How the Universe Works - S07E03 - The Interstellar Mysteries
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00:00Interstellar space is the space between the stars.
00:10Interstellar space is vast, largely unknown, and largely unmet.
00:18Now astronomers are probing this great abyss and discovering something remarkable.
00:31Interstellar space is busy, it's filled with activity.
00:35There are rogue planets that are not attached to a star.
00:39There are cosmic rays, there are interstellar gas clouds.
00:42We've even got high velocity stars, all of that is careening around out there.
00:47The greatest secrets in our universe.
00:51Interstellar space is where we came from.
00:53Could lie between the stars.
01:16We live in a small solar system in the suburbs of the Milky Way galaxy.
01:24Eight planets and more than 180 moons, all orbiting the sun.
01:31In our solar system, the sun is the sheriff of the town.
01:35We do whatever the sun wants us to do.
01:40The sun's influence stretches more than one light year in every direction and defines
01:47the boundary of our solar system.
01:50Some place out there is a place where the sun's influence ends and the other stars begin.
01:56That's the entrance to interstellar space.
02:05Interstellar space is the region between star systems in our galaxy.
02:12Until now, we've known little about it.
02:17For so long we thought of the space in between the stars as entirely empty, but this turns
02:21out not to be true at all.
02:23There's a lot going on out there and it's the forefront of astronomy.
02:29One of the biggest clues about interstellar space came right to our doorstep.
02:41October 2017, the Pan-STARRS-1 telescope spots something unusual.
02:49Pan-STARRS is an observatory in Hawaii and it's scanning large sections of the sky looking
02:55for things that change.
03:00All of a sudden there was this tiny little visitor just screaming through the solar system.
03:05It 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 and
03:14also its trajectory was such that it seemed like its orbit was not bound to the sun.
03:20It was totally unlike.
03:22Any other path, any other trajectory, any other orbit in our solar system.
03:30Astronomers reached an extraordinary conclusion.
03:34It became very clear that yeah, this was not some solar system object falling from a long
03:40way away.
03:42This was something that came from another star and I think everybody was pretty amazed
03:47by that.
03:53Our first known interstellar visitor on a flyby through our solar system.
04:00It was the very first object that we had ever discovered that had originated outside the
04:06solar 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 I can
04:21only dream of but had never thought it would actually be a reality.
04:29Scientists 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
04:44what could it be?
04:50The object's shape was mystifying.
04:55It's almost sort of shaped like a cigar.
04:57It's ten times longer than it is wide.
05:00And this is extraordinary.
05:01There's no object in our solar system that we've ever measured that is this elongated.
05:07Oumuamua looked so unnatural, it sparked scientists' imaginations.
05:15One of the things to remember about scientists is that we're still human beings.
05:20We have read science fiction.
05:21We have imaginations.
05:22I have to admit, when I first heard about it, my first thought is that it was Rama.
05:29From an Arthur C. Clarke story, Rendezvous with Rama, this is a very elongated spaceship
05:34that came from another star.
05:38It reminded me of some designs we had for interstellar spacecrafts that have to be much
05:44longer than they're wide in order to minimize friction with the interstellar gas.
05:53Could Oumuamua be an alien interstellar spacecraft?
06:00Astronomers, including Professor Avi Loeb, took the idea seriously.
06:08We decided to follow this object using the best telescopes in the world and observe whether
06:13there is any radio transmission from it.
06:19Astronomers hunted for signs of alien communication.
06:27But after eight hours of listening across multiple frequencies, nothing.
06:33Sadly, no emissions were detected.
06:37It's almost certainly a natural object.
06:39I would bet all of my money on that.
06:41I was disappointed.
06:42We would have been much more excited if we have found evidence for an alien civilization.
06:52No little green men this time.
06:54Oumuamua is a natural object.
06:58But what exactly is it?
07:01At first, observers thought it might be a comet.
07:06Something that's mostly ice with a little bit of rock.
07:08Those are the sorts of bodies that exist really far out from the star and are the easiest
07:12things to eject.
07:15But a comet passing this close to the sun would warm up, turning the ice into a gas,
07:23forming 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
07:36into a gas.
07:38It was really mysterious and so everybody who was observing it thought it was an asteroid.
07:47As teams tracked the Oumuamua across the sky, there was an unexpected twist.
07:55As Oumuamua passed through our solar system, it basically was falling in toward the sun,
08:00speeding up immensely as it passed the sun before exiting the solar system in almost
08:05the opposite direction.
08:06But then something weird happened.
08:08As it was moving away from the sun, it was slowing down as you'd expect.
08:12But it wasn't slowing down fast enough.
08:16Oumuamua gets a boost through our solar system.
08:21But how?
08:23So we think the reason is that it's outgassing.
08:26In other words, it was emitting a little bit of gas and that was acting as a little bit
08:30of a rocket motor push on it.
08:32It's kind of like a little jet engine on the surface.
08:35Just gives it a little thrust over time.
08:38This tiny nudge reveals Oumuamua's true identity.
08:45So in that case, it is looking more like a comet.
08:48It's just that that emission wasn't enough to see.
08:57Powered by outgassing, this interstellar nomad might travel from star to star.
09:02But figuring out where in the galaxy it came from just got more difficult.
09:09Now that we know that Oumuamua has outgassed, which changes its velocity and changes its
09:14trajectory, it makes it much harder to do that.
09:19Oumuamua may now be safely racing away.
09:22But the solar system faces bombardment from another interstellar source, firing at Earth
09:30at close to the speed of light.
09:33Cosmic rays are the bullets of the universe and they are flooding interstellar space.
09:40Oumuamua's surface tells the story of its journey through interstellar space.
10:03The interesting thing about Oumuamua is its color.
10:06It's actually red.
10:08I'm standing on a surface that's a nice analog for the surface of Oumuamua.
10:12As you look around, you see a really dark, kind of shiny coating to all of the rocks.
10:17And it extends up the valley and even onto the mountains behind me.
10:24Scientists think Oumuamua's red sheen comes from tholins, organic molecules that are the
10:30building blocks of life.
10:34How cool is it that something came out from some other origin, passed through our neighborhood,
10:40and it possessed some form of organics?
10:42That could be a possible gold mine for us.
10:47In our own solar system, distant objects, like comets and asteroids, also carry tholins.
10:56This happens because their surfaces are bombarded by cosmic rays and that changes the nature
11:02of the chemicals on the surface.
11:04So we think the same thing has happened to Oumuamua.
11:06It's been out there in interstellar space and been bombarded by cosmic rays over the
11:10eons.
11:15Galactic cosmic rays are high-energy particles that tear through the universe.
11:26Interstellar space is filled to the brim with these cosmic rays.
11:32Things like protons and electrons, or perhaps some heavier and more exotic particles that
11:36are literally whizzing through the universe.
11:40Some cosmic rays can travel as fast as 99% the speed of light.
11:44Incredibly fast, energetic things.
11:49It takes a lot of energy to accelerate anything close to the speed of light.
11:55Cosmic rays come from many energetic and powerful and violent sources in our universe.
12:04Everything that's big and blasting generates cosmic rays.
12:10One of the most powerful cosmic ray generators is the death of a giant star, a supernova.
12:23A supernova is a really energetic explosion.
12:28It's so energetic that it can create all kinds of interesting things.
12:34When a star runs out of fuel, it collapses.
12:38The mass of the star crashes inwards, triggering a huge explosion.
12:49The shock wave slams into surrounding gas, amplifying magnetic fields.
12:54If you get a particle caught in there, trapped in the magnetic fields of this gas, it can
13:00bounce back and forth, be accelerated very rapidly.
13:04It goes dink, dink, dink, dink, dink, dink, dink, dink, like that.
13:08Eventually, the particle moves so fast that the magnetic field can no longer hold it.
13:14And it gets shot out at very near the speed of light.
13:23Cosmic rays have mass and they wreak havoc.
13:30Cosmic rays are the bullets of the universe and they are flooding interstellar space.
13:38But thankfully, we're protected.
13:45Cosmic rays from interstellar space battle with another superpower.
13:52Our own bodyguard in the solar system, the sun.
13:58We think of the sun as the source of energy and warmth for Earth, the giver of life.
14:03But it's also protecting us in ways you might not be aware of.
14:08The sun emits a stream of charged particles called the solar wind.
14:15The particles hurtle out past the planets at more than a million miles an hour.
14:24But they do eventually run out of power.
14:28There's this region where the solar wind grinds to a stop.
14:31It'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
14:46solar system.
14:47We call that the heliosphere, helio for sun and sphere for this giant magnetic field.
14:54It acts basically like a shield protecting us from these galactic cosmic rays.
14:59If that weren't there, the radiation levels hitting the Earth would actually increase.
15:04So in a real way, the sun is protecting us from the dangerous environment of interstellar
15:08space.
15:12The heliosphere protects us from the majority of cosmic rays.
15:16But some still make it into the solar system.
15:20Fortunately, for us, Earth also has its own defense mechanisms.
15:27We have our magnetic field that can redirect the lowest energy cosmic rays.
15:33And we have our nice, thick security blanket of an atmosphere, which absorbs most of the
15:40high energy cosmic rays before they even get a chance to reach us here on the surface.
15:52Cosmic rays from interstellar space can alter DNA and cause diseases.
15:58But without them, we might not be here at all.
16:03Even that tiny fraction of cosmic rays that makes it through our atmosphere to the surface
16:06of the Earth can have a profound influence on the evolution of life.
16:12Cosmic rays can damage the DNA that carries the information of life.
16:19When those molecules are broken apart, the atoms altered by collisions with cosmic rays,
16:24the information carried is changed.
16:26That's a mutation.
16:27That's what drives natural selection.
16:30So life and we ourselves are deeply connected to interstellar space around us.
16:40But interstellar space is also home to much larger objects.
16:45Objects that could wipe out life altogether.
17:06Our solar system races around the center of the Milky Way at 143 miles per second.
17:13And at its center, the sun, just one of around 200 billion stars in our galaxy.
17:21We're not living in an isolated bubble all on our own here in the galaxy.
17:24We're living in a swarm, a neighborhood of other stars.
17:31And the movement of all these stars can have far-reaching effects on our solar system.
17:40Between the planets and our heliosphere, lies the Oort Cloud.
17:51Right on the border of true interstellar space.
17:56The Oort Cloud is the remnants of the formation of the solar system, small, icy, dirty bodies
18:03a.k.a. comets.
18:10The comets in the Oort Cloud are so far out, they're only weakly bound to the sun.
18:16They spend most of their lives perfectly happy orbiting the sun lazily in their frigid depths.
18:23But every once in a while, they can be perturbed.
18:30Our sun is moving through interstellar space, and so are other stars.
18:36As our sun orbits the galaxy and encounters other stellar neighbors, inevitably there
18:42is going to be one that's going to pass through or near our Oort Cloud.
18:48The gravity of a nearby star could disrupt the Oort Cloud, sending showers of comets
18:58barreling through the solar system.
19:05Some of them could strike Earth.
19:22Comets falling down into the inner solar system is something that we really want to pay attention
19:25to.
19:26That could actually be dangerous to life here on Earth.
19:28So one of the things we do is look out into the galaxy and see if any stars are going
19:32to be coming nearby any time in the near future.
19:38With a new space observatory called Gaia, astronomers keep watch over millions of neighboring
19:44stars in our galaxy, tracking their movements through interstellar space.
19:53So what's the next star that's going to pass the Earth?
19:55And it turns out we may know.
19:57There's an orange dwarf.
19:58It's called Gliese 710.
20:01In 2018, new data shows Gliese 710 is on a collision course with our Oort Cloud.
20:11It's going to kick up a lot of dirt, kick up a lot of dust, and it might be bad news
20:16for the inner solar system.
20:18We might get a lot of unwanted visitors.
20:27Luckily for us, Gliese 710 won't arrive for another 1.3 million years.
20:35But there are other rogue stars out there.
20:39All the stars that you can see in our sky are in the disk of the Milky Way galaxy, and
20:43they tend to be moving in the same direction at about 100 miles per second around the center.
20:50Gaia discovers stars that follow different rules.
20:55They don't seem to be moving around with the motion of the galaxy.
20:58Instead, they're actually flying through space.
21:04And they are screaming.
21:05These are cannonballs.
21:07They're moving three, four, five times faster than the other stars in the galaxy.
21:11And they tend to be moving away from the center.
21:16These cosmic cannonballs are known as hypervelocity stars.
21:24What could cause them to move so quickly?
21:28Some of these stars originated from binary star systems in which one of the components
21:33went supernova, removing that gravitational tie to the other star, allowing that star
21:38to escape and basically be ejected through the galaxy on its own very high-speed trajectory.
21:48Some hypervelocity stars have a darker past.
21:54They're flung from a black hole.
21:57There are trillions of black holes in the universe.
22:01There are giant black holes at the centers of nearly all large galaxies, including our
22:07own.
22:10And these monsters inflict chaos on paired stars.
22:14Again, you have a binary system of stars.
22:17And they are orbiting the black hole in the center of our galaxy.
22:21When they get too close, one of the stars falls into the black hole and the other one
22:24is ejected away at high speed.
22:30These hypervelocity stars blaze through interstellar space.
22:35Their stellar winds can bring beauty out of chaos.
22:41A lot of these hypervelocity stars that we see are very massive stars, much larger and
22:46hotter and more luminous than the sun.
22:48Well, as they're plowing through the material in between the stars, their wind is expanding
22:53and slamming into the gas and the dust.
22:57And so what you see when you look at them is this beautiful arc, like the bow wave off
23:02of a ship.
23:05And we have images of these, and they're gorgeous, beautiful, beautiful patterns.
23:15Hypervelocity stars paint the canvas of the universe.
23:22It looks serene, but interstellar space can be anything but tranquil.
23:35It's no man's land.
23:36It's the Wild West.
23:37There are no rules.
23:38You can do whatever you want.
23:40In the badlands of the galaxy, outlaws reign supreme.
23:52Tens of light years from the sun, mysterious objects lurk in the darkness.
24:08We've only seen a fraction of the stuff that's out there, you know, so this is really the
24:12next great frontier.
24:15In 2016, scientists spot a tiny source of infrared light 95 light years from Earth.
24:29It's too dim to be a star, and not orbiting a star either.
24:36It can only be a rogue planet.
24:39When we think of a planet, we think of an object that's orbiting a star.
24:43In fact, that's the very definition of a planet today.
24:46Well, what if it doesn't orbit anything?
24:49We call those rogue planets.
24:58The following year, astronomers take more detailed images.
25:03They find it's not just one world, but two.
25:09And that's incredible, right?
25:10There's this object out in the middle of space.
25:12They're not orbiting stars.
25:13These are rogue planets orbiting each other.
25:19Planets with four times the mass of Jupiter, over 300 million miles apart, more than three
25:25times the distance between the Earth and the sun, they circle each other once a century.
25:33Think about not just one rogue planet, but a binary rogue planet.
25:37Two planets circling around each other.
25:40They may still be gas giants like Jupiter, and if that's the case, they don't have a
25:44surface.
25:45But if they're really old, they could actually have had enough time to cool, and maybe they
25:49do have a surface.
25:50We don't really know, but they would be very dark.
25:53There's no star nearby to light them up.
25:59Rogue planets drift in eternal darkness through the frigid expanses of interstellar space.
26:08Untouched by light for millions of years.
26:13Let's say you found yourself standing on the surface of one of these rogue planets.
26:16I mean, it would be such a bizarre sight.
26:18There wouldn't be a sun.
26:20You know, it would just be the night sky all around you.
26:25Think about the darkest, moonless night you can possibly imagine here on the Earth.
26:30That's the light level that you have out there in interstellar space.
26:37Scientists now believe there could be billions of rogue planets in our galaxy.
26:42One for every four stars.
26:46The question is, why do these rogue planets exist at all?
26:50Did they form freely, or were they somehow cast out of their solar system?
26:55The answer is probably both.
27:04Some rogue planets formed from clumps of gas that never quite became stars.
27:10Others formed like planets around a star, in solar systems like our own.
27:18When solar systems are formed, they're violent places.
27:23Sometimes planets just crash into each other and become a single object.
27:27But sometimes they're near misses, and they'll scatter away from each other and be ejected.
27:34So these rogue planets spend almost their entire lives completely alone.
27:47Without a star to keep them warm, rogue planets seem to be an unlikely place for life.
27:53A rogue planet on its own out in space, probably not going to be habitable.
27:58It's cold out there, right?
27:59So if it's the size of the Earth, it's probably a frozen ball.
28:04But in 2018, astronomers announced that life could be possible on a moon around a rogue planet.
28:14There are icy moons orbiting Jupiter and Saturn that are heated by the gravity of the planets they orbit.
28:20It has nothing to do with the sun.
28:24As these moons are warped by the planet's gravity, friction generates heat that keeps the water liquid.
28:34So it's entirely possible that if a rogue planet was able to keep its moons, and these moons are icy,
28:40they could have liquid oceans under their surface.
28:42They don't need a star.
28:43They've got their planet keeping them warm.
28:52Interstellar space is far from empty.
28:55It's loaded with disconnected bodies that don't have a home.
29:01You can think of interstellar space as almost sort of a cosmic pinball machine.
29:05You've got high-velocity stars.
29:06You've got rogue planets.
29:08You've even got moons that have been thrown out from around planets.
29:10All of that is careening around out there.
29:14Interstellar space is more active and alive than we ever imagined.
29:19As it turns out, it even has clouds that sing.
29:41Hundreds of light-years away, vast amounts of gas and dust drift through interstellar space.
29:50Think about all that space between the stars, full of gas, dust,
29:53full of the stories about how stars and planets formed.
29:56We've been missing a lot.
29:59Scientists call the gas and dust between the stars the interstellar medium.
30:07It's the most common stuff out there in the galaxy.
30:11It's hydrogen atoms, a few helium atoms here and there.
30:19The interstellar medium isn't distributed evenly throughout the galaxy.
30:24It's patchy. It's clumpy.
30:26And there are some regions that have more stuff and some regions that have less.
30:31The regions with more stuff are called interstellar clouds.
30:39An interstellar cloud is really just a slightly denser concentration of gas
30:43and possibly dust that we see scattered across our galaxy.
30:50Interstellar clouds can stretch vast distances across the cosmos,
30:56some reaching a million times the mass of the sun.
31:01You know, it boggles my mind when I look at these interstellar clouds
31:05and realize that they're light-years in size.
31:12Interstellar clouds are more than just clumps of gas and dust.
31:17They're alive.
31:20We know that these are places where stars form.
31:24And they're also places that are themselves formed by dying stars.
31:36Stars form when an interstellar cloud collapses.
31:41Gravity pulls matter together, igniting the core.
31:49But astronomers don't have a full understanding of the process.
31:55Understanding the shape and structure of a cloud like this
31:57is important to understanding the process of star formation.
32:02Some shapes and structures just aren't big enough in some dimensions
32:05to allow a cloud to collapse.
32:07Everything we can learn about this sort of thing really depends on its shape.
32:12So knowing that shape is the key to understanding it.
32:18But there's a problem.
32:21When we look out into the universe, we're seeing everything projected onto the sky.
32:26So we may look at a structure like an interstellar cloud
32:30and have very little information about its depth.
32:34That's one of the big challenges for astronomers,
32:36is to decode the full three-dimensional shape of these clouds.
32:44In 2018, scientists get a breakthrough in their efforts to understand star formation.
32:53Around 490 light years from Earth lies an interstellar cloud known as Musca.
33:01It looks like a thin snake.
33:04Optically, this dark doodle, if you will, looks like a dark cloud.
33:07It looks rather two-dimensional,
33:09silhouetted against the background stars on the sky.
33:13Astronomers examine Musca in infrared and discover it's singing.
33:23It vibrates and it sets up waves that move through this cloud back and forth.
33:28And these are called magnetohydrodynamic waves, which sounds awesome.
33:36The team converted the waves into musical notes, producing Musca's song.
33:56Turns out that if you study this,
33:58you can actually determine the three-dimensional shape of this cloud
34:01by the way the waves move through it.
34:09It's a little bit like listening to the frequency of sound
34:11coming from some instrument that you don't see
34:14and trying to reconstruct what kind of an instrument that must be.
34:24A low note tells you you're listening to something large, like a cello.
34:31While a high note represents something smaller, like a violin.
34:37And just as different instruments make very different sounds,
34:43clouds with different structures will vibrate in very different ways.
34:48They'll sing very different songs.
34:52The sounds, if you will, the frequencies coming from that cloud
34:56are a clue, ultimately, to its shape and structure.
35:00With this Musca cloud, even though it just looks like a line in the sky,
35:03astronomers were able to determine its 3D shape.
35:06And it's not just a filament, it's actually a disc.
35:09It's like we're seeing a disc edge on.
35:16Musca is really more of a pancake than a snake.
35:20We've just been looking at the pancake from the side.
35:25That's amazing.
35:27It's like putting on 3D glasses for the first time
35:29and finally seeing depth in the universe.
35:36The same technique can be used to study other interstellar clouds.
35:42It brings with it a whole new wealth of knowledge
35:44on the structure and processes that are going on there.
36:00We're discovering that the interstellar space in our galaxy is full of stuff.
36:07But something doesn't quite add up.
36:11It turns out that if we take all of the matter we see around the universe today
36:16and add it up, it doesn't equal the total amount that we know must be there.
36:24A third of the matter in the universe is missing.
36:27So where is it?
36:30To find it, we have to look beyond interstellar space
36:35and into the dark, mysterious reaches of intergalactic space.
36:56The Milky Way is one of trillions of galaxies in the observable universe.
37:04The Milky Way galaxy is a disk.
37:06It's about 100,000 light years across.
37:08It's filled with stars, lots of planets and gas and dust.
37:13But where does our galaxy end?
37:16And where do the other galaxies begin?
37:19A structure like our galaxy doesn't really have a hard edge to it.
37:24It actually becomes less and less dense,
37:27and it gradually peters out as you move into true intergalactic space.
37:36Between the galaxies are huge gaps.
37:41Intergalactic space.
37:45But like interstellar space, this region isn't empty.
37:54New research reveals it holds the answer to a major mystery.
38:01We know how much normal matter was made in the Big Bang.
38:05And we can look around us today and count up all the normal matter we see.
38:08And the problem is they don't equal up.
38:14There's something wrong with the galaxies in our universe.
38:18They're not massive enough.
38:21A third of the normal matter in the universe is missing.
38:27There is more normal matter that is not bound inside of galaxies.
38:32So where is it?
38:37One idea for where this missing normal matter could be
38:39is that it's actually floating outside of our galaxy in a hot gas.
38:49Scientists suspected this hot gas might exist in long strands between the galaxies.
38:57But the gas is so thin and diffuse, it's been hard to detect.
39:04Until now.
39:11In 2018, astronomers study a bright, distant quasar called 1ES1553.
39:20A quasar is when a black hole feeds.
39:27It gives off light and we can see it all the way across the universe.
39:34The quasar's light takes over four billion years to reach us.
39:40But observers notice something unusual.
39:44Something is absorbing the light as it passes through the universe.
39:51The culprit?
39:54Ghostly strands of gas suspended in the spaces between galaxies.
40:02These results suggest that a good fraction of the normal matter in our universe
40:09is not enclosed inside of galaxies.
40:12They don't live in the city limits.
40:14Instead, they live in long, thin streams that connect the galaxies together.
40:25Heated by shock waves to millions of degrees,
40:28these strands of gas could extend throughout the universe
40:35and account for the matter that's been missing all this time.
40:45This opens up a very interesting question.
40:48Has this matter always been there and just failed to accumulate onto the galaxies?
40:54Or was it started in galaxies and get blown out?
40:58We honestly don't know.
41:06Interstellar space and now intergalactic space are more alive than we thought.
41:17From rogue planets to singing clouds of gas,
41:25interstellar space is stranger than fiction.
41:29And we've only just begun to tell its story.
41:35Just because there's so much we don't understand about interstellar space,
41:38it makes it that much more critical to explore and try to figure it out.
41:43There's more to find out about interstellar space than what we know.
41:46That's the beauty of exploration and the beauty of knowledge.
41:49It's ever expanding and that frontier is always there.
41:53Who knows what else is out there?
41:54What else could be lurking out in the dark between the stars?