{353}{490}In March 2000, two astronomers |made an extraordinary discovery.
{515}{682}one that is set to overturn our understanding |of how the Universe formed.
{710}{803}We're never going to see a time |like this in astronomy again.
{805}{937}Really the air is filled |with new discoveries and new ideas.
{977}{1065}What they discovered was |a very simple relationship,
{1072}{1149}a relationship between |the galaxy we live in
{1151}{1254}and the most destructive force |in the Universe.
{1301}{1390}A supermassive black hole.
{1441}{1535}It set the world |of cosmology alight.
{1582}{1694}Six months ago people were not that excited |about supermassive black holes.
{1696}{1780}The general astronomer did not care |that much about supermassive black holes.
{1782}{1841}Now they have to |and now they'd better!
{2312}{2421}Supermassive Black Holes
{2663}{2828}The ultimate aim of cosmology is |to understand how the Universe was formed.
{2920}{3041}One of the most important questions |is how galaxies were created,
{3043}{3138}because without them |we wouldn't exist.
{3169}{3266}Galaxies contain almost all the stars |we see in the Universe
{3268}{3362}and maybe the places where all stars |in the Universe will be created
{3364}{3499}and stars are what produce |oxygen, carbon, planets,
{3501}{3542}everything you need for life
{3544}{3617}and without life |you don't get astronomers.
{3664}{3735}We see our galaxy, the Milky Way,
{3738}{3808}as a band of stars in the sky.
{3864}{4047}In fact it's a giant rotating disc |200,000 light years wide.
{4096}{4203}It contains over 200 billion stars |like our own sun,
{4206}{4279}circling slowly around the centre,
{4362}{4491}but we are just one |in 125 billion galaxies
{4493}{4600}of different shapes and sizes |spinning through space.
{4619}{4683}Yet scientists haven't been |able to explain
{4685}{4787}how a single one |of these galaxies was created.
{4861}{4958}Galaxy formation is a very complicated process.
{4960}{5005}It involves gravity
{5010}{5118}and it involves large balls |of gas colliding,
{5120}{5205}it involves the dynamics of stars,
{5207}{5283}it involves the chemistry |of the gas coming together.
{5342}{5429}All we know is that |when the Universe was young
{5431}{5492}there were no stars or planets,
{5494}{5589}just great swirling clouds |of hydrogen gas.
{5610}{5726}The mystery is how each |of these clouds turned into:
{5728}{5832}the complex galaxies |of stars we see today.
{5918}{5972}We just don't know how they do it,
{5974}{6114}how galaxies formed out |of the, the ionised hot gas
{6116}{6257}that filled the Universe is still physics |that we do not really understand yet.
{6281}{6350}Exactly how galaxies were created
{6352}{6476}has troubled the world's leading astronomers |and physicists for decades,
{6479}{6625}but 6 months ago scientists found |evidence for an extraordinary answer.
{7070}{7179}The Nuker team is a group |of world respected astronomers,
{7200}{7265}but they're not galaxy experts.
{7296}{7450}They are experts in the most violent |and destructive forces known to science:
{7481}{7553}supermassive black holes.
{7660}{7797}Until recently, supermassive |black holes were mere theory.
{7799}{7928}These are giant black holes |of apocalyptic proportion.
{8067}{8228}Supermassive black holes are a million to a billion |times the mass of, of a, of a typical black hole.
{8230}{8297}They could fill a whole solar system.
{8431}{8585}A supermassive black hole |is quite simply gravity gone mad.
{8647}{8718}An object of such concentrated matter
{8720}{8819}its gravitational pull is insatiable.
{9024}{9066}Nothing can escape it,
{9068}{9124}not even light itself.
{9126}{9163}Anything that gets close
{9165}{9319}- gas, stars and entire solar systems |- are sucked into oblivion.
{9351}{9448}It even destroys |the very fabric of the Universe.
{9715}{9810}If you think of the Universe |as a space-time web,
{9812}{9946}the gravity of ordinary stars |and planets creates a dent in this web,
{10062}{10188}but the immense gravity |of a supermassive black hole is so destructive
{10190}{10283}that it distorts space-time |to breaking point.
{10672}{10744}At the heart |of a supermassive black hole
{10746}{10889}is one of the most mysterious things |in physics - the singularity,
{10891}{11081} a point where space, time |and all known laws of physics fall apart.
{11092}{11192}What happens at the centre |of the singularity is a complete mystery
{11202}{11315}and solving it is going to require |new physics that we just don't have right now.
{11317}{11383}Some people think that you can |fall through the singularity
{11385}{11462}and pop out in another part |of the Universe.
{11465}{11570}The theories for the singularity are, |some of them are very, very radical.
{11572}{11600}We just don't know.
{11730}{11805}Supermassive black holes are so bizarre
{11808}{11907}that until recently many scientists |doubted they existed at all.
{11920}{11958}They were an extreme idea,
{11972}{12084}dreamt up to explain a very rare |and distant type of galaxy:
{12117}{12169}active galaxies.
{12199}{12288}These are amongst the brightest objects |in the Universe.
{12299}{12373}These galaxies have |a brilliant burning core
{12375}{12473}with vast jets of energy |spurting out of the centre.
{12840}{12984}This ferocious heart of brilliant |hot gas is called a quasar.
{13003}{13176}Scientists thought this whirling mass might be caused |by a giant black hole sucking up gas and stars,
{13178}{13270}literally feeding on the centre |of the galaxy.
{13386}{13498}The idea is that the quasars that we see |that look so bright are not the black hole,
{13500}{13534}the supermassive black hole,
{13536}{13613}they are the gas that's just about |to fall into the supermassive black hole,
{13615}{13650}that's going around it,
{13656}{13757}shining very brightly just before |it disappears down the black hole.
{13857}{13977}A giant black hole would have |a gravitational pull so overwhelming
{13979}{14103}it would hurl gas and stars around it |at almost the speed of light.
{14106}{14258}The violent clashing would heat |the gas up to over a million degrees.
{14294}{14353}The gas rubs against itself essentially
{14355}{14398}and gets extremely hot
{14400}{14479}and extremely hot gas shines very brightly.
{14506}{14588}In reality, although a quasar burns brightly,
{14590}{14678}it is actually impossible to see |if there's a black hole in the middle.
{14681}{14821}Paradoxically the black hole is made |invisible by the fact that it swallows light.
{14894}{14944}So for years no-one could be certain
{14946}{15118}if supermassive black holes really did exist |at the heart of these strange active galaxies.
{15225}{15359}The Nukers have spent the last two decades |hunting for these elusive monsters.
{15369}{15519}The first problem they faced was to prove |that supermassive black holes existed at all.
{15530}{15673}What they were to discover would be stranger |than most people could have imagined.
{15800}{15921}One of the first of the Nukers |to try to find one was Alan Dressler.
{15986}{16090}In 1983 he came to the Palomar |Telescope in California,
{16092}{16238}convinced that he'd found a way |to prove that supermassive black holes exist.
{16255}{16362}You can't see a black hole directly |- that's what makes it a black hole
{16365}{16442}- so what you're looking for |is evidence of its gravity,
{16445}{16562}you're looking at how it pulls on |the stars that are coming nearby.
{16653}{16732}Dressler knew that although |a black hole is invisible,
{16735}{16902}its immense gravity would hurl stars |around it at over 500,000 kilometres an hour.
{16957}{17025}By measuring how fast |these stars were moving,
{17027}{17160}he could prove if there really was |a black hole at the centre of an active galaxy.
{17175}{17302}I picked a galaxy nearby |which is called NGC1068,
{17304}{17388}an active galaxy, which meant that |it probably had a supermassive black hole in it,
{17390}{17458}at least that's what we wanted to prove.
{17488}{17617}To be certain that the stars |were moving unnaturally fast in NGC1068,
{17619}{17759}Dressler wanted to compare them with stars |in a normal galaxy, without a black hole.
{17790}{17923}Stars circling around a weak centre |of gravity would move at half the speed.
{17950}{18060}So for this comparison he chose |the very ordinary galaxy next door to us,
{18062}{18192}Andromeda, with a quiet, |inactive centre like our own.
{18336}{18441}To measure the speed of the stars |in these two very different galaxies,
{18443}{18527}Dressler used an instrument |called a spectroscope.
{18540}{18596}This looks at the changing |pattern of light
{18598}{18699}coming from stars as they rotate |around the galaxy core.
{18778}{18883}The spectroscope shows the centre |of the galaxy as a white band
{18885}{19030}and the movement of stars around the core |is traced by a dark vertical line.
{19065}{19153}If the stars at the galaxy's |centre are circling slowly
{19155}{19246}then the dark band would |show hardly any change,
{19364}{19424}but if they're travelling |at great speed,
{19426}{19547}whizzing towards and away from us |either side of a supermassive black hole
{19549}{19689}then the dark band should show a sudden |shift across the centre of the galaxy.
{19794}{19928}I would expect to see some |rather rapid change in this dark line
{19930}{19992}so that there'd be |a very big change in the speed
{19994}{20056}from one side of the galaxy |to the other,
{20058}{20101}very suddenly, |right over the centre,
{20103}{20180}and that would show that |the stars were moving very rapidly
{20182}{20211}in the centre of the galaxy
{20213}{20279}because of the influence |of a great mass in the centre,
{20281}{20319}the supermassive black hole.
{20669}{20876}Over the next few nights Dressler measured the speed |of the stars in NGC1068 and in Andromeda.
{21175}{21240}When the results came down |from the telescope
{21242}{21342}he saw something |that was completely unexpected.
{21415}{21465}The picture from the active galaxy,
{21467}{21565}where he hoped to find |a black hole, was unreadable.
{21567}{21726}NGC1068 was just too far away |for the telescope to get a clear picture.
{21803}{21970}The surprise came from Andromeda, |the quiet, normal galaxy right next to us.
{22330}{22473}I was astonished when I found what |I was looking for, but not where I was looking for it.
{22475}{22654}This jog in this dark band shows that |on one side the stars were moving very rapidly
{22656}{22826}away from us at 150 kilometres a second, |which is 500,000 kilometres an hour.
{22868}{22936}Dressler thought |there could only be one thing
{22938}{23010}that would cause the stars |to move this fast:
{23012}{23098}a supermassive black hole
{23127}{23185}and he wasn't alone.
{23204}{23331}Fellow Nuker John Kormendy |had found exactly the same thing.
{23399}{23445}The moment I could see that wiggle
{23447}{23495}I knew essentially instantly
{23497}{23599}that there was a very good chance |that this would be a supermassive black hole.
{23608}{23706}When you see something like that |you know you're on to something.
{23750}{23865}They'd found evidence of the most |terrifying force in nature,
{23867}{23977}but worryingly it wasn't |in some far-off active galaxy.
{23979}{24168}This supermassive black hole was |in the very ordinary galaxy right next door to us.
{24359}{24482}Andromeda seemed to have |a black hole but no bright quasar.
{24498}{24591}If there was a supermassive black hole |why wasn't it shining?
{24597}{24675}That suggested that there was |not stuff falling in.
{24677}{24799}Maybe lots of galaxies could have a dormant phase |where they had a supermassive black hole
{24801}{24883}but they weren't being fed |so they weren't shining.
{24909}{24993}A few theorists had predicted |this very thing:
{24998}{25104}supermassive black holes |could exist in two states.
{25136}{25279}When it's feeding a giant black hole |creates a bright burning gas disk around it
{25298}{25359}and then for some reason |it stops feeding,
{25361}{25509}leaving a dark, deadly core lurking |menacingly in the centre of the galaxy
{25642}{25792}and one of these dark, silent monsters |had been found in our neighbouring galaxy.
{26015}{26107}The discovery of a massive |black hole lurking so close to us
{26109}{26174}made headlines around the world,
{26198}{26290}but many scientists found |the news impossible to believe.
{26293}{26400}They didn't think the evidence was |good enough for such an extreme idea.
{26403}{26507}Even the Nukers themselves |began to have doubts.
{26550}{26606}There is always the danger |that instead of being a black hole,
{26608}{26688}it's a dense cluster of something else |that's dark, that's not a black hole.
{26690}{26805}I thought there was a fair chance that |we'd made some terrible bone-headed mistake
{26807}{26871}and that somebody within a year |was going to write a paper
{26873}{27005}and show that we were a bunch of idiots |and we would feel terrible about it.
{27037}{27078}To convince the sceptics,
{27080}{27225}they needed to find more supermassive |black holes in many more galaxies.
{27235}{27347}For this they needed |to look further into space.
{27495}{27586}So they turned |to Hubble Space Telescope.
{27771}{27947}From 1994 Hubble began a systematic survey |of the centres of distant galaxies
{27984}{28157}searching for the tell-tale signature of stars |speeding around a supermassive black hole.
{28282}{28431}Astronomers started by looking |at an active galaxy, M87.
{28433}{28612}As expected it had a giant feeding black hole |shooting a great jet of energy into space.
{28702}{28809}But it was when the search broadened out |to include inactive galaxies as well,
{28811}{28877}that something incredible happened.
{28942}{29013}In every galaxy |scientists looked at
{29015}{29123}they found evidence |for a supermassive black hole.
{29180}{29232}(SANDRA FABER) NGC3115.
{29234}{29271}(JOHN KORMENDY) NGC3377.
{29273}{29309}(KARL GEBHARDT) NGC3379.
{29311}{29345}(DOUG RICHSTONE) M31 and M32.
{29347}{29466}In total there's probably 20-30 |or so black holes that have been found.
{29507}{29595}Supermassive black holes |were supposed to be rare,
{29599}{29670}but Hubble was finding them everywhere,
{29673}{29813}both feeding in active galaxies |and lurking quietly in ordinary galaxies.
{29843}{29938}Pretty soon we got used to the idea
{29949}{30039}that everything we would look at |would have a black hole in it.
{20041}{30115}You know, after the first three |or four cases we were beginning to wonder:
{30117}{30167}does every one |have a black hole.
{30169}{30358}One by one we were seeing this picture |sort of emerge out of the fog
{30360}{30478}that, that every galaxy, or almost every galaxy, |had a supermassive black hole in it.
{30480}{30529}It was really quite astonishing.
{30586}{30648}Far from being |rare freaks of nature,
{30650}{30806}the Nukers began to suspect that all galaxies |could have giant black holes at their hearts.
{30844}{31007}If this was true it would revolutionise |ideas of what a galaxy actually is.
{31041}{31140}More disturbingly, it meant |there could be a supermassive black hole
{31142}{31261}lurking at the heart |of our very own galaxy, the Milky Way.
{31617}{31714}Andrea Ghez has been coming |to Hawaii for the last five years,
{31716}{31853}trying to find out if there's a supermassive |black hole in the middle of the Milky Way.
{31972}{32029}When I first started thinking |about astronomy
{32031}{32149}it never occurred to me that there might be |a supermassive black hole at the centre of our galaxy.
{32151}{32260}The idea was that galaxies rotated |just around the mass of the centre,
{32262}{32383}which was just stars and gas and dust |and nothing particularly exotic.
{32385}{32497}Andrea Ghez has been using a telescope |even more powerful than Hubble
{32499}{32656}- the Keck Telescope, perched 14,000ft up |on the sacred mountain of Mauna Kea.
{32709}{32813}The Keck telescope is the biggest |optical telescope in the world.
{32815}{32899}It has a vast mirror, |10 metres across,
{32901}{33021}made up of 36 segments |of highly polished aluminised glass.
{33036}{33109}The Keck telescope |is a fabulous telescope to use.
{33111}{33156}It's great because it's large.
{33158}{33209}This is a case |where bigger is better.
{33211}{33301}You get to collect a lot of photons, |you can see very faint things
{33303}{33373}and it allows you |to see very fine details.
{33608}{33793}Four times a year, Ghez focuses the telescope |on the stars at the very heart of our Milky Way.
{34013}{34159}She's looking for the tell-tale high speeds |that reveal the presence of a black hole.
{34205}{34276}The centre of the Milky Way |is so near
{34278}{34333}and the Keck telescope |so powerful
{34335}{34503}Ghez is able to see closer into the centre |of the galaxy than anyone has ever done before.
{34791}{34895}Here's an example of one of the images |we got just last night.
{34910}{35026}The seeing was, it was kind of a typical night, |not the best night, not the worst night.
{35028}{35107}Each one of these blobs |here is a star
{35109}{35225}and what you see is each star is distorted |- that's what the atmosphere does.
{35227}{35264}It's like looking through a pond,
{35266}{35323}like you want to look at a penny |at the bottom of a pond
{35325}{35383}and the water's moving, |it looks all distorted
{35385}{35433}and it looks different |every time you look,
{35435}{35542}so this is one exposure |and the next exposure looks like this.
{35554}{35650}By superimposing thousands |of these pictures taken overnight,
{35652}{35738}the computer can compensate |for the atmosphere's distortion
{35740}{35837}producing a detailed picture |of the centre of the galaxy.
{35848}{35918}You can see the position |of the stars very accurately.
{35921}{35990}If we go into the centre here
{35992}{36026}and rescale it,
{36028}{36113}we actually see that there are fainter stars |towards the centre of our field of view
{36115}{36177}and these stars |are extremely important.
{36203}{36335}It's the motion of these stars |that reveal the presence of the black hole.
{36425}{36540}Ghez has been following the motions |of these stars for the last five years.
{36542}{36631}If there was no black hole |they'd be moving very slowly,
{36633}{36762}but she's discovered they're circling |at speeds of over 1,000 kilometres a second.
{36788}{36933}These stars that we've been watching are 2 light |weeks from the, from the centre of our galaxy,
{36935}{37016}so their motion, the fact they are going |1,000 kilometres per second
{37018}{37221}tells us that within 2 light weeks there's |2 million times the mass of the sun of matter there.
{37256}{37345}There's only one thing |in the Universe this dense.
{37348}{37505}Lying at the centre of this necklace |of spinning stars is a supermassive black hole.
{37507}{37592}You can't see it, |but it's there.
{37648}{37860}The most destructive force in the Universe is lurking |at the heart of our very own galaxy, the Milky Way.
{37971}{38116}The puzzle for cosmologists now is |what affect it has on the galaxy around it.
{38249}{38374}If, as it now seems, every single galaxy |has a black hole at its heart,
{38376}{38437}this can't be a coincidence.
{38550}{38654}Perhaps black holes are |an essential part of what galaxies are
{38657}{38704}and how they work.
{38745}{38830}We found that there's a relationship |between the mass of the black hole
{38832}{38900}and the mass |of the surrounding host galaxy
{38908}{39019}in the sense that small galaxies have |small black holes of around a million solar masses
{39021}{39130}and big galaxies have big black holes |of round a billion solar masses.
{39205}{39350}Every single black hole was almost exactly |in proportion to the size of its galaxy.
{39352}{39397}No matter how big or small,
{39399}{39560}bizarrely the galaxy always had a black hole |half a percent of its entire mass.
{39607}{39705}This was surprising |and immediately leads to questions: why?
{39800}{39955}No-one had expected that black hole size |and galaxy size could possibly be related.
{39965}{40117}It suggested some mysterious invisible |connection between a galaxy and its black hole,
{40119}{40286}but what this was a mystery scientists |would have to wait three years to solve.
{40500}{40624}The first breakthrough came when a new |instrument was added to Hubble Space Telescope.
{40674}{40772}This dramatically accelerated |the discovery of new black holes,
{40774}{40874}giving scientists a wealth |of new potential leads to follow.
{40937}{41040}For three years the data |has been coming down to Earth.
{41055}{41179}Amongst those who've been sifting through it |are two young competing researchers.
{41238}{41386}What they were to discover this year |would turn the world of cosmology on its head.
{41388}{41466}Every day I go to work I don't really |know what's going to happen,
{41468}{41570}but I can count that it's going |to be something exciting every single day.
{41572}{41685}These past six months have been phenomenal |in terms of black hole research.
{41687}{41719}We've been extremely excited,
{41721}{41873}we're finding these black holes in, in, in numbers |that we had never been able to do before.
{41965}{42096}Karl Gebhardt and Laura Ferrarese were trying |to find the fundamental connection
{42098}{42177}linking black holes |and their galaxies,
{42189}{42287}so they searched through |all the different galaxy characteristics
{42293}{42402}looking for any new links |that might give a clue.
{42502}{42581}But it wasn't until they looked |at a property called sigma
{42583}{42709}that the mystery began to unravel.
{42711}{42859}Sigma is a just a very, very fancy name |for something that's actually very simple.
{42881}{43028}Sigma is the speed at which the stars |are circling in the outer reaches of the galaxy.
{43058}{43160}The stars at the edge of the galaxy |are so far away from the black hole
{43162}{43247}that they're completely |unaffected by its gravity.
{43310}{43365}Those stars don't feel |the black hole,
{43367}{43425}they feel the rest |of the stars in the galaxy,
{43427}{43480}they don't know or care |that the black hole is there.
{43482}{43607}If you took the black hole away from the galaxy |they'd be moving at exactly the same speeds.
{43617}{43666}This has lead scientists to believe
{43668}{43765}there couldn't possibly by any connection |between the size of the black hole
{43767}{43854}and the speed of the stars |at the edge of the galaxy.
{43878}{43955}They were about |to be proved wrong.
{44107}{44176}As the two researchers |went through the new data,
{44178}{44274}they first had to calculate |the mass of each black hole.
{44316}{44450}Then they found out the speed at which |the stars were moving at the edge of the galaxy
{44468}{44542}and plotted all these figures |on a graph.
{44655}{44748}As they came in I would take |that new black hole mass
{44750}{44865}and the sigma for that galaxy |and add it to my plot.
{44886}{44959}There should be no relationship |between the two,
{44995}{45122}yet as they added each new point marking the speed |of the stars against the mass of the black hole,
{45124}{45192}a clear pattern started to emerge.
{45327}{45463}To their amazement the points lay |in an obvious band across the graph.
{45465}{45525}The properties were clearly related:
{45527}{45693}the bigger the black hole, the faster the speed |of the stars at the edge of the galaxy.
{45855}{45974}What we discovered is that the supermassive |black holes at the centre of galaxies
{45976}{46100}and the galaxies themselves |are really very tightly intertwined.
{46144}{46276}The stars on the edge of the galaxy have |no physical connection with the black hole.
{46278}{46457}Yet somehow their speed is tightly bound |with the size of the black hole billions of miles away.
{46471}{46549}If the two things aren't |physically linked now,
{46551}{46674}it means they must have been |at some point in the past.
{46731}{46806}The fact that we see there's |such a tight relationship
{46808}{46841}between the speed of the stars
{46843}{46887}and the black hole in the middle
{46889}{46970}is a probe to what happened |early on in the galaxy.
{46972}{47052}It screams at you something |that you don't yet understand
{47054}{47156}about the connection between galaxy |formation and black hole formation.
{47181}{47281}The relationship points |at an extraordinary idea:
{47283}{47429}that galaxies and their giant black holes |could be linked from birth.
{47431}{47532}In fact, scientists thought |that supermassive black holes
{47534}{47673}might even be involved in the formation |of the galaxies themselves.
{47715}{47772}This correlation's |the most important thing
{47774}{47861}we've learned about supermassive |black holes so far.
{47863}{47919}Astronomers are always looking |for correlations.
{47921}{48001}Whenever you find one |that's really tight, like this one,
{48003}{48113}it's a sign that there's some basic physics |there that you need to look for.
{48193}{48277}As it happens, the physics |that might explain what was going on
{48279}{48328}had been suggested years before:
{48330}{48421}by theorists Martin Rees and Jo Silk.
{48492}{48622}Jo Silk has spent much of his life |trying to solve the mystery of galaxy formation.
{48646}{48768}Three years ago it became clear |that he'd been missing a vital ingredient.
{48774}{48842}If there was a black hole |in every galaxy,
{48844}{48940}then scientists would need |to explain what it was doing there.
{48971}{49092}We had to rethink our ideas |of how galaxies were made.
{49094}{49167}To understand the first light |of the Universe
{49169}{49343}we really have to include the role of these |supermassive black holes in galaxy formation.
{49452}{49586}All previous ideas of galaxy formation |had assumed that gas in the early Universe
{49588}{49674}simply condensed |to form stars and galaxies.
{49899}{50012}Silk and Rees came up |with a completely different idea.
{50060}{50258}They proposed that the centre |of each early gas cloud could have collapsed
{50277}{50351}to form a giant black hole.
{50445}{50538}The black hole would immediately |start feeding on the gas around it,
{50540}{50602}creating a brilliant quasar.
{50774}{50872}Silk realised that the energy |from this newly formed quasar
{50874}{50987}would create intense temperature |changes in the surrounding gas.
{51034}{51098}This would cause the gas |around the black hole
{51100}{51248}and its newly formed quasar |to condense into stars,
{51411}{51461}which means, in effect,
{51463}{51586}that the black hole could have helped |to trigger the birth of the galaxy.
{51703}{51856}We think of black holes normally as being |destructive influences on their surroundings.
{51858}{51905}In this case they're creative,
{51907}{52033}they're having a very positive impact |on the formation of the galaxies.
{52048}{52091}But there was more.
{52109}{52313}This theory predicted when and why the black hole |would eventually stop feeding and go quiet.
{52405}{52460}They calculated |that this would happen
{52462}{52535}when the feeding black hole |grew so large
{52537}{52632}that the vast amount of energy |spewing from its bright quasar
{52634}{52758}would literally force the rest |of the galaxy out of its reach.
{52860}{53028}It has the effect of pushing |a wind against the surrounding gas
{53030}{53150}and driving the surrounding gas |away like a snowplough.
{53216}{53308}With only its hot whirling |quasar within its reach,
{53310}{53434}the black hole would swallow |that up and then stop feeding.
{53440}{53547}It would be left invisible |at the centre of the galaxy.
{53640}{53709}Silk and Rees calculated |that this moment
{53711}{53796}when the black hole pushed |the surrounding galaxy away,
{53798}{53961}would depend, bizarrely, on how fast |the stars in the outer galaxy were moving.
{53976}{54045}The faster these stars |were circling,
{54047}{54129}the harder it would be |to push them away
{54138}{54207}and the bigger the black hole |would need to grow
{54209}{54330}to produce enough energy to overcome |the motion of the circling stars.
{54381}{54449}Which means the size |of the black hole in the end
{54451}{54614}depends on how fast the stars are moving |in the newly formed galaxy around it.
{54644}{54686}If our theory is correct
{54688}{54827}there should be a simple relation |between the mass of the central black hole
{54829}{54997}and the speed or the sigma of the stars |in the newly formed surrounding galaxy.
{55030}{55122}And this is exactly |what has just been found.
{55393}{55500}It means that Silk and Rees's |theory may be right
{55508}{55664}and if it is also right that supermassive |black holes helped trigger star formation,
{55668}{55843}then it must mean that all giant black holes |and their galaxies are connected from birth.
{55847}{55933}It means the answer |to the mystery of galaxy formation
{55935}{56087}may lie in the creation |of the supermassive black holes at their heart.
{56100}{56247}The real implication of the relation is that |whatever controlled the formation of the galaxy
{56249}{56344}and whatever controlled the formation |of the supermassive black hole
{56346}{56382}is basically the same thing,
{56384}{56487}there is only one thing |behind everything.
{56504}{56557}So a supermassive black hole,
{56559}{56616}a force of terrible destruction,
{56618}{56729}could also be fundamental |in the creation of our galaxy.
{56762}{56922}Nevertheless, its latent destructive |power should not be underestimated.
{56990}{57121}Back in Hawaii Andrea Ghez |has made a new discovery.
{57123}{57253}She's discovered a new source |of light in the centre of our galaxy.
{57255}{57344}The black hole may |be starting to feed again.
{57432}{57505}All of a sudden we saw something |that looks like a star,
{57507}{57541}but maybe isn't a star,
{57543}{57627}but it's definitely |a new object in our map
{57629}{57744}and the interesting thing is that |it's located where we think the black hole is.
{57793}{57892}Ghez thinks this spot of light |could be something amazing.
{57907}{57995}One idea that I'm particularly |intrigued by at the moment
{57997}{58121}is the idea that perhaps |the black hole is feeding more right now.
{58211}{58298}Andrea thinks that the light |she sees is coming from hot gas
{58300}{58384}being sucked into the vortex |of the black hole.
{58450}{58527}So if our black hole |has started feeding again,
{58529}{58668}could this affect the Earth |even though we're 24,000 light years away?
{58743}{58879}We're in absolutely no danger of being |eaten by the supermassive black hole
{58881}{59053}and in fact if we do think the black hole is going |through a slightly larger feeding at the moment,
{59055}{59069}it's tiny,
{59071}{59186}it's tiny compared to |what other galaxy, galaxies are doing
{59188}{59252}so in fact still this is |a very quiet black hole.
{59254}{59394}In spite of the fact that there might be |new emission from it it's still extremely low.
{59481}{59574}Our black hole is merely having |the equivalent of a small snack,
{59576}{59668}feeding on a wisp of gas |that's strayed too close.
{59699}{59799}The black hole stopped growing |billions of years ago.
{59836}{59936}Only a major catastrophe |could make it fire up again,
{59939}{60075}something violent enough to hurl stars |from the safety of our galaxy's edge
{60077}{60150}into its deadly heart
{60156}{60277}and we now know that one day |this catastrophe could happen.
{60455}{60636}In January 2000, John Dubinski set out to calculate |the final fate of our galaxy, the Milky Way,
{60638}{60728}and that of our nearest |neighbour, Andromeda.
{60762}{60888}The Andromeda galaxy is actually |falling towards the Milky Way
{60890}{61016}which means they'll probably have |some close encounter at some point in the future.
{61019}{61164}At the moment Andromeda is moving |towards us at 400,000 kilometres per hour
{61166}{61269}and scientists think |one day it will hit us.
{61293}{61405}So Dubinski decided to work out |what'll happen to us in 3 billion years,
{61407}{61488}when the two galaxies |finally collide.
{61589}{61655}After a long |and complex calculation
{61657}{61766}the result was a vivid picture |of the impending collision.
{61861}{61996}A detailed prediction |of how the Milky Way will end.
{62289}{62396}The clouds of gas hit each other at these huge |velocities, hundreds of kilometres per second,
{62398}{62491}and that basically |creates great shockwaves
{62493}{62569}which move through the gas |and heat it to great temperature.
{62618}{62671}At the heart of this maelstrom
{62673}{62797}the boiling gas is hurled |towards the two converging black holes.
{62987}{63076}This kick starts |a violent dual feeding frenzy
{63078}{63173}as the two monsters spiral |towards each other.
{63393}{63561}And eventually those two independent black holes |with their accretion discs will spiral together
{63563}{63698}and merge themselves and form |an even more massive black hole.
{63715}{63781}Dubinski worked out |that this violent collision
{63783}{63887}would knock the Earth |and its Solar System out of orbit.
{63946}{64016}Two possible fates await us.
{64060}{64150}If we're on one side of the galaxy |when this clash happens,
{64152}{64242}we could be thrown out |into the emptiness of space
{64244}{64290}- if we're lucky.
{64302}{64441}The second possibility is that we're on the other side |of the galaxy at the time of the collision
{64443}{64624}in which case we could be thrown right |into the centre of this chaos.
{64768}{64840}In the active centre |of the merging galaxy
{64842}{65020}the huge feeding black hole will trigger |giant stellar explosions and supernovae.
{65136}{65215}This is bad news for Earth.
{65251}{65323}There could be |a horrible catastrophe.
{65359}{65452}The wave of radiation |from the blast wave of the supernova
{65454}{65599}would hit the atmosphere |and boil it off in an instant,
{65652}{65698}so the atmosphere would be gone,
{65700}{65786}the seas would boil off into space
{65788}{65897}and the Earth would be toast.