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00:00All across our galaxy, stunning clouds of gas and dust, nebulas.
00:08They contain secrets of the cosmic circle of life, the birth and death of stars, planets, and us.
00:18These things are really cradles of creation.
00:21You are intimately related to the nebulas. You are a nebula. Come alive.
00:28The story of how our solar system formed starts with a nebula.
00:34If you want to build a solar system, you're going to need a nebula.
00:38Look around you. Everything you see, everywhere, was once inside of a nebula.
00:44Now, scientists are pulling back the veil.
00:49Opening our eyes to the true expanse of our universe.
00:54Solving the riddles of these engines of creation.
01:00There are mysteries waiting inside that we haven't even guessed at yet.
01:04Sound Effects
01:20The Milky Way. A spiral galaxy full of regions of gas and dust called nebulas.
01:28And everyone has their favorite.
01:31The Horsehead Nebula. It just looks awesome.
01:34The Cat's Eye Nebula has always been really captivating to me.
01:38My favorite nebula is the Orion Nebula.
01:42The Orion Nebula is perhaps the best place to understand the evolution of stars.
01:48And it's right here in our own backyard.
01:51The Orion Nebula is maybe one of the most famous nebulas because you can go outside at night and see it with your own eyes.
01:59Humans have been observing this fuzzy patch of sky for centuries.
02:03The Maya of Central America called it the Fire of Creation.
02:09The Maya were more right than they knew.
02:12Almost every part of the life cycle of a star you can see in a nebula.
02:17We can't understand the life cycle of stars without understanding the life cycle of nebulas.
02:24They are intertwined.
02:27Orion has it all.
02:29From massive stars on the brink of death to newborn stars swaddled in gas.
02:35You see the intricate wisps of material.
02:39The thin veils enveloping newborn stars.
02:43Pillars colliding into each other.
02:46You see stars plowing through clouds of gas.
02:49You see this frenzied hive of activity operating right before our eyes.
02:57In 2018, using new data, NASA creates a groundbreaking 3D visualization of Orion's interior.
03:08For the first time in history, we have the right tools to actually explore the hearts of these nebulas.
03:16It was already beautiful to begin with, but now we have even more vivid images
03:20to really appreciate how great of a structure this is.
03:25At Orion's heart lies a cluster of young stars.
03:29Together, they blast out charged particles in solar winds,
03:34blowing open a gap at the center, creating a window inside.
03:40We actually see the structures and the volume.
03:43We can actually see the processes happening right before our eyes.
03:48The cluster's intense starlight energizes the surrounding gas, causing it to glow pink and blue.
03:57The pinks come from light emitted from hydrogen atoms in the nebula, glowing like the gas in a neon tube.
04:03The blues tend to come from the light from the hot new stars reflected off of dust particles.
04:11These hot new stars illuminate the Orion Nebula, but they were actually born in the dark.
04:19One particular type of nebula is a dark nebula, and basically that's when the concentration of dust is a lot greater.
04:29Dense clouds of dust block out visible light from the stars behind,
04:35creating shadowy shapes like the Horsehead Nebula.
04:39This nebula is so large and dense, it has enough mass to make about 30 stars the size of our sun.
04:46And now astronomers can peer inside.
04:50Only recently have we been able to start doing this,
04:55thanks to detectors that can see light in the infrared.
04:59The infrared allows us to sort of see through the dust of a nebula and see what's going on deep in its heart.
05:08Humans can't see infrared light, but we can feel it as heat.
05:14Infrared detectors tell us these dark, star-forming clouds are cold, hundreds of degrees Fahrenheit below freezing.
05:25But deep inside are hot spots.
05:31If you look at it with infrared, you see, ah, the signature of incredible densities and incredible temperatures,
05:39the signs that a new star is being born.
05:44A knot of matter comes together under the force of gravity.
05:48As it grows, so does the gravity.
05:51It pulls in more gas, growing bigger and bigger.
05:58That gets very massive, very dense, and very hot.
06:02Eventually it gets high enough pressure and temperature in the center of that object that you ignite fusion.
06:09A star is born.
06:15One of the hundreds of billions that make up our galaxy.
06:20The latest in a stellar production line going all the way back to the dawn of time
06:26and the very first nebula.
06:30If we want to unravel the history of the Milky Way, we want to start in the beginning, and that's the Big Bang.
06:4213.8 billion years ago, the universe sparks into life.
06:49At first, it's pure energy.
06:53But over 300,000 years, that energy cools into hydrogen and helium gas.
07:00Back then, the entire universe was one enormous cloud.
07:06The essential ingredients of our universe spread as the universe expanded,
07:11and so the universe started as one giant nebula.
07:16Over time, the primordial nebula starts to collapse and fragment into smaller clumps.
07:24These regions become so dense, they collapse into disks with super hot balls of gas in their cores.
07:38The first stars ignite.
07:41They start out as nearly pure hydrogen, but as they age, they make other heavier elements.
07:49Stars forge new elements. That's what they do.
07:53The very definition of a star is in its core, it's fusing hydrogen atoms into helium and releasing energy.
08:00But many of those first simple stars were massive, and massive stars don't live for long.
08:08They burned through their supply of hydrogen incredibly rapidly, and they burned themselves out,
08:14and they died after a few million years.
08:18They go out with a bang.
08:25An explosion that releases more complex elements back into the primordial nebula.
08:33After that first generation of stars started to form, there was this huge burst of new elements
08:39that formed and that were dispersed throughout the universe to be able to form that next generation of stars.
08:45As the second generation of stars lives and dies, it adds even more ingredients to the cosmic mix.
08:53The next generation of stars fused more elements, exploded, died, spread the material,
08:59new generation of nebula, new generation of stars.
09:03Each generation having more and more elements in the periodic table than the last.
09:13And around 300 million years after the Big Bang, our galaxy, the Milky Way, takes shape.
09:21Galaxies like the Milky Way formed out of essentially a proto-galactic nebula,
09:26some gigantic gas cloud that collapsed down and formed our galaxy.
09:33There is a rich cosmic symphony playing back and forth between stars and nebulas,
09:40and we now know that we are a part of that symphony.
09:49Eventually, our element-rich sun is born.
09:56We think that our sun is a third generation star.
10:00So it was actually a nebula, a star, a nebula, a star, a nebula before it became our sun.
10:07It took around 10 billion years to create a cosmic mix of elements rich enough to build planets and life.
10:16Carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.
10:21These are the key ingredients to life as we understand it, and those need to be made in stars.
10:28These elements are created during the life of a star,
10:32but it takes an incredibly violent process to liberate them into the cosmos.
10:40An event that can be seen clear across the universe, a supernova.
10:58The most beautiful nebulas in our galaxy are born out of incredible violence, the deaths of giant stars.
11:09Some of the most colorful nebulas in our galaxy are remnants of supernova explosions,
11:13things like the Crab Nebula, Castiopia A, also the Veil Nebula.
11:18Those all happened when a giant star exploded violently.
11:26The Crab Nebula was once a massive star with around 10 times the mass of the sun.
11:38In its core, that star crushed atoms together to form heavier elements,
11:44a process that releases huge amounts of energy.
11:49A massive star can fuse heavier elements and those heavier elements into even heavier elements until it gets to iron,
11:55and when it gets to iron, that's when things go bad really fast.
12:00Iron atoms are so big that fusing them takes up more energy than it produces.
12:07The core starts to collapse on itself, setting off a catastrophic explosion,
12:18blasting elements out into space.
12:23When a star goes supernova, it violently rips itself apart,
12:27and all of the material of the star can be spread across light years.
12:31We call this, rather obviously, a supernova remnant nebula.
12:36Now you have a nebula filled with all of these interesting chemicals.
12:39All of those are illuminated by the energy of the supernova explosion.
12:45Supernova remnant nebulas glow brightly in many different colors.
12:51The colors in a nebula are kind of like a fingerprint or a DNA test of the elements inside.
13:00Every atom has a shell, a cloud of electrons that orbits around its nucleus,
13:05and as those electrons change energy levels, the frequencies of light associated with those energy changes
13:11are emitted into space and contribute to the broad spectrum of colors that we see.
13:18So we can look at a distant nebula and we can say,
13:22it's this much hydrogen, this much helium, a little bit of platinum, oh, we got a lot of oxygen in that one.
13:31The colors of a nebula reveal the elements created during a star's life and death.
13:39But a nebula's shape can reveal what happens after a star dies.
13:45You would think that one exploding star would be pretty similar to every other one.
13:49They would make the same sort of nebula.
13:51And then you see the Crab Nebula with this beautifully complex shape,
13:55all of these different arcs and whirls of gas and dust.
13:58Something must be shaping it from the inside.
14:03Within the Crab Nebula lurks a stellar corpse called a pulsar.
14:09Pulsars are a kind of neutron star, a ball of super-dense matter.
14:15They're born from the death of massive stars.
14:20This is the leftover core of the star that exploded.
14:23It just collapsed down and formed a very tiny ball of neutrons and a little bit of normal matter
14:28that's very, very hot and has a very, very strong magnetic field.
14:34This pulsar is spinning at around 30 times a second,
14:40blasting out beams of radiation that sweep through space like a frenzied cosmic lighthouse.
14:48And the pulsar in the Crab Nebula doesn't just emit light.
14:52It's also blasting out a wind of charged particles.
14:58The gas cloud itself around it is the Pulsar Wind Nebula.
15:01So it's taking all that leftover stuff from the supernova and blowing it out into that expanding cloud.
15:09Pulsar winds plow through the surrounding gas, creating the twists and folds of the Crab Nebula.
15:22Supernovas create the elements.
15:27Their winds spread them throughout the cosmos, forming new nebulas.
15:35Nebulas that might form a solar system like ours.
15:41The nebula is essentially the starting point of the recipe for the solar system.
15:47So it's got all the ingredients, all of the chemicals, all the gases, solids that we see in our solar system today.
15:54Think about the major elements that make up the planet Earth.
15:57What happened to bring all that together?
16:01How did a gassy cloud of elements become our planet and our sun?
16:06What turned a nebula into our solar system?
16:23Once upon a time, there was no sun, no solar system, no us.
16:30Just a cloud of gas and dust, a solar nebula.
16:36We are here today because billions of years ago, there was a nebula containing all the necessary ingredients.
16:46Everything that we see in our solar system today, that was all part originally of the cloud of gas and dust that was our solar nebula.
16:57Almost five billion years ago, a solar nebula was prepared to give birth to our sun.
17:04So we have, billions of years ago, our solar nebula, a cloud of gas and dust.
17:09And it's hanging out, but it's unstable.
17:12What tips the balance to turn a cloud of gas into solid objects?
17:17Something has to change.
17:19Inside a nebula, something has to trigger the formation of stars and planets.
17:23And that remains a mystery.
17:26So what's the answer to this five billion year old mystery?
17:37There are two theories.
17:40Both start with fossils.
17:43Fossils that make their way from the edge of the solar system towards Earth,
17:49break through our atmosphere,
17:52and find their way to us.
17:58Meteorites are really important for us to understand and study because they're time capsules to when the solar system was basically first forming.
18:09Mina Wadhwa curates one of the largest collections of meteorites on the planet.
18:15These rocks hold a pristine record of the very early history of the solar system.
18:22There was nothing else around in the solar system before these rocks were formed.
18:28There was no Earth. There were no other planets. It's mind blowing.
18:32The first solid objects form out of a cloud of dust surrounding our newborn star.
18:38Asteroids and meteorites forming at the same time contain the chemical fingerprint of our solar nebula.
18:46They actually contain some of the oldest materials,
18:50oldest solids that condensed from the cloud of gas and dust as our solar system was forming.
18:55And so they came together and formed this big rock that you see here.
19:01In 2017, researchers analyzing the composition of a type of rocky meteorite called chondrites
19:08find a clue about how our solar system was formed.
19:13There might be, in fact, a smoking gun somewhere in the chemistry of these rocks
19:18that could tell us about what exactly happened and how our solar system was formed.
19:23This smoking gun is a radioactive element called Iron-60,
19:29and it's thought to be created only in supernovas.
19:36If you have a nebula which is about ready to start forming stars,
19:40and a supernova goes off next to it,
19:42that supernova is going to dump all those heavy elements into that gas cloud,
19:47but it's also going to trigger the formation of stars by slamming into that gas and compressing it.
19:54A nearby star goes supernova.
19:57The shockwave strikes our solar nebula, injecting it with Iron-60.
20:06But the collision starts a runaway gravitational collapse in the core of the nebula.
20:13The gas cloud clumps together, becoming hot and dense.
20:18Our sun is born.
20:21As the sun is forming, there's basically a cloud of junk all around the sun,
20:26and as it orbits the sun, it kind of accretes or sticks together and grows into these balls.
20:34Over the next hundred million years, these balls get bigger and bigger,
20:40forming asteroids, moons, and planets.
20:45All of the planets in our solar system seem very different.
20:49Some ice giants, some gas giants, some rocky bodies.
20:53But in fact, all of these planets came from the same pre-solar nebula.
20:59And on one small planet, the right cocktail of elements gave rise to us.
21:08Everything, every atom in our bodies, was once part of the pre-solar nebula.
21:16The theory that a supernova nudged our solar system into existence is compelling.
21:23But not everyone agrees.
21:25Sometimes, the biggest arguments among scientists are caused by the littlest things.
21:30And in this case, I'm talking about little tiny radioactive atoms.
21:36In 2017, studies reveal other meteorites contain a different radioactive signature,
21:43a rare isotope of aluminum called aluminum-26.
21:49That's a rather odd atom that is not formed very easily in supernovas.
21:53So that had to come from somewhere else.
21:57That somewhere else is a rare type of giant star 40 to 50 times the mass of our sun,
22:05a Wolf-Rayet star.
22:09Stars can be very weird, and the very massive stars are incredibly weird.
22:14The largest type of star that we've seen is what's known as a Wolf-Rayet star.
22:21Wolf-Rayet stars burn the hottest of all stars,
22:25producing heavy elements like aluminum-26 during their short lives.
22:30These are massive and hot and luminous.
22:33And they blow off a tremendous wind.
22:36This stellar wind ejects tons of matter from the star into the surrounding space,
22:42creating a bubble structure.
22:46Scientists see this process at work in the Bubble Nebula, 7,000 light-years from Earth.
22:54In the middle of the nebula is one of these giant stars with a massive stellar wind,
23:00high-energy particles, radiation, and just like the name suggests,
23:04it's blowing a bubble in the larger nebula around it.
23:06The walls or shell of the bubble are dense and full of matter.
23:11The stellar wind pushes more and more matter into the shell,
23:17until this material collapses under its own gravity and condenses into stars.
23:25It's entirely possible that what we're seeing in the Bubble Nebula
23:29is what happened here four and a half or more billion years ago
23:32to form the Sun and the planets.
23:35If our solar system formed within a Wolf-Rayet Bubble Nebula,
23:40it would explain why so much aluminum-26 is present in meteorites.
23:48But the jury is still out.
23:52What we do know is that our story began with the collapse of the solar nebula.
23:57But one day, our star will die.
24:01Will the Sun turn into a stunning nebula, or will it just fade to black?
24:20Nebulas make stars.
24:23Stars make nebulas.
24:26The most massive stars do so in violent supernovas.
24:33But 99% of stars aren't big enough to go out with a bang.
24:40Some will just burn themselves out.
24:42But others can create beautiful nebulas with the misleading name Planetary Nebulas.
24:50From a distance, they look like planets.
24:53But really, they're the ghosts of stars.
24:57When stars like our Sun begin to die,
25:00they bloat up into the atmosphere,
25:03and when they do, they become a nebula.
25:06And when they do, they become a nebula.
25:09When stars like our Sun begin to die,
25:12they bloat up into what we call red giant stars.
25:16As a Sun-sized star reaches the end of its life,
25:21its core gets hotter and hotter.
25:24As it heats up, the surrounding gas expands,
25:27transforming the star into a red giant.
25:34It gets so big,
25:35its outer layers are no longer held in place by gravity.
25:40The outer layers of that star begin to drift away.
25:43They kind of lose touch with that central core in the middle,
25:46and they just begin to blow into beautiful shells,
25:49beautiful colors, beautiful shapes.
25:51We call these dying stars Planetary Nebulas.
25:54We've discovered over 3,000 Planetary Nebulas in our galaxy.
25:59Some look like an hourglass, or looks like an owl,
26:01or a clown, or a sphere, or a donut.
26:06But if they're all the ghosts of the same type of stars,
26:09why do they look so different?
26:12If you have a star that's just sitting there,
26:15no planets, nothing else around it,
26:17it's going to blow off its wind in a spherical shell.
26:19And so if you see a Planetary Nebula like that,
26:21it looks like a soap bubble in space.
26:23But only 20% of Planetary Nebulas
26:26have this perfectly symmetrical bubble shape.
26:29Most of them have these weird shapes.
26:32They can be two lobes,
26:34looks something like two squids kissing,
26:37all kinds of different shapes to these things.
26:42Experts think the strange shapes of these Planetary Nebulas
26:46may be linked to how a star dies.
26:51And now, new research may reveal the fate of our own star.
26:56Would we be a beautiful, bright Planetary Nebula,
26:59or would we just fade away into darkness?
27:02For the first time now, we think we may have the answer.
27:07It's a long-running debate.
27:09Is our sun big enough to form a spectacular nebula?
27:13It's kind of a funny coincidence.
27:15The model shows that you need a certain mass
27:18to make a Planetary Nebula.
27:20By coincidence, the sun is pretty much right in the middle.
27:23By coincidence, the sun is pretty much right on that limit.
27:29The new data suggests that our sun is going to go out in style.
27:36As the sun dies, it'll expand into a red giant,
27:40filling up the sky.
27:44We're used to our gentle yellow sun coming over the horizon,
27:47so imagine a giant, bloated, brilliant red glowing ball
27:51coming over the horizon for the sunrise.
27:54The expanding sun engulfs Mercury,
27:58then Venus.
28:01It'll cook the surface of the Earth,
28:04turning it into a molten hell.
28:08So the sad news is, is that once the sun expands as a red giant,
28:13it will absolutely boil away the oceans on the Earth.
28:16Life will no longer be sustainable.
28:19It's like sticking your head in an oven set to broil.
28:20It's not like it's going to be a fun time on the Earth.
28:25Some think it could even mean the destruction of the planet.
28:29We think the sun will eventually become large enough
28:32to swallow up where the Earth is now.
28:34So instead of there being a sunrise and a sunset,
28:37we're going to find ourselves inside the sun.
28:46The sun sheds its outer layers,
28:48ejecting over half of its total mass,
28:52revealing the stellar core.
28:55And so when we look at this core,
28:58which is now called a white dwarf,
29:00about the size of Earth,
29:02they're very hot,
29:04like hundreds of thousands of degrees.
29:07This white-hot core radiates UV light and X-rays.
29:15These hit the Earth,
29:17these hit the outer layers of gas
29:20and turn them into brightly glowing rings,
29:24a planetary nebula that will shine for about 10,000 years.
29:29One thing is for sure,
29:31and that is the solar system,
29:33when the sun turns into a planetary nebula,
29:35is going to look a whole lot different than it does now.
29:37It'll be unrecognizable.
29:40The planetary nebula will mean the end of the solar system as we know it.
29:46The sun will eventually die away
29:48and unravel itself back into space.
29:50But then the cycle begins again.
29:52This is not just an ending,
29:54it's also a new beginning.
29:57It's going to provide the ingredients
29:59that will foster yet a new solar system.
30:04As one solar system dies,
30:07another solar system is born.
30:09So really this is the cosmic cycle of life.
30:12Nebulas always signal change in the universe,
30:17intimately linked with star birth and star death.
30:22Now, new observations reveal
30:25that some of our favorite nebulas are also dying.
30:30Could the famous pillars of creation be dead already?
30:42Deep inside the Eagle Nebula
30:45is a dense region of cold molecular gas.
30:49Perhaps the best-known image in all astronomy,
30:53the pillars of creation.
30:56One of the images that really changed things
30:59was the pillars of creation.
31:01And it was an image that was very evocative.
31:03It really made me feel very emotional.
31:05It made me feel like I was part of something.
31:07The pillars are five light-years across
31:10and silhouetted by the light from a nearby star cluster.
31:14And it was these stars that carved out the shape of the pillars.
31:21The surface of these stars are energetic and boiling
31:25and constantly streaming particles off of them.
31:2910,000 mile-an-hour stellar winds
31:32are blowing through the pillars.
31:3510,000 mile-an-hour stellar winds
31:38ravage the surrounding gas clouds.
31:41Eventually, they completely dissipate
31:45their surrounding nebula.
31:48As the nebula disappears,
31:50columns of thicker, denser clouds survive.
31:54But for how long?
31:57When you look at these beautiful Hubble images
32:00of the pillars of creation, the Eagle Nebula,
32:01you see some blue, very diffuse gas
32:04around the pillars themselves.
32:06And this is a clue as to how the pillars formed
32:08and how they're going to change over time.
32:11This hazy blue gas is actually superheated material
32:15evaporating off the pillars themselves.
32:18Nearby stars are slowly eroding the pillars.
32:23This is similar to how weather erosion works here on Earth.
32:29Think about Monument Valley.
32:31You see these amazing stone pillars
32:34and really unlikely shapes coming up out of the ground.
32:37Well, those are denser areas of rock
32:39that used to be covered up by soil and sand.
32:42Over millions of years,
32:44that lighter material was blown away,
32:46exposing the denser rock underneath.
32:48And that's exactly the same thing that's happened here.
32:53This process is ongoing.
32:56Nebulas like the pillars are constantly evolving.
32:59The thing you keep in mind about the pillars of creation
33:02is this is actually a pretty transient feature
33:04in the life of the galaxy.
33:06It's not going to last forever.
33:08And in fact, over the course of time,
33:10even that we've taken images with the Hubble Space Telescope,
33:12we've seen it change.
33:15When astronomers compare new data
33:18to the original Hubble image from 1995,
33:21they discover a jet blasting out of the nebula
33:25at 450,000 miles an hour.
33:29Extending 100 billion miles into space.
33:35What could be the source of all this energy?
33:38These jets are associated with the moment a star turns on.
33:42The stars being born inside of the pillars
33:45are basically eating their way out.
33:47They're eating up this material
33:49and then they're going to blast it away.
33:52Newborn stars are a lot like little kids on a sugar rush.
33:56They gorge on gas,
33:58spin out of control.
34:00But stars also have a magnetic field.
34:04That magnetic field is rapidly rotating.
34:06It's sweeping up this material around it
34:09and shooting it out in two jets
34:11going out of the poles of the star.
34:14Jets and stellar winds are destroying
34:16the pillars of creation from the inside out.
34:23What's more,
34:25some of these baby stars are growing so fast
34:28they could soon reach the end of their short, violent lives.
34:34When stars die,
34:36they send shock waves,
34:38high energy radiation, particles.
34:44Supernova explosions like these
34:46could blow the pillars to pieces.
34:52Some have already suggested
34:54that the pillars may have already been destroyed
34:56thousands of years ago.
35:00Eagle Nebula is about 7,000 light years away
35:04and so we are literally seeing the Eagle Nebula
35:07as it was 7,000 years ago,
35:09not as it is today.
35:12It's a sad fact of life.
35:14Nebulas are destroyed by the stars they create.
35:18That's happening all the time.
35:20Everything changes.
35:22Our most famous, favorite nebulas
35:24don't exist forever.
35:26It's really sad,
35:28but this is just how the universe works.
35:30It's a transitory state.
35:32It's something in the act of changing.
35:35Where today we see pillars of creation,
35:38in the future,
35:40there will just be clusters of stars.
35:43But this eternal recycling
35:45of gas and dust into stars
35:47can't last forever.
35:50Nebulas across the universe
35:52are disappearing.
35:54Is our galaxy running out of gas?
36:13New research shows
36:15that across the universe
36:17the birth rate of stars
36:19is falling fast.
36:21Researchers predict
36:23that 95% of all the stars
36:25that will ever exist
36:27have already been born.
36:29In order for a galaxy
36:31to be healthy,
36:33to keep making stars,
36:35it needs to keep collecting
36:37new reservoirs of gas,
36:39of raw material.
36:41Our galaxy is running out of gas
36:43and in fact galaxies
36:45all across the universe
36:47are slowly running out of gas.
36:49That cycle is winding down
36:51and someday it will stop.
36:58More and more gas
37:00is locked up in low-mass stars
37:02that never go supernova.
37:05And the massive stars
37:07that do go out in a blast
37:09push the gas away.
37:12Galaxies eject material.
37:14Supernova winds
37:16and fountains
37:18are constantly sending
37:20streams of gas
37:22and particles
37:24outside the galaxy.
37:26But stars are not acting alone.
37:28They're in cahoots
37:30with something even bigger.
37:32Experts think the main culprit
37:34lies at the center
37:36of every galaxy,
37:38a supermassive black hole.
37:41In the past,
37:43even the Milky Way
37:45has experienced this gas loss.
37:46Just a few hundreds of millions
37:48of years ago,
37:50the central black hole
37:52was pretty massive
37:54and it gobbled up some material.
37:56In this process,
37:58it released a lot of energy.
38:00It sort of burped up
38:02a lot of energy.
38:04It released gas
38:06and some of that
38:08probably escaped the galaxy
38:10altogether.
38:12Right now,
38:14our galaxy is still
38:16refueling.
38:18Galaxies run on hydrogen.
38:20It's what creates nebulas,
38:22what creates stars.
38:24So it looks now like we may have
38:26reached a bit of a refueling stop.
38:28In space, we've discovered
38:30a giant cloud of hydrogen
38:32heading right for us.
38:34This hydrogen cloud
38:36is massive.
38:3810,000 light years long
38:40by 3,000 wide.
38:42Scientists call it
38:44Smith's cloud.
38:46It's orbiting our Milky Way
38:48and in about 27 million years,
38:50it's going to slam into
38:52the disk of our galaxy.
38:54The collision will re-energize
38:56the galaxy,
38:58jump-starting star formation.
39:00There's a lot of gas in there.
39:02There's about a million times
39:04the mass of the sun.
39:06You could make a million suns.
39:08But this is only a snack.
39:11To keep forming stars,
39:13the galaxy needs regular feeding.
39:16Here in the Milky Way,
39:18we're still forming stars
39:20and that's because
39:22our galaxy is a cannibal.
39:24It's surrounded by dwarf galaxies
39:26and it's eating them
39:28and it's still in their gas
39:30and their dust.
39:32We're the product of mergers,
39:34many small galaxies
39:36coming together and colliding.
39:38When a new galaxy collides
39:40with the Milky Way,
39:42it brings with it new gas,
39:44new dust,
39:46and of its own kind,
39:48the Milky Way is pulling out
39:50a few billion more years
39:52of star formation.
39:54But our galaxy is always
39:56looking for its next meal.
39:58And in a few billion years,
40:00it will feast on its
40:02next-door neighbor,
40:04the Andromeda galaxy.
40:06When Andromeda merges
40:08with the Milky Way,
40:10it's almost certainly going
40:12to deliver a fresh amount of gas.
40:14Although this is a catastrophic
40:16scale, it's actually
40:18kind of a good thing
40:20because when it happens,
40:22more stars will be born
40:24inside of the Milky Way.
40:26That's going to extend
40:28the life of our galaxy,
40:30if you want to think of it
40:32that way.
40:34But there are only so many
40:36galaxies nearby for the
40:38Milky Way to feed on.
40:40Eventually, over the long run,
40:42the nebular gas is being
40:44used up.
40:46With no gas
40:48to replenish them,
40:50nebulas will disappear
40:52across the universe.
40:54The universe really
40:56is winding down.
40:58Nebulas themselves
41:00are being depleted
41:02and dying away.
41:04The last stars
41:06will eventually blink out.
41:08From here on out,
41:10everything goes dark.
41:12Nebulas,
41:14one of the most spectacular
41:16things in the universe.
41:18One of the things that make
41:20nebulas so appealing is that
41:22they're just so beautiful,
41:24but it's more than just
41:26beautiful.
41:28They are cradles of creation.
41:30Nebulas are quite literally
41:32the starting point and the
41:34ending point of stars and
41:36therefore planets in life.
41:38I think it's incredible that
41:40we can learn about the cosmos
41:42and I think in the end,
41:44we're really learning
41:46about the cosmos like
41:48analogy for our own lives.
41:50They're incredibly beautiful,
41:52but yet,
41:54they're transitory.
41:56They're not going to be here
41:58forever and that's the story
42:00of our universe.
42:02It's a story of change.
42:04So seize the day.