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White dwarfs.

Small stars that pack a big punch.

When white dwarfs were first discovered,

the astronomers' reaction was,

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

What's going on inside these things can only be described as seriously weird.

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.

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.

And there's a dirty secret at the heart of white-dwarf science.

We see dead stars exploding and we still don't understand why they're doing it.

Have scientists finally discovered how these small stars

could be such massive galactic players?

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 centre,

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?

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?

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.

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.

Stars that get too close to a black hole get torn apart.

They sort of get attacked by the black hole.

Some of that material is also getting launched off in very powerful winds

and jets and streams getting out.

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 is 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.

The sun-like star makes more and more helium, which builds up in its centre.

Gradually, the immense weight of the star's outer layers

crushes the helium core.

As the core ages, it gets smaller and hotter,

which increases the rate of nuclear reactions.

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.

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 centre.

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.

All that remains is 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.

The black hole has almost eaten all of the juicy parts,

all the easy to get at parts of the star.

Leaving behind the sort of bone or the leftovers of the white dwarf.

This white dwarf is just a fifth of the mass of the sun.

How can such a small star survive, being so close to a black hole?

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

it's not gonna last very long, cos there's not that much stuff there to eat.

It turns out it's quite the opposite.

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.

The same mass, but now packed way more tightly.

So a basketball-worth of this stuff

would weigh as much as 35 blue whales.

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.

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.

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

It's gonna stay in orbit around a supermassive black hole

for billions of years.

Talk about David and Goliath.

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 sub-atomic particles,

has the answer.

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 an effect called "degeneracy pressure".

These degenerate electrons stop white dwarfs from collapsing.

But they give these stars strange qualities.

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.

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's 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.

Beneath the thin atmosphere lies a surface of dense helium, around 30 miles thick.

It surrounds an interior

made of super-heated 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.

Eventually, over billions of years,

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

As the carbon and oxygen atoms cool down, they form a crystal.

Diamonds are actually crystals of carbon.

So at the centre of these cool white dwarfs could be a diamond the size of the Earth.

White dwarfs gradually give off their remaining energy,

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

A black dwarf.

We've never seen what we call a black dwarf.

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.

This is the dark destiny of most mid-sized 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.

They might be small and they might be dim,

but they are essential for our understanding of physics.

New research into white dwarfs may answer

one of the biggest questions of all.

Can life survive the death of its star?

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.

In December 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 sulphur

in amounts never before seen on the surface of a white dwarf.

We know what the chemical signature for a white dwarf is

and this stuck out like a sore thumb.

Normally, hydrogen and helium make up the outer layers of a white dwarf.

Oxygen and sulphur are heavier than hydrogen and helium.

They should have sunk down, but we still see them there.

So they must have gotten there recently.

Using ESO's very large telescope in Chile,

the astronomers took a closer look.

They discovered a small Earth-sized white dwarf,

surrounded by a huge gas disc,

roughly ten times the width of the sun.

The disc contained hydrogen, oxygen and sulphur.

A system like this had never been seen before.

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.

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.

The white dwarf is bombarding the planet

with high-energy radiation, X-rays, UV rays.

It's pulverising the ice molecules in its atmosphere

and blowing them out into space.

The ice molecules are streaming behind the planet, like the tail of a comet.

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.

It sounds like that could be curtains for the planet,

but, remember, the planet is large and the star is cooling down.

As it cools, it will start 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.

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?

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, some time after the red-giant phase,

in some kind of cosmic pool game, if you will.

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.

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.

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.

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.

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.

Rocky planets can hold onto their stuff better,

whereas gas can be blown away much more easily.

These new discoveries raise questions about habitability around stars.

Could white-dwarf systems support life?

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.

When it comes to supporting life,

white dwarfs have some surprising advantages.

Even though there's no fusion happening,

they have all of this internal energy stored up

that they release, that warms the nearby planets.

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.

Eventually, it's gonna die and we have to deal with that.

That's not a problem with the white dwarf.

So, if life can gain a foothold,

it has a nice stable home.

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.

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

Most of these "zombie" stars

slowly cool down over billions of years.

Most, but not all.

Some go out in a spectacular explosion

known as a Type Ia supernova.

A Type Ia 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.

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 neighbourhood.

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 2014 - J was the closest Type Ia 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.

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 Ia supernova, but no-one had found them.

Now, scientists had their chance

and the technology to see the elusive rays.

Using ESA'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 tell-tale signal of gamma rays.

It's the best evidence yet

for white dwarfs exploding in Type Ia supernovas.

- The reason Supernova 2014 - J was so cool is that this observation

gave scientists the evidence white dwarfs would explode

to create this specific type of supernova.

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 neighbours.

A white dwarf in a binary system, 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.

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...

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,

till you get to that Chandrasekhar Limit

and then blam, there's a supernova.

In a flash, carbon undergoes nuclear fusion,

releasing a tremendous amount of energy.

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.

This equal brightness of all Type Ia supernovas

is vital to our understanding of space.

Type Ias are known as "standard candles"

and are useful tools for calculating vast 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 Ia supernovas?

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

A red giant is 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.

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 'em will be worse for wear, but they'll still exist.

Scientists search through the remains of 70 Type Ia 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.

If red giants don't cause the majority of Type Ia 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?

If we don't really know what a Type Ia 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.

Our whole model of the universe falls apart.

Is our understanding of the cosmos completely wrong?

White dwarfs explode in spectacular Type Ia 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 prove this doesn't explain

how most Type Ia supernovas occur.

The majority of Type Ia explosions remain a mystery.

We call the explosions from white dwarfs "standard candles",

but they're really not that standard, there's different types of explosions.

It may be imperative to our understanding of the entire universe that we get this straight,

because the reason we think the expansion rate of the universe is accelerating,

it's based on the brightness of Type I supernovas all being the same.

Maybe that's not the case.

Researchers suspect that a theoretical type of merger

could be responsible for more Type Ia 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.

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 I supernova,

but it won't be the standard candle, it'll be brighter than we expect.

But no white dwarf mergers have been found,

because detecting one after it happens is virtually impossible.

If two white dwarfs merge together, it's almost impossible to tell.

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.

So, we can't just look when there's a bright flash.

We have to go look for the ticking time bombs in the galaxy.

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.

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.

They're so close together, they take just four hours to orbit each other

and they're getting closer.

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

spiralling closer and closer and closer and we know

that disaster is coming.

In around 700 million years, these stars will merge and explode

in a Type Ia 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 Ia supernovas.

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 Ia.

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 Ias.

These mysterious white dwarfs that we don't quite understand

die off much quicker than regular white dwarf supernovas.

The explosions are less violent than normal Type Ia 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.

We know that not all Type Ia supernovas come from Chandra-mass white dwarfs.

There's actually a variety of Type Ia supernovas,

a variety of white dwarf masses and configurations that can explode.

These new discoveries mean researchers now study the chemistry

and duration of Type Ia supernovas, not just their brightness.

But mysteries remain.

We still don't know what triggers the actual explosion.

Something has to set off a supernova.

It's like a sort of tinderbox, this star is ready to be set alight,

but something has actually got to set it alight in the first place.

And the question is, what exactly is doing that?

Our best hope of understanding white dwarf supernovas

is to run computer simulations,

experimenting with ways to trigger fusion in the heart of the star.

It turns out you need a spark to get that fusion going.

Otherwise, the usual failure in computer models of a supernova is

oop, never saw anything.

We do not understand what creates the explosion.

We don't know what the mechanism for that is yet.

While computer simulations are getting closer,

we still don't fully understand Type Ia supernovas.

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 Ia supernovas?

White dwarfs are surprisingly difficult to understand.

They behave in completely unexpected ways.

But these oddballs may help answer

the remaining questions about Type Ia supernovas.

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

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.

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.

To find three more, that's telling you that something is going on

and whatever it is that's going on happens a lot.

So what sent these renegades racing across the galaxy?

LP 40-365 and these other weird white dwarfs could be the result of failed supernovas.

People have theorised that maybe these things didn't finish exploding.

If so, we should find some unburnt fractions wandering around the galaxy.

In the last 20 years, we have 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 I supernova.

But the Type I 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.

One of the things that occurred is that these stars

got sent hurling across space at these incredible speeds.

Stars could be sent flying so fast, that they're no longer bound by

the gravitational pull of their home galaxy.

LP 40-365 is known as a hypervelocity star

and is moving so fast,

it's definitely headed out of the Milky Way.

We call them Type Iax supernovas.

They could make up between 10% and 30% of Type Ia supernovas.

Many could throw out a runaway star.

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

The 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?

Too massive? Was the companion star not feeding them the material in the right way?

Something happened there to make these stars not, basically, blow themselves to bits.

That's telling us something about the way Type Ias do explode.

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 is stealing material from,

it does not spell a death sentence for that white dwarf.

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 M31 - N 2018-12a.

This is not a supernova. It is 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

somewhat regularly, every ten years, every 100 years,

but finding one that goes off every year is a remarkable discovery.

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!

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 M31 - N is 400 light-years wide.

This particular remnant is much bigger than even supernova remnants.

It's much larger, much denser and brighter then 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.

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.

- Recurrent novas, like M31 - N, 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.

- M31 - N may very well be the missing link that shows us

that some nova systems eventually become supernova systems.

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.

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.

Magnetars are scary, they just are.

I mean, it's even in the name. The word "magnetar" sounds scary.

They are the reigning champion of the largest magnetic field in the universe.

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 any more.

So you can just throw out every chemistry textbook in the world.

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.

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.

They're known as fast radio bursts or FRBs.

Some FRBs don't repeat, they're one and done.

You're talking about an incredible amount of energy

released in less than a second, then it's over.

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.

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.

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.

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.

Those screams are the fast radio bursts.

This could be the most difficult childbirth in the cosmos.

Few suspected that white dwarfs could create something as violent as a magnetar.

But, in 2015,

astronomers found yet another strange magnetic white dwarf,

in a binary system called AR Scorpii.

We don't really know why white dwarfs become magnetic.

But what we do know is the ones that tend to be the most magnetic are often the heaviest.

One possibility is there's a big star

that has come to the end of its life and shrunk down into a white dwarf.

And if that star had its own magnetic field, as it shrinks down,

it actually has a kind of concentrating effect

and the magnetic field gets even stronger as that happens,

so it's incredibly strong.

As well as being very magnetic,

AR Scorpii's white dwarf is spinning very fast.

When you combine a fast spin with a strong magnetic field,

what you get is some really crazy physics.

The white dwarf starts to act a bit like a lighthouse,

sending out intense radiation into the cosmos.

As the white dwarf spins, this beam of radiation

hits its red dwarf neighbour, making it glow.

This is highly unusual. No other system glows like this.

White dwarfs like this can help reveal some of the mysteries of magnetism.

When you have a magnetic field that is this strong,

it's something like 100,000 times stronger than any magnetic field

than we can create here on Earth,

it means that by studying what's going on in this very remote system,

you're actually learning something about physics

that you could never learn here on Earth.

White dwarfs are emerging from out of the shadows,

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.

White dwarfs can sort of be seen as these underdogs of the universe.

It's really become an exciting and cutting-edge area of research.

Now we think these objects may have

a lot of exciting science to deliver.

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.

Discount these things at your own risk, because they're one

of the driving forces in the universe.

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

Don't underestimate a white dwarf.

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