How the Universe Works - S03E07 - Did a Black Hole Build the Milky Way
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00:00The Milky Way, an empire of over 200 billion stars.
00:11The Earth is our home, the sun is our star, and the Milky Way is our galaxy.
00:16It's us.
00:17It's our home.
00:18But where did it all come from?
00:21Why do galaxies form at all?
00:24Something has to happen.
00:25Something has to mix things up.
00:28So what sparked our galaxy into life?
00:34New research suggests an unlikely hero.
00:38At the center of our galaxy is a massive black hole, and by massive I mean really massive.
00:45Even though this thing is terrifying, our galaxy depends on it.
00:49Could this monster, the great destroyer of the universe, actually be a great creator?
00:56Could a black hole build our home, the Milky Way?
01:01The black hole may be responsible for the beginning of our galaxy, and it'll definitely
01:05ultimately be responsible for its death.
01:21Look around the universe, and you will see galaxies of every kind, a kaleidoscopic array
01:28of unique shapes and sizes.
01:32These grand galactic structures fill the cosmos.
01:38The basic building block of the universe is the galaxy, and there are hundreds of billions
01:44of galaxies in the universe.
01:47The same way that cells make up your body or bricks make up a building, galaxies make
01:51up the universe.
01:54We should thank our lucky stars for galaxies.
01:59Galaxies are the only place in the universe where stars and planets form.
02:03We don't see stars out between the galaxies.
02:06This is the only place where the hydrogen is brought together, heated up, and a generation
02:11of life can begin.
02:14There are hundreds of billions of galaxies in the universe, but only one gave birth to
02:20us.
02:21I sometimes ask my students to identify where they live.
02:27Well, you would say, for example, New York City, U.S. of A, planet Earth, third planet
02:35from the sun, and then you would say the Milky Way galaxy.
02:45The Milky Way galaxy is our home.
02:49Because we see it from within, all we see is a band of stars stretched across the sky.
02:56But viewed from outside, we'd see a spectacular giant spiral galaxy, made up of over 200 billion
03:05stars.
03:08Our sun is just a dot within one of its enormous arms.
03:14Our Milky Way galaxy is huge.
03:17It's actually one of the biggest galaxies in the universe, as a matter of fact.
03:20I'd probably put it in the top 10 percent, certainly.
03:25Massive, magnificent, our galaxy has long hidden its secrets at its heart.
03:32The greatest question, how did it form?
03:36At stake is not just the answer to the origin of our galaxy, but the origins of our solar
03:43system, our star, the sun, and ultimately us.
03:49The Milky Way's past and the whole story leads us to where we are now and who we are now.
03:57So what created the Milky Way?
04:00How did it grow into the majestic galaxy we see today?
04:08To answer that, we must travel back to the infant universe, to just after the Big Bang.
04:2113.6 billion years ago, there are no stars, no planets, and no galaxies.
04:31How do we go from that early universe that's almost perfectly, perfectly featureless to
04:36this complex and very interesting universe that we see around us today?
04:41The early universe is a thick, uniform soup of gas, with some tiny irregularities.
04:49But it's enough to set gravity to work, pulling gas together.
04:56Gravity keeps on compressing the gas down to a point, and that's when temperatures rise
05:00dramatically to 50 to 100 million degrees.
05:04At that point, you get ignition.
05:06At that point, hydrogen fuses into helium, and we get a star.
05:13A star is born.
05:19In this theory, not one, but millions of stars burst into life.
05:26Slowly, gravity brings them together.
05:31After a few million years, they form a rotating sphere of stars, and a galaxy is born.
05:42There's a problem, though.
05:44There's too much gravity.
05:48Nothing other than just the stars must be holding them together.
05:53But what is it?
05:56Turns out the answer lies at the center of our own galaxy.
06:03At the very heart of the Milky Way, you see stars orbiting something that isn't there.
06:08And if you do the calculations, the amount of mass needed at the very center is about
06:13four million times the mass of our sun.
06:17So stars are basically orbiting like planets around this empty object with four million
06:22times the mass of the sun.
06:27This object must be colossal.
06:30It must be unimaginably dense.
06:33It could only be one thing, a black hole, a supermassive black hole.
06:45If the moon goes around the earth, and the earth goes around the sun, then what does
06:50the sun go around?
06:53The sun goes around a massive black hole at the center of the galaxy.
07:00Within the Milky Way, scientists find their first supermassive black hole.
07:07But it wasn't the last.
07:09Turns out they're everywhere.
07:12We know that most big galaxies have a supermassive black hole right in their center.
07:18That's telling us that these two things are related.
07:21They come as a pair.
07:24Somehow the black holes and the galaxies and their origin and evolution are tied together.
07:30Amazingly, the Milky Way, this sparkling expanse of stars, is all intrinsically linked to the
07:40darkest and most enigmatic entity in the universe, a supermassive black hole.
07:48It is an object of tremendous fascination and mystery.
07:51How did it get there?
07:52How did it grow to be so large?
07:54Is it going to continue to grow?
07:58To figure out the origins of our galaxy, we must first find out how it got its black
08:03hole.
08:12In the early universe, the first stars burst into life.
08:19But these stars are nothing like our sun we see today.
08:25Those first stars were very, very massive.
08:28And one of the things that happens with massive stars is they explode quickly.
08:35In just a few hundred million years, the biggest burned through their hydrogen fuel and died.
08:50They would have exploded as incredibly powerful supernovae, exploding stars.
08:55Their cores would have collapsed to form black holes, and this may have been the very first
08:59black holes that formed in the universe.
09:04These black holes would start small.
09:08Over billions of years, one would eat and grow into the monster that now sits at the
09:14heart of our galaxy.
09:20It's a solid theory, but there's a problem.
09:25Astronomers find super bright lights in the very early universe.
09:34These aren't stars.
09:37They are called quasars.
09:42Quasars are the bad boys of astronomy.
09:45When we first found them, we were puzzled because how can an object emit so much energy?
09:51The energy output is sufficient to light up the entire universe.
10:00These quasars, though smaller than our solar system, somehow outshine one hundred galaxies
10:06put together.
10:15The energy emitted vastly exceeds the energy in a star.
10:19The only process we know that would produce that kind of energy is the collapse of huge
10:25amounts of matter into a massive black hole.
10:30We realize, oh my God, these are in fact huge raging black holes.
10:39They are much bigger than those made at the end of a star's life.
10:44We're not just talking about a stellar mass black hole, which might have five or ten or
10:48twenty times the mass of the sun.
10:50We're talking about a true monster that has millions or billions of times the mass of
10:54the sun.
10:57So where do these primal black holes come from?
11:02They are way too big to be the result of early exploding stars.
11:08They have to have formed in another way.
11:12The theory that stars form first, converging to build galaxies, needs a radical overhaul.
11:21Instead, does a black hole come first?
11:25Is it the mother of all creation, giving birth to the Milky Way, the stars, and us?
11:44The Milky Way, our vast, incandescent galaxy, has a heart of darkness.
11:52But which came first, the light or the dark?
11:57It's almost sort of like a chicken and an egg.
11:59Which came first, the galaxy or the black hole?
12:02Do you need a black hole to make a galaxy, or do you need a large galaxy to make a large
12:07black hole?
12:08Did the black hole come first, or did the stars and the galaxy come first?
12:17In one theory, stars come first.
12:22The biggest die creating a black hole during their death throes.
12:31But the discovery of quasars challenged this.
12:34They are supermassive black holes at the very start of the universe, far too large
12:40to be remnants of the first stars.
12:45So where do they come from, and could they go on to create galaxies?
12:56Enter the new theory of direct collapse.
13:01In this theory, in the very early universe, you have a giant gas cloud that collapses
13:07straight into a black hole.
13:11It's just like the birth of a star, but the star dies before it's born.
13:18The theory goes like this.
13:20Clouds of gas clump together.
13:25They spiral into a central point, becoming incredibly dense.
13:30At this point in star formation, the core would ignite.
13:35But here, too much gas and dust has piled in.
13:39The mass of it all is so great that gravity becomes unstoppable.
13:47It crushes the gas, making it denser and denser, until it reaches breaking point.
13:55Finally, the gas collapses.
14:00So violently, it rips through the fabric of space.
14:06A massive black hole is born.
14:09I'm talking about making a black hole that's way bigger than any kind of black hole that
14:13would form at the end of a star's life.
14:18This could explain how the black holes in the quasars are so huge so early on in the
14:24universe.
14:26If true, then it might be black holes come first, before stars.
14:34But for now, it's just a theory.
14:41The jury is still out on how our galaxy first forms.
14:49The chicken and egg question is, do the black holes cause the galaxies to coalesce around
14:55them?
14:56Or do the galaxies build up and hit some crucial, critical size beyond which black holes must
15:02form at their center?
15:03And we want to learn about that.
15:04And the only way to learn about that is to look out in the universe and try and find
15:07out.
15:10We need observational evidence to prove one of our theories.
15:15And a small dwarf galaxy might provide it.
15:19Henae's 210 is young.
15:22Many of its stars are just a few million years old.
15:27It might be a look back at our Milky Way in its infant years.
15:33Henae's 210 is a very interesting, tiny dwarf galaxy.
15:38Originally, I was studying this galaxy because it has all this star formation going on.
15:43But when I started looking at all of the data, I was sort of shocked and very excited.
15:49I found a supermassive black hole at the center of this little galaxy.
15:56Finding a black hole in a galaxy is nothing new.
16:00But it's the size of this monster black hole that's the real discovery.
16:09Our best estimate for the mass of the black hole in Henae's 210 is a million or two solar
16:14masses.
16:15Now, this is comparable to the mass of the black hole in our own Milky Way galaxy.
16:20But the Milky Way is 100,000 light years across, whereas Henae's 210 is only a few thousand
16:26light years across.
16:28It's amazing to find a black hole that is so massive in a small dwarf galaxy.
16:35Before this discovery, scientists didn't think such a tiny galaxy could contain such a colossus.
16:44This is completely unexpected.
16:47Usually supermassive black holes are found in much larger, much more massive galaxies.
16:53Amy's discovery is groundbreaking.
16:57In Henae's 210, the black hole is more developed than the galaxy.
17:03This evidence suggesting the black hole is older, that it came first.
17:10Could this be the same for other galaxies?
17:15How many dwarf galaxies host massive black holes?
17:18Is Henae's 210 a unique case, or are there lots of other examples?
17:23We've searched through the Sloan Digital Sky Survey and found over 100 more dwarf galaxies
17:29that have supermassive black holes.
17:34Henae's 210 could be a blueprint for how all galaxies first form, including our own galaxy,
17:43the Milky Way.
17:46It's fascinating because it could be the evidence that the big black holes form first and then
17:51the galaxies form around them.
17:56Everything we see in our sky, the stars, our sun, the planets, our whole galaxy, might
18:06all start as a supermassive black hole.
18:12But how do you go from this to something as glorious as the Milky Way we see today?
18:20Where do the stars come from?
18:2613 billion years ago, the Milky Way may have started life as a supermassive black hole.
18:41A huge sphere of black, surrounded by a maelstrom of gas and dust.
18:49This is our galaxy.
18:52So how do you go from this to the shimmering sweep of stars we see today?
19:03People think of black holes as being gigantic cosmic vacuum cleaners that suck everything
19:08down.
19:09That's not really true.
19:10If you get too close to one, yeah, you can fall in and you'll never get back out.
19:14But they can be a force for creation as well.
19:19How can a black hole be creative?
19:22To conclude, black holes aren't just black.
19:25Far from it.
19:26You can think of black holes as one of the biggest paradoxes in the universe.
19:32They're black so they don't emit any light, but they can cause some of the brightest things
19:36in the entire universe.
19:39Quasars show us this.
19:42These massive black holes throw out more light than whole galaxies.
19:48Black holes don't just swallow matter.
19:51They also spit it out.
19:55A supermassive black hole is a messy eater.
19:58It's trying to suck matter in, but it ends up superheating matter and expelling matter,
20:03and sometimes it will even belch during its meal and have an outburst.
20:10In the early universe, the supermassive black hole, the beginnings of the Milky Way, is
20:16surrounded by gas and dust.
20:22The black hole feasts on the matter.
20:27But not all of it is doomed.
20:30When it eats too much too quickly, it generates so much energy that even the black hole's
20:36gravity can't contain it.
20:42Suddenly the Milky Way fires off highly energized atoms and light from the core, pumping up
20:53to a trillion times more energy than our sun.
20:58If you were to have a close encounter with a supermassive black hole, you're going to
21:03have to go through a very dangerous environment.
21:06You have to survive the intense radiation, you have to survive the jet.
21:13So how do stars form around such violence?
21:18Astronomers find a black hole which might hold the key to how our galaxy first got its
21:24stars.
21:26There's a really exciting discovery of a supermassive black hole, the kind we normally only find
21:30at the hearts of galaxies, sitting out there by itself with no galaxy around it.
21:36This thing's shining like crazy, so we know it's gobbling up gas.
21:40HE04502958 sits 5 billion light years from Earth, a black hole with a huge jet.
21:52This jet is smashing into dust and gas in its neighboring galaxy.
21:57You would think it would destroy the galaxy, but instead it's helping to build it.
22:04It's next to a big galaxy, and this big galaxy is forming stars like crazy.
22:10So we think what's going on is because of the stuff coming off of the black hole as
22:14it's growing, there are stars being triggered to form in this galaxy next to it.
22:22The black hole's colossal jet is the spark needed to create a star factory.
22:29The black hole is emitting radiation, and when this radiation runs into all the gas
22:34in the galaxy, this causes the gas to clump together and new stars get made.
22:41Direct evidence that black holes can create stars.
22:46HE0450-2958 might be a look back into the Milky Way's past.
22:55Our galaxy's supermassive black hole's violent feasting sparks stars into life.
23:03These stars are drawn together by the black hole's huge gravity in orbit, building the
23:09galaxy.
23:11The black hole could actually stimulate star formation.
23:14So some people believe that the very fact that we have galaxies is due to the fact that
23:20we have a raging black hole at the center, which helps to initiate star formation.
23:28It's possible that the black hole could have created many of the stars we see in our sky
23:34today, including the one star we couldn't live without, our sun.
23:43It's kind of amazing that black holes existed as theoretical constructs that many of the
23:48physicists who were involved in developing those constructs didn't believe in.
23:51Now we understand that even perhaps our very existence depends upon them.
23:56We've gone from objects in our imagination to objects on which our life depends.
24:06Even though this black hole in the center is terrifying to conceive of, in fact, our
24:11galaxy depends on it, and our own planet and star may have formed because of this system.
24:24Thirteen billion years ago, the first stars of the Milky Way spark into life.
24:32The galaxy starts to take shape.
24:38The Milky Way is now big enough to throw its weight around.
24:43But in the early universe, it's not alone.
24:47Its cosmic neighbors become its prey.
24:51The Milky Way becomes a cannibal.
25:06The young Milky Way is growing.
25:09It already contains millions of stars.
25:13Now it's big enough to enter its next stage of evolution.
25:19It's time to get violent.
25:21Our galaxy turns on its cosmic sibling.
25:27Galaxies are gorgeous, huge pinwheels spiraling elegantly throughout the universe.
25:34But there's a dark side to these galaxies.
25:36The process of building up galaxies is one of cannibalism.
25:39The galaxies don't form en masse as large objects.
25:43What they do, like many things, is form by eating smaller objects.
25:51If we could view the infant universe, we would see a battle raging.
25:57Dwarf galaxies collide and merge, and in this arena, the winner is always the biggest.
26:10It's a cosmic roller derby match.
26:15The players represent dwarf galaxies, which populate the early universe.
26:21If you look at a roller derby match, you might get a better idea about what galaxy formation
26:25is like.
26:31You've got people skating around the middle of a rink, there's people slamming all over
26:40the place.
26:41It's a very violent process, really chaotic, and it's exactly the same way around the galaxy.
26:54In a galaxy, you've got this middle that's attracting everything, and stuff is swimming
26:58around it.
27:00Dwarf galaxies smash into one another.
27:03The larger always gets the upper hand.
27:07You've got all this stuff slamming together, stars are getting thrown all over the place.
27:11They strip mass from each other, they collide, and if there are any smaller objects in between,
27:16they get eaten up.
27:19It's billions of years of destructive man.
27:24It's just this crazy violent dance that just goes on over and over again.
27:31The Milky Way grows bigger in the chaos of collisions.
27:40Today our galaxy dominates our part of the universe, and even now, it's still devouring
27:48other galaxies.
27:52There's a galaxy called Sagittarius, which has left a huge trail of stars around the
27:56Milky Way, and is essentially in the process of being devoured.
28:01There's a giant stream of stars coming off of it, so it's totally just being ripped apart
28:06by the Milky Way itself.
28:09But in this battle, the Milky Way does not go unscathed.
28:14This collision could have triggered the formation of the spiral arms of the Milky Way itself.
28:18So the reason why the Milky Way is a spiral galaxy might be because it's eating up Sagittarius.
28:28Violence doesn't just build our galaxy, it sculpts it, smashing the Milky Way into shape
28:37and rearranging the positions of the stars, perhaps even our sun.
28:46It's possible that the sun was actually born much closer to the middle of the galaxy, and
28:50it's migrated out here to the suburbs over the course of the last couple billion years.
28:54And it's possible that when Sagittarius hit the disk, it created some spiral arms that
28:59then allowed the sun to migrate out.
29:04The sun and our solar system are now about 26,000 light years from the galaxy's center,
29:12which is good news for life on Earth.
29:15If you're too close to the big black hole in the center, there's a lot going on that
29:19can actually hurt life.
29:20There's high energy radiation, there are bursts of star formation, supernova explosions.
29:25We're in a quieter kind of outlying suburb of the galaxy, and things there are much more
29:30conducive to life.
29:33Our galaxy's cannibalism proves essential for life on Earth.
29:39Through violence, we are able to live, and our galaxy continues to grow.
29:48But can anything stop our cannibal galaxy?
29:55Looking out at the Milky Way, astronomers find hardly any new stars.
30:00Turns out something is shutting our galaxy's growth down.
30:04The biggest flamethrower in the universe.
30:19The Milky Way started small.
30:22Over billions of years, it has grown huge, spawning over 200 billion stars and counting.
30:30But the count is slowing.
30:33On the Milky Way right now, there are stars that are being born, and there's about one
30:37star per year somewhere in our giant galaxy that's being born.
30:40Star formation's not done in the Milky Way, but it's settled down.
30:46In its past, the Milky Way was bursting with star formation.
30:50So what's changed?
30:51So one of the big questions in galaxy formation today is, why isn't more gas turning into
30:58stars?
30:59And the answer is that black holes actually might be limiting this process.
31:06In the early universe, our black hole may have sparked stars into life.
31:12Now it might be stopping stars forming.
31:17To find out why, we need to look at the Milky Way's supermassive black hole in detail.
31:25Now, thanks to one of NASA's newest space telescopes, NuSTAR, we can.
31:34Fiona Harrison runs the NuSTAR mission.
31:37Its first target, the black hole at the center of our galaxy.
31:44NuSTAR can see the very highest energy x-rays that can penetrate through dust and gas.
31:49It enables us to have this view of this black hole.
31:55NuSTAR's x-ray vision sees only the most violent events.
32:01Black hole tantrums are rare, but NuSTAR got lucky.
32:06We looked, and about six hours after we looked, we saw the black hole get 100 times brighter.
32:17How long did that last?
32:18Only a few hours.
32:19Then it faded away back into oblivion, but this event was what we were looking for.
32:26We were all just amazed.
32:29There were cheers in the room.
32:30It was just one of the most exciting moments, and so early on in the mission, too.
32:37Its direct evidence our black hole is still active and still has the muscle to control
32:42the galaxy.
32:48The black hole's power is revealed when it lights up a disk of gas and dust which spins
32:54around it.
32:57As this material is swirling around the black hole in a disk, it rubs against each other,
33:01and there's also magnetic fields and other forces.
33:04All of this heats that disk to much hotter even than the sun.
33:11NuSTAR detects gas around the black hole is heating up to 180 million degrees Fahrenheit.
33:19That's 18,000 times hotter than the surface of the sun.
33:24This superheated gas is bad news for star formation.
33:29The gas has to get cold in order for it to eventually form stars, and that's because
33:34the gas has to get very, very dense so that eventually the gas can collapse into something
33:38that's going to have nuclear fusion in its core.
33:41So in regions around black holes, because they're so hot, they heat up the gas around
33:45them, and that totally limits the ability for that gas to turn into stars.
33:52Massive amounts of energy are emitted, and that actually can not only destroy stars,
33:57it can blow the gas away that would later on form stars.
34:04Star birth shuts down.
34:09For our galaxy's life, our supermassive black hole drags gas and dust towards it,
34:15the ingredients needed for star formation.
34:19In its infancy, its power slams these gas clouds together, sparking stars into life.
34:26Now it blows them apart with its extreme heat, regulating the population of stars in the
34:33galaxy.
34:35The black hole in the center acts a little bit like a valve, controlling how stars form
34:40in the galaxy itself.
34:42There's a remarkable symbiotic relationship between black holes and galaxies.
34:47Black holes act like cosmic regulators, increasing at certain times star formation and governing
34:54the rate at which galaxies evolve.
34:58We're not sure why our black hole stops some star formation and sparks others.
35:06But we do know this regulation might be good for us.
35:11When it made the stars, the black hole might have helped create our sun.
35:17Now it limits star formation, which could bring lethal radiation near planet Earth.
35:25If we were living in an area where there were lots of young stars and supernovae blowing
35:28up, that would not be so good for life on Earth.
35:33Now the conditions for life are perfect.
35:37Looking up at our night sky, it looks unchanging, eternal.
35:45But in the universe, nothing lasts forever.
35:51Our galaxy is gearing up for its next big change.
35:55So what does the future hold?
35:59The answer is that we won't be a spiral galaxy for much longer.
36:02Our lifetime as a spiral galaxy is about two-thirds of the way into its final death throes.
36:10The Milky Way has a giant sister out there, too close for comfort.
36:16Their sibling rivalry will set the night on fire and pit two of the biggest heavyweights
36:25in the cosmos in a fight to the death.
36:39Around 13 billion years ago, the Milky Way forms around a supermassive black hole.
36:46It adds hundreds of billions of stars, settles into a flat disk, and is sculpted into a spiral.
36:55Our galaxy has constantly evolved.
36:59Its future is no different, and it's going to get violent.
37:07Go about the night and look at the night sky with a pair of binoculars, and you can see
37:11the Andromeda Galaxy.
37:15That is our future.
37:17Perhaps four or five billion years from now, we will be on a collision course with our
37:23next-door neighbor, and it could be like a hostile takeover.
37:30Andromeda is heading straight for us.
37:34Collisions are, of course, nothing new.
37:37In its infancy, our galaxy grew by colliding and eating other galaxies.
37:44But this time, it's different.
37:47The original schoolyard bully is going to meet its match.
37:54The Milky Way has always been the biggest thing around.
37:56So any little dwarf galaxy that's gotten near has gotten torn apart, but the Milky Way just
38:00keeps right on going.
38:02Now, there's another really big galaxy that's actually headed right for us right now.
38:06That's Andromeda.
38:07It's another disk, and when these two big disks come together, there's not going to
38:11be a disk left.
38:12Neither of those disks is going to win.
38:15As the collision nears, our night sky will change completely.
38:20Today, if you look out when it's really dark, you see the big band of the Milky Way.
38:25It's a beautiful thing.
38:27A few billion years from now, what you would see is not just one band of stars, but another
38:31band of stars that crisscrosses like this.
38:37Andromeda grows larger and larger in our sky as it nears.
38:42Finally, the galaxies smash into one another.
38:47Stars are torn from their orbits.
38:51The stars don't actually collide.
38:53Stars are extremely small compared to the space in between them.
38:56But that's not true for gas clouds.
38:58Gas clouds are very large.
39:00They can actually slam into each other.
39:02When they collide, that creates new star formation.
39:05All of this gas and dust is going to get set on fire.
39:08It will be a crazy thing going on and maybe even begin to look like fireworks in the sky
39:13as stars are born.
39:15Huge gas clouds blazing out light from the massive stars forming in them.
39:19It would be magnificent.
39:26This is our galaxy's swan song.
39:31This burst of star formation marks the end of our galaxy.
39:40The Milky Way and Andromeda rip each other to shreds.
39:47When these two beautiful structured spirals smack into each other, that really orderly
39:51shape is going to be destroyed.
39:55And what's probably going to be left is sort of a big blob of stars that's called an elliptical
40:00galaxy.
40:01Those two galaxies are going to turn into a ball of stars.
40:04You won't see any bands at all.
40:06It'll just be stars spread across the sky.
40:12The Milky Way and Andromeda are gone.
40:17In their place, a new galaxy, Milkomeda.
40:24But it's not over.
40:27There are two supermassive black holes hurtled towards each other.
40:32Those black holes are going to be hunting for each other.
40:35So you've got two giant black holes, both more than a million times the mass of the
40:39sun, spiraling in towards each other.
40:41As this is happening, both of them will probably start gobbling up gas that happens to be around
40:46them.
40:47They're both trying to eat all the gas that's around them and they're going to get bright.
40:49So it's going to be a crazy event.
40:51It will be fantastic.
40:53Two fireballs rotating around each other until the black holes at the center of them
41:00finally coalesce.
41:04The black holes merge, forming an even larger supermassive black hole, a new king to rule
41:11over the new galaxy.
41:17But this new galaxy is already dying.
41:21For billions of years, the stars slowly die out, as there is no fuel left to replace them.
41:28What you're left with is basically a dark galaxy.
41:31It's not generating any energy, any heat, any light.
41:34It's just black.
41:37One hundred trillion years after it was formed in the darkness of the early universe, the
41:43voracious black hole returns to darkness.
41:47Here, it is left to feast on the galaxy it built, eating the dead remains of stars and
41:55planets.
41:56The orbits of the stars decay and they fall in toward the supermassive black hole.
42:01And ultimately it's thought galaxies like the Milky Way would just form one supermassive
42:06black hole.
42:09In literature, beginnings and endings are always tied together, but the same is true
42:13for our galaxy and black hole.
42:15It is quite possible that without the formation of the black hole at its center, our galaxy
42:20would not have coalesced around it and have the properties it has.
42:23But the ultimate future of our galaxy is to collapse into a massive black hole.
42:27So in that sense, the black hole may be responsible for the beginning of our galaxy, and it'll
42:32definitely ultimately be responsible for its death.
42:37Our galaxy is magnificent.
42:40All this, everything we see in our night sky, could be down to one of the most fearsome
42:46objects in the universe, a supermassive black hole that could have been our creator and
42:54will be the destroyer of our galaxy, and all the galaxies in the universe.