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How Neutron Stars are Created | How The Universe Works | Science Channel - Video học tiếng Anh
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How Neutron Stars are Created | How The Universe Works | Science Channel
How Neutron Stars are Created | How The Universe Works | Science Channel
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Phụ đề (108)
0:05
Neutron stars.
0:07
Manhattan sized, but with a mass twice that of our sun.
0:14
So dense.
0:15
A teaspoon of their matter weighs a billion tons.
0:20
Mind blowing objects that arrive with a bang.
0:24
Neutron stars spark into life amid the death of their parent star.
0:28
They are the ultimate story of resurrection or of life from death.
0:34
It's all part of a cosmic cycle.
0:37
Stars are born from giant clouds of very cold gas.
0:42
Those clouds collapse under their own gravity, and the density of the core at the
0:47
center of that collapse starts to increase.
0:54
A star is a huge nuclear fusion reactor.
0:58
The force of its gravity is so powerful that it fuses atoms together to make progressively
1:04
heavier and heavier elements.
1:08
The star fuses hydrogen into helium once it exhausts its hydrogen.
1:13
Then, if it's massive enough, it can start fusing helium at its core.
1:19
Fusion continues forming carbon, oxygen, nitrogen all the way up to iron.
1:28
Once the star has iron in the core, it's almost like you've poisoned it, because this
1:33
extinguishes the nuclear reactions in the core of the star.
1:37
You fuse something into iron and you get no energy.
1:41
All of a sudden, there's nothing to support.
1:43
The crush of gravity.
1:44
No radiation pressure.
1:45
Pushing out means no pressure keeping the outer regions from falling in.
1:50
And that's what they do.
1:52
As the star collapses in its death throes, its core becomes the wildest, craziest, and
1:59
freakiest pressure cooker in the whole universe.
2:05
The ingredients are all in place.
2:07
Time to start cooking up a neutron star.
2:12
If we were to scale up an atomic nucleus to be the size of a baseball in a normal atom,
2:18
the nearest electron would be way over in those trees.
2:23
But in the extreme conditions that lead to the formation of a neutron star, those
2:28
electrons can be pushed closer to the nucleus.
2:31
They can come zipping in from any direction, and if the temperatures and pressures are
2:36
high enough, they can even strike the nucleus and enter it and they can hit a
2:41
proton. And when they do, they become converted into more neutrons.
2:46
So in the formation of one of these objects, the protons and electrons disappear and
2:52
you're left with almost entirely pure neutrons, with nothing to stop them from
2:56
cramming together and filling up this entire baseball with neutrons, leading to incredibly
3:03
high densities.
3:05
With the sea of electrons now absorbed into the atomic nuclei, the matter in the stars
3:11
can now press together a lot tighter.
3:15
It's like squeezing 300 million tons of mass into a single sugar cube.
3:22
As the star collapses, enormous amounts of gas fall towards the core.
3:29
The core is small in size, but huge in mass.
3:33
Billions of tons of gas bounce off of it, then erupt into the biggest fireworks display
3:39
in the cosmos. A supernova.
3:45
It's massive, it's bright, it's imposing.
3:49
Supernova are among the most dramatic events to happen in the universe.
3:54
The single star dying, one star dying can outshine an entire galaxy.
4:04
And arising out of this cataclysm, a new and very strange cosmic entity.
4:13
When the smoke finally clears from the supernova explosion, you're left with one of
4:17
the most real, fascinating, unbelievable monsters in the entire universe.
4:21
Humans have been witnessing supernovas for thousands of years, but we're only now just
4:26
starting to understand what we've truly been witnessing.
4:30
The births of neutron stars.
4:34
But while supernovas are big and bright, neutron stars are small, and many don't even
4:41
give off light.
4:43
So how many neutron stars are out there?
4:47
We know of about 2000 neutron stars in our galaxy, but there probably are many, many
4:52
more. I'm talking about tens of millions in the Milky Way alone, and certainly billions
4:57
throughout the universe.
5:01
Neutron stars may be small, but some give themselves away shooting beams across the
5:08
universe. Unmistakable pulsing strobes of a cosmic lighthouse.
5:21
Our knowledge of neutron stars is expanding fast.
5:28
But we didn't even know they existed until a lucky discovery just over 50 years ago.
5:35
Cambridge, the Mullard Radio Observatory.
5:38
Jocelyn Bell.
5:39
Grad student operating the new radio telescope, scanning the sky, doing all sorts
5:46
of cool astronomy stuff and sees what she calls a bit of scruff in the data.
5:52
This scruff is a short but constantly repeating burst of radiation originating a
5:59
thousand light years from Earth.
6:01
It's so stable and regular that Bell is convinced there's something wrong with her
6:06
telescope.
6:07
She returns to that spot and finds a repeating regular signal, a single point in
6:15
the sky that is flashing at us, continually saying, hai, hai hai, blip.
6:22
Blip, blip.
6:24
Boom boom boom.
6:26
Pulse pulse pulse.
6:28
Nothing that we know of in the universe has such a steady, perfectly spaced in time
6:33
pulse. It seems so perfect that it must have been artificial.
6:39
It looks like someone is making that.
6:42
But it turns out it's not a person, but a thing.
6:46
What she discovered is called a pulsar.
6:52
A pulsar is a type of rapidly spinning neutron star.
6:59
Neutron stars had been theorized in the 1930s, but were thought to be too faint to be
7:05
detected.
7:06
Neutron stars were hypothesized to exist, but not really taken seriously.
7:14
It was just a oh, that's cute.
7:16
Maybe they're out there, but probably not.
7:20
The signal Bell detected seemed like something from science fiction.
7:26
No one had ever seen this in astronomy before, and some people even speculated that
7:31
it was an alien signal.
7:33
She even called them LGM objects little green men.
7:38
But then Bell found a second signal.
7:43
Little green men went back to being fiction and pulsars became science fact.
7:50
The discovery of pulsars came out of the blue.
7:53
Nobody was expecting this.
7:54
So it was an amazing breakthrough, really important.
8:00
Pulsars pulse because they're born to spin.
8:06
They burst into life as their parents star collapses during a supernova.
8:13
Any object at all that is undergoing any sort of compression event.
8:18
If it has any initial angular momentum at all, it will eventually end up spinning.
8:25
As the star shrinks, it spins faster and faster.
8:31
They spin so quickly because the earth sized core of a massive star collapsed to something
8:38
as small as a city.
8:40
So because the size of the object became so much smaller, the rate of spin had to
8:46
increase by a tremendous amount.
