Interstellar space is the space between the stars.
Interstellar space is vast, largely unknown,
and largely unmapped.
Now astronomers are probing this great abyss
and discovering something remarkable.
Interstellar space is busy.
It's filled with activity.
There are rogue planets that are not attached to a star.
There are cosmic rays, there are interstellar gas clouds.
We've even got high-velocity stars.
All of that is careening around out there.
The greatest secrets in our universe...
Interstellar space is where we came from.
...Could lie between the stars.
captions paid for by discovery communications
we live in a small solar system
in the suburbs of the milky way galaxy ...
8 planets and more than 180 moons all orbiting the sun.
In our solar system, the sun is the sheriff of the town.
We do whatever the sun wants us to do.
The sun's influence stretches more than one light-year
in every direction
and defines the boundary of our solar system.
Someplace out there is a place where the sun's influence ends
and the other stars' begins.
That's the entrance to interstellar space.
Interstellar space is the region
between star systems in our galaxy.
Until now, we've known little about it.
For so long, we've thought the space
in between the stars as entirely empty,
but this turns out not to be true at all.
There's a lot going on out there,
and it's the forefront of astronomy.
One of the biggest clues about interstellar space
came right to our doorstep.
October 2017.
The pan-starrs1 telescope spots something unusual.
Pan-starrs is an observatory in Hawaii,
and it's scanning large sections of the sky,
looking for things that change.
All of a sudden, there was this tiny, little visitor
just screaming through the solar system.
It was going about 200,000 miles an hour.
It was a much faster object
than what might be expected for a solar-system object.
And also its trajectory was such
that it seemed like its orbit was not bound to the sun.
It was totally unlike any other path, any other trajectory,
any other orbit in our solar system.
Astronomers reached an extraordinary conclusion.
It became very clear that, yeah,
this was not some solar-system object
falling from a long way away.
This was something that came from another star,
and I think everybody was pretty amazed by that.
Our first known interstellar visitor
on a fly-by through our solar system.
It was the very first object that we had ever discovered
that had originated outside the solar system.
Everything else we've seen ... every comet, every asteroid ...
originated within our solar system.
A big, mega solid object
entering in our own solar system,
that's something that, you know, I can only dream of
but had never thought it would actually be a reality.
Scientists named the object 'oumuamua,
Hawaiian for "a messenger from afar arriving first."
This thing came from interstellar space
into our solar system,
and the main question is, what could it be?
The object's shape was mystifying.
It's almost sort of shaped like a cigar.
It's 10 times longer than it is wide.
And this is extraordinary.
There's no object in our solar system
that we've ever measured that is this elongated.
'Oumuamua looked so unnatural,
it sparked scientists' imaginations.
One of the things to remember about scientists
is that we're still human beings.
We have read science fiction.
We have imaginations.
I 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."
This is a very elongated spaceship
that came from another star.
It reminded me of some designs
we had for interstellar space crafts
that have to be much longer than they are wide
in order to minimize friction with the interstellar gas.
Could 'oumuamua be an alien interstellar spacecraft?
astronomers, including professor avi loeb,
took the idea seriously.
We decided to follow this object
using the best telescopes in the world
and observe whether there is any radio transmission from it.
Astronomers hunted for signs of alien communication.
But after eight hours of listening
across multiple frequencies, nothing.
Sadly, no emissions were detected.
It's almost certainly a natural object.
I would bet all of my money on that.
I was disappointed.
I would've been much more excited
if we had found evidence for an alien civilization.
No little green men this time.
'Oumuamua is a natural object.
But what exactly is it?
At first, observers thought it might be a comet.
Something 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.
But a comet passing this close to the sun
would warm up,
turning the ice into a gas, forming a vapor trail.
On 'oumuamua, astronomers saw no sign of this happening.
There was no fuzziness around it
that you would expect from a comet
as the ice was turned into a gas.
It was really mysterious,
and so everybody who was observing it
thought it was an asteroid.
As team's track 'oumuamua across the sky,
there was an unexpected twist.
As 'oumuamua passed through our solar system,
basically, it was falling in toward the sun,
speeding up immensely as it passed the sun,
before exiting the solar system
in almost the opposite direction.
But then something weird happened.
As it was moving away from the sun,
it was slowing down as you'd expect,
but it wasn't slowing down fast enough.
'Oumuamua gets a boost through our solar system,
but how?
So we think the reason is that it's outgassing.
In 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.
It's kind of like a little jet engine on the surface ...
just gives it a little thrust over time.
This tiny nudge reveals 'oumuamua's
true identity.
So, in that case, it is looking more like a comet.
It's just that that emission wasn't enough to see.
Powered 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.
Now that we know 'oumuamua has outgassed,
which changes its velocity and changes its trajectory,
it makes it much harder to do that.
'Oumuamua 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.
Cosmic rays are the bullets of the universe,
and they are flooding interstellar space.
'Oumuamua's surface tells the story of its journey
through interstellar space.
Radebaugh: The interesting thing about 'oumuamua is its color.
It's actually red.
I'm standing on a surface that's a nice analogue
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.
Scientists think 'oumuamua's red sheen
comes from tholins,
organic molecules that are the building blocks of life.
How cool is it that something came out from some other origin,
passed through our neighborhood,
and it possessed some sort of organics?
That could be a possible gold mine for us.
In our own solar system,
distant objects like comets and asteroids
also carry tholins.
This happens because their surfaces are bombarded
by cosmic rays and that changes the nature
of the chemicals on the surface.
So 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.
Galactic cosmic rays are high-energy particles
that tear through the universe.
interstellar space is filled to the brim with these cosmic rays.
Things like protons and electrons or perhaps
some heavier, the more exotic particles
that are literally whizzing through the universe.
Some cosmic rays can travel as fast
as 99% the speed of light ...
incredibly fast, energetic things.
It takes a lot of energy
to accelerate anything close to the speed of light.
Cosmic rays come from many energetic and powerful
and violent sources in our universe.
Everything that's big and blasting generates cosmic rays.
One of the most powerful cosmic-ray generators
is the death of a giant star, a supernova.
a supernova is a really energetic explosion.
It's so energetic that it can create all kinds
of interesting things.
When a star runs out of fuel, it collapses.
The mass of the star crashes inwards,
triggering a huge explosion.
the shock wave slams into surrounding gas,
amplifying magnetic fields.
If 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.
It goes ding, ding, ding-ding-ding-ding.
Like that.
Eventually, the particle moves so fast
that the magnetic field can no longer hold it.
And, pyew, it gets shot out at very near the speed of light.
Cosmic rays have mass, and they wreak havoc.
Cosmic rays are the bullets of the universe,
and they are flooding interstellar space.
But, thankfully, we're protected.
Cosmic rays from interstellar space battle
with another superpower ...
our own bodyguard in the solar system ... the sun.
We think of the sun as the source of energy
and warmth for earth, the giver of life,
but it's also protecting us in ways
you might not be aware of.
The sun emits a stream of charged particles
called the solar wind.
The particles hurtle out past the planets
at more than a million miles an hour.
But they do eventually run out of power.
There's this region where the solar wind grinds to a stop.
It's plowing into this material between the stars
and eventually slows and stops.
The solar wind carries the sun's magnetic field with it,
forming a bubble around our solar system.
We call that the heliosphere, "helio" for the sun
and "sphere" for this giant magnetic field.
It acts, basically, like a shield,
protecting us from these galactic cosmic rays.
If that weren't there,
the radiation levels hitting the earth would actually increase.
So, in a real way, the sun is protecting us
from the dangerous environment of interstellar space.
The heliosphere protects us
from the majority of cosmic rays,
but some still make it into the solar system.
Fortunately for us, earth also has its own defense mechanisms.
We have our magnetic field that can redirect
the lowest energy cosmic rays, and we have our nice,
thick security blanket of an atmosphere,
which absorbs most of the high-energy cosmic rays
before they even get a chance to reach us here on the surface.
Cosmic rays from interstellar space
can alter DNA and cause diseases.
But without them, we might not be here at all.
Even that tiny fraction of cosmic rays
that makes it through our atmosphere
to the surface of the earth
can have a profound influence on the evolution of life.
Cosmic rays can damage the DNA
that carries the information of life.
When those molecules are broken apart,
the atom is altered by collisions with cosmic rays.
The information carried is changed.
That's a mutation.
That's what drives natural selection.
So life and we ourselves are deeply connected
to interstellar space around us.
But interstellar space is also home to much larger objects,
objects that could wipe out life all together.
Our solar system races around the center of the milky way
at 143 miles per second.
At its center, the sun,
just 1 of around 200 billion stars in our galaxy.
We're not living in an isolated bubble
all on our own here in the galaxy.
We're living in a swarm, a neighborhood of other stars.
And the movement of all these stars
can have far-reaching effects on our solar system.
Beyond the planets and our heliosphere...
Lies the oort cloud
right on the border of true interstellar space.
The oort cloud is the remnants of the formation
of the solar system ... small, icy, dirty bodies,
aka comets.
The comets in the oort cloud
are so far out they're only weakly bound to the sun.
They spend most their lives perfectly happy,
orbiting the sun lazily in their frigid depths,
but every once in a while, they can be perturbed.
Our sun is moving through interstellar space,
and so are other stars.
As our sun orbits the galaxy
and encounters other stellar neighbors,
inevitably, there is going to be one
that's going to pass through or near our oort cloud.
The gravity of a nearby star
could disrupt the oort cloud...
Sending showers of comets
barreling through the solar system.
Some of them could strike earth.
Comets falling down into the inner solar system
is something that we really want to pay attention to,
that could actually be dangerous to life here on earth.
So one of the things we do is look out into the galaxy
and see if any stars are gonna be coming nearby
anytime in the near future.
With a new space observatory called Gaia,
astronomers keep watch over millions of neighboring stars
in our galaxy,
tracking their movements through interstellar space.
So what's the next star that's gonna pass the earth?
And it turns out we may know.
There's an orange dwarf.
It's called gliese 710.
In 2018, new data shows
gliese 710 is on a collision course
with our oort cloud.
It's gonna kick up a lot of dirt,
kick up a lot of dust,
and it might be bad news for the inner solar system.
We might get a lot of unwanted visitors.
Luckily for us, gliese 710 won't arrive
for another 1.3 million years.
But there are other rogue stars out there.
All the stars that you can see in our sky
Are in the disc of the milky way galaxy,
and they tend to be moving in the same direction
at about 100 miles per second around the center.
Gaia discovers stars that follow different rules.
They don't seem to be moving around
with the motion of the galaxy.
Instead, they're actually flying through space.
And they are screaming.
These are cannonballs.
They're moving, three, four, five times faster
than the other stars in the galaxy,
and they tend to moving away from the center.
These cosmic cannonballs are known as hypervelocity stars.
What could cause them to move so quickly?
Some of these stars originated from binary star systems
in which one of the components went supernova,
removing that gravitational tie to the other star,
allowing that star to escape
and basically be ejected through the galaxy
on its own very, you know, high-speed trajectory.
Some hypervelocity stars have a darker past.
They're flung from a black hole.
There are trillions of black holes in the universe.
There are giant black holes at the centers
of nearly all large galaxies, including our own.
And these monsters inflict chaos on paired stars.
Again, you have a binary system of stars,
and they are orbiting the back hole
in the center of our galaxy.
When they get too close,
one of the stars falls into the black hole,
and the other one is ejected away at high speed.
These hypervelocity stars Blaze through
interstellar space.
Their stellar winds can bring beauty out of chaos.
A lot of these hypervelocity stars
that we see are very massive stars,
much larger and hotter and more luminous than the sun.
Well, as they're plowing through the material
in between the stars their wind is expanding
and slamming into the gas and the dust.
And so what you see when you look at them
is this beautiful arc, like the bow wave off of a ship.
And we have images of these, and they're gorgeous.
These are beautiful, beautiful patterns.
Hypervelocity stars paint the canvas
of the universe.
It looks serene,
but interstellar space can be anything but tranquil.
it's no man's land. It's the wild west.
There are no rules.
You can do whatever you want.
In the badlands of the galaxy, outlaws reign supreme.
Tens of light-years from the sun,
mysterious objects lurk in the darkness.
We've only seen a fraction of the stuff that's out there,
you know, so this is really the next great frontier.
In 2016, scientists spot a tiny source
of infrared light 95 light-years from earth.
it's too dim to be a star and not orbiting a star either.
It can only be a rogue planet.
When we think of a planet, we think of an object
that's orbiting a star.
In fact, that's the very definition of a planet today.
Well, what if it doesn't orbit anything?
We call those rogue planets.
The following year,
astronomers take more detailed images.
They find it's not just one world but two.
And that's incredible, right?
There's this object out in the middle of space.
They're not orbiting stars.
These are rogue planets orbiting each other.
Planets with 4 times the mass of Jupiter
over 300 million miles apart,
more than 3 times the distance between the earth and the sun,
they circle each other once a century.
Think about not just one rogue planet
but a binary rogue planet,
two planets circling around each other.
They may still be gas giants, like Jupiter,
and if that's the case, they don't have a surface.
But if they're really old,
they could actually have had enough time to cool
and maybe they do have a surface.
We don't really know, but they would be very dark.
There's no star nearby to light them up.
Rogue planets drift in eternal darkness
through the frigid expanses of interstellar space,
untouched by light for millions of years.
Let's say you found yourself standing on the surface
of one of these rogue planets.
I mean, it would be such a bizarre sight.
There wouldn't be a sun.
You know, it would just be the night sky all around you.
Think about the darkest,
moonless night you can possibly imagine here on the earth.
That's the light level that you have out there
in interstellar space.
Physicists now believe there could be billions
of rogue planets in our galaxy, one for every four stars.
The question is, why do these rogue planets exist at all?
Did they form freely,
or were they somehow cast out of their solar system?
The answer is probably both.
Some rogue planets formed from lumps of gas
that never quite became stars.
Others formed like planets
around a star in solar systems like our own.
When solar systems are formed, they're violent places.
Sometimes planets just crash into each other
and become a single object.
But sometimes there are near misses,
and they'll scatter away from each other and be ejected.
So these rogue planets spend almost their entire lives
completely alone.
Without a star to keep them warm,
rogue planets seem to be an unlikely place for life.
A rogue planet on its own out in space,
probably not gonna be habitable.
It's cold out there, right?
So if it's the size of the earth,
it's probably a frozen ball.
But in 2018, astronomers announced that life
could be possible on a moon around a rogue planet.
There are icy moons orbiting Jupiter and saturn
that are heated by the gravity of the planets they orbit.
It has nothing to do with the sun.
As these moons are warped by the planet's gravity,
friction generates heat that keeps the water liquid.
So it's entirely possible that if a rogue planet
was able to keep its moons and these moons are icy,
they could have liquid oceans under their surface.
They don't need a star.
They've got their planet keeping them warm.
Interstellar space is far from empty.
It's loaded with disconnected bodies that don't have a home.
You can think of interstellar space
as almost sort of a cosmic pinball machine.
You've got high-velocity stars.
You've got rogue planets.
You've even moons that have been thrown out from around planets.
All of that is careening around out there.
Interstellar space is more active and alive
than we ever imagined.
As it turns out, it even has clouds that sing.
Hundreds of light-years away,
vast amounts of gas
and dust drift through interstellar space.
Think about all that space between the stars,
full of gas, dust ...
full of the stories about how stars and planets formed.
We've been missing a lot.
Scientists call the gas and dust
between the stars the interstellar medium.
It's the most common stuff out there in the galaxy.
It's hydrogen atoms, a few helium atoms here and there.
The interstellar medium isn't distributed
evenly throughout the galaxy.
It's patchy. It's clumpy.
And there's some regions that have more stuff,
and some regions that have less.
The regions with more stuff are called interstellar clouds.
An interstellar cloud is really just
a slightly denser concentration of gas
and possibly dust that we see scattered across our galaxy.
Interstellar clouds can stretch vast distances
across the cosmos ...
some reaching a million times the mass of the sun.
You know, it boggles my mind
when I look at these interstellar clouds
and realize that they're light-years in size.
Interstellar clouds are more than just clumps
of gas and dust.
They're alive.
Scharf: We know that these are places where stars form,
and they're also places that are, themselves,
formed by dying stars.
Stars form when an interstellar cloud collapses.
Gravity pulls matter together, igniting the core.
but astronomers don't have a full
understanding of the process.
Understanding the shape and structure of a cloud
like this is important to understanding
the process of star formation.
Some shapes and structures just aren't big enough,
in some dimensions, to allow a cloud to collapse.
Everything we can learn about this sort of thing
really depends on its shape.
So knowing that shape is the key to understanding it.
But there's a problem.
When we look out into the universe,
we're seeing everything projected onto the sky.
So we may look at the structure like an interstellar cloud
and have very little information about its depth.
That's one of the big challenges for astronomers,
is to decode the full three-dimensional shape
of these clouds.
In 2018, scientists get a breakthrough
in their efforts to understand star formation.
Around 490 light-years from earth
lies an interstellar cloud known as musca.
It looks like a thin snake.
Optically, this dark doodle,
if you will, looks like a dark cloud.
It looks rather two-dimensional,
silhouetted against the background stars on the sky.
Astronomers examine musca in infrared,
and discover it's singing.
It vibrates, and it sets up waves
that move through this cloud, back and forth.
And these are called magnetohydrodynamic waves,
which sounds awesome.
The team converted the waves into musical notes,
producing musca's song.
it turns 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.
It'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.
A low notes tells you you're listening
to something large, like a cello,
while a high note represents something smaller,
like a violin.
And just as different instruments
make very different sounds,
clouds with different structures will vibrate in different ways.
They'll "sing" different songs.
The sounds, if you will,
the frequencies coming from that cloud,
are a clue ultimately to its shape and structure.
And with this musca cloud,
even though it just looks like a line in the sky,
astronomers were able to determine its 3-d shape.
And it's not just a filament.
It's actually a disc.
It's like we're seeing a disc edge-on.
Musca is more of a pancake than a snake.
We've just been looking at the pancake from the side.
That's amazing.
It's like putting on 3-d glasses for the first time
and finally seeing depth in the universe.
The same technique can be used
to study other interstellar clouds.
It brings with it a whole new wealth of knowledge
on the structure and processes that are going on there.
We're discovering that the interstellar space
in our galaxy is full of stuff,
but something doesn't quite add up.
It turns out that if we take all of the matter
we see around the universe today
and add it up, it doesn't equal the total amount
that we know must be there.
1/3 of the matter in the universe is missing.
So where is it?
To find it, we have to look beyond interstellar space
into the dark, mysterious reaches of intergalactic space.
The milky way is one of trillions of galaxies
in the observable universe.
The milky way galaxy is a disc.
It's about 100,000 light-years across.
It's filled with stars, lots of planets, and gas and dust.
But where does our galaxy end
and the other galaxies begin?
A structure like our galaxy
doesn't really have a hard edge to it.
It actually becomes less and less dense,
and it gradually Peters out as you move
into true intergalactic space.
Between the galaxies are huge gaps ...
intergalactic space.
But, like interstellar space, this region isn't empty.
new research reveals, it holds the answer to a major mystery.
We know how much normal matter was made in the big bang.
And we can look around us today
and count up all the normal matter we see,
and the problem is, they don't equal up.
There's something wrong with the galaxies
in our universe ... they're not massive enough.
About 1/3 of the normal matter in the universe is missing.
There is more normal matter that is not bound inside of galaxies.
So where is it?
One idea for where this missing normal matter could be,
is that it's actually floating outside of our galaxy
in a hot gas.
Scientists suspected this hot gas
might exist in long strands between the galaxies,
but the gas is so thin and diffuse,
it has been hard to detect...
Until now.
in 2018, astronomers study a bright distant quasar
called 1es 1553.
A quasar is when a black hole feeds.
It gives off light,
and we can see it all the way across the universe.
The quasar's light takes over 4 billion years
to reach us,
but observers notice something unusual.
Something is absorbing the light
as it passes through the universe.
The culprit?
Ghostly strands of gas
suspended in the spaces between galaxies.
These results suggest that a good fraction
of the normal matter in our universe
is not enclosed inside of galaxies.
They don't live in the city limits.
Instead, they live in long,
thin streams that connect the galaxies together.
Heated by shock waves to millions of degrees,
these strands of gas could extend
throughout the universe...
And account for the matter
that's been missing all this time.
this opens up a very interesting question ...
has this matter always been there
and just failed to accumulate onto the galaxies,
or was it started in galaxies and gets blown out?
We honestly don't know.
Interstellar space,
and now intergalactic space,
are more alive than we thought.
From rogue planets
to singing clouds of gas,
interstellar space is stranger than fiction.
And we've only just begun to tell its story.
Just 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.
There's more to find out about interstellar space
than what we know,
and that's the beauty of exploration
and the beauty of knowledge, is it's ever-expanding,
and that frontier is always there.
Who knows what else is out there?
What else could be lurking out in the dark,
between the stars?