 00:51:29,710 --> 00:51:36,610 77 have made close passages to M81 taking essentially accreted gas, 461 00:51:36,760 --> 00:51:43,780 which is falling onto these and and creating the immense starburst that we see here. 462 00:51:44,410 --> 00:51:55,989 If I put a bring up the diagram I showed you earlier with the normal galaxies in the Milky Way and add these various peculiar galaxies, 463 00:51:55,990 --> 00:52:01,510 the centres of galaxies like 37 objects, like ARP 220. 464 00:52:01,810 --> 00:52:07,450 You see, they extend the diversity of star formation even more radically. 465 00:52:08,290 --> 00:52:13,780 Now these galaxies form up to actually over a larger part of the universe, 466 00:52:13,960 --> 00:52:21,010 up to a few thousand solar masses per year, with concentrations over a million times higher. 467 00:52:22,990 --> 00:52:29,830 And so you have an extraordinary phenomenology that you want to try to understand. 468 00:52:30,280 --> 00:52:35,410 Running a little short on time. So I'm going to skip through a few things. 469 00:52:35,770 --> 00:52:45,100 The. I can't leave without, of course, trying to explain the structure you're seeing here, 470 00:52:45,250 --> 00:52:50,470 the stars, young stars forming or are buried even in the infrared, they're highly obscured. 471 00:52:50,710 --> 00:52:57,130 We're at a very tight cluster buried in the centre, and everything else you're seeing here is an outflow. 472 00:52:57,310 --> 00:53:06,640 It's the star formation has been so intense that the the star formation is an extra thermal process. 473 00:53:06,850 --> 00:53:13,210 The stars pour more energy into their birth clouds than they consume in being formed. 474 00:53:13,720 --> 00:53:19,180 Stars explode massive stars as supernovae. They inject radiation into the interstellar. 475 00:53:19,330 --> 00:53:28,840 They inject gas and winds. And it's actually, in this case, blowing the gas that fell in and blowing completely out of the the galaxy. 476 00:53:28,840 --> 00:53:34,960 In fact, this will be a self terminating process. You're in the end, 477 00:53:35,890 --> 00:53:43,870 we look at what the main power of supernovae like the supernova of 1054 that made the Crab Nebula 478 00:53:44,080 --> 00:53:52,000 but on a grand scale in 30 doradus we see these are X-ray bubbles powered by individual supernovae. 479 00:53:52,210 --> 00:53:54,160 But in a case like M82, 480 00:53:54,400 --> 00:54:03,760 what you're seeing are the collective effects of literally thousands of supernovae that have occurred over the last few tens of thousands of years. 481 00:54:04,000 --> 00:54:13,480 Blowing that away on this feed. This so-called feedback has profound effects on galaxies. 482 00:54:14,630 --> 00:54:23,860 The the if you look at the distribution of masses of galaxies in this case, in the local universe, it has a very characteristic shape. 483 00:54:24,890 --> 00:54:29,140 It has power law over a restricted range. 484 00:54:29,350 --> 00:54:42,100 But it but galaxies are very high mass and very low mass tend to be suppressed relative to the distribution of dark matter particles. 485 00:54:43,030 --> 00:54:47,589 If, if, if there was no feedback from these processes, 486 00:54:47,590 --> 00:54:56,410 we think galaxies of the distribution masses would follow a very similar power law to that of the dark matter that sees the formation of galaxies. 487 00:54:56,590 --> 00:55:01,720 But something is suppressing the very most massive and lowest mass galaxies. 488 00:55:01,930 --> 00:55:05,500 And here's a little cartoon picture actually from a previous civilian, 489 00:55:05,680 --> 00:55:12,490 Professor Joe Silk, that sort of explains that in the very most mass of galaxies, 490 00:55:12,610 --> 00:55:18,339 the process that's limiting is feedback from quasars and supermassive black holes regularly. 491 00:55:18,340 --> 00:55:26,560 If you came to the last lecture in the series, talked about that, I'm sure it's related to what we looked at in Perseus, 492 00:55:26,830 --> 00:55:37,180 but it's feedback like that you see in M82 that actually not only limits the number and size of the size of these galaxies, 493 00:55:37,180 --> 00:55:43,380 we think in the lowest masses actually disperses galaxies before they can completely of form. 494 00:55:44,800 --> 00:55:49,960 Here's the part I will not have much time to say, but I can give you the punch line. 495 00:55:50,140 --> 00:55:57,100 Everything I've said up to now characterises star formation in the current present day universe. 496 00:55:58,690 --> 00:56:06,370 But as we Hubble and other instruments, Herschel and Spitzer allow us to look out in the universe. 497 00:56:06,370 --> 00:56:10,929 Of course, when you look out it further out, you look in the universe. 498 00:56:10,930 --> 00:56:14,320 You're seeing the universe as it was further back in time. 499 00:56:14,620 --> 00:56:18,970 And we have through work of Andy Bunker and many other people, 500 00:56:19,120 --> 00:56:24,160 we're putting a picture together, a time lapse movie of how these galaxies came together. 501 00:56:24,460 --> 00:56:28,420 As you go further back, the objects look more and more primitive. 502 00:56:28,420 --> 00:56:35,620 We're actually seeing the assembly process of galaxies going on, at least in a statistical sense, in these. 503 00:56:37,450 --> 00:56:46,870 And if you measure the amounts of star formation as you go back, you see lots of changes as you go back. 504 00:56:47,200 --> 00:56:50,620 You maintain this for a while back in time. 505 00:56:50,620 --> 00:56:52,210 This is today. 506 00:56:52,450 --> 00:57:02,710 If you go back to the universe and was about 40% of its current age, you still have the Hubble sequence of elliptical galaxies and spirals. 507 00:57:02,980 --> 00:57:10,180 But two things happen is over time the proportion of the number of elliptical 508 00:57:10,420 --> 00:57:16,930 and lenticular galaxies decreases because even they were actively star forming. 509 00:57:16,930 --> 00:57:20,980 This is back when the universe was about 15 20% of the present age. 510 00:57:21,250 --> 00:57:30,220 And if you look at the amount of star formation that was going on, it was 10 to 100 times higher than it is in those galaxies today. 511 00:57:30,400 --> 00:57:38,080 Those objects would populate this part of the diagram and actually upwards and onwards and. 512 00:57:38,400 --> 00:57:48,300 You can actually measure the total amount of star formation in the air over a very large volume of cosmic time over the history of the universe. 513 00:57:48,570 --> 00:57:51,360 Here we are today at the present time. 514 00:57:52,290 --> 00:57:59,220 And as you can see, about 10 billion years ago, star formation peaked at a level averaged over the whole universe. 515 00:57:59,460 --> 00:58:05,490 That was higher. It was higher by over a factor of ten. 516 00:58:06,330 --> 00:58:12,090 Essentially what you're seeing is back then the andromeda's, which are relatively quiet today, 517 00:58:12,090 --> 00:58:20,730 the mass of galaxies of they're quiet today because they converted their gas to stars much more rapidly in the past than they do today. 518 00:58:21,210 --> 00:58:24,640 Finally, I can't let you go. I'm going to have to run two or 3 minutes. 519 00:58:24,640 --> 00:58:28,709 So you know what the law is. I don't like talking about my own work. 520 00:58:28,710 --> 00:58:31,920 You probably have gotten that idea. I always save it for the end. 521 00:58:33,870 --> 00:58:37,770 Can we understand this incredible diversity? 522 00:58:38,760 --> 00:58:45,180 Fair to say there's no theory. I can. You know, this is a difficult problem, multi scale problem. 523 00:58:45,720 --> 00:58:53,970 No one, either on a computer or in an analytical calculation, can explain this diversity of properties. 524 00:58:54,210 --> 00:59:03,600 But we do have a we've uncovered some empirical patterns and we can begin to understand some of the underlying physics. 525 00:59:03,810 --> 00:59:09,930 And the key to doing it is in addition to measuring the star formation, just to make maps of the cold gas, 526 00:59:10,170 --> 00:59:21,210 molecular gas and atomic gas and correlate that with the star formation, either on an integrated basis or on a point by point basis in galaxies. 527 00:59:21,390 --> 00:59:30,930 So you've seen this plot many times. If I, for example, look at the properties of this incredible, diverse array of nearby galaxies, 528 00:59:31,110 --> 00:59:36,630 star formation, rate per unit area, and look at as a function of, say, absolute star formation rate. 529 00:59:36,780 --> 00:59:42,810 Even though this number is the denominator of this number, there are orders of magnitude dispersion. 530 00:59:43,110 --> 00:59:51,750 However, for these galaxies, those where you can make the measurements, if I plot on the x axis rather than the surface density of star formation, 531 00:59:51,960 --> 01:00:02,370 the surface density of cold gas, not the mass, but the surface density of that cold gas using the same essentially y axis as this. 532 01:00:02,730 --> 01:00:04,890 The plot tightens up to this, 533 01:00:05,160 --> 01:00:16,230 that among among the normal galaxies you have a very tight power law correlation between concentration of gas and concentration of star formation. 534 01:00:16,590 --> 01:00:25,260 And if you make a plot for the two twenties and maybe twos, you get another power law relation that sits on the extrapolation of this. 535 01:00:25,530 --> 01:00:33,570 And if you add the circum nuclear regions, they fit here, the dwarf starburst galaxies, they fit on it and you get a relation. 536 01:00:33,580 --> 01:00:37,710 Now you might be thinking, okay, more gas, more stars. 537 01:00:37,800 --> 01:00:44,160 Trivial, who cares? What makes this significant is it's not a linear relation. 538 01:00:44,160 --> 01:00:48,000 It isn't ten times more gas, ten times more stars. 539 01:00:48,300 --> 01:00:54,959 It's got a slope of about one and a half and power law, which means 100 times more concentration of gas, 540 01:00:54,960 --> 01:00:59,160 about a thousand times or several hundred times more star formation. 541 01:00:59,160 --> 01:01:05,310 So the more you concentrate the gas, it's a very nonlinear nature. 542 01:01:06,240 --> 01:01:10,860 Nature, you squeeze the gas a little, you get more star formation out. 543 01:01:11,160 --> 01:01:19,139 In the end, don't have time. But it's this is actually when you look at a spatially resolved basis is a combination of 544 01:01:19,140 --> 01:01:25,500 a steep power life threshold at low density and a more linear relation at high density. 545 01:01:26,040 --> 01:01:31,500 We'll leave it there. I'm not going to go through these in detail, but this law, 546 01:01:31,530 --> 01:01:39,030 the reason people make a fuss about this law is, you know, it explains all kinds of things at once. 547 01:01:39,330 --> 01:01:45,719 It explains why when you bang two galaxies together, you can get off where you doubled the gas mass. 548 01:01:45,720 --> 01:01:54,390 You can get 100 times more star formation. It's climbing up this nonlinear relation that explains why high redshift. 549 01:01:54,600 --> 01:02:00,299 There was much more star formation today because there was more fuel and if there was ten times more fuel, 550 01:02:00,300 --> 01:02:04,800 you'd get a you'll get, you know, 30, 40 times more star formation. 551 01:02:05,070 --> 01:02:11,880 That explains why massive galaxies evolved more quickly than low mass galaxies, like the Magellanic Clouds. 552 01:02:12,150 --> 01:02:18,090 You even can explain some of the size of evolution and growth, and I don't have time, 553 01:02:18,270 --> 01:02:26,970 but actually explains why all the most active regions of star formation were completely invisible in the. 554 01:02:28,540 --> 01:02:42,190 I think invisible in the in the optical, because the intense star formation only occurs where you have high concentrations of gas. 555 01:02:42,490 --> 01:02:47,050 And that's also if you express that in concentrations of dust. 556 01:02:47,740 --> 01:02:56,860 This line is essentially where 98% or 99% of the jet of the light starlight is absorbed. 557 01:02:57,190 --> 01:03:01,960 And so it all sorts of of hangs together. 558 01:03:02,380 --> 01:03:05,710 And for the cargo cente you begin putting this together, 559 01:03:06,040 --> 01:03:17,140 you can begin to understand this whole restricted space of, of, of why galaxies are following the locus they have. 560 01:03:17,440 --> 01:03:25,420 It's a combination of cosmology which sets a maximum size for galaxies and then fundamental timescales of galaxies. 561 01:03:25,720 --> 01:03:33,580 The only observational limit and the one is that diagonal, which is just the resolution limit of the instruments we have today. 562 01:03:34,360 --> 01:03:38,799 Finally, less like 5 minutes over. 563 01:03:38,800 --> 01:03:45,160 So as the field is evolving, I hope you want this is progress made. 564 01:03:45,460 --> 01:03:52,120 You can see many, many unanswered questions. You may think that's just as I went through things too fast and you didn't understand half of it? 565 01:03:52,120 --> 01:04:00,310 Nope. There's lots of mystery even for the experts, but there is great promise for pushing this. 566 01:04:00,520 --> 01:04:07,089 The is already being advanced transformational lead by the Atacama Large millimetre array and in a 567 01:04:07,090 --> 01:04:13,330 millimetre array that can map the molecular gas and dust in galaxies with a better resolution than Hubble, 568 01:04:14,560 --> 01:04:17,440 the successor to Hubble, the James Webb Space Telescope, 569 01:04:17,680 --> 01:04:24,550 that will allow these kinds of measurements to be carried out to the highest redshifts, the very first stars and galaxies. 570 01:04:24,670 --> 01:04:28,809 And I'm afraid, I hope a dream sort of. Well, Leicester City. 571 01:04:28,810 --> 01:04:32,020 So the Leicester City is equivalent for us astronomers. 572 01:04:32,350 --> 01:04:40,150 There's a mission called Spike, a Japanese led mission that would be the next infrared, the successor to Spitzer and Herschel. 573 01:04:40,870 --> 01:04:51,160 Apologies to run over, but I hope I have given you some sense of this beautiful convergence of understandings that is happening. 574 01:04:51,370 --> 01:04:56,770 And please stay tuned, because much more to be learned in the coming years. 575 01:04:56,800 --> 01:04:57,190 Thank you.