All language subtitles for How the Universe Works s01e05 Supernovas.eng

This is an exploding star.

lt's called a supernova.

A supernova
is the greatest cataclysm

in the history
of the entire universe.

Supernovas come
in different sizes and types.

All of them are so bright,

they can be seen
across the universe.

A supernova is the most violent
death of a star you can imagine.

But this
violent destruction of a star

is also the birth of everything
we see around us.

Really big stars go out
with a bang, called a supernova.

A supernova can outshine
an entire galaxy,

releasing trillions of times
the energy of our Sun.

They're so violent,

if one of them exploded just
a few dozen light-years away,

planet Earth would be toast.

A nearby supernova
would really ruin our day.

First of all,

the sudden burst of radiation
would scorch the atmosphere.

The only place to go
is underground.

Underground,

you could then withstand
the blistering burst of x-rays

which hit the Earth.

And then it would scorch
all plant life.

And with the collapse
of the food chain,

we're talking about a possible
extinction on the Earth.

Supernovas are killers.

But they also create the basic
elements that make up our world.

Our planet, our star,
everything around us

formed out of the debris
of a dead exploded star.

Everything that makes up
our bodies and the skyline

came from supernovae.

All of the iron,
all of the silicon,

all of the elements that went
into these buildings.

The things that make up
my blood, my body,

the gold in my wedding ring...

everything you see here
is a supernova.

But our Sun
won't become a supernova.

lt's too small.

Like all stars, it's basically
a giant nuclear reactor.

The fusion reactor
inside a star burns hydrogen,

the simplest,
most common element.

The reaction fuses
hydrogen atoms together...

...producing helium and energy.

And when the hydrogen runs out,

stars keep burning
by fusing helium into carbon...

...then carbon into o xygen.

When small stars like our Sun
make carbon,

they begin to die.

During the lifetime of a star,

there's a balance
between gravity pulling in

and pressure pushing out.

For a star that's generating
energy, there's no problem.

But once energy generation
switches off,

the pressure goes away,
and gravity wins.

Now gravity begins to
crush the center of the star.

The star's outer layers
are pushed outwards.

They expand into a huge ball
of gas called a red giant.

Our Sun, when it dies 4 1 /2
to 5 billion years from now,

its corona will go
all the way out to Mars.

Everything on the planet Earth
will vaporize.

While the outer layers expand,

in the center of the Sun,

gravity will have
the opposite effect.

lt'll crush the Sun's core

to just a millionth
of its original size...

about the size of the Earth.

Now it's a dense ball of o xygen
and carbon called a white dwarf.

ln our solar system,

this will be the end
of the story.

The gas from the dying star
will gradually disperse,

but the tiny white dwarf
will burn for billions of years.

But our solar system is unusual.

lt has just one star.

The fact is, the vast majority
of stars orbit in pairs.

When one of the two stars dies
and becomes a white dwarf,

if it's close enough,

it starts stealing material
from the other star.

Think of two stars
rotating around each other.

One star's slowly sucking
all the hydrogen and helium

from its companion star.

lt's like a vampire.

As the white dwarf
sucks more and more fuel

out of its companion star,

it gets heavier and denser
and less stable.

lnside, carbon and o xygen atoms
are about to fuse together,

and that's bad news.

A white dwarf, in some sense,

is like a bomb
waiting to be lit.

There's a huge amount
of energy stored in that star...

gravitational energy
and nuclear energy.

This white dwarf
is turning into a monster...

a type 1 A monster.

A type 1 A supernova

is a 20-billion-billion-billion-
megaton

thermonuclear carbon bomb.

lt's one of the most explosive
substances in the universe.

Eventually,

the white dwarf drains so much
material from its companion,

it goes into nuclear overload.

The carbon and o xygen inside it

start to turn into a common
but dangerous element...

at least to stars.

You've probably
seen in "Star Trek"

the idea that there is some
sort of secret technology

that kills a star.

Well, l mean,
it's in your frying pan

that you used this morning
for breakfast... iron.

The moment the white-dwarf star

starts to fuse carbon and o xygen
into iron, it's doomed.

Suddenly,
the white dwarf explodes.

The nuclear explosion
of a white dwarf include,

among other things,
huge amounts of iron.

And, in fact, type 1 A supernovae

are of vital importance
to populating the universe

with the kind of elements
that are important to us.

Type 1 A supernovas blast
iron trillions of miles into space.

lt's where most of the iron
in the cosmos comes from.

But what about all the elements
that are heavier than iron,

like gold and silver?

Where do they come from?

The answer, again,
is other stars...

single stars,

bigger stars.

Supernovas make
everything in the universe.

Everything we see,

all the material
in planet Earth,

was created inside a supernova.

Even you and l are made
from dying stars.

Without supernovae,
we wouldn't be here.

Every atom in your body was once
inside a star that exploded.

And the atoms in your left hand

may have come
from a different star

than the atoms
in your right hand.

You are literally stardust.

Almost all of the iron
in our solar system

came from
a double-star supernova

that exploded more
than five billion years ago.

From our planet's molten core...

To our skyscrapers...

To the hemoglobin
in our blood...

...it's all made of iron
from type 1 A supernovas.

But the heavier elements
in our world,

like gold, silver, and uranium,

come from another type
of supernova...

...a single-star supernova.

This is our Sun.

A single star has to weigh
much more than our Sun

to go supernova.

And there are some
monster stars out there.

Some are dozens of times
heavier than our Sun.

And some are hundreds
of times more massive.

The heavier the star,
the faster it burns.

And when these massive stars
begin to age and die,

the nuclear reactions
inside them speed up.

Giant stars burn through
their nuclear fuel very, very fast...

sort of the, you know,
the "live fast, die young."

The more mass a star has,
the hotter it burns inside,

the faster it burns
through its fuel.

Unlike double-star supernovas,

really massive single stars

create lots of elements
before they explode.

Once they turn hydrogen
into helium,

helium into carbon,
and carbon into o xygen,

they don't collapse
into white-dwarf stars.

lnstead,
giant stars keep on burning,

building up layer after layer
of new elements

deep in their core.

Big stars don't stop

after they've burned helium
to carbon and o xygen.

They go ahead and burn carbon
to still heavier elements

and then neon and o xygen
to silicon...

Until you get
this nested Russian-doll

spherical layer cake
kind of thing.

These elements are the
building blocks of the universe.

But they're trapped
inside the giant star.

Somehow, they've got to get out.

Studying exploding stars

has taught us how the heavy
elements of the universe

came to be.

They were formed by
nuclear reactions inside stars.

But if some of those stars
were not to explode,

then those elements
would be locked up forever.

The trigger
that'll release the elements

in the single giant star
is the same element

that causes the type 1 A
supernova to blow up...

iron.

lron eats up all the energy
of the star's nuclear fusion.

Without the energy from
nuclear fusion pushing out,

gravity begins to crush down.

The big star is doomed.

The last moments of a star
are really phenomenal.

The star might last
for 1 0 million years

on the way
to becoming a supernova,

but the last little bit
takes place very rapidly.

Once you have an iron core
and once it gets out of balance,

it collapses
in a thousandth of a second,

a millisecond,
from the size of the Earth

down to the size of manhattan.

lt's traveling about 1 /3
of the speed of light

as it crunches down.

As the star becomes unstable,

the massive power of gravity
causes the core to collapse.

This happens
with such incredible power,

even the atoms inside
start to crush together.

As it gets smaller and denser,

the core builds up
more and more energy.

lt's something with about
1 1 /2 times the mass of the Sun

that is collapsed to something

that's only
about 1 5 miles across.

lt's got incredible density.

lt's a thousand trillion times
the density of water.

Now the star explodes.

The blast rips through
the star's outer layers

and in the process,

makes all the elements
heavier than iron.

lron becomes cobalt.

Cobalt becomes nickel.

And on and on to gold, platinum,
and uranium.

The explosion is so brief,

it only makes small amounts
of these heavier elements,

which is why they're so rare.

The supernova
blasts these new elements

billions of miles into space.

The only method we know,

the only mechanism that we have
found anywhere in the universe

for creating new elements

is in the death throes of a star
called a supernova.

lt seems incredible

that anything could survive
a supernova explosion.

But we now know that some of the
biggest bangs in the universe

leave a corpse behind.

And these
are some of the strangest

and most deadly objects
ever discovered.

When a giant star
goes supernova and explodes,

it's not always the end.

Sometimes there's a corpse.

What kind of corpse depends
on the size of the star.

Supernovas from stars more than
eight times bigger than our Sun

leave behind a neutron star.

And it's one of the strangest
objects in the universe.

These things
you can almost think of

as sort of the zombies
of the stellar world.

They're very dangerous,
they're very weird,

and stars make them
all the time.

They're all around us.

As a giant star goes supernova,

the core is crushed
from the size of a planet

to the size of a city.

The pressure in the core
is so intense,

even the atoms inside it
are crushed together.

When the atoms are packed
that tightly

and there's no space
left between them,

the massive energy buildup
means something's got to give.

The core blasts off
the outer layers of the star.

And what remains
is a superdense neutron star.

A neutron star
has the mass of a star

crunched into
a very small volume,

and that means the density
is incredibly high.

Well, imagine taking the empire
state building here behind me,

crushing it into the size
of a grain of sand.

That's the density
of the entire neutron star.

So if you had something
that dense, if you dropped it,

it would fall
straight through the Earth,

just like a hot knife
through butter.

A teaspoon of neutron
star would weigh 1 00 million tons.

lmagine something
as heavy as a star

but only the size
of New York City.

And it's spinning.

Some of them may be born
rotating 1,000 times a second.

l mean, think about it...

something 1 1 /2 times
the mass of the Sun

going around
1,000 times a second.

Some neutron
stars spin so fast,

they generate huge pulses
of energy...

...beams of radiation

blasting out of the star's
north and south poles.

This neutron star
is called a pulsar.

There's one of these things in
the center of the Crab Nebula...

a place where there was
a supernova explosion

about 1,000 years ago.

And it's one of the fastest
spinning of these objects.

This is the actual
sound a pulsar makes,

recorded by radio telescope.

lt will flash 30 times a second
for millions of years.

But pulsars
aren't the strangest thing

a supernova can leave behind.

When stars 30 times bigger
than our Sun explode,

they produce a type of
neutron star called a magnetar.

Magnetars are even weirder
than pulsars

and generate powerful
magnetic fields.

Now, in the most extreme case,

the magnetic field
can be 1 0 to the 1 5,

you know, a...
a hundred trillion times

the magnetic field of the Earth.

That's so strong,

it would suck the iron
right out of your blood

from thousands of miles away.

But even pulsars and magnetars

aren't the most dangerous
objects

a supernova can leave behind.

When the core of
a supermassive star collapses,

it doesn't just crush atoms,

it crushes space
and time itself.

And that is when a supernova
creates a black hole.

When stars over 1 00 times
heavier than our Sun explode,

they make a supernova
explosion so big...

...scientists call them
hypernovas.

And it was a hypernova that
almost started World War lll.

ln 1 963,

the U.S. and Soviet Union

agreed to ban
testing nuclear weapons.

To keep tabs on the Russians,

the U.S. launched
spy satellites.

When they heard this sound
coming from deep space,

they suspected the worst.

United States government
launched the Vela satellite,

looking for nuclear detonations.

And then,
looking in outer space,

they saw these monster
explosions take place.

And the military thought,
"Oh, my God, the Russians!

The Russians are testing secret
atomic weapons in space."

But these weren't
secret atomic-bomb tests,

and the Russians had nothing
to do with them.

They began to look at where
this radiation came from.

lt came from all over
the galaxy, beyond the galaxy.

Now, there's no way the
Russians could shoot explosions

in outer space
beyond the galaxy.

And then people began to realize

that we were staring
something new in the face.

They were
super-powerful explosions

of high-energy radiation
called gamma-ray bursts.

The question was,
where did they come from?

The answer was
exploding hypernovas.

During a regular
supernova explosion,

gravity crushes a star's core
into a neutron star.

But during
a hypernova explosion,

the giant star is so much bigger

that gravity crushes the core
into something much stranger...

...a black hole.

And the black hole

immediately begins to devour
the dying star around it.

The rest of the star
can't all go

in that little bitty hole
in the middle.

lt starts to swirl around,
and it forms an accretion disk,

which is feeding the black hole

at about a million
earth masses a second.

And so, as you might imagine,

something dramatic
is gonna happen here.

A million earth masses a second

is too much for the black hole
to consume all at once.

So it spits a lot of it back out
at nearly the speed of light.

This creates two beams
of pure energy

blasting their way
out of the black hole.

Takes it about eight seconds
to bore through the star,

keeping a very tight focus,
and erupt from the surface.

Now, if we're standing
in the opening of this jet,

we'll see gamma-ray bursts.

The gamma rays
produced from the black hole

tear through the outer layers
of the star and into space.

Gamma-ray bursts
are the most violent event

that we know of in the universe.

A giant star blows itself to
pieces and forms a black hole.

lt's incredibly spectacular.

These gamma-ray bursts
are so energetic,

they light up
the entire universe.

Any point in the universe

will eventually pick up
this astounding radiation

coming from a gamma-ray burst.

That's how energetic they are.

They are the brightest
things in the known universe.

To put things in perspective,

a typical supernova explosion

is about what the Sun
will put out

in its entire
1 0-billion-year lifetime.

A gamma-ray burst viewed jet on

is a hundred million times
more luminous than a supernova.

They're the champions
for brightness, for sure.

They're not only
bright, they're lethal.

lf a gamma-ray burst
were to hit the Earth,

it would destroy most
of the atmosphere in seconds.

A gamma-ray burster
is like a rifle shot.

And if you're
in the line of sight...

Watch out.

Once the radiation hits you,

it'll bathe the entire surface
of the Earth with nitric o xides,

which will wipe out
the ozone layer.

Blistering radiation would hit
plant life, hit algae.

The whole food chain
would collapse.

lf the burst was close enough,

it would cause mass extinctions.

Gamma-ray bursts
turn out to be a lot more common

than we thought they would be.

So it's possible
that some of these

have even hit the Earth
in the past.

That's a pretty scary scenario.
lt may already have happened.

The question is,
if it happened before,

could it happen again?

A gamma-ray burster is basically
a supernova on steroids.

You need a giant star
to die violently.

Now, the nearest star to us that
might do that is Eta Carinae,

and it's a spectacular nebula.

There's all kinds of material
flying off this star.

lt's very unstable.

lt may already have exploded
in a gamma-ray burst.

But Eta Carinae
may not be the only threat.

There are other
dying stars out there.

Believe it or not, one of them
is pointed in our direction.

We are staring down
the gun barrel of WR1 04...

two dying stars that will one
day undergo the gamma-ray burst.

Not a question of if,
a question of when.

That WR1 04
may have our name on it.

But the good news is

we probably wouldn't know
about it in advance.

The shock would hit us before
we had a chance to do anything.

So there's no sense
worrying about it anyway.

The truth is,

we'll never know if a star
is about to go hypernova

and explode.

Anyway, by the time we see it,
it'll already be too late.

ln fact, we're already exposed
to rays from dying stars

every second of every day.

When giant stars explode...

...they make the biggest bangs
in the universe.

But what gives them
so much punch?

Until recently, no one knew.

Scientists,

when they tried to simulate
a supernova explosion

in a computer, had a problem.

They simply could not get enough
energy out of the dying star

to create a supernova.

This was a calamity
in astronomy.

Computer models couldn't
make the simulated stars blow up.

To blow up a star,
you need a lot of energy.

The trouble was,
astronomers couldn't find it.

The visible
radiation that you see

is a tiny fraction
of the total energy emitted.

Even the energy of motion
of the expanding gases

is only 1 % of the total energy.

Where was
the missing 99% of the energy

from the explosion?

The only way scientists

could get their simulations
to match the real thing

was to add in a mysterious
particle called the neutrino.

Without it,
their numbers didn't add up.

That was the easy bit.

Their next step

was to prove supernovas
really do produce neutrinos.

ln 1 987, they got lucky.

1 68,000 years ago,

a supernova exploded
in a nearby galaxy

called
the Large Magellanic Cloud.

When scientists saw the light
from the blast,

they called it supernova 1 987.

Supernova 1 987 A
is really important

in the study of supernovae
because it's the first one

since the invention
of the telescope.

lt's the one that
we've been able to study

right from the time of explosion
through now,

using all the instruments
that we've developed.

One of those instruments

was a giant neutrino detector
buried deep underground.

And bingo...
we saw a burst of radiation

go through
our neutrino detectors,

and we said,
"Aha! That's the proof!"

The discovery of
neutrinos from supernova 1 987 A

was a tremendous thing

because for many years
people had been saying,

"That's where 99%
of the energy goes,"

but no one had ever seen it.

This is now the smoking gun

that we can now prove
that neutrinos

carry the energy of a supernova,

and we detected it
right on the Earth

as we saw a supernova
in outer space.

Neutrinos are trillions
of times smaller than atoms.

They're created by all sorts
of nuclear reactions...

...from nuclear power plants
and bombs to exploding stars.

lf you had "neutrino-vision,"
you'd see them everywhere.

Neutrinos
are ghostlike particles.

Literally, trillions of them
are going through my body

even as we speak.

ln fact, neutrinos come
from the bottom of the floor,

right through the Earth,

and even hit me
right through my legs.

Pretty strange.

lmagine so many tiny particles
zooming through our bodies.

But where do they get
all their energy?

When a core crushes down just
before a supernova explosion,

the atoms inside it
are broken up.

The core gets so hot,

it turns this atomic debris
into blazing neutrinos.

We think that supernovae
produce a stupendous sum of neutrinos

when the core collapses
to a neutron star.

For about 1 0 seconds,

that core shines
with a neutrino luminosity

that is greater than all
of the energy being produced

in the rest of the universe
at that time.

ln other words,
it's really bright.

But gravity can't hold
these neutrinos in the core.

They burst free
in a blinding flash of light

that rips the dying star apart.

The discovery of neutrinos

transformed the science
of supernovas.

But supernovas
were about to reveal

the most mysterious force
of all...

one that's changing the destiny
of the universe.

Supernova explosions
are so bright,

we can see them
across the entire universe.

This has helped astronomers

unlock one of the deepest
mysteries of the cosmos.

The universe came to life

in the Big Bang
1 4 billion years ago.

lt expanded from a tiny ball
of energy smaller than an atom

to a universe billions and
billions of light-years across.

And it's still expanding.

l've often wondered
how far future people

will even know
the Big Bang happened,

because we know
the Big Bang happened

from watching all the galaxies
fly away from us.

Someday, the galaxies will be
so far away from each other,

it will be impossible to see
anything else in the sky.

Scientists used to think

the expanding universe
was slowing down,

but there was no way
to prove it...

...until they found double-star
supernovas, type 1 AS.

They always explode
when the white-dwarf star

reaches exactly 1 .4 times
the mass of our Sun.

And their explosions

always release exactly
the same amount of light.

They are the perfect markers
to measure distance in space.

Type 1 A supernovae,

when we know how bright they are
and how bright they look,

we can tell the distance,

'cause the farther away
they are,

the less bright they'll look
in the telescope.

And that has allowed us to
accurately measure distances

not just to nearby galaxies

but to galaxies at the other end
of the visible universe...

billions of light-years.

And that has allowed us to make
incredible discoveries.

Astronomers
thought they had found a way

to prove the expansion rate of
the universe was slowing down.

What they got
was a big surprise.

ln 1 998,

astronomers made a remarkable
and unexpected discovery.

lt was recognized
that the universe,

which should be slowing down,

'cause gravity, after all,
is attractive,

and the mass of objects
should cause the expansion

of the universe to slow down.

But the expansion
is speeding up.

lt's accelerating.

The constant light
from type 1 A supernovas

completely changed
the way astronomers

understand the universe.

Every science textbook
on the Earth

says that the universe
is expanding and slowing down.

Wrong.

We now have to rewrite
all the science textbooks

on the planet Earth.

But astronomers
still didn't know

why the universe is expanding
faster and faster.

They began to think it's some
kind of unknown energy.

They called it "dark energy,"

but it's difficult to prove

because it can't be seen
or touched or detected.

We really don't have
a very good clue

as to the physical nature
and origin of dark energy.

lt's perhaps the number-one

observationally motivated
problem

in all of physics right now...
the nature of the dark energy.

From dark energy to black holes,

supernovas have revealed

some of the most profound
mysteries of the universe.

These exploding stars

give us the building blocks
of the universe

and show us how it's all made.

lt's hard to imagine,

but the atoms
in our bodies today

were made by a supernova
billions of years ago.

The Bible say,
"From dust to dust."

Astronomers say,
"From stardust to stardust."

So supernovae are the key link
in this cycle of life.

People think
of space as being something

very distant and very remote.

lt's light-years away,
hugely distant from us.

That's completely wrong.

Supernovae are right here.

We are their children.

They made us,
literally put us together.

We are star stuff.

Without the supernovas,
we could not exist.

So when we walk around at night
and we look up at the night sky

and we see the stars and we feel
somehow a part of them...

...the truth is, we are.

They are our parents.

Some scientists believe the
age of supernovas could be ending.

Smaller, slower-burning stars,
like our Sun,

will become more common

and giant stars
become more rare.

Supernovas
have given us galaxies,

solar systems, stars,
and planets.

They made us
and everything we see.

They are where destruction
and creation meet.

The destiny of the universe

lies in the ashes
of dying stars.

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