0:00:05 > 0:00:07On this month's Sky at Night,
0:00:07 > 0:00:09we'll be taking you to one of the most spectacular
0:00:09 > 0:00:13and fascinating places in the whole night sky.
0:00:13 > 0:00:15It's officially known as M51,
0:00:15 > 0:00:18but most of us know it by its more romantic name -
0:00:18 > 0:00:20the Whirlpool Galaxy.
0:00:22 > 0:00:25M51 is a stunning sight.
0:00:25 > 0:00:28But it's more than just beautiful to look at.
0:00:29 > 0:00:31It is also one of the most fascinating places
0:00:31 > 0:00:33we have ever discovered.
0:00:34 > 0:00:38Its sculptured spiral arms are a maelstrom of star formation...
0:00:40 > 0:00:42..lit up by the light of hot young stars.
0:00:45 > 0:00:47But it is also a stellar graveyard,
0:00:47 > 0:00:51in which we can see neutron stars and black holes
0:00:51 > 0:00:53tearing other stars apart.
0:00:55 > 0:00:57So why is this galaxy so active,
0:00:57 > 0:00:59and how did it get its majestic
0:00:59 > 0:01:02and surprisingly prominent spiral shape?
0:01:02 > 0:01:04Welcome to The Sky at Night.
0:01:32 > 0:01:35We're making this Whirlpool Galaxy Day.
0:01:35 > 0:01:36On this one day,
0:01:36 > 0:01:40we're going to be pointing as many telescopes as we can at the object.
0:01:40 > 0:01:42We've got amateur back-yard telescopes,
0:01:42 > 0:01:44professional instruments like the dish behind me,
0:01:44 > 0:01:48and on mountaintops around the world, large observatories,
0:01:48 > 0:01:51several of which have got better weather than here in Cambridge!
0:01:51 > 0:01:54We'll even be going above the weather, because we've got
0:01:54 > 0:01:57special permission to use one of Nasa's space telescopes.
0:01:57 > 0:02:01We'll be looking M51 at different wavelengths of light and different
0:02:01 > 0:02:05magnifications to create a unique portrait of this remarkable galaxy.
0:02:07 > 0:02:10We've come to the Mullard Radio Astronomy Observatory
0:02:10 > 0:02:11just outside Cambridge.
0:02:11 > 0:02:13Founded in 1957,
0:02:13 > 0:02:18it helped pioneer a completely new way of observing the sky.
0:02:18 > 0:02:20It was here...well, actually, just over that hedge,
0:02:20 > 0:02:23that Jocelyn Bell discovered the first pulsars
0:02:23 > 0:02:26and, later on, we'll be using some of the modern instruments
0:02:26 > 0:02:28that still operate on the site
0:02:28 > 0:02:30to take a close look at the Whirlpool Galaxy.
0:02:30 > 0:02:35But our exploration of M51 doesn't start in this slightly damp field.
0:02:35 > 0:02:38It starts somewhere with much clearer skies.
0:02:44 > 0:02:46It's nine o'clock in the morning,
0:02:46 > 0:02:48it's a terrible time to be trying to observe a galaxy,
0:02:48 > 0:02:51at least from here, but this laptop is connected
0:02:51 > 0:02:54to a telescope in Hawaii, where it's still dark.
0:02:54 > 0:02:57It's a 0.4-metre telescope on top of the island of Maui,
0:02:57 > 0:03:00on a dormant volcano, and you can see from this camera
0:03:00 > 0:03:04just outside the observatory that they've got brilliant, clear skies.
0:03:04 > 0:03:07See a couple of planets, the nice Milky Way,
0:03:07 > 0:03:11and this region of sky, where M51, our target, is located.
0:03:11 > 0:03:15Now, the telescope's already slewed to the source
0:03:15 > 0:03:17and it's taking a five-minute exposure
0:03:17 > 0:03:19and so, in just a few minutes,
0:03:19 > 0:03:22we should see our first image of the Whirlpool Galaxy.
0:03:28 > 0:03:30Well, there it is, this is our image,
0:03:30 > 0:03:33and you can see immediately the spiral arms in the galaxy
0:03:33 > 0:03:35which wind round this central, bright nucleus,
0:03:35 > 0:03:38and then the second thing you notice
0:03:38 > 0:03:41is that there are two galaxies in the frame.
0:03:41 > 0:03:44There's this companion which has stretched out this bright material
0:03:44 > 0:03:47from the main galaxy, so you get this arm joining the two,
0:03:47 > 0:03:52and there's lots of faint gas and dust around that secondary galaxy.
0:03:52 > 0:03:54And really that's what the Whirlpool Galaxy gives us -
0:03:54 > 0:03:58it's a chance to watch a collision between two galaxies in action.
0:03:58 > 0:04:01It's something we can't see this well anywhere else in the sky.
0:04:01 > 0:04:04It really is a beautiful image.
0:04:05 > 0:04:08Maggie showed this image to galaxy expert Rob Kennicutt
0:04:08 > 0:04:11to ask about the Whirlpool's amazing structure
0:04:11 > 0:04:14and its relationship with its companion.
0:04:14 > 0:04:15It is absolutely wonderful.
0:04:15 > 0:04:19So there's two spiral arms. They look almost perfect.
0:04:19 > 0:04:22The classic spiral galaxy. So how are they formed?
0:04:22 > 0:04:28Almost all disc galaxies like this system do have spiral structure
0:04:28 > 0:04:32but, as you say, these are spectacularly prominent arms,
0:04:32 > 0:04:34and were quite certain now
0:04:34 > 0:04:38that to produce such strong spiral structure,
0:04:38 > 0:04:39you need the driving force
0:04:39 > 0:04:42of interaction with a companion galaxy.
0:04:42 > 0:04:44Now, you see, to me, that seems counterintuitive,
0:04:44 > 0:04:46cos when I think of collisions, I think of chaos,
0:04:46 > 0:04:48things being thrown everywhere.
0:04:48 > 0:04:50I don't think of structure being formed that way.
0:04:50 > 0:04:52I agree with you - it's not intuitive,
0:04:52 > 0:04:55but this computer simulation is designed to show
0:04:55 > 0:04:57how these collisions between galaxies
0:04:57 > 0:05:00can excite spiral structure.
0:05:00 > 0:05:03So you have two galaxies, disc galaxies, much like the spiral.
0:05:03 > 0:05:06It's looking a bit messy now, but... Wow!
0:05:06 > 0:05:09You see, actually, the spiral forming due to the collision,
0:05:09 > 0:05:10and in both galaxies.
0:05:10 > 0:05:13But in this simulation, we had two similar-sized galaxies.
0:05:13 > 0:05:16What if you had something that was more akin to the Whirlpool Galaxy?
0:05:16 > 0:05:21What we have here is a second computer simulation,
0:05:21 > 0:05:25and this one is actually specifically tailored
0:05:25 > 0:05:29- to try to reproduce the two galaxies in the Whirlpool system.- Right.
0:05:29 > 0:05:33So this kind of spiral structure you see in the beginning
0:05:33 > 0:05:35is actually the sort of spiral structure
0:05:35 > 0:05:36that is common
0:05:36 > 0:05:38in galaxies like the Milky Way.
0:05:38 > 0:05:40So, even before the interaction,
0:05:40 > 0:05:43Whirlpool probably was a spiral galaxy,
0:05:43 > 0:05:46but now you see the companion making its appearance.
0:05:46 > 0:05:48Now, that doesn't look like a companion galaxy.
0:05:48 > 0:05:49It looks more like a point mass.
0:05:49 > 0:05:52I think that's right, to save on computing time,
0:05:52 > 0:05:55I think they modelled the companion galaxy as a point mass,
0:05:55 > 0:05:58and now you're beginning to see its effects already -
0:05:58 > 0:06:02the spiral pattern is being amplified, and let's keep going.
0:06:02 > 0:06:03- And there you are.- Whoa!
0:06:03 > 0:06:05You've got the two distinct spiral arms,
0:06:05 > 0:06:07and you've got the companion galaxy at one of the ends
0:06:07 > 0:06:10- of the spiral arm, so that is a good recreation...- Indeed.
0:06:10 > 0:06:12..of the Whirlpool and its companion.
0:06:12 > 0:06:16But notice this is 300 million years after the start of the calculation.
0:06:16 > 0:06:17Yes.
0:06:17 > 0:06:20- But you think of this as now, in our world, right?- OK, yes.
0:06:20 > 0:06:22So now, the computer's going to predict
0:06:22 > 0:06:24what this system will look like in the future.
0:06:24 > 0:06:27- Ah, the future of the Whirlpool Galaxy.- Indeed.
0:06:27 > 0:06:31So, as you see, the companion continues to get closer
0:06:31 > 0:06:33and closer to the centre of the spiral,
0:06:33 > 0:06:36it's still on the way in, and as it goes,
0:06:36 > 0:06:38the spiral arms are amplified even more than today,
0:06:38 > 0:06:40- if that can be imagined.- Yes.
0:06:40 > 0:06:42- But it's getting a lot messier! - Indeed.
0:06:42 > 0:06:45It's now reached closest approach, and on the way out,
0:06:45 > 0:06:49- it's leaving kind of a train wreck behind.- Yes!
0:06:49 > 0:06:52And now, you see, the companion is coming in for a second time,
0:06:52 > 0:06:56and the movie stops at this point, but if we were to continue it,
0:06:56 > 0:06:59the two galaxies would totally merge together.
0:06:59 > 0:07:02But that means that the Whirlpool Galaxy in all its perfection,
0:07:02 > 0:07:06as it looks today, is transitory, so it will pass through that phase,
0:07:06 > 0:07:09and at some point end up maybe more like this.
0:07:09 > 0:07:12Yeah, indeed, and look at the scale, in about 70 million years,
0:07:12 > 0:07:15the phase of spiral structure will be long over,
0:07:15 > 0:07:18and you'll be left within 100 million years
0:07:18 > 0:07:21with one galaxy where there were two before.
0:07:21 > 0:07:24So, it just makes me appreciate the Whirlpool Galaxy all the more,
0:07:24 > 0:07:26because we can appreciate its beauty right at the moment,
0:07:26 > 0:07:28- but it won't last!- Indeed.
0:07:29 > 0:07:33The telescope in Hawaii actually took three pictures of the galaxy,
0:07:33 > 0:07:35each at a different wavelength.
0:07:37 > 0:07:39When composited together,
0:07:39 > 0:07:44they give us a colour view of the Whirlpool in all its glory.
0:07:44 > 0:07:46But it's not just professional telescopes
0:07:46 > 0:07:49that can capture spectacular images like these.
0:07:50 > 0:07:52Pete has been trying to demonstrate
0:07:52 > 0:07:55how you can view the galaxy for yourself.
0:07:55 > 0:07:59And he's been exploring the history of our observation of this galaxy.
0:08:00 > 0:08:04Astronomy in the UK can be a bit frustrating at times,
0:08:04 > 0:08:05and the clouds have now come in,
0:08:05 > 0:08:10and I really don't think I'm going to get a view of M51 tonight.
0:08:10 > 0:08:12So welcome to the great British summer!
0:08:17 > 0:08:20It really is a pity that it's cloudy this evening,
0:08:20 > 0:08:24because M51 is one of the best deep sky objects up there.
0:08:24 > 0:08:27And at the moment, it's really high up in the sky,
0:08:27 > 0:08:30which means it's well away from any murk close to the horizon,
0:08:30 > 0:08:33and that will give you a good view of it.
0:08:34 > 0:08:37And it's pretty simple to find, too.
0:08:37 > 0:08:41To locate it, first identify the Plough or Saucepan,
0:08:41 > 0:08:43which is part of Ursa Major,
0:08:43 > 0:08:47and is one of the most recognisable patterns in the entire night sky.
0:08:47 > 0:08:50Identify the star in the middle of the handle
0:08:50 > 0:08:52and the one at the end of the handle.
0:08:52 > 0:08:56Draw a line between them and turn by 90 degrees,
0:08:56 > 0:08:58and move for about half that distance again,
0:08:58 > 0:09:01and that'll take you to exactly where M51 is in the sky.
0:09:03 > 0:09:05You can't see M51 with the naked eye,
0:09:05 > 0:09:08but it is possible to see it with just a pair of binoculars.
0:09:08 > 0:09:12And if you've got a telescope like this, then it looks quite amazing,
0:09:12 > 0:09:15and that will also allow you to take a picture of it.
0:09:15 > 0:09:18And I've got a picture here I took a little while ago,
0:09:18 > 0:09:21and you can really start to make out some of the structure of the galaxy.
0:09:21 > 0:09:24You've got the spiral arms, they're very evident there.
0:09:24 > 0:09:27You've also got the little satellite galaxy, as well.
0:09:27 > 0:09:28That's very obvious.
0:09:28 > 0:09:31So if you CAN get a view of M51,
0:09:31 > 0:09:34it's a really rewarding object to have a look at.
0:09:37 > 0:09:41'But not everyone has always thought that M51 was fascinating.'
0:09:43 > 0:09:48The Whirlpool Galaxy was discovered by Charles Messier in 1773,
0:09:48 > 0:09:54and added to his famous catalogue as the 51st entry, hence the name M51.
0:09:55 > 0:10:00But Messier wasn't interested in how fascinating M51 was.
0:10:01 > 0:10:03He was a comet hunter,
0:10:03 > 0:10:06irritated by wasting his time pointing his telescope
0:10:06 > 0:10:09at things that superficially resembled comets,
0:10:09 > 0:10:12but which on closer inspection
0:10:12 > 0:10:14were revealed to be something else entirely.
0:10:16 > 0:10:19So he set about making a catalogue of what were, to him,
0:10:19 > 0:10:20frustrating objects,
0:10:20 > 0:10:23so he could ignore them in his search for comets.
0:10:24 > 0:10:27But the irony was that in doing so,
0:10:27 > 0:10:30he had compiled a list of nearly all of the most spectacular
0:10:30 > 0:10:33deep sky objects -
0:10:33 > 0:10:36nebulae like the Orion Nebula,
0:10:36 > 0:10:39open star clusters like the Pleiades,
0:10:39 > 0:10:42and galaxies like M51.
0:10:43 > 0:10:47'To be fair, Messier probably couldn't resolve the Whirlpool
0:10:47 > 0:10:50'to be much more than an indistinct, diffuse cloud -
0:10:50 > 0:10:52'a nebula.'
0:10:53 > 0:10:56The first time the Whirlpool Galaxy was seen in all its glory
0:10:56 > 0:11:01was in 1845, when William Parsons, the third Earl of Rosse,
0:11:01 > 0:11:06pointed a 1.8 metre reflecting telescope, based in Birr, Ireland,
0:11:06 > 0:11:11which was then the largest telescope in the world, at M51.
0:11:11 > 0:11:14And this is a sketch he made of that object,
0:11:14 > 0:11:16and it's absolutely incredible.
0:11:16 > 0:11:18There's so much structure to see here,
0:11:18 > 0:11:22but what's really evident is the spiral nature of the galaxy.
0:11:22 > 0:11:26And that was the first time this had ever been recorded
0:11:26 > 0:11:27in a celestial object.
0:11:30 > 0:11:32The picture was quite a sensation at the time,
0:11:32 > 0:11:35and was published all over the world.
0:11:36 > 0:11:39It's even suggested that his swirling drawing
0:11:39 > 0:11:43was the inspiration for Van Gogh's Starry Night.
0:11:45 > 0:11:49But we still didn't know what the Whirlpool was or where it was,
0:11:49 > 0:11:53and it was only in 1924 that Edwin Hubble demonstrated
0:11:53 > 0:11:56that nebulous objects like these
0:11:56 > 0:11:58were in fact distant galaxies in space.
0:12:00 > 0:12:03We now know it's about 30 million light years away,
0:12:03 > 0:12:08and although much smaller than the Milky Way, the disc is huge,
0:12:08 > 0:12:10measuring 60,000 light years across.
0:12:14 > 0:12:17Images like these, taken by Sky At Night viewers,
0:12:17 > 0:12:21clearly show why M51 is one of the most exciting places
0:12:21 > 0:12:22in the universe.
0:12:25 > 0:12:26But they cannot show us
0:12:26 > 0:12:31many of the secrets that are hidden deep within those spiral arms.
0:12:34 > 0:12:35'To reveal those secrets,
0:12:35 > 0:12:39'we need to find different ways to look at the galaxy.'
0:12:44 > 0:12:47These dishes are radio telescopes.
0:12:47 > 0:12:50They're just a receiver, not too dissimilar to an FM radio,
0:12:50 > 0:12:52but they're much, much bigger.
0:12:52 > 0:12:55That's because the signals they're trying to pick up from space
0:12:55 > 0:12:58are absolutely minuscule.
0:13:00 > 0:13:02In fact, it has been calculated
0:13:02 > 0:13:05that if you add up every radio signal ever picked up
0:13:05 > 0:13:08by all the radio telescopes in the world,
0:13:08 > 0:13:10the combined energy of that radiation
0:13:10 > 0:13:14would be enough to melt just three snowflakes.
0:13:16 > 0:13:18These telescopes are actually lining up right now
0:13:18 > 0:13:22to come in line with M51, the Whirlpool Galaxy,
0:13:22 > 0:13:28which lies around 30 million light years away in that direction.
0:13:30 > 0:13:32These are the radio images
0:13:32 > 0:13:35captured by the Mullard Observatory dishes.
0:13:35 > 0:13:38Superficially, these pictures are not as impressive,
0:13:38 > 0:13:41but they show details that we could never reveal
0:13:41 > 0:13:43with conventional telescopes.
0:13:43 > 0:13:46The result of intense magnetic fields
0:13:46 > 0:13:49and the glow of hot gas around young stars.
0:13:50 > 0:13:52And this remarkable image,
0:13:52 > 0:13:55from the Very Large Array Radio Telescope in New Mexico,
0:13:55 > 0:13:59reveals the distribution of hydrogen throughout the galaxy -
0:13:59 > 0:14:01the raw material from which the stars are made
0:14:01 > 0:14:04stretching far beyond the main disc.
0:14:07 > 0:14:09And as Maggie's been discovering,
0:14:09 > 0:14:12radio astronomy is just one of the many alternative ways
0:14:12 > 0:14:14we have to observe M51.
0:14:19 > 0:14:24For centuries, we only had one way of studying the night sky -
0:14:24 > 0:14:27using telescopes that operated in visible light -
0:14:27 > 0:14:30that tiny part of the electromagnetic spectrum
0:14:30 > 0:14:32that our eyes can detect.
0:14:34 > 0:14:38We can only see things if they're actively emitting light
0:14:38 > 0:14:41or reflecting light in the visible part of the spectrum,
0:14:41 > 0:14:43and if there's no source...
0:14:43 > 0:14:45then we can't see anything at all.
0:14:46 > 0:14:48But in addition to radio waves,
0:14:48 > 0:14:51there's a lot more to the electromagnetic spectrum,
0:14:51 > 0:14:53and if we tune into this,
0:14:53 > 0:14:56then we can detect a lot more of what's out there,
0:14:56 > 0:14:58hidden in the darkness.
0:15:00 > 0:15:04Now, this is a camera that is sensitive to infrared light.
0:15:04 > 0:15:06That's a wavelength that is slightly longer
0:15:06 > 0:15:07than we can detect with our eyes,
0:15:07 > 0:15:09and it allows us to see things
0:15:09 > 0:15:11that would otherwise appear to be invisible.
0:15:13 > 0:15:17We can see things in the infrared because of their temperature.
0:15:17 > 0:15:23On Earth, all objects radiate part of their heat as infrared light.
0:15:23 > 0:15:27How much and that what frequency depends on how hot they are.
0:15:27 > 0:15:29It's just the same in space.
0:15:29 > 0:15:30There's a lot of stuff hiding out there
0:15:30 > 0:15:33that we just can't detect with visible light,
0:15:33 > 0:15:36but if we tune our telescopes to detect infrared wavelengths,
0:15:36 > 0:15:39then suddenly, a lot more is revealed.
0:15:42 > 0:15:46Most of the infrared radiation from space is absorbed by the atmosphere,
0:15:46 > 0:15:51so infrared telescopes have to be situated on top of tall mountains.
0:15:53 > 0:15:55This is the Liverpool Telescope,
0:15:55 > 0:16:01located at over 2,300 metres on the island of La Palma in the Canaries.
0:16:01 > 0:16:03Late on the night of the 31st of May,
0:16:03 > 0:16:07it took an infrared image of the Whirlpool Galaxy
0:16:07 > 0:16:09especially for The Sky At Night.
0:16:10 > 0:16:12This is the infrared image taken for us
0:16:12 > 0:16:15by the Liverpool Telescope just last night.
0:16:15 > 0:16:17Actually, it's two images,
0:16:17 > 0:16:19because the galaxy doesn't fit on a single frame.
0:16:19 > 0:16:22What we can see in this image is light from more stars
0:16:22 > 0:16:24than we'd otherwise see in the visible.
0:16:24 > 0:16:27By using the infrared, we're able to peer through the dust
0:16:27 > 0:16:30that would otherwise obscure our view.
0:16:30 > 0:16:33But this is an image in the near infrared -
0:16:33 > 0:16:35we're only just past the red in the visible,
0:16:35 > 0:16:37and we can go further than that,
0:16:37 > 0:16:38and the colour here
0:16:38 > 0:16:40represents the different wavelengths of infrared light.
0:16:40 > 0:16:44You can immediately see there's a difference between the two galaxies.
0:16:44 > 0:16:47The small companion galaxy is bright blue,
0:16:47 > 0:16:51and in this image, blue light comes from old stars,
0:16:51 > 0:16:53so this galaxy has an old stellar population -
0:16:53 > 0:16:56there's not much going on there right now.
0:16:56 > 0:17:01In contrast, the Whirlpool itself has this brilliant red glow.
0:17:01 > 0:17:04That's light from the dust and gas, the fuel of star formation,
0:17:04 > 0:17:07which you can see is spread throughout the disc,
0:17:07 > 0:17:10and has this wonderful structure, not just the spiral arms,
0:17:10 > 0:17:13but these filaments and these spokes in the disc, as well.
0:17:13 > 0:17:16But if you look along the spiral arms themselves,
0:17:16 > 0:17:18and only on the spiral arms,
0:17:18 > 0:17:19you see these bright knots,
0:17:19 > 0:17:22these bright blobs that are shining very brightly,
0:17:22 > 0:17:24and these are nebulae -
0:17:24 > 0:17:27they're places where thousands of stars are being born,
0:17:27 > 0:17:30and it's the light from those young stars
0:17:30 > 0:17:33that is causing these blobs to glow quite so brightly.
0:17:35 > 0:17:38We have similar features in our own galaxy.
0:17:38 > 0:17:44Places like the Orion Nebula, where stars are still being born today.
0:17:44 > 0:17:46But this is happening on a much grander scale
0:17:46 > 0:17:48in the Whirlpool Galaxy.
0:17:48 > 0:17:51Each of these bright dots is a stellar nursery
0:17:51 > 0:17:54100 times bigger than the Orion Nebula.
0:17:55 > 0:17:58These are all signs that the spiral arms in the Whirlpool
0:17:58 > 0:18:00are active - very active.
0:18:00 > 0:18:02So what this tells us
0:18:02 > 0:18:05is that it's not enough to have the raw materials for star formation -
0:18:05 > 0:18:08there's dust and there's gas throughout the disc -
0:18:08 > 0:18:12but it's only when it gets twisted up into these spiral arms
0:18:12 > 0:18:15that it can become dense enough to form stars.
0:18:15 > 0:18:18The spiral arms are where the action is.
0:18:18 > 0:18:21But to find out what's actually going on in there,
0:18:21 > 0:18:24we're going to need yet another way of looking at the galaxy,
0:18:24 > 0:18:26and to use a very, very special piece of kit.
0:18:26 > 0:18:28RADIO CRACKLE
0:18:28 > 0:18:32MUSIC PLAYS ON RADIO
0:18:32 > 0:18:33'Radio waves and infrared
0:18:33 > 0:18:38'are both from the lower energy end of the electromagnetic spectrum.'
0:18:38 > 0:18:39SHE TURNS RADIO OFF
0:18:39 > 0:18:42'But we can also pick up higher energy radiation.
0:18:45 > 0:18:50'Radiation in the ultraviolet and X-ray bands of the spectrum.'
0:18:50 > 0:18:52They're both familiar to us.
0:18:52 > 0:18:56X-rays can penetrate our skin and flesh, but not the bone,
0:18:56 > 0:18:58and that turns out to be really useful medically.
0:18:58 > 0:19:02UV rays from the sun are powerful enough to damage our skin -
0:19:02 > 0:19:04that's what causes sunburn.
0:19:05 > 0:19:08In space, this high-energy radiation is only generated
0:19:08 > 0:19:10in really extreme conditions,
0:19:10 > 0:19:15where the temperature is impossibly high - millions of degrees.
0:19:15 > 0:19:18Now, UV and X-ray emissions coming from something as far away
0:19:18 > 0:19:23as the M51 galaxy is so weak that it gets absorbed by our atmosphere,
0:19:23 > 0:19:27so the only way to observe it is to get up above our atmosphere.
0:19:27 > 0:19:29That's why we're incredibly lucky
0:19:29 > 0:19:34to have been given time on one of Nasa's space telescopes, Swift.
0:19:34 > 0:19:35And right now,
0:19:35 > 0:19:39it's slewing its way round to set its sights on the Whirlpool Galaxy.
0:19:41 > 0:19:43The Swift satellite sits in an orbit
0:19:43 > 0:19:46almost 600km above the Earth's surface.
0:19:47 > 0:19:51It is armed with telescopes designed to detect gamma rays,
0:19:51 > 0:19:55ultraviolet, X-rays, and visible light.
0:19:56 > 0:20:00And these are the images that the Swift telescope captured for us.
0:20:00 > 0:20:03They show the galaxy in both ultraviolet light,
0:20:03 > 0:20:06revealing the familiar spiral again,
0:20:06 > 0:20:08and in X-rays that transform the galaxy
0:20:08 > 0:20:12into a patchwork of bright points of light.
0:20:14 > 0:20:18I asked astronomer Karen Masters what these images tell us
0:20:18 > 0:20:21about star formation in M51.
0:20:21 > 0:20:24When you, somebody who studies galaxies, look at this,
0:20:24 > 0:20:25what do you see?
0:20:25 > 0:20:28Well, obviously you can see the main body of the Whirlpool Galaxy here.
0:20:28 > 0:20:31The spiral arms are really, really emphasised in the UV.
0:20:31 > 0:20:33When we see a galaxy that's bright in the UV,
0:20:33 > 0:20:35we know that it's forming stars vigorously,
0:20:35 > 0:20:40and that's because it's only the very hottest, most massive stars
0:20:40 > 0:20:42that glow so brightly in the UV,
0:20:42 > 0:20:44and those massive, hot stars have very short lifetimes -
0:20:44 > 0:20:46just tens of millions of years.
0:20:46 > 0:20:48And that's pretty quick for anything astronomical.
0:20:48 > 0:20:50That's hugely quick for astronomical timescales.
0:20:50 > 0:20:53And so, when you see a galaxy that's very bright in UV,
0:20:53 > 0:20:55you know that it's been forming stars vigorously.
0:20:55 > 0:20:57Basically right now on astronomical timescales,
0:20:57 > 0:20:58ten million years is nothing.
0:20:58 > 0:21:00And how would this compare to our Milky Way?
0:21:00 > 0:21:02Well, if you do the sums, you can sort of estimate
0:21:02 > 0:21:05the star formation rate of the galaxy from that UV image.
0:21:05 > 0:21:08You have it forming about five solar masses' worth of stars every year.
0:21:08 > 0:21:11That's two, three, four, five times the rate of the Milky Way.
0:21:11 > 0:21:14That's right, yeah, and the Whirlpool Galaxy is not as big
0:21:14 > 0:21:15as the Milky Way, either,
0:21:15 > 0:21:17so it's a galaxy smaller than the Milky Way,
0:21:17 > 0:21:19forming stars at a faster rate than the Milky Way.
0:21:19 > 0:21:22Well, that's the ultraviolet, but we can have a look at a different view.
0:21:22 > 0:21:26So Swift is also an X-ray telescope, and here, slightly smaller,
0:21:26 > 0:21:30is the X-ray view, and it looks like the spiral arms have disappeared.
0:21:30 > 0:21:31What are we seeing here?
0:21:31 > 0:21:33So, there's a nice contrast here with X-ray and UV.
0:21:33 > 0:21:35The UV is picking out the birth of stars,
0:21:35 > 0:21:38whereas the X-ray here is really going to be picking out
0:21:38 > 0:21:39mostly the deaths of stars.
0:21:39 > 0:21:40To create X-rays,
0:21:40 > 0:21:43the very short wavelength, very energetic emission,
0:21:43 > 0:21:45we need some of the most energetic processes
0:21:45 > 0:21:47that happen in the universe,
0:21:47 > 0:21:49and we need material that's falling onto massive objects,
0:21:49 > 0:21:52and what we've got going on in the centre of these galaxies
0:21:52 > 0:21:54is a supermassive black hole.
0:21:54 > 0:21:56There's a supermassive black hole in the centre of pretty much
0:21:56 > 0:21:59every galaxy, but again, what you're seeing glowing in X-ray there
0:21:59 > 0:22:01is the material falling down onto that black hole,
0:22:01 > 0:22:03and the gravitational energy it picks up
0:22:03 > 0:22:04as it falls onto that black hole.
0:22:04 > 0:22:07And the friction as it moves against the rest of the material
0:22:07 > 0:22:10falling onto the black hole and orbiting it in this accretion disc
0:22:10 > 0:22:12makes that material so hot that it starts glowing in X-rays.
0:22:15 > 0:22:20The black hole at the centre of M51 is affecting its surroundings.
0:22:20 > 0:22:24We can see that in this remarkable picture of the galactic core,
0:22:24 > 0:22:28showing two doughnut-shaped rings of dust surrounding the black hole.
0:22:29 > 0:22:33But the Swift image also shows many other sources of X-ray emission -
0:22:33 > 0:22:37places where we must find equally extreme conditions.
0:22:39 > 0:22:42Mostly, these are going to be binary stars in the galaxy,
0:22:42 > 0:22:43but very special binary stars -
0:22:43 > 0:22:46one of the pair will have come to the end of its main sequence life,
0:22:46 > 0:22:49gone supernovae, and either turned into a neutron star or black hole,
0:22:49 > 0:22:52and managed to do that without completely disrupting its companion.
0:22:52 > 0:22:54But the companion then gets close enough
0:22:54 > 0:22:57that it starts losing material onto that black hole or neutron star,
0:22:57 > 0:22:59which spirals around it in an accretion disc,
0:22:59 > 0:23:02and all of the energy that it picks up makes it incredibly hot,
0:23:02 > 0:23:04and so starts glowing in the X-ray,
0:23:04 > 0:23:07and so, you see stellar death, really, in this image.
0:23:07 > 0:23:08And so, from Swift,
0:23:08 > 0:23:10you might be forgiven for thinking there are just these few
0:23:10 > 0:23:13interesting sources, but I've got another X-ray image,
0:23:13 > 0:23:15this one from Chandra, which is a larger,
0:23:15 > 0:23:17more sensitive X-ray telescope, and here,
0:23:17 > 0:23:19you see not just the individual points,
0:23:19 > 0:23:21the X-ray stars that we were looking at,
0:23:21 > 0:23:24but now there's this purple glow, as well.
0:23:24 > 0:23:26What are we seeing there?
0:23:26 > 0:23:28This is hot gas, but not tied to individual stars.
0:23:28 > 0:23:31This is now hot shocked gas in the spiral arms.
0:23:31 > 0:23:33It's actually revealing the physics
0:23:33 > 0:23:35which is starting the star formation in those spiral arms -
0:23:35 > 0:23:39the compression of gas being driven very quickly from supernovae,
0:23:39 > 0:23:43or winds from hot stars shocking it, and causing star formation to start.
0:23:43 > 0:23:45Really, just seeing this glowing
0:23:45 > 0:23:47is evidence that this is a dynamic place.
0:23:47 > 0:23:49What's driving those changes?
0:23:49 > 0:23:51The whole structure is driven by this companion
0:23:51 > 0:23:53and the interaction with this companion,
0:23:53 > 0:23:56and the timescales there are hundreds of millions of years.
0:23:56 > 0:23:58So it did its last pass about 100 million years ago,
0:23:58 > 0:24:00and a few hundred million years from now,
0:24:00 > 0:24:03it's going to have merged completely with the Whirlpool Galaxy.
0:24:03 > 0:24:04It's a strange thought, isn't it,
0:24:04 > 0:24:06that it's going to change quite so utterly,
0:24:06 > 0:24:08and this familiar shape will disappear.
0:24:08 > 0:24:10I suppose we're just lucky to be able to see it
0:24:10 > 0:24:12while all of this is going on.
0:24:15 > 0:24:17This is the beauty of modern astronomy.
0:24:18 > 0:24:20By using all the tools available
0:24:20 > 0:24:23to look at M51 in different wavelengths,
0:24:23 > 0:24:26we can reveal the secrets of the Whirlpool Galaxy.
0:24:27 > 0:24:31We can understand its past and its future.
0:24:32 > 0:24:34The optical wavelengths show us light
0:24:34 > 0:24:36from just some of the stars in the galaxy,
0:24:36 > 0:24:39radio reveals the distribution of gas,
0:24:39 > 0:24:43and infrared, the clouds of dust from which the stars are made.
0:24:46 > 0:24:50UV light detects the hot young stars formed from that gas and dust...
0:24:52 > 0:24:53..and X-ray emissions pinpoint
0:24:53 > 0:24:56what happens to those stars when they die.
0:24:57 > 0:25:01And all these processes are concentrated in the spiral arms -
0:25:01 > 0:25:04dense waves of material created by the collision
0:25:04 > 0:25:07between the Whirlpool and its companion galaxy.
0:25:09 > 0:25:12All this information allows us to build a portrait of the galaxy -
0:25:12 > 0:25:17one that reveals it in all of its beauty and complexity.
0:25:19 > 0:25:23And isn't it amazing to think what else might be going on in M51?
0:25:23 > 0:25:27Around those stars, there must be planets.
0:25:28 > 0:25:29But is there life?
0:25:31 > 0:25:34Or even other civilisations looking back at us?
0:25:36 > 0:25:39Thanks to everybody who contributed images for tonight's programme.
0:25:39 > 0:25:41But if you want to do some more astronomy,
0:25:41 > 0:25:43even if you don't have a telescope,
0:25:43 > 0:25:46we're letting you participate in some live research,
0:25:46 > 0:25:50all part of the BBC's Do Something Great season,
0:25:50 > 0:25:53because we want you to become comet hunters.
0:25:54 > 0:25:57We need you to take part in an exciting project,
0:25:57 > 0:26:01searching for a new population of comets hidden in the asteroid belt.
0:26:01 > 0:26:04'It's run by Meg Schwamb.'
0:26:04 > 0:26:05- Hi, Meg.- Hi.
0:26:05 > 0:26:08Now, you're one of the lead scientists on this project,
0:26:08 > 0:26:11but can you tell me, why are you hunting comets?
0:26:11 > 0:26:14Well, we're looking for a unique type of comet,
0:26:14 > 0:26:17and these are really wolves in sheep's clothing,
0:26:17 > 0:26:20so these are asteroids that start looking like comets.
0:26:20 > 0:26:22So when you think of a traditional comet,
0:26:22 > 0:26:25you think of an icy body coming in from the outer solar system
0:26:25 > 0:26:27and heating up, and sublimating its ices off,
0:26:27 > 0:26:30but these are very different. So these are typical, plain,
0:26:30 > 0:26:34ordinary asteroids sitting between Jupiter and Mars,
0:26:34 > 0:26:36and when we occasionally look at these objects,
0:26:36 > 0:26:38we start to see that they have tails.
0:26:38 > 0:26:42Like in this image here, where you see this dust tail.
0:26:42 > 0:26:45Very similar to what you see with a comet, but that's still an asteroid.
0:26:45 > 0:26:47So what do you think is causing this?
0:26:47 > 0:26:49We don't know what the dominant mechanism is,
0:26:49 > 0:26:52but one source is water ice, which shouldn't be there,
0:26:52 > 0:26:54but there could be buried water ice
0:26:54 > 0:26:56underneath the surfaces of some of these asteroids
0:26:56 > 0:26:58that somehow gets exposed.
0:26:58 > 0:27:00So why is this of scientific interest,
0:27:00 > 0:27:01the fact that we have these comets,
0:27:01 > 0:27:03and they could potentially contain water?
0:27:03 > 0:27:06Well, water is important for life,
0:27:06 > 0:27:08and one of the interesting things is to wonder,
0:27:08 > 0:27:09where did Earth's water come from?
0:27:09 > 0:27:11And we don't fully know.
0:27:11 > 0:27:14And potentially, there's now a new source of water ice
0:27:14 > 0:27:16that could have been deposited on the Earth early on,
0:27:16 > 0:27:18and so understanding where these
0:27:18 > 0:27:21main-belt comets originally came from,
0:27:21 > 0:27:23how did they get into the asteroid belt,
0:27:23 > 0:27:25and how many of them are there,
0:27:25 > 0:27:27might tell us about whether or not this could be a source
0:27:27 > 0:27:28for Earth's water.
0:27:28 > 0:27:31So the point of the project is to find many, many more examples,
0:27:31 > 0:27:33hopefully. How can our viewers help?
0:27:33 > 0:27:37Well, you can go to comethunters.org and get started right away.
0:27:37 > 0:27:40All you need is a web browser and your eyes.
0:27:40 > 0:27:42So what does the website look like?
0:27:42 > 0:27:44So, what we're showing is two images of the asteroid
0:27:44 > 0:27:46taken at two different times during the night,
0:27:46 > 0:27:49and what we want you to do is use your eyes to spot the tail.
0:27:49 > 0:27:52Human beings are really good at spotting patterns
0:27:52 > 0:27:56and things that don't match and so we need the eyeballs of anyone
0:27:56 > 0:27:58who wants to look, and for the viewers of The Sky At Night
0:27:58 > 0:28:03to help us because you are better than a machine at finding these.
0:28:03 > 0:28:06This is your chance to be able to help discover a comet.
0:28:06 > 0:28:08Well, you've convinced me. I want to go and find a comet,
0:28:08 > 0:28:10so thank you very much.
0:28:10 > 0:28:13If you want to get involved, the website is on the screen
0:28:13 > 0:28:16right now, so good luck, and happy hunting.
0:28:20 > 0:28:23That's all for this month, but when we come back next month,
0:28:23 > 0:28:27we'll be reporting from Nasa's Jet Propulsion Laboratory
0:28:27 > 0:28:30as the Juno probe arrives at Jupiter.
0:28:31 > 0:28:34- Until then, get outside, get looking up!- Good night.