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White dwarfs.

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Small stars that pack a big punch.

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When white dwarfs were first
discovered,

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the astronomers' reaction was,

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

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

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They're the cooling corpses of stars
like our sun.

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But new research proves white dwarfs
are one of the driving forces of our
universe.

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They eat planets. They flare out
in high-energy light.

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They can really explode.

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And they can tell us literally about
the nature of the universe itself.

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

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

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Have scientists finally discovered
how these small stars

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could be such massive galactic
players?

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December 2018.

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Astronomers spot strange flares
coming from a galaxy

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250 million light-years from Earth.

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GSN 069.

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We know that GSN 069 has
a supermassive black hole
in its centre,

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equal to about half a million times
the mass of the sun.

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That's a big black hole.

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And it blasts out X-rays

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in a very very steady pace,

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every nine hours.

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Why?

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The flares are so energetic and
regular,

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the supermassive black hole
must be eating

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the mass of the planet Mercury

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three times a day.

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The big question is, what's feeding
this black hole such a huge dinner?

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In March 2020, scientists found
the answer.

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An unlucky star
at the end of its life

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had wandered into the death zone of
the black hole.

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A star getting too close to
a supermassive black hole

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is like a glazed doughnut getting
too close to me!

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That thing just is not
gonna make it.

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

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They sort of get attacked by
the black hole.

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

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and jets and streams getting out.

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Somehow, the star survives
its close encounter

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with the supermassive black hole.

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Further investigation reveals it's a
small, compact star. A white dwarf.

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So what makes this tiny star
almost indestructible?

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The answer lies in how it's formed.

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

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It's burning hydrogen into helium.

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That's causing nuclear fusion

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and that causes a star
to stay stable.

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There is this delicate balance
between radiation pressure

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from that nuclear fusion
pushing out

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and gravitational pressure
pulling in.

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

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they run out of hydrogen fuel.

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

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

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crushes the helium core.

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As the core ages,
it gets smaller and hotter,

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which increases the rate of
nuclear reactions.

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These nuclear fusion reactions
produce more energy,

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which pushes the outer layer
or "envelope" outwards.

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Because there's more energy flowing
through the envelope,

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the envelope swells up.

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The star expands to around 100 times
its original size.

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The yellow star becomes a red giant.

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Eventually, red giants shed
their outer layers,

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forming stunning gas shells
called "planetary nebulas".

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Planetary nebulae are the most
beautiful objects in space.

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They're all spectacular.

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

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leaves behind a white dwarf at the
centre.

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This white dwarf is, essentially,
a cinder, a stellar cinder.

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It's what's left after nuclear
fusion is no longer possible for
that particular star.

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All that remains is a glowing
white dwarf.

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The leftover core of the dead star.

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But in Galaxy GSN 069,

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the supermassive black hole
turbocharged the process.

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It stripped off the outer layers of
the red giant in a matter of days.

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

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all the easy to get at
parts of the star.

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

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

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

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

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

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It turns out it's quite
the opposite.

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

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

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but because it's such a dense,
tight ball of matter, it survives.

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Imagine taking the sun
and crushing it down

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to just about the size of the Earth.

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The same mass, but now packed
way more tightly.

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So a basketball-worth of this stuff

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would weigh as much as
35 blue whales.

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The white dwarf's extreme density
protects it

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from the gravitational onslaught of
the supermassive black hole.

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

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Every time it encounters the black
hole, some of its material gets
sipped off.

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They're playing a game of
interstellar tug-of-war
with one another.

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

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

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

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

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for billions of years.

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Talk about David and Goliath.

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When astronomers first discovered
white dwarfs, they thought they
shouldn't exist.

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How could something have such
an extreme density

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and not collapse
under its own weight?

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Quantum mechanics, the science of
atomic and sub-atomic particles,

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has the answer.

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We're used to the rules of physics
up here in the macroscopic world,

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but when you zoom down into the
subatomic world, things get weird.

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Here we have the electron.

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One of the tiniest particles
in the universe.

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And it's these little electrons

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that are doing the work of
supporting an entire star.

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Electrons really don't like being
squashed into a small space.

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

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they'll push back really hard and
this an effect called "degeneracy
pressure".

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These degenerate electrons stop
white dwarfs from collapsing.

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But they give these stars
strange qualities.

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White dwarfs behave very differently
than normal matter.

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Take planets and stars.

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They become bigger
when they gain mass.

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White dwarfs are the exact opposite.

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As they gain mass, they get smaller.

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The more massive a white dwarf,

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the tighter the electrons squeeze
together

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and the smaller and denser
the star gets.

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The high-density means the white
dwarf's structure is also strange.

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It has an extremely thin atmosphere
made of hydrogen

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or, occasionally, helium gas.

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If you were to take an Earth's
skyscraper

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and put it on a white dwarf star,
if you climb to the top of

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that skyscraper, you'd be outside of
the white dwarf's atmosphere,
you'd actually be in space.

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

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It surrounds an interior

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made of super-heated
liquid carbon and oxygen.

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A white dwarf at its surface can be
a half a million degrees.

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It's even hotter in the interior.

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And so, that kind of material,

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

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Eventually, over billions of years,

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

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

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Diamonds are actually
crystals of carbon.

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

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White dwarfs gradually give off
their remaining energy,

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

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A black dwarf.

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

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There's a simple reason for that.

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It takes a tremendous
amount of time,

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many tens of billions of years,

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longer than the age of the universe,
to reach that point.

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This is the dark destiny of most
mid-sized stars, including our sun.

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

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But these tiny stars could answer
some big questions about
our universe.

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They might be small
and they might be dim,

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but they are essential for
our understanding of physics.

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New research into white dwarfs
may answer

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one of the biggest questions of all.

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Can life survive the death of
its star?

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In the past, we've underestimated
white dwarfs.

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But now they're causing a buzz
among astronomers.

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One of the big questions over the
last decade is could a planet

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survive around a white dwarf?

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The logical answer would be no.

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On their way to becoming white
dwarfs, stars evolve through
a red-giant phase.

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They expand to become very huge.

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So we figured any planets around
these stars might just get eaten.

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In December 2019, evidence from
the constellation of Cancer

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turned that idea on its head.

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Astronomers spotted a strange-looking
white dwarf

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about 1,500 light-years from Earth.

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Subtle variations in light
from the star revealed a mystery.

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The elements oxygen and sulphur

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

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We know what the chemical signature
for a white dwarf is

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and this stuck out
like a sore thumb.

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

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Oxygen and sulphur are heavier than
hydrogen and helium.

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

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So they must have gotten there
recently.

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Using ESO's very large telescope
in Chile,

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the astronomers took a closer look.

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They discovered a small Earth-sized
white dwarf,

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surrounded by a huge gas disc,

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roughly ten times
the width of the sun.

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The disc contained hydrogen, oxygen
and sulphur.

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A system like this had never been
seen before.

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So the next step was to look at
a profile of these elements

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and figure out where we'd seen
something similar.

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And the amazing thing is we have.

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

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of our solar system,
Uranus and Neptune.

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Hidden in the gas ring is a giant,
Neptune-like, icy planet.

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It's twice as large as the star.

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But the fierce 50,000 degree heat
from the white dwarf

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is slowly evaporating
this orbiting planet.

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The white dwarf is bombarding
the planet

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

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It's pulverising the ice molecules
in its atmosphere

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and blowing them out into space.

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

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00:12:38,960 --> 00:12:44,360
The icy planet loses mass at a rate
of over 500,000 tons per second.

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00:12:44,440 --> 00:12:48,680
That's the equivalent of 300 aircraft
carriers every minute.

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00:12:48,760 --> 00:12:52,280
It sounds like that could be
curtains for the planet,

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

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As it cools, it will start blasting
the planet so intently and that
stream of gas will cease.

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00:13:02,040 --> 00:13:06,360
The planet will probably end up
losing only a few percent of
its total mass.

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00:13:06,440 --> 00:13:11,000
So the planet should survive and
continue orbiting the white dwarf.

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00:13:12,880 --> 00:13:14,880
But a mystery remains.

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00:13:14,960 --> 00:13:17,840
Why didn't the closely-orbiting
planet die,

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00:13:17,920 --> 00:13:20,320
when the star swelled to a red giant?

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It had to have started farther out
and moved inwards.

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Our best guess is that other
ice giants were probably lurking

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somewhere in the outer regions
of the system

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and knocked that planet inwards,

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towards the white dwarf, some time
after the red-giant phase,

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00:13:38,760 --> 00:13:41,600
in some kind of cosmic pool game,
if you will.

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

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00:13:46,960 --> 00:13:49,960
About 570 light-years from Earth,

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

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00:13:56,800 --> 00:13:59,520
After studying the star
for five years,

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researchers report that
the white dwarf is ripping apart

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00:14:03,600 --> 00:14:05,880
and eating a mini rocky planet.

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00:14:05,960 --> 00:14:10,520
So, as the planet is being torn up,
we see this huge cloud of dust,

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blocking out 50% of the light
of the star

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00:14:12,960 --> 00:14:15,880
and huge chunks of rock
passing in front of the star.

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00:14:15,960 --> 00:14:17,720
It's exciting to see

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00:14:17,800 --> 00:14:19,800
this planet being torn apart,

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00:14:19,880 --> 00:14:22,920
because it's not often
that we get to see an event,

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we get to see something
in the process,

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00:14:25,280 --> 00:14:27,600
that we can observe
and we can learn from.

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00:14:30,000 --> 00:14:33,880
There's more and more evidence that
planetary systems can survive

238
00:14:33,960 --> 00:14:37,360
the death of their star and
the formation of a white dwarf.

239
00:14:37,440 --> 00:14:40,640
It just depends on the planet's
composition

240
00:14:40,720 --> 00:14:42,720
and location.

241
00:14:42,800 --> 00:14:47,160
The distance from the planet to
the star is a critical factor.

242
00:14:47,240 --> 00:14:51,800
As you move farther and farther out
from a star, the intensity

243
00:14:51,880 --> 00:14:54,360
of that solar radiation decreases.

244
00:14:54,440 --> 00:14:57,680
So, the farther you go out,
the less heat you have,

245
00:14:57,760 --> 00:15:01,840
the less high-energy particles are
reaching the surface of that planet.

246
00:15:02,920 --> 00:15:05,960
Also, rocky planets can survive
better than gas giants.

247
00:15:06,040 --> 00:15:08,600
Rocky planets can hold onto
their stuff better,

248
00:15:08,680 --> 00:15:11,120
whereas gas can be blown away
much more easily.

249
00:15:13,160 --> 00:15:18,560
These new discoveries raise questions
about habitability around stars.

250
00:15:18,640 --> 00:15:21,480
Could white-dwarf systems
support life?

251
00:15:21,560 --> 00:15:27,320
If we limit ourselves to only
looking for life on planets
orbiting stars, like our sun,

252
00:15:27,400 --> 00:15:30,640
we would be doing ourselves
a huge disservice.

253
00:15:30,720 --> 00:15:34,680
Far more important, is to look
for, around whatever star,

254
00:15:34,760 --> 00:15:37,680
the habitable zone,
the Goldilocks Zone,

255
00:15:37,760 --> 00:15:41,800
the region around a star
where a planet could support life.

256
00:15:43,000 --> 00:15:45,320
When it comes to supporting life,

257
00:15:45,400 --> 00:15:48,720
white dwarfs have some surprising
advantages.

258
00:15:48,800 --> 00:15:51,680
Even though there's no fusion
happening,

259
00:15:51,760 --> 00:15:53,960
they have all of this internal
energy stored up

260
00:15:54,040 --> 00:15:56,920
that they release, that warms
the nearby planets.

261
00:15:57,000 --> 00:16:00,880
Life might even prefer hanging out
around a white dwarf,

262
00:16:00,960 --> 00:16:05,680
because it doesn't change much over
the course of billions of years.

263
00:16:05,760 --> 00:16:10,080
With something like our sun, there
are flares and coronal-mass
ejections.

264
00:16:10,160 --> 00:16:13,480
Eventually, it's gonna die
and we have to deal with that.

265
00:16:13,560 --> 00:16:16,560
That's not a problem
with the white dwarf.

266
00:16:16,640 --> 00:16:19,120
So, if life can gain a foothold,

267
00:16:19,200 --> 00:16:21,480
it has a nice stable home.

268
00:16:23,560 --> 00:16:28,520
We now think 25% to 50% of white
dwarfs have planetary systems.

269
00:16:28,600 --> 00:16:32,480
Perhaps, one day, we'll find one
with an Earth-like planet

270
00:16:32,560 --> 00:16:34,560
and maybe even life.

271
00:16:38,560 --> 00:16:42,320
White dwarfs are the dead remains of
stars like the sun.

272
00:16:44,000 --> 00:16:46,000
Most of these "zombie" stars

273
00:16:46,080 --> 00:16:48,560
slowly cool down
over billions of years.

274
00:16:50,640 --> 00:16:52,640
Most, but not all.

275
00:16:55,800 --> 00:16:58,720
Some go out in a spectacular
explosion

276
00:16:58,800 --> 00:17:01,000
known as a Type Ia supernova.

277
00:17:02,480 --> 00:17:08,320
A Type Ia supernova is one of the
most violent, powerful, energetic
events in the universe.

278
00:17:08,400 --> 00:17:11,160
We are talking about a star
exploding.

279
00:17:11,240 --> 00:17:13,560
They can outshine entire galaxies.

280
00:17:13,640 --> 00:17:17,800
They can create devastation over
hundreds and hundreds of
light-years.

281
00:17:17,880 --> 00:17:19,680
They're a big deal.

282
00:17:22,000 --> 00:17:25,120
We'd seen the aftermath of these
cosmic fireworks,

283
00:17:25,200 --> 00:17:26,920
but, for over 60 years,

284
00:17:27,000 --> 00:17:31,000
we had little direct evidence
they came from white dwarfs.

285
00:17:31,080 --> 00:17:35,800
Then, students from University
College, London, UK, got lucky.

286
00:17:37,640 --> 00:17:42,440
While taking routine photographs,
they spotted a supernova explosion

287
00:17:42,520 --> 00:17:44,760
in our own cosmic neighbourhood.

288
00:17:46,000 --> 00:17:50,560
M82, the Cigar Galaxy, is actually
really close to us on cosmic terms.

289
00:17:50,640 --> 00:17:53,160
It's only about 12 million
light-years away.

290
00:17:53,240 --> 00:17:56,560
This makes it one of the closest
galaxies in the sky.

291
00:17:56,640 --> 00:18:02,240
- The blast called Supernova 2014
- J was
the closest Type Ia supernova

292
00:18:02,320 --> 00:18:04,320
for over 20 years.

293
00:18:04,400 --> 00:18:07,640
Its proximity allowed us
to look for the signature

294
00:18:07,720 --> 00:18:09,720
of a white dwarf supernova.

295
00:18:10,840 --> 00:18:12,840
A blast of gamma rays.

296
00:18:12,920 --> 00:18:17,600
Gamma rays are a type of light
that's incredibly energetic.

297
00:18:17,680 --> 00:18:22,880
They're the most energetic type of
rays or photons on the
electromagnetic spectrum.

298
00:18:22,960 --> 00:18:27,120
White dwarfs should release
gamma rays when they explode.

299
00:18:28,200 --> 00:18:31,680
But dust in interstellar space
soaks up the rays.

300
00:18:32,760 --> 00:18:36,800
So unless an explosion is close by,
they're hard to detect.

301
00:18:36,880 --> 00:18:40,080
For years, astronomers had been
looking for the gamma rays

302
00:18:40,160 --> 00:18:44,040
that should be emitted by a Type Ia
supernova, but no-one had found
them.

303
00:18:46,280 --> 00:18:48,560
Now, scientists had their chance

304
00:18:48,640 --> 00:18:51,240
and the technology
to see the elusive rays.

305
00:18:53,160 --> 00:18:55,160
Using ESA's INTEGRAL satellite,

306
00:18:55,240 --> 00:18:59,600
they sifted through the shockwaves
sent out by the explosion in M82.

307
00:18:59,680 --> 00:19:02,960
It was tough, but finally
they got a reading.

308
00:19:03,040 --> 00:19:05,640
The tell-tale signal of gamma rays.

309
00:19:05,720 --> 00:19:07,720
It's the best evidence yet

310
00:19:07,800 --> 00:19:11,800
for white dwarfs exploding in
Type Ia supernovas.

311
00:19:12,880 --> 00:19:17,280
- The reason Supernova 2014
- J was
so cool is that this observation

312
00:19:17,360 --> 00:19:20,960
gave scientists the evidence
white dwarfs would explode

313
00:19:21,040 --> 00:19:23,840
to create this specific type of
supernova.

314
00:19:23,920 --> 00:19:26,120
So, which white dwarfs fade out?

315
00:19:26,200 --> 00:19:28,400
And which ones go out with a bang?

316
00:19:31,920 --> 00:19:37,040
A survey of stars revealed around
30% of white dwarfs live in
binary systems.

317
00:19:38,040 --> 00:19:40,920
But white dwarfs are not good
neighbours.

318
00:19:41,000 --> 00:19:44,280
A white dwarf in a binary system,
it's like a zombie.

319
00:19:44,360 --> 00:19:47,320
It's the corpse of a star
that used to be alive,

320
00:19:47,400 --> 00:19:51,440
but now it is eating the material
from a star that is still alive.

321
00:19:51,520 --> 00:19:54,000
They very literally
suck the material

322
00:19:54,080 --> 00:19:56,280
and suck the life out of that star,

323
00:19:56,360 --> 00:19:58,680
by swallowing up
all of its outer layers.

324
00:20:00,160 --> 00:20:03,520
The white dwarf zombie tendencies
can backfire.

325
00:20:04,600 --> 00:20:07,400
Adding mass
to a white dwarf is like this.

326
00:20:07,480 --> 00:20:09,480
We keep adding mass

327
00:20:09,560 --> 00:20:11,760
from that companion star.

328
00:20:12,840 --> 00:20:15,520
A little bit of hydrogen at a time,

329
00:20:15,600 --> 00:20:19,200
building up that atmosphere
and, for a long time,

330
00:20:19,280 --> 00:20:21,280
everything's fine.

331
00:20:21,360 --> 00:20:23,560
Until you add too much mass

332
00:20:23,640 --> 00:20:26,440
and you reach that critical
threshold and then...

333
00:20:31,160 --> 00:20:36,160
The real-world consequences of
reaching the threshold are
devastating.

334
00:20:36,240 --> 00:20:39,960
The extra weight of gas stolen
from the companion star

335
00:20:40,040 --> 00:20:43,760
compresses carbon deep in the core
of the white dwarf.

336
00:20:45,000 --> 00:20:48,720
When the white dwarf reaches
1.4 times the mass of our sun,

337
00:20:48,800 --> 00:20:52,960
it hits a tipping point known as
"the Chandrasekhar Limit".

338
00:20:53,040 --> 00:20:55,720
You add up the mass,
little by little by little,

339
00:20:55,800 --> 00:20:58,120
till you get to that
Chandrasekhar Limit

340
00:20:58,200 --> 00:21:00,200
and then blam, there's a supernova.

341
00:21:00,280 --> 00:21:03,400
In a flash, carbon undergoes
nuclear fusion,

342
00:21:03,480 --> 00:21:06,360
releasing a tremendous amount
of energy.

343
00:21:08,520 --> 00:21:11,720
If the white dwarf explodes at
the Chandrasekhar Limit,

344
00:21:11,800 --> 00:21:13,600
it's a little bit like fireworks

345
00:21:13,680 --> 00:21:16,080
that all have the same amount of
gunpowder.

346
00:21:16,160 --> 00:21:19,440
They'll all go off in the same way,
they'll be equally loud.

347
00:21:19,520 --> 00:21:22,120
Well, the supernovas will be
equally bright.

348
00:21:23,200 --> 00:21:26,760
This equal brightness
of all Type Ia supernovas

349
00:21:26,840 --> 00:21:29,800
is vital to our understanding
of space.

350
00:21:29,880 --> 00:21:33,040
Type Ias are known as
"standard candles"

351
00:21:33,120 --> 00:21:37,680
and are useful tools for calculating
vast cosmic distances.

352
00:21:37,760 --> 00:21:41,920
They were the key to the Nobel
Prize-winning discovery that

353
00:21:42,000 --> 00:21:45,320
the expansion of our universe is
accelerating.

354
00:21:45,400 --> 00:21:50,120
But what kind of companion star
triggers Type Ia supernovas?

355
00:21:51,960 --> 00:21:56,040
For decades, the number one suspect
was red-giant stars.

356
00:21:56,120 --> 00:22:00,880
A red giant is a good candidate,
because it's a very big, puffy star.

357
00:22:00,960 --> 00:22:05,120
That material becomes easy pickings
for the white dwarf to siphon off,

358
00:22:05,200 --> 00:22:07,360
until it gets big enough to explode.

359
00:22:08,440 --> 00:22:11,840
To prove the theory, we needed
to find evidence in the debris

360
00:22:11,920 --> 00:22:13,920
left behind after a supernova.

361
00:22:15,000 --> 00:22:18,000
Stars are surprisingly hardy
objects.

362
00:22:18,080 --> 00:22:20,840
They can survive an explosion
of a nearby star.

363
00:22:20,920 --> 00:22:23,960
Some of these companion stars should
still be there.

364
00:22:24,040 --> 00:22:27,320
A lot of 'em will be worse for wear,
but they'll still exist.

365
00:22:28,440 --> 00:22:33,000
Scientists search through the remains
of 70 Type Ia supernovas.

366
00:22:34,440 --> 00:22:39,080
Only one blast zone contained
the glowing remains of a red giant.

367
00:22:39,160 --> 00:22:44,160
The fact that we've only found
maybe this one example
suggests that, actually,

368
00:22:44,240 --> 00:22:47,320
they're not quite
the serial killers we thought.

369
00:22:47,400 --> 00:22:53,160
It's probably likely that this is
the minority of these types of
supernova explosions.

370
00:22:53,240 --> 00:22:56,520
Indeed, we now think that only
a small fraction

371
00:22:56,600 --> 00:23:00,200
of these white dwarf supernovas
involve a red giant.

372
00:23:00,280 --> 00:23:04,440
Despite the fact that, in the
standard textbooks for decades,

373
00:23:04,520 --> 00:23:06,600
that was the preferred explanation.

374
00:23:08,000 --> 00:23:13,520
If red giants don't cause
the majority of Type Ia supernovas,
what does?

375
00:23:13,600 --> 00:23:17,200
New evidence suggests
colliding white dwarfs.

376
00:23:17,280 --> 00:23:21,280
Star mergers that could exceed
the Chandrasekhar Limit,

377
00:23:21,360 --> 00:23:24,880
producing explosions
with different brightness,

378
00:23:24,960 --> 00:23:27,840
but if the explosions
vary in brightness,

379
00:23:27,920 --> 00:23:31,000
can they still be used
as standard candles?

380
00:23:31,080 --> 00:23:34,800
If we don't really know
what a Type Ia supernova is,

381
00:23:34,880 --> 00:23:39,560
then when we use them to map out
the universe and the way
the universe is expanding,

382
00:23:39,640 --> 00:23:42,920
we just can't be sure any longer
what it is we're looking at.

383
00:23:43,000 --> 00:23:47,080
If we're wrong about that,
then we're wrong about
so many other things.

384
00:23:47,160 --> 00:23:49,640
Our whole model of the universe
falls apart.

385
00:23:49,720 --> 00:23:53,000
Is our understanding of the cosmos
completely wrong?

386
00:24:01,080 --> 00:24:04,840
White dwarfs explode in spectacular
Type Ia supernovas.

387
00:24:05,920 --> 00:24:09,120
They're a crucial tool for measuring
the universe,

388
00:24:09,200 --> 00:24:11,200
but there is a problem.

389
00:24:12,600 --> 00:24:19,040
The standard model says that
white dwarfs gradually steal mass
from a red-giant star.

390
00:24:19,120 --> 00:24:23,600
Until they reach a tipping point
called the Chandrasekhar Limit.

391
00:24:24,680 --> 00:24:28,280
But recent observations prove
this doesn't explain

392
00:24:28,360 --> 00:24:30,760
how most Type Ia supernovas occur.

393
00:24:32,280 --> 00:24:35,920
The majority of Type Ia explosions
remain a mystery.

394
00:24:36,000 --> 00:24:39,520
We call the explosions from
white dwarfs "standard candles",

395
00:24:39,600 --> 00:24:44,000
but they're really not that
standard, there's different types of
explosions.

396
00:24:44,080 --> 00:24:48,720
It may be imperative to our
understanding of the entire universe
that we get this straight,

397
00:24:48,800 --> 00:24:52,840
because the reason we think the
expansion rate of the universe is
accelerating,

398
00:24:52,920 --> 00:24:56,160
it's based on the brightness of
Type I supernovas all being
the same.

399
00:24:56,240 --> 00:24:57,760
Maybe that's not the case.

400
00:24:57,840 --> 00:25:01,920
Researchers suspect that
a theoretical type of merger

401
00:25:02,000 --> 00:25:05,760
could be responsible
for more Type Ia supernovas.

402
00:25:05,840 --> 00:25:09,720
The result of two white dwarfs
crashing together.

403
00:25:10,800 --> 00:25:13,080
But this messes with the math.

404
00:25:13,160 --> 00:25:17,320
The Chandrasekhar Limit says
white dwarfs should explode

405
00:25:17,400 --> 00:25:20,360
when they reach 1.4 times
the mass of our sun.

406
00:25:21,600 --> 00:25:24,880
Two white dwarfs colliding
can exceed this mass.

407
00:25:24,960 --> 00:25:27,560
More mass means a bigger bang

408
00:25:27,640 --> 00:25:29,920
and a brighter explosion.

409
00:25:31,480 --> 00:25:35,640
You're not adding gas little by
little, you're adding a whole other
white dwarf.

410
00:25:35,720 --> 00:25:38,480
That will go off. It will look like
a Type I supernova,

411
00:25:38,560 --> 00:25:42,160
but it won't be the standard candle,
it'll be brighter than we expect.

412
00:25:43,240 --> 00:25:46,360
But no white dwarf mergers
have been found,

413
00:25:46,440 --> 00:25:51,040
because detecting one after it
happens is virtually impossible.

414
00:25:51,120 --> 00:25:55,400
If two white dwarfs merge together,
it's almost impossible to tell.

415
00:25:55,480 --> 00:25:59,480
The DNA of the two systems is
all mixed together and it's all
identical.

416
00:25:59,560 --> 00:26:04,280
You can't tell that there was
a separate companion
in the first place.

417
00:26:04,360 --> 00:26:07,800
So, we can't just look
when there's a bright flash.

418
00:26:07,880 --> 00:26:11,720
We have to go look for the ticking
time bombs in the galaxy.

419
00:26:11,800 --> 00:26:16,120
Astronomers investigating
a strange-shaped cloud of gas

420
00:26:16,200 --> 00:26:18,200
made a breakthrough.

421
00:26:18,280 --> 00:26:22,680
Using ESO's very large telescope,
they focused in on

422
00:26:22,760 --> 00:26:27,400
a planetary nebula
called Henize 2-428.

423
00:26:27,480 --> 00:26:29,960
Planetary nebulas are normally
symmetric,

424
00:26:30,040 --> 00:26:33,360
because red giants shed
their outer layers evenly,

425
00:26:33,440 --> 00:26:35,240
as they become white dwarfs.

426
00:26:36,320 --> 00:26:38,320
But this one is lopsided.

427
00:26:38,400 --> 00:26:43,240
We think, in this case, there might
be the presence of a companion star,

428
00:26:43,320 --> 00:26:48,320
that shapes and twists and sculpts
that planetary nebula.

429
00:26:49,840 --> 00:26:52,880
Researchers peeled back
the gaseous layers

430
00:26:52,960 --> 00:26:55,440
and discovered something shocking.

431
00:26:55,520 --> 00:26:57,520
A two-star system,

432
00:26:57,600 --> 00:27:02,600
made up of the most massive orbiting
white dwarf pair ever discovered.

433
00:27:04,000 --> 00:27:07,200
Each star is 90% as massive
as our sun.

434
00:27:07,280 --> 00:27:12,440
They're so close together, they take
just four hours to orbit each other

435
00:27:12,520 --> 00:27:14,520
and they're getting closer.

436
00:27:15,720 --> 00:27:19,400
If you've ever seen a car crash
about to happen,

437
00:27:19,480 --> 00:27:23,720
you know that sense of
inevitability, as you witness that.

438
00:27:23,800 --> 00:27:26,560
That's what we're seeing
in this system.

439
00:27:26,640 --> 00:27:29,160
We see these two massive
white dwarfs

440
00:27:29,240 --> 00:27:32,720
spiralling closer and closer
and closer and we know

441
00:27:32,800 --> 00:27:34,600
that disaster is coming.

442
00:27:35,680 --> 00:27:40,000
In around 700 million years, these
stars will merge and explode

443
00:27:40,080 --> 00:27:42,080
in a Type Ia supernova.

444
00:27:46,960 --> 00:27:51,120
Now, thanks to the discovery of
more systems like Henize 2-428,

445
00:27:51,200 --> 00:27:54,400
we think white dwarf collisions
could be responsible

446
00:27:54,480 --> 00:27:57,520
for the majority of
Type Ia supernovas.

447
00:27:59,520 --> 00:28:02,280
Two white dwarfs can merge together

448
00:28:02,360 --> 00:28:06,320
and if the sum of their masses is
greater than 1.4 solar masses,

449
00:28:06,400 --> 00:28:09,080
then you can get
a Super-Chandra Type Ia.

450
00:28:10,160 --> 00:28:14,040
We've now observed nine
Super-Chandra explosions.

451
00:28:14,120 --> 00:28:16,720
And to complicate matters further,

452
00:28:16,800 --> 00:28:20,840
we've spotted another form of
white dwarf supernovas.

453
00:28:20,920 --> 00:28:22,920
Sub-Chandra Type Ias.

454
00:28:24,600 --> 00:28:27,760
These mysterious white dwarfs
that we don't quite understand

455
00:28:27,840 --> 00:28:31,160
die off much quicker than regular
white dwarf supernovas.

456
00:28:33,160 --> 00:28:37,040
The explosions are less violent than
normal Type Ia supernovas

457
00:28:37,120 --> 00:28:39,120
and fade away faster,

458
00:28:39,200 --> 00:28:41,200
but we don't know why.

459
00:28:42,280 --> 00:28:46,560
Maybe it has something to do with
the properties of the star
or the rotation,

460
00:28:46,640 --> 00:28:49,360
but the Chandrasekhar Limit
may not be so exact.

461
00:28:49,440 --> 00:28:51,840
It's kind of a Chandrasekhar Range.

462
00:28:51,920 --> 00:28:56,240
The physics textbooks are now being
sort of rewritten or at least
modified.

463
00:28:56,320 --> 00:29:01,720
We know that not all Type Ia
supernovas come from Chandra-mass
white dwarfs.

464
00:29:02,840 --> 00:29:06,840
There's actually a variety of
Type Ia supernovas,

465
00:29:06,920 --> 00:29:12,320
a variety of white dwarf masses and
configurations that can explode.

466
00:29:13,400 --> 00:29:17,640
These new discoveries mean
researchers now study the chemistry

467
00:29:17,720 --> 00:29:21,880
and duration of Type Ia supernovas,
not just their brightness.

468
00:29:24,280 --> 00:29:26,280
But mysteries remain.

469
00:29:26,360 --> 00:29:30,520
We still don't know what triggers
the actual explosion.

470
00:29:30,760 --> 00:29:33,640
Something has to set off
a supernova.

471
00:29:33,720 --> 00:29:37,680
It's like a sort of tinderbox, this
star is ready to be set alight,

472
00:29:37,760 --> 00:29:41,440
but something has actually got to
set it alight in the first place.

473
00:29:41,520 --> 00:29:44,240
And the question is,
what exactly is doing that?

474
00:29:47,520 --> 00:29:50,640
Our best hope of understanding
white dwarf supernovas

475
00:29:50,720 --> 00:29:52,880
is to run computer simulations,

476
00:29:52,960 --> 00:29:56,680
experimenting with ways to trigger
fusion in the heart of the star.

477
00:29:57,680 --> 00:30:00,680
It turns out you need a spark
to get that fusion going.

478
00:30:00,760 --> 00:30:04,440
Otherwise, the usual failure in
computer models of a supernova is

479
00:30:04,520 --> 00:30:06,520
oop, never saw anything.

480
00:30:07,680 --> 00:30:10,560
We do not understand
what creates the explosion.

481
00:30:10,640 --> 00:30:13,440
We don't know what the mechanism
for that is yet.

482
00:30:13,520 --> 00:30:16,240
While computer simulations are
getting closer,

483
00:30:16,320 --> 00:30:19,320
we still don't fully understand
Type Ia supernovas.

484
00:30:21,520 --> 00:30:25,000
The deeper we investigate,
the more mysteries we uncover.

485
00:30:26,120 --> 00:30:29,560
Like rogue white dwarfs streaking
across the galaxy.

486
00:30:30,640 --> 00:30:33,960
And tiny stars that explode
over and over again.

487
00:30:35,040 --> 00:30:37,040
Can these odd white dwarfs

488
00:30:37,120 --> 00:30:40,520
shed more light on the mystery of
Type Ia supernovas?

489
00:30:44,000 --> 00:30:47,720
White dwarfs are surprisingly
difficult to understand.

490
00:30:49,080 --> 00:30:52,040
They behave in completely
unexpected ways.

491
00:30:54,720 --> 00:30:57,040
But these oddballs may help answer

492
00:30:57,120 --> 00:31:00,640
the remaining questions
about Type Ia supernovas.

493
00:31:00,720 --> 00:31:03,080
These are white dwarfs,
but not as we know them.

494
00:31:04,200 --> 00:31:06,000
2017.

495
00:31:06,080 --> 00:31:08,560
Astronomers spot a rebellious star

496
00:31:08,640 --> 00:31:12,120
raising hell in the Little Dipper
constellation.

497
00:31:13,480 --> 00:31:18,440
It's like a zombie, but this isn't
one shambling down the road, it runs
like Usain Bolt.

498
00:31:18,520 --> 00:31:21,840
This thing is screaming through
the galaxy at a much higher speed

499
00:31:21,920 --> 00:31:23,800
than you'd expect
for a star like it.

500
00:31:25,640 --> 00:31:30,560
The white dwarf called LP 40-365 is
moving incredibly fast

501
00:31:30,640 --> 00:31:33,400
towards the edge of the Milky Way.

502
00:31:33,480 --> 00:31:35,920
It's not the only star
behaving oddly.

503
00:31:37,000 --> 00:31:41,560
In 2019, we spotted three more white
dwarfs racing across the galaxy.

504
00:31:41,640 --> 00:31:46,040
Finding one white dwarf blasting its
way through space is weird enough.

505
00:31:46,120 --> 00:31:50,080
To find three more, that's telling
you that something is going on

506
00:31:50,160 --> 00:31:52,840
and whatever it is that's going on
happens a lot.

507
00:31:53,920 --> 00:31:57,600
So what sent these renegades racing
across the galaxy?

508
00:31:58,840 --> 00:32:04,840
LP 40-365 and these other weird
white dwarfs could be the result of
failed supernovas.

509
00:32:04,920 --> 00:32:08,800
People have theorised that maybe
these things didn't finish
exploding.

510
00:32:08,880 --> 00:32:12,880
If so, we should find some unburnt
fractions wandering around
the galaxy.

511
00:32:14,560 --> 00:32:19,560
In the last 20 years, we have spotted
some unusually dim supernovas,

512
00:32:19,640 --> 00:32:24,200
that could have sent LP 40-365
and friends flying.

513
00:32:24,280 --> 00:32:28,040
So, what looks like happened is
that, in a binary pair,

514
00:32:28,120 --> 00:32:30,520
there was stuff dumping onto
a white dwarf

515
00:32:30,600 --> 00:32:33,080
and we were about to have
a Type I supernova.

516
00:32:33,160 --> 00:32:36,440
But the Type I supernova didn't go
off symmetrically.

517
00:32:36,520 --> 00:32:39,720
Some of it actually exploded
and some of it didn't.

518
00:32:39,800 --> 00:32:42,600
That energy didn't go out
in all directions.

519
00:32:42,680 --> 00:32:45,480
One of the things that occurred is
that these stars

520
00:32:45,560 --> 00:32:48,880
got sent hurling across space
at these incredible speeds.

521
00:32:51,680 --> 00:32:55,640
Stars could be sent flying so fast,
that they're no longer bound by

522
00:32:55,720 --> 00:32:58,520
the gravitational pull
of their home galaxy.

523
00:33:00,920 --> 00:33:04,920
LP 40-365 is known as
a hypervelocity star

524
00:33:05,000 --> 00:33:06,840
and is moving so fast,

525
00:33:06,920 --> 00:33:09,760
it's definitely headed out of
the Milky Way.

526
00:33:13,000 --> 00:33:16,200
We call them Type Iax supernovas.

527
00:33:17,480 --> 00:33:21,800
They could make up between 10% and
30% of Type Ia supernovas.

528
00:33:23,120 --> 00:33:25,640
Many could throw out a runaway star.

529
00:33:26,760 --> 00:33:30,200
But we still don't know why
the supernova fails.

530
00:33:30,280 --> 00:33:36,040
The funny thing about science is
things that fail still teach you
what's going on.

531
00:33:36,120 --> 00:33:39,200
Why are these ones different?
Were they not massive enough?

532
00:33:39,280 --> 00:33:43,520
Too massive? Was the companion star
not feeding them the material
in the right way?

533
00:33:43,600 --> 00:33:48,720
Something happened there to make
these stars not, basically, blow
themselves to bits.

534
00:33:50,000 --> 00:33:53,520
That's telling us something about
the way Type Ias do explode.

535
00:33:55,520 --> 00:34:00,240
It seems that life in a binary star
system can be rough for white dwarfs.

536
00:34:00,320 --> 00:34:03,840
But for some lucky stars,
their lives can be more...

537
00:34:03,920 --> 00:34:05,520
mellow.

538
00:34:05,600 --> 00:34:10,800
Just because a white dwarf has
a normal star companion that it is
stealing material from,

539
00:34:10,880 --> 00:34:14,000
it does not spell a death sentence
for that white dwarf.

540
00:34:15,080 --> 00:34:17,080
February 2013.

541
00:34:17,160 --> 00:34:20,960
Astronomers discover a star
in the Andromeda Galaxy

542
00:34:21,040 --> 00:34:24,560
that flashes over and over
and over again.

543
00:34:24,640 --> 00:34:29,920
With each flare, it shines a million
times brighter than our sun,

544
00:34:30,000 --> 00:34:32,720
before dimming to its normal state.

545
00:34:32,800 --> 00:34:37,360
- It's called M31
- N 2018-12a.

546
00:34:40,040 --> 00:34:44,320
This is not a supernova.
It is its little sibling, a nova.

547
00:34:44,400 --> 00:34:48,960
But what's weird about this one is
that it happens every year.

548
00:34:49,040 --> 00:34:53,240
Astronomers have known for a long
time that there are these cases of

549
00:34:53,320 --> 00:34:55,320
these nova that go off

550
00:34:55,400 --> 00:34:58,920
somewhat regularly, every ten years,
every 100 years,

551
00:34:59,000 --> 00:35:03,200
but finding one that goes off every
year is a remarkable discovery.

552
00:35:04,760 --> 00:35:08,520
Much like supernovas, novas occur in
a close binary system,

553
00:35:08,600 --> 00:35:12,000
where a white dwarf and another star
orbit each other.

554
00:35:14,000 --> 00:35:17,920
The white dwarf pulls in hydrogen
from the companion star.

555
00:35:18,000 --> 00:35:20,120
The gas falls onto its surface.

556
00:35:20,200 --> 00:35:24,680
And so, as that hydrogen piles up,
eventually, it gets to the point

557
00:35:24,760 --> 00:35:28,160
where it can fuse into helium
and goes bang!

558
00:35:30,080 --> 00:35:34,800
In supernovas, fusion happens
deep inside the star's core.

559
00:35:35,880 --> 00:35:39,360
But in novas, fusion only occurs
on the surface.

560
00:35:39,440 --> 00:35:43,600
An explosion flares across
the white dwarf's exterior,

561
00:35:43,680 --> 00:35:46,880
hurling unburned hydrogen
out into space.

562
00:35:47,960 --> 00:35:50,920
The result?
An object called a remnant.

563
00:35:52,000 --> 00:35:56,800
- The remnant from nova M31
- N is
400 light-years wide.

564
00:35:56,880 --> 00:36:02,080
This particular remnant is much
bigger than even supernova remnants.

565
00:36:02,160 --> 00:36:05,960
It's much larger, much denser
and brighter then most normal
remnants are.

566
00:36:06,040 --> 00:36:08,720
But that makes sense, if the star
flares up so often.

567
00:36:08,800 --> 00:36:12,360
Think about the star flaring away
for millions of years.

568
00:36:13,440 --> 00:36:16,120
You build up a gigantic
nova remnant.

569
00:36:16,200 --> 00:36:19,960
The repeating flares explain
the huge size of the remnant.

570
00:36:20,040 --> 00:36:23,440
But why does the nova explode
so frequently?

571
00:36:23,520 --> 00:36:28,320
Classically, we thought that when
a nova went off on the surface

572
00:36:28,400 --> 00:36:30,200
of a white dwarf star,

573
00:36:30,280 --> 00:36:33,880
that the white dwarf star's mass
didn't change very much.

574
00:36:33,960 --> 00:36:35,960
Or maybe it got a little smaller.

575
00:36:36,040 --> 00:36:40,800
Now we think that, after a nova,
the white dwarf gains a bit of mass.

576
00:36:43,000 --> 00:36:48,280
- Recurrent novas, like M31
- N, steal
more mass from their companion star,

577
00:36:48,360 --> 00:36:51,160
than they blow off in each explosion.

578
00:36:51,240 --> 00:36:54,880
Some gain more and more mass,
exploding more frequently,

579
00:36:54,960 --> 00:36:57,960
until they reach
the Chandrasekhar Limit

580
00:36:58,040 --> 00:37:00,520
and go full-on supernova.

581
00:37:01,600 --> 00:37:06,000
- M31
- N may very well be
the missing link that shows us

582
00:37:06,080 --> 00:37:10,800
that some nova systems eventually
become supernova systems.

583
00:37:10,880 --> 00:37:14,000
Working out how novas become
supernovas

584
00:37:14,080 --> 00:37:16,560
and why some supernovas fail...

585
00:37:17,960 --> 00:37:22,680
..might help us understand
what makes white dwarfs explode.

586
00:37:24,680 --> 00:37:26,840
But just when we think
we get a break,

587
00:37:26,920 --> 00:37:29,560
white dwarfs hit us
with another bombshell.

588
00:37:29,640 --> 00:37:31,640
Death rays.

589
00:37:40,000 --> 00:37:43,360
White dwarfs can explode
in violent supernovas.

590
00:37:45,000 --> 00:37:47,680
But that's not their only
deadly trick.

591
00:37:48,680 --> 00:37:51,920
They might also create
the most magnetic

592
00:37:52,000 --> 00:37:55,000
and terrifying beast in the universe.

593
00:37:55,080 --> 00:37:57,080
A magnetar.

594
00:37:58,160 --> 00:38:00,560
Magnetars are scary, they just are.

595
00:38:00,640 --> 00:38:04,360
I mean, it's even in the name.
The word "magnetar" sounds scary.

596
00:38:04,440 --> 00:38:08,840
They are the reigning champion of
the largest magnetic field
in the universe.

597
00:38:10,840 --> 00:38:15,040
The magnetic fields around magnetars
are so strong

598
00:38:15,120 --> 00:38:19,280
that they can stretch
and distort individual atoms.

599
00:38:19,360 --> 00:38:22,760
They can turn an atom into
a long, thin pencil-shape.

600
00:38:22,840 --> 00:38:26,520
Once you start stretching atoms out
into this shape,

601
00:38:26,600 --> 00:38:30,000
they can't bond together
in the usual ways any more.

602
00:38:30,080 --> 00:38:33,600
So you can just throw out every
chemistry textbook in the world.

603
00:38:34,680 --> 00:38:38,600
If an astronaut were unlucky enough
to get close to a magnetar,

604
00:38:38,680 --> 00:38:40,280
say within 600, 700 miles,

605
00:38:40,360 --> 00:38:44,040
the whole body of the astronaut
would be completely obliterated.

606
00:38:44,120 --> 00:38:46,120
They would, more or less, dissolve.

607
00:38:46,200 --> 00:38:49,320
The origin of these fearsome
creatures is a mystery,

608
00:38:49,400 --> 00:38:51,760
but it must be something
very violent.

609
00:38:51,840 --> 00:38:54,640
We think they send out a clue
as they form.

610
00:38:54,720 --> 00:38:56,720
Powerful blasts of energy

611
00:38:56,800 --> 00:38:58,640
shooting across the cosmos.

612
00:38:58,720 --> 00:39:03,280
In the past few decades,
we've noticed these very odd,

613
00:39:03,360 --> 00:39:05,960
very confusing and very brief

614
00:39:06,040 --> 00:39:09,440
flashes of intense radio energy.

615
00:39:09,520 --> 00:39:13,520
They're known as fast radio bursts
or FRBs.

616
00:39:14,600 --> 00:39:17,080
Some FRBs don't repeat,
they're one and done.

617
00:39:17,160 --> 00:39:20,080
You're talking about
an incredible amount of energy

618
00:39:20,160 --> 00:39:22,760
released in less than a second,
then it's over.

619
00:39:22,840 --> 00:39:27,560
Because these non-repeating FRBs are
so powerful, we think they could

620
00:39:27,640 --> 00:39:29,640
come from a huge collision.

621
00:39:29,720 --> 00:39:33,000
The heavier and denser
the objects colliding...

622
00:39:33,080 --> 00:39:35,080
the bigger the bang.

623
00:39:36,640 --> 00:39:40,240
New research suggests
a white dwarf star hitting

624
00:39:40,320 --> 00:39:42,520
a dense, heavy neutron star

625
00:39:42,600 --> 00:39:45,480
could be enough to birth a magnetar,

626
00:39:45,560 --> 00:39:48,560
sending out FRBs in the process.

627
00:39:49,760 --> 00:39:54,560
A neutron star is like
a white dwarf, even more so.

628
00:39:54,640 --> 00:39:58,400
It is the leftover core
of a giant star.

629
00:39:58,480 --> 00:40:02,400
They're effectively giant balls of
neutrons, squeezed together

630
00:40:02,480 --> 00:40:04,600
into things
about the size of a city.

631
00:40:04,680 --> 00:40:06,480
You have a neutron star.

632
00:40:06,560 --> 00:40:09,760
An incredibly nasty, complicated,
exotic object.

633
00:40:09,840 --> 00:40:14,000
And a white dwarf. An incredibly
nasty, ugly, complicated object.

634
00:40:14,080 --> 00:40:16,320
Crashing headlong into each other.

635
00:40:17,640 --> 00:40:20,040
As the two stars orbit more closely,

636
00:40:20,120 --> 00:40:23,480
the neutron star strips gas
from the white dwarf.

637
00:40:24,560 --> 00:40:27,680
This material spirals onto
the neutron star,

638
00:40:27,760 --> 00:40:30,560
causing it to spin faster and faster.

639
00:40:32,560 --> 00:40:36,360
The rapid rotation amplifies
its magnetic fields.

640
00:40:38,000 --> 00:40:40,000
Until the two stars collide.

641
00:40:41,080 --> 00:40:43,960
Creating a very magnetic monster.

642
00:40:44,040 --> 00:40:46,240
A magnetar.

643
00:40:46,320 --> 00:40:49,120
It's a turbulent situation.
You could think of it

644
00:40:49,200 --> 00:40:52,800
as a newborn baby coming into
the world, kicking and screaming.

645
00:40:52,880 --> 00:40:57,600
The turbulence produces a powerful
blast of electromagnetic radiation.

646
00:40:58,800 --> 00:41:02,960
It races out of the collision site
at the speed of light,

647
00:41:03,040 --> 00:41:05,240
until we detect it

648
00:41:05,320 --> 00:41:07,320
as a fast radio burst.

649
00:41:08,400 --> 00:41:13,600
We can hear the screams of agony
from millions of light-years away.

650
00:41:13,680 --> 00:41:17,280
Those screams are
the fast radio bursts.

651
00:41:17,360 --> 00:41:20,440
This could be the most difficult
childbirth in the cosmos.

652
00:41:26,000 --> 00:41:31,600
Few suspected that white dwarfs
could create something as violent
as a magnetar.

653
00:41:34,600 --> 00:41:36,600
But, in 2015,

654
00:41:36,680 --> 00:41:40,680
astronomers found yet another strange
magnetic white dwarf,

655
00:41:40,760 --> 00:41:43,880
in a binary system called AR Scorpii.

656
00:41:43,960 --> 00:41:47,320
We don't really know why
white dwarfs become magnetic.

657
00:41:47,400 --> 00:41:51,960
But what we do know is the ones that
tend to be the most magnetic are
often the heaviest.

658
00:41:53,040 --> 00:41:55,280
One possibility is
there's a big star

659
00:41:55,360 --> 00:41:59,920
that has come to the end of its life
and shrunk down into a white dwarf.

660
00:42:00,000 --> 00:42:04,160
And if that star had its own
magnetic field, as it shrinks down,

661
00:42:04,240 --> 00:42:07,080
it actually has a kind of
concentrating effect

662
00:42:07,160 --> 00:42:10,760
and the magnetic field gets even
stronger as that happens,

663
00:42:10,840 --> 00:42:13,000
so it's incredibly strong.

664
00:42:15,000 --> 00:42:17,280
As well as being very magnetic,

665
00:42:17,360 --> 00:42:20,800
AR Scorpii's white dwarf is spinning
very fast.

666
00:42:22,400 --> 00:42:26,000
When you combine a fast spin
with a strong magnetic field,

667
00:42:26,080 --> 00:42:28,400
what you get is some really crazy
physics.

668
00:42:31,400 --> 00:42:34,400
The white dwarf starts to act
a bit like a lighthouse,

669
00:42:34,480 --> 00:42:37,480
sending out intense radiation
into the cosmos.

670
00:42:38,880 --> 00:42:41,960
As the white dwarf spins,
this beam of radiation

671
00:42:42,040 --> 00:42:45,440
hits its red dwarf neighbour,
making it glow.

672
00:42:48,160 --> 00:42:51,480
This is highly unusual.
No other system glows like this.

673
00:42:54,000 --> 00:42:58,960
White dwarfs like this can help
reveal some of the mysteries of
magnetism.

674
00:42:59,040 --> 00:43:02,240
When you have a magnetic field
that is this strong,

675
00:43:02,320 --> 00:43:06,480
it's something like 100,000 times
stronger than any magnetic field

676
00:43:06,560 --> 00:43:08,760
than we can create here on Earth,

677
00:43:08,840 --> 00:43:13,000
it means that by studying what's
going on in this very remote system,

678
00:43:13,080 --> 00:43:15,960
you're actually learning something
about physics

679
00:43:16,040 --> 00:43:18,360
that you could never learn
here on Earth.

680
00:43:18,440 --> 00:43:22,120
White dwarfs are emerging from out of
the shadows,

681
00:43:22,200 --> 00:43:28,280
taking their rightful place as one of
the most fascinating objects in the
universe.

682
00:43:28,360 --> 00:43:31,560
When we first observed white dwarfs,
they were weird,

683
00:43:31,640 --> 00:43:34,320
they were curious, but just like
a sideshow.

684
00:43:34,400 --> 00:43:38,400
But now white dwarfs are showing us
what they're truly capable of.

685
00:43:38,480 --> 00:43:42,520
White dwarfs can sort of be seen as
these underdogs of the universe.

686
00:43:42,600 --> 00:43:46,760
It's really become an exciting and
cutting-edge area of research.

687
00:43:47,840 --> 00:43:49,920
Now we think these objects
may have

688
00:43:50,000 --> 00:43:52,000
a lot of exciting science
to deliver.

689
00:43:52,080 --> 00:43:56,080
Will the universe expand forever?
What is the ultimate fate
of the universe?

690
00:43:56,160 --> 00:43:59,320
All of that may be waiting for
us inside a white dwarf.

691
00:44:01,400 --> 00:44:04,320
Discount these things at your own
risk, because they're one

692
00:44:04,400 --> 00:44:06,800
of the driving forces
in the universe.

693
00:44:06,880 --> 00:44:09,680
Just because it's little,
it don't mean it ain't bad.

694
00:44:09,760 --> 00:44:11,720
Don't underestimate
a white dwarf.

695
00:44:11,800 --> 00:44:13,800
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