Galaxies are locked in continual combat across the universe, and our own Milky Way will face its biggest opponent ever, the Andromeda Galaxy, in a titanic and deadly struggle that could create a new and unrecognizable super galaxy.
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LearningTranscript
00:00our universe is at war the universe is very violent and deadly place entire galaxies fight
00:13to the death talk about clash of the titans it doesn't get more titanic than this it's a slaughter
00:20it's a massacre only the strongest survive if a galaxy wants to stay alive it has to feed
00:26on other galaxies our own galaxy also fights for survival we are facing the ultimate destruction
00:36of the milky way galaxy these battles are how galaxies live grow and die these collisions
00:46got us to where we are today and they're going to determine the future of the universe
00:56in 2018 astronomers used the gaia space telescope to map our milky way galaxy they tracked the
01:13movements of a billion stars and they found that some behave very strangely when astronomers
01:22were mapping stars in our galaxy they found a whole bunch that were on similar but very
01:28strange orbits most stars of the milky way are orbiting in a sort of regular pattern but these
01:34stars at the center they're in these highly elongated orbits coming in from very far swinging around
01:41the center of our galaxy and then going back out again it's a little bit like a comet does this
01:47group of stars plunges wildly through the center of our galaxy when you track their direction and
01:53speed on a chart you get a shape that looks a bit like a sausage this doesn't sound very sciencey but
02:03this sausage is really what the stars look like if you look at the shapes of their orbits in a certain
02:08configuration what sent so many stars on such a strange path it must have been a huge event
02:17we think these stars are the result of a past cosmic collision
02:22they are casualties from an enormous battle between the milky way and a foreign galactic army
02:31they don't move like stars in the milky way because they're not from the milky way these stars are
02:40actually alien stars they're invaders from outer outer space the attackers left their mark on the
02:48milky way we find similar battle scars on galaxies across the universe our models of galaxy formation are
02:58still pretty uncertain we still don't really understand how galaxies got to where they are how
03:03we go from the big bang to the milky way wars between galaxies have profound consequences for the
03:11winners the losers and for us what we're learning is that these galactic battles have had a huge impact
03:19on what the universe looks like today our understanding of galaxies has changed entirely in the last few
03:25decades we understand now that every big galaxy like the milky way started from many smaller things
03:30colliding changing each other as they went nearly 10 billion years ago the sausage stars were part of a
03:39foreign galaxy it was on a collision course with our home the milky way we call this invading army
03:49the sausage galaxy or gaia enceladus the galaxy that we fought probably had about 50 billion stars so
03:59we're talking about something that is a significant fraction of the size of the milky way
04:03gaia enceladus was a tough opponent
04:08but the milky way was 20 times its mass and that makes a huge difference
04:16when galaxies interact with each other size definitely matters the bigger galaxies are going to
04:23dominate over the smaller ones ripping them apart and essentially consuming them galaxy interactions
04:30are all about bullies the bigger you are the badder you are when two galaxies collide it's like
04:38two massive armies marching towards each other these galaxies aren't fighting with knives or spears or
04:48guns or even nuclear bombs they're fighting with something much more powerful gravity itself
04:56each galaxy contains billions of stars and planets and a supermassive black hole millions of times the mass of
05:05the sun that's a lot of gravitational firepower as these galaxies approach each other you can get
05:14tidal effects the same way that the moon can raise tides on one side of the earth and the opposite side
05:22one galaxy can stretch another galaxy along a certain direction
05:28as gaia enceladus advanced towards us our galaxy's superior gravity grabbed hold of the smaller galaxy
05:42as it approached the gravity from the milky way would have stretched it out
05:48gaia enceladus was distorted but not defeated the battle was just beginning it would have passed through
05:56our galaxy maybe orbiting a couple of times before being torn apart by our gravity
06:05the milky way's gravitational power ripped gaia enceladus apart and captured billions of its stars
06:15eventually most of those stars would have then settled down into the disk of the milky way and
06:20become a part of it little galaxy try to take on the milky way you're gonna get what's coming to you
06:27despite winning the battle the milky way suffered serious damage
06:33the collision with the sausage galaxy left a scar on the milky way and when we look near the center
06:38of our galaxy we see a bulge that's left over from that collision
06:42the milky way isn't the only galaxy scarred by war
06:50across the universe rival armies made up of billions of stars slug it out
06:57leaving behind distorted and damaged casualties of war
07:04there's a million different subcategories of them there's tadpole galaxies that have long tails
07:09longer than our own galaxy there are things like art mador 2026 where you see this eerie glowing face
07:16two big eyes looking right at you from across the universe there are galaxies that look like they
07:21might have collided with one another and blown holes through each other
07:28these battle scars give us important clues about one of the biggest mysteries in astronomy
07:34how galaxies develop and grow but there's a problem we can't watch these battles in real time
07:45the scale of galaxies is huge they're hundreds of thousands of light years across it's going to take
07:50them millions or billions of years to come together so it's like looking at one frame for a really
07:57energetic fight scene in a movie by piecing these snapshots together astronomers can
08:03build up a detailed picture of past conflicts and discover how these battles transformed galaxies
08:12over billions of years we have pictures of isolated galaxies we have pictures of interacting galaxies
08:18and we have pictures of aftermath galaxies and that's helped us discover something alarming
08:26the milky way faces yet another attack from an enemy armed with an enormous secret weapon will our solar
08:36system survive the onslaught
08:38across the universe galaxies are at war
08:56their main weapon gravity it tears the combatants into weird and wonderful shapes
09:03our galaxy didn't escape the mayhem it's peppered with battle scars
09:12the overall shape of the milky way is a flat disk of stars and gas except recently we have found
09:18out that at the edges it's actually warped a little bit like the brim of a fedora the stars actually
09:25dip down below the plane on one side and dip above it on the other
09:28we think the attacker was one of our satellites a galaxy that orbits the milky way like the moon
09:37orbits the earth it's called the sagittarius dwarf galaxy from looking at how the stars move in the
09:44milky way we suspect that the sagittarius dwarf galaxy has actually crashed through the milky way
09:51a few times on its course of its orbit around the galaxy
09:54it came in about six billion years ago hit the disk hard about two billion years ago and crashed
09:59again about a billion years ago and our gravity has pulled it out into a gigantic looping stream
10:05of stars that is moving in and out of our milky way
10:11the war is not over the insurgent galaxy will return
10:18when galaxies interact often they're caught in this huge cosmic dance where they
10:23revolve around each other a few times or they even crash through each other and then come back
10:28around the sagittarius dwarf galaxy looks like it's crashing in with ever increasing frequency
10:35a new skirmish could take place in the next hundred million years
10:40so should we be worried about these attacks because the sagittarius dwarf galaxy is so small compared to
10:47the milky way it will do some damage at the beginning but because we're so massive we can absorb the
10:54impact i mean this galaxy it's looking for a fight but it's also 10 000 times smaller than us so this is
11:01gonna be no sweat at all
11:06so far the milky way has been victorious but the danger isn't over we are surrounded by enemies
11:17our local neighborhood of galaxies has three major galaxies but up to 50 smaller ones all these galaxies
11:26are potential troublemakers each one of these could be armies that rise up against us
11:34the two most famous galaxies that orbit the milky way are the large and small magellanic clouds
11:41these are two independent dwarf galaxies that you can see in the night sky from the southern hemisphere
11:46we thought the large magellanic cloud orbited our galaxy at a safe distance of 160 000 light years
11:59we thought it would stay that way and we thought it was harmless now a new discovery shows we were wrong
12:08on all counts the new factor that changed our view of the magellanic cloud
12:14is we found out it has a lot more dark matter than we thought
12:20dark matter the most mysterious stuff in the universe
12:26a dark matter is literally what it sounds like it's matter that we cannot see
12:31but it has gravity and can affect objects that we can see
12:37adding in this extra dark matter makes the large magellanic cloud
12:42at least twice as massive as predicted so its gravity is double what we thought
12:51it's secretly been gathering allies has been gathering dark matter on its side
12:57and now it's a much bigger threat than we thought before
13:02so it's not just going to orbit us it's going to collide with the milky way
13:06moving at nearly a million miles an hour the large magellanic cloud will not swing past us
13:15it will attack the large magellanic cloud is one tenth the mass of the milky way
13:23that's enough to make a pretty big punch
13:26in about two and a half billion years it will smash into our galaxy
13:36it's going to plow through the disk of the milky way it's going to blow a cavity
13:41it might even damage our spiral arms
13:46earth sits in one of those spiral arms
13:49could our planet become collateral damage
13:56if the large magellanic cloud passes through the plane of our galaxy near our location that
14:01could have dire consequences the gravitational clash between the invader and the milky way
14:09could hurl stars and planets out of our galaxy earth could be one of them
14:16our planet's very close to its own star so the odds are that you'll just get ripped out along with
14:24your star so we'd be moving along with the sun even as the sun gets jettisoned from our galaxy
14:31and it'll move off out into intergalactic space and that's not terrible i mean it's not going to get
14:36destroyed but it's a little lonely
14:38our view of the night sky would radically change
14:47we'd be able to see much more of the milky way especially if we got kicked up above the plane of
14:54the galaxy we'd be able to see the whole shebang just look at any image of a spiral galaxy they're
15:01gorgeous now imagine seeing your night sky filled with the face on spiral galaxy
15:07that would be like waking up to my face every morning spectacular
15:18if we were unlucky our home planet could have a close encounter with an invading star
15:25the odds are very low that another star will pass close by the sun but those odds aren't zero it could
15:33happen that another star passes close enough to affect the planets and if that were to happen it
15:39could upset the delicate balance in the solar system we don't know where the earth could end up
15:48it might find its way into the sun you just don't know or there might just be a rain of comets into
15:54our inner solar system our own planet might be flung out in which case this would be a death knell for
16:01all life on earth i'm not someone who's like a doom and gloom person but like that would be insane
16:08you don't know what's gonna happen but most of the options are bad
16:14all these nightmare scenarios will extinguish life
16:22earth might survive but our cosmic zip code will take a severe beating
16:27the milky way galaxy is bigger than the large magellana cloud so we are gonna win
16:35but it's gonna hurt us for a long time
16:39the large magellana cloud will leave our galaxy battered bruised but ultimately undefeated
16:47but there's a far bigger threat looming over the milky way it's gonna face an opponent that it can't
16:54defeat will this mega collision be the milky way's last stand
17:12for billions of years the milky way conquered galaxy after galaxy tearing its smaller rivals to pieces
17:19but our galaxy is about to meet its match
17:27in the not too distant future galactically speaking a much much larger battle is due for the milky way
17:36a battle with a local superpower the andromeda galaxy we thought this huge galaxy might wound us
17:46in the future now recent evidence reveals it's going to make a full-scale assault
17:55we've known for a long time that andromeda is heading more or less toward us but we didn't know
18:01exactly in what direction but in recent years we've been able to pinpoint this a lot better
18:07and uh yeah it's it's heading right for us data from the hubble space telescope shows
18:16the two galaxies will collide in about four billion years
18:23and it will be a monumental battle this collision that is coming and it is coming is not going to be
18:31anything like the milky way has experienced before in its 10 or 12 billion year history this is a galaxy
18:37of comparable size this is two heavyweight prize fighters coming at it warriors with the same
18:44gravitational firepower simulations suggest a clash of the titans each of them with half a trillion
18:52stars in them that sounds like a pretty spectacular collision fights between equally matched galaxies
19:01are rare and messy when the battle kicks off there will be no good news for either side
19:11when the andromeda galaxy and the milky way galaxy start to get close
19:15they're going to start affecting each other profoundly tendrils of stars are going to be thrown out
19:20gas is going to be thrown out
19:22it won't be a single impact gravity will send the two opponents into a spiraling dance of death
19:35the first pass is actually not a direct hit they're going to swing past each other in fact
19:40and at this point their gravitational interaction is going to slow them down and they're going to come
19:45back toward each other the galaxies will collide and fly apart again inflicting more and more damage
19:52with each clash if you were to go outside and look up you could see the disk of our galaxy getting
19:59ripped apart by tidal interactions with andromeda
20:02the two beautiful spiral galaxies will tear each other apart leaving one vast elliptical galaxy
20:18the fate of the andromeda milky way battle is that they will merge this is going to be one gigantic galaxy
20:28and that presents a problem what are we going to call this new galaxy of course my nerd colleagues
20:37have come up with names like milkometer and drama way whatever those are corny we should just call it hakeem
20:51with a trillion stars it will be one of the biggest galaxies in the universe
20:56in the hakeem galaxy thing is going to be completely new first off it's going to be a really good
21:05looking galaxy let's get that straight from the get-go second is going to be powerful and i'm talking
21:12powerful this may be the most remarkable galaxy in the history of the universe
21:19milkomita or hakeem if you prefer will become the undisputed boss of our cosmic neighborhood
21:26it's calm appearance concealing a history of violence
21:35it's the result of a complete war zone of mergers over the course of billions of years many galaxies
21:40crashing together fully reconfiguring each time and slowly you grow this smooth placid big blob of stars
21:48after billions of years of warfare our galaxy will finally be peaceful
21:59but before its honorable discharge milkomita may produce one final devastating act of war
22:08imagine world war ii and then all of a sudden one of the sides comes up with the death star that's what
22:15we're talking about here a weapon of cosmic destruction
22:29so
22:38when giant galaxies clash the battles are spectacular and destructive
22:47the victors steal huge numbers of stars and vast amounts of gas as fuel for the ultimate super weapon
22:55the special weapon that these monster galaxies have is a giant death ray a jet of material racing across
23:07thousands of light years
23:11these huge outbursts of energy blast out of the center of the colliding galaxies
23:17they produce more energy in one second than the sun will in its entire 10 billion year lifetime
23:25we call them jets
23:29these incredibly powerful jets aren't just brief features they can be sustained for millions of years
23:37and they can maintain their structure for thousands of light years
23:41it's like turning on a garden hose in chicago and using it to water a garden in london
23:50exactly what triggered these jets was a mystery then in june 2018 astronomers in hawaii captured
23:57something stunning a jet forming during a galactic collision
24:03the team found something really incredible they found two galaxies that were in a cosmic collision
24:11and actually found an active jet in one of these galaxies it was the first time anything like this has been discovered
24:20when galaxies collide the clash drives huge clouds of gas and dust towards their centers
24:26the supermassive black holes the supermassive black holes start to feed
24:33the gas that was in those galaxies starts to funnel toward the black hole and fall upon it
24:40not all this gas ends up inside the supermassive black hole powerful magnetic fields carry some of this
24:47matter to the poles and blasted out in tight narrow jets a super weapon is born
24:55this discovery helps us understand how giant elliptical galaxies form
25:02knowing that mergers of spiral galaxies can cause these jets helps us put together a complete picture
25:08of how these huge elliptical galaxies might be formed
25:14the discovery doesn't answer all our questions there's another mystery how did the supergiant galaxies that
25:22dwarf the milky way get so big our milky way galaxy is big ish it's slightly bigger than average
25:32but ic 1101 for example is more than 50 times larger than our home galaxy and has more than a trillion with
25:39a t a trillion stars in it the biggest galaxies make the milky way look like an ant
25:46planet these galactic giants pose a problem there hasn't been enough time since the birth of the
25:54universe for them to become so large even by conquering smaller galaxies when we look into the distant
26:03universe we see something very strange that we don't quite understand we see enormous galaxies that existed
26:09just a billion years after the big bang and even though these cosmic collisions help explain how galaxies get bigger
26:16they don't quite explain everything about how galaxies grow over time so we still have a big mystery on our hands here
26:26so in 2019 an international team investigated a very large galaxy over 300 million light years away
26:35we call it ngc 6240. ngc 6240 was being studied because it had two supermassive black holes in it
26:46now the galaxy itself looked like it had been disturbed like something had happened so they thought
26:51that potentially it had had a recent merger
26:53they were expecting to see two supermassive black holes in the galaxy's heart as the researchers peered
27:07through the layers of gas and dust they discovered something surprising what we found was staggering we
27:15found not two but three supermassive black holes lurking in the center
27:23it's the first time we found a galaxy with three supermassive black holes evidence of a three galaxy pileup
27:36this galaxy is an active battlefield of not two but three armies colliding at once
27:46and because there are three armies involved there are three galaxies involved with
27:50three times as much mass three times as many stars three times as much material and three times as much
27:57violence this three-way battle may explain how the largest galaxies got so big so fast
28:06it could be that galaxy mergers are more frequent than what we thought previously and therefore galaxies
28:13become more massive faster than previously expected
28:19in the past galaxies may have battled and collided more often than today
28:24back then galaxies were more densely packed together
28:30our universe is expanding as it ages which means in the past all the galaxies in the universe were closer
28:37together and that means they had greater chance for their gravitational interactions to pull them
28:42together and smash them together the early universe was at war conflicts between galaxies were common
28:53they collided frequently and grew quickly but not every galaxy profited from the carnage
29:01some brave galaxies took on the big guns and nearly died as a result
29:21when galaxies fight the big get bigger more mass means more gravity the vital ingredient for victory
29:31to spread out 기분 to price to continue to achieve greater change by falling space
29:39improbablecribers it is the pure end of our society, but galactic conflict doesn't always result in growth
29:47a strange new astronomical object had scientists confused
29:49beautiful space-based telescopes, it was possible to look at these stars again and actually
29:56discover that they were galaxies.
30:03They're kind of crazy.
30:05They're a huge number of stars, but crammed into an incredibly tiny space on an astrophysical
30:12scale, something 500 times smaller than our Milky Way galaxy.
30:16We call them ultra-compact dwarf galaxies, or UCDs.
30:23You might imagine the difference between the Milky Way galaxy and a UCD as the difference
30:31between a cloud and a rock, where the rock is just the same kind of material but compressed
30:38to just incredibly high densities compared to some fluffy, gaseous thing.
30:41What are these strange galaxies?
30:47They seem to break all the rules.
30:50To find out, astronomers zoomed in to a particularly dense ultra-compact dwarf galaxy called M60UCD1.
31:01M60UCD1 is 300 light-years across.
31:06It's tiny.
31:07It's a pinpoint compared to our enormous galaxy.
31:10Our galaxy has 200 or more billion stars in it, and M60UCD1 only has 140 million, but
31:17they're packed into this incredibly tight volume.
31:20The night sky inside the galaxy would look very different from our own.
31:25On Earth, when you look at the night sky, you see a few thousand stars, but if you were
31:31in M60UCD1, you wouldn't just see a few thousand stars, you would see hundreds of thousands of
31:38stars in the night sky.
31:40That would be amazing.
31:41As the astronomers look deeper into the heart of this tiny galaxy, things got even weirder.
31:55They found a supermassive black hole, much bigger than expected.
32:02It actually has a black hole that's bigger, five times bigger than the black hole at the
32:07center of our Milky Way galaxy.
32:08When we see supermassive black holes inside of galaxies, they tend to scale with the size
32:15of the galaxy itself.
32:16A bigger galaxy has a bigger supermassive black hole.
32:20Why does such a tiny little object have such an oversized central black hole?
32:26The only possible explanation?
32:28This tiny galaxy was once much larger.
32:33These galaxies might have begun their lives as, in fact, much bigger galaxies, and that what
32:38we see today was really just the very central, densest part of a much larger galaxy.
32:45Based on the size of its supermassive black hole, M60UCD1 may once have contained many billions
32:54of stars.
32:56Something captured them.
32:57And we don't have to look far to find the aggressor, a nearby supergalaxy with lots of gravitational
33:04firepower, M60.
33:08M60 is a monster.
33:10It has a trillion stars in it.
33:12It's bigger than the Milky Way.
33:13We're pretty big.
33:14The battle was not a full-on frontal assault.
33:18M60 raided its smaller opponent, capturing its troops.
33:23This is more of a stealthy guerrilla hit and run where we're going to move in, pick off some
33:29of your troops, and then get out before you even notice.
33:32All that's left from one of these drive-by galaxy interactions is this supermassive black
33:40hole with a fraction of its original stars.
33:44The conflict devastated M60UCD1.
33:49Over 98% of its stellar army were captured and became prisoners of war.
33:54It used to be a big galaxy, but it suffered one too many defeats, and now it's a fallen empire.
34:04We can frame this battle between M60 and M60UCD1 as just a battle, but in fact, it's a slaughter.
34:12It's a massacre.
34:14These small galaxies get all their troops removed, but the HQ, the supermassive black hole, remains,
34:21but it doesn't have any troops left.
34:25Eventually, M60 will conquer its battered opponent, destroying what's left of the compact galaxy.
34:33It'll get ripped apart even further, and more and more stars will be consumed by the bigger galaxy.
34:38So, chances are, this little dwarf is eventually going to be pulled apart and become a part of M60.
34:45In the great game of galactic warfare, losing can be catastrophic.
34:51For weak and small galaxies, resistance is futile.
34:58Pillaged for resources by their more powerful opponents, they slowly become burnt-out wrecks.
35:03But, some peaceful galaxies face an equally terrible fate.
35:12They starve to death.
35:13Cosmic wars are vicious.
35:27They destroy many galaxies.
35:30But violent conflicts can also give galaxies new life.
35:33Case in point, galaxy NGC 4485.
35:41NGC 4485 has a nickname of the Two-Face Galaxy, like the Batman villain, because it has two different halves of the galaxy doing completely different things.
35:50Half of the galaxy is sort of old and calm and relatively quiescent, whereas half of it appears to be undergoing a sort of fireworks display of new star formation.
36:02Why are new stars only born in one half of this galaxy?
36:06We found a clue on the edge of a photo taken by the Hubble Space Telescope.
36:15It was evidence of an attack by another galaxy.
36:18We think that another galaxy passed through it just off-center in a way that strongly perturbed the gas on one half of the galaxy.
36:27The Two-Face Galaxy skirmish gave it a gravitational jolt, forcing clouds of gas together.
36:38When we think of galaxies, we think of stars.
36:41And, of course, galaxies are made of stars.
36:42But, of course, gas is the stuff that stars are made of.
36:48When two galaxies collide, the gravitational duel can trigger a huge burst of star formation.
36:57You need something to give a galaxy a push.
37:01And that's exactly what a galaxy collision does.
37:04And when gas clouds collide, they compress.
37:07And when they compress, you get knots in them that can compress more and form stars.
37:15So you can think of these collisions as very violent events, but ultimately it can breathe new life into a galaxy.
37:22But the spoils of war don't last long.
37:25In the short term, the victor galaxy can come out glorious with so many new stars.
37:33But this celebration is short-lived because that round of star formation quickly uses up the material available.
37:41If a galaxy wants to stay alive, it has to feed on other galaxies.
37:45So galaxies constantly need to raid new targets.
37:51And that raises an important question.
37:54What happens if there's a galaxy just alone in space?
37:56Nothing else is colliding with it.
37:57Sort of a pacifist galaxy.
37:59The poster child for these peace-loving galaxies is NGC-1277.
38:08NGC-1277 is a very peculiar galaxy.
38:12It's pretty big and its stars are extremely old.
38:16It basically hasn't formed new stars in the last 10 billion years.
38:20So it's kind of the veterans' home of galaxies.
38:25NGC-1277 lives in a rough part of the cosmos called the Perseus Cluster.
38:31Thousands of other galaxies surround NGC-1277, and they are all ready for a fight.
38:38So you might ask, why hasn't it had encounters with other galaxies that might rejuvenate it?
38:43The answer, once again, is gravity.
38:49NGC-1277 sits inside this massive galaxy cluster that has a ton of mass.
38:54And if you look at its position, it's fairly near the center of the cluster.
39:00The combined gravity of thousands of galaxies pulls on NGC-1277,
39:07accelerating it to 2 million miles an hour.
39:10And so it has spent the last few billion years traveling faster and faster,
39:18until now it's almost at its fastest pace.
39:23It's very hard for gravity to catch it or catch one of its neighbors
39:27and bring them together to merge with each other.
39:31NGC-1277 has no chance of grabbing new gas to make new stars.
39:38It's dying.
39:38All it has left are old, red stars.
39:43When it comes to galaxies, red is dead.
39:47No new stars means no big stars, no blue stars, just small, dim red dwarfs.
39:58Galaxies that don't fight just fade away.
40:00At that point, the history of the universe becomes really kind of boring.
40:06All the stars will simply start to die out.
40:09Eventually, there will be the last star formed in the Milky Way,
40:12with no new galaxy bringing fresh material.
40:14Without galaxy collisions, the universe dies.
40:17Galactic battles mix things up and replenish gas supplies.
40:30And our own galaxy has reaped the benefits.
40:35Our Milky Way galaxy fought a massive battle.
40:38But that battle may have been necessary to build solar systems like the one we live in right now.
40:49Clashes with the Sagittarius dwarf galaxy occurred at the same time the sun formed.
40:54It's possible that we owe our very existence to the collision with the Sagittarius dwarf galaxy.
41:02Maybe the gas that ultimately gave rise to the birth of our solar system once came from another galaxy entirely.
41:12So galactic wars are both creative and destructive.
41:18Galaxies are built from collisions.
41:21Galaxies survive from collisions.
41:25And galaxies can also die from collisions.
41:28Far from being destructive events, colliding galaxies may be the reason that you and I are here.
41:37Intergalactic warfare has revolutionized our understanding of how galaxies live and die.
41:45Ultimately, it's these galaxy mergers that are one of the great engines of all structure growth in the universe.
41:51These collisions got us to where we are today.
41:55And they're going to determine the future of all the universe.