Sous-titres (108)
0:07Manhattan sized, but with a mass twice that
of our sun.
0:15A teaspoon of their matter weighs a billion
tons.
0:20Mind blowing objects that arrive with a
bang.
0:24Neutron stars spark into life amid the death
of their parent star.
0:28They are the ultimate story of resurrection
or of life from death.
0:34It's all part of a cosmic cycle.
0:37Stars are born from giant clouds of very cold
gas.
0:42Those clouds collapse under their own
gravity, and the density of the core at the
0:47center of that collapse starts to increase.
0:54A star is a huge nuclear fusion reactor.
0:58The force of its gravity is so powerful that
it fuses atoms together to make progressively
1:04heavier and heavier elements.
1:08The star fuses hydrogen into helium once it
exhausts its hydrogen.
1:13Then, if it's massive enough, it can start
fusing helium at its core.
1:19Fusion continues forming carbon, oxygen,
nitrogen all the way up to iron.
1:28Once the star has iron in the core, it's
almost like you've poisoned it, because this
1:33extinguishes the nuclear reactions in the
core of the star.
1:37You fuse something into iron and you get no
energy.
1:41All of a sudden, there's nothing to support.
1:43The crush of gravity.
1:44No radiation pressure.
1:45Pushing out means no pressure keeping the
outer regions from falling in.
1:50And that's what they do.
1:52As the star collapses in its death throes,
its core becomes the wildest, craziest, and
1:59freakiest pressure cooker in the whole
universe.
2:05The ingredients are all in place.
2:07Time to start cooking up a neutron star.
2:12If we were to scale up an atomic nucleus to
be the size of a baseball in a normal atom,
2:18the nearest electron would be way over in
those trees.
2:23But in the extreme conditions that lead to
the formation of a neutron star, those
2:28electrons can be pushed closer to the
nucleus.
2:31They can come zipping in from any direction,
and if the temperatures and pressures are
2:36high enough, they can even strike the
nucleus and enter it and they can hit a
2:41proton. And when they do, they become
converted into more neutrons.
2:46So in the formation of one of these objects,
the protons and electrons disappear and
2:52you're left with almost entirely pure
neutrons, with nothing to stop them from
2:56cramming together and filling up this entire
baseball with neutrons, leading to incredibly
3:05With the sea of electrons now absorbed into
the atomic nuclei, the matter in the stars
3:11can now press together a lot tighter.
3:15It's like squeezing 300 million tons of mass
into a single sugar cube.
3:22As the star collapses, enormous amounts of
gas fall towards the core.
3:29The core is small in size, but huge in mass.
3:33Billions of tons of gas bounce off of it,
then erupt into the biggest fireworks display
3:39in the cosmos. A supernova.
3:45It's massive, it's bright, it's imposing.
3:49Supernova are among the most dramatic events
to happen in the universe.
3:54The single star dying, one star dying can
outshine an entire galaxy.
4:04And arising out of this cataclysm, a new and
very strange cosmic entity.
4:13When the smoke finally clears from the
supernova explosion, you're left with one of
4:17the most real, fascinating, unbelievable
monsters in the entire universe.
4:21Humans have been witnessing supernovas for
thousands of years, but we're only now just
4:26starting to understand what we've truly been
witnessing.
4:30The births of neutron stars.
4:34But while supernovas are big and bright,
neutron stars are small, and many don't even
4:43So how many neutron stars are out there?
4:47We know of about 2000 neutron stars in our
galaxy, but there probably are many, many
4:52more. I'm talking about tens of millions in
the Milky Way alone, and certainly billions
4:57throughout the universe.
5:01Neutron stars may be small, but some give
themselves away shooting beams across the
5:08universe. Unmistakable pulsing strobes of a
cosmic lighthouse.
5:21Our knowledge of neutron stars is expanding
fast.
5:28But we didn't even know they existed until a
lucky discovery just over 50 years ago.
5:35Cambridge, the Mullard Radio Observatory.
5:39Grad student operating the new radio
telescope, scanning the sky, doing all sorts
5:46of cool astronomy stuff and sees what she
calls a bit of scruff in the data.
5:52This scruff is a short but constantly
repeating burst of radiation originating a
5:59thousand light years from Earth.
6:01It's so stable and regular that Bell is
convinced there's something wrong with her
6:07She returns to that spot and finds a
repeating regular signal, a single point in
6:15the sky that is flashing at us, continually
saying, hai, hai hai, blip.
6:28Nothing that we know of in the universe has
such a steady, perfectly spaced in time
6:33pulse. It seems so perfect that it must have
been artificial.
6:39It looks like someone is making that.
6:42But it turns out it's not a person, but a
thing.
6:46What she discovered is called a pulsar.
6:52A pulsar is a type of rapidly spinning
neutron star.
6:59Neutron stars had been theorized in the
1930s, but were thought to be too faint to be
7:06Neutron stars were hypothesized to exist, but
not really taken seriously.
7:14It was just a oh, that's cute.
7:16Maybe they're out there, but probably not.
7:20The signal Bell detected seemed like
something from science fiction.
7:26No one had ever seen this in astronomy
before, and some people even speculated that
7:31it was an alien signal.
7:33She even called them LGM objects little green
men.
7:38But then Bell found a second signal.
7:43Little green men went back to being fiction
and pulsars became science fact.
7:50The discovery of pulsars came out of the
blue.
7:53Nobody was expecting this.
7:54So it was an amazing breakthrough, really
important.
8:00Pulsars pulse because they're born to spin.
8:06They burst into life as their parents star
collapses during a supernova.
8:13Any object at all that is undergoing any sort
of compression event.
8:18If it has any initial angular momentum at
all, it will eventually end up spinning.
8:25As the star shrinks, it spins faster and
faster.
8:31They spin so quickly because the earth sized
core of a massive star collapsed to something
8:40So because the size of the object became so
much smaller, the rate of spin had to
8:46increase by a tremendous amount.
