All language subtitles for How.the.Universe.Works.S06E02.Twin.Suns.The.Alien.Mysteries.1080p.WEB.x264-CRiMSON

Across the universe,
there are stellar systems

completely unlike our own

containing two stars
instead of one.

Our sun isn't so
typical after all.

Even the most fantastical
imaginings of Sci-Fi writers,

it doesn't even come close
to what nature can produce.

These are binary stars,

and they create
some of the deadliest

places in the universe.

Any planet that's close by
is gonna get cooked.

But some binaries may
have an unexpected trick

up their sleeve,

one that transforms
our search for alien worlds.

When it comes to the occurrence
of life on a planet,

it may very well be
that having two stars

could be a lot better
than having one.

Imagine living in
the light of two suns.

Are we missing out?

Could two stars
be better than one?

Captions by vitac...
www.vitac.com

captions paid for by
discovery communications

Look at our sky.

You see the same
solitary sun rising

and setting day after day.

But throughout the galaxy,
alien civilizations

could be enjoying twin
sunrises and twin sunsets

because they orbit
two stars instead of one.

Half the star systems
in our galaxy are binary stars.

It appears to be a common root

of stellar formation
and evolution.

So, we can't just focus
on the single-star systems

and think we have
a complete picture.

The complete picture
may include planets

orbiting binary stars...

Alien worlds rooted
in Sci-Fi fantasies

that have inspired
scientists for decades.

If there is one single
event that can most link

to why I became a scientist,

it was going to see
the original "star wars" movie,

"episode iv,"
when I was 7 years old.

And I can remember that scene
of Luke Skywalker

standing out on
the deserts of Tatooine,

and there's a double sunset.

The music swells up, and I
can remember my 7-year-old heart

kind of leaping out of my chest.

That's the moment
when I realized I wanted

to be an astronomer.

Could two stars
be even better than one?

Living on a planet that orbits
a binary system

could be really exciting.

Imagine seeing two stars
in the sky every day.

That's pretty cool.

But you know what?

Sometimes it can get
too exciting.

Some binary systems

are not
places for Sci-Fi adventures.

They're horror stories.

In some cases,
the interactions between

binary stars get deadly.

The stars can actually
turn on each other.

Binary stars are kind of
like siblings.

They're born together
and they grow up together.

But sometimes one of
those siblings can be evil.

This evil sibling is a pulsar.

It starts life billions
of years ago

as the big brother in a binary.

But something transforms
it into a monster.

When a large star dies,
it will end its life

as a supernova
with a crazy big explosion.

And a pulsar
is what's left behind.

This big brother's
death triggers

one of the biggest
bangs in the universe.

In the midst of the explosion,
the star's core collapses,

crushing material down
into a hyper-dense ball.

Rapid rotation and intense
magnetic fields

jump start twin beams
of deadly radiation,

and the pulsar comes to life.

The pulsar has to be one of
the most amazing monsters

that the universe
has ever thought of.

They're only about
10 miles across,

and yet they contain
the mass of at least the sun

or even sometimes twice the sun.

The pulsar's sibling

is lucky
to live through the chaos

of the nearby supernova.

But it now orbits
a brother from hell

in a cosmic no-man's land.

Orbiting a pulsar would be
a pretty rough experience

for any object in its vicinity.

Pulsars are spitting out
tremendous amounts

of lethal radiation
from their poles.

It wouldn't be good to live
on a planetary system

near a pulsar
because you are gonna be pointed

toward a laser
of planetary death.

But these death rays
can't last forever.

Within a few million years,

the pulsar spins itself
to death.

With its evil sibling dead,

can the other star
finally live in peace?

Stars, as I tell students,
are a lot like people.

As they age, they tend
to expand a bit.

For a single star, it can expand
and be as big as it likes.

But in a binary,
there's a problem.

Now, this is where the story
gets really interesting.

See, you've got your companion
star that's swelled up

into a red giant.

Some of that red giant material
now can get incorporated

back into the pulsar

and spin it up into something
called a millisecond pulsar.

The bloated red giant

can't hold on to
its outer layers,

and the pulsar begins to feed.

Matter streams into it,

transferring momentum
into the pulsar,

spinning it faster and faster

until it rotates hundreds
of times a second.

The beams re-ignite.

Our pulsar is back
from the dead once more.

They're dying and resurrecting
over and over and over again.

It's like a zombie
you just can't kill.

The red giant extends
the life of its zombie brother

billions of years longer.

We know of hundreds of
millisecond pulsars

scattered throughout the cosmos.

A terrifying thought.

But it gets even scarier.

Some of them are alone.

What's happened
to their sibling?

Binary stars are
ultimately responsible

for the existence
of millisecond pulsars.

They only exist because
they've sucked the life

out of their companion stars.

The millisecond pulsars
that we see that are all alone

may have just gotten
rid of the body.

This is PSR j1311-3430,

a rare breed of millisecond
pulsar known as a black widow.

Like its spider namesake,
it's deadly,

one of the most massive
fast-spinning pulsars

in the universe,

spitting out 100 times more
radiation than a regular one.

A black widow pulsar is right
on the edge of physics.

Any larger and it
would be a black hole.

The intense radiation
is amazing.

It's hard to fathom
that these things exist.

But generally, the rule is
the following with the universe,

which is big and old.

If it can happen,
it does happen.

The black widow pulsar
is the stuff of nightmares.

Its radiation heats
the companion star

to over
21,000 degrees Fahrenheit,

more than twice as hot
as the surface of our sun.

It is nothing less than
stellar annihilation.

Pulsars are already dramatic,
energetic events.

Now you're adding in,
"hey, let's destroy a star."

Black widow spiders
famously eat their mates,

and that's exactly what
a black widow pulsar does.

It actually uses the material
from its companion star

to spin itself up,

and then it obliterates
it completely.

The companion star vanishes,

murdered by its zombie sibling.

It's the ultimate
cosmic ingratitude.

Here you have a companion star

that's brought the pulsar back
to life after it's died twice,

and now its entire body
is eviscerated

by the radiation of the pulsar

without a speck of dust
to suggest it was ever there.

These black widow pulsars

are like the assassins
of the galaxy.

Not only do they
destroy the star,

they get rid of the evidence.

When pulsars are involved,

two stars
are much worse than one.

But could the opposite
also be true?

Can two stars create an oasis
for habitable alien worlds?

Binary stars offer
an exciting possibility...

Alien exoplanets orbiting
two stars instead of one.

These binary stars
are everywhere,

so the universe could
actually be something like

what we see in Sci-Fi movies.

The Tatooine sky
could be a real thing.

There could be a planet
with life and civilization,

and in the sky,
there could be two suns.

What would it be like
to live on these worlds?

Could two stars
be even better for life?

Our home planet orbits
a solitary sun

in a safe region
where life could evolve.

Today we're familiar
with a very stable,

well-behaved star...
Our own sun.

And of course we know
there's some solar weather.

Sometimes it throws out
high-energy particles

that create the northern
and Southern lights,

but it's a very reliable star.

It wasn't always that way.

When the sun was much younger,
it was more active,

it was more violent.

Our young sun rotated
over 10 times faster

than it does today,

causing its magnetic field
to twist and tangle,

sending out huge solar flares.

Solar flares can be very bad for

the habitability of a planet,

particularly if you're
very close to the star,

and the reason's
because solar flares

essentially represent
high-energy radiation.

For example,
high-energy protons.

They smash into the atmosphere
and they can strip away

gas off the atmosphere.

Picture the early
solar system...

Flares and solar storms

attack the atmospheres
of rocky planets.

Deadly charged particles can rip
them away molecule by molecule.

Without an atmosphere,
liquid water cannot survive,

and no liquid water
means no life.

In the very early stages, our
solar system was an awful place.

The sun was young
and highly irregular

and emitting lots of energy
in our region.

It took a long time,
probably 500 million years or so

before the solar system

calmed down enough to imagine

that anything like life
could evolve here on earth.

This is a galaxy-wide problem

for planets orbiting one star.

Take Proxima Centauri,
the closest star to our sun.

It's a red dwarf,

the most common type of star
in the milky way.

And it even has its own planet
named Proxima B.

But Proxima Centauri has not
treated its planet gently.

If Proxima B
has any liquid water,

it would have
to be extremely lucky.

Proxima Centauri
would have caused

huge amounts of energy
to come out,

and it would
effectively strip away

Proxima B of any kind of
atmosphere or surface water,

thereby removing any chance
of there being habitable world.

The only hope we have left
for Proxima B

is a strong magnetic field.

This would surround
and protect the planet

from the onslaught
of violent energy

that comes out
of Proxima Centauri,

and that way, there could
still be an ocean,

there could be
an oxygen-rich atmosphere,

and perhaps habitable
environment,

somewhere where life
could have started.

But right now for Proxima B,
odds are stacked against it.

Earth's strong magnetic field

protects us from the sun's
worst outbursts,

allowing liquid water
to survive.

But other planets,
like Mars and Mercury,

have not been so lucky.

Solar storms blasted
their young atmospheres...

Until they became thin and weak,

snuffing out any
chances for life.

But could binary systems
actually make things easier,

where planets orbit around
two stars instead of one?

Young stars can be
very violent and chaotic,

but in the system
where there are two stars,

the interaction of those stars
can slow down their rotation,

and that means that that
violence can be slowed down.

These solar storms
can be tempered

so they're not as violent,
they're not as frequent,

and if any young planet
is formed with an atmosphere,

it can keep it.

So, when it comes to the
occurrence of life on a planet,

it may very well be
that having two stars

could be a lot better
than having one.

Gravitational interactions

can slow down the spin
of two close sun-like stars,

giving life the chance
to develop.

But not just on one world...

On many planets
throughout the system.

With two stars in the middle
of a solar system,

you have twice
the amount of heat,

twice the amount of light,

and that extends
the habitable zone

farther out
into the solar system.

For planetary
scientist Jani Radebaugh,

exploring systems like this
would be a dream come true.

To me, it is so thrilling that
worlds like this could exist

and that they might
even harbor life.

I mean, there could be a Sci-Fi
desert planet like this one

with twin suns, my
personal favorite and one

that I can't wait to visit,
or if we wanted,

we could just hop over
to another habitable planet

and find something
completely different.

Galactic backpackers
could explore

a variety of Sci-Fi landscapes.

Perhaps alien civilizations
are already out there,

living on these
habitable worlds.

Two suns could create
better star systems than one,

but they could also
make things chaotic,

shooting entire worlds
into space at hyper speed.

what would life be like

on a planet in a binary system?

Could it be better?

Or is planet earth really
as good as it gets?

If you're looking for an
abode for life in the galaxy,

we tend to, you know, look for a
rather cozy existence out there,

but, you know, it's possible
that stars can take you

on a bit of a wild ride
sometimes.

Over the past decade,

we've observed
mysterious objects

hurtling through the galaxy.

Scientists call them
hypervelocity stars.

When we say hypervelocity stars,

we're talking some
hyper velocities.

They've been observed moving up
to 620 miles per second.

You're talking about something
the size of a star, the sun,

an octillion tons of mass or
something like that

getting flung away way
faster than a rifle bullet.

These hypervelocity stars

start off in a binary system,

but something tears them apart...
Something big.

In order to create
a hypervelocity star,

you need a very intense source
of gravitational power.

Well, the most intense
source we know of

is the black hole
at the center of the galaxy.

This black hole
is Sagittarius a-star.

It is supermassive...

Four million times
the mass of our sun.

Two stars stray
a little too close,

and the enormous gravity
of the black hole pulls at them.

But the star closest feels
a much stronger tug,

and this binary system
gets ripped apart.

It's a little bit like
the Olympic hammer throw,

where the hammer is
one star in the binary system

and the Olympian
is the other star,

with the cord
connecting the hammer

being the gravitational tie

between the binary stars.

If you cut that cord,
the other star can go flying off

at very, very high speed.

Once the cord is cut,

the binary stars
separate forever.

One is trapped
in the gravitational grip

of the black hole.

The other is flung
out of the galaxy,

becoming
a literal shooting star.

But the star may not be alone.

If a planet is gravitationally
bound to a star

and that star gets ejected
from the system,

if conditions are right,

that planet can hitch a ride
with that star.

Where the star goes,
the planet goes.

If you're on planet
around a hypervelocity star,

you would be the envy of poets
and scientists everywhere

because you would have the most
breathtaking view imaginable.

You would start at the very
center of the galaxy,

you'll have this beautiful view
of the supermassive black hole.

Generation after generation

on this hypervelocity planet

would be treated to thrilling
new views of the galaxy.

By the time you're done
as you're ejected,

you would see
the entire milky way galaxy,

everything, and it would recede
away from you

as you moved off into space
to who knows where.

Hypervelocity planets
just go to show

that the universe is way
stranger than fiction.

As we learn more about
stars and stellar systems,

even the most fantastical
imaginings of Sci-Fi writers,

it doesn't even come close
to what nature can produce.

This hypervelocity
star and planet

go on the journey of a lifetime,

but what about the stranded
companion star,

stuck in the center
of the galaxy

next to a supermassive
black hole?

It, too, could have
a planet orbiting it,

but it's a world
living on borrowed time.

If there's a planet orbiting
the star that gets left behind

by the hypervelocity star,

so the planet is now orbiting

the star that's orbiting
the black hole,

that's not probably
gonna last very long.

Typically, the little guy...
Pew! Gets shot away.

So it's entirely possible
that we have hypervelocity

rogue planets, planets
without a star

that are shooting
out of the galaxy

at high speed, as well.

But it's not a trip
you'd want to take.

Because this world is
destined to wander

the emptiness of space
forever and alone.

The problem with the planet

is that it's no longer
bound to a star,

so the outer surface
would most likely freeze.

Binary stars

can create weird environments
for planets.

You could get an exhilarating
view of the galaxy,

or freeze on an icy wasteland.

But astronomers are finding
bizarre new systems

where stars are not
being torn apart,

they're being driven together,

creating a cosmic event
coming soon to our galaxy.

are two stars better than one?

Binary systems are certainly
very dramatic.

There's even one that has
two stars so close,

they're touching.

KIC 9832227 is a very
interesting binary system.

It's what we call
a contact binary.

So this means that the two stars
are basically in contact,

but they're separate stars.

They share a common
atmosphere or envelope.

One's about a third the mass
of the sun,

one about 1.4 times
the mass of the sun,

and they're rotating around
each other every 11 hours.

2017...
Scientists from Calvin college

reveal an exciting discovery.

These binary stars are
moving even closer together.

They do the math
and make a bold prediction.

So, this star is different from
all other contact binary stars

we've studied
because this one, we believe,

in the next five years
is going to merge,

spiral in together, and explode.

But it's a star
close enough to us...

Only 1,800 light years away...

That when it explodes,
it'd be bright enough

to see with your naked eye.

Two stars crashing together...

An event known as a red Nova.

If this is true,
if you really see it,

it would be fabulous,

because not only
would it validate

this amazing prediction,

but we have something new to
look at in the night sky.

If this comes through,
this would just be

the event of my lifetime.

We don't get to predict
too many things in astronomy

except, you know,

"a billion years from now,
this thing will happen."

So you have to appreciate
what this thing is.

These stars are probably
billions of years old.

We're just so lucky to be able
to see this right at the end

where we just have
a few years left...

A few years out of
a billion-year life span.

It's an amazing
cosmic coincidence

brought to you
by the number three.

Before these stars
came into close contact,

they may have had a neighbor...

A distant third star
that set this all in motion.

Whenever you have three objects,

the gravitational dynamics
becomes incredibly complicated.

The third star pulls
on the binary

as the two orbit each other,

stretching them out basically
into an elongated orbit.

The two stars resist that,

trying to circularize
their orbit again.

That back and forth interaction

pushes the third star
further away,

pulls the two stars closer.

The stars have been
shoved together,

but their story is about
to get even weirder.

Matter will stream off
the smaller star

until it is too gravitationally
weak to hold its position...

Driving their orbits
even tighter together,

moving them faster and faster.

Finally, the smaller star
will plunge into the larger one,

tearing through it...

And blasting hundreds of
trillions of tons of debris

in every direction.

This would be an enormous
amount of energy.

Explosion at its peak
will be 10,000 times

brighter than the star is today.

This collision will
also be an act of creation.

The cores of the two stars
will collide and become one,

creating a super hot
blue ball of gas,

a newborn star.

Just think about
how cool that is.

In the constellation Cygnus,
in about five years' time,

a new star is gonna turn on
created from two older stars...

An entirely new way of
seeing a star being born.

Around the star,

searing-hot gas
will expand outwards,

turning red as it cools,
becoming the red Nova.

The explosion will create
a brand-new light

as bright as the north star
in our night sky.

It's just phenomenal
that we get this opportunity.

This is what every
astronomer wants to do.

We are at a safe distance

from this colliding star duo.

But would we feel the same way
if we were on a planet

orbiting this binary system.

This is a very,
very energetic event.

Could life survive
such an event?

I wouldn't want to be there
as the test Guinea pig.

All this energy
comes pouring in,

and your atmosphere
is likely to be stripped away.

If there are oceans
on this world,

they're likely to be vaporized,

and there may be very little
left other than rock.

A Nova is nothing you want
to fool around with.

Any planet that's close by
is gonna get cooked.

It's gonna get sandblasted,
and then, you know, there it is.

If that's the kind of place
you want to be,

hey, more power to you,
but I like earth.

Earth has a good thing
going these days

with our single star.

No collisions,
no explosions, no drama.

For two stars to be
better than one,

we need to find rocky planets
in a binary system.

But so far, we haven't,
raising the question...

Can they really exist at all?

The Kepler space telescope

has blown the search for alien
worlds wide open,

discovering
thousands of exoplanets

orbiting single stars.

But finding rocky planets
in binary systems

is proving difficult.

We have found planets
orbiting binary star systems,

and that's a big leap forward
in our understanding

of how the universe works.

Unfortunately, those planets
have all been gas giants,

and they're not really
good for forming life.

For alien civilizations
to exist around two suns,

they need solid ground.

The hunt for the world
of our Sci-Fi dreams

has so far been fruitless.

We always have to consider
that maybe rocky planets

around binary stars

just don't exist for some reason
that we currently don't know.

And that would mean
there would be no Tatooine.

Could paired stars
make it impossible

for a rocky planet to form.

If you're a planet trying to
form around a binary system,

the gravity in the middle
is always changing.

Instead of a single star,
you have two stars

orbiting each other.

These two infant stars

start a gravitational
tug-of-war.

The material between them is
pulled in different directions,

making it harder for bits of
rock and dust to stick together.

The system seems too chaotic
for rocky planets to form.

The complex
gravitational interactions

at play destabilize
a lot of potential orbits.

There aren't a lot of
opportunities for a young planet

that might want to form to find
a stable, long-term home

that lasts for billions of years
around that binary system.

It's relatively easy to get
ejected or consumed

by the stars themselves.

So, why can't
rocky planets survive

when gas giants can?

As any good realtor will tell
you, it's all about

location, location, location.

We think that rocky planets tend
to form close in around stars

where it's nice and warm, but
further out where it's colder,

you have the gas giant
planets forming.

So, if you have
a binary star system,

it's like a gravitational
tornado whipping out

all of that rocky material

so that you're only left
with the cold stuff,

which can form
gas giants further out.

If a two-star system
were a city,

the gas giants are out
in the suburbs.

A nice, peaceful spot away from
the competing gravity

of the two stars.

Perhaps one-star systems
are better than two.

Gas giants aren't great
for life,

and those are the planets we're
finding in these binary systems.

The very reason that we're here
could be down to the fact

that we have one star
rather than two.

But in 2017,

a discovery
around 2,000 light years away

gives us new hope.

So, as we discover
new things in the universe,

we tend to give them
catalogue names,

which can be very boring

and very difficult
to keep track of.

But SDSS 1557
is worth remembering.

We've seen a binary system
that is a white dwarf...

Which is the core
of a star like the sun

after it's gotten very old,

blown off its outer layers...
That's orbited by a brown dwarf,

an object which is
sort of on the border

between a planet and a star.

What's most exciting
about the SDSS 1557 system

is that we've found
rocky debris.

We see the basic materials,

the basic ingredients are there
for forming planets.

This is a really
exciting discovery

because we've seen
the remnants of asteroids

and rocks orbiting about
this ancient binary system,

systems that we thought
could've never had surviving

rocky-type things
around it before.

This binary system
is billions of years old,

and through all that time,

the rocky material
hasn't been wiped out.

It has survived.

This is a huge stepping stone
to finding our rocky planet

with two suns.

The system provides evidence
there's rocky material

close in around
a binary star system,

so it's a signpost
that rocky planet formation

can occur around
binary star systems.

The odds might be longer,
but it's still possible.

Could there even still
be a planet in this system?

There may still be planetary
objects around SDS 1557.

We just haven't seen them yet,
but they may still be there.

The search is still on.

A rocky planet orbiting
two stars could really exist.

So, for those of us hoping
for that Tatooine out there,

that planet
with the double sunset,

these debris fields
actually give us hope.

Maybe the conditions, at least,
are right for the formation

of rocky planets
around binary stars.

I think it's out there.

I think finding it is more
a question of when than if.

As an astronomer, this is
a fantastic time to be alive

at the cusp of discovery.

As a science fiction fan, this
is a fantastic time to be alive

because the stuff I read
as a kid is coming true.

But perhaps
the biggest Sci-Fi fantasy

is much closer to home,

because new research is
suggesting something stunning...

Our own sun could have a twin.

A new study in 2017
throws into question

our understanding of the sun.

For the first time now,
astronomers are able to peer

inside the clouds
that form stars,

and the amazing thing is that
the evidence is suggesting

that every single sun-like star
forms as part of a binary pair.

The scientists study
the Perseus molecular cloud,

a stellar nursery around
750 light years from us,

packed with stars
just like our sun.

Many of them are in wide
binary systems,

traveling in huge orbits
around each other

that span centuries or more.

And all of these binaries
are babies,

less than 500,000 years old.

The only way to explain
these young systems

is that they formed this way...
Not alone, but in a pair.

Just based on statistics
and our understanding

of what's going on inside
these star-forming clouds,

it is highly likely that
the sun formed with a twin.

Perhaps 4.5 billion years ago,

our sun burst into life
with a sibling.

Could this twin
still be out there

in a distant orbit
that we haven't seen?

There was an idea that
the sun could have a companion,

which was nicknamed Nemesis,

and this thing would've
orbited way far out,

way past Neptune
in the solar system.

Scientists searched
for this Nemesis star,

but they came back empty handed.

We've looked... we've had
telescopic surveys of the sky,

including infrared surveys
where these types of objects

would be very bright,

and we've swept the entire
sky multiple times

and we've seen nothing.

What happened to our
sun's sibling is a mystery.

How do we end up with one star
as opposed to binary?

We really don't
quite understand.

If it doesn't orbit us now,

it may have left
our system long ago.

Over time, some of
these binary stars

get closer together
and stay together,

and others get ripped apart
and lose each other entirely.

It's very possible that our sun,
at some point,

had a twin that got ejected.

We don't know exactly when

our sister star was torn away.

It could be clear on the other
side of the galaxy

from us by now.

But after everything
we've seen in binary systems,

we may be much
better off without it.

I'm pretty happy
with having just one sun,

so I'm fine to live
in this solar system.

A binary sunset would be
more beautiful,

but only more beautiful
if you were alive.

And yet binary stars

don't just
bring death and destruction.

They could also create systems

with a series
of habitable worlds.

There's so much we don't know
about our own environment

and how it compares to
other places in the universe.

It seems like we're in
a very lucky place.

The sun is very stable,
it's a single star,

we're in a nice orbit around it,

but maybe there are places out
there that are even better.

We just didn't even know to ask.

It's certainly possible

that two stars are better
for life than one,

but until we find
these alien worlds,

it remains an open question.

It's hard to say whether
we're lucky or unlucky

to be on a planet
orbiting a single star.

It's probably a little
boring here

compared to what
it would seem like

in these binary star systems.

You know, from a romantic,
visual perspective,

I kind of wish we did live
in a binary star system.

Can you imagine somebody
living on a circum-binary planet

and finding an earthlike planet
orbiting a solitary star.

Would they think, "oh, how
interesting that would be.

Can you imagine
having one sunset?

What would that look like?"

I can imagine them
asking themselves

the questions we ask ourselves.

So it's just a matter
of perspective, you know?

Grass is always greener on the
other side of the binary system.

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