All language subtitles for How the Universe Works Series 9 Part 5 Curse of the White Dwarf 1080p

ROWE: White dwarfs,

small stars that pack
a big punch.

When white dwarfs
were first discovered,

astronomers' reaction
was no, no, no, no,

no, no, no, that can't be real.

BULLOCK: What's going on
inside these things

can only be described
as seriously weird.

ROWE: They're the cooling
corpses of stars

like our sun,

but new research proves
white dwarfs are

one of the driving forces of
our universe.

PLAIT: They eat planets, they
flare out in high-energy light.

They can really explode.

And they can tell us literally

about the nature of
the universe itself.

NARRATOR:
And there's a dirty secret at

the heart of
white dwarf science.

HOPKINS:
We see dead stars exploding,

and we still don't understand
why they're doing it.

ROWE: Have scientists finally
discovered how these small

stars could be such massive
galactic players?

[explosion blasts]

December 2018.

Astronomers spot
strange flares coming from

a galaxy 250 million
light-years from Earth,

GSN 069.

We know that GSN 069 has
a supermassive black hole in

its center, equal to about

half a million
times the mass of the sun.

That's a big black hole,

and it blasts out X-rays in

a very, very steady pace,

every nine hours. Why?

ROWE: The flares are
so energetic and regular,

the supermassive black hole
must be eating the mass of

the planet Mercury
three times a day.

The big question is what's
feeding this black hole

such a huge dinner?

ROWE: In March 2020,
scientists found the answer.

An unlucky star at the end of
its life

had wandered into the death
zone of the black hole.

OLUSEYI: A star getting
too close to a supermassive

black hole is like
a glazed doughnut

getting too close to me.

That thing just is not
gonna make it.

HOPKINS: Stars to get too close
to a black hole

get torn apart.

They sort of get attacked
by the black hole,

and some of that material
is also getting launched

off in very powerful winds
and jets and streams

getting out.

ROWE: Somehow, the star
survives its close

encounter with
the supermassive black hole.

Further investigation reveals
it's a small, compact star,

a white dwarf.

So what makes this tiny star
almost indestructible?

The answer lies in how
it's formed.

We get a clue if we look at
the life cycle of a star.

It's burning hydrogen into
helium, that's causing nuclear

fusion, and that causes a star
to stay stable.

There's this delicate balance
between radiation pressure

from that nuclear fusion pushing
out and gravitational pressure

pulling in.

But when stars like our sun
near the end of their life,

they run out of hydrogen fuel.

ROWE: The sun-like star makes
more and more helium,

which builds up in its center.

Gradually, the immense weight of

the star's outer layers crushes
the helium core.

OLUSEYI: As the core ages,
it gets smaller and hotter,

which increases the rate of
nuclear reactions.

ROWE: These nuclear fusion
reactions produce more energy,

which pushes the outer layer,
or envelope, outwards.

Because there's more energy
flowing through the envelope,

the envelope swells up.

ROWE: The star expands to around
100 times its original size.

The yellow star
becomes a red giant.

Eventually, red giants shed
their outer layers,

forming stunning gas shells
called planetary nebulas.

Planetary nebulae are the most
beautiful objects in space.

They're all spectacular.

A star that ends its life in
one of these planetary nebulas

leaves behind a white dwarf
at the center,

and this white dwarf is
essentially a cinder,

a stellar cinder.

It's what's left after
nuclear fusion

is no longer possible for that
particular star.

ROWE: All that remains,
a glowing white dwarf,

the leftover core
of the dead star.

But in galaxy GSN 069,

the supermassive black hole
turbocharged the process.

It stripped off the outer
layers of the red giant

in a matter of days.

HOPKINS: The black hole
has almost eaten

all the juicy parts,
all the easy-to-get-at parts

of star, leaving behind
the sort of

bone or the leftovers
of the white dwarf.

ROWE:
This white dwarf is just 1/5

of the mass of the sun.

How can such a small
star survive

being so close to a black hole?

PLAIT: You might think that
because a white dwarf is small,

it's not gonna last very long,

because there's not that much
stuff there to eat,

but it turns out
it's quite the opposite.

ROWE: The pocket-sized white
dwarf is packed full of matter.

If it were a normal star,
it would have been shredded

long ago,
but because it's such a dense,

tight ball of matter,
it survives.

Imagine taking the sun
and crushing it down

to just about the size
of the Earth.

Same mass, but now packed way

more tightly,
so a basketball-worth of this

stuff would weigh as much
as 35 blue whales.

ROWE: The white dwarf's extreme
density protects it from

the gravitational onslaught of
the supermassive black hole.

Its orbit takes it near that
black hole every nine hours,

and every time it encounters
the black hole, some of its

material gets sipped off.

They're playing a game
of interstellar

tug of war with one another.

The black hole is bigger,
so it's going to win.

But the white dwarf is very
dense, so it's very tough,

and it's able to hang in there
for quite a long time.

OLUSEYI: It's gonna stay
in orbit around

a supermassive black hole for
billions of years.

Talk about David and Goliath.

ROWE: When astronomers first
discovered white dwarfs,

they thought
they shouldn't exist.

How could something have
such an extreme density

and not collapse under
its own weight?

Quantum mechanics,
the science of atomic

and subatomic particles
has the answer.

SUTTER: We're used to the rules
of physics up here

in the macroscopic world,

but when you zoom down into
the subatomic world,

things get weird.

Here we have the electron,
one of the tiniest

particles in the universe,

and it's these little
electrons that are doing

the work of supporting
an entire star.

Electrons really don't like
being squashed

into a small space.

If you try to squash too many
of them into too small a space,

they'll push back really hard,

and this is an effect
called degeneracy pressure.

ROWE: These degenerate
electrons stop white dwarfs

from collapsing,

but they give these stars
strange qualities.

OLUSEYI: White dwarfs behave

very differently
than normal matter.

Take planets and stars.

They become bigger
when they gain mass.

White dwarfs
are the exact opposite.

As they gain mass,
they get smaller.

ROWE: The more massive
a white dwarf,

the tighter the electrons
squeeze together,

and the smaller and denser
the star gets.

The high density means

the white dwarf's structure
is also strange.

It has an extremely
thin atmosphere,

made of hydrogen
or, occasionally, helium gas.

If you were to take an Earth
skyscraper and put it on

a white dwarf star,

if you climb to the top of
that skyscraper,

you'd be outside of the white
dwarf's atmosphere.

You'd actually be in space.

ROWE: Beneath the thin
atmosphere lies a surface

of dense helium
around 30 miles thick.

It surrounds an interior made

of superheated liquid carbon
and oxygen.

A white dwarf at its surface

can be a half a million degrees.

It's even hotter in
the interior,

and so that kind of material,

it's not gonna behave
the way normal matter does.

ROWE: Eventually,
over billions of years,

the center of the white dwarf
cools down into a solid.

CHRISTIANSEN: As the carbon
and oxygen atoms cool down,

they form a crystal.

Diamonds are actually crystals
of carbon,

so at the center of
these cool white dwarfs

could be a diamond the size
of the Earth.

ROWE: White dwarfs gradually
give off their remaining energy

until there's just a cold,
dead ball of matter,

a black dwarf.

HOPKINS: We've never seen what
we call a black dwarf,

and there's a simple reason
for that.

It takes a tremendous amount
of time,

many tens of billions of years,
longer than the age of

the universe,
to reach that point.

ROWE: This is the dark destiny
of most midsized stars,

including our sun.

This long, slow death may make
white dwarfs seem ordinary,

but these tiny stars
could answer

some big questions
about our universe.

PONTZEN: They might be small,
and they might be dim,

but they are essential for
our understanding of physics.

ROWE: New research into
white dwarfs may answer

one of the biggest questions
of all...

Can life survive the death
of its star?

ROWE: In the past,
we've underestimated

white dwarfs,

but now they're causing
a buzz among astronomers.

One of the big questions
over the last

decade is could a planet
survive around a white dwarf?

The logical answer would be no.

On their way to becoming
white dwarfs,

stars evolve through
a red giant phase.

They expand to become very huge.

So we figured any planets around

these stars might just
get eaten.

ROWE: In December of 2019,
evidence from the constellation

of Cancer turned that idea
on its head.

Astronomers spotted
a strange-looking white dwarf

about 1,500 light-years
from Earth.

Subtle variations in light
from the star

revealed a mystery...

The elements oxygen and sulfur
in amounts never

before seen on the surface of
a white dwarf.

We know what the chemical
signature of a white dwarf is,

and this stuck out
like a sore thumb.

ROWE:
Normally, hydrogen and helium

make up the outer layers
of a white dwarf.

Oxygen and sulfur

are heavier than hydrogen
and helium,

and they should have sunk
down, but we still see them

there, so they must have
gotten there recently.

ROWE: Using ESO's Very Large
Telescope in Chile,

astronomers took a closer look.

They discovered a small,
Earth-sized white dwarf

surrounded by a huge gas disc
roughly 10 times

the width of the sun.

The disc contained hydrogen,
oxygen, and sulfur.

SHIELDS: A system like this had
never been seen before,

and so the next step was to
look at a profile of these

elements and figure out where

we'd seen something similar.

And the amazing thing is,
we have.

We've seen these elements in
the deeper layers of the ice

giants of our solar system,

Uranus and Neptune.

ROWE: Hidden in the gas ring
is a giant,

Neptune-like icy planet.

It's twice as large as the star,

but the fierce 50,000-degree
heat from the white dwarf is

slowly evaporating
this orbiting planet.

SHIELDS: The white dwarf

is bombarding the planet with
high-energy radiation, X-rays,

UV rays.

It's pulverizing the ice
molecules in its atmosphere

and blowing them out into space,

and the ice molecules are
streaming behind

the planet like
the tail of a comet.

ROWE:
The icy planet loses mass at

a rate of over 500,000 tons
per second.

That's the equivalent of
300 aircraft carriers

every minute.
- CHRISTIANSEN: It sounds like

that could be curtains
for the planet.

But remember,
the planet is large,

and the star is cooling down.
- SHIELDS: As it cools,

it will stop blasting
the planet so intently,

and that stream of
gas will cease.

The planet will probably
end up losing

only a few percent of
its total mass.

ROWE:
So the planet should survive

and continue orbiting
the white dwarf.

But a mystery remains.

Why didn't the closely
orbiting planet die

when the star swelled
to a red giant?

SHIELDS: It had to have started
farther out and moved inwards.

Our best guess is that other
ice giants were probably

lurking somewhere
in the outer regions

of the system and knocked
that planet inwards,

towards the white dwarf,
sometime after the red giant

phase in some kind of
cosmic pool game,

if you will.

ROWE: This isn't the only white
dwarf with evidence of planets.

About 570 light-years
from Earth,

there's a white dwarf star
called WD 1145+017.

After studying the star
for five years,

researchers report that
the white dwarf is ripping apart

and eating a mini rocky planet.

CHRISTIANSEN: So as the planet
is being torn up,

we see this huge cloud of
dust blocking out 50% of

the light of the star
and huge chunks of rock

passing in front of the star.

BYWATERS: It's exciting to see
this planet being torn apart,

because it's not often
that we get to see an event,

we get to see something
in the process

that we can observe
and we can learn from.

ROWE:
There's more and more evidence

that planetary systems
can survive

the death of their star and
the formation of a white dwarf.

It just depends on
the planet's composition

and location.

The distance from the planet to
the star is a critical factor,

because as you move farther
and farther out from a star,

the intensity of that solar
radiation decreases.

So the farther you go out,
the less heat you have,

the less high-energy particles
are reaching the surface of

that planet.

Also, rocky planets can
survive better than gas giants,

because rocky planets can hold
onto their stuff better,

whereas gas can be blown
away much more easily.

ROWE:
These new discoveries raise

questions about habitability
around stars.

Could white dwarf systems
support life?

SHIELDS: If we limit
ourselves to only looking

for life on planets
orbiting stars like our sun,

we would be doing ourselves
a huge disservice.

Far more important is to look
for, around whatever star,

the habitable zone,

the Goldilocks zone,
the region around a star where

a planet could support life.

ROWE: When it comes to
supporting life,

white dwarfs have some
surprising advantages.

CHRISTIANSEN: Even though
there's no fusion happening,

they have all of this internal
energy stored up that they

release that warms
the nearby planets.

SUTTER: Life might even prefer
hanging out around

a white dwarf, because

it doesn't change much over
the course

of billions of years.

With something like our sun,
there are flares and coronal

mass ejections, and then
eventually, it's gonna die,

and we have to deal with that.

That's not a problem with
a white dwarf.

So if life can gain a foothold,

it has a nice, stable home.

ROWE: We now think 25 to 50% of

white dwarfs
have planetary systems.

Perhaps one day,
we'll find one with

an Earth-like planet,
and maybe even life.

But not all of these tough
little stars are good hosts.

White dwarfs
have a volatile nature.

They can explode in some of the
biggest bangs in the cosmos.

[explosion blasts]

ROWE: White dwarfs are the dead
remains of stars like the sun.

Most of these zombie
stars slowly

cooled down
over billions of years.

Most, but not all.

Some go out in a spectacular
explosion known

as a type 1a supernova.

A type 1a supernova

is one of the most
violent, powerful,

energetic events
in the universe.

We are talking about
a star exploding.

They can outshine
entire galaxies.

They can create devastation over

hundreds and hundreds of
light-years.

They're a big deal.

ROWE: We'd seen the aftermath
of these cosmic fireworks,

but for over 60 years, we had
little direct evidence

they came from white dwarfs.

Then students from University
College London UK got lucky.

While taking
routine photographs,

they spotted
a supernova explosion

in our own cosmic neighborhood.

PLAIT: M82, the cigar galaxy,
is actually really

close to us on cosmic terms.

It's only about 12 million
light-years away.

This makes it one of
the closest galaxies in the sky.

The blast called
Supernova 2014J was

the closest type 1a supernova
for over 20 years.

Its proximity allowed us
to look for

the signature of
a white dwarf supernova,

a blast of gamma rays.

Gamma rays are a type of light
that's incredibly energetic.

They're the most energetic
type of rays,

or photons, on
the electromagnetic spectrum.

ROWE:
White dwarfs should release

gamma rays when they explode.

But dust in interstellar space
soaks up the rays,

so unless an explosion is close
by, they're hard to detect.

For years, astronomers had
been looking for the gamma rays

that should be emitted by
a type 1a supernova,

but no one had found them.

ROWE: Now, scientists had
their chance

and the technology to see
the elusive rays.

Using ISA's integral satellite,

they sifted through
the shockwaves sent out by

the explosion in M82.

It was tough, but finally,
they got a reading,

the telltale signal of
gamma rays.

It's the best evidence yet
for white dwarfs

exploding in type 1a supernovas.

The reason Supernova 2014J
was so cool is that this

observation gave scientists
evidence, it's white dwarfs that

explode to create this specific
type of supernova.

ROWE:
So which white dwarfs fade out

and which ones
go out with a bang?

A survey of stars revealed

around 30% of white dwarfs
live in binary systems,

but white dwarfs are not
good neighbors.

A white dwarf in a binary
system is... it's like a zombie.

It's the corpse of a star
that used to be alive.

But now it is eating
the material

from a star that is still alive.

They very literally suck
the material

and suck the life
out of that star

by swallowing up all of
its outer layers.

ROWE: The white dwarf zombie
tendencies can backfire.

Adding mass to
a white dwarf is like this.

We keep adding mass from that
companion star

a little bit of hydrogen
at a time,

building up that atmosphere,
and for a long time,

everything's fine.

Until you add too much mass,
and you reach that critical

threshold, and then...

ROWE:
The real-world consequences of

reaching the threshold
are devastating.

The extra weight of gas stolen
from the companion star

compresses carbon deep in
the core of the white dwarf.

When the white dwarf reaches
1.4 times the mass of our sun,

it hits a tipping point known
as the Chandrasekhar limit.

You add up the mass little by
little by little until

you get to that Chandrasekhar
limit and then blam,

there's a supernova.
- ROWE: In a flash,

carbon undergoes nuclear fusion,

releasing a tremendous
amount of energy.

FILIPPENKO:
If the white dwarf explodes

at the Chandrasekhar limit,

it's a little bit like
fireworks that all have

the same amount of gunpowder.

They'll all go off in the same
way, they'll be equally loud.

Well, the supernovas
will be equally bright.

ROWE: This equal brightness
of all type 1a

supernovas is vital to
our understanding of space.

Type 1a's are known as
standard candles

and are useful tools for
calculating fast

cosmic distances.

They were the key
to the Nobel Prize winning

discovery that the expansion
of our universe

is accelerating.

But what kind of companion star
triggers type 1a supernovas?

For decades, the number one
suspect was red giant stars.

HOPKINS: A red giant's

a good candidate, because it's
a very big, puffy star.

That material becomes easy
pickings for the white dwarf

to siphon off until it gets
big enough to explode.

ROWE: To prove the theory,
we needed to find

evidence in the debris left
behind after a supernova.

Stars are surprisingly
hardy objects.

They can survive an explosion
of a nearby star.

Some of these companion stars
should still be there.

A lot of them will be, you know,
worse for the wear,

but they'll still exist.

ROWE: Scientists search
through the remains

of 70 type 1a supernovas.

Only one blast zone contained

the glowing remains
of a red giant.

The fact that we've only found
maybe this one example suggests

that actually, they're not
quite the serial killers

we thought.

It's probably likely
that this is

the minority of these types of
supernova explosions.

Indeed, we now think that only
a small fraction of

these white dwarf supernovas
involve a red giant,

despite the fact that, in
the standard textbooks, for

decades, that was
the preferred explanation.

ROWE: If red giants don't cause

the majority of
type 1a supernovas,

what does?

New evidence suggests

colliding white dwarfs,

star mergers that could exceed

the Chandrasekhar limit,

producing explosions with
different brightness.

But if the explosions
vary in brightness,

can they still be used

as standard candles?

PONTZEN: If we don't really know
what a type 1a supernova is,

then when we use them to map out

the universe and the way
the universe is expanding,

we just can't be sure any longer
what it is we're looking at.

If we're wrong about that,

then we're wrong about so many
other things that our whole

model of the universe
falls apart.

ROWE: Is our understanding of
the cosmos completely wrong?

ROWE: White dwarfs explode in
spectacular type 1a supernovas.

They're a crucial tool for
measuring the universe,

but there is a problem.

The standard model
says that white dwarfs

gradually steal mass
from a red giant star

until they reach a tipping point

called the Chandrasekhar limit.

But recent observations
proved this doesn't explain

how most type 1a
supernovas occur.

The majority of type 1a
explosions remain a mystery.

We call the explosions from
white dwarfs standard candles,

but they're really not
that standard.

We actually think there's
different types of explosions.

THALLER: It may be imperative
to our understanding

of the entire universe
that we really get

this straight, because
the reason we think

the expansion rate of
the universe is accelerating

is based on the brightness of
type 1 supernovas

all being the same,
and maybe that's not the case.

ROWE: Researchers suspected
a theoretical type of

merger could be responsible

for more type 1a supernovas,

the result of two white dwarfs
crashing together.

But this messes with the math.

The Chandrasekhar limit says
white dwarfs should

explode when they reach

1.4 times the mass of our sun.

Two white dwarfs colliding
can exceed this mass,

and more mass means
a bigger bang

and a brighter explosion.

You're not adding gas

little by little,
you're adding a whole

other white dwarf...
That will go off.

It will look like
a type 1 supernova,

but it won't be
the standard candle.

It'll be brighter than
we expect.

ROWE: But no white dwarf mergers
have been found, because

detecting one after it happens
is virtually impossible.

HOPKINS: If two white dwarfs
merge together,

it's almost impossible to tell,
because the DNA of the two

systems is all mixed together,
and it's all identical.

You can't tell that there was
a separate companion in

the first place.

SUTTER: So we can't just look at
when there's a bright flash.

We have to go look for
the ticking time bombs in

the galaxy.

ROWE: Astronomers
investigating a strange shaped

cloud of gas made
a breakthrough.

Using ESO's Very
Large Telescope,

they focused in on a planetary
nebula called Henize 2-428.

Planetary nebulas are
normally symmetric,

because red giants shed

their outer layers evenly
as they become white dwarfs.

But this one is lopsided.

We think, in this case, there
might be the presence of

a companion star that shapes
and twists and sculpts

that planetary nebula.

ROWE: Researchers peeled back

the gaseous layers and
discovered something shocking,

a two-star system made up of

the most massive orbiting
white dwarf pair

ever discovered.

Each star is 90%
as massive as our sun,

and they're so close together,
they take

just four hours
to orbit each other.

And they're getting closer.

SUTTER: If you've ever seen
a car crash about to happen,

you know that sense of
inevitability

as you witness that.

That's what we're seeing in
this system.

We see these two massive white
dwarfs spiraling closer

and closer and closer, and we
know that disaster is coming.

ROWE:
In around 700 million years,

these stars will
merge and explode

in a type 1a supernova.

Now, thanks to the discovery
of more systems

like Henize 2-428,

we think white dwarf
collisions could be responsible

for the majority of
type 1a supernovas.

[explosion blasts]

Two white dwarfs
can merge together.

And if the sum of their masses
is greater than

1.4 solar masses,

then you can get
a Super-Chandra type 1a.

ROWE: We've now observed

nine Super-Chandra explosions,

and to complicate
matters further,

we've spotted another form of
white dwarf supernovas,

Sub-Chandra type 1as.

These mysterious white dwarfs
that we don't quite understand

die off much quicker than
regular white dwarf supernovas.

[explosion blasts]

ROWE: The explosions are less
violent than normal

type 1a supernovas
and fade away faster.

But we don't know why.

Maybe it has something to
do with

the properties of the star
or the rotation,

but the Chandrasekhar limit
may not be so exact.

It's kind of
a Chandrasekhar range.

The physics textbooks are
now being sort of rewritten,

or at least modified, because
we know that not all type 1a

supernovas come from Chandra
mass white dwarfs.

There's actually a variety of
type 1a supernovas,

a variety of white dwarf masses
and configurations

that can explode.

ROWE: These new discoveries
mean researchers now study

the chemistry and duration of
type 1a supernovas,

not just their brightness.

The deeper we investigate,
the more mysteries we uncover,

like rogue white dwarfs
streaking across the galaxy

and tiny stars that explode
over and over again.

Can these odd white dwarfs
shed more

light on the mystery of type
1a supernovas?

ROWE: White dwarfs are

surprisingly difficult
to understand.

They behave in completely
unexpected ways.

But these oddballs may
help answer

the remaining questions about
type 1a supernovas.

These are white dwarfs,
but not as we know them.

ROWE: 2017... astronomers spot
a rebellious star

raising hell in
the Little Dipper constellation.

It's like a zombie, but this
isn't one shambling down

the road,
it runs like Usain Bolt.

This thing is screaming
through the galaxy at a much

higher speed than you'd expect
for a star like it.

ROWE: The white dwarf
called LP 40-365

is moving incredibly fast

towards the edge
of the Milky Way.

It's not the only star
behaving oddly... in 2019,

we spotted three more
white dwarfs racing across

the galaxy.

Finding one white dwarf
blasting its way

through space is weird enough.

But to find three more, that's
telling you that something is

going on, and whatever it is

that's going on happens a lot.

ROWE:
So what sent these renegades

racing across the galaxy?

LP 40-365 and these other
weird white dwarfs

could be the results
of failed supernovas.

People have theorized that maybe

these things didn't
finish exploding.

And if so, we should find

some unburnt fractions
wandering around the galaxy.

ROWE: In the last 20 years,
we've spotted some unusually dim

supernovas that could have sent

LP 40-365 and friends flying.

So what looks like happened is
that in a binary pair,

there was stuff dumping
onto a white dwarf,

and we were about to have
a type 1 supernova.

But the type 1 supernova
didn't go off symmetrically.

Some of it actually exploded,
and some of it didn't.

That energy didn't go out in
all directions.

And one of the things that
occurred is that these stars

got sent hurling across space
at these incredible speeds.

ROWE: We call them
type 1ax supernovas.

They could make up between
10 and 30%

of type 1a supernovas.

Many could throw out
a runaway star.

But we still don't know why
the supernova fails.

PLAIT: A funny thing
about science is things

that fail still teach you
what's going on.

Why are these ones different?
Were they not massive enough?

Where they too massive?
Was the companion star

not feeding them the material
the right way?

Something happened there to
make these stars

not basically blow
themselves to bits.

And that's telling us
something about

the way type 1as do explode.

ROWE: It seems that life
in a binary star system

can be rough for white dwarfs,

but for some lucky stars,
their lives can

be more mellow.

Just because a white dwarf

has a normal star companion that

it's stealing material from
does not spell a death sentence

for that white dwarf.

ROWE: February 2013.

Astronomers discover a star in
the Andromeda galaxy

that flashes over and over
and over again.

With each flare,

it shines a million times
brighter than our sun

before dimming to its
normal state.

It's called M31N 2018-12a.

This is not a supernova,
it's its little sibling,

a nova.

But what's weird about this
one is that it happens

every year.

Astronomers have known for
a long time that there are these

cases of these nova that go off,

you know, somewhat regularly,
every 10 years,

every 100 years.

But finding one that goes off

every year is
a remarkable discovery.

ROWE: Much like supernovas,

novas occur in a close
binary system,

where a white dwarf and
another star orbit each other.

The white dwarf pulls in
hydrogen

from the companion star.

The gas falls onto its surface.

And so as
that hydrogen piles up,

eventually, it gets to
the point where

it can fuse into helium
and goes bang.

ROWE: In supernovas,

fusion happens deep inside
the star's core,

but in novas, fusion only
occurs on the surface.

An explosion flares across
the white dwarf's exterior,

hurling unburned hydrogen
out into space.

The result... an object
called a remnant.

The remnant from Nova M31N
is 400 light-years wide.

This particular remnant is much

bigger than even
supernova remnants.

It's much larger, much denser

and brighter than most
normal remnants are.

But that makes sense

if the star flares up so often.

Think about the star flaring
away for millions of years.

You build up a gigantic
nova remnant.

ROWE:
The repeating flares explain

the huge size of the remnant.

But why does the nova explode
so frequently?

Classically, we thought that
when a nova went off

on the surface of

a white dwarf star that
the white dwarf star's mass

didn't change very much.

Or maybe it got
a little smaller.

Now we think that after a nova,

the white dwarf
gains a bit of mass.

ROWE: Recurrent novas, like
M31N, steal more mass from

their companion star than they
blow off in each explosion.

Some gain more and more mass,

exploding more frequently
until they reach

the Chandrasekhar limit

and go full-on supernova.

M31N may very well be

the missing link that shows us

that some nova systems
eventually become

supernova systems.

ROWE:
Working out how novas become

supernovas and why some
supernovas fail

might help us understand what
makes white dwarfs explode.

But just when we think
we get a break,

white dwarfs hit us
with another bombshell...

death rays.

ROWE: White dwarfs can explode
in violent supernovas,

but that's not
their only deadly trick.

They might also create the most

magnetic and terrifying beast
in the universe...

A magnetar.

Magentars are scary.
They just are.

I mean, it's even in the name.

The word magnetar sounds scary.

They're the reigning champion of

the largest magnetic field in
the universe.

SUTTER: The magnetic fields
around magnetars are so strong

that they can stretch
and distort individual atoms.

They can turn an atom into
a long, thin pencil shape.

Once you start stretching
atoms out into this shape,

they can't bond together
in the usual ways anymore.

And so you can just throw out

every chemistry textbook
in the world.

BULLOCK: If an astronaut were
unlucky enough to get close to

a magnetar, say, within

600, 700 miles,
the whole body of the astronaut

would be completely obliterated.

They would more
or less dissolve.

ROWE: The origin of these
fearsome creatures is a mystery,

but it must be something
very violent.

We think they send out
a clue as they form,

powerful blasts of energy
shooting across the cosmos.

In the past few decades,
we've noticed these very odd,

very confusing and very brief

flashes of intense radio energy.

ROWE: They're known as fast
radio bursts, or FRBs.

Some FRBs don't repeat.
They're one and done.

So you're talking about
an incredible amount

of energy released in less
than a second,

then it's over.

ROWE: Because these
non-repeating FRBs are

so powerful, we think they could
come from a huge collision.

The heavier and denser
the objects colliding,

the bigger the bang.

New research suggests a white
dwarf star hitting a dense,

heavy neutron star could be
enough to birth

a magnetar,

sending out FRBs in the process.

A neutron star is
like a white dwarf.

Even more so...
It is the leftover core

of a giant star.

They're effectively giant
balls of neutrons

squeezed together

into things about the size
of a city.

SUTTER: You have a neutron star,
an incredibly nasty,

complicated exotic object
and a white dwarf,

an incredibly nasty,
ugly, complicated object,

crashing headlong into
each other.

ROWE: As the two stars
orbit more closely,

the neutron star strips gas
from the white dwarf.

This material spirals
onto the neutron star,

causing it to spin faster
and faster.

The rapid rotation amplifies
its magnetic fields

until the two stars collide,

creating
a very magnetic monster,

a magnetar.

It's a turbulent situation.

You could think of it as
a newborn baby coming into

the world,
kicking and screaming.

ROWE: The turbulence produces

a powerful blast of
electromagnetic radiation.

It races out of the collision
site at the speed of light

until we detect it
as a fast radio burst.

We can hear the screams of
agony from millions

of light-years away,

and those screams are
the fast radio bursts.

This could be the most
difficult childbirth in

the cosmos.

ROWE: Few suspected
that white dwarfs could create

something as violent as
a magnetar.

White dwarfs are emerging
from out of

the shadows and taking
their rightful place

as one of the most
fascinating objects

in the universe.

When we first observed white
dwarfs, they were weird.

They were curious,
but just like a sideshow.

But now white dwarfs
are showing us

what they're truly capable of.

STRAUGHN: White dwarfs
can sort of be seen

as these underdogs
of the universe,

but it's really become
an exciting and cutting edge

area of research.

THALLER: Now we think
these objects may have

a lot of exciting science
to deliver, things like,

will the universe
expand forever?

What is the ultimate fate of
the universe?

All of that may be waiting for
us inside a white dwarf.

PLAIT: Discount these things
at your own risk,

because honestly,

they are one of the driving
forces in the universe.

Just because it's little
don't mean it ain't bad.

Don't underestimate
a white dwarf.