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.