1 00:00:05,620 --> 00:00:07,340 On this month's Sky at Night, 2 00:00:07,340 --> 00:00:09,980 we'll be taking you to one of the most spectacular 3 00:00:09,980 --> 00:00:13,420 and fascinating places in the whole night sky. 4 00:00:13,420 --> 00:00:16,260 It's officially known as M51, 5 00:00:16,260 --> 00:00:18,660 but most of us know it by its more romantic name - 6 00:00:18,660 --> 00:00:21,140 the Whirlpool Galaxy. 7 00:00:22,980 --> 00:00:26,140 M51 is a stunning sight. 8 00:00:26,140 --> 00:00:28,460 But it's more than just beautiful to look at. 9 00:00:29,860 --> 00:00:31,980 It is also one of the most fascinating places 10 00:00:31,980 --> 00:00:33,460 we have ever discovered. 11 00:00:35,020 --> 00:00:38,540 Its sculptured spiral arms are a maelstrom of star formation... 12 00:00:40,420 --> 00:00:42,980 ..lit up by the light of hot young stars. 13 00:00:45,540 --> 00:00:48,060 But it is also a stellar graveyard, 14 00:00:48,060 --> 00:00:51,540 in which we can see neutron stars and black holes 15 00:00:51,540 --> 00:00:53,340 tearing other stars apart. 16 00:00:55,380 --> 00:00:57,860 So why is this galaxy so active, 17 00:00:57,860 --> 00:01:00,220 and how did it get its majestic 18 00:01:00,220 --> 00:01:02,740 and surprisingly prominent spiral shape? 19 00:01:02,740 --> 00:01:04,980 Welcome to The Sky at Night. 20 00:01:32,860 --> 00:01:35,340 We're making this Whirlpool Galaxy Day. 21 00:01:35,340 --> 00:01:36,580 On this one day, 22 00:01:36,580 --> 00:01:40,620 we're going to be pointing as many telescopes as we can at the object. 23 00:01:40,620 --> 00:01:42,860 We've got amateur back-yard telescopes, 24 00:01:42,860 --> 00:01:45,060 professional instruments like the dish behind me, 25 00:01:45,060 --> 00:01:48,900 and on mountaintops around the world, large observatories, 26 00:01:48,900 --> 00:01:51,780 several of which have got better weather than here in Cambridge! 27 00:01:51,780 --> 00:01:54,460 We'll even be going above the weather, because we've got 28 00:01:54,460 --> 00:01:57,940 special permission to use one of Nasa's space telescopes. 29 00:01:57,940 --> 00:02:01,460 We'll be looking M51 at different wavelengths of light and different 30 00:02:01,460 --> 00:02:05,620 magnifications to create a unique portrait of this remarkable galaxy. 31 00:02:07,420 --> 00:02:10,340 We've come to the Mullard Radio Astronomy Observatory 32 00:02:10,340 --> 00:02:12,260 just outside Cambridge. 33 00:02:12,260 --> 00:02:14,100 Founded in 1957, 34 00:02:14,100 --> 00:02:18,380 it helped pioneer a completely new way of observing the sky. 35 00:02:18,380 --> 00:02:20,940 It was here...well, actually, just over that hedge, 36 00:02:20,940 --> 00:02:23,780 that Jocelyn Bell discovered the first pulsars 37 00:02:23,780 --> 00:02:26,420 and, later on, we'll be using some of the modern instruments 38 00:02:26,420 --> 00:02:28,380 that still operate on the site 39 00:02:28,380 --> 00:02:30,980 to take a close look at the Whirlpool Galaxy. 40 00:02:30,980 --> 00:02:35,820 But our exploration of M51 doesn't start in this slightly damp field. 41 00:02:35,820 --> 00:02:39,180 It starts somewhere with much clearer skies. 42 00:02:44,740 --> 00:02:46,420 It's nine o'clock in the morning, 43 00:02:46,420 --> 00:02:49,060 it's a terrible time to be trying to observe a galaxy, 44 00:02:49,060 --> 00:02:51,820 at least from here, but this laptop is connected 45 00:02:51,820 --> 00:02:54,780 to a telescope in Hawaii, where it's still dark. 46 00:02:54,780 --> 00:02:58,100 It's a 0.4-metre telescope on top of the island of Maui, 47 00:02:58,100 --> 00:03:00,780 on a dormant volcano, and you can see from this camera 48 00:03:00,780 --> 00:03:04,820 just outside the observatory that they've got brilliant, clear skies. 49 00:03:04,820 --> 00:03:08,100 See a couple of planets, the nice Milky Way, 50 00:03:08,100 --> 00:03:12,300 and this region of sky, where M51, our target, is located. 51 00:03:12,300 --> 00:03:15,660 Now, the telescope's already slewed to the source 52 00:03:15,660 --> 00:03:17,820 and it's taking a five-minute exposure 53 00:03:17,820 --> 00:03:19,380 and so, in just a few minutes, 54 00:03:19,380 --> 00:03:22,460 we should see our first image of the Whirlpool Galaxy. 55 00:03:28,780 --> 00:03:30,380 Well, there it is, this is our image, 56 00:03:30,380 --> 00:03:33,660 and you can see immediately the spiral arms in the galaxy 57 00:03:33,660 --> 00:03:36,260 which wind round this central, bright nucleus, 58 00:03:36,260 --> 00:03:38,620 and then the second thing you notice 59 00:03:38,620 --> 00:03:41,500 is that there are two galaxies in the frame. 60 00:03:41,500 --> 00:03:45,020 There's this companion which has stretched out this bright material 61 00:03:45,020 --> 00:03:47,940 from the main galaxy, so you get this arm joining the two, 62 00:03:47,940 --> 00:03:52,580 and there's lots of faint gas and dust around that secondary galaxy. 63 00:03:52,580 --> 00:03:55,020 And really that's what the Whirlpool Galaxy gives us - 64 00:03:55,020 --> 00:03:58,500 it's a chance to watch a collision between two galaxies in action. 65 00:03:58,500 --> 00:04:02,140 It's something we can't see this well anywhere else in the sky. 66 00:04:02,140 --> 00:04:04,380 It really is a beautiful image. 67 00:04:05,820 --> 00:04:09,100 Maggie showed this image to galaxy expert Rob Kennicutt 68 00:04:09,100 --> 00:04:11,900 to ask about the Whirlpool's amazing structure 69 00:04:11,900 --> 00:04:14,540 and its relationship with its companion. 70 00:04:14,540 --> 00:04:16,140 It is absolutely wonderful. 71 00:04:16,140 --> 00:04:19,620 So there's two spiral arms. They look almost perfect. 72 00:04:19,620 --> 00:04:23,260 The classic spiral galaxy. So how are they formed? 73 00:04:23,260 --> 00:04:29,100 Almost all disc galaxies like this system do have spiral structure 74 00:04:29,100 --> 00:04:32,980 but, as you say, these are spectacularly prominent arms, 75 00:04:32,980 --> 00:04:35,020 and were quite certain now 76 00:04:35,020 --> 00:04:38,340 that to produce such strong spiral structure, 77 00:04:38,340 --> 00:04:40,140 you need the driving force 78 00:04:40,140 --> 00:04:43,100 of interaction with a companion galaxy. 79 00:04:43,100 --> 00:04:45,260 Now, you see, to me, that seems counterintuitive, 80 00:04:45,260 --> 00:04:47,300 cos when I think of collisions, I think of chaos, 81 00:04:47,300 --> 00:04:48,740 things being thrown everywhere. 82 00:04:48,740 --> 00:04:50,900 I don't think of structure being formed that way. 83 00:04:50,900 --> 00:04:52,900 I agree with you - it's not intuitive, 84 00:04:52,900 --> 00:04:56,140 but this computer simulation is designed to show 85 00:04:56,140 --> 00:04:58,220 how these collisions between galaxies 86 00:04:58,220 --> 00:05:00,420 can excite spiral structure. 87 00:05:00,420 --> 00:05:04,180 So you have two galaxies, disc galaxies, much like the spiral. 88 00:05:04,180 --> 00:05:06,380 It's looking a bit messy now, but... Wow! 89 00:05:06,380 --> 00:05:09,380 You see, actually, the spiral forming due to the collision, 90 00:05:09,380 --> 00:05:11,020 and in both galaxies. 91 00:05:11,020 --> 00:05:14,060 But in this simulation, we had two similar-sized galaxies. 92 00:05:14,060 --> 00:05:17,100 What if you had something that was more akin to the Whirlpool Galaxy? 93 00:05:17,100 --> 00:05:21,940 What we have here is a second computer simulation, 94 00:05:21,940 --> 00:05:25,420 and this one is actually specifically tailored 95 00:05:25,420 --> 00:05:29,860 to try to reproduce the two galaxies in the Whirlpool system. Right. 96 00:05:29,860 --> 00:05:33,820 So this kind of spiral structure you see in the beginning 97 00:05:33,820 --> 00:05:35,780 is actually the sort of spiral structure 98 00:05:35,780 --> 00:05:37,180 that is common 99 00:05:37,180 --> 00:05:39,060 in galaxies like the Milky Way. 100 00:05:39,060 --> 00:05:41,300 So, even before the interaction, 101 00:05:41,300 --> 00:05:43,460 Whirlpool probably was a spiral galaxy, 102 00:05:43,460 --> 00:05:46,700 but now you see the companion making its appearance. 103 00:05:46,700 --> 00:05:48,700 Now, that doesn't look like a companion galaxy. 104 00:05:48,700 --> 00:05:50,220 It looks more like a point mass. 105 00:05:50,220 --> 00:05:52,660 I think that's right, to save on computing time, 106 00:05:52,660 --> 00:05:55,820 I think they modelled the companion galaxy as a point mass, 107 00:05:55,820 --> 00:05:58,700 and now you're beginning to see its effects already - 108 00:05:58,700 --> 00:06:02,380 the spiral pattern is being amplified, and let's keep going. 109 00:06:02,380 --> 00:06:03,740 And there you are. Whoa! 110 00:06:03,740 --> 00:06:05,860 You've got the two distinct spiral arms, 111 00:06:05,860 --> 00:06:08,180 and you've got the companion galaxy at one of the ends 112 00:06:08,180 --> 00:06:11,060 of the spiral arm, so that is a good recreation... Indeed. 113 00:06:11,060 --> 00:06:12,580 ..of the Whirlpool and its companion. 114 00:06:12,580 --> 00:06:16,980 But notice this is 300 million years after the start of the calculation. 115 00:06:16,980 --> 00:06:18,060 Yes. 116 00:06:18,060 --> 00:06:21,300 But you think of this as now, in our world, right? OK, yes. 117 00:06:21,300 --> 00:06:23,260 So now, the computer's going to predict 118 00:06:23,260 --> 00:06:25,180 what this system will look like in the future. 119 00:06:25,180 --> 00:06:27,900 Ah, the future of the Whirlpool Galaxy. Indeed. 120 00:06:27,900 --> 00:06:31,500 So, as you see, the companion continues to get closer 121 00:06:31,500 --> 00:06:33,500 and closer to the centre of the spiral, 122 00:06:33,500 --> 00:06:36,420 it's still on the way in, and as it goes, 123 00:06:36,420 --> 00:06:39,100 the spiral arms are amplified even more than today, 124 00:06:39,100 --> 00:06:40,900 if that can be imagined. Yes. 125 00:06:40,900 --> 00:06:43,220 But it's getting a lot messier! Indeed. 126 00:06:43,220 --> 00:06:46,260 It's now reached closest approach, and on the way out, 127 00:06:46,260 --> 00:06:49,460 it's leaving kind of a train wreck behind. Yes! 128 00:06:49,460 --> 00:06:53,100 And now, you see, the companion is coming in for a second time, 129 00:06:53,100 --> 00:06:57,100 and the movie stops at this point, but if we were to continue it, 130 00:06:57,100 --> 00:07:00,100 the two galaxies would totally merge together. 131 00:07:00,100 --> 00:07:03,140 But that means that the Whirlpool Galaxy in all its perfection, 132 00:07:03,140 --> 00:07:07,020 as it looks today, is transitory, so it will pass through that phase, 133 00:07:07,020 --> 00:07:09,460 and at some point end up maybe more like this. 134 00:07:09,460 --> 00:07:12,900 Yeah, indeed, and look at the scale, in about 70 million years, 135 00:07:12,900 --> 00:07:15,540 the phase of spiral structure will be long over, 136 00:07:15,540 --> 00:07:18,460 and you'll be left within 100 million years 137 00:07:18,460 --> 00:07:21,540 with one galaxy where there were two before. 138 00:07:21,540 --> 00:07:24,500 So, it just makes me appreciate the Whirlpool Galaxy all the more, 139 00:07:24,500 --> 00:07:26,820 because we can appreciate its beauty right at the moment, 140 00:07:26,820 --> 00:07:29,020 but it won't last! Indeed. 141 00:07:30,180 --> 00:07:34,060 The telescope in Hawaii actually took three pictures of the galaxy, 142 00:07:34,060 --> 00:07:36,140 each at a different wavelength. 143 00:07:38,100 --> 00:07:39,900 When composited together, 144 00:07:39,900 --> 00:07:44,460 they give us a colour view of the Whirlpool in all its glory. 145 00:07:44,460 --> 00:07:46,380 But it's not just professional telescopes 146 00:07:46,380 --> 00:07:49,820 that can capture spectacular images like these. 147 00:07:51,020 --> 00:07:53,260 Pete has been trying to demonstrate 148 00:07:53,260 --> 00:07:55,940 how you can view the galaxy for yourself. 149 00:07:55,940 --> 00:07:59,940 And he's been exploring the history of our observation of this galaxy. 150 00:08:01,060 --> 00:08:04,460 Astronomy in the UK can be a bit frustrating at times, 151 00:08:04,460 --> 00:08:05,940 and the clouds have now come in, 152 00:08:05,940 --> 00:08:10,500 and I really don't think I'm going to get a view of M51 tonight. 153 00:08:10,500 --> 00:08:12,420 So welcome to the great British summer! 154 00:08:18,140 --> 00:08:20,940 It really is a pity that it's cloudy this evening, 155 00:08:20,940 --> 00:08:25,060 because M51 is one of the best deep sky objects up there. 156 00:08:25,060 --> 00:08:27,820 And at the moment, it's really high up in the sky, 157 00:08:27,820 --> 00:08:31,100 which means it's well away from any murk close to the horizon, 158 00:08:31,100 --> 00:08:33,700 and that will give you a good view of it. 159 00:08:34,820 --> 00:08:37,980 And it's pretty simple to find, too. 160 00:08:37,980 --> 00:08:41,740 To locate it, first identify the Plough or Saucepan, 161 00:08:41,740 --> 00:08:43,620 which is part of Ursa Major, 162 00:08:43,620 --> 00:08:47,940 and is one of the most recognisable patterns in the entire night sky. 163 00:08:47,940 --> 00:08:50,460 Identify the star in the middle of the handle 164 00:08:50,460 --> 00:08:53,020 and the one at the end of the handle. 165 00:08:53,020 --> 00:08:56,420 Draw a line between them and turn by 90 degrees, 166 00:08:56,420 --> 00:08:58,540 and move for about half that distance again, 167 00:08:58,540 --> 00:09:01,940 and that'll take you to exactly where M51 is in the sky. 168 00:09:03,700 --> 00:09:05,820 You can't see M51 with the naked eye, 169 00:09:05,820 --> 00:09:09,300 but it is possible to see it with just a pair of binoculars. 170 00:09:09,300 --> 00:09:13,300 And if you've got a telescope like this, then it looks quite amazing, 171 00:09:13,300 --> 00:09:16,380 and that will also allow you to take a picture of it. 172 00:09:16,380 --> 00:09:18,980 And I've got a picture here I took a little while ago, 173 00:09:18,980 --> 00:09:22,140 and you can really start to make out some of the structure of the galaxy. 174 00:09:22,140 --> 00:09:24,900 You've got the spiral arms, they're very evident there. 175 00:09:24,900 --> 00:09:27,620 You've also got the little satellite galaxy, as well. 176 00:09:27,620 --> 00:09:29,300 That's very obvious. 177 00:09:29,300 --> 00:09:31,620 So if you CAN get a view of M51, 178 00:09:31,620 --> 00:09:34,860 it's a really rewarding object to have a look at. 179 00:09:37,500 --> 00:09:42,260 'But not everyone has always thought that M51 was fascinating.' 180 00:09:44,340 --> 00:09:48,700 The Whirlpool Galaxy was discovered by Charles Messier in 1773, 181 00:09:48,700 --> 00:09:54,860 and added to his famous catalogue as the 51st entry, hence the name M51. 182 00:09:55,980 --> 00:10:00,300 But Messier wasn't interested in how fascinating M51 was. 183 00:10:02,100 --> 00:10:03,940 He was a comet hunter, 184 00:10:03,940 --> 00:10:07,260 irritated by wasting his time pointing his telescope 185 00:10:07,260 --> 00:10:10,100 at things that superficially resembled comets, 186 00:10:10,100 --> 00:10:12,380 but which on closer inspection 187 00:10:12,380 --> 00:10:14,860 were revealed to be something else entirely. 188 00:10:16,500 --> 00:10:19,380 So he set about making a catalogue of what were, to him, 189 00:10:19,380 --> 00:10:20,940 frustrating objects, 190 00:10:20,940 --> 00:10:24,020 so he could ignore them in his search for comets. 191 00:10:25,300 --> 00:10:27,900 But the irony was that in doing so, 192 00:10:27,900 --> 00:10:31,260 he had compiled a list of nearly all of the most spectacular 193 00:10:31,260 --> 00:10:33,460 deep sky objects - 194 00:10:33,460 --> 00:10:36,620 nebulae like the Orion Nebula, 195 00:10:36,620 --> 00:10:40,060 open star clusters like the Pleiades, 196 00:10:40,060 --> 00:10:43,020 and galaxies like M51. 197 00:10:44,380 --> 00:10:47,820 'To be fair, Messier probably couldn't resolve the Whirlpool 198 00:10:47,820 --> 00:10:51,100 'to be much more than an indistinct, diffuse cloud - 199 00:10:51,100 --> 00:10:52,340 'a nebula.' 200 00:10:53,900 --> 00:10:57,300 The first time the Whirlpool Galaxy was seen in all its glory 201 00:10:57,300 --> 00:11:02,020 was in 1845, when William Parsons, the third Earl of Rosse, 202 00:11:02,020 --> 00:11:07,100 pointed a 1.8 metre reflecting telescope, based in Birr, Ireland, 203 00:11:07,100 --> 00:11:11,580 which was then the largest telescope in the world, at M51. 204 00:11:11,580 --> 00:11:14,780 And this is a sketch he made of that object, 205 00:11:14,780 --> 00:11:16,740 and it's absolutely incredible. 206 00:11:16,740 --> 00:11:19,260 There's so much structure to see here, 207 00:11:19,260 --> 00:11:23,140 but what's really evident is the spiral nature of the galaxy. 208 00:11:23,140 --> 00:11:26,460 And that was the first time this had ever been recorded 209 00:11:26,460 --> 00:11:27,900 in a celestial object. 210 00:11:30,380 --> 00:11:33,300 The picture was quite a sensation at the time, 211 00:11:33,300 --> 00:11:35,460 and was published all over the world. 212 00:11:36,900 --> 00:11:39,980 It's even suggested that his swirling drawing 213 00:11:39,980 --> 00:11:43,300 was the inspiration for Van Gogh's Starry Night. 214 00:11:45,980 --> 00:11:50,060 But we still didn't know what the Whirlpool was or where it was, 215 00:11:50,060 --> 00:11:54,220 and it was only in 1924 that Edwin Hubble demonstrated 216 00:11:54,220 --> 00:11:56,500 that nebulous objects like these 217 00:11:56,500 --> 00:11:59,140 were in fact distant galaxies in space. 218 00:12:00,740 --> 00:12:03,620 We now know it's about 30 million light years away, 219 00:12:03,620 --> 00:12:08,300 and although much smaller than the Milky Way, the disc is huge, 220 00:12:08,300 --> 00:12:10,940 measuring 60,000 light years across. 221 00:12:14,900 --> 00:12:18,300 Images like these, taken by Sky At Night viewers, 222 00:12:18,300 --> 00:12:21,980 clearly show why M51 is one of the most exciting places 223 00:12:21,980 --> 00:12:23,140 in the universe. 224 00:12:25,380 --> 00:12:27,100 But they cannot show us 225 00:12:27,100 --> 00:12:31,300 many of the secrets that are hidden deep within those spiral arms. 226 00:12:34,420 --> 00:12:36,020 'To reveal those secrets, 227 00:12:36,020 --> 00:12:39,300 'we need to find different ways to look at the galaxy.' 228 00:12:44,500 --> 00:12:47,420 These dishes are radio telescopes. 229 00:12:47,420 --> 00:12:51,180 They're just a receiver, not too dissimilar to an FM radio, 230 00:12:51,180 --> 00:12:53,140 but they're much, much bigger. 231 00:12:53,140 --> 00:12:56,180 That's because the signals they're trying to pick up from space 232 00:12:56,180 --> 00:12:58,460 are absolutely minuscule. 233 00:13:00,700 --> 00:13:02,620 In fact, it has been calculated 234 00:13:02,620 --> 00:13:06,140 that if you add up every radio signal ever picked up 235 00:13:06,140 --> 00:13:08,500 by all the radio telescopes in the world, 236 00:13:08,500 --> 00:13:11,140 the combined energy of that radiation 237 00:13:11,140 --> 00:13:14,540 would be enough to melt just three snowflakes. 238 00:13:16,620 --> 00:13:19,020 These telescopes are actually lining up right now 239 00:13:19,020 --> 00:13:22,980 to come in line with M51, the Whirlpool Galaxy, 240 00:13:22,980 --> 00:13:28,340 which lies around 30 million light years away in that direction. 241 00:13:30,820 --> 00:13:32,740 These are the radio images 242 00:13:32,740 --> 00:13:36,020 captured by the Mullard Observatory dishes. 243 00:13:36,020 --> 00:13:39,140 Superficially, these pictures are not as impressive, 244 00:13:39,140 --> 00:13:41,940 but they show details that we could never reveal 245 00:13:41,940 --> 00:13:44,020 with conventional telescopes. 246 00:13:44,020 --> 00:13:46,340 The result of intense magnetic fields 247 00:13:46,340 --> 00:13:49,340 and the glow of hot gas around young stars. 248 00:13:50,900 --> 00:13:52,540 And this remarkable image, 249 00:13:52,540 --> 00:13:55,700 from the Very Large Array Radio Telescope in New Mexico, 250 00:13:55,700 --> 00:13:59,380 reveals the distribution of hydrogen throughout the galaxy - 251 00:13:59,380 --> 00:14:02,100 the raw material from which the stars are made 252 00:14:02,100 --> 00:14:04,580 stretching far beyond the main disc. 253 00:14:07,460 --> 00:14:09,460 And as Maggie's been discovering, 254 00:14:09,460 --> 00:14:12,620 radio astronomy is just one of the many alternative ways 255 00:14:12,620 --> 00:14:15,260 we have to observe M51. 256 00:14:20,220 --> 00:14:24,540 For centuries, we only had one way of studying the night sky - 257 00:14:24,540 --> 00:14:28,260 using telescopes that operated in visible light - 258 00:14:28,260 --> 00:14:31,020 that tiny part of the electromagnetic spectrum 259 00:14:31,020 --> 00:14:32,460 that our eyes can detect. 260 00:14:34,860 --> 00:14:38,540 We can only see things if they're actively emitting light 261 00:14:38,540 --> 00:14:41,580 or reflecting light in the visible part of the spectrum, 262 00:14:41,580 --> 00:14:44,020 and if there's no source... 263 00:14:44,020 --> 00:14:45,860 then we can't see anything at all. 264 00:14:47,180 --> 00:14:48,900 But in addition to radio waves, 265 00:14:48,900 --> 00:14:51,660 there's a lot more to the electromagnetic spectrum, 266 00:14:51,660 --> 00:14:53,580 and if we tune into this, 267 00:14:53,580 --> 00:14:57,140 then we can detect a lot more of what's out there, 268 00:14:57,140 --> 00:14:59,060 hidden in the darkness. 269 00:15:01,300 --> 00:15:04,580 Now, this is a camera that is sensitive to infrared light. 270 00:15:04,580 --> 00:15:06,460 That's a wavelength that is slightly longer 271 00:15:06,460 --> 00:15:08,060 than we can detect with our eyes, 272 00:15:08,060 --> 00:15:09,580 and it allows us to see things 273 00:15:09,580 --> 00:15:12,140 that would otherwise appear to be invisible. 274 00:15:14,020 --> 00:15:18,060 We can see things in the infrared because of their temperature. 275 00:15:18,060 --> 00:15:23,380 On Earth, all objects radiate part of their heat as infrared light. 276 00:15:23,380 --> 00:15:27,500 How much and that what frequency depends on how hot they are. 277 00:15:27,500 --> 00:15:29,540 It's just the same in space. 278 00:15:29,540 --> 00:15:31,300 There's a lot of stuff hiding out there 279 00:15:31,300 --> 00:15:33,900 that we just can't detect with visible light, 280 00:15:33,900 --> 00:15:37,220 but if we tune our telescopes to detect infrared wavelengths, 281 00:15:37,220 --> 00:15:40,260 then suddenly, a lot more is revealed. 282 00:15:42,540 --> 00:15:46,860 Most of the infrared radiation from space is absorbed by the atmosphere, 283 00:15:46,860 --> 00:15:51,460 so infrared telescopes have to be situated on top of tall mountains. 284 00:15:53,540 --> 00:15:55,500 This is the Liverpool Telescope, 285 00:15:55,500 --> 00:16:02,020 located at over 2,300 metres on the island of La Palma in the Canaries. 286 00:16:02,020 --> 00:16:04,140 Late on the night of the 31st of May, 287 00:16:04,140 --> 00:16:07,460 it took an infrared image of the Whirlpool Galaxy 288 00:16:07,460 --> 00:16:09,540 especially for The Sky At Night. 289 00:16:10,780 --> 00:16:13,180 This is the infrared image taken for us 290 00:16:13,180 --> 00:16:15,740 by the Liverpool Telescope just last night. 291 00:16:15,740 --> 00:16:17,460 Actually, it's two images, 292 00:16:17,460 --> 00:16:20,100 because the galaxy doesn't fit on a single frame. 293 00:16:20,100 --> 00:16:23,060 What we can see in this image is light from more stars 294 00:16:23,060 --> 00:16:25,060 than we'd otherwise see in the visible. 295 00:16:25,060 --> 00:16:28,300 By using the infrared, we're able to peer through the dust 296 00:16:28,300 --> 00:16:30,580 that would otherwise obscure our view. 297 00:16:30,580 --> 00:16:33,340 But this is an image in the near infrared - 298 00:16:33,340 --> 00:16:35,820 we're only just past the red in the visible, 299 00:16:35,820 --> 00:16:37,420 and we can go further than that, 300 00:16:37,420 --> 00:16:38,500 and the colour here 301 00:16:38,500 --> 00:16:41,340 represents the different wavelengths of infrared light. 302 00:16:41,340 --> 00:16:44,420 You can immediately see there's a difference between the two galaxies. 303 00:16:44,420 --> 00:16:48,100 The small companion galaxy is bright blue, 304 00:16:48,100 --> 00:16:51,460 and in this image, blue light comes from old stars, 305 00:16:51,460 --> 00:16:54,260 so this galaxy has an old stellar population - 306 00:16:54,260 --> 00:16:56,820 there's not much going on there right now. 307 00:16:56,820 --> 00:17:01,380 In contrast, the Whirlpool itself has this brilliant red glow. 308 00:17:01,380 --> 00:17:05,260 That's light from the dust and gas, the fuel of star formation, 309 00:17:05,260 --> 00:17:07,660 which you can see is spread throughout the disc, 310 00:17:07,660 --> 00:17:10,620 and has this wonderful structure, not just the spiral arms, 311 00:17:10,620 --> 00:17:14,020 but these filaments and these spokes in the disc, as well. 312 00:17:14,020 --> 00:17:16,740 But if you look along the spiral arms themselves, 313 00:17:16,740 --> 00:17:18,380 and only on the spiral arms, 314 00:17:18,380 --> 00:17:20,060 you see these bright knots, 315 00:17:20,060 --> 00:17:22,860 these bright blobs that are shining very brightly, 316 00:17:22,860 --> 00:17:24,900 and these are nebulae - 317 00:17:24,900 --> 00:17:27,860 they're places where thousands of stars are being born, 318 00:17:27,860 --> 00:17:30,420 and it's the light from those young stars 319 00:17:30,420 --> 00:17:33,860 that is causing these blobs to glow quite so brightly. 320 00:17:35,500 --> 00:17:38,780 We have similar features in our own galaxy. 321 00:17:38,780 --> 00:17:44,540 Places like the Orion Nebula, where stars are still being born today. 322 00:17:44,540 --> 00:17:47,140 But this is happening on a much grander scale 323 00:17:47,140 --> 00:17:48,780 in the Whirlpool Galaxy. 324 00:17:48,780 --> 00:17:51,820 Each of these bright dots is a stellar nursery 325 00:17:51,820 --> 00:17:54,340 100 times bigger than the Orion Nebula. 326 00:17:55,700 --> 00:17:58,700 These are all signs that the spiral arms in the Whirlpool 327 00:17:58,700 --> 00:18:01,060 are active - very active. 328 00:18:01,060 --> 00:18:02,420 So what this tells us 329 00:18:02,420 --> 00:18:06,140 is that it's not enough to have the raw materials for star formation - 330 00:18:06,140 --> 00:18:09,260 there's dust and there's gas throughout the disc - 331 00:18:09,260 --> 00:18:12,860 but it's only when it gets twisted up into these spiral arms 332 00:18:12,860 --> 00:18:16,300 that it can become dense enough to form stars. 333 00:18:16,300 --> 00:18:18,580 The spiral arms are where the action is. 334 00:18:18,580 --> 00:18:21,380 But to find out what's actually going on in there, 335 00:18:21,380 --> 00:18:24,420 we're going to need yet another way of looking at the galaxy, 336 00:18:24,420 --> 00:18:27,260 and to use a very, very special piece of kit. 337 00:18:27,260 --> 00:18:28,460 RADIO CRACKLE 338 00:18:28,460 --> 00:18:32,540 MUSIC PLAYS ON RADIO 339 00:18:32,540 --> 00:18:34,340 'Radio waves and infrared 340 00:18:34,340 --> 00:18:38,700 'are both from the lower energy end of the electromagnetic spectrum.' 341 00:18:38,700 --> 00:18:39,860 SHE TURNS RADIO OFF 342 00:18:39,860 --> 00:18:43,180 'But we can also pick up higher energy radiation. 343 00:18:46,180 --> 00:18:51,140 'Radiation in the ultraviolet and X-ray bands of the spectrum.' 344 00:18:51,140 --> 00:18:52,860 They're both familiar to us. 345 00:18:52,860 --> 00:18:56,340 X-rays can penetrate our skin and flesh, but not the bone, 346 00:18:56,340 --> 00:18:58,980 and that turns out to be really useful medically. 347 00:18:58,980 --> 00:19:03,060 UV rays from the sun are powerful enough to damage our skin - 348 00:19:03,060 --> 00:19:04,660 that's what causes sunburn. 349 00:19:05,700 --> 00:19:09,220 In space, this high-energy radiation is only generated 350 00:19:09,220 --> 00:19:11,140 in really extreme conditions, 351 00:19:11,140 --> 00:19:15,420 where the temperature is impossibly high - millions of degrees. 352 00:19:15,420 --> 00:19:19,220 Now, UV and X-ray emissions coming from something as far away 353 00:19:19,220 --> 00:19:24,340 as the M51 galaxy is so weak that it gets absorbed by our atmosphere, 354 00:19:24,340 --> 00:19:27,980 so the only way to observe it is to get up above our atmosphere. 355 00:19:27,980 --> 00:19:30,020 That's why we're incredibly lucky 356 00:19:30,020 --> 00:19:34,700 to have been given time on one of Nasa's space telescopes, Swift. 357 00:19:34,700 --> 00:19:35,980 And right now, 358 00:19:35,980 --> 00:19:39,900 it's slewing its way round to set its sights on the Whirlpool Galaxy. 359 00:19:41,980 --> 00:19:44,340 The Swift satellite sits in an orbit 360 00:19:44,340 --> 00:19:47,100 almost 600km above the Earth's surface. 361 00:19:48,300 --> 00:19:52,180 It is armed with telescopes designed to detect gamma rays, 362 00:19:52,180 --> 00:19:55,380 ultraviolet, X-rays, and visible light. 363 00:19:56,580 --> 00:20:00,980 And these are the images that the Swift telescope captured for us. 364 00:20:00,980 --> 00:20:03,980 They show the galaxy in both ultraviolet light, 365 00:20:03,980 --> 00:20:06,500 revealing the familiar spiral again, 366 00:20:06,500 --> 00:20:09,180 and in X-rays that transform the galaxy 367 00:20:09,180 --> 00:20:12,380 into a patchwork of bright points of light. 368 00:20:15,300 --> 00:20:18,540 I asked astronomer Karen Masters what these images tell us 369 00:20:18,540 --> 00:20:21,380 about star formation in M51. 370 00:20:21,380 --> 00:20:24,460 When you, somebody who studies galaxies, look at this, 371 00:20:24,460 --> 00:20:26,020 what do you see? 372 00:20:26,020 --> 00:20:29,060 Well, obviously you can see the main body of the Whirlpool Galaxy here. 373 00:20:29,060 --> 00:20:32,020 The spiral arms are really, really emphasised in the UV. 374 00:20:32,020 --> 00:20:33,940 When we see a galaxy that's bright in the UV, 375 00:20:33,940 --> 00:20:36,180 we know that it's forming stars vigorously, 376 00:20:36,180 --> 00:20:40,500 and that's because it's only the very hottest, most massive stars 377 00:20:40,500 --> 00:20:42,380 that glow so brightly in the UV, 378 00:20:42,380 --> 00:20:44,900 and those massive, hot stars have very short lifetimes - 379 00:20:44,900 --> 00:20:46,420 just tens of millions of years. 380 00:20:46,420 --> 00:20:48,660 And that's pretty quick for anything astronomical. 381 00:20:48,660 --> 00:20:50,940 That's hugely quick for astronomical timescales. 382 00:20:50,940 --> 00:20:53,660 And so, when you see a galaxy that's very bright in UV, 383 00:20:53,660 --> 00:20:55,820 you know that it's been forming stars vigorously. 384 00:20:55,820 --> 00:20:57,980 Basically right now on astronomical timescales, 385 00:20:57,980 --> 00:20:59,380 ten million years is nothing. 386 00:20:59,380 --> 00:21:01,140 And how would this compare to our Milky Way? 387 00:21:01,140 --> 00:21:03,260 Well, if you do the sums, you can sort of estimate 388 00:21:03,260 --> 00:21:05,740 the star formation rate of the galaxy from that UV image. 389 00:21:05,740 --> 00:21:09,300 You have it forming about five solar masses' worth of stars every year. 390 00:21:09,300 --> 00:21:11,940 That's two, three, four, five times the rate of the Milky Way. 391 00:21:11,940 --> 00:21:14,380 That's right, yeah, and the Whirlpool Galaxy is not as big 392 00:21:14,380 --> 00:21:15,660 as the Milky Way, either, 393 00:21:15,660 --> 00:21:17,500 so it's a galaxy smaller than the Milky Way, 394 00:21:17,500 --> 00:21:19,740 forming stars at a faster rate than the Milky Way. 395 00:21:19,740 --> 00:21:22,780 Well, that's the ultraviolet, but we can have a look at a different view. 396 00:21:22,780 --> 00:21:26,820 So Swift is also an X-ray telescope, and here, slightly smaller, 397 00:21:26,820 --> 00:21:30,580 is the X-ray view, and it looks like the spiral arms have disappeared. 398 00:21:30,580 --> 00:21:31,900 What are we seeing here? 399 00:21:31,900 --> 00:21:34,180 So, there's a nice contrast here with X-ray and UV. 400 00:21:34,180 --> 00:21:36,020 The UV is picking out the birth of stars, 401 00:21:36,020 --> 00:21:38,380 whereas the X-ray here is really going to be picking out 402 00:21:38,380 --> 00:21:39,580 mostly the deaths of stars. 403 00:21:39,580 --> 00:21:40,740 To create X-rays, 404 00:21:40,740 --> 00:21:43,900 the very short wavelength, very energetic emission, 405 00:21:43,900 --> 00:21:46,100 we need some of the most energetic processes 406 00:21:46,100 --> 00:21:47,580 that happen in the universe, 407 00:21:47,580 --> 00:21:50,100 and we need material that's falling onto massive objects, 408 00:21:50,100 --> 00:21:52,900 and what we've got going on in the centre of these galaxies 409 00:21:52,900 --> 00:21:54,380 is a supermassive black hole. 410 00:21:54,380 --> 00:21:57,020 There's a supermassive black hole in the centre of pretty much 411 00:21:57,020 --> 00:21:59,820 every galaxy, but again, what you're seeing glowing in X-ray there 412 00:21:59,820 --> 00:22:01,980 is the material falling down onto that black hole, 413 00:22:01,980 --> 00:22:03,740 and the gravitational energy it picks up 414 00:22:03,740 --> 00:22:05,340 as it falls onto that black hole. 415 00:22:05,340 --> 00:22:07,860 And the friction as it moves against the rest of the material 416 00:22:07,860 --> 00:22:10,700 falling onto the black hole and orbiting it in this accretion disc 417 00:22:10,700 --> 00:22:13,180 makes that material so hot that it starts glowing in X-rays. 418 00:22:15,740 --> 00:22:20,860 The black hole at the centre of M51 is affecting its surroundings. 419 00:22:20,860 --> 00:22:24,580 We can see that in this remarkable picture of the galactic core, 420 00:22:24,580 --> 00:22:28,420 showing two doughnut-shaped rings of dust surrounding the black hole. 421 00:22:29,740 --> 00:22:34,340 But the Swift image also shows many other sources of X-ray emission - 422 00:22:34,340 --> 00:22:38,100 places where we must find equally extreme conditions. 423 00:22:39,620 --> 00:22:42,420 Mostly, these are going to be binary stars in the galaxy, 424 00:22:42,420 --> 00:22:43,940 but very special binary stars - 425 00:22:43,940 --> 00:22:46,940 one of the pair will have come to the end of its main sequence life, 426 00:22:46,940 --> 00:22:50,100 gone supernovae, and either turned into a neutron star or black hole, 427 00:22:50,100 --> 00:22:53,100 and managed to do that without completely disrupting its companion. 428 00:22:53,100 --> 00:22:54,820 But the companion then gets close enough 429 00:22:54,820 --> 00:22:58,140 that it starts losing material onto that black hole or neutron star, 430 00:22:58,140 --> 00:23:00,300 which spirals around it in an accretion disc, 431 00:23:00,300 --> 00:23:02,900 and all of the energy that it picks up makes it incredibly hot, 432 00:23:02,900 --> 00:23:04,820 and so starts glowing in the X-ray, 433 00:23:04,820 --> 00:23:07,620 and so, you see stellar death, really, in this image. 434 00:23:07,620 --> 00:23:08,700 And so, from Swift, 435 00:23:08,700 --> 00:23:11,220 you might be forgiven for thinking there are just these few 436 00:23:11,220 --> 00:23:13,660 interesting sources, but I've got another X-ray image, 437 00:23:13,660 --> 00:23:15,940 this one from Chandra, which is a larger, 438 00:23:15,940 --> 00:23:18,140 more sensitive X-ray telescope, and here, 439 00:23:18,140 --> 00:23:20,300 you see not just the individual points, 440 00:23:20,300 --> 00:23:22,300 the X-ray stars that we were looking at, 441 00:23:22,300 --> 00:23:25,060 but now there's this purple glow, as well. 442 00:23:25,060 --> 00:23:26,660 What are we seeing there? 443 00:23:26,660 --> 00:23:28,940 This is hot gas, but not tied to individual stars. 444 00:23:28,940 --> 00:23:31,940 This is now hot shocked gas in the spiral arms. 445 00:23:31,940 --> 00:23:33,660 It's actually revealing the physics 446 00:23:33,660 --> 00:23:36,180 which is starting the star formation in those spiral arms - 447 00:23:36,180 --> 00:23:40,380 the compression of gas being driven very quickly from supernovae, 448 00:23:40,380 --> 00:23:44,060 or winds from hot stars shocking it, and causing star formation to start. 449 00:23:44,060 --> 00:23:45,580 Really, just seeing this glowing 450 00:23:45,580 --> 00:23:47,860 is evidence that this is a dynamic place. 451 00:23:47,860 --> 00:23:49,980 What's driving those changes? 452 00:23:49,980 --> 00:23:52,060 The whole structure is driven by this companion 453 00:23:52,060 --> 00:23:53,860 and the interaction with this companion, 454 00:23:53,860 --> 00:23:56,380 and the timescales there are hundreds of millions of years. 455 00:23:56,380 --> 00:23:58,940 So it did its last pass about 100 million years ago, 456 00:23:58,940 --> 00:24:00,740 and a few hundred million years from now, 457 00:24:00,740 --> 00:24:03,460 it's going to have merged completely with the Whirlpool Galaxy. 458 00:24:03,460 --> 00:24:05,020 It's a strange thought, isn't it, 459 00:24:05,020 --> 00:24:07,020 that it's going to change quite so utterly, 460 00:24:07,020 --> 00:24:09,100 and this familiar shape will disappear. 461 00:24:09,100 --> 00:24:10,980 I suppose we're just lucky to be able to see it 462 00:24:10,980 --> 00:24:12,620 while all of this is going on. 463 00:24:15,460 --> 00:24:17,740 This is the beauty of modern astronomy. 464 00:24:18,860 --> 00:24:20,540 By using all the tools available 465 00:24:20,540 --> 00:24:23,580 to look at M51 in different wavelengths, 466 00:24:23,580 --> 00:24:27,100 we can reveal the secrets of the Whirlpool Galaxy. 467 00:24:28,180 --> 00:24:31,660 We can understand its past and its future. 468 00:24:32,700 --> 00:24:34,860 The optical wavelengths show us light 469 00:24:34,860 --> 00:24:37,260 from just some of the stars in the galaxy, 470 00:24:37,260 --> 00:24:40,140 radio reveals the distribution of gas, 471 00:24:40,140 --> 00:24:43,660 and infrared, the clouds of dust from which the stars are made. 472 00:24:46,460 --> 00:24:51,060 UV light detects the hot young stars formed from that gas and dust... 473 00:24:52,420 --> 00:24:54,260 ..and X-ray emissions pinpoint 474 00:24:54,260 --> 00:24:56,580 what happens to those stars when they die. 475 00:24:57,620 --> 00:25:01,980 And all these processes are concentrated in the spiral arms - 476 00:25:01,980 --> 00:25:04,980 dense waves of material created by the collision 477 00:25:04,980 --> 00:25:08,060 between the Whirlpool and its companion galaxy. 478 00:25:09,380 --> 00:25:13,380 All this information allows us to build a portrait of the galaxy - 479 00:25:13,380 --> 00:25:17,580 one that reveals it in all of its beauty and complexity. 480 00:25:19,660 --> 00:25:24,220 And isn't it amazing to think what else might be going on in M51? 481 00:25:24,220 --> 00:25:27,540 Around those stars, there must be planets. 482 00:25:28,540 --> 00:25:30,020 But is there life? 483 00:25:31,700 --> 00:25:35,060 Or even other civilisations looking back at us? 484 00:25:36,900 --> 00:25:40,300 Thanks to everybody who contributed images for tonight's programme. 485 00:25:40,300 --> 00:25:42,020 But if you want to do some more astronomy, 486 00:25:42,020 --> 00:25:43,820 even if you don't have a telescope, 487 00:25:43,820 --> 00:25:47,140 we're letting you participate in some live research, 488 00:25:47,140 --> 00:25:50,540 all part of the BBC's Do Something Great season, 489 00:25:50,540 --> 00:25:53,380 because we want you to become comet hunters. 490 00:25:54,620 --> 00:25:58,020 We need you to take part in an exciting project, 491 00:25:58,020 --> 00:26:02,060 searching for a new population of comets hidden in the asteroid belt. 492 00:26:02,060 --> 00:26:04,460 'It's run by Meg Schwamb.' 493 00:26:04,460 --> 00:26:06,300 Hi, Meg. Hi. 494 00:26:06,300 --> 00:26:09,220 Now, you're one of the lead scientists on this project, 495 00:26:09,220 --> 00:26:11,860 but can you tell me, why are you hunting comets? 496 00:26:11,860 --> 00:26:14,700 Well, we're looking for a unique type of comet, 497 00:26:14,700 --> 00:26:17,940 and these are really wolves in sheep's clothing, 498 00:26:17,940 --> 00:26:21,100 so these are asteroids that start looking like comets. 499 00:26:21,100 --> 00:26:22,820 So when you think of a traditional comet, 500 00:26:22,820 --> 00:26:25,740 you think of an icy body coming in from the outer solar system 501 00:26:25,740 --> 00:26:28,100 and heating up, and sublimating its ices off, 502 00:26:28,100 --> 00:26:31,300 but these are very different. So these are typical, plain, 503 00:26:31,300 --> 00:26:34,980 ordinary asteroids sitting between Jupiter and Mars, 504 00:26:34,980 --> 00:26:37,260 and when we occasionally look at these objects, 505 00:26:37,260 --> 00:26:39,260 we start to see that they have tails. 506 00:26:39,260 --> 00:26:42,540 Like in this image here, where you see this dust tail. 507 00:26:42,540 --> 00:26:45,900 Very similar to what you see with a comet, but that's still an asteroid. 508 00:26:45,900 --> 00:26:48,180 So what do you think is causing this? 509 00:26:48,180 --> 00:26:50,100 We don't know what the dominant mechanism is, 510 00:26:50,100 --> 00:26:53,260 but one source is water ice, which shouldn't be there, 511 00:26:53,260 --> 00:26:54,980 but there could be buried water ice 512 00:26:54,980 --> 00:26:57,100 underneath the surfaces of some of these asteroids 513 00:26:57,100 --> 00:26:58,380 that somehow gets exposed. 514 00:26:58,380 --> 00:27:00,420 So why is this of scientific interest, 515 00:27:00,420 --> 00:27:02,020 the fact that we have these comets, 516 00:27:02,020 --> 00:27:04,220 and they could potentially contain water? 517 00:27:04,220 --> 00:27:06,420 Well, water is important for life, 518 00:27:06,420 --> 00:27:08,500 and one of the interesting things is to wonder, 519 00:27:08,500 --> 00:27:10,300 where did Earth's water come from? 520 00:27:10,300 --> 00:27:11,580 And we don't fully know. 521 00:27:11,580 --> 00:27:14,740 And potentially, there's now a new source of water ice 522 00:27:14,740 --> 00:27:17,300 that could have been deposited on the Earth early on, 523 00:27:17,300 --> 00:27:19,260 and so understanding where these 524 00:27:19,260 --> 00:27:21,420 main-belt comets originally came from, 525 00:27:21,420 --> 00:27:23,540 how did they get into the asteroid belt, 526 00:27:23,540 --> 00:27:25,540 and how many of them are there, 527 00:27:25,540 --> 00:27:28,180 might tell us about whether or not this could be a source 528 00:27:28,180 --> 00:27:29,340 for Earth's water. 529 00:27:29,340 --> 00:27:31,900 So the point of the project is to find many, many more examples, 530 00:27:31,900 --> 00:27:34,180 hopefully. How can our viewers help? 531 00:27:34,180 --> 00:27:38,300 Well, you can go to comethunters.org and get started right away. 532 00:27:38,300 --> 00:27:40,540 All you need is a web browser and your eyes. 533 00:27:40,540 --> 00:27:42,500 So what does the website look like? 534 00:27:42,500 --> 00:27:44,780 So, what we're showing is two images of the asteroid 535 00:27:44,780 --> 00:27:46,860 taken at two different times during the night, 536 00:27:46,860 --> 00:27:50,260 and what we want you to do is use your eyes to spot the tail. 537 00:27:50,260 --> 00:27:52,740 Human beings are really good at spotting patterns 538 00:27:52,740 --> 00:27:56,420 and things that don't match and so we need the eyeballs of anyone 539 00:27:56,420 --> 00:27:59,180 who wants to look, and for the viewers of The Sky At Night 540 00:27:59,180 --> 00:28:03,340 to help us because you are better than a machine at finding these. 541 00:28:03,340 --> 00:28:06,900 This is your chance to be able to help discover a comet. 542 00:28:06,900 --> 00:28:09,220 Well, you've convinced me. I want to go and find a comet, 543 00:28:09,220 --> 00:28:10,420 so thank you very much. 544 00:28:10,420 --> 00:28:13,700 If you want to get involved, the website is on the screen 545 00:28:13,700 --> 00:28:16,860 right now, so good luck, and happy hunting. 546 00:28:21,220 --> 00:28:24,340 That's all for this month, but when we come back next month, 547 00:28:24,340 --> 00:28:27,900 we'll be reporting from Nasa's Jet Propulsion Laboratory 548 00:28:27,900 --> 00:28:30,340 as the Juno probe arrives at Jupiter. 549 00:28:31,460 --> 00:28:35,020 Until then, get outside, get looking up! Good night.