0:00:05 > 0:00:10Each night, after the sun sets, sit back,
0:00:10 > 0:00:16look up and you can witness an epic drama playing above our heads.
0:00:19 > 0:00:22One involving a cast of billions.
0:00:26 > 0:00:27The stars.
0:00:28 > 0:00:32Every one with its own story to tell.
0:00:34 > 0:00:37There are old Red Giants,
0:00:37 > 0:00:40so puffed up they're coming apart at the seams.
0:00:42 > 0:00:46Supernovae, the most spectacular firework displays in the universe.
0:00:47 > 0:00:50Mysterious black holes,
0:00:50 > 0:00:54stellar tombstones that we are only beginning to understand.
0:01:00 > 0:01:05And when the sun rises again, we can see a star in the prime of its life.
0:01:11 > 0:01:13Unravelling the life and times
0:01:13 > 0:01:16of these stars has revealed extraordinary secrets
0:01:16 > 0:01:20about the universe and our own place within it.
0:01:25 > 0:01:30At the tale's end lie clues to one of the biggest mysteries in science.
0:01:36 > 0:01:38This is the story of the stars.
0:01:54 > 0:01:58For thousands of years, we've told stories about the sun and stars,
0:01:58 > 0:02:02populating the heavens with gods and giants.
0:02:05 > 0:02:08Ancient Egyptians worshipped the sun, calling it Ra.
0:02:11 > 0:02:14Orion the Hunter strode the heavens.
0:02:18 > 0:02:21Stars and whole constellations were characters
0:02:21 > 0:02:25that moved above our head with the changing seasons.
0:02:30 > 0:02:32In the 20th century,
0:02:32 > 0:02:36modern astronomers discovered that, in a way, our instincts were right.
0:02:39 > 0:02:44The stars in the twinkling night sky aren't all the same.
0:02:46 > 0:02:49Powerful telescopes have revealed the sheer variety
0:02:49 > 0:02:51of their brightnesses and colours.
0:02:53 > 0:02:58And in that diversity, scientists have discovered a new story.
0:02:59 > 0:03:04When we see the stars in the sky, they look all different,
0:03:04 > 0:03:08but once we put them together in order of colour,
0:03:08 > 0:03:12in order of brightness, this is where we get, some kind of sense
0:03:12 > 0:03:16of order, and this is what makes the whole story so interesting.
0:03:18 > 0:03:23Dr Francisco Diego has devoted his career to understanding the stars,
0:03:23 > 0:03:27their individual natures
0:03:27 > 0:03:30and the connections that can be found between them.
0:03:34 > 0:03:40For example, this is Arcturus, a very bright, red star that goes here.
0:03:41 > 0:03:45This is Beta Centauri, which is a very hot, blue star.
0:03:47 > 0:03:50The sun is at a medium temperature.
0:03:50 > 0:03:52It has to go more or less in-between.
0:03:57 > 0:04:00By plotting stars according to their characteristics,
0:04:00 > 0:04:02astronomers uncovered a pattern...
0:04:05 > 0:04:07..one that reveals different types of star,
0:04:07 > 0:04:12each with its own personality and contribution to the universe.
0:04:15 > 0:04:19But the patterns are a clue to something more fundamental.
0:04:22 > 0:04:26This is telling us that, as time goes on,
0:04:26 > 0:04:32the stars themselves start to change and to develop, to evolve.
0:04:32 > 0:04:34And then we have a pattern here,
0:04:34 > 0:04:37a kind of cycle, the lifecycle of stars.
0:04:40 > 0:04:44In discovering the seven ages of the stars, scientists have uncovered
0:04:44 > 0:04:49the story of the universe, and, just like for us,
0:04:49 > 0:04:52it all begins with birth.
0:05:08 > 0:05:11One of the most gazed at patches of sky throughout history
0:05:11 > 0:05:14is the one containing a cluster called the Pleiades.
0:05:23 > 0:05:26But the ancient astronomers didn't know that
0:05:26 > 0:05:28the Pleiades hold a secret...
0:05:31 > 0:05:33..one that modern astronomers have revealed.
0:05:51 > 0:05:55This cluster, the Pleiades, mentioned by Homer in the Odyssey,
0:05:55 > 0:05:59they appear in the Bible and in some of the codices by the Aztecs
0:05:59 > 0:06:00and the Maya.
0:06:01 > 0:06:05But the interesting thing is that the Pleiades are so young
0:06:05 > 0:06:09that early dinosaurs never saw them,
0:06:09 > 0:06:12because at that time, the Pleiades hadn't been formed yet.
0:06:17 > 0:06:20At 100 million years old, they are like baby stars,
0:06:20 > 0:06:23very, very young stars.
0:06:24 > 0:06:27Some of the youngest stars that we can see in the sky.
0:06:32 > 0:06:35A star is being born somewhere every day.
0:06:40 > 0:06:43Each time, it's one of the most magical events in the cosmos.
0:06:48 > 0:06:51One that requires mighty forces of nature.
0:06:55 > 0:06:59And to set the process going, just an element of chance.
0:07:03 > 0:07:08The tale starts in the cold, dark clouds of dust and gas
0:07:08 > 0:07:10that lurk in deep space...
0:07:12 > 0:07:16..and that have filled the mind and imagination
0:07:16 > 0:07:19of Professor Serena Viti throughout her career
0:07:19 > 0:07:21studying the birth of stars.
0:07:25 > 0:07:27These clouds are really vast.
0:07:27 > 0:07:30They can be up to 300 light years across.
0:07:30 > 0:07:33And many stars form there, which is why
0:07:33 > 0:07:36we call sometimes these clouds stellar nurseries.
0:07:36 > 0:07:40Many regions within these clouds can stay like that for ever,
0:07:40 > 0:07:43for millions of years, until something happens, a trigger,
0:07:43 > 0:07:45and then a star forms.
0:07:47 > 0:07:51The trigger for such a monumental event doesn't have to be much.
0:07:52 > 0:07:55Two clouds can bump as they pass,
0:07:55 > 0:08:00or a distant cosmic event can send a shockwave,
0:08:00 > 0:08:03just something to give the cloud a squeeze.
0:08:05 > 0:08:09All you need is a little bit of pressure to allow the gas
0:08:09 > 0:08:12to be dense enough for gravity to take over and collapse to start.
0:08:15 > 0:08:19The particles of dust and gas that had been quietly floating in space
0:08:19 > 0:08:21now start being pulled together.
0:08:25 > 0:08:28Gravitational attraction draws them towards each other,
0:08:28 > 0:08:30faster and faster.
0:08:34 > 0:08:37As the collapse continues to happen, the gas and the dust
0:08:37 > 0:08:40will fall into the centre and they will become denser and denser,
0:08:40 > 0:08:44and the centre of the cloud will become hotter and hotter.
0:08:48 > 0:08:52The laws of nature mean that when matter gets compressed, it heats up.
0:08:56 > 0:09:01Over millions of years, the protostar grows,
0:09:01 > 0:09:04increasing the pressure and heat in its core,
0:09:04 > 0:09:08until, finally, it reaches a critical temperature.
0:09:10 > 0:09:12About 15 million degrees,
0:09:12 > 0:09:16and a fundamental process will start in the core of the embryonic star.
0:09:18 > 0:09:22Almost in a flash, the core of the star,
0:09:22 > 0:09:26like our own sun's once did, dazzlingly lights up.
0:09:31 > 0:09:32A star is born.
0:09:41 > 0:09:44If you look at the night sky and you look up at a twinkling star,
0:09:44 > 0:09:46you think of this little pinpoint of light,
0:09:46 > 0:09:49almost like a Christmas tree light.
0:09:49 > 0:09:51And, actually, what it is
0:09:51 > 0:09:54is this incredible cauldron of energy being released.
0:09:57 > 0:10:00To witness what's going on inside these points of light,
0:10:00 > 0:10:02you have to go somewhere closer to home.
0:10:05 > 0:10:10To the Joint European Torus, JET, in Oxfordshire.
0:10:13 > 0:10:18Where they study what happens in the heart of stars,
0:10:18 > 0:10:22the hydrogen fusion that brings them to life.
0:10:26 > 0:10:28What we're trying to do in JET is essentially to make
0:10:28 > 0:10:31a little star on Earth.
0:10:31 > 0:10:34We're trying to create the conditions necessary
0:10:34 > 0:10:41to create the fusion of hydrogen, and with it, to create
0:10:41 > 0:10:43copious amounts of energy, lots and lots of energy.
0:10:45 > 0:10:47If you're going to attempt to create a star on Earth,
0:10:47 > 0:10:52you need something able to withstand the incredible energies involved.
0:10:53 > 0:10:56You need a torus,
0:10:56 > 0:10:59a giant, doughnut-shaped structure
0:10:59 > 0:11:04where temperatures can reach over 100 million degrees.
0:11:06 > 0:11:11Inside, an incredibly powerful magnetic field holds
0:11:11 > 0:11:13the hydrogen fuel.
0:11:14 > 0:11:18- OK.- Right, trigger, please.
0:11:19 > 0:11:23The conditions are so extreme that each attempt at star creation
0:11:23 > 0:11:25is a tense event.
0:11:25 > 0:11:28..nine, eight, seven...
0:11:28 > 0:11:31So what's happening now on JET is that they are powering up
0:11:31 > 0:11:35the magnets, and as they power up the magnets,
0:11:35 > 0:11:38it will be pushing the electric current round the loop.
0:11:38 > 0:11:41If you can see that red colour beginning to be there,
0:11:41 > 0:11:43that's the beginning of the plasma firing up.
0:11:45 > 0:11:47First, they have to pull apart
0:11:47 > 0:11:50the basic building blocks of matter, atoms.
0:11:52 > 0:11:57Then hurl them together again so they fuse and create starlight.
0:11:59 > 0:12:01You can see the plasma hitting the bottom,
0:12:01 > 0:12:04and so the lighting up on the bottom there... Oh, now it's really
0:12:04 > 0:12:07in full bloom - this is probably about 30 million degrees right now.
0:12:11 > 0:12:14This is a little bit of a star, here on Earth.
0:12:14 > 0:12:15APPLAUSE
0:12:17 > 0:12:22And, yes, it seems like that was about 2.5 million amps
0:12:22 > 0:12:24going through that plasma right there,
0:12:24 > 0:12:27and I think we had a successful shot because of all the excitement.
0:12:31 > 0:12:35It lasted just a brief moment, but at JET, they've managed to replicate
0:12:35 > 0:12:41what happens in the biggest objects in the universe, the stars.
0:12:44 > 0:12:46And they've done it because scientists
0:12:46 > 0:12:50like Professor Steve Cowley understand the smallest.
0:12:54 > 0:12:58At the centre of each hydrogen atom is a proton.
0:12:59 > 0:13:04And around that proton is an electron going round in a sort of an orbit.
0:13:07 > 0:13:10With enough heat and pressure, the orbiting electron
0:13:10 > 0:13:14will be stripped away from the proton at the centre.
0:13:16 > 0:13:19Do it to enough atoms, and you create a plasma,
0:13:19 > 0:13:22a soup of unattached particles.
0:13:23 > 0:13:26And if the conditions are intense enough,
0:13:26 > 0:13:29something extraordinary happens.
0:13:29 > 0:13:31A chain reaction begins.
0:13:32 > 0:13:34The protons are running around
0:13:34 > 0:13:36and because they're positively charged
0:13:36 > 0:13:38and they repel each other at distance,
0:13:38 > 0:13:41most of the time, they just glance off each other.
0:13:42 > 0:13:45At high energy, they bump into each other hard enough
0:13:45 > 0:13:47that, occasionally, they'll stick.
0:13:47 > 0:13:49That's the fusion process.
0:13:52 > 0:13:55When four hydrogen protons ultimately fuse,
0:13:55 > 0:13:57they create a new element.
0:13:57 > 0:13:59Hydrogen becomes helium,
0:13:59 > 0:14:01and an enormous amount of energy is released.
0:14:05 > 0:14:08This is what happens when a star is born,
0:14:08 > 0:14:12and it's all down to mass and the most famous equation in physics.
0:14:14 > 0:14:18That helium nucleus that you just made weighs less
0:14:18 > 0:14:22than the four hydrogens you used to make it.
0:14:23 > 0:14:26Somehow, mass has disappeared in the process.
0:14:29 > 0:14:34Anybody who knows any equation from physics knows that mass and energy
0:14:34 > 0:14:37are linked by Einstein's most famous equation,
0:14:37 > 0:14:43his equation E equals mc squared.
0:14:43 > 0:14:47So that missing mass is energy.
0:14:49 > 0:14:52But because c squared is such a large number,
0:14:52 > 0:14:56a tiny little bit of mass creates a phenomenal amount of energy.
0:15:00 > 0:15:03The sun only needs to use an infinitesimal amount
0:15:03 > 0:15:07of its colossal mass each day to generate vast megawatts of energy.
0:15:12 > 0:15:17Nuclear fusion is the process that not only brings stars into being,
0:15:17 > 0:15:19it's what keeps them alive.
0:15:23 > 0:15:26But when a star is born and starts its life story,
0:15:26 > 0:15:27scientists have discovered
0:15:27 > 0:15:30that something else very important can begin.
0:15:36 > 0:15:38The first person to get an inkling
0:15:38 > 0:15:42of this second story of creation was Nicholas Copernicus,
0:15:42 > 0:15:44the father of modern astronomy.
0:15:48 > 0:15:51And accidental social revolutionary.
0:15:55 > 0:15:58In 1543, he published a book that overturned
0:15:58 > 0:16:01more than 1,000 years of astronomical thought.
0:16:03 > 0:16:07The belief that the sun revolved around the Earth.
0:16:11 > 0:16:12Well, this is exciting.
0:16:12 > 0:16:16This is one of the most important books in the history of science.
0:16:16 > 0:16:19You can see from the title page that it's Copernicus's
0:16:19 > 0:16:22Six Books On The Revolution Of The Heavenly Spheres,
0:16:22 > 0:16:25and as well as being astronomically explosive,
0:16:25 > 0:16:29it was also explosive in terms of changing humankind's understanding
0:16:29 > 0:16:33of its place in the universe. And we can see that, I think, quite clearly
0:16:33 > 0:16:36if we look at the famous diagram here, and you can see that here
0:16:36 > 0:16:39at the centre is not the Earth, as people had thought for thousands
0:16:39 > 0:16:44of years, but sol, Latin for sun, and here is the Earth going around
0:16:44 > 0:16:49the central sun in this revolutionary new conception of the universe.
0:16:51 > 0:16:55Earth had been relegated from the centre of the universe
0:16:55 > 0:16:57to just the third rock circling the sun.
0:17:00 > 0:17:03The traditional story of how the cosmos was constructed
0:17:03 > 0:17:05had been shaken to its foundations.
0:17:08 > 0:17:11And, in the 16th century,
0:17:11 > 0:17:14this had deeply subversive implications.
0:17:15 > 0:17:18At this time, people very much believed that God had created
0:17:18 > 0:17:20a template for the heavens
0:17:20 > 0:17:22and he'd used pretty much the same template to create
0:17:22 > 0:17:27the society as well, and so with this "as above so below" belief,
0:17:27 > 0:17:31any change in the heavens immediately had huge cultural implications.
0:17:31 > 0:17:36By 1611, Copernicanism was sufficiently known that
0:17:36 > 0:17:42the poet John Donne says, "The new philosophy calls all in doubt,
0:17:42 > 0:17:45" 'tis all in pieces, all coherence gone."
0:17:47 > 0:17:51Our view of our relationship with the sun had completely changed.
0:17:53 > 0:17:55What Copernicus didn't know,
0:17:55 > 0:17:59but what scientists have now worked out, is that the sun isn't just
0:17:59 > 0:18:04at the centre of our solar system, it's the creator of it.
0:18:07 > 0:18:10The birth of a star leads to the birth
0:18:10 > 0:18:12of any planets that surround it.
0:18:17 > 0:18:22Planets are the natural consequences of star formation.
0:18:24 > 0:18:32Planets are the left-over debris of the gas and the dust forming a star.
0:18:32 > 0:18:34They are like the afterbirth, if you like.
0:18:36 > 0:18:40As the new star is born, the orbiting remnants of the cloud
0:18:40 > 0:18:44from which it formed start creating a disc,
0:18:44 > 0:18:48and over millions of years in this disc,
0:18:48 > 0:18:50the dust grains start to stick together.
0:18:54 > 0:18:56Blank out the light of a young star
0:18:56 > 0:18:59in the northern constellation of Pegasus,
0:18:59 > 0:19:03and you can see white dots, which are the planets forming
0:19:03 > 0:19:05in the disc of dust that surrounds the star.
0:19:10 > 0:19:14Eventually, the star is encircled by its children.
0:19:18 > 0:19:21This whole process explains the distinctive shape
0:19:21 > 0:19:24of all solar systems, including our own.
0:19:27 > 0:19:30The reason why you see all the planets
0:19:30 > 0:19:33going around the sun in the same direction on the same plane
0:19:33 > 0:19:37is because they are all formed from the same belt, from the same disc.
0:19:43 > 0:19:47Remarkably, just using observations with the naked eye
0:19:47 > 0:19:49and the power of deduction,
0:19:49 > 0:19:55Copernicus had created the first accurate family portrait of a star,
0:19:55 > 0:19:57surrounded by its offspring, the planets.
0:20:03 > 0:20:04But birth is just the beginning.
0:20:21 > 0:20:26Every morning at dawn, the sun becomes the only star
0:20:26 > 0:20:28that we can see in the sky.
0:20:32 > 0:20:38A star in middle age, like 90% of all the other ones.
0:20:40 > 0:20:45It's only special to us because it's so close.
0:20:47 > 0:20:52Once it was realised that the sun was a star, it opens up
0:20:52 > 0:20:57an enormous window to our understanding of the universe,
0:20:57 > 0:21:00because the sun really is the only star that we can properly see,
0:21:00 > 0:21:02and by looking at the sun,
0:21:02 > 0:21:05we have this magnificent laboratory so close to us,
0:21:05 > 0:21:07we can actually see it, we can actually study it,
0:21:07 > 0:21:09we can actually see the surface,
0:21:09 > 0:21:13make models of the interior, measure a lot of things in the atmosphere.
0:21:13 > 0:21:17And by studying the sun in that way, we are studying the stars.
0:21:19 > 0:21:23What most of us have learnt is that the sun's reliable,
0:21:23 > 0:21:25dependable, unchanging.
0:21:30 > 0:21:33But its serene outward appearance that we take for granted
0:21:33 > 0:21:36belies a truth about all middle-aged stars.
0:21:40 > 0:21:43Beneath the surface, there's a battle raging...
0:21:45 > 0:21:48..uncovered by the scientists who know it better.
0:21:53 > 0:21:56The sun is in the prime of its life.
0:21:56 > 0:21:59It's a middle-aged star, but it's actually very dynamic,
0:21:59 > 0:22:01very full of life.
0:22:07 > 0:22:09I regard the sun as a sort of personal friend of mine
0:22:09 > 0:22:12and like to know what's happening on the sun each day,
0:22:12 > 0:22:14and I look at the satellite pictures to find out.
0:22:14 > 0:22:17It's almost as if the sun sometimes doesn't want you to know
0:22:17 > 0:22:18what's happening on it, though,
0:22:18 > 0:22:21because sometimes the data links are down or something
0:22:21 > 0:22:22and you can't actually see it.
0:22:22 > 0:22:23That's quite frustrating,
0:22:23 > 0:22:26because you want to know how your friend's getting on each day.
0:22:27 > 0:22:30Dr Helen Mason's intimate relationship with the sun
0:22:30 > 0:22:34has turned her into one of the world's leading solar physicists.
0:22:36 > 0:22:38People think of it as quiet and boring,
0:22:38 > 0:22:41but it's not at all quiet and boring,
0:22:41 > 0:22:44and that makes it really interesting to study.
0:22:45 > 0:22:48The work of scientists like Helen has revealed
0:22:48 > 0:22:51that inside the sun, there's a fight
0:22:51 > 0:22:54between two of nature's fundamental forces
0:22:54 > 0:22:58that's key to the star's entire life history.
0:23:02 > 0:23:06The gravity that created a star is pulling it inwards,
0:23:06 > 0:23:08trying to crush it.
0:23:10 > 0:23:14And the nuclear fusion that brought it to life is pushing outwards,
0:23:14 > 0:23:16ready to blow it apart.
0:23:19 > 0:23:22It will be disaster for the star
0:23:22 > 0:23:25if either of these two forces gets the upper hand.
0:23:30 > 0:23:34One 17th-century scientist who studied the sun didn't know this.
0:23:37 > 0:23:39But he did quickly realise
0:23:39 > 0:23:42that our parent star was more turbulent than it seemed.
0:23:47 > 0:23:49That man was Galileo Galilei.
0:23:54 > 0:23:57He used one of the earliest telescopes to project
0:23:57 > 0:23:59detailed images of the sun,
0:23:59 > 0:24:03completely transforming our understanding of it.
0:24:08 > 0:24:11In the process, he shocked the world.
0:24:14 > 0:24:17Well, when Galileo looked at a projection of the sun,
0:24:17 > 0:24:20very much in the way that I'm doing,
0:24:20 > 0:24:22what he saw were these, these spots,
0:24:22 > 0:24:23these black spots on the sun.
0:24:24 > 0:24:26People had seen them, previously -
0:24:26 > 0:24:29I think the ancient Chinese had seen them through the fog -
0:24:29 > 0:24:32but the important thing was that Galileo was actually saying
0:24:32 > 0:24:34that these sunspots were on the sun
0:24:34 > 0:24:37rather than satellites or something going in front of the sun,
0:24:37 > 0:24:40in defiance of thousands of years of Catholic thought
0:24:40 > 0:24:42that everything was supposed to be perfect,
0:24:42 > 0:24:46and yet here we are with blemishes and spots on it.
0:24:50 > 0:24:56Galileo's controversial work led him to end his days under house arrest,
0:24:56 > 0:25:01but his observations revolutionised our knowledge of the sun.
0:25:03 > 0:25:07Sunspots appeared and disappeared,
0:25:07 > 0:25:13and by tracking them for several days, Galileo showed they moved,
0:25:13 > 0:25:15revealing that the sun rotated.
0:25:19 > 0:25:23What Galileo discovered overturned centuries of belief.
0:25:30 > 0:25:34The sun wasn't a god-like immaculate disc
0:25:34 > 0:25:36but a body that was constantly changing.
0:25:38 > 0:25:40So this meant that the sun was not sublime any more.
0:25:40 > 0:25:43It was made of the same sort of stuff as the Earth,
0:25:43 > 0:25:44and therefore scientific processes
0:25:44 > 0:25:47that were applied to the Earth could also be applied to the sun.
0:25:49 > 0:25:52This underpins our subsequent discoveries about the sun,
0:25:52 > 0:25:55the other stars and all of astronomy, really.
0:25:58 > 0:26:00Building on Galileo's work,
0:26:00 > 0:26:05scientists have discovered that the sun's active, changeable nature is,
0:26:05 > 0:26:09in fact, the characteristic that has the biggest impact on us.
0:26:13 > 0:26:17The sunspots he observed are linked to solar flares.
0:26:23 > 0:26:27Sudden, colossal releases of energy that can spew
0:26:27 > 0:26:31over a million tonnes of material into space.
0:26:34 > 0:26:38This stream of charged particles is able to scramble
0:26:38 > 0:26:40satellite communications -
0:26:40 > 0:26:44in extreme cases, knock out power grids.
0:26:47 > 0:26:51And all caused by the turbulent nature of the sun's magnetic field.
0:26:53 > 0:26:56Sometimes these magnetic fields get twisted up.
0:26:56 > 0:27:00The foot points move around, and they get really twisted up,
0:27:00 > 0:27:04and they get so knotted up that eventually they crack and break.
0:27:05 > 0:27:09And we have solar flares, huge explosion.
0:27:09 > 0:27:12Particles are shot out into space.
0:27:12 > 0:27:15In fact, this little active region, I mean, it's quite big, actually,
0:27:15 > 0:27:18that we've been looking at recently, has been flaring continuously
0:27:18 > 0:27:20over the past few days.
0:27:25 > 0:27:28But while the sun's violent outbursts can harm us,
0:27:28 > 0:27:32its active nature is what allows us to live at all.
0:27:35 > 0:27:38Because the sun also ejects the solar wind,
0:27:38 > 0:27:43an energised stream of particles that head out into space.
0:27:46 > 0:27:48And that we can see passing Earth
0:27:48 > 0:27:51as it bounces off our atmosphere...
0:27:54 > 0:27:55..the aurorae.
0:28:03 > 0:28:05Then the solar wind flies on.
0:28:08 > 0:28:12Putting on the same show at the poles of Jupiter...
0:28:16 > 0:28:18..and Saturn too.
0:28:24 > 0:28:28Until, finally, 100 Earth sun distances away,
0:28:28 > 0:28:34it loses its momentum and forms a boundary with deep space...
0:28:37 > 0:28:41..creating a protective bubble that shields our solar system
0:28:41 > 0:28:47from dangerous galactic radiation and cosmic rays -
0:28:47 > 0:28:49the heliosphere.
0:28:55 > 0:29:00Within it, life on a planet just the right distance away can thrive.
0:29:12 > 0:29:17We are beneficiaries of the energy the sun generates
0:29:17 > 0:29:21as nuclear fusion fights back against gravity.
0:29:30 > 0:29:35Energy isn't created or destroyed, it's transferred, so it's transferred
0:29:35 > 0:29:40from the centre of the sun through the atmospheres to us,
0:29:40 > 0:29:43in many forms, warmth and light, via the plants
0:29:43 > 0:29:46and via the food that we eat.
0:29:46 > 0:29:48'As dawn throws into shadowy relief
0:29:48 > 0:29:50'the giant pillars of Stonehenge,
0:29:50 > 0:29:52'the successors of the ancient Druids await
0:29:52 > 0:29:55'the first rays of midsummer sun.'
0:29:55 > 0:29:56I can really understand
0:29:56 > 0:29:59why ancient civilisations would have worshipped it,
0:29:59 > 0:30:03because it is like a god in a sense of it provides everything
0:30:03 > 0:30:06that's so important, that without it, the...life would cease to exist.
0:30:12 > 0:30:16Ancient man was right to worry whether the sun would rise again.
0:30:24 > 0:30:28It's been burning for five billion years,
0:30:28 > 0:30:32but it's now used up half its hydrogen fuel resisting gravity.
0:30:36 > 0:30:42One morning, the sun will rise on a last perfect day on Earth.
0:30:44 > 0:30:48For many years, we had no idea when the end would come.
0:30:54 > 0:30:58But now we can predict the sun's fate...
0:30:58 > 0:31:00and our own.
0:31:02 > 0:31:06We've learnt it, not by studying the sun,
0:31:06 > 0:31:09but by observing all the other stars in the sky.
0:31:13 > 0:31:18The breakthrough came when American astronomer Henry Norris Russell
0:31:18 > 0:31:23and the Dane, Ejnar Hertzsprung, tried to create a pattern
0:31:23 > 0:31:26that made sense of all the stars in the night sky.
0:31:30 > 0:31:33No matter what their size,
0:31:33 > 0:31:35or whether they burned hotter or dimmer.
0:31:41 > 0:31:45This finally revealed that stars had a lifecycle.
0:31:48 > 0:31:51At the turn of the 20th century,
0:31:51 > 0:31:53astronomers have already a wealth of data about the stars.
0:31:53 > 0:31:57Mainly, they have measured the colours
0:31:57 > 0:31:59and the real luminosities of them.
0:32:01 > 0:32:05So what Hertzsprung and Russell did was to organise
0:32:05 > 0:32:11the stars in order of temperatures and in order of luminosities,
0:32:11 > 0:32:15and this is the birth of the Hertzsprung-Russell diagram.
0:32:18 > 0:32:21On one axis, they plotted how bright the stars would be
0:32:21 > 0:32:25if they were all the same distance away from us,
0:32:25 > 0:32:27from the dimmest to the brightest.
0:32:30 > 0:32:33On the other axis was their temperature,
0:32:33 > 0:32:35as indicated by their colour,
0:32:35 > 0:32:38from blue and white hot to cooler red.
0:32:42 > 0:32:45What was revelatory was the pattern that emerged.
0:32:47 > 0:32:50Almost all the stars fell into a central diagonal line,
0:32:50 > 0:32:53known as the main sequence.
0:32:55 > 0:32:59These are the middle-aged stars, ones who still have enough hydrogen
0:32:59 > 0:33:04in their cores to fuse into helium and resist the force of gravity.
0:33:07 > 0:33:10But on either side were two small outcrops.
0:33:15 > 0:33:18By deciphering the diagram, scientists discovered
0:33:18 > 0:33:22that these outlying groups predicted the future of our sun.
0:33:24 > 0:33:29Now, the sun will be burning hydrogen, as the stars do
0:33:29 > 0:33:32in the main sequence, until the hydrogen is exhausted in the core,
0:33:32 > 0:33:35and at that point, the star starts to die.
0:33:35 > 0:33:37The outer layers of the sun will expand.
0:33:37 > 0:33:43The sun will move away from the main sequence to become a Red Giant star.
0:33:46 > 0:33:50From the apparent disorder of the night sky,
0:33:50 > 0:33:52a map had been created...
0:33:54 > 0:33:58..on which you could chart a star's journey through life.
0:34:02 > 0:34:06It revealed that the fate of our own star was written in the night sky.
0:34:10 > 0:34:15Once its hydrogen runs out, it will head off the main sequence
0:34:15 > 0:34:18and move into the next phase of its life,
0:34:18 > 0:34:21as a Red Giant.
0:34:38 > 0:34:42Middleweight stars, like our sun, don't age gracefully
0:34:42 > 0:34:45but catastrophically.
0:34:49 > 0:34:51They swell up and become some of the largest,
0:34:51 > 0:34:54most bloated stars in the universe.
0:35:00 > 0:35:03Stars 200 times the size of our sun.
0:35:05 > 0:35:07Thousands of times brighter.
0:35:09 > 0:35:11Stars that are some of the most destructive in the universe
0:35:11 > 0:35:16but also the most creative,
0:35:16 > 0:35:20shining a rancid red in the inky sky.
0:35:24 > 0:35:28Arcturus is a Red Giant star, very easy to find.
0:35:29 > 0:35:33The tail of the Plough, the tail of the Big Bear, you follow that
0:35:33 > 0:35:35and you reach the star Arcturus,
0:35:35 > 0:35:38so it is in a way following the Big Bear, as a bear-taker,
0:35:38 > 0:35:40which is what Arcturus means.
0:35:49 > 0:35:54Surprisingly, Arcturus's striking colour is not because it's hotter
0:35:54 > 0:35:56but because it's cooler.
0:36:01 > 0:36:05As the balance between the opposing forces of gravity
0:36:05 > 0:36:07and nuclear fusion breaks down,
0:36:07 > 0:36:10the size of the star changes.
0:36:10 > 0:36:14Red Giants expand,
0:36:14 > 0:36:20their fiery energy spreading over a larger area,
0:36:20 > 0:36:23which makes their temperature drop.
0:36:25 > 0:36:30They fall from blue or white hot
0:36:30 > 0:36:32to red hot,
0:36:32 > 0:36:34but because they are so large,
0:36:34 > 0:36:38these stars are still some of the brightest in the sky.
0:36:40 > 0:36:42That's Arcturus.
0:36:49 > 0:36:54When we see bright stars like Arcturus in the sky,
0:36:54 > 0:36:57no doubt in many, many civilisations in the past,
0:36:57 > 0:36:59they have some associations with these stars
0:36:59 > 0:37:01and something that happens.
0:37:06 > 0:37:10"Each star has its own distinct personality
0:37:10 > 0:37:14"and it creates effects according to its character.
0:37:16 > 0:37:20"When Arcturus rises, it is nearly always accompanied
0:37:20 > 0:37:22"by a terrible hailstorm."
0:37:22 > 0:37:23THUNDER
0:37:29 > 0:37:32Actually, Arcturus is an omen
0:37:32 > 0:37:35of something far worse than bad weather.
0:37:37 > 0:37:41A portent of a drama more intense than any Hollywood could imagine.
0:37:50 > 0:37:53When our own sun eventually becomes a Red Giant,
0:37:53 > 0:37:56in five billion years' time,
0:37:56 > 0:38:02it will turn into a destroyer, rather than a protector, of worlds.
0:38:06 > 0:38:09Dr Robin Catchpole has devoted his middle years to studying
0:38:09 > 0:38:12these devouring beasts of the night.
0:38:15 > 0:38:19Their story starts the day the hydrogen in their core runs out.
0:38:22 > 0:38:26Most of the star's life it spends fusing hydrogen into helium,
0:38:26 > 0:38:29and this, of course, provides the pressure
0:38:29 > 0:38:31that resists the force of gravity.
0:38:34 > 0:38:37When the hydrogen runs out in the core and we've just got pure helium,
0:38:37 > 0:38:39then there's no source of energy,
0:38:39 > 0:38:43so the core starts to collapse
0:38:43 > 0:38:47and as it collapses, under the force of gravity, it heats up.
0:38:49 > 0:38:51And the temperature becomes high enough
0:38:51 > 0:38:55to start nuclear fusion reactions in the shell around the core.
0:38:57 > 0:39:00So we have what we call shell hydrogen burning.
0:39:02 > 0:39:04Fusion has stopped in the core.
0:39:05 > 0:39:07It's still hot, but it's dead.
0:39:09 > 0:39:14The star is now fundamentally different from our twinkling sun.
0:39:14 > 0:39:19The light we're seeing is still being generated by nuclear fusion,
0:39:19 > 0:39:22but it's happening in a ring of hydrogen
0:39:22 > 0:39:25that surrounds the core instead.
0:39:27 > 0:39:32This is our new source of energy and this, of course, resists the force
0:39:32 > 0:39:33of gravity and, in fact,
0:39:33 > 0:39:36causes the outer atmosphere of the star to expand.
0:39:44 > 0:39:49The star has begun its dramatic transformation into a Red Giant.
0:39:53 > 0:39:59For our own sun, the change will be awe-inspiring
0:39:59 > 0:40:04as, in its final years, it turns against the planets in its care.
0:40:07 > 0:40:11The first thing that happens is it expands up
0:40:11 > 0:40:14as far as Mercury's orbit here and swallows Mercury.
0:40:14 > 0:40:18At this stage, it's about 1,000 times more luminous
0:40:18 > 0:40:20than the sun is today.
0:40:20 > 0:40:23It continues to expand and, within another million years or so,
0:40:23 > 0:40:27it gets as far as Venus, and that's the end of Venus.
0:40:27 > 0:40:32Venus is swallowed up, and then the sun continues out towards the Earth.
0:40:38 > 0:40:41If we could see it, we would see something
0:40:41 > 0:40:45nearly 3,000 times brighter than the sun is today.
0:40:45 > 0:40:48It would be 260 times bigger than it is today,
0:40:48 > 0:40:53but it would not have that beautiful tight compactness of the sun today.
0:40:53 > 0:40:55Gas would be streaming off the surface,
0:40:55 > 0:40:59it would be red and turbulent, slightly transparent.
0:40:59 > 0:41:02It would almost seem to be coming apart at the seams.
0:41:05 > 0:41:10Our only chance of survival would be to flee long before this crisis
0:41:10 > 0:41:14and go in search of another solar system to call home.
0:41:20 > 0:41:24In its angry old age, the sun will show no mercy,
0:41:24 > 0:41:26even to its favoured child.
0:41:30 > 0:41:32And the Earth disappears into the sun,
0:41:32 > 0:41:36and I'm afraid that's curtains for the Earth.
0:41:40 > 0:41:44Our planet will be engulfed by a ball of fiery gases,
0:41:44 > 0:41:45never to be seen again.
0:41:56 > 0:41:59The star that created and nurtured us
0:41:59 > 0:42:03will ultimately, in its bloated old age, destroy us.
0:42:07 > 0:42:11But while Red Giants bring annihilation,
0:42:11 > 0:42:14scientists have uncovered in them the beginning of another story.
0:42:17 > 0:42:22A story of creation that is about us, as well as about the stars.
0:42:26 > 0:42:29They discovered that in the last stages of the battle
0:42:29 > 0:42:34between gravity and nuclear fusion, Red Giants generate
0:42:34 > 0:42:36two of the most abundant building blocks of the universe.
0:42:40 > 0:42:45And these vital elements are being built in the heart of the Red Giant.
0:42:47 > 0:42:52About half a million years after the poor old Earth has disappeared
0:42:52 > 0:42:56into the sun, we get the temperature rising to the point
0:42:56 > 0:42:59where we can suddenly start helium fusion,
0:42:59 > 0:43:03and this is the next phase of the life of the star,
0:43:03 > 0:43:06is a stage where helium is being fused in the core
0:43:06 > 0:43:09to produce carbon and oxygen.
0:43:11 > 0:43:16Stars, scientists discovered, aren't just twinkling points of light.
0:43:16 > 0:43:20They're alchemists, creating the materials the cosmos is made of.
0:43:27 > 0:43:29Most of the carbon in your body comes
0:43:29 > 0:43:32from the discarded envelope of a Red Giant.
0:43:35 > 0:43:38As the war between gravity and nuclear fusion
0:43:38 > 0:43:45reaches its conclusion, the vast outer layers of the star detach
0:43:45 > 0:43:50from the hot core, recycling carbon and oxygen into the universe.
0:43:54 > 0:43:59What's left after this remarkable process is a remnant.
0:44:03 > 0:44:08The star is ready to enter the next, enigmatic, phase of its life.
0:44:26 > 0:44:30White Dwarfs baffled astronomers for decades.
0:44:32 > 0:44:35The first problem was finding them.
0:44:39 > 0:44:42It turned out they'd been hidden in plain sight.
0:44:43 > 0:44:46We just needed a bigger telescope to see them.
0:44:48 > 0:44:51The winter sky in the northern hemisphere brings
0:44:51 > 0:44:57a set of fantastic constellations like this one, Canis Major.
0:44:57 > 0:45:01Canis Major contains the brightest star in the night sky.
0:45:01 > 0:45:03It's called Sirius.
0:45:07 > 0:45:10A lovely star, also known as the Dog Star.
0:45:16 > 0:45:19And it was discovered in the 19th century,
0:45:19 > 0:45:22when the telescopes were really, really high quality
0:45:22 > 0:45:26that Sirius has a companion, a very faint companion
0:45:26 > 0:45:29that is lost in the glare of the very bright star.
0:45:33 > 0:45:37This tiny companion to the bright Dog Star was dubbed the Pup,
0:45:37 > 0:45:44and by 1922, this new type of star had an official classification.
0:45:44 > 0:45:46It was called a White Dwarf.
0:45:51 > 0:45:55But naming it was the least of scientists' problems.
0:45:57 > 0:46:00When they compared its size to its mass,
0:46:00 > 0:46:02something extraordinary emerged.
0:46:02 > 0:46:04It was denser than anything on Earth,
0:46:04 > 0:46:08denser than anything previously imagined.
0:46:11 > 0:46:14They were a type of star that shouldn't exist.
0:46:16 > 0:46:19The burnt-out remains of one whose fusion has stopped.
0:46:22 > 0:46:25Their fuel is exhausted, so how can they still shine?
0:46:30 > 0:46:34Mysteries that have long intrigued Professor John Ellis.
0:46:36 > 0:46:38Throughout their lives, stars make their energy
0:46:38 > 0:46:43by fusing together light nuclei to make heavier ones.
0:46:43 > 0:46:47They start off with hydrogen and they make helium,
0:46:47 > 0:46:50then they go on to fuse together helium to make carbon and oxygen.
0:46:52 > 0:46:56And as time goes on, they burn up more and more of this fuel
0:46:56 > 0:46:59until, eventually, it's like a car, you run out of gas.
0:47:02 > 0:47:05With its helium-burning days at an end,
0:47:05 > 0:47:08the White Dwarf's active life is over.
0:47:10 > 0:47:13All it's left with is a dead core of carbon and oxygen.
0:47:16 > 0:47:20It's not really a star at all but a cinder.
0:47:22 > 0:47:25And the internal battle raging in the heart of the star,
0:47:25 > 0:47:29between gravity and fusion, now has a clear victor.
0:47:30 > 0:47:32Once the fusion stops,
0:47:32 > 0:47:36the whole thing collapses under its own weight to form a White Dwarf.
0:47:39 > 0:47:44So you've got this very small blob, which is incredibly dense.
0:47:44 > 0:47:47It's going to be something like a million times denser
0:47:47 > 0:47:54than it started off, so dense, in fact, that if you had a piece
0:47:54 > 0:47:58the size of my mobile phone, it would weigh something like ten tonnes.
0:48:02 > 0:48:05The core of the massive Red Giant collapses,
0:48:05 > 0:48:08leaving the White Dwarf denser than anything
0:48:08 > 0:48:11that had previously been discovered.
0:48:15 > 0:48:19This raises another perplexing question.
0:48:22 > 0:48:24Why doesn't gravity completely destroy them?
0:48:27 > 0:48:32They were such baffling objects that one British astronomer commented,
0:48:32 > 0:48:35"An appropriate response to the message from a White Dwarf
0:48:35 > 0:48:39"was 'Shut up, don't talk nonsense.' "
0:48:44 > 0:48:49It took a whole new revolutionary form of physics to emerge
0:48:49 > 0:48:52before their secrets could be unravelled.
0:48:54 > 0:48:59Quantum mechanics revealed much more about the innards of atoms,
0:48:59 > 0:49:02enabling astronomers to begin to solve
0:49:02 > 0:49:04the mystery of the White Dwarf.
0:49:06 > 0:49:09In physics, we've got two different types of particles.
0:49:09 > 0:49:11There are some particles that are very gregarious,
0:49:11 > 0:49:15that like to get together, and then we've got other particles,
0:49:15 > 0:49:16like the electron,
0:49:16 > 0:49:18which like to be different from each other.
0:49:19 > 0:49:22They're a little bit like people at a party
0:49:22 > 0:49:24who are wearing the same colour dress.
0:49:24 > 0:49:27They don't want to be standing next to each other,
0:49:27 > 0:49:30so they're going to tend to naturally push away from each other.
0:49:32 > 0:49:35That's...that's like what we physicists call pressure.
0:49:37 > 0:49:41This pressure is created as the particles jostle for position.
0:49:44 > 0:49:46It's a principle of quantum mechanics,
0:49:46 > 0:49:49and when it was applied to stars,
0:49:49 > 0:49:52the lives of dead White Dwarfs suddenly made sense.
0:49:54 > 0:49:57What stopped them collapsing completely
0:49:57 > 0:50:00was that gravity was resisted by the pressure generated
0:50:00 > 0:50:02between the particles themselves.
0:50:04 > 0:50:06In a White Dwarf, you've got a delicate balance
0:50:06 > 0:50:10between the gravity which is trying to squeeze it together,
0:50:10 > 0:50:14and the pressure of these electrons trying not to all have
0:50:14 > 0:50:18their dresses in the same place, that are trying to push out.
0:50:18 > 0:50:22And it's the balance between this gravity pulling in
0:50:22 > 0:50:26and the electrons pushing out that keeps the White Dwarf the size it is.
0:50:28 > 0:50:32It's also what lets a star with no fuel supply
0:50:32 > 0:50:34shine for billions of years.
0:50:37 > 0:50:39These White Dwarfs are very small,
0:50:39 > 0:50:42so they've got a very small surface area,
0:50:42 > 0:50:44which means that although they are white hot,
0:50:44 > 0:50:49the light that they emit, the heat energy which they send out,
0:50:49 > 0:50:53is still very limited just because of the very small size of the surface.
0:50:53 > 0:50:59Now, it carries on radiating light and it gradually cools down,
0:50:59 > 0:51:01it gradually gets dimmer and dimmer.
0:51:03 > 0:51:09It's a little bit like a retired person sitting in an old stars' home.
0:51:09 > 0:51:11It's still, you know, ticking along, but it gradually gets
0:51:11 > 0:51:15sort of slower and slower, dimmer and dimmer.
0:51:16 > 0:51:22There are White Dwarfs cluttering up our galaxy, all the other galaxies.
0:51:26 > 0:51:30The enigma of the White Dwarf had been resolved.
0:51:32 > 0:51:36Scientists had discovered how the vast majority of stars,
0:51:36 > 0:51:39including our own sun, will end their days.
0:51:42 > 0:51:46As White Dwarfs gently fading into the darkness of the universe.
0:51:51 > 0:51:53But not all stars go so quietly.
0:51:57 > 0:52:02For the most massive stars, something extraordinary happens.
0:52:02 > 0:52:06They make their exit with one last spectacular hurrah.
0:52:22 > 0:52:25Supernovae are the explosive, dramatic death throes
0:52:25 > 0:52:27of the most massive stars in the universe.
0:52:31 > 0:52:33Explosions so bright and intense
0:52:33 > 0:52:37that they can briefly rival the output of ten billion suns.
0:52:41 > 0:52:46They leave behind traces that paint the sky with a rainbow of colours.
0:52:49 > 0:52:52Today, we know that these spectacular events
0:52:52 > 0:52:56play a crucial role in creating the world around us.
0:52:58 > 0:53:00Yet it took us centuries to discover it.
0:53:09 > 0:53:14They're so rare that for hundreds of years, no-one saw any at all.
0:53:17 > 0:53:19So the first challenge was to find them.
0:53:22 > 0:53:23And that takes dedication,
0:53:23 > 0:53:28perseverance and a love of the thrill of the chase.
0:53:28 > 0:53:34Not just any kind of astronomer but a supernova hunter
0:53:34 > 0:53:36and one with perfect timing.
0:53:38 > 0:53:42You know, usually nothing much happens in astronomy.
0:53:42 > 0:53:44Stars live for millions or billions of years,
0:53:44 > 0:53:47so everything's the same from one night to another,
0:53:47 > 0:53:50but not with a supernova.
0:53:50 > 0:53:52It brightens dramatically over the course of just one night.
0:53:52 > 0:53:54It happens on a human timescale.
0:53:58 > 0:54:03Supernovae are so rarely seen in our own galaxy, the Milky Way,
0:54:03 > 0:54:07that you need to peer much, much further to find many more.
0:54:10 > 0:54:13You need to hunt for them in other galaxies.
0:54:18 > 0:54:21Professor Alex Filippenko runs
0:54:21 > 0:54:24one of the most successful search teams on Earth for doing just that.
0:54:27 > 0:54:31In their best year, they discovered almost 100.
0:54:34 > 0:54:35There's no calendar telling you
0:54:35 > 0:54:38where and when to look for supernovae.
0:54:38 > 0:54:42You just look kind of randomly at as many galaxies as you can,
0:54:42 > 0:54:46repeatedly, and occasionally a supernova will go off in one of them.
0:54:52 > 0:54:56I mean, they're rare, only two or three supernovae per galaxy
0:54:56 > 0:55:00per century, so you really have to scan thousands of galaxies
0:55:00 > 0:55:03in order to increase your odds of finding a few each year.
0:55:08 > 0:55:11This robotic telescope automatically takes pictures
0:55:11 > 0:55:15of over 1,000 galaxies a night, and it compares those new pictures
0:55:15 > 0:55:19with pictures of the same galaxies it had taken previously.
0:55:19 > 0:55:22If there's something new in one of the new pictures,
0:55:22 > 0:55:25like a new star, that's an excellent candidate supernova.
0:55:25 > 0:55:28That's the kind of thing that we want to keep studying.
0:55:36 > 0:55:39The supernovae that Alex photographs
0:55:39 > 0:55:42are hundreds of millions of light years away.
0:55:46 > 0:55:49The only reason he can photograph them so distinctly
0:55:49 > 0:55:54is because they are such colossal explosions.
0:56:00 > 0:56:03And appreciating the power of a supernova's explosion
0:56:03 > 0:56:07has been key to understanding the very composition of the universe.
0:56:17 > 0:56:19For centuries, scientists have known
0:56:19 > 0:56:23that everything we see on Earth is made up of 92 elements.
0:56:27 > 0:56:29And the stars are made of the very same ones.
0:56:32 > 0:56:35We can see it in their starlight.
0:56:36 > 0:56:39Different elements give off different colours of light
0:56:39 > 0:56:42when they're heated, when they're energised.
0:56:42 > 0:56:46So if we look at a glowing cloud of gas in the sky, we can determine
0:56:46 > 0:56:50what chemical elements it's made from by seeing what colours it has.
0:56:51 > 0:56:57Potassium should produce a violet colour. Oh, look at that, wow!
0:56:57 > 0:56:59Strontium.
0:56:59 > 0:57:02Whoa, look at the strontium go!
0:57:02 > 0:57:05Sodium, a bit like the light of the flames.
0:57:07 > 0:57:09And, finally, I've got some copper here.
0:57:13 > 0:57:16Look at the remnant of a supernova,
0:57:16 > 0:57:19and you can spot the signature colours of some elements.
0:57:21 > 0:57:25Modern scientists can reveal the full story
0:57:25 > 0:57:30by splitting the light with a prism to create a spectrum.
0:57:30 > 0:57:31And so I can see
0:57:31 > 0:57:34that there's hydrogen being produced by this supernova,
0:57:34 > 0:57:37and over here, the yellow/orange light
0:57:37 > 0:57:40is due to glowing atoms of sodium.
0:57:40 > 0:57:42It's the same sodium glow that we saw
0:57:42 > 0:57:45when I sprinkled the chemical into the fire.
0:57:45 > 0:57:48These ones here, in the green part, are iron,
0:57:48 > 0:57:51and down here, in the violet part of the spectrum, is calcium.
0:57:58 > 0:58:01The question that baffled scientists for decades, though,
0:58:01 > 0:58:04was where did all the elements come from?
0:58:11 > 0:58:16The breakthrough came from the mind of a doughty Yorkshireman,
0:58:16 > 0:58:18Fred Hoyle.
0:58:20 > 0:58:24The origin of the elements was a big question that scientists
0:58:24 > 0:58:28were trying to tackle 50 years ago, and Fred Hoyle and his colleagues
0:58:28 > 0:58:33thought that supernovae may be a key to unravelling the mystery.
0:58:35 > 0:58:38At the time, this was a radical idea.
0:58:42 > 0:58:45But Fred Hoyle was never a stranger to controversy.
0:58:47 > 0:58:50'Fred Hoyle blows up stars by computer.
0:58:50 > 0:58:54'This cosmic anarchist is the most controversial of theorists.'
0:58:54 > 0:58:59If you think there's a mystery about why stars explode,
0:58:59 > 0:59:01then you've got it all wrong.
0:59:04 > 0:59:06Hoyle devoted ten years of his career
0:59:06 > 0:59:10to proving his revolutionary theory on the origin of the elements.
0:59:14 > 0:59:18He deduced that Red Giants are alchemists,
0:59:18 > 0:59:23but he knew that they weren't hot enough to create all the elements.
0:59:29 > 0:59:33He thought the ferocity of the supernova's explosion, though,
0:59:33 > 0:59:36would make them the perfect furnace
0:59:36 > 0:59:41and, with his colleagues, he did the calculations to prove it.
0:59:44 > 0:59:48The key was the conditions created in the final stages
0:59:48 > 0:59:50of a massive star's fight against gravity.
0:59:53 > 0:59:56These stars are so massive and hot
0:59:56 > 1:00:00that they can go through a whole series of nuclear reactions.
1:00:00 > 1:00:03The ashes of one set of nuclear reactions
1:00:03 > 1:00:06becomes the fuel for the next set of nuclear reactions.
1:00:09 > 1:00:15The most massive stars are able to fuse heavier and heavier elements
1:00:15 > 1:00:17in a series of layers,
1:00:17 > 1:00:22creating the energy to resist the relentless inward pull of gravity.
1:00:25 > 1:00:28There is neon and magnesium and more oxygen.
1:00:28 > 1:00:30Then there's silicon and sulphur
1:00:30 > 1:00:35and, finally, in the middle, a core of iron.
1:00:36 > 1:00:38And that's where the fusion stops.
1:00:40 > 1:00:45With fusion at an end, there's no more energy to fight back,
1:00:45 > 1:00:48and gravity wins the battle.
1:00:49 > 1:00:51The star is doomed.
1:00:53 > 1:00:57When that ball of iron reaches a certain critical mass,
1:00:57 > 1:01:00about the size of the Earth, but much, much more massive,
1:01:00 > 1:01:03the electron pressure is no longer able to support it
1:01:03 > 1:01:08against the inward force of gravity, so it starts to collapse.
1:01:08 > 1:01:12It collapses to a ball about the size of a city
1:01:12 > 1:01:14and then rebounds and that rebounds...
1:01:14 > 1:01:16hits the surrounding layers,
1:01:16 > 1:01:19launching a supernova explosion.
1:01:24 > 1:01:28It's the speed and violence of the collapse of the star's iron core
1:01:28 > 1:01:30that triggers the supernova,
1:01:30 > 1:01:33an implosion that launches an explosion...
1:01:35 > 1:01:39..creating enough heat and energy to forge almost all the other elements.
1:01:43 > 1:01:46The supernova explosion is able to produce
1:01:46 > 1:01:49some of the very rare elements heavier than iron -
1:01:49 > 1:01:52the zinc, the gold, the platinum, the silver.
1:01:52 > 1:01:56These things are ejected into the cosmos, having produced them
1:01:56 > 1:02:00in these very special conditions of an exploded star.
1:02:04 > 1:02:08The very atoms of which we are made, the oxygen that we breathe,
1:02:08 > 1:02:09the calcium in our bones,
1:02:09 > 1:02:12the iron in our red blood cells,
1:02:12 > 1:02:14were produced billions of years ago
1:02:14 > 1:02:17in stars, specifically in dying stars,
1:02:17 > 1:02:21and these dying stars ejected these elements into the cosmos,
1:02:21 > 1:02:25making them available for raw material for the production
1:02:25 > 1:02:28of new stars, planets and, ultimately, life.
1:02:35 > 1:02:37We are stardust
1:02:37 > 1:02:41or rather, less romantically, nuclear waste.
1:02:44 > 1:02:47In a way, the ancients were right.
1:02:49 > 1:02:53The stars ARE like gods.
1:02:53 > 1:02:56They are the creators of us.
1:03:01 > 1:03:03To make our Earth,
1:03:03 > 1:03:07several hundred generations of stars needed to come and go.
1:03:17 > 1:03:20Stars born from collapsing clouds of dust and gas.
1:03:23 > 1:03:28Bursting into life, to shine for millions or billions of years.
1:03:32 > 1:03:35Bloating in old age to become Red Giants.
1:03:39 > 1:03:41Their cores contracting into White Dwarfs.
1:03:46 > 1:03:50The most massive ones exploding as supernovae,
1:03:50 > 1:03:54flinging the elements they've created out into space
1:03:54 > 1:03:58to form the materials for the next generation of stars.
1:04:01 > 1:04:03But that's not the end of the story.
1:04:08 > 1:04:13Supernovae may look like the death of a star, but for some,
1:04:13 > 1:04:15there is life beyond the grave.
1:04:17 > 1:04:21Understanding that took a particular breed of scientist.
1:04:25 > 1:04:27They probed deep into their own imagination
1:04:27 > 1:04:30and a world of calculations.
1:04:33 > 1:04:37And what they found there were predictions of objects so bizarre,
1:04:37 > 1:04:40so weird, that we're only beginning to understand them.
1:04:42 > 1:04:47In the process, unravelling even deeper secrets about the universe.
1:05:02 > 1:05:06The faintest of signals picked up from deepest space have revealed
1:05:06 > 1:05:10to modern scientists exotic stellar tombstones.
1:05:14 > 1:05:18Tombstones first predicted in the theoretical calculations
1:05:18 > 1:05:21of the maverick Swiss astronomer Fritz Zwicky,
1:05:21 > 1:05:23more than 80 years ago.
1:05:27 > 1:05:32He was sure that when a supernova exploded, it left behind a kernel
1:05:32 > 1:05:37so dense that a cupful would be as heavy as a mountain.
1:05:39 > 1:05:42He called it a neutron star.
1:05:45 > 1:05:49It seemed so preposterous that Zwicky's ideas were dismissed.
1:05:51 > 1:05:55Until, that is, a new way of scouring the heavens emerged -
1:05:55 > 1:05:57radio astronomy.
1:06:08 > 1:06:12In 1967, the fledgling discipline picked up
1:06:12 > 1:06:15a strange repetitive message from outer space.
1:06:19 > 1:06:22Now, the people here say that if they got three signals
1:06:22 > 1:06:26as exactly spaced as that, it would be very unusual.
1:06:26 > 1:06:28If they got four, it would be phenomenal.
1:06:28 > 1:06:32Well, they've had pulses as exactly spaced as that 24 hours of the day
1:06:32 > 1:06:34since November.
1:06:37 > 1:06:41These pulses were so exact and predictable in their pattern
1:06:41 > 1:06:44that scientists even considered aliens as their source.
1:06:47 > 1:06:50It turned out they were being transmitted by something
1:06:50 > 1:06:52equally unlikely
1:06:52 > 1:06:54and just as unfamiliar.
1:06:55 > 1:06:58The most important question of all - what are they?
1:06:58 > 1:07:00Well, we know that they're very small.
1:07:00 > 1:07:03They're objects about the size of a planet.
1:07:03 > 1:07:06We know also that they are very energetic and that the source
1:07:06 > 1:07:09of energy must be far greater than a planet could really provide.
1:07:09 > 1:07:11It must be something like a star compressed
1:07:11 > 1:07:13into a volume the size of a planet.
1:07:17 > 1:07:22Scientists worked out that the new star had to be denser
1:07:22 > 1:07:24than any type previously discovered.
1:07:26 > 1:07:29Could these be the neutron stars predicted by Zwicky?
1:07:32 > 1:07:36Astronomers nicknamed them pulsars and immediately
1:07:36 > 1:07:40set their telescopes, searching for further clues about them.
1:07:46 > 1:07:50Just a year later, they found one,
1:07:50 > 1:07:54in the perfect place to put Zwicky's theory to the test.
1:07:57 > 1:07:59In the winter,
1:07:59 > 1:08:01we have access to the beautiful part of the sky
1:08:01 > 1:08:05that contains the constellation of Taurus, the Bull.
1:08:05 > 1:08:08Here we have the Pleiades, or the Seven Sisters,
1:08:08 > 1:08:11down here we have another cluster of the stars, which are the Hyades,
1:08:11 > 1:08:16that contain the bright star Aldebaran, the angry eye of the bull.
1:08:16 > 1:08:19And if we follow from Aldebaran in this direction towards
1:08:19 > 1:08:25that star there, just about there, we will find the closest pulsar
1:08:25 > 1:08:27to the solar system, the Crab Pulsar.
1:08:31 > 1:08:36What particularly excited scientists when they discovered the Crab Pulsar
1:08:36 > 1:08:40was that it was buried deep within the remains of a supernova.
1:08:43 > 1:08:48In this amazing picture, we see the remnant of a supernova explosion,
1:08:48 > 1:08:51but when we scan the central part of this nebula,
1:08:51 > 1:08:53we find the pulsar,
1:08:53 > 1:08:58which is the remnant of the core of the star that exploded.
1:09:03 > 1:09:07Now that a pulsar was definitively connected to a supernova,
1:09:07 > 1:09:11scientists realised that they had discovered
1:09:11 > 1:09:13another of the seven ages of starlight.
1:09:21 > 1:09:26It showed Swiss astronomer Zwicky was correct all along.
1:09:26 > 1:09:29His theoretical equations predicted
1:09:29 > 1:09:33how a supernova could leave behind such a dense remnant.
1:09:35 > 1:09:40The calculations focused on a strange quality of all matter.
1:09:42 > 1:09:47It's one that defies common sense but is fundamental
1:09:47 > 1:09:50to the work of astrophysicists like Professor Doug Leonard.
1:09:53 > 1:09:54Solidity is an illusion.
1:09:56 > 1:09:59If I run up with my fist and punch a brick wall, it will hurt like heck,
1:09:59 > 1:10:03but, essentially, my fist and the wall
1:10:03 > 1:10:05are almost entirely empty space.
1:10:08 > 1:10:11The illusion comes because we're made out of atoms,
1:10:11 > 1:10:14the fundamental building blocks of matter,
1:10:14 > 1:10:18and most of what an atom is is empty space.
1:10:19 > 1:10:23So, if this is an atomic nucleus containing the protons and neutrons,
1:10:23 > 1:10:27the electrons would be roughly where those buildings are
1:10:27 > 1:10:28in the background.
1:10:32 > 1:10:35Zwicky predicted the one thing violent enough to ram together
1:10:35 > 1:10:39atomic particles and fill all this empty space
1:10:39 > 1:10:43is the collapse of a massive star during a supernova.
1:10:45 > 1:10:48A collapse that happens in a matter of seconds.
1:10:50 > 1:10:51In a supernova,
1:10:51 > 1:10:56the very first thing that happens is the iron core implodes,
1:10:56 > 1:10:59from something about the size of the Earth down to something the size
1:10:59 > 1:11:02of a small city, and in that implosion,
1:11:02 > 1:11:04the densities become so high
1:11:04 > 1:11:07that the protons and the electrons get squeezed together
1:11:07 > 1:11:09to form neutrons.
1:11:11 > 1:11:16And, essentially, all the air of the atoms gets squeezed out of it,
1:11:16 > 1:11:20and what you're left with at the end is a ball of neutrons,
1:11:20 > 1:11:23an incredibly dense object that we call a neutron star.
1:11:28 > 1:11:33And as the neutron star formed, its magnetic field intensified.
1:11:36 > 1:11:39And became billions of times stronger than our suns.
1:11:42 > 1:11:46Now, as the star span,
1:11:46 > 1:11:50it channelled out radio signals from its north and south poles.
1:11:55 > 1:11:58Signals that swept past Earth with every rotation of the star.
1:12:03 > 1:12:06This was the source of the mysterious pulses.
1:12:08 > 1:12:11Some are so regular that pulsars are among
1:12:11 > 1:12:14the most accurate clocks in the universe.
1:12:18 > 1:12:22The discovery of neutron stars was a vindication of the power
1:12:22 > 1:12:24of theoretical physics.
1:12:26 > 1:12:29It set astronomers wondering if other strange bodies
1:12:29 > 1:12:33that had been predicted could be lurking in space.
1:12:35 > 1:12:38And there was one hypothetical object
1:12:38 > 1:12:41that was even weirder than a neutron star.
1:12:59 > 1:13:02The last stage of a star's life
1:13:02 > 1:13:06is as much an idea of science fiction as a physical reality.
1:13:08 > 1:13:12Put forward by science writer Adrian Berry in his book The Iron Sun,
1:13:12 > 1:13:14the suggestion is that, in the future,
1:13:14 > 1:13:17man could use black holes to transport himself instantly
1:13:17 > 1:13:21around the universe, and when I say instantly, I really mean like that.
1:13:24 > 1:13:29For years, most scientists dismissed black holes as fanciful conjecture.
1:13:31 > 1:13:35They were apparently nonsensical structures of space and time,
1:13:35 > 1:13:38spat out when Albert Einstein's equations were taken
1:13:38 > 1:13:41to their extreme conclusion.
1:13:41 > 1:13:44Einstein's theory of relativity does lead us into very strange
1:13:44 > 1:13:46and unfamiliar paths.
1:13:48 > 1:13:51Einstein himself didn't believe in black holes.
1:13:53 > 1:13:56But in our search to understand them, we might have found
1:13:56 > 1:13:58a clue to the biggest question of all.
1:14:01 > 1:14:04The very origin of the universe.
1:14:10 > 1:14:13It's like there's just a huge question mark in the sky,
1:14:13 > 1:14:15where one of these things exists.
1:14:16 > 1:14:19They are the most mysterious objects in space.
1:14:21 > 1:14:24It's where the equations themselves break down.
1:14:27 > 1:14:31Black holes are so complex, so fantastical,
1:14:31 > 1:14:34that even now we know they ARE real,
1:14:34 > 1:14:37they throw up more questions than answers.
1:14:39 > 1:14:44How can they exist? They simply don't make sense.
1:14:45 > 1:14:51A black hole represents a spot in space around which the gravity
1:14:51 > 1:14:55is so intense that nothing, not even light, can get away.
1:14:57 > 1:15:00It's a region bounded by something called the event horizon
1:15:00 > 1:15:04within which all events are beyond the horizon of someone outside,
1:15:04 > 1:15:08meaning they cannot see anything that's happening inside there,
1:15:08 > 1:15:13so it's a region of space from which no information can ever escape.
1:15:15 > 1:15:19Scientists think that these extraordinary monsters in space
1:15:19 > 1:15:23are created by the death of the most massive stars.
1:15:27 > 1:15:32Rare stars whose cores are so huge that when they collapse,
1:15:32 > 1:15:34they don't turn into a pulsar.
1:15:34 > 1:15:37The collapse just keeps on going.
1:15:42 > 1:15:45It remains, to some extent, a theory...
1:15:47 > 1:15:50..but Doug Leonard has got as close as anyone
1:15:50 > 1:15:52to actually seeing it happen.
1:15:57 > 1:15:59It started by getting an alert on the computer
1:15:59 > 1:16:03that a supernova had gone off in a very nearby galaxy,
1:16:03 > 1:16:05only 210 million light years away.
1:16:08 > 1:16:13Here's a picture of the supernova indicated by the arrow,
1:16:13 > 1:16:14and so what we immediately did
1:16:14 > 1:16:18was trawl through the Hubble Space Telescope archives
1:16:18 > 1:16:22to see if we could find a picture of that exact spot in the sky
1:16:22 > 1:16:24taken before the star had actually exploded,
1:16:24 > 1:16:27and, as luck would have it, someone did.
1:16:30 > 1:16:32The image revealed that the supernova
1:16:32 > 1:16:37was the explosion of a star dubbed LBV-1, in a distant galaxy.
1:16:43 > 1:16:47Doug and his team realised that they had an unprecedented opportunity.
1:16:49 > 1:16:52Because the star had been a super-massive one,
1:16:52 > 1:16:56at least 50 times the mass of the sun.
1:16:57 > 1:17:02It was exactly the size to test out the theoretical equations.
1:17:04 > 1:17:07Could this possibly be the birth of a black hole?
1:17:11 > 1:17:14Two years we waited for all of the fireworks
1:17:14 > 1:17:17and embers of the supernova to disappear and go away,
1:17:17 > 1:17:21so that we could get a third picture long after the supernova was gone
1:17:21 > 1:17:27to see if that star in fact had disappeared, and in fact it had.
1:17:27 > 1:17:28It was now gone.
1:17:28 > 1:17:32It was an extremely luminous star, it blew up and now it was gone.
1:17:36 > 1:17:40The evidence suggested that billions of tonnes of matter
1:17:40 > 1:17:44from a massive star had shrunk to nothing.
1:17:56 > 1:18:00So what we're left with here is this mind-boggling idea
1:18:00 > 1:18:05of mass contained in zero volume, and that just makes your head spin,
1:18:05 > 1:18:07but that's what we call a black hole.
1:18:09 > 1:18:13It's these very qualities that make some scientists think
1:18:13 > 1:18:17understanding black holes could hold the key not to death
1:18:17 > 1:18:22but to the birth of the very first stars.
1:18:26 > 1:18:30It's really an awe-inspiring story,
1:18:30 > 1:18:33much more so than the classical creation myths
1:18:33 > 1:18:35that make it seem so easy.
1:18:40 > 1:18:42Scientists have discovered that there's one other place
1:18:42 > 1:18:47you can find a point of infinite density and zero volume.
1:18:55 > 1:19:00That's at the instant the universe began,
1:19:00 > 1:19:04a moment studied by astronomer Dr Alan Dressler.
1:19:04 > 1:19:08Today, it's scientific orthodoxy, but it wasn't always that way.
1:19:10 > 1:19:13The idea that the universe had a creation event
1:19:13 > 1:19:17from a scientific perspective was a revolutionary idea.
1:19:19 > 1:19:23Every bit as remarkable a revolution as the idea
1:19:23 > 1:19:27that the sun and not the Earth was the centre of the solar system.
1:19:29 > 1:19:32Scientists call it the Big Bang,
1:19:32 > 1:19:36and it was predicted by the very same equations
1:19:36 > 1:19:39that discovered black holes.
1:19:39 > 1:19:42There's the Big Bang theory according to which...
1:19:42 > 1:19:47The universe began with a gigantic fireball on creation day,
1:19:47 > 1:19:50some 10,000 million years ago.
1:19:57 > 1:20:00It was here, at the beginning of the universe,
1:20:00 > 1:20:02that scientists found the answer
1:20:02 > 1:20:06to the ultimate question about the lives of stars.
1:20:11 > 1:20:15Where did the hydrogen to make the very first ones come from?
1:20:18 > 1:20:23From this very early instant came a primordial soup of energy and matter
1:20:23 > 1:20:27that had to cool before it could become the elements of hydrogen
1:20:27 > 1:20:31and helium that made everything else in the universe we know today.
1:20:35 > 1:20:38Every hydrogen atom that fuelled every star
1:20:38 > 1:20:41was made in those first few minutes of the Big Bang.
1:20:45 > 1:20:49The extraordinary thing about the lifecycle of the stars
1:20:49 > 1:20:52is that it's revealed the origin of the universe,
1:20:52 > 1:20:56the elements, even of us.
1:20:58 > 1:21:01But that isn't quite the end of the star story.
1:21:05 > 1:21:08Astronomers have discovered one other tantalising fact
1:21:08 > 1:21:11as they've looked out into the dark sky.
1:21:15 > 1:21:18In nebulae, formed from the remnants of stars
1:21:18 > 1:21:21and where the next generation are born,
1:21:21 > 1:21:25they've discovered the earliest stirrings of life.
1:21:43 > 1:21:47Even for NASA, nebulae are too far away to visit...
1:21:51 > 1:21:56..so they've built one of their own here on Earth.
1:21:58 > 1:22:0340 years ago, scientists peered into the clouds of dust and gas
1:22:03 > 1:22:07created from the remains of stars and, to their surprise,
1:22:07 > 1:22:11found not just elements but organic molecules.
1:22:14 > 1:22:18I think it really is a shift in people's thinking about this.
1:22:18 > 1:22:1950, 60 years ago, people didn't think
1:22:19 > 1:22:22space had any of this kind of molecular complexity.
1:22:22 > 1:22:23Now we know it does.
1:22:25 > 1:22:28Many of these molecules are organic molecules.
1:22:28 > 1:22:31Many of them may be complex, and, in fact, some of them
1:22:31 > 1:22:34are likely to be the kinds of molecules you like to have around
1:22:34 > 1:22:35if you want to have life get started.
1:22:37 > 1:22:41Dr Scott Sandford is at the cutting edge of research at NASA
1:22:41 > 1:22:45where they're trying to answer an extraordinary question about stars.
1:22:48 > 1:22:52Just how many steps towards life can be made in the nebulae
1:22:52 > 1:22:56that are the stellar nurseries and graveyards of outer space?
1:23:00 > 1:23:02What we have right now is a nice little simulation
1:23:02 > 1:23:05of an interstellar dense molecular cloud,
1:23:05 > 1:23:08so this is a star formation region in a jar, basically.
1:23:08 > 1:23:11And now we just need to let it cook for 24 hours
1:23:11 > 1:23:15and then we'll be ready to pull the sample out and see what we made.
1:23:22 > 1:23:26When Scott and other scientists have analysed their results,
1:23:26 > 1:23:29what they've found is that as the nebulae create stars,
1:23:29 > 1:23:33they make the building blocks of living things on Earth.
1:23:36 > 1:23:39There's just a whole host of compounds we make.
1:23:39 > 1:23:42We find that many of these compounds are very interesting,
1:23:42 > 1:23:44because they play roles in life on Earth,
1:23:44 > 1:23:48and so it's clear we're making many of the building blocks of life
1:23:48 > 1:23:51by these very processes that happen in space.
1:23:55 > 1:23:58These molecules might hold the secret
1:23:58 > 1:24:01to how life began on our planet.
1:24:04 > 1:24:09If they were part of the process, they'd have to firstly get to Earth,
1:24:09 > 1:24:12and scientists have found a delivery system.
1:24:16 > 1:24:19This is part of a meteorite that crashed from outer space
1:24:19 > 1:24:23to Earth in Australia.
1:24:23 > 1:24:26In it were found many of the organic compounds
1:24:26 > 1:24:29vital to life on our planet.
1:24:29 > 1:24:32The amino acids in this meteorite predate the arrival
1:24:32 > 1:24:35of this meteorite to the Earth, so in fact these amino acids
1:24:35 > 1:24:38had to have been made in space in some environment,
1:24:38 > 1:24:41and so amino acids do exist out there in space
1:24:41 > 1:24:43and they do get delivered to plants.
1:24:44 > 1:24:48Perhaps life didn't have to start from scratch here on Earth.
1:24:48 > 1:24:52Could the building blocks have been scattered from space?
1:24:54 > 1:24:56We don't know if the origin of life on the Earth
1:24:56 > 1:24:59owes its existence to these kinds of materials being delivered from space,
1:24:59 > 1:25:01because we don't understand how life got started.
1:25:01 > 1:25:05However, the analogy is if you're trying to build a Lego castle,
1:25:05 > 1:25:08it's probably a lot easier if Legos fall out of the sky on you
1:25:08 > 1:25:10than if you have to build Lego blocks from scratch
1:25:10 > 1:25:12and then make your Lego castle.
1:25:13 > 1:25:17And if those Lego pieces were available to Earth,
1:25:17 > 1:25:20they could be available to planets orbiting other stars.
1:25:20 > 1:25:24Well, given that we know that just about anywhere you make stars,
1:25:24 > 1:25:26you're going to make these Lego blocks,
1:25:26 > 1:25:29and the fact that there are a huge number of environments
1:25:29 > 1:25:31where these Lego blocks will be delivered,
1:25:31 > 1:25:33I personally would be quite surprised
1:25:33 > 1:25:36if there isn't other life out there.
1:25:39 > 1:25:42We may never know for sure whether there is life elsewhere.
1:25:46 > 1:25:49But we do know a lot about where we came from.
1:25:54 > 1:25:59And that's because we've learnt so much about things here on Earth
1:25:59 > 1:26:03from looking far out into space.
1:26:07 > 1:26:10The discovery that stars are not eternal,
1:26:10 > 1:26:16that they actually have their birth, their lives and they eventually die,
1:26:16 > 1:26:20is one of the greatest achievements of modern science.
1:26:20 > 1:26:22And even more amazing,
1:26:22 > 1:26:25that we have achieved that from this little vantage point
1:26:25 > 1:26:29in the corner of a galaxy, the Milky Way.
1:26:31 > 1:26:36Imagine that we live in a completely clouded planet, say like Venus,
1:26:36 > 1:26:41that nobody ever has seen the stars, the movements of the sky,
1:26:41 > 1:26:46I wonder, our culture, our science would have been completely different.
1:26:46 > 1:26:48Our lives would be completely different.
1:26:48 > 1:26:51So how lucky we are to be here on this planet
1:26:51 > 1:26:55with this beautiful transparent atmosphere that allows us
1:26:55 > 1:26:59to admire the majestic display of the starry night.
1:27:03 > 1:27:07By looking at the stars, generations of imaginative scientists
1:27:07 > 1:27:11have stretched the boundaries of knowledge,
1:27:11 > 1:27:17discovering truths stranger than fiction...
1:27:17 > 1:27:22and, through the stars, uncovered the story of the universe.
1:27:24 > 1:27:28But like all good tales, it will eventually come to an end.
1:27:35 > 1:27:37About 100 trillion years from now,
1:27:37 > 1:27:42the raw materials for new stars will run out.
1:27:43 > 1:27:48The last will play out their lives and their remnants gradually fade,
1:27:48 > 1:27:55until, finally, the one remaining cinder goes cold
1:27:55 > 1:28:00and light will be extinguished from the universe.
1:28:17 > 1:28:21Subtitles by Red Bee Media Ltd