Discoveries about interstellar space, the space between the universe's stars, reveal that it's not empty and unremarkable as previously thought, but filled with weird objects and strange phenomena that might hold the darkest secrets of the cosmos.
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LearningTranscript
00:00Interstellar space is the space between the stars.
00:07Interstellar space is vast, largely unknown and largely unmapped.
00:16Now astronomers are probing this great abyss
00:21and discovering something remarkable.
00:27Interstellar space is busy, it's filled with activity.
00:34There are rogue planets that are not attached to a star.
00:39There are cosmic rays, there are interstellar gas clouds.
00:43We've even got high velocity stars, all of that is careening around out there.
00:47The greatest secrets in our universe...
00:50Interstellar space is where we came from.
00:53...could lie between the stars.
00:57We live in a small solar system in the suburbs of the Milky Way galaxy.
01:12Eight planets and more than 180 moons, all orbiting the sun.
01:27In our solar system, the sun is the sheriff of the town.
01:34We do whatever the sun wants us to do.
01:39The sun's influence stretches more than one light year in every direction...
01:44...and defines the boundary of our solar system.
01:49Some place out there is a place where the sun's influence ends and the other stars begin.
01:55That's the entrance to interstellar space.
01:58Interstellar space is the region between star systems and our galaxy.
02:08Until now, we've known little about it.
02:15For so long, we thought of the space in between the stars as entirely empty.
02:20But this turns out not to be true at all.
02:23There's a lot going on out there, and it's the forefront of astronomy.
02:27One of the biggest clues about interstellar space came right to our doorstep.
02:42October 2017.
02:44The PanSTARS-1 telescope spots something unusual.
02:49PanSTARS is an observatory in Hawaii, and it's scanning large sections of the sky, looking for things that change.
02:59All of a sudden, there was this tiny little visitor just screaming through the solar system.
03:04It was going about 200,000 miles an hour.
03:08It was a much faster object than what might be expected for a solar system object,
03:13and also its trajectory was such that it seemed like its orbit was not bound to the sun.
03:18It was totally unlike any other path, any other trajectory, any other orbit in our solar system.
03:29Astronomers reached an extraordinary conclusion.
03:35It became very clear that, yeah, this was not some solar system object falling from a long way away.
03:41This was something that came from another star.
03:44And I think everybody was pretty amazed by that.
03:53Our first known interstellar visitor on a flyby through our solar system.
03:59It was the very first object that we'd ever discovered that had originated outside the solar system.
04:07Everything else we've seen, every comet, every asteroid, originated within our solar system.
04:14A big mega solid object entering in our own solar system, and that's something that, you know, I can only dream of, but had never thought it would actually be a reality.
04:26Scientists named the object, Oumuamua, Hawaiian, for a messenger from afar, arriving first.
04:39This thing came from interstellar space into our solar system, and the main question is, what could it be?
04:45The object's shape was mystifying.
04:52It's almost sort of shaped like a cigar. It's ten times longer than it is wide.
04:59And this is extraordinary. There's no object in our solar system that we've ever measured that is this elongated.
05:06Oumuamua looked so unnatural, it sparked scientists' imaginations.
05:17One of the things to remember about scientists is that we're still human beings.
05:20We have read science fiction. We have imaginations.
05:25I have to admit, when I first heard about it, my first thought is that it was Rama from an Arthur C. Clarke story, Rendezvous with Rama.
05:31This is a very elongated spaceship that came from another star.
05:35It reminded me of some designs we had for interstellar spacecrafts that have to be much longer than they're wide in order to minimize friction with the interstellar gas.
05:52Could Oumuamua be an alien interstellar spacecraft?
05:56Astronomers, including Professor Avi Loeb, took the idea seriously.
06:06We decided to follow this object using the best telescopes in the world and observe whether there is any radio transmission from it.
06:15Astronomers hunted for signs of alien communication.
06:21But after eight hours of listening across multiple frequencies, nothing.
06:34Sadly, no emissions were detected. It's almost certainly a natural object. I would bet all of my money on that.
06:41I was disappointed. I would have been much more excited if we have found evidence for an alien civilization.
06:52No little green men this time. Oumuamua is a natural object. But what exactly is it?
07:00At first, observers thought it might be a comet.
07:05Something that's mostly ice with a little bit of rock. Those are the sorts of bodies that exist really far out from the star and are the easiest things to eject.
07:13But a comet passing this close to the sun would warm up, turning the ice into a gas, forming a vapor trail.
07:26On Oumuamua, astronomers saw no sign of this happening.
07:31There was no fuzziness around it that you would expect from a comet as the ice was turned into a gas.
07:37It was really mysterious. And so everybody who was observing it thought it was an asteroid.
07:46As teams tracked Oumuamua across the sky, there was an unexpected twist.
07:53As Oumuamua passed through our solar system, it basically was falling in toward the sun, speeding up immensely as it passed the sun,
08:02before exiting the solar system in almost the opposite direction.
08:07But then something weird happened. As it was moving away from the sun, it was slowing down, as you'd expect.
08:12But it wasn't slowing down fast enough.
08:15Oumuamua gets a boost through our solar system.
08:20But how?
08:22So we think the reason is that it's outgassing.
08:24In other words, it was emitting a little bit of gas, and that was acting as a little bit of a rocket motor push on it.
08:32It's kind of like a little jet engine on the surface. It just gives it a little thrust over time.
08:37This tiny nudge reveals Oumuamua's true identity.
08:43So in that case, it is looking more like a comet. It's just that that emission wasn't enough to see.
08:51Powered by outgassing, this interstellar nomad might travel from star to star, but figuring out where in the galaxy it came from just got more difficult.
09:08Now that we know that Oumuamua has outgassed, which changes its velocity and changes its trajectory, it makes it much harder to do that.
09:16Oumuamua may now be safely racing away, but the solar system faces bombardment from another interstellar source, firing at Earth at close to the speed of light.
09:33Cosmic rays are the bullets of the universe, and they are flooding interstellar spaces.
09:40Oumuamua's surface tells the story of its journey through interstellar space.
09:41Oumuamua's surface tells the story of its journey through interstellar space.
09:45The interesting thing about Oumuamua is its color. It's actually red.
09:58I'm standing on a surface that's a nice analog for the surface of Oumuamua. As you look around, you see a really dark, kind of shiny coating to all of the rocks, and it extends up the valley and even onto the mountains behind me.
10:11Scientists think Oumuamua's red sheen comes from tholins, organic molecules that are the building blocks of life.
10:24How cool is it that something came out from some other origin, passed through our neighborhood, and it possessed some form of organics? That could be a possible gold mine for us.
10:38In our own solar system, distant objects like comets and asteroids also carry tholins.
10:59This happens because their surfaces are bombarded by cosmic rays, and that changes the nature of the chemicals on the surface.
11:08So we think the same thing has happened to Oumuamua. It's been out there in interstellar space and been bombarded by cosmic rays over the eons.
11:20Galactic cosmic rays are high-energy particles that tear through the universe.
11:25Interstellar space is filled to the brim with these cosmic rays.
11:36Things like protons, electrons, or perhaps some heavier and more exotic particles that are literally whizzing through the universe.
11:44Some cosmic rays can travel as fast as 99% the speed of light. Incredibly fast, energetic things.
11:50It takes a lot of energy to accelerate anything close to the speed of light.
11:57Cosmic rays come from many energetic and powerful and violent sources in our universe.
12:05Everything that's big and blasting generates cosmic rays.
12:11One of the most powerful cosmic ray generators is the death of a giant star, a supernova.
12:24A supernova is a really energetic explosion. It's so energetic that it can create all kinds of interesting things.
12:39When a star runs out of fuel, it collapses.
12:42The mass of the star crashes inwards, triggering a huge explosion.
12:53The shock wave slams into surrounding gas, amplifying magnetic fields.
12:59If you get a particle caught in there, trapped in the magnetic fields of this gas, it can bounce back and forth, be accelerated very rapidly.
13:09It goes ding, ding, ding, ding, ding, ding, like that.
13:13Eventually, the particle moves so fast that the magnetic field can no longer hold it.
13:18And it gets shot out at very near the speed of light.
13:28Cosmic rays have mass.
13:31And they wreak havoc.
13:35Cosmic rays are the bullets of the universe.
13:40And they are flooding interstellar space.
13:43But thankfully, we're protected.
13:45Cosmic rays from interstellar space battle with another superpower.
13:55Our own bodyguard in the solar system.
14:00The sun.
14:02We think of the sun as the source of energy and warmth for Earth, the giver of life.
14:08But it's also protecting us in ways you might not be aware of.
14:11The sun emits a stream of charged particles called the solar wind.
14:18The particles hurtle out past the planets at more than a million miles an hour.
14:25But they do eventually run out of power.
14:29There's this region where the solar wind grinds to a stop.
14:36It's plowing into this material between the stars and eventually slows and stops.
14:40The solar wind carries the sun's magnetic field with it, forming a bubble around our solar system.
14:52We call that the heliosphere.
14:55Helio for sun and sphere for this giant magnetic field.
14:59It acts basically like a shield protecting us from these galactic cosmic rays.
15:04If that weren't there, the radiation levels hitting the Earth would actually increase.
15:08So in a real way, the sun is protecting us from the dangerous environment of interstellar space.
15:17The heliosphere protects us from the majority of cosmic rays.
15:21But some still make it into the solar system.
15:25Fortunately for us, Earth also has its own defense mechanisms.
15:30We have our magnetic field that can redirect the lowest energy cosmic rays.
15:38And we have our nice thick security blanket of an atmosphere,
15:43which absorbs most of the high energy cosmic rays before they even get a chance to reach us here on the surface.
15:50Cosmic rays from interstellar space can alter DNA and cause diseases.
16:03But without them, we might not be here at all.
16:07Even that tiny fraction of cosmic rays that makes it through our atmosphere to the surface of the Earth
16:12can have a profound influence on the evolution of life.
16:14Cosmic rays can damage the DNA that carries the information of life.
16:21When those molecules are broken apart, the atoms altered by collisions with cosmic rays,
16:29the information carried is changed. That's a mutation.
16:33That's what drives natural selection.
16:35So life and we ourselves are deeply connected to interstellar space around us.
16:40But interstellar space is also home to much larger objects.
16:50Objects that could wipe out life altogether.
17:10Our solar system races around the center of the Milky Way at 143 miles per second.
17:23At its center, the Sun.
17:26Just one of around 200 billion stars in our galaxy.
17:31We're not living in an isolated bubble all on our own here in the galaxy.
17:35We're living in a swarm, a neighborhood of other stars.
17:38And the movement of all these stars can have far-reaching effects on our solar system.
17:47Beyond the planets and our heliosphere
17:53Lies the Oort Cloud.
18:00Right on the border of true interstellar space.
18:04The Oort Cloud is the remnants of the formation of the solar system.
18:11Small, icy, dirty bodies, AKA comets.
18:20The comets in the Oort Cloud are so far out, they're only weakly bound to the Sun.
18:25They spend most of their lives perfectly happy orbiting the Sun lazily in their frigid depths.
18:34But every once in a while they can be perturbed.
18:36Our Sun is moving through interstellar space and so are other stars.
18:45As our Sun orbits the galaxy and encounters other stellar neighbors,
18:51inevitably there is going to be one that's going to pass through or near our Oort Cloud.
18:55The gravity of a nearby star could disrupt the Oort Cloud.
19:06Sending showers of comets barreling through the solar system.
19:10Some of them could strike Earth.
19:17Comets falling down into the inner solar system is something that we really want to pay attention to.
19:23That could actually be dangerous to life here on Earth.
19:25So one of the things we do is look out into the galaxy and see if any stars are going to be coming nearby anytime in the near future.
19:44With a new space observatory called Gaia, astronomers keep watch over millions of neighboring stars in our galaxy.
19:59Tracking their movements through interstellar space.
20:03So what's the next star that's going to pass the Earth?
20:05And it turns out we may know.
20:07There's an orange dwarf, it's called Gliese 710.
20:10In 2018, new data shows Gliese 710 is on a collision course with our Oort Cloud.
20:21It's going to kick up a lot of dirt, kick up a lot of dust, and it might be bad news for the inner solar system.
20:29We might get a lot of unwanted visitors.
20:31Luckily for us, Gliese 710 won't arrive for another 1.3 million years.
20:45But there are other rogue stars out there.
20:49All the stars that you can see in our sky are in the disk of the Milky Way galaxy.
20:53And they tend to be moving in the same direction at about 100 miles per second around the center.
20:57Gaia discovers stars that follow different rules.
21:04They don't seem to be moving around with the motion of the galaxy.
21:09Instead, they're actually flying through space.
21:14And they are screaming. These are cannonballs.
21:17They're moving three, four, five times faster than the other stars in the galaxy.
21:21And they tend to be moving away from the center.
21:23These cosmic cannonballs are known as hyper-velocity stars.
21:34What could cause them to move so quickly?
21:37Some of these stars originated from binary star systems in which one of the components went supernova,
21:44removing that gravitational tie to the other star, allowing that star to escape
21:48and basically be ejected through the galaxy on its own very, you know, high-speed trajectory.
21:57Some hyper-velocity stars have a darker past.
22:02They're flung from a black hole.
22:05There are trillions of black holes in the universe.
22:11There are giant black holes at the centers of nearly all large galaxies, including our own.
22:20And these monsters inflict chaos on paired stars.
22:24Again, you have a binary system of stars.
22:27And they are orbiting the black hole in the center of our galaxy.
22:31When they get too close, one of the stars falls into the black hole and the other one is ejected away at high speed.
22:37These hyper-velocity stars blaze through interstellar space.
22:43Their stellar winds can bring beauty out of chaos.
22:50A lot of these hyper-velocity stars that we see are very massive stars, much larger and hotter and more luminous than the sun.
22:58Well, as they're plowing through the material in between the stars, their wind is expanding and slamming into the gas and the dust.
23:05And so what you see when you look at them is this beautiful arc, like the bow wave off of a ship.
23:14And we have images of these, and they're gorgeous, beautiful, beautiful patterns.
23:24Hyper-velocity stars paint the canvas of the universe.
23:28It looks serene, but interstellar space can be anything but tranquil.
23:45It's no man's land. It's the Wild West. There are no rules. You can do whatever you want.
23:51In the badlands of the galaxy, outlaws reign supreme.
23:58Tens of late years from the sun, mysterious objects lurk in the darkness.
24:21We've only seen a fraction of the stuff that's out there, you know, so this is really the next great frontier.
24:31In 2016, scientists spot a tiny source of infrared light 95 light-years from Earth.
24:38It's too dim to be a star and not orbiting a star either.
24:48It can only be a rogue planet.
24:53When we think of a planet, we think of an object that's orbiting a star.
24:59In fact, that's the very definition of a planet today.
25:02Well, what if it doesn't orbit anything?
25:04We call those rogue planets.
25:05The following year, astronomers take more detailed images.
25:18They find it's not just one world, but two.
25:22And that's incredible, right? There's this object out in the middle of space.
25:27They're not orbiting stars. These are rogue planets orbiting each other.
25:34Planets with four times the mass of Jupiter.
25:37Over 300 million miles apart, more than three times the distance between the Earth and the Sun,
25:44they circle each other once a century.
25:48Think about not just one rogue planet, but a binary rogue planet.
25:52Two planets circling around each other.
25:56They may still be gas giants like Jupiter, and if that's the case, they don't have a surface.
26:00But if they're really old, they could actually have had enough time to cool.
26:03And maybe they do have a surface.
26:06We don't really know, but they would be very dark.
26:08There's no star nearby to light them up.
26:14Rogue planets drift in eternal darkness through the frigid expanses of interstellar space.
26:23Untouched by light for millions of years.
26:28Let's say you found yourself standing on the surface of one of these rogue planets.
26:31I mean, it would be such a bizarre sight.
26:34There wouldn't be a Sun.
26:36You know, it would just be the night sky all around you.
26:40Think about the darkest, moonless night you can possibly imagine here on the Earth.
26:45That's the light level that you have out there in interstellar space.
26:51Physicists now believe there could be billions of rogue planets in our galaxy.
26:56One for every four stars.
27:02The question is, why do these rogue planets exist at all?
27:05Did they form freely or were they somehow cast out of their solar system?
27:11The answer is probably both.
27:12Some rogue planets formed from clumps of gas that never quite became stars.
27:25Others formed like planets around a star in solar systems like our own.
27:30When solar systems are formed, they're violent places.
27:37Sometimes planets just crash into each other and become a single object.
27:42But sometimes they're near misses and they'll scatter away from each other and be ejected.
27:47So these rogue planets spend almost their entire lives completely alone.
28:02Without a star to keep them warm, rogue planets seem to be an unlikely place for life.
28:07A rogue planet on its own out in space, probably not going to be habitable.
28:13It's cold out there, right?
28:14So if it's the size of the Earth, it's probably a frozen ball.
28:19But in 2018, astronomers announced that life could be possible on a moon around a rogue planet.
28:26There are icy moons orbiting Jupiter and Saturn that are heated by the gravity of the planets they orbit.
28:36It has nothing to do with the Sun.
28:39As these moons are warped by the planet's gravity, friction generates heat that keeps the water liquid.
28:49So it's entirely possible that if a rogue planet was able to keep its moons and these moons are icy,
28:54they could have liquid oceans under their surface.
28:57They don't need a star, they've got their planet keeping them warm.
29:07Interstellar space is far from empty.
29:10It's loaded with disconnected bodies that don't have a home.
29:16You can think of interstellar space as almost sort of a cosmic pinball machine.
29:19You've got high velocity stars.
29:21You've got rogue planets.
29:23You've even got moons that have been thrown out from around planets.
29:26All of that is careening around out there.
29:29Interstellar space is more active and alive than we ever imagined.
29:34As it turns out, it even has clouds that sing.
29:50Hundreds of light years away, vast amounts of gas and dust drift through interstellar space.
30:10Think about all that space between the stars.
30:13Full of gas, dust, full of the stories about how stars and planets formed.
30:16We've been missing a lot.
30:19Scientists call the gas and dust between the stars the interstellar medium.
30:27It's the most common stuff out there in the galaxy.
30:31It's hydrogen atoms, a few helium atoms here and there.
30:39The interstellar medium isn't distributed evenly throughout the galaxy.
30:43It's patchy, it's clumpy and there are some regions that have more stuff and some regions that have less.
30:50The regions with more stuff are called interstellar clouds.
30:55An interstellar cloud is really just a slightly denser concentration of gas and possibly dust that we see scattered across our galaxy.
31:06Interstellar clouds can stretch vast distances across the cosmos.
31:14Some reaching a million times the mass of the sun.
31:20You know, it boggles my mind when I look at these interstellar clouds and realize that they're light years in size.
31:24Interstellar clouds are more than just clumps of gas and dust.
31:37They're alive.
31:38We know that these are places where stars form and they're also places that are themselves formed by dying stars.
31:49Stars form when an interstellar cloud collapses.
32:00Gravity pulls matter together, igniting the core.
32:04But astronomers don't have a full understanding of the process.
32:15Understanding the shape and structure of a cloud like this is important to understanding the process of star formation.
32:22Some shapes and structures just aren't big enough in some dimensions to allow a cloud to collapse.
32:26Everything we can learn about this sort of thing really depends on its shape.
32:32So knowing that shape is the key to understanding it.
32:38But there's a problem.
32:40When we look out into the universe, we're seeing everything projected onto the sky.
32:46So we may look at a structure like an interstellar cloud and have very little information about its depth.
32:53That's one of the big challenges for astronomers is to decode the full three-dimensional shape of these clouds.
33:04In 2018, scientists get a breakthrough in their efforts to understand star formation.
33:13Around 490 light years from Earth lies an interstellar cloud known as Musca.
33:19It looks like a thin snake.
33:23Optically, this dark doodle, if you will, looks like a dark cloud.
33:27It looks rather two-dimensional, silhouetted against the background stars on the sky.
33:32Astronomers examine Musca in infrared and discover its singing.
33:41It vibrates and it sets up waves that move through this cloud back and forth.
33:49And these are called magnetohydrodynamic waves, which sounds awesome.
33:56The team converted the waves into musical notes, producing Musca's song.
34:01Turns out that if you study this, you can actually determine the three-dimensional shape of this cloud by the way the waves move through it.
34:23It's a little bit like listening to the frequency of sound coming from some instrument that you don't see and trying to reconstruct what kind of an instrument that must be.
34:36A low note tells you you're listening to something large, like a cello, while a high note represents something smaller, like a violin.
34:55And just as different instruments make very different sounds, clouds with different structures will vibrate in very different ways.
35:09They'll sing very different songs.
35:13The sounds, if you will, the frequencies coming from that cloud are a clue, ultimately, to its shape and structure.
35:19And with this Musca cloud, even though it just looks like a line in the sky, astronomers were able to determine its 3D shape.
35:26And it's not just a filament. It's actually a disk. It's like we're seeing a disk edge on.
35:36Musca is really more of a pancake than a snake.
35:40We've just been looking at the pancake from the side.
35:43That's amazing. It's like putting on 3D glasses for the first time and finally seeing depth in the universe.
35:56The same technique can be used to study other interstellar clouds.
36:01It brings with it a whole new wealth of knowledge on the structure and processes that are going on there.
36:07We're discovering that the interstellar space in our galaxy is full of stuff.
36:25But something doesn't quite add up.
36:29It turns out that if we take all of the matter we see around the universe today and add it up,
36:37it doesn't equal the total amount that we know must be there.
36:44A third of the matter in the universe is missing.
36:48So where is it?
36:49To find it, we have to look beyond interstellar space.
36:55Into the dark, mysterious reaches of intergalactic space.
37:00The Milky Way is one of trillions of galaxies in the observable universe.
37:23The Milky Way is one of trillions of galaxies in the observable universe.
37:26The Milky Way galaxy is a disk. It's about 100,000 light years across.
37:33It's filled with stars, lots of planets and gas and dust.
37:38But where does our galaxy end?
37:41And where do the other galaxies begin?
37:44A structure like our galaxy doesn't really have a hard edge to it.
37:48It actually becomes less and less dense and it gradually peters out as you move into true intergalactic space.
38:01Between the galaxies are huge gaps.
38:05Intergalactic space.
38:07But, like interstellar space, this region isn't empty.
38:19New research reveals it holds the answer to a major mystery.
38:24We know how much normal matter was made in the Big Bang.
38:30And we can look around us today and count up all the normal matter we see.
38:34And the problem is, they don't equal up.
38:39There's something wrong with the galaxies in our universe.
38:43They're not massive enough.
38:44About a third of the normal matter in the universe is missing.
38:51There is more normal matter that is not bound inside of galaxies.
38:57So where is it?
39:01One idea for where this missing normal matter could be is that it's actually floating outside of our galaxy in a hot gas.
39:10Scientists suspected this hot gas might exist in long strands between the galaxies.
39:22But the gas is so thin and diffuse, it's been hard to detect.
39:29Until now.
39:30In 2018, astronomers study a bright, distant quasar called 1ES1553.
39:46A quasar is when a black hole feeds.
39:52It gives off light and we can see it all the way across the universe.
39:56The quasar's light takes over four billion years to reach us.
40:03But observers notice something unusual.
40:09Something is absorbing the light as it passes through the universe.
40:16The culprit?
40:20Ghostly strands of gas suspended in the spaces between galaxies.
40:27These results suggest that a good fraction of the normal matter in our universe is not enclosed inside of galaxies.
40:37They don't live in the city limits.
40:40Instead, they live in long, thin streams that connect the galaxies together.
40:46Heated by shock waves to millions of degrees, these strands of gas could extend throughout the universe.
41:01And account for the matter that's been missing all this time.
41:04All this time.
41:10This opens up a very interesting question.
41:13Has this matter always been there and just failed to accumulate onto the galaxies?
41:19Or was it started in galaxies and get blown out?
41:24We honestly don't know.
41:25The space interstellar space and now intergalactic space are more alive than we thought.
41:39From rogue planets, to singing clouds of gas, interstellar space is stranger than fiction, and we've only just begun to tell its story.
41:57Just because there's so much we don't understand about interstellar space, it makes it that much more critical to explore and try to figure it out.
42:08There's more to find out about interstellar space than what we know.
42:11That's the beauty of exploration and the beauty of knowledge.
42:14It's ever-expanding and that frontier is always there.
42:17Who knows what else is out there?
42:20What else could be lurking out in the dark between the stars?