Y Cosmos: Llwybr Llaethog Y Cosmos
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Transcript
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-Subtitles | 0:00:00 | 0:00:00 | |
-Subtitles - -Subtitles | 0:00:00 | 0:00:02 | |
-Earth - our planet. | 0:00:03 | 0:00:05 | |
-The sun is our closest star. | 0:00:07 | 0:00:09 | |
-And along with -200 billion other stars... | 0:00:13 | 0:00:16 | |
-..we live in a galaxy -called the Milky Way. | 0:00:16 | 0:00:19 | |
-But where did all the stars -come from? | 0:00:22 | 0:00:24 | |
-How was our galaxy created? | 0:00:26 | 0:00:28 | |
-Scientists finally know the answer. | 0:00:33 | 0:00:35 | |
-Our solar system orbits a black hole -at the centre of our galaxy. | 0:00:38 | 0:00:43 | |
-It's responsible -for the death and birth of stars. | 0:00:47 | 0:00:51 | |
-In this programme, -we follow the story... | 0:00:54 | 0:00:57 | |
-..of how the Milky Way was created. | 0:00:58 | 0:01:00 | |
-And we reveal -how it will one day die. | 0:01:01 | 0:01:03 | |
-Subtitles | 0:01:13 | 0:01:15 | |
-The cosmos is full of galaxies - -an array of shapes and sizes. | 0:01:23 | 0:01:28 | |
-There are billions of galaxies -in the universe. | 0:01:32 | 0:01:36 | |
-And one of them is our home - -the Milky Way. | 0:01:36 | 0:01:39 | |
-When you go out on a dark night, you -see what's called the Milky Way... | 0:01:46 | 0:01:51 | |
-..a band of stars -travelling across the night sky. | 0:01:52 | 0:01:57 | |
-It looks like a disc of stars -with spiral arms... | 0:02:02 | 0:02:06 | |
-..and a small, thicker bulge -in the middle. | 0:02:07 | 0:02:10 | |
-I sometimes ask my students -to identify where they live. | 0:02:14 | 0:02:18 | |
-Well, you would say for example, -New York City, US of A... | 0:02:19 | 0:02:24 | |
-..planet earth, -third planet from the sun... | 0:02:24 | 0:02:27 | |
-..and then you would say -the Milky Way galaxy. | 0:02:29 | 0:02:33 | |
-The Milky Way galaxy is our home. | 0:02:37 | 0:02:39 | |
-Looking up at the night sky, we can -see some of the 200 billion stars... | 0:02:41 | 0:02:46 | |
-..that make up the Milky Way. | 0:02:47 | 0:02:49 | |
-From afar, these stars -create a huge spiral galaxy. | 0:02:53 | 0:02:57 | |
-Our sun is just a dot -within one of its enormous arms. | 0:03:01 | 0:03:05 | |
-It's around -100,000 light years across. | 0:03:07 | 0:03:10 | |
-Light takes -approximately 100,000 years... | 0:03:11 | 0:03:15 | |
-..to travel from one side -of the disc to the other. | 0:03:16 | 0:03:20 | |
-Until recently, our massive galaxy -kept a big secret. | 0:03:23 | 0:03:28 | |
-For years, scientists have wondered -how the Milky Way was formed. | 0:03:33 | 0:03:38 | |
-The Milky Way's past -and the story... | 0:03:41 | 0:03:44 | |
-..leads us to where we are -and who we are. | 0:03:44 | 0:03:47 | |
-To reveal -how our galaxy was formed... | 0:03:50 | 0:03:53 | |
-..we must go back -to the beginning of everything. | 0:03:53 | 0:03:57 | |
-Back to the Big Bang... | 0:04:02 | 0:04:05 | |
-..some 13.6 billion years ago. | 0:04:14 | 0:04:16 | |
-There are no stars, no planets -and no galaxies. | 0:04:17 | 0:04:21 | |
-How do we go from the early universe -that's almost featureless... | 0:04:23 | 0:04:28 | |
-..to this complex -and interesting universe? | 0:04:28 | 0:04:31 | |
-The early cosmos -is a thick, uniform soup of gas. | 0:04:35 | 0:04:39 | |
-But then, gravity starts to work. | 0:04:42 | 0:04:46 | |
-After reaching a certain point, -the gas becomes self-gravitating. | 0:04:48 | 0:04:53 | |
-As it starts to smooth out, -there's a little spin on it... | 0:04:54 | 0:04:58 | |
-..and it rotates, like a ball. | 0:04:58 | 0:05:00 | |
-At a certain point, it becomes -dense enough for stars to form. | 0:05:02 | 0:05:06 | |
-Millions of stars burst into life. | 0:05:11 | 0:05:13 | |
-The stars move closer together, -over time, and they start to rotate. | 0:05:19 | 0:05:24 | |
-A galaxy has formed. | 0:05:30 | 0:05:31 | |
-But what's -holding these stars together? | 0:05:34 | 0:05:37 | |
-The answer lies -at the centre of the galaxy. | 0:05:41 | 0:05:45 | |
-We took photographs of the centre -of our galaxy... | 0:05:47 | 0:05:51 | |
-..then we waited a year -and took another photo. | 0:05:51 | 0:05:54 | |
-When you do this, you see how -the stars move around the centre. | 0:05:55 | 0:05:59 | |
-Once you've worked out -the orbits of these stars... | 0:05:59 | 0:06:04 | |
-..you know that the centre contains -something with a vast gravity. | 0:06:07 | 0:06:12 | |
-There is no light -shining in there... | 0:06:14 | 0:06:16 | |
-..so the only thing it could be -is a black hole... | 0:06:17 | 0:06:20 | |
-..with a mass tens of thousands -times bigger than the sun. | 0:06:20 | 0:06:24 | |
-Just as the planets -in our solar system orbit the sun... | 0:06:26 | 0:06:30 | |
-..our solar system -orbits a supermassive black hole... | 0:06:31 | 0:06:37 | |
-..which lies at the centre -of our galaxy. | 0:06:37 | 0:06:41 | |
-Within the Milky Way, scientists -find a supermassive black hole. | 0:06:47 | 0:06:52 | |
-Similar black holes can be found -in other galaxies too. | 0:06:54 | 0:06:58 | |
-There is a direct relationship... | 0:07:03 | 0:07:05 | |
-..between the frequencies -of the rays radiated by galaxies... | 0:07:06 | 0:07:10 | |
-..and the mass of the black hole -at its centre. | 0:07:13 | 0:07:16 | |
-We believe that there are -many black holes in the universe... | 0:07:17 | 0:07:22 | |
-..the largest of which can be found -at the centre of galaxies. | 0:07:22 | 0:07:26 | |
-Somehow, the Milky Way with its -billions of bright stars... | 0:07:28 | 0:07:32 | |
-..is intrinsically linked -to one supermassive black hole. | 0:07:34 | 0:07:38 | |
-It is an object -of fascination and mystery. | 0:07:43 | 0:07:45 | |
-How did it get there? -How did it grow to be so large? | 0:07:45 | 0:07:48 | |
-Is it going to continue to grow? | 0:07:49 | 0:07:51 | |
-To work out -the origins of our galaxy... | 0:07:53 | 0:07:56 | |
-..we must first find out -how it got its black hole. | 0:07:57 | 0:08:01 | |
-In the early universe, -the first stars burst into life. | 0:08:05 | 0:08:10 | |
-But these stars -are nothing like our sun. | 0:08:14 | 0:08:17 | |
-Those first stars -were very, very massive. | 0:08:18 | 0:08:21 | |
-One thing that happens with massive -stars is they explode quickly. | 0:08:22 | 0:08:26 | |
-Before long, the big stars -come to the end of their life... | 0:08:30 | 0:08:34 | |
-..and they explode. | 0:08:34 | 0:08:36 | |
-They exploded as incredibly powerful -supernovae - exploding stars. | 0:08:45 | 0:08:49 | |
-Their cores collapsed -to form black holes. | 0:08:49 | 0:08:52 | |
-These may be the first black holes -to form in the universe. | 0:08:52 | 0:08:55 | |
-Some scientists believe that -a number of smaller black holes... | 0:08:59 | 0:09:03 | |
-..came together... | 0:09:04 | 0:09:05 | |
-..to create the supermassive black -hole at the centre of our galaxy. | 0:09:06 | 0:09:12 | |
-But there's a problem. | 0:09:16 | 0:09:17 | |
-Scientists have found superbright -lights in the very early universe. | 0:09:18 | 0:09:24 | |
-These aren't stars. | 0:09:26 | 0:09:28 | |
-They're called quasars. | 0:09:31 | 0:09:33 | |
-Quasars come from galaxies -that are emitting a lot of energy. | 0:09:34 | 0:09:39 | |
-At first, they look like stars... | 0:09:39 | 0:09:41 | |
-..but once you calculate -how far away they are... | 0:09:41 | 0:09:45 | |
-..you realize they aren't stars. | 0:09:45 | 0:09:47 | |
-Quasars are scattered -across the universe. | 0:09:48 | 0:09:51 | |
-It seems they're part -of every galaxy's formation. | 0:09:52 | 0:09:56 | |
-So a black hole evolves... | 0:09:57 | 0:09:59 | |
-..and starts to swallow up -everything around it. | 0:09:59 | 0:10:03 | |
-This creates a quasar. | 0:10:04 | 0:10:05 | |
-These quasars are brighter -than anything else in the cosmos. | 0:10:11 | 0:10:15 | |
-When you think of the energy created -when a supernova explodes... | 0:10:18 | 0:10:23 | |
-..or when two black holes -fuse together... | 0:10:23 | 0:10:26 | |
-..the energy in quasars is massive. | 0:10:28 | 0:10:30 | |
-We still don't know how they create -all that energy. | 0:10:35 | 0:10:38 | |
-We just know that a lot of energy -comes from this black hole. | 0:10:39 | 0:10:43 | |
-Where these supermassive black holes -came from... | 0:10:44 | 0:10:48 | |
-..is still a matter for conjecture. | 0:10:48 | 0:10:51 | |
-This black hole is far larger than -anything created when a star dies. | 0:10:54 | 0:10:59 | |
-When you consider the mass of -these supermassive black holes... | 0:11:01 | 0:11:05 | |
-..you're talking about millions -of times more mass than our sun. | 0:11:06 | 0:11:10 | |
-A stellar black hole is only five -to ten times the mass of the sun. | 0:11:10 | 0:11:15 | |
-There's a supermassive black hole -at the centre of our Milky Way. | 0:11:21 | 0:11:26 | |
-But where did this black hole -come from? | 0:11:28 | 0:11:31 | |
-Can everything we see around us... | 0:11:33 | 0:11:36 | |
-..have come from the darkest depths -of a black hole? | 0:11:36 | 0:11:40 | |
-. | 0:11:46 | 0:11:47 | |
-Subtitles | 0:11:56 | 0:11:56 | |
-Subtitles - -Subtitles | 0:11:56 | 0:11:58 | |
-Our galaxy - the Milky Way. | 0:12:08 | 0:12:11 | |
-And at the centre of this cluster -of billions of stars... | 0:12:15 | 0:12:19 | |
-..there's a supermassive black hole. | 0:12:19 | 0:12:22 | |
-The idea of black holes -is fairly old. | 0:12:22 | 0:12:25 | |
-They were first mentioned -by a French mathematician... | 0:12:25 | 0:12:29 | |
-..in the 18th century. | 0:12:29 | 0:12:31 | |
-Evidence that these things -really exist in our universe... | 0:12:31 | 0:12:36 | |
-..has only been found recently. | 0:12:36 | 0:12:38 | |
-We now believe -they are a crucial part... | 0:12:43 | 0:12:46 | |
-..of the development of each galaxy, -including ours. | 0:12:46 | 0:12:50 | |
-They've come from a 1930s idea that -nobody actually thought was true... | 0:12:52 | 0:12:57 | |
-..to be a fundamental part of our -understanding of how galaxies form. | 0:12:57 | 0:13:03 | |
-Some scientists believe that -the stars form first... | 0:13:08 | 0:13:12 | |
-..and then create a black hole -at the end of their life. | 0:13:12 | 0:13:16 | |
-But the discovery of quasars -challenges this. | 0:13:21 | 0:13:24 | |
-A quasar is a bright light -that's produced by black holes... | 0:13:24 | 0:13:28 | |
-..at the beginning of the universe. | 0:13:29 | 0:13:31 | |
-But how can a black hole... | 0:13:35 | 0:13:37 | |
-..create something as remarkable -as our Milky Way? | 0:13:38 | 0:13:41 | |
-If we think that galaxies form early -in the history of the universe... | 0:13:45 | 0:13:50 | |
-..perhaps in the first billion years -of the start of the universe... | 0:13:50 | 0:13:55 | |
-..black holes would have formed. | 0:13:56 | 0:13:58 | |
-So they are very old - -much older than our sun. | 0:13:59 | 0:14:03 | |
-Go back to the early days -of the cosmos... | 0:14:05 | 0:14:08 | |
-..to a time before any stars appear. | 0:14:09 | 0:14:11 | |
-Back then, -there were clouds of gas everywhere. | 0:14:15 | 0:14:19 | |
-Over time, gravity begins to -clump the gas together into a ball. | 0:14:21 | 0:14:26 | |
-A star is born. | 0:14:28 | 0:14:30 | |
-But here, too much gas and dust -is piled in. | 0:14:33 | 0:14:36 | |
-Gravity crushes the gas, -making it denser and denser... | 0:14:36 | 0:14:40 | |
-..until it reaches -its breaking point. | 0:14:40 | 0:14:43 | |
-Finally, the gas collapses -so violently... | 0:14:43 | 0:14:46 | |
-..it rips through -the fabric of space. | 0:14:46 | 0:14:49 | |
-A supermassive black hole is born. | 0:14:54 | 0:14:57 | |
-A black hole that's way bigger -than any black hole... | 0:15:04 | 0:15:07 | |
-..that would form -at the end of a star's life. | 0:15:07 | 0:15:11 | |
-This could explain how black holes -and quasars are so huge... | 0:15:11 | 0:15:16 | |
-..so early on in the universe. | 0:15:16 | 0:15:18 | |
-Some believe that black holes -come first, before stars. | 0:15:22 | 0:15:27 | |
-What about galaxies? -How do they form? | 0:15:35 | 0:15:37 | |
-The chicken and egg question is... | 0:15:39 | 0:15:42 | |
-..do black holes cause galaxies -to coalesce around them... | 0:15:42 | 0:15:47 | |
-..or do the galaxies build up and -hit some crucial, critical size... | 0:15:47 | 0:15:51 | |
-..beyond which black holes -must form at their centre? | 0:15:51 | 0:15:55 | |
-The only way to learn about that... | 0:15:55 | 0:15:57 | |
-..is to look out in the universe -and try and find out. | 0:15:57 | 0:16:01 | |
-After years of searching... | 0:16:03 | 0:16:05 | |
-..scientists believe they've found a -young galaxy forming in the cosmos. | 0:16:06 | 0:16:10 | |
-Henize 2-10 -is a perfect opportunity... | 0:16:11 | 0:16:14 | |
-..to observe -how a young galaxy develops. | 0:16:14 | 0:16:17 | |
-Henize 2-10 is a very interesting, -tiny dwarf galaxy. | 0:16:24 | 0:16:28 | |
-Originally, -I was studying this galaxy... | 0:16:29 | 0:16:32 | |
-..because it has -all this star formation going on. | 0:16:32 | 0:16:35 | |
-But when I looked at all the data, -I was sort of shocked and excited. | 0:16:36 | 0:16:40 | |
-I found a supermassive black hole -at the centre of this galaxy. | 0:16:40 | 0:16:44 | |
-We can't see these -black holes directly. | 0:16:47 | 0:16:50 | |
-They only release -a small amount of energy... | 0:16:50 | 0:16:54 | |
-..and any energy that is released -escapes in a particular way. | 0:16:54 | 0:16:58 | |
-The only way we see them... | 0:16:59 | 0:17:02 | |
-..is by observing stars -being swallowed up by them. | 0:17:02 | 0:17:05 | |
-This process has ended -in many galaxies... | 0:17:06 | 0:17:09 | |
-..so we don't see any evidence -of black holes in these situations. | 0:17:09 | 0:17:14 | |
-But we do see energy coming from -black holes in some galaxies... | 0:17:14 | 0:17:18 | |
-..where stars -are being swallowed up. | 0:17:19 | 0:17:21 | |
-Finding a black hole in a galaxy -is nothing new. | 0:17:23 | 0:17:27 | |
-But the real discovery is the size -of this monster black hole. | 0:17:27 | 0:17:31 | |
-Our best estimate for the mass -of the black hole in Henize 2-10... | 0:17:34 | 0:17:38 | |
-..is a million or two solar masses. | 0:17:39 | 0:17:41 | |
-This is comparable to the mass of -the black hole in the Milky Way. | 0:17:41 | 0:17:46 | |
-But the Milky Way -is 100,000 light years across... | 0:17:46 | 0:17:49 | |
-..but Henize 2-10 is only -a few thousand light years across. | 0:17:49 | 0:17:53 | |
-It's amazing to find a black hole -that is so massive... | 0:17:54 | 0:17:58 | |
-..in a small dwarf galaxy. | 0:17:58 | 0:18:00 | |
-Scientists didn't think -such a tiny galaxy... | 0:18:03 | 0:18:06 | |
-..could contain -such a large black hole. | 0:18:07 | 0:18:09 | |
-It's a groundbreaking discovery. | 0:18:17 | 0:18:19 | |
-In Henize 2-10, the black hole -is more developed than the galaxy. | 0:18:19 | 0:18:24 | |
-It suggests the black hole -came first, then the galaxy. | 0:18:25 | 0:18:29 | |
-Henize 2-10 could be a blueprint -for how all galaxies first form... | 0:18:38 | 0:18:42 | |
-..including our own galaxy, -the Milky Way. | 0:18:44 | 0:18:47 | |
-It's fascinating. | 0:18:48 | 0:18:50 | |
-It could be evidence -that black holes form first... | 0:18:50 | 0:18:53 | |
-..then galaxies form around them. | 0:18:53 | 0:18:55 | |
-Everything we see in our sky - -the stars and the planets... | 0:18:59 | 0:19:03 | |
-..may all have started -as a supermassive black hole. | 0:19:04 | 0:19:08 | |
-But how can something -so dark and frightening... | 0:19:14 | 0:19:18 | |
-..create something -as glorious as the Milky Way? | 0:19:18 | 0:19:22 | |
-Where did the stars come from? | 0:19:23 | 0:19:25 | |
-. | 0:19:28 | 0:19:29 | |
-Subtitles | 0:19:38 | 0:19:38 | |
-Subtitles - -Subtitles | 0:19:38 | 0:19:40 | |
-Some scientists now believe -that our galaxy, the Milky Way... | 0:19:53 | 0:19:58 | |
-..was created -from a supermassive black hole. | 0:19:58 | 0:20:01 | |
-But how can something -so dark and frightening... | 0:20:05 | 0:20:08 | |
-..create billions of bright stars? | 0:20:09 | 0:20:11 | |
-Because black holes -aren't just black - far from it. | 0:20:22 | 0:20:26 | |
-The name comes from the idea -that nothing escapes a black hole. | 0:20:32 | 0:20:38 | |
-But even though -a black hole is a dark place... | 0:20:43 | 0:20:46 | |
-..the gases and matter -around the black holes thrive. | 0:20:47 | 0:20:52 | |
-Quasars prove that -these massive black holes... | 0:20:58 | 0:21:02 | |
-..throw out more light -than whole galaxies. | 0:21:02 | 0:21:05 | |
-Black holes -don't just swallow matter. | 0:21:07 | 0:21:10 | |
-They also spit it out. | 0:21:10 | 0:21:11 | |
-Some matter leaks from around -the edges of these black holes. | 0:21:13 | 0:21:19 | |
-But more often than not... | 0:21:19 | 0:21:21 | |
-..once matter is sucked -into a black hole... | 0:21:22 | 0:21:25 | |
-..it stays there -for the lifespan of the galaxy. | 0:21:25 | 0:21:29 | |
-In the early universe, -the supermassive black hole... | 0:21:34 | 0:21:38 | |
-..starts to feast -on the gas and dust around it. | 0:21:38 | 0:21:42 | |
-But when it eats too much, -it generates so much energy... | 0:21:46 | 0:21:50 | |
-..that even the black hole's gravity -can't contain it. | 0:21:50 | 0:21:54 | |
-Suddenly, highly energized atoms -and light is thrown from the core. | 0:21:59 | 0:22:04 | |
-How do stars form -around such violence? | 0:22:10 | 0:22:13 | |
-Scientists have found a black hole -which may hold the key. | 0:22:16 | 0:22:20 | |
-A naked black hole. | 0:22:21 | 0:22:24 | |
-A naked black hole sits on its own -in the universe... | 0:22:26 | 0:22:29 | |
-..without stellar matter around it. | 0:22:30 | 0:22:33 | |
-It's very unusual. | 0:22:33 | 0:22:34 | |
-This naked black hole -has either escaped from a galaxy... | 0:22:36 | 0:22:40 | |
-..or eaten its host galaxy. | 0:22:40 | 0:22:42 | |
-It begins to eat -any gas that surrounds it... | 0:22:43 | 0:22:46 | |
-..and, as a result, -it generates emissions. | 0:22:47 | 0:22:50 | |
-This black hole emits -a huge jet of light from its centre. | 0:22:51 | 0:22:56 | |
-This jet is smashing into dust -and gas in its neighbouring galaxy. | 0:22:58 | 0:23:03 | |
-Rather than destroy that galaxy, -it's helping to build it. | 0:23:04 | 0:23:09 | |
-There's a lot of indirect evidence -about the behaviour of black holes. | 0:23:11 | 0:23:16 | |
-We see a gravitational effect... | 0:23:17 | 0:23:19 | |
-..as they draw matter -from other galaxies. | 0:23:19 | 0:23:22 | |
-As our sun and moon -create tides on earth... | 0:23:22 | 0:23:26 | |
-..we see a tidal effect -between a black hole and galaxies. | 0:23:26 | 0:23:30 | |
-This colossal jet is the spark -needed to create billions of stars. | 0:23:30 | 0:23:35 | |
-The black hole -is emitting radiation. | 0:23:36 | 0:23:38 | |
-When this radiation runs into -all the gas in the galaxy... | 0:23:39 | 0:23:43 | |
-..gas clumps together -and new stars get made. | 0:23:43 | 0:23:46 | |
-Direct evidence -that black holes can create stars. | 0:23:49 | 0:23:53 | |
-After these stars are created, they -start to orbit the black hole... | 0:24:00 | 0:24:05 | |
-..building the galaxy. | 0:24:06 | 0:24:08 | |
-It's possible that the black hole... | 0:24:14 | 0:24:17 | |
-..could have created -many of the stars we see today... | 0:24:18 | 0:24:21 | |
-..including our closest star - -the sun. | 0:24:22 | 0:24:25 | |
-It's amazing that black holes -existed as theoretical constructs... | 0:24:29 | 0:24:33 | |
-..that many physicists involved in -developing them didn't believe in. | 0:24:33 | 0:24:37 | |
-Now we see that even perhaps our -very existence depends upon them. | 0:24:38 | 0:24:42 | |
-They've gone -from objects in our imagination... | 0:24:42 | 0:24:46 | |
-..to objects -on which our life depends. | 0:24:46 | 0:24:49 | |
-The first stars of the Milky Way... | 0:24:56 | 0:24:59 | |
-..sparked into life -13 billion years ago. | 0:24:59 | 0:25:02 | |
-The galaxy starts to take shape. | 0:25:06 | 0:25:08 | |
-And in the early cosmos, -the Milky Way is not alone. | 0:25:12 | 0:25:17 | |
-Before long, -it does something remarkable. | 0:25:20 | 0:25:23 | |
-It becomes a cannibal -and begins to eat other galaxies. | 0:25:23 | 0:25:27 | |
-From time to time, galaxies -can move closer to each other. | 0:25:34 | 0:25:38 | |
-When they do come together... | 0:25:41 | 0:25:44 | |
-..the bigger of the two galaxies -starts to eat the other. | 0:25:44 | 0:25:48 | |
-This in turn -creates one vast galaxy. | 0:25:49 | 0:25:52 | |
-We have evidence that the Milky Way -has eaten several other galaxies. | 0:25:56 | 0:26:01 | |
-The stream of stars -we see in the night sky... | 0:26:03 | 0:26:06 | |
-..is the remnants of a galaxy -torn apart by the Milky Way. | 0:26:06 | 0:26:10 | |
-It happens throughout the universe. -Bigger galaxies eat smaller ones. | 0:26:11 | 0:26:16 | |
-The infant universe -is like a war zone. | 0:26:19 | 0:26:22 | |
-Dwarf galaxies battle each other... | 0:26:23 | 0:26:26 | |
-..and join forces -to create larger galaxies. | 0:26:26 | 0:26:29 | |
-To understand how a galaxy is formed -from this chaos... | 0:26:36 | 0:26:40 | |
-..each skater represents a -small galaxy in the infant universe. | 0:26:41 | 0:26:46 | |
-The process of a big galaxy -swallowing a smaller one... | 0:26:48 | 0:26:52 | |
-..isn't like Pac-Man, -gobbling it up. | 0:26:53 | 0:26:56 | |
-It pulls the galaxy apart -by using the tidal force. | 0:26:57 | 0:27:01 | |
-This breaks down the smaller galaxy. | 0:27:02 | 0:27:05 | |
-All that remains -are strings of stars. | 0:27:12 | 0:27:15 | |
-Smaller galaxies start to orbit -around the Milky Way... | 0:27:18 | 0:27:22 | |
-..and slowly they're dismantled -by our galaxy. | 0:27:23 | 0:27:26 | |
-Dwarf galaxies -smash into each other. | 0:27:26 | 0:27:29 | |
-The larger one always wins. | 0:27:30 | 0:27:32 | |
-All this stuff slams together. -Stars are thrown all over the place. | 0:27:33 | 0:27:37 | |
-They strip mass from each other. -They collide. | 0:27:37 | 0:27:40 | |
-And any small objects in-between -get eaten up. | 0:27:41 | 0:27:44 | |
-The game lasts -for over a billion years. | 0:27:46 | 0:27:49 | |
-In the chaos of collisions, -the Milky Way grows bigger. | 0:27:55 | 0:27:59 | |
-But it's still hungry. | 0:28:05 | 0:28:06 | |
-Even this second - -it's eating another galaxy. | 0:28:08 | 0:28:12 | |
-A lot cannibalism goes on -in the universe. | 0:28:14 | 0:28:17 | |
-The Milky Way is now devouring -a dwarf galaxy... | 0:28:18 | 0:28:21 | |
-..which orbits our galaxy. | 0:28:21 | 0:28:23 | |
-That dwarf galaxy -is called Sagittarius... | 0:28:24 | 0:28:28 | |
-..and it's currently -being eaten by the Milky Way. | 0:28:29 | 0:28:32 | |
-But in this battle with Sagittarius, -the Milky Way doesn't go unscathed. | 0:28:40 | 0:28:45 | |
-You can see different populations -of stars in the sky. | 0:28:47 | 0:28:50 | |
-One population -is original to the Milky Way... | 0:28:51 | 0:28:54 | |
-..but others -have come from other galaxies. | 0:28:55 | 0:28:58 | |
-So you can see many stars -which weren't born in the Milky Way. | 0:28:59 | 0:29:03 | |
-We're not sure how it affects us. | 0:29:04 | 0:29:07 | |
-It's possible this will cause us -to travel further out in our galaxy. | 0:29:09 | 0:29:14 | |
-Away from the centre. | 0:29:15 | 0:29:16 | |
-But it could do the opposite, -and move us closer to the centre. | 0:29:18 | 0:29:23 | |
-We don't know. | 0:29:24 | 0:29:26 | |
-Many questions remain unanswered. | 0:29:27 | 0:29:29 | |
-All that eating -builds and sculpts our galaxy. | 0:29:33 | 0:29:37 | |
-Some scientists say it repositioned -the stars in the Milky Way... | 0:29:41 | 0:29:45 | |
-..including our star - the sun. | 0:29:47 | 0:29:50 | |
-It's possible that the sun was born -closer to the middle of the galaxy. | 0:29:51 | 0:29:55 | |
-It migrated to the suburbs over the -course of a couple of billion years. | 0:29:55 | 0:30:00 | |
-It's possible that, -when Sagittarius hit the disc... | 0:30:00 | 0:30:03 | |
-..it created some spiral arms that -then allowed the sun to migrate out. | 0:30:03 | 0:30:07 | |
-The sun is now a long way away... | 0:30:11 | 0:30:13 | |
-..from the supermassive black hole -at the galaxy's centre. | 0:30:13 | 0:30:18 | |
-That's good news for life on earth. | 0:30:18 | 0:30:21 | |
-The black hole -eats everything around it... | 0:30:25 | 0:30:28 | |
-..so we're lucky to be so far away -from the centre of our galaxy. | 0:30:28 | 0:30:32 | |
-It'll take a long time to eat -everything, so we're safe here. | 0:30:33 | 0:30:38 | |
-By eating smaller galaxies, -the Milky Way continues to grow. | 0:30:42 | 0:30:47 | |
-And throughout the cosmos... | 0:30:49 | 0:30:51 | |
-..it's the same story -for every galaxy. | 0:30:51 | 0:30:54 | |
-But each collision is different, -making each galaxy unique. | 0:30:57 | 0:31:01 | |
-Galaxies come in -many shapes and sizes. | 0:31:03 | 0:31:06 | |
-Some are very small and shapeless. | 0:31:06 | 0:31:08 | |
-Others are huge elliptical galaxies -like giant cotton balls. | 0:31:08 | 0:31:12 | |
-Some are like our galaxy... | 0:31:12 | 0:31:14 | |
-..flat discs with a central bulge -and sweeping spiral arms. | 0:31:14 | 0:31:18 | |
-We think those big galaxies -got so big by cannibalizing. | 0:31:18 | 0:31:22 | |
-By eating their brethren. | 0:31:22 | 0:31:24 | |
-The most common type of galaxy -are spiral galaxies... | 0:31:29 | 0:31:33 | |
-..and the Whirlpool Galaxies. | 0:31:33 | 0:31:36 | |
-Some are discs, -like the Sombrero Galaxy... | 0:31:38 | 0:31:41 | |
-..with a circle of gas and dust. | 0:31:41 | 0:31:44 | |
-Some, like the golden M87, are among -the oldest galaxies in the universe. | 0:31:45 | 0:31:50 | |
-There are hundreds of billions -of galaxies in the universe. | 0:31:54 | 0:31:59 | |
-Each one started small -and grew by devouring others. | 0:31:59 | 0:32:03 | |
-And our galaxy -continues to grow too. | 0:32:06 | 0:32:10 | |
-Like a huge cannibal... | 0:32:10 | 0:32:12 | |
-..our galaxy has devoured other -galaxies over billions of years. | 0:32:14 | 0:32:19 | |
-In turn, this created the perfect -conditions for us here on earth. | 0:32:21 | 0:32:27 | |
-But can anything stop the juggernaut -of our cannibal galaxy? | 0:32:28 | 0:32:34 | |
-Recently, scientists have found -hardly any new stars. | 0:32:35 | 0:32:40 | |
-Something is preventing our galaxy -from growing. | 0:32:41 | 0:32:45 | |
-What is it? | 0:32:45 | 0:32:47 | |
-. | 0:32:53 | 0:32:54 | |
-Subtitles | 0:33:05 | 0:33:05 | |
-Subtitles - -Subtitles | 0:33:05 | 0:33:07 | |
-Our galaxy - the Milky Way - -is one of the largest in the cosmos. | 0:33:18 | 0:33:23 | |
-It's now home to billions of stars. | 0:33:25 | 0:33:28 | |
-It contains 1,000,000,000 stars -and that's a lot of stars! | 0:33:32 | 0:33:36 | |
-It's a spiral galaxy. | 0:33:37 | 0:33:40 | |
-We believe the spiral galaxies were -formed by eating smaller galaxies. | 0:33:41 | 0:33:47 | |
-The best theory we have -about how galaxies formed... | 0:33:49 | 0:33:52 | |
-..when the cosmos was very young... | 0:33:53 | 0:33:56 | |
-..is that dwarf galaxies form first. | 0:33:59 | 0:34:02 | |
-Then, a cloud of gas and dust -forms the first stars. | 0:34:03 | 0:34:08 | |
-They started out -as dwarf galaxies... | 0:34:11 | 0:34:14 | |
-..and with time, -dwarf galaxies united... | 0:34:14 | 0:34:17 | |
-..to create the giant galaxies -we see today. | 0:34:17 | 0:34:21 | |
-In the past, the Milky Way was -bursting with star formation. | 0:34:22 | 0:34:27 | |
-So what's changed? | 0:34:27 | 0:34:28 | |
-In the early universe... | 0:34:37 | 0:34:39 | |
-..our black hole -may have sparked stars into life. | 0:34:39 | 0:34:43 | |
-But now, that same black hole -may be stopping stars from forming. | 0:34:43 | 0:34:48 | |
-To find out why... | 0:34:52 | 0:34:53 | |
-..scientists must examine the -Milky Way's supermassive black hole. | 0:34:53 | 0:34:58 | |
-And that's exactly what they did, -thanks to NASA's latest telescope. | 0:34:59 | 0:35:04 | |
-Fiona Harrison -runs the NuSTAR mission. | 0:35:07 | 0:35:11 | |
-NuSTAR can see -the highest energy X-rays... | 0:35:14 | 0:35:17 | |
-..that can penetrate dust and gas. | 0:35:17 | 0:35:20 | |
-It enables us to have this view -of this black hole. | 0:35:20 | 0:35:24 | |
-Scientists didn't have to wait long -to see the black hole in action. | 0:35:26 | 0:35:32 | |
-We looked and about six hours -after we looked... | 0:35:38 | 0:35:41 | |
-..we saw the black hole -get 100 times brighter. | 0:35:41 | 0:35:45 | |
-How long did that last? | 0:35:46 | 0:35:48 | |
-Only a few hours, -then it faded back into oblivion. | 0:35:48 | 0:35:52 | |
-But this event -was what we were looking for. | 0:35:52 | 0:35:55 | |
-We were all amazed. -There were cheers in the room. | 0:35:56 | 0:36:00 | |
-It was one of -the most exciting moments... | 0:36:01 | 0:36:04 | |
-..and so early on -in the mission too. | 0:36:04 | 0:36:06 | |
-It's direct evidence that -our black hole is still active... | 0:36:08 | 0:36:12 | |
-..and still has the muscle -to control the galaxy. | 0:36:13 | 0:36:17 | |
-And surrounding the black hole... | 0:36:17 | 0:36:20 | |
-..scientists discover -remnants of past violence. | 0:36:20 | 0:36:24 | |
-Huge lobes of old material hang -above and below the Milky Way disc. | 0:36:32 | 0:36:37 | |
-These are scars -from the black hole's violent past. | 0:36:44 | 0:36:48 | |
-The black hole's power -is revealed... | 0:36:53 | 0:36:56 | |
-..when it lights up a disc of gas -and dust which spins around it. | 0:36:56 | 0:37:00 | |
-You can see the gases -collecting into a stream... | 0:37:06 | 0:37:09 | |
-..flowing towards the black hole. | 0:37:09 | 0:37:12 | |
-They gather into a disc -and get hotter... | 0:37:12 | 0:37:15 | |
-..before disappearing -into the black hole. | 0:37:15 | 0:37:20 | |
-NuSTAR detects that gas around -the black hole is heating up... | 0:37:23 | 0:37:27 | |
-..to 180 million degrees Fahrenheit. | 0:37:28 | 0:37:30 | |
-This super heated gas -is bad news for star formation. | 0:37:34 | 0:37:38 | |
-Gas has to get cold -for it to form stars. | 0:37:41 | 0:37:43 | |
-That's because the gas -has to get very, very dense... | 0:37:44 | 0:37:47 | |
-..so it can collapse into something -with nuclear fusion in its core. | 0:37:47 | 0:37:51 | |
-So in regions around black holes, -because they're so hot... | 0:37:52 | 0:37:55 | |
-..they heat up gas around them... | 0:37:56 | 0:37:57 | |
-..limiting the ability -for that gas to turn into stars. | 0:37:58 | 0:38:01 | |
-Star formation shuts down. | 0:38:07 | 0:38:09 | |
-Before this... | 0:38:14 | 0:38:16 | |
-..the black hole was responsible -for gathering gases and dust... | 0:38:16 | 0:38:20 | |
-..igniting the cloud -and forming stars. | 0:38:22 | 0:38:25 | |
-But now that's changed. | 0:38:29 | 0:38:30 | |
-The heat generated by the black hole -blows away the cloud of gases. | 0:38:31 | 0:38:35 | |
-The black hole regulates the number -of stars created in a galaxy. | 0:38:39 | 0:38:44 | |
-There's a relationship -between the size of a black hole... | 0:38:48 | 0:38:52 | |
-..and the size of the galaxy itself. | 0:38:54 | 0:38:57 | |
-This is a recent discovery. | 0:39:01 | 0:39:03 | |
-The size of the black hole... | 0:39:05 | 0:39:08 | |
-..affects the position of our galaxy -in the family of galaxies. | 0:39:10 | 0:39:15 | |
-We've only known about this -symbiotic relationship for 15 years. | 0:39:21 | 0:39:27 | |
-It gives us a clearer picture -of galaxy formation. | 0:39:27 | 0:39:30 | |
-Scientists are still not sure why -our black hole behaves in this way. | 0:39:35 | 0:39:40 | |
-All we know is that this regulation -might be essential for us. | 0:39:42 | 0:39:47 | |
-Looking up at our night sky... | 0:39:55 | 0:39:57 | |
-..it looks like our galaxy -is unchanging, eternal. | 0:39:58 | 0:40:02 | |
-But in the universe, -nothing lasts forever. | 0:40:05 | 0:40:09 | |
-So what does the future hold -for the Milky Way? | 0:40:12 | 0:40:15 | |
-It's difficult to predict because -our time on earth is so short... | 0:40:18 | 0:40:23 | |
-..compared to -the timescales involved. | 0:40:23 | 0:40:27 | |
-The Milky Way -is setting its own course. | 0:40:29 | 0:40:32 | |
-If other galaxies come too close, -they'll be swallowed. | 0:40:32 | 0:40:36 | |
-If the Milky Way veers too close to -a huge galaxy, we'll be swallowed. | 0:40:36 | 0:40:41 | |
-This process -would take billions of years. | 0:40:42 | 0:40:45 | |
-Within 5 billion years, -the Andromeda Galaxy will hit us. | 0:40:49 | 0:40:53 | |
-The Milky Way is used to -bumping into smaller galaxies... | 0:40:56 | 0:41:00 | |
-..and swallowing them -in order to grow. | 0:41:00 | 0:41:03 | |
-But Andromeda is huge. | 0:41:07 | 0:41:08 | |
-As Andromeda approaches, it will -appear larger in the night sky. | 0:41:13 | 0:41:18 | |
-When it approaches us, -you'll see many more stars. | 0:41:19 | 0:41:23 | |
-At present, we can see a few -thousand stars with the naked eye. | 0:41:26 | 0:41:32 | |
-As Andromeda gets closer, the -numbers would increase dramatically. | 0:41:33 | 0:41:38 | |
-As the collision nears, -our night sky changes completely. | 0:41:42 | 0:41:46 | |
-It would be an awesome sight. | 0:41:50 | 0:41:52 | |
-But it would have a detrimental -effect on both galaxies. | 0:41:57 | 0:42:01 | |
-Andromeda is bigger than our galaxy, -so we may come off worse. | 0:42:01 | 0:42:06 | |
-As it nears, Andromeda grows -larger and larger in our sky. | 0:42:10 | 0:42:15 | |
-Finally, the galaxies -smash into each other. | 0:42:15 | 0:42:18 | |
-Stars are torn from their orbits. | 0:42:18 | 0:42:21 | |
-What's interesting about the event -is that the stars don't collide. | 0:42:24 | 0:42:30 | |
-Stars are extremely small -compared to the galaxy. | 0:42:31 | 0:42:35 | |
-It's like two crowds of people -running past each other. | 0:42:36 | 0:42:41 | |
-Where the two galaxies collide, -a huge explosion creates new stars. | 0:42:46 | 0:42:52 | |
-One half of the night sky... | 0:42:53 | 0:42:55 | |
-..has a huge number of stars. | 0:42:56 | 0:42:58 | |
-The other half is as it is now. | 0:42:59 | 0:43:01 | |
-There will be thousands of stars -in the sky | 0:43:02 | 0:43:05 | |
-What an amazing sight! | 0:43:05 | 0:43:07 | |
-The night sky will be full of stars. | 0:43:11 | 0:43:13 | |
-Colourful gas clouds -will erupt like fireworks. | 0:43:13 | 0:43:18 | |
-It will be great! | 0:43:19 | 0:43:21 | |
-This is the beginning of the end. | 0:43:26 | 0:43:28 | |
-The Milky Way and Andromeda -will rip each other apart. | 0:43:31 | 0:43:36 | |
-Some people believe -that elliptical galaxies form... | 0:43:42 | 0:43:46 | |
-..when two spiral galaxies -come together. | 0:43:47 | 0:43:51 | |
-The pattern of stars in the disc -is destroyed... | 0:43:52 | 0:43:56 | |
-..by all the gravity that's created -when two galaxies collide. | 0:43:56 | 0:44:01 | |
-Interestingly, elliptical galaxies -don't contain many new stars. | 0:44:01 | 0:44:06 | |
-New stars are created all the time -in spiral galaxies... | 0:44:07 | 0:44:11 | |
-..but few are created -in elliptical galaxies. | 0:44:11 | 0:44:15 | |
-Elliptical galaxies have no -disc of gas at their centre. | 0:44:16 | 0:44:21 | |
-They suffered so much damage when -the two galaxies came together... | 0:44:25 | 0:44:30 | |
-..everything was destroyed. | 0:44:31 | 0:44:33 | |
-When two galaxies collide, -like us and Andromeda... | 0:44:40 | 0:44:43 | |
-..thousands of stars -are created within a year. | 0:44:44 | 0:44:47 | |
-All the gases coalesce -to create a new generation of stars. | 0:44:48 | 0:44:53 | |
-The Milky Way and Andromeda -have gone. | 0:45:00 | 0:45:03 | |
-In their place, a new galaxy. | 0:45:03 | 0:45:05 | |
-But it's not over. | 0:45:10 | 0:45:12 | |
-Their two supermassive black holes -hurtle towards each other. | 0:45:13 | 0:45:18 | |
-Those black holes -will most probably join together. | 0:45:21 | 0:45:26 | |
-They have so much mass... | 0:45:26 | 0:45:28 | |
-..their huge gravitational force -will draw them towards each other. | 0:45:28 | 0:45:33 | |
-The result is an even bigger -supermassive black hole. | 0:45:34 | 0:45:38 | |
-It will be fantastic. | 0:45:42 | 0:45:43 | |
-Two fireballs -rotating around each other... | 0:45:44 | 0:45:47 | |
-..until the black holes at the -centre of them finally coalesce. | 0:45:48 | 0:45:53 | |
-The black holes merge... | 0:45:55 | 0:45:57 | |
-..forming a huge supermassive black -hole to rule over a new galaxy. | 0:45:58 | 0:46:03 | |
-But this new galaxy -is already dying. | 0:46:07 | 0:46:09 | |
-Over billions of years, -the stars slowly die out. | 0:46:10 | 0:46:14 | |
-There's no fuel left to create -new stars and replace them. | 0:46:16 | 0:46:20 | |
-The black hole absorbs all the -matter at the centre of the galaxy. | 0:46:24 | 0:46:29 | |
-We also believe that black holes -can influence... | 0:46:32 | 0:46:36 | |
-..the formation of new stars. | 0:46:36 | 0:46:38 | |
-Black holes are responsible -for the death and birth of stars. | 0:46:39 | 0:46:43 | |
-Our galaxy, -with its billions of bright stars... | 0:46:47 | 0:46:51 | |
-..has been created -from a supermassive black hole. | 0:46:51 | 0:46:55 | |
-It's ruled over our Milky Way -from the start. | 0:46:56 | 0:46:59 | |
-And one day, everything will return -to the place it all began. | 0:47:00 | 0:47:05 | |
-Back into a supermassive black hole. | 0:47:06 | 0:47:09 | |
-S4C subtitles by Eirlys A Jones | 0:47:37 | 0:47:40 | |
-. | 0:47:40 | 0:47:41 |