How the Universe Works - S07E04 - How Black Holes Made Us
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00:00Black holes, long considered the bullies of the cosmos, but are they really so bad?
00:13Black holes aren't violent.
00:15They are elegant.
00:16They are incredibly powerful objects, but they're beautifully simple.
00:22Simple but unpredictable, black holes rip planets to shreds, but they also give birth
00:29to stars.
00:31Black holes are like the ultimate recycling trash bin combination.
00:38They build galaxies and may have lit up the dark infant universe.
00:45It's one of the biggest changes that happen.
00:49Someone switches the lights on and transforms our universe.
00:54They come in all sizes, from microscopic to ultra-massive, controlling the fate of
01:01everything around them.
01:02The story of the universe and how it's arranged is the story of black holes.
01:07Black holes are the master architects of the universe, and without them, we would not exist.
01:35Black holes were riveted by their destructive power.
01:41Black holes are dangerous.
01:44Black holes are hazards.
01:46Black holes are not friendly for their environments.
01:51There's just no good ends to anything that falls into a black hole.
01:55Perhaps one of the most frightening objects in the universe.
02:00But what exactly are these scary objects?
02:04Black holes are created when you get enough matter in a small region of space.
02:09This happens when a massive star dies and collapses in on itself.
02:19A supernova.
02:24A black hole is the ultimate consequence of gravity.
02:27It's an object that has so much mass, crushed into such a small space, that its escape velocity
02:33becomes greater than the speed of light.
02:40They are a one-way street.
02:43You go in, nothing escapes, not even light.
02:50But do black holes really deserve their bad rap?
02:55In some ways, I think we set up black holes to be more villains than they actually are.
02:59Black holes suffer a bit of a PR problem.
03:02I think they're a lot more menacing in science fiction and popular media than they really
03:06are.
03:13There are trillions of galaxies in the known universe.
03:18And most of them have a supermassive black hole at their center.
03:27These monsters are millions of times the mass of our sun.
03:32Their immense gravity can send stars flying.
03:36They're instrumental in choreographing the dance of stars in their vicinity.
03:44Supermassive black holes shoot out torrents of lethal radiation and violent cosmic winds
03:51and gobble up anything that comes close.
03:55Now scientists are beginning to realize these cosmic giants may also have a creative side.
04:05Most people think of black holes as being like giant vacuum cleaners in space, and basically
04:09everything falls into them.
04:11But that's not actually the case.
04:13They're better thought of as the engines of cosmic change.
04:18Although black holes are the end states of stars, they can actually influence the formation
04:25of stars as well in a bunch of different ways.
04:29A galaxy's job is to make stars.
04:34But uncontrolled star growth isn't healthy.
04:37Too many stars can drain a galaxy's gas supply.
04:42Black holes are very important.
04:45It appears that galaxy evolution is tied to black hole evolution.
04:50We don't know exactly how yet, but the marriage appears certain.
04:58One idea is that supermassive black holes act as cosmic control mechanisms.
05:07Black holes can act like a thermostat in your house.
05:09If your house gets too hot, the thermostat will kick on the air conditioner.
05:14And if it gets too cold, it'll kick on the heater.
05:17Black holes do the same things for galaxies.
05:21Supermassive black holes regulate star formation by pulling gas in and shooting it back out
05:28into the galaxy.
05:30When these black holes are consuming matter, they're drawing matter into themselves, but
05:35they're also spewing stuff out.
05:38Basically black holes eat like little babies, very sloppily.
05:43So a lot of what they eat comes flying back out again.
05:47They eat stars, they eat planets, but most often they eat giant clouds of gas.
05:53The black hole drags gas and dust into an accretion disk around it.
05:58This disk spins faster and faster.
06:02Magnetic energy builds up.
06:05With the accretion disk swirling around the black hole, there are also magnetic fields
06:09that are going on.
06:10The material is moving so rapidly that the magnetic field sort of winds up, coils up,
06:15and forms a vortex like a tornado.
06:17Astronomers call them jets.
06:26These jets propagate outward like freight trains plowing through the galaxy over hundreds
06:31and thousands of light years.
06:34These are like death rays.
06:37The jets disrupt the star-forming gas clouds, limiting excess star formation in the main
06:43body of the galaxy.
06:45But in the very outer reaches of the galaxy, they can spark star birth.
06:52Things are more gentle out there.
06:53You're not as close to the energetic heart.
06:55So stars, planets, and life can form out there partially because of the material that the
07:00black hole has moved out there.
07:03So black holes can have outsized influence on the regions that they inhabit.
07:11Right around them, they can prevent the formation of stars, whereas on very, very large scales,
07:18they can actually instigate the formation of stars.
07:252018, black holes hit the front page.
07:34Scientists discovered black holes gobbling up gas so fast that they seem to be outgrowing
07:40their host galaxies.
07:43It naturally makes the question come up, how big can a black hole get?
07:49Now we have the answer.
07:51They can reach size XXXL, becoming ultramassive black holes.
08:0410 Billion Solar Masses
08:14Ultramassive black holes are so cool because it's just mind-boggling that black holes so
08:20large can exist.
08:23Ultramassive black holes are very rare and typically have masses of more than 10 billion
08:28times the mass of the sun.
08:3010 Billion Solar Masses, that's a 10 followed by nine zeros.
08:38Ultramassive black holes are real beasts.
08:41The black hole at the center of our galaxy is 4 million solar masses.
08:45Imagine black holes that are 2,500 times bigger.
08:49That's what we're talking about here.
08:52An ultramassive black hole this big would be as wide as the solar system and weigh as
09:01much as all the stars in the Milky Way.
09:07There are inside galaxies that aren't a whole lot bigger.
09:10That really surprised the hell out of everybody.
09:12And in 2018, scientists discover a 20 billion solar mass ultramassive black hole, growing
09:21faster than any other black hole.
09:26This ravenous behemoth devours the mass of our sun every two days.
09:35These big black holes are really good at gobbling up other things.
09:39They'll literally eat anything.
09:40They're monsters of the universe.
09:43This kind of voracious eating can have devastating consequences.
09:49It blasts so much energy and turbulence into the galaxy that stars no longer form.
09:57And the bigger the black hole, the faster the galaxy dies.
10:02The primary thing these ultramassive black holes do is they create a black hole that
10:08ultramassive black holes do to galaxies is they shut down all star formation.
10:12And so in that sense, they kind of kill galaxies.
10:15And so these things could even wipe out their host galaxies.
10:21Ultramassive black holes are a problem for scientists too.
10:26They might be the fastest eaters.
10:30But that doesn't explain how they got so large.
10:34With these ultramassive black holes, these black holes that are
10:37tens of billions of times more massive than our sun,
10:40you can't just grow them from the slow accretion of gas over time.
10:44There's just not enough gas and there's just not enough time.
10:49It gives us a new mystery to solve.
10:51How do you make black holes that are just that big?
10:54There's not a clear answer so far as to how these ultramassive black holes were formed.
11:00People wonder if there's some other mechanism.
11:02There's some other mechanism by which you could make black holes.
11:05A mechanism so violent it also throws supermassive black holes clean out of galaxies.
11:24We now know that ultramassive black holes, billions of times the mass of the sun, exist.
11:31But we have no idea how they got so big.
11:37We've detected lightweight stellar mass black holes colliding.
11:42They merged into a new larger black hole and generated huge amounts of energy.
11:52But what about supermassive black holes?
11:56When galaxies merge, their central supermassive black holes
12:00will fall to the center of the newly formed galaxy.
12:05Could these supermassive black holes caught up in galactic mergers
12:10combine to form an ultramassive black hole?
12:14In 2017, the Hubble Space Telescope spotted something strange
12:19in a distant galaxy called 3C 186.
12:26It detected an incredibly bright spot thousands of light-years from the galaxy's center.
12:34Scientists suspect it's a quasar.
12:37A quasar is an incredibly bright, active galactic nucleus
12:41that's powered by a supermassive black hole.
12:46We regularly spot black hole-powered quasars,
12:49but always at the centers of galaxies, until now.
12:56When we actually got this data from Hubble,
12:58we were able to see that the black hole was actually a supermassive black hole.
13:04When we actually got this data from Hubble,
13:06we were absolutely stunned to discover that the quasar
13:09that we've long known to exist in the center of this galaxy
13:12wasn't actually at the center.
13:14This black hole is offset from the center of the galaxy by about 35,000 light-years.
13:19That's really weird.
13:20It is an incredibly rare and bizarre event
13:24to find a quasar, a supermassive black hole,
13:26that is not at the center of the galaxy.
13:28When scientists looked closer,
13:30they discovered that the quasar is hurtling through space,
13:34away from the center of the galaxy.
13:38Now, mind you, this is a black hole
13:40with the mass of about a billion times the sun,
13:43and it's screaming away at four million miles an hour.
13:47This black hole, which was probably originally in the galaxy's center,
13:51has somehow been shot out at high velocity
13:54by some incredibly powerful supermassive black hole.
13:58It's an incredibly violent event.
14:01It's hard to imagine what kind of event
14:03would pump that much energy into such a huge object
14:06to shoot it away from the center of a galaxy.
14:09Who kicked it out, how, and why?
14:13Scientists have an idea.
14:163C186 may be the remnant of a galaxy merger.
14:20The merged galaxies' supermassive black holes circle each other,
14:25sending out blasts of energy in the form of gravitational waves.
14:33Gravitational waves are all around us.
14:36They're ripples in the fabric of space-time.
14:41Every time mass moves, gravitational waves are produced.
14:45So if I wave my hand, I am making gravitational waves.
14:50A hand produces imperceptible waves.
14:55When objects as huge as supermassive black holes collide,
15:00the energy released as gravitational waves is phenomenal.
15:07Scientists think these black holes might have been different sizes.
15:12It's possible that if one of the black holes is really massive
15:15and the other one isn't quite as massive,
15:17that when they spiral around and merge,
15:20they send out gravitational waves in an asymmetric way.
15:25This asymmetry has a catastrophic effect.
15:32As the two black holes collide and merge,
15:34they shoot out a huge blast of gravitational waves,
15:37but only in one direction.
15:42This blast of energy kicks the newly combined black hole
15:46out of the galactic center.
15:49Think of a black hole as a black hole
15:52in the galactic center.
15:54Think of a shotgun recoil, but supersized.
16:00There's so much energy in that emission
16:03that it acts like a rocket
16:04and it actually pushes the merged black hole away.
16:07It would have been one of the most energetic events ever witnessed.
16:11They're so energetic,
16:13they are literally shaking the fabric of space.
16:16We didn't witness the actual collision,
16:20but 3C186 could be evidence
16:23that supermassive black holes can collide and merge,
16:28building even larger black holes.
16:32This would be a mechanism by which you would create
16:35ultimately an ultramassive black hole.
16:38As for the ejected black hole,
16:40the gravitational recoil is a mechanism
16:44sent it on a one-way ride to oblivion.
16:51So gravitational waves kicked this supermassive black hole
16:55and sent it flying through space.
16:57In 20 million years, it's expected to exit its galaxy.
17:02The ejected supermassive black hole
17:04may eventually hit another galaxy
17:07and merge with its supermassive black hole.
17:14These largest of black holes seem to throw their weight around,
17:19bullying galaxies and other black holes.
17:23Now, researchers have discovered a vampire black hole
17:28that's draining the lifeblood of its neighbor.
17:44Ultramassive black holes seem to destroy their galaxies,
17:49while supermassive black holes seem to regulate star formation.
17:55But are all supermassive black holes forces for good?
18:05Hundreds of galaxies surround the Milky Way.
18:08Large and small.
18:11But most of the largest galaxies are red.
18:17This is not a good omen.
18:19In space, red means danger.
18:24If you have active, ongoing star birth,
18:26then you have massive stars, and massive stars tend to be blue.
18:30But they don't live very long, and they don't have a lot of life.
18:32And so, if you have a black hole,
18:34then you have massive stars, and massive stars tend to be blue.
18:37But they don't live very long, and they blow up.
18:44Once you stop star formation after some amount of time,
18:46the galaxy turns red.
18:50The only stars left alive are small, long-lived red stars,
18:55called red dwarfs.
18:57A red galaxy with only red dwarfs is a dying galaxy.
19:05One galaxy, around 340 million light-years away, stood out.
19:25It was named after a Japanese anime character, Akira.
19:30It's very red. All the stars in it are red, and that means they're old.
19:34So we know that Akira has not had any active star formation in a long time.
19:41The Akira galaxy doesn't form stars because it doesn't have the cool,
19:44calm gas needed to build them.
19:49Something is heating the gas, making it turbulent.
19:54One of the ways in which a black hole can drive the evolution of the galaxy in which it resides
19:59is by simply powering a wind.
20:02These are winds that are literally driven by light.
20:08When a black hole feeds, it drags gas into an accretion disk.
20:14The disk heats up and gives off light radiation.
20:20The radiation pressure from the accretion disk around this black hole
20:24couples to the ambient gas and dust and pushes it outwards at very high velocity.
20:32These winds that are driven out by the black hole
20:35essentially warm up the gas in the galaxy, preventing further star formation.
20:44However, whatever's fueling the black hole in Akira is a mystery.
20:49Here's a weird thing. There is an outflow, a wind coming out of this galaxy,
20:54and that means there's gas feeding that black hole in the center,
20:58and it's blowing it out. Where is this gas coming from?
21:01Ah, it's stealing it.
21:06It has a small companion galaxy, which is nicknamed Tetsuo, and that has gas in it.
21:14Akira's supermassive black hole pulls gas from Tetsuo
21:19and drags it into the center of the galaxy.
21:24The black hole is taking the gas from this companion galaxy,
21:28and that's what's falling around the black hole and creating this wind.
21:31So Akira is actually sort of a dead galaxy, but it's being rejuvenated by its companion Tetsuo.
21:40Like a cosmic vampire, Akira's supermassive black hole feeds off Tetsuo.
21:49The black hole drags gas and dust into its accretion disk, which spins faster and faster.
21:58And these particles are rubbing against each other. Well, that generates friction.
22:03Friction may not seem like that big of a deal. I mean,
22:05you can rub your hands together on a cold day to get warm,
22:08but imagine rubbing your hands together at very nearly the speed of light.
22:12How much friction is that going to generate? It's going to make a lot of heat.
22:17Over a million degrees Fahrenheit.
22:21So hot, the accretion disk lights up.
22:28Its temperature goes up and he starts emitting light. It becomes incredibly bright.
22:34Even though there's a black hole in the core, its surroundings are intensely bright.
22:41This heats up the surrounding gas, generating a hot wind,
22:46which extends thousands of light years from the black hole.
22:51And those winds carry with them a lot of energy. And that energy, if it couples to the gas in the
22:57galaxy, can blow that gas out. They inject energy into nearby gas clouds and heat them up and
23:03prevent them from forming stars. Stars don't form, the galaxy dies.
23:13These dying galaxies are called red geysers.
23:20Scientists think around 10% of the red galaxies we see around us died this way.
23:28They were heated up by this galactic warming.
23:35We think that the source of some of this galactic warming is in the growth of supermassive black
23:39holes themselves. Because when you grow a supermassive black hole, you must liberate
23:45an enormous amount of energy. You can't grow a black hole for free. And that energy gets dumped
23:51back into the ambient surroundings and keeps this halo of gas hot. It prevents it from cooling and
23:56forming stars.
24:01Sagittarius A-star, the supermassive black hole at the heart of our galaxy, the Milky Way,
24:08could turn into a red geyser.
24:11If you were suddenly to dump an enormous amount of gas onto Sagittarius A-star,
24:16you could have what is effectively a red geyser effect, a very powerful wind driven by all of this
24:22energy. Star formation would stop and our Milky Way would become another dying red galaxy.
24:39Now, new research suggests that Sagittarius A-star has already affected the inner region of our
24:46galaxy, not by killing stars, but by transforming planets from gas giants into super-Earths.
24:54At the center of our galaxy lies a supermassive black hole, Sagittarius A-star.
25:20We think it's calm, dormant, safe.
25:25Relative to other supermassive black holes in the universe, ours is relatively quiet.
25:30It's been active in the past, and it could flare up in the future.
25:37It could be active tomorrow for all we know. All you need to do to light it up is start dumping
25:41some gas on it. And there is almost certainly a giant cloud of gas that we don't currently know
25:46of on its way to the center of our galaxy, and it will find itself one day in the vicinity of our
25:51supermassive black hole, and it will start to light up like a Christmas tree. In February of
25:572018, scientists at Harvard simulated Sagittarius A-star during a feeding frenzy to understand the
26:06impact of an active supermassive black hole on its local environment. They found that as
26:16Sagittarius A-star gobbled up gas and dust, it belched out bright flares of high energy radiation,
26:25which radically affected the region around the black hole.
26:30The environment near the center of a galaxy that has an actively feeding black hole
26:36is the worst place in the universe. You've got this tremendous object which is heating up this gas
26:42to millions of degrees. This is no place that you want to be.
26:49The model revealed what would happen to any planets in the line of fire. Think about being
26:56in the way of one of these black hole burps. All of a sudden there's a tremendous wind radiation
27:01that comes through your solar system. That could actually strip away the outer layers of gas
27:06of a planet like Neptune. The high energy radiation from the supermassive black holes
27:13would hit the gas planets and heat up their atmospheres. Maybe this would actually strip
27:19away the outer layers, leaving the solid material in the middle. You could actually turn a gas giant
27:24planet into a terrestrial solid planet, all because you're close to a black hole.
27:30This radiation strips away the gas, leaving the core. Now a new rocky planet, but a giant one,
27:40a super earth. Normally you think of rocky planets being about the size of the earth,
27:45but this would be a way of making so-called super earths. Super earths are one of the most common
27:52type of planets discovered in our galaxy. It's possible that any super earths close
27:59to Sagittarius A star were created by these blasts of energy.
28:09Away from our galactic center, a much smaller stellar mass black hole
28:14is also radically transforming its environment.
28:17January 2017, researchers discover something strange in a cloud of gas called W44.
28:28W44 is a supernova remnant. It's the debris, the expanding cloud from a star that blew up.
28:35The explosive shockwave from a supernova pushes gas and dust out from the dead star,
28:42pushing gas and dust out from the dead star, forming a huge nebula.
28:50We see a lot of these. I mean, they're catastrophic, amazing, incredible events.
28:54But as far as they go, this one appears to be pretty standard, except for one weird thing.
29:00In the heart of it, there's something very mysterious going on.
29:03There seems to be something shooting out of the very center of this explosion.
29:13A thin protrusion, trillions of miles long, streams out from the cloud.
29:21It's moving at over 60 miles a second against the flow of the galaxy.
29:27It's very strange that it's moving backwards against the rotation of the Milky Way.
29:32When you see a giant, giant, very massive cloud of gas
29:36that is moving counter to the rotation of the Milky Way, it needed to be like a bullet from
29:40a gun fired it against a headwind in the opposite direction.
29:44So what is that gun? What fired that bullet of gas?
29:49The tip of the bullet cloud is expanding at 75 miles a second.
29:54That's 270,000 miles an hour, over 150 times faster than a bullet.
30:02What in the cosmos has the power to accelerate gas to such high speed?
30:07Could that actually be a black hole moving very, very quickly?
30:12Researchers think a stellar mass black hole hidden in the bullet cloud
30:17is powering the movement of the gas.
30:20Gravity from this black hole is incredibly strong,
30:22and so it will latch onto this gas cloud as it passes through it,
30:25and it can completely disrupt the motions of this cloud.
30:29This is a very interesting stream of gas that's somehow connected to a black hole.
30:33And we don't know whether it's there because the black hole is moving through the gas
30:37and it's creating a wake, or whether somehow this black hole
30:41is spitting out a stream of material in some way.
30:45The black hole could be dragging gas into an accretion disk around it.
30:50The gas heats up and expands, giving the initial supernova explosion, W44, an extra kick,
30:59driving this bullet-like cloud out in front of it.
31:04Or the black hole could be racing away from the nebula,
31:08dragging the gas behind it, like a wake.
31:18Ultramassive, supermassive, and stellar mass black holes
31:22all play a role in shaping the cosmos.
31:26But there may be another type of black hole even more dangerous than the rest.
31:34A microscopic black hole.
31:55We have so far detected XXXL ultramassive black holes,
32:01large supermassive black holes,
32:04medium-sized intermediate black holes,
32:08and small stellar mass black holes.
32:12Now, scientists have another to add to the roster.
32:16Microscopic black holes.
32:19We know there are supermassive black holes at the centers of galaxies.
32:22We know there are star-sized black holes from the deaths of stars.
32:26That's what we know for sure.
32:28It's possible there are much smaller black holes, microscopically small black holes.
32:33Microscopic black holes are virtually invisible to the naked eye.
32:38But magnified, they look like regular stellar mass black holes.
32:44The definition of a black hole is an object that has so much mass,
32:49crushed into such a small space,
32:51that its escape velocity becomes greater than the speed of light.
32:54So it could be something the size of a star, the size of a galaxy.
32:58It could also be the mass of a planet.
33:02If you could crush the Earth down far enough, it could become a black hole.
33:07The density of a black hole is something that the human brain
33:10really doesn't wrap itself around very easily.
33:12When you think about something the size of the Earth,
33:14how small would the Earth have to be to be a black hole?
33:17And the answer is something on the order of a marble.
33:20So think about taking the entire Earth and compressing it down to the size of just a marble.
33:25So where do these strange little black holes come from?
33:31These very small black holes can only be formed in the exotic
33:36conditions of the incredibly early universe.
33:41Our universe might get flooded with these small black holes
33:44that simply persist to the present day.
33:49It's the only time in the history of the universe where you could take a small amount of matter
33:52and crush it down so tightly that it could become a black hole.
33:55Those conditions don't exist anymore.
33:57So if these things exist, they would be primordial.
34:01They would be as old as the universe itself.
34:10These primordial black holes may be ancient, but they still pack a punch.
34:15Black holes' size doesn't matter for a black hole.
34:19What matters is mass.
34:22Mass determines its gravitational attraction, its gravitational effects on its environments.
34:29And when it comes to black holes, the smaller black holes are actually more dangerous.
34:34Because their mass is concentrated into such a small volume,
34:39you can have differences.
34:41You can have differences, strong differences in gravity,
34:46between different distances from that black hole.
34:52If Paul or an interstellar robotic probe visited a supermassive black hole
34:57or even an ultramassive black hole, they wouldn't be immediately ripped to shreds.
35:05One of the most fun questions about black holes is how close could you get to a black hole before
35:09the gravity would rip you apart?
35:11And that actually depends on the volume of the black hole.
35:14If the black hole is very large, you could get very, very close.
35:18The more massive they are, the slightly softer they are in how they tear things apart.
35:23So a supermassive black hole, actually, you can cross within the event horizon
35:28and not really notice it.
35:30You're never going to get back out,
35:31but you won't necessarily be stretched to your death while you cross inside.
35:35So a probe could visit a supermassive black hole and not be destroyed
35:42until it crossed the event horizon and traveled deep inside.
35:48Then it would be torn to pieces.
35:53But microscopic black holes are currently just a theory.
35:59Microscopic black holes have been studied for a long time.
36:03Microscopic black holes have been the focus for some researchers for many years,
36:09but currently there's no evidence to support their existence.
36:15Microscopic primordial black holes may or may not have been around since the Big Bang.
36:23Now, scientists have discovered supermassive black holes from the very early universe.
36:30They're shedding light on one of the most mysterious eras, the cosmic dark ages.
36:50Black holes don't just shape the universe now.
36:54They've been shaping it from almost the dawn of time.
36:58Scientists think black holes may have triggered one of the universe's greatest transformations,
37:04turning from dark and foggy to transparent and light.
37:17At the beginning of time, the universe was a tiny ball of super hot energy, the Big Bang.
37:24Shortly after our Big Bang, our universe was shining bright because it was full of hot,
37:30glowing gas.
37:32Then it cooled off and entered the so-called dark ages, until eventually something lit it up again.
37:40It's one of the biggest changes that happened in our universe.
37:42Someone switched lights on and transformed the universe.
37:47During the dark ages, the universe was a tiny ball of super hot energy.
37:53The universe was blanketed in a thick fog.
37:57Then something lit it up in a process called reionization.
38:04We still don't really know for sure whether reionization was mainly caused by
38:09young stars or whether it was mainly black holes that ate stuff and spewed out a bunch of radiation.
38:17Then, in December of 2017, researchers in Chile scan a region of space so far away
38:25it takes light 13 billion years to reach us.
38:30They spot an object from just 690 million years after the Big Bang,
38:36when the universe was only 5% of its current age.
38:40It's called Quasar J1342 plus 0928.
38:49The thing that's so amazing about this farthest quasar is we may actually have seen the boundary
38:54of these dark ages.
38:56This particular supermassive black hole slash quasar tells us something about the formation
39:02of the early universe.
39:05It's a supermassive black hole that's been orbiting the universe for thousands of years.
39:10It's thought that quasars helped drag the universe out of the dark ages.
39:15They gobbled up so much hydrogen gas and belched out jets of energy and cleared up the fog.
39:24Those jets could have actually put so much energy into the universe that it made it clear
39:29again.
39:30We may actually be seeing the moment where something punches through this boundary of
39:34the dark ages.
39:35Pockets of reionization opened up throughout the early universe.
39:41They came in different sizes, depending on what created them.
39:47While our universe was being reionized, there was kind of like all these holes that kept
39:52growing.
39:54If the reionization was made by a large number of little stars, you would have many, many
39:59small holes, much like a space shuttle.
40:01Whereas if you had a small number of monster black holes doing it, you'd have a lot of
40:06big holes, like the end of Swiss cheese.
40:15At present, we can't measure the ionized pockets to determine if it was stars or black
40:21holes that lit up the early universe.
40:24Perhaps it was both.
40:25The more we investigate black holes, the more we learn about their role as architects of
40:30the universe.
40:55I think scientists of my generation are very lucky to be able to be at the beginning of
41:00this revolution.
41:04We used to portray black holes as monsters.
41:07Now, we know that without them, the universe would be a very different place.
41:12They made life possible.
41:14Without black holes, we probably wouldn't exist.
41:18We're discovering just how black holes shaped the universe.
41:25But the more we learn, the more questions they pose.
41:31I've spent my career studying black holes, and I want to spend the rest of my career
41:35studying black holes.
41:36And I guarantee you that at the end of my career, on the day I retire, I will probably
41:42have more questions about black holes than I do today.
41:48This is an incredibly exciting time for black hole science.
41:52Who knows what we're going to discover?