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There's a killer lurking
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in our galaxy, a star ready
to explode into a supernova.
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00:00:11,878 --> 00:00:13,545
These are the most
visually stunning
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00:00:13,646 --> 00:00:15,214
events in the universe.
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00:00:15,315 --> 00:00:18,150
Seen from Earth, it
would have a terrible beauty.
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00:00:18,251 --> 00:00:20,953
But for us, it could be fatal.
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00:00:21,054 --> 00:00:24,390
In a few seconds, it
can release as much energy
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as the sun will over
its entire lifetime.
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00:00:28,094 --> 00:00:31,663
We're trying to hunt
it down, but it's lying low.
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00:00:31,765 --> 00:00:33,899
We haven't seen a
supernova in the Milky Way
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in over 400 years.
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It could be anywhere.
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00:00:41,608 --> 00:00:45,244
It is nearly impossible
to predict where and when
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the next supernova will happen.
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00:00:48,748 --> 00:00:52,718
The hunt is on
to find the next supernova
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00:00:52,819 --> 00:00:55,054
before it finds us.
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-== [ www.OpenSubtitles.org ] ==-
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October 2019, one of the
brightest stars in the sky
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looks dangerously unstable.
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00:01:23,183 --> 00:01:25,484
If you look at the
constellation of Orion,
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one of the shoulders of Orion
is a star that is obviously red.
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This is Betelgeuse.
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I could go into my
backyard and see it.
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You could clearly see that
it was getting dimmer.
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Is this a warning?
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00:01:47,173 --> 00:01:52,544
Is Betelgeuse about to die in
a massive cosmic explosion,
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a supernova?
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00:01:55,315 --> 00:01:58,750
We've been studying this
star for hundreds of years.
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00:01:58,852 --> 00:02:03,155
And one thing we're sure about
is that it's big, very big.
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00:02:05,592 --> 00:02:09,061
Betelgeuse is a massive
star, maybe 15 or 20 times
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00:02:09,162 --> 00:02:10,629
the mass of our sun.
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00:02:10,730 --> 00:02:12,397
And it's near the
end of its life.
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00:02:14,501 --> 00:02:19,037
It is a massive,
enormous, luminous star.
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00:02:19,139 --> 00:02:21,306
And one day, it's
going to go boom.
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00:02:24,444 --> 00:02:28,480
Betelgeuse is on our
list of supernova candidates
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00:02:28,581 --> 00:02:29,815
because of this massive size.
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00:02:32,252 --> 00:02:33,819
The bigger star
they are, actually the
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00:02:33,920 --> 00:02:34,920
shorter the lifespan.
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00:02:38,758 --> 00:02:40,659
The lifespan of a star depends
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00:02:40,760 --> 00:02:43,929
on a delicate balance between
two competing forces...
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00:02:45,365 --> 00:02:49,668
Gravity pulling in and heat
and pressure pushing out.
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00:02:51,137 --> 00:02:54,106
Stars exist because
they're held up.
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00:02:54,207 --> 00:02:56,241
They're not held up by pillars.
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00:02:56,342 --> 00:02:59,111
They're held up by energy
flowing out of the core
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00:02:59,212 --> 00:03:00,846
toward the surface of the star.
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00:03:00,947 --> 00:03:04,183
That stops the
gravitational contraction.
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00:03:04,317 --> 00:03:05,594
Stars get their energy
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00:03:05,618 --> 00:03:08,120
from nuclear fusion
reactions right in the core.
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00:03:08,221 --> 00:03:10,822
And the most basic one is
taking two hydrogen atoms
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00:03:10,924 --> 00:03:12,844
and slamming them together
to form a helium atom.
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00:03:14,227 --> 00:03:16,428
And you might think, OK,
the more hydrogen you have,
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00:03:16,529 --> 00:03:19,431
the more stuff you have, maybe
the longer the start will live.
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00:03:19,532 --> 00:03:22,034
Turns out it's exactly opposite.
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00:03:22,135 --> 00:03:24,469
The reason... gravity.
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00:03:24,571 --> 00:03:27,072
The more mass a star
has, the stronger
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00:03:27,173 --> 00:03:31,009
its gravity, gravity
that crushes its hydrogen
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00:03:31,110 --> 00:03:32,811
atoms closer together.
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00:03:34,280 --> 00:03:35,714
As you crush
things more and more,
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00:03:35,815 --> 00:03:38,283
the temperature gets hotter
and hotter and hotter.
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00:03:38,384 --> 00:03:41,153
And the nuclear fusion
reactions burn faster.
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00:03:41,254 --> 00:03:44,523
So bigger stars burn their
fuel very, very quickly
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00:03:44,624 --> 00:03:45,958
and live short lives.
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00:03:46,059 --> 00:03:48,694
Smaller stars burn their
fuel much more slowly
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00:03:48,795 --> 00:03:50,662
and live long, protracted lives.
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00:03:50,763 --> 00:03:52,764
So when you are a
big star, you live fast
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00:03:52,865 --> 00:03:53,865
and you die young.
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00:04:01,641 --> 00:04:06,612
Betelgeuse burns
brighter than 125,000 suns.
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00:04:06,713 --> 00:04:10,048
But now it's running out
of its hydrogen fuel.
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00:04:10,149 --> 00:04:13,919
So it's burning whatever it
has left just to stay alive.
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00:04:17,457 --> 00:04:20,225
Stars are basically
factories for burning
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00:04:20,326 --> 00:04:21,727
hydrogen into helium.
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00:04:21,828 --> 00:04:23,929
And then, once the
helium is burned,
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00:04:24,030 --> 00:04:27,566
they start burning heavier and
heavier elements, like carbon
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00:04:27,667 --> 00:04:32,004
and nitrogen and oxygen.
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00:04:32,105 --> 00:04:34,873
It's a little like, you
burn something, you get ash.
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00:04:34,974 --> 00:04:36,508
But then if you
crush the ash enough,
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00:04:36,609 --> 00:04:38,377
you could burn it again.
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00:04:38,511 --> 00:04:41,179
And then you crush it some more,
and you can burn it yet again.
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00:04:43,416 --> 00:04:45,256
But this process
can't go on forever.
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00:04:46,986 --> 00:04:51,423
As the size of the atomic nuclei
being fused together grows,
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00:04:51,524 --> 00:04:53,425
the amount of energy
released falls.
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The fuel the star needs to
resist the pull of gravity
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00:04:58,364 --> 00:04:59,364
is running out.
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00:05:00,533 --> 00:05:02,601
Unfortunately,
the amount of energy
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00:05:02,702 --> 00:05:05,737
you can extract by putting
two nuclei together
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00:05:05,838 --> 00:05:10,742
gets smaller and smaller the
bigger the nuclei are until you
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00:05:10,843 --> 00:05:14,613
come to making iron,
and iron, it turns out,
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00:05:14,714 --> 00:05:16,648
is the last thing you
can make that way.
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00:05:16,749 --> 00:05:19,518
The problem with iron
is, when you fuse it,
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00:05:19,619 --> 00:05:21,386
it doesn't make energy.
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00:05:21,487 --> 00:05:22,854
It takes it away.
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00:05:22,955 --> 00:05:26,958
So when the star builds up
that iron core, it's doomed.
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00:05:27,060 --> 00:05:29,995
It can no
longer create energy in its core
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00:05:30,096 --> 00:05:33,198
to flow out toward the
surface strong enough
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00:05:33,299 --> 00:05:34,700
to keep it from collapsing.
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00:05:34,801 --> 00:05:36,601
So collapse is what they do.
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00:05:39,672 --> 00:05:41,406
In a fraction of a second,
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00:05:41,507 --> 00:05:45,477
the star's core collapses
down from the size of a planet
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00:05:45,578 --> 00:05:47,479
to about the size
of a small city.
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00:05:48,881 --> 00:05:51,583
And when that happens,
all hell breaks loose.
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00:05:56,723 --> 00:05:58,323
A huge amount of energy
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00:05:58,424 --> 00:06:00,859
is suddenly released,
which forces
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00:06:00,960 --> 00:06:03,662
the collapsing layers back out.
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00:06:03,763 --> 00:06:08,266
The result... an enormous
explosion we call a supernova.
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00:06:13,139 --> 00:06:14,650
The shockwave from a supernova
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00:06:14,674 --> 00:06:17,542
rips out at thousands
of miles per second.
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00:06:17,643 --> 00:06:19,121
And for a brief period
of time, they're
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00:06:19,145 --> 00:06:20,479
brighter than an entire galaxy.
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00:06:23,549 --> 00:06:26,118
A supernova could
devastate life on Earth.
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00:06:28,721 --> 00:06:32,924
And the evidence can be found
at the bottom of our oceans.
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00:06:34,160 --> 00:06:35,504
There are layers and layers
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00:06:35,528 --> 00:06:36,828
of silt that have built up.
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00:06:36,929 --> 00:06:40,465
And there seem to be a layer,
about 2.6 million years ago,
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that was enriched in a very
strange chemical element,
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00:06:43,302 --> 00:06:45,370
something called iron-60.
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00:06:45,471 --> 00:06:48,373
Iron-60 is a
radioactive isotope of iron,
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00:06:48,474 --> 00:06:51,510
and it doesn't last very long,
just a few million years.
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00:06:51,611 --> 00:06:54,846
And the only place that we
know of that can make iron-60
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00:06:54,947 --> 00:06:57,983
is a supernova in
an exploding star.
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00:07:05,525 --> 00:07:09,161
That means there must have
been a supernova close enough
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00:07:09,262 --> 00:07:12,664
to the Earth within the
past couple of million years
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00:07:12,765 --> 00:07:16,001
to have physically deposited
material on our planet.
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00:07:17,603 --> 00:07:19,371
That freaks me out.
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00:07:21,240 --> 00:07:24,242
The sign of this
shocking assault on our planet
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00:07:24,343 --> 00:07:28,380
is a thin layer of this
very rare type of iron.
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00:07:28,481 --> 00:07:31,817
We find it in the mud
of every ocean floor
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00:07:31,918 --> 00:07:34,753
and always at the same depth.
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00:07:34,854 --> 00:07:37,556
This interstellar dust
must have drenched
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00:07:37,657 --> 00:07:43,295
our world in one enormous
burst 2.6 million years ago.
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00:07:43,396 --> 00:07:44,896
It was a terrible time.
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00:07:44,997 --> 00:07:50,068
A third of large animal species
in the sea suddenly died out.
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00:07:50,169 --> 00:07:51,547
There were some
pretty amazing fish.
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00:07:51,571 --> 00:07:54,139
Probably the most
amazing is the megalodon,
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00:07:54,240 --> 00:07:57,843
a giant shark... teeth the size
of dinner plates and so on.
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00:07:57,944 --> 00:08:00,712
But they went extinct
2.6 million years ago
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00:08:00,813 --> 00:08:02,380
at the end of the Pliocene.
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00:08:02,482 --> 00:08:03,482
What happened?
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00:08:05,985 --> 00:08:08,353
A lot of sea creatures died.
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00:08:08,454 --> 00:08:10,689
And a lot of them were
in shallow waters,
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00:08:10,790 --> 00:08:14,392
whereas deep-water
animals tended to survive.
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00:08:14,494 --> 00:08:16,428
That sounds kind of
like a supernova.
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00:08:16,529 --> 00:08:19,297
That can do things that
would affect our atmosphere,
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00:08:19,398 --> 00:08:21,800
would affect shallow water,
but not deeper water.
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00:08:23,970 --> 00:08:26,805
Supernovas create
huge amounts of cosmic rays.
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00:08:29,242 --> 00:08:30,976
When they crash
into other atoms,
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00:08:31,077 --> 00:08:35,146
they break up and produce
showers of dangerous shrapnel
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00:08:35,248 --> 00:08:36,248
called muons.
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00:08:38,217 --> 00:08:41,520
These charged particles
are similar to electrons,
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00:08:41,621 --> 00:08:43,121
only 200 times heavier.
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00:08:45,057 --> 00:08:48,193
So they penetrate more
deeply and cause more damage.
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00:08:50,229 --> 00:08:52,130
They can pierce
through our atmosphere,
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00:08:52,231 --> 00:08:54,933
pierce through our
skin, get into a cell,
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00:08:55,034 --> 00:08:56,801
and disrupt the DNA.
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00:08:56,903 --> 00:08:59,471
They'll go right through
a mouse but deposit
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00:08:59,572 --> 00:09:01,540
in the body of a larger animal.
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00:09:01,641 --> 00:09:03,808
So the impact on an animal
the size of a megalodon,
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00:09:03,910 --> 00:09:05,410
say, could be pretty extreme.
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00:09:08,014 --> 00:09:12,717
Muons can shatter DNA,
causing mutations and cancer.
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00:09:12,818 --> 00:09:14,819
But their power
weakens as they travel
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00:09:14,921 --> 00:09:17,856
through water, which
may be why only
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00:09:17,957 --> 00:09:19,257
deep sea creatures survived.
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00:09:20,993 --> 00:09:24,062
The extinction really
tells us that we're not
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00:09:24,163 --> 00:09:26,598
separate and apart from
the universe and the goings
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00:09:26,699 --> 00:09:27,732
on up there, right?
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Supernova going off
and things like that...
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OK, it's a pretty light show.
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No.
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00:09:31,938 --> 00:09:34,406
It is a direct impact
to life on Earth and us.
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00:09:36,242 --> 00:09:38,910
So are we in
danger of extinction?
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Is Betelgeuse about to explode?
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00:09:54,794 --> 00:09:57,429
When stars explode
as supernovas,
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they can devastate planets
hundreds of light years away.
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Betelgeuse is about 550
light years from Earth.
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00:10:06,339 --> 00:10:10,141
So, when it dramatically
dimmed in 2019,
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scientists were concerned.
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00:10:14,680 --> 00:10:16,181
But Betelgeuse
has dimmed before.
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Betelgeuse varies
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quite a lot over the years.
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00:10:22,021 --> 00:10:24,255
There are some
cycles, and sometimes
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00:10:24,357 --> 00:10:26,958
these cycles come together,
and you get a deep minimum.
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00:10:28,728 --> 00:10:31,863
So dimming is part
of the star's natural cycle
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as it nears the end of its life.
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00:10:36,002 --> 00:10:39,704
But to get a full picture, we
took Betelgeuse's temperature.
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If the star was dimming, that
would mean that the surface
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00:10:43,743 --> 00:10:45,210
was cooling over time.
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00:10:45,311 --> 00:10:47,589
We actually made measurements
of the temperature of Betelgeuse
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and found out that
wasn't happening.
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It hardly cooled at all.
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It cooled, like,
50 or 100 degrees.
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00:10:53,219 --> 00:10:55,286
You might expect
a much, much more
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00:10:55,388 --> 00:10:57,489
dramatic change in the
surface temperature
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00:10:57,590 --> 00:10:58,710
if it were about to explode.
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00:11:01,827 --> 00:11:04,295
So, if Betelgeuse wasn't cooling
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00:11:04,397 --> 00:11:06,464
much, what was making it dim?
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00:11:08,668 --> 00:11:12,904
To take a closer look, we
used a very large telescope
196
00:11:12,972 --> 00:11:16,141
and an exoplanet
hunting instrument
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00:11:16,242 --> 00:11:20,011
called SPHERE and came up
with an extraordinary image.
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00:11:23,249 --> 00:11:27,218
When I first saw this image
of Betelgeuse, it blew me away.
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00:11:27,319 --> 00:11:28,653
I almost gasped.
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00:11:28,754 --> 00:11:30,955
I may have said a
word I can't say on TV.
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00:11:32,725 --> 00:11:34,025
That was very exciting.
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00:11:35,761 --> 00:11:38,029
The image reveals
that, while the upper part
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00:11:38,130 --> 00:11:41,166
of Betelgeuse was
still bright, the lower
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00:11:41,267 --> 00:11:44,169
part was noticeably dimmer.
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00:11:44,270 --> 00:11:47,072
We had images of
Betelgeuse from before,
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00:11:47,173 --> 00:11:49,474
and we were able to compare
the new ones with it.
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00:11:49,575 --> 00:11:52,343
And so you could see
that half of Betelgeuse
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00:11:52,445 --> 00:11:53,878
looked pretty much the same.
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00:11:53,979 --> 00:11:56,748
But the other half was
significantly dimmer.
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00:11:56,849 --> 00:12:00,018
And what could make a
star dim that quickly?
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00:12:00,119 --> 00:12:02,721
And remember how
big this star is.
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00:12:02,822 --> 00:12:04,956
Nothing happens on
Betelgeuse quickly.
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00:12:05,057 --> 00:12:07,659
So this must be something
happening right on the surface.
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00:12:10,863 --> 00:12:12,797
As heavier
material like silicone
215
00:12:12,898 --> 00:12:16,067
emerges from the
surface of Betelgeuse,
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00:12:16,168 --> 00:12:19,304
it cools and condenses.
217
00:12:19,405 --> 00:12:21,216
It's kind of like sticking
the hose in the wrong end
218
00:12:21,240 --> 00:12:22,307
of your vacuum cleaner.
219
00:12:22,408 --> 00:12:24,219
Instead of pulling stuff in,
220
00:12:24,243 --> 00:12:26,044
it blows all this
dust out into space.
221
00:12:28,481 --> 00:12:31,783
Betelgeuse
has cosmic indigestion
222
00:12:31,884 --> 00:12:36,621
and is belching dust, which
makes the star seem dim.
223
00:12:36,722 --> 00:12:37,722
But it's not over.
224
00:12:39,191 --> 00:12:42,393
All through 2020,
Betelgeuse first brightened
225
00:12:42,495 --> 00:12:44,195
and then dimmed again.
226
00:12:45,998 --> 00:12:50,001
So astronomers are watching this
massive star with bated breath.
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00:12:52,171 --> 00:12:53,471
It's going to explode.
228
00:12:53,572 --> 00:12:55,640
The question is, when?
229
00:12:55,741 --> 00:12:58,376
It's probably sometime
in the next 100,000 years.
230
00:12:58,477 --> 00:12:59,544
But it could be tomorrow.
231
00:12:59,645 --> 00:13:01,189
It could have already
exploded and we're
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00:13:01,213 --> 00:13:03,515
just waiting to see the light.
233
00:13:03,616 --> 00:13:06,751
With luck, if
Betelgeuse blows, all we'll see
234
00:13:06,852 --> 00:13:08,086
is a beautiful light show.
235
00:13:10,656 --> 00:13:13,691
At a distance of
550 light years,
236
00:13:13,793 --> 00:13:16,327
it's probably too far
to do serious damage.
237
00:13:19,031 --> 00:13:22,634
But is there another star
we should worry about?
238
00:13:26,472 --> 00:13:30,408
A closer star, just 150
light years from Earth,
239
00:13:30,509 --> 00:13:34,946
could do us some major
damage, a star like IK Pegasi.
240
00:13:37,416 --> 00:13:40,451
But it isn't this star which
we can see in our night
241
00:13:40,553 --> 00:13:41,986
sky that's the threat.
242
00:13:44,056 --> 00:13:47,659
The main star is only about
1.6 times the mass of the sun.
243
00:13:47,760 --> 00:13:50,161
That's nowhere near enough
mass to go supernova.
244
00:13:50,262 --> 00:13:54,432
And yet, we think it is the
progenitor for a supernova.
245
00:13:54,500 --> 00:13:55,500
How can that be?
246
00:13:56,802 --> 00:13:58,403
The main star isn't alone.
247
00:13:59,805 --> 00:14:02,540
It has a more
dangerous accomplice.
248
00:14:05,411 --> 00:14:08,746
There's another star there
orbiting the larger star.
249
00:14:08,848 --> 00:14:10,826
And this is what
we call a binary system...
250
00:14:10,850 --> 00:14:12,250
Two stars orbiting each other.
251
00:14:13,652 --> 00:14:15,253
Right now, the system is stable.
252
00:14:15,354 --> 00:14:17,499
But things aren't always going
to be the way they are now,
253
00:14:17,523 --> 00:14:20,358
and sometime in
the future, things
254
00:14:20,459 --> 00:14:21,993
are going to change a lot.
255
00:14:24,396 --> 00:14:26,264
IK Pegasi is really made up
256
00:14:26,365 --> 00:14:34,339
of IK Pegasi A, a large white
star, and its accomplice,
257
00:14:34,440 --> 00:14:41,812
a white dwarf called IK
Pegasi B. This tiny star
258
00:14:41,881 --> 00:14:43,248
is the real threat to Earth.
259
00:14:45,217 --> 00:14:49,721
You can think of a
white dwarf as a zombie.
260
00:14:49,822 --> 00:14:53,658
You know, it's a dead star,
and they can eat living stars.
261
00:14:53,759 --> 00:14:57,362
If there's a normal star like
the sun near a white dwarf,
262
00:14:57,463 --> 00:15:00,298
the white dwarf has very,
very intense gravity.
263
00:15:00,399 --> 00:15:03,401
It can literally pull
material off that normal star,
264
00:15:03,502 --> 00:15:06,104
and that material will
then pile up on the surface
265
00:15:06,205 --> 00:15:07,071
of the white dwarf.
266
00:15:07,172 --> 00:15:09,707
So it really is
eating a living star.
267
00:15:12,611 --> 00:15:14,746
These stars
orbit each other just
268
00:15:14,847 --> 00:15:18,049
18.5 million miles apart.
269
00:15:18,150 --> 00:15:21,552
That's closer than
Mercury is to our sun.
270
00:15:21,654 --> 00:15:26,457
But they're not interacting
with each other, yet.
271
00:15:26,558 --> 00:15:28,960
The problem is,
sometime in the future,
272
00:15:29,061 --> 00:15:31,329
that normal star is
going to run out of fuel.
273
00:15:31,430 --> 00:15:34,165
And when it does, it's going
to expand into a red giant.
274
00:15:36,268 --> 00:15:38,169
When it gets
to the end of its life,
275
00:15:38,270 --> 00:15:43,241
IK Pegasi A will cool and
swell up to become a red giant.
276
00:15:45,377 --> 00:15:48,613
And that's it, no big explosion.
277
00:15:48,714 --> 00:15:51,749
It won't become a supernova.
278
00:15:51,850 --> 00:15:57,055
But that's just when it's
accomplice, IK Pegasi B,
279
00:15:57,156 --> 00:15:58,156
will start to feed.
280
00:15:59,992 --> 00:16:02,460
A lot of that material
will gravitationally
281
00:16:02,561 --> 00:16:04,896
be attracted to the white dwarf
and fall under the surface.
282
00:16:06,632 --> 00:16:08,399
As the white
dwarf pulls material
283
00:16:08,500 --> 00:16:10,802
from its bloated
red giant neighbor,
284
00:16:10,903 --> 00:16:12,103
it gets more and more massive.
285
00:16:13,706 --> 00:16:16,441
It's gravitational
pull increases,
286
00:16:16,542 --> 00:16:17,976
so it feeds even faster.
287
00:16:21,880 --> 00:16:24,782
Eventually, it can no longer
support its own weight.
288
00:16:26,919 --> 00:16:29,087
The core of the star
is actually very dense.
289
00:16:29,188 --> 00:16:31,289
In fact, if you had, like,
a teaspoon of material,
290
00:16:31,390 --> 00:16:34,058
it would weigh about as
much as an 18-wheel truck.
291
00:16:34,159 --> 00:16:36,661
And it's basically right at
the limit of normal matter
292
00:16:36,762 --> 00:16:38,863
being able to hold
up at that density.
293
00:16:38,964 --> 00:16:41,132
You dump more and
more stuff onto it,
294
00:16:41,233 --> 00:16:43,568
and eventually there's
a limit that's reached.
295
00:16:43,669 --> 00:16:47,538
And it either collapses
or, more generally, blows up.
296
00:16:53,612 --> 00:16:56,948
When, this
happens IK Pegasi will
297
00:16:57,016 --> 00:17:00,752
be brighter than the
full moon in our sky
298
00:17:00,853 --> 00:17:03,554
because it's only
150 light years away.
299
00:17:07,292 --> 00:17:10,595
Having a supernova 150 light
years sounds like a bad idea,
300
00:17:10,696 --> 00:17:11,696
and it is.
301
00:17:11,730 --> 00:17:13,264
That's close enough
that it might
302
00:17:13,399 --> 00:17:15,199
have some physical
effects on the Earth.
303
00:17:19,038 --> 00:17:21,873
Right now, IK
Pegasi is about as far
304
00:17:21,974 --> 00:17:25,043
from Earth as the
supernova suspected
305
00:17:25,144 --> 00:17:26,511
of killing off the megalodon.
306
00:17:29,281 --> 00:17:31,916
So how worried should we be?
307
00:17:33,919 --> 00:17:36,220
The good news is
the IK Peg system
308
00:17:36,321 --> 00:17:38,489
is moving away from
the sun and the Earth
309
00:17:38,590 --> 00:17:40,892
right now at a decent clip.
310
00:17:40,993 --> 00:17:43,494
So if it's not going to blow
up for a while, that means
311
00:17:43,595 --> 00:17:47,398
it could be on the other side of
the galaxy by the time it does.
312
00:17:47,466 --> 00:17:49,767
By that time, we'll
be completely safe.
313
00:17:49,868 --> 00:17:52,437
As an astronomer and an
astronomer who has studied
314
00:17:52,538 --> 00:17:55,106
supernovas professionally,
having them
315
00:17:55,207 --> 00:17:58,042
far away is fine with me, close
enough that we can study them
316
00:17:58,143 --> 00:18:00,511
well but not so close
that I can study
317
00:18:00,612 --> 00:18:03,314
them personally on a physical
level on my own body.
318
00:18:03,415 --> 00:18:04,415
Yeah, no.
319
00:18:09,688 --> 00:18:12,757
A close supernova
would be devastating for life
320
00:18:12,858 --> 00:18:13,858
on Earth.
321
00:18:14,927 --> 00:18:19,597
Will there be any
warning signs before one
322
00:18:19,698 --> 00:18:22,667
of our prime suspects
is about to blow?
323
00:18:40,119 --> 00:18:42,720
To find a supernova
warning signal,
324
00:18:42,821 --> 00:18:46,424
we need to know what's
happening deep inside the core
325
00:18:46,525 --> 00:18:47,625
of an exploding star.
326
00:18:49,361 --> 00:18:51,796
At the very beginning
of a supernova explosion,
327
00:18:51,897 --> 00:18:54,465
the core of a massive
star is collapsing.
328
00:18:54,533 --> 00:18:56,434
There's no more nuclear
fusion going on,
329
00:18:56,535 --> 00:18:59,170
and it is compressing to
higher and higher densities.
330
00:19:00,706 --> 00:19:02,373
The star's gravity crushes
331
00:19:02,474 --> 00:19:05,510
protons and electrons
so close together
332
00:19:05,611 --> 00:19:07,311
they merge to form neutrons.
333
00:19:09,181 --> 00:19:12,850
The star's core becomes one
of the densest materials
334
00:19:12,951 --> 00:19:14,585
in the universe.
335
00:19:14,686 --> 00:19:17,688
It's like a gigantic
atomic nucleus...
336
00:19:17,789 --> 00:19:22,460
Roughly half a million Earths
compressed into the volume,
337
00:19:22,561 --> 00:19:24,262
the size of a city.
338
00:19:24,363 --> 00:19:27,198
That's really,
really dense stuff.
339
00:19:27,299 --> 00:19:29,367
If you had about a
teaspoon full of material,
340
00:19:29,468 --> 00:19:31,669
that would be about as
much mass as Mount Everest.
341
00:19:36,909 --> 00:19:39,644
Forcing protons
and electrons together
342
00:19:39,745 --> 00:19:42,914
releases a huge amount
of energy in the form
343
00:19:43,015 --> 00:19:47,985
of tiny, elusive, subatomic
particles called neutrinos.
344
00:19:49,755 --> 00:19:51,235
Neutrinos are one
of the most abundant
345
00:19:51,290 --> 00:19:52,423
particles in the universe.
346
00:19:52,524 --> 00:19:54,604
But they don't interact with
things very much at all.
347
00:19:56,795 --> 00:19:59,076
Neutrinos are
often called ghost particles
348
00:19:59,131 --> 00:20:00,665
because they do what ghosts do.
349
00:20:00,766 --> 00:20:02,466
They walk through walls.
350
00:20:02,568 --> 00:20:04,468
But neutrinos walk through us.
351
00:20:04,570 --> 00:20:05,647
They walk through the planet.
352
00:20:05,671 --> 00:20:07,471
They walk through stars.
353
00:20:07,573 --> 00:20:09,140
They're super ghosts.
354
00:20:11,443 --> 00:20:14,011
At first, these
neutrinos can fly straight
355
00:20:14,112 --> 00:20:15,846
out of the core of the star.
356
00:20:15,948 --> 00:20:19,450
But, as the star
collapses, it gets so dense
357
00:20:19,551 --> 00:20:21,752
that some neutrinos
get trapped and
358
00:20:21,853 --> 00:20:25,089
their energy turned into heat.
359
00:20:25,190 --> 00:20:28,392
And that creates a shockwave
that rips the star apart.
360
00:20:28,493 --> 00:20:31,796
And the ensuing explosion is
brighter than billions of stars
361
00:20:31,897 --> 00:20:32,897
all put together.
362
00:20:36,301 --> 00:20:40,471
This light show may
be spectacular, but it's only 1%
363
00:20:40,572 --> 00:20:43,040
of the energy released
in a supernova.
364
00:20:43,141 --> 00:20:47,378
The rest is in the form of a
massive burst of neutrinos.
365
00:20:47,479 --> 00:20:52,550
So neutrinos could act as a
supernova early warning system.
366
00:20:52,651 --> 00:20:54,218
At least that's the idea.
367
00:20:57,422 --> 00:21:02,293
On February 24th, 1987,
that idea was tested.
368
00:21:05,063 --> 00:21:08,032
An astronomer was doing a
routine survey of a dwarf
369
00:21:08,133 --> 00:21:09,734
galaxy close to ours.
370
00:21:12,004 --> 00:21:15,206
He was taking pictures of
it, develops the pictures,
371
00:21:15,307 --> 00:21:17,608
and says, hey,
there's a star here
372
00:21:17,709 --> 00:21:19,710
that wasn't there yesterday.
373
00:21:22,881 --> 00:21:25,516
He basically got up, walked
outside, and looked and went,
374
00:21:25,617 --> 00:21:27,485
oh, there's that star.
375
00:21:27,586 --> 00:21:30,655
And it turns out he had
discovered a supernova.
376
00:21:32,924 --> 00:21:34,502
Because it
was the first supernova
377
00:21:34,526 --> 00:21:41,065
spotted that year, it was
called Supernova 1987A.
378
00:21:41,166 --> 00:21:45,836
1987A a was an amazing event
in the world of astronomy.
379
00:21:45,937 --> 00:21:50,041
Essentially, a supernova
went off in our own backyard.
380
00:21:50,142 --> 00:21:52,209
It was very close to us,
381
00:21:52,311 --> 00:21:55,746
occurring in a neighbor
galaxy of the Milky Way.
382
00:21:55,847 --> 00:21:59,750
And so it was the brightest
thing seen in our skies
383
00:21:59,851 --> 00:22:01,852
since the invention
of the telescope.
384
00:22:04,923 --> 00:22:08,659
Supernova 1987A
blazed with the power
385
00:22:08,760 --> 00:22:10,461
of 100 million suns.
386
00:22:11,797 --> 00:22:14,365
But that wasn't the
most exciting part.
387
00:22:14,466 --> 00:22:17,668
For the first time, we
received an early warning
388
00:22:17,769 --> 00:22:20,938
that a supernova was about
to appear three hours
389
00:22:21,039 --> 00:22:22,940
before it lit up our night sky.
390
00:22:24,409 --> 00:22:27,578
Neutrino observatories
around the world
391
00:22:27,679 --> 00:22:31,515
saw a sudden surge in neutrinos
from the same direction
392
00:22:31,616 --> 00:22:32,616
on the sky.
393
00:22:38,223 --> 00:22:41,759
Neutrinos' ability
to zip across the galaxy,
394
00:22:41,860 --> 00:22:45,062
slipping through stars
and planets like ghosts,
395
00:22:45,163 --> 00:22:48,032
gives them an unbeatable head
start during a supernova.
396
00:22:50,268 --> 00:22:53,938
The neutrinos are released
in the very earliest moments
397
00:22:54,039 --> 00:22:55,473
of this supernova blast.
398
00:22:55,574 --> 00:22:58,709
And they slip through the
atmosphere of the star
399
00:22:58,810 --> 00:23:01,078
before it goes boom.
400
00:23:03,582 --> 00:23:06,717
Neutrinos can escape
in as little as 10 seconds.
401
00:23:08,787 --> 00:23:10,888
But it can take hours
for the shockwave
402
00:23:10,989 --> 00:23:15,192
to travel right through the star
and blast off the outer layers,
403
00:23:15,293 --> 00:23:17,261
revealing the light.
404
00:23:17,362 --> 00:23:19,530
The result is that
we see neutrinos
405
00:23:19,631 --> 00:23:22,633
from a supernova explosion
before we see the actual light.
406
00:23:28,540 --> 00:23:31,642
So if we want to spot the
next supernova explosion,
407
00:23:31,743 --> 00:23:34,645
we've got to be paying
attention to the neutrinos.
408
00:23:38,016 --> 00:23:40,684
Astronomers set
up the SuperNova Early
409
00:23:40,786 --> 00:23:46,190
Warning System, a network
of neutrino detectors
410
00:23:46,291 --> 00:23:47,291
all around the world.
411
00:23:49,361 --> 00:23:51,595
It should give astronomers
several hours notice
412
00:23:51,730 --> 00:23:53,164
of an impending supernova.
413
00:23:56,401 --> 00:23:58,869
But, so far, nothing.
414
00:23:58,970 --> 00:24:01,172
No supernovas have
occurred near enough
415
00:24:01,273 --> 00:24:02,306
for the system to detect.
416
00:24:04,576 --> 00:24:07,411
Neutrinos are like the
friend that never comes.
417
00:24:07,512 --> 00:24:09,079
We're sitting here
waiting for him.
418
00:24:09,181 --> 00:24:11,261
But we don't know when it's
going to actually happen.
419
00:24:14,319 --> 00:24:18,389
But when they do
come, we might be in trouble
420
00:24:18,490 --> 00:24:21,826
because some supernovas are
armed with the most powerful
421
00:24:21,927 --> 00:24:23,227
weapon in the universe...
422
00:24:25,130 --> 00:24:26,130
Gamma rays.
423
00:24:38,076 --> 00:24:41,178
Our hunt for the Milky
Way's next supernova
424
00:24:41,279 --> 00:24:43,514
has identified some
potential suspects...
425
00:24:45,217 --> 00:24:50,888
Very massive, lonely stars and
stars with smaller sidekicks.
426
00:24:53,391 --> 00:24:58,162
In 2018, astronomers
found a system called Apep
427
00:24:58,263 --> 00:25:04,635
8,000 light years away with two
very massive stars, each one
428
00:25:04,736 --> 00:25:06,237
about as massive as Betelgeuse.
429
00:25:08,573 --> 00:25:13,677
These are giant stars
nearing the end of their lives
430
00:25:13,778 --> 00:25:19,083
with massive outer layers of
gas that continually contract
431
00:25:19,184 --> 00:25:21,318
and heat up again and again.
432
00:25:23,054 --> 00:25:24,332
They become really
433
00:25:24,356 --> 00:25:26,957
huge and bloated and
swollen, and they're
434
00:25:27,058 --> 00:25:28,993
prone to huge outbursts.
435
00:25:31,863 --> 00:25:35,900
These unstable stars
are called Wolf-Rayet stars.
436
00:25:39,838 --> 00:25:44,608
They're very rare and so hot and
bright they emit more radiation
437
00:25:44,709 --> 00:25:47,611
than a million sunlike stars.
438
00:25:47,712 --> 00:25:51,348
This intense energy is
blasting their outer layers off
439
00:25:51,449 --> 00:25:52,449
into space.
440
00:25:53,685 --> 00:25:56,587
Mass loss has been
occurring from the star,
441
00:25:56,688 --> 00:26:00,658
so much so that you've
actually lost all the hydrogen
442
00:26:00,759 --> 00:26:03,127
that wasn't burned into helium.
443
00:26:03,228 --> 00:26:06,096
So now you have a star
that's made entirely
444
00:26:06,197 --> 00:26:08,432
of helium and heavier elements.
445
00:26:08,533 --> 00:26:11,168
With no hydrogen
left, these massive stars
446
00:26:11,269 --> 00:26:13,070
are running low on usable fuel.
447
00:26:15,640 --> 00:26:18,208
They're like ticking
time bombs, made
448
00:26:18,310 --> 00:26:22,012
even more dangerous because
they're spinning so fast.
449
00:26:24,049 --> 00:26:26,417
It's spinning so
quickly, it's on the verge
450
00:26:26,518 --> 00:26:28,419
of ripping itself apart.
451
00:26:28,520 --> 00:26:30,955
And this means that,
when this thing blows,
452
00:26:31,056 --> 00:26:32,323
it's going to blow hard.
453
00:26:34,125 --> 00:26:38,395
When a star goes
supernova, its core collapses.
454
00:26:38,496 --> 00:26:40,698
The smaller it gets,
the faster it spins.
455
00:26:42,400 --> 00:26:47,037
Some cores collapse into
fast, spinning neutron stars.
456
00:26:47,138 --> 00:26:51,208
Heavier ones, like Apep,
collapse into even denser
457
00:26:51,309 --> 00:26:52,910
and more mysterious objects...
458
00:26:54,245 --> 00:26:55,245
Black holes.
459
00:26:58,049 --> 00:27:01,385
The immense gravity within
Apep's collapsing core
460
00:27:01,486 --> 00:27:05,689
will drag back some of the gas
and dust into a spinning disk.
461
00:27:08,660 --> 00:27:11,495
As the material
falls on to the core,
462
00:27:11,596 --> 00:27:14,198
it compresses and it speeds up.
463
00:27:15,700 --> 00:27:17,534
The dying star spins faster
464
00:27:17,636 --> 00:27:19,603
and faster as it collapses.
465
00:27:21,473 --> 00:27:25,309
And this incredible
rotation drives the creation
466
00:27:25,410 --> 00:27:29,413
of massive magnetic fields
that are capable of funneling
467
00:27:29,514 --> 00:27:32,983
material around and
up and out in the form
468
00:27:33,084 --> 00:27:35,419
of huge beams of radiation.
469
00:27:38,423 --> 00:27:41,158
So the energy from
the supernova collapse,
470
00:27:41,259 --> 00:27:44,361
instead of being admitted
spherically in every direction,
471
00:27:44,462 --> 00:27:46,930
comes at us in a
tightly focused beam.
472
00:27:48,266 --> 00:27:50,734
Like a laser from
the Death Star,
473
00:27:50,835 --> 00:27:52,803
it is pointed in one direction.
474
00:27:56,174 --> 00:27:58,075
This is a gamma ray burst.
475
00:28:00,178 --> 00:28:02,546
It is the single scariest thing
476
00:28:02,647 --> 00:28:04,515
the universe has to offer.
477
00:28:04,616 --> 00:28:08,719
This is an explosion so
powerful that, in a few seconds
478
00:28:08,820 --> 00:28:11,789
or minutes, it can
release as much energy
479
00:28:11,890 --> 00:28:14,792
as the sun will over
its entire lifetime.
480
00:28:16,528 --> 00:28:20,364
You do not want to get
caught in a gamma ray burst.
481
00:28:20,465 --> 00:28:21,545
Let's just put it that way.
482
00:28:27,372 --> 00:28:29,039
The impact of a nearby gamma ray
483
00:28:29,140 --> 00:28:31,842
burst on our home
planet is almost
484
00:28:31,943 --> 00:28:33,210
too terrible to think about.
485
00:28:34,546 --> 00:28:37,181
It would be a very
bad day for Earth.
486
00:28:40,585 --> 00:28:43,287
Earth's atmosphere could
be partly blown away,
487
00:28:43,388 --> 00:28:44,888
and there could be
chemical reactions
488
00:28:44,989 --> 00:28:46,356
in the atmosphere
that would form
489
00:28:46,458 --> 00:28:48,325
all kinds of noxious products.
490
00:28:51,930 --> 00:28:53,370
A gamma ray burst from Apep
491
00:28:53,431 --> 00:28:56,300
might last only 10
seconds, but its impact
492
00:28:56,434 --> 00:28:57,434
would last for decades.
493
00:28:58,570 --> 00:29:03,040
The generation of nitrogen
oxide from a gamma ray burst
494
00:29:03,141 --> 00:29:04,541
would be disastrous.
495
00:29:04,642 --> 00:29:06,143
In the upper
atmosphere, it would
496
00:29:06,244 --> 00:29:07,878
eat away at our ozone layer.
497
00:29:07,979 --> 00:29:12,683
In the lower atmosphere, it
would come out as acid rain.
498
00:29:12,817 --> 00:29:15,953
And the acid rain would
destroy our crops.
499
00:29:18,323 --> 00:29:22,025
Nitrogen dioxide
also filters out sunlight,
500
00:29:22,127 --> 00:29:24,895
turning the skies dark and
cooling the Earth enough
501
00:29:24,996 --> 00:29:26,930
to trigger a new Ice Age.
502
00:29:30,502 --> 00:29:34,104
Any life on the land, in
the shallow parts of the sea,
503
00:29:34,205 --> 00:29:37,441
or that live near the sea
surface would be done.
504
00:29:37,542 --> 00:29:40,911
In fact, it would ultimately
result in extinction.
505
00:29:45,183 --> 00:29:49,219
Blasted by ultraviolet
radiation from our sun,
506
00:29:49,320 --> 00:29:53,690
freezing cold and
hungry, humanity's future
507
00:29:53,792 --> 00:29:54,792
would be bleak.
508
00:29:58,029 --> 00:30:02,132
So we really need to know,
when Apep goes supernova
509
00:30:02,233 --> 00:30:06,937
and produces its deadly
beam of gamma rays,
510
00:30:07,038 --> 00:30:08,238
are we in its line of fire?
511
00:30:10,542 --> 00:30:12,910
The good news is
that we are probably
512
00:30:13,011 --> 00:30:16,446
not right in the direct
firing line of Apep.
513
00:30:16,548 --> 00:30:19,817
The axis of
rotation of the Apep system
514
00:30:19,918 --> 00:30:22,820
is pointed 30
degrees away from us.
515
00:30:22,921 --> 00:30:26,390
So if it does blow, it's
likely that the jets
516
00:30:26,491 --> 00:30:28,025
are going to miss us.
517
00:30:28,126 --> 00:30:30,727
It makes me feel
better that this gamma
518
00:30:30,829 --> 00:30:32,429
ray burst isn't pointing at us.
519
00:30:32,530 --> 00:30:35,732
But, of course, there are
many other cosmic catastrophes
520
00:30:35,834 --> 00:30:38,168
potentially waiting to get us.
521
00:30:38,269 --> 00:30:42,506
Apep is on the edge
of an enormous explosion.
522
00:30:42,607 --> 00:30:45,209
Its huge gravity
and incredible spin
523
00:30:45,310 --> 00:30:48,178
should produce a
spectacular supernova.
524
00:30:51,015 --> 00:30:55,385
But what if some stars
are too big to blow?
525
00:31:11,202 --> 00:31:18,375
Galaxy NGC 6946... a local galaxy
just 20 million light years
526
00:31:18,476 --> 00:31:23,046
away and well known to
supernova detectives.
527
00:31:23,147 --> 00:31:26,216
It's the fireworks galaxy
because it has produced so many
528
00:31:26,317 --> 00:31:28,485
supernovas in the past century.
529
00:31:28,553 --> 00:31:30,654
And they notice that
one star that they
530
00:31:30,755 --> 00:31:34,124
thought would become a
supernova instead blinked out.
531
00:31:36,294 --> 00:31:37,995
The star under investigation
532
00:31:38,096 --> 00:31:45,035
is N6946-BH1, a
cosmic heavyweight 25
533
00:31:45,136 --> 00:31:46,870
times the mass of our sun.
534
00:31:49,040 --> 00:31:51,742
That's way more than the
eight solar masses we
535
00:31:51,843 --> 00:31:53,777
thought guaranteed a supernova.
536
00:31:55,113 --> 00:31:57,347
This is a very
massive, very luminous
537
00:31:57,448 --> 00:32:00,851
star, the prototype
of what you expect
538
00:32:00,952 --> 00:32:03,921
to explode as a supernova.
539
00:32:04,022 --> 00:32:05,833
And over
the last couple of years,
540
00:32:05,857 --> 00:32:07,524
its brightness
has been changing.
541
00:32:07,625 --> 00:32:10,327
Maybe the star was beginning
to go a bit unstable.
542
00:32:10,428 --> 00:32:12,329
But then, right in
front of our eyes,
543
00:32:12,430 --> 00:32:15,365
this star just
completely disappeared.
544
00:32:20,204 --> 00:32:22,005
This is a huge mystery.
545
00:32:22,106 --> 00:32:23,307
Why didn't this thing blow up?
546
00:32:24,943 --> 00:32:27,311
How could a star just disappear?
547
00:32:28,613 --> 00:32:30,147
There had to be
something left behind.
548
00:32:32,884 --> 00:32:35,953
So astronomers began
a search for evidence
549
00:32:36,054 --> 00:32:37,354
and found a crucial clue.
550
00:32:39,791 --> 00:32:41,458
When you look in
the infrared, you
551
00:32:41,559 --> 00:32:42,893
can still see some light there.
552
00:32:42,994 --> 00:32:44,962
So there was something
happening there.
553
00:32:45,063 --> 00:32:46,063
But what?
554
00:32:47,699 --> 00:32:50,867
We think the infrared
light is heat coming off
555
00:32:50,969 --> 00:32:52,569
the debris of the dead star.
556
00:32:56,007 --> 00:32:59,042
Something is pulling
it inwards, something
557
00:32:59,143 --> 00:33:02,646
powerful but also invisible...
558
00:33:02,747 --> 00:33:03,747
A black hole.
559
00:33:05,750 --> 00:33:07,517
The outer stuff
from the star is still
560
00:33:07,618 --> 00:33:09,753
falling on to that
black hole, and it's
561
00:33:09,854 --> 00:33:11,288
powering a little bit of light.
562
00:33:11,389 --> 00:33:13,457
A little bit of the infrared
light still gets out.
563
00:33:18,029 --> 00:33:19,563
How can a giant star become
564
00:33:19,664 --> 00:33:23,600
a black hole without exploding
into a supernova first?
565
00:33:26,537 --> 00:33:30,273
The answer lies in how
dying stars burn their fuel.
566
00:33:32,310 --> 00:33:35,479
For stars that are about, say,
20 times the mass of the sun,
567
00:33:35,613 --> 00:33:37,681
you're actually going to
burn things convectively.
568
00:33:37,782 --> 00:33:41,318
That means the gases inside
the core are moving around.
569
00:33:41,419 --> 00:33:45,355
A good analogy is water
in a boiling pot of water.
570
00:33:45,456 --> 00:33:47,157
You've got your
potatoes up here.
571
00:33:47,258 --> 00:33:48,525
You're trying to boil them.
572
00:33:48,626 --> 00:33:51,795
You've got convective cells
of water that are heated.
573
00:33:51,896 --> 00:33:53,930
Bring the heat up to the top.
574
00:33:54,032 --> 00:33:55,432
Get the potatoes hot.
575
00:33:55,533 --> 00:33:59,403
And then those blobs of water
cool down, become denser,
576
00:33:59,504 --> 00:34:01,071
and settle down to
the bottom again
577
00:34:01,172 --> 00:34:02,539
where they're heated once more.
578
00:34:04,876 --> 00:34:06,777
As fusion turns hydrogen
579
00:34:06,878 --> 00:34:11,014
to helium and then to
carbon, convection mixes
580
00:34:11,115 --> 00:34:12,616
the carbon so it burns up.
581
00:34:15,620 --> 00:34:18,388
Convection cells work inside
582
00:34:18,489 --> 00:34:21,958
of a star like
massive elevators that
583
00:34:22,060 --> 00:34:24,961
take hot gas from
the central regions,
584
00:34:25,063 --> 00:34:28,365
bring it up to the surface,
allow it to cool, and then
585
00:34:28,466 --> 00:34:30,734
pull that material back down.
586
00:34:30,835 --> 00:34:35,338
They're constantly churning
back and forth inside of a star.
587
00:34:37,675 --> 00:34:40,510
But stars more
massive than roughly 20 times
588
00:34:40,611 --> 00:34:45,482
the mass of the
sun, like N6946-BH1,
589
00:34:45,583 --> 00:34:47,084
don't burn carbon this way.
590
00:34:49,520 --> 00:34:51,621
Instead of mixing,
the heavier atoms
591
00:34:51,722 --> 00:34:54,991
created by the fusion reactions
just start to pile up.
592
00:34:57,562 --> 00:34:58,882
That means there's
a layer of very
593
00:34:58,963 --> 00:35:02,065
dense material building up on
just the surface of the core.
594
00:35:02,166 --> 00:35:04,034
All of the stuff is
just ready to collapse.
595
00:35:06,504 --> 00:35:08,772
It's possible that, if
you have enough mass sitting
596
00:35:08,873 --> 00:35:11,007
around, the collapse
is so powerful
597
00:35:11,109 --> 00:35:13,143
that it actually collapses
into a black hole
598
00:35:13,244 --> 00:35:15,912
before any supernova goes off.
599
00:35:16,013 --> 00:35:18,615
That, then, is a
failed supernova.
600
00:35:18,716 --> 00:35:20,717
It's a star that
pretty much directly
601
00:35:20,818 --> 00:35:22,385
collapses to form a black hole.
602
00:35:26,591 --> 00:35:30,827
If many of the massive
stars we expect to go supernova
603
00:35:30,928 --> 00:35:33,029
won't, that's a problem.
604
00:35:36,601 --> 00:35:39,402
We used to think we had the
basics of supernovas cracked.
605
00:35:39,504 --> 00:35:41,624
Any time you have a star
more massive than eight times
606
00:35:41,706 --> 00:35:43,373
the mass of the
sun, it was destined
607
00:35:43,474 --> 00:35:45,175
to explode as a supernova.
608
00:35:45,276 --> 00:35:47,911
And then along comes a star
that screws everything up.
609
00:35:50,515 --> 00:35:52,616
To make things
worse, we found no clear
610
00:35:52,717 --> 00:35:55,051
distinction between
stars that go out with
611
00:35:55,153 --> 00:35:56,887
a bang and those that don't.
612
00:35:59,824 --> 00:36:05,462
As many as 30% of massive stars
could die without exploding.
613
00:36:05,563 --> 00:36:08,131
Our search for the
next killer supernova
614
00:36:08,232 --> 00:36:09,232
is getting even harder.
615
00:36:10,568 --> 00:36:12,869
Stars blow up
when we don't expect them to.
616
00:36:12,970 --> 00:36:15,605
They don't blow up
when we expect them to.
617
00:36:15,706 --> 00:36:17,741
They can have several
stars orbiting each other,
618
00:36:17,842 --> 00:36:19,686
and the one that blows up
isn't necessarily the one
619
00:36:19,710 --> 00:36:20,710
you think it will.
620
00:36:23,714 --> 00:36:27,050
So right now we
can't identify a prime suspect,
621
00:36:27,151 --> 00:36:28,285
but the hunt continues.
622
00:36:30,755 --> 00:36:31,999
As far as we know, there
623
00:36:32,023 --> 00:36:34,257
are no life-threatening
stars out there,
624
00:36:34,358 --> 00:36:37,928
but we haven't done
a complete survey.
625
00:36:38,029 --> 00:36:41,398
So please keep funding astronomy
so we can keep looking.
626
00:36:43,668 --> 00:36:44,935
Supernovas destroy.
627
00:36:47,138 --> 00:36:49,105
But can they also create?
628
00:36:52,476 --> 00:36:56,580
Did a supernova spark
humanity's rise to dominate
629
00:36:56,681 --> 00:36:59,416
our world and our solar system?
630
00:37:11,462 --> 00:37:19,202
Supernovas are spectacular,
devastating, and frightening.
631
00:37:21,806 --> 00:37:24,608
But without them,
we wouldn't exist.
632
00:37:26,277 --> 00:37:28,712
The iron in your blood and
the calcium in your bones
633
00:37:28,813 --> 00:37:32,983
was literally forged inside of
a star that exploded billions
634
00:37:33,084 --> 00:37:35,018
of years ago as a supernova.
635
00:37:35,119 --> 00:37:38,054
And I think this is one of the
most beautiful and the most
636
00:37:38,155 --> 00:37:40,991
profound things that we've
learned in astronomy,
637
00:37:41,092 --> 00:37:44,894
that we're literally viscerally
connected to the cosmos
638
00:37:44,996 --> 00:37:46,730
and the cosmos is
connected to us.
639
00:37:49,767 --> 00:37:52,369
With every breath,
we are inhaling
640
00:37:52,470 --> 00:37:55,205
oxygen that was created
in a supernova explosion.
641
00:37:59,210 --> 00:38:02,979
This is almost literally
a cosmic cycle of life.
642
00:38:09,620 --> 00:38:11,187
And the supernova may even
643
00:38:11,289 --> 00:38:14,758
be responsible for the
dawning of our intelligence
644
00:38:14,859 --> 00:38:17,894
by causing lightning.
645
00:38:17,995 --> 00:38:19,275
It might sound
rather incredible,
646
00:38:19,363 --> 00:38:21,575
but a supernova might actually
influence, directly, weather
647
00:38:21,599 --> 00:38:22,732
right here on the Earth.
648
00:38:22,833 --> 00:38:26,503
The cosmic rays from a
supernova will create charges
649
00:38:26,604 --> 00:38:28,371
in the lower atmosphere.
650
00:38:28,472 --> 00:38:30,840
That energy will
break apart molecules,
651
00:38:30,941 --> 00:38:34,678
excite atoms and molecules,
and it will ionize them.
652
00:38:34,779 --> 00:38:38,748
And an ionized
atmosphere means that now
653
00:38:38,849 --> 00:38:40,550
it can conduct electricity.
654
00:38:40,651 --> 00:38:43,453
So it probably increased
lightning across the planet.
655
00:38:46,991 --> 00:38:49,893
It's possible the
same gamma ray burst that caused
656
00:38:49,994 --> 00:38:54,264
a mass extinction
2.6 million years ago
657
00:38:54,365 --> 00:38:58,168
also affected
Earth's atmosphere,
658
00:38:58,269 --> 00:39:01,571
triggering tremendous
bursts of lightning,
659
00:39:01,672 --> 00:39:04,841
which caused forest fires.
660
00:39:06,477 --> 00:39:09,212
We have
evidence of widespread fires
661
00:39:09,313 --> 00:39:10,313
at this time.
662
00:39:10,414 --> 00:39:12,882
So it could be that
lightning was increased,
663
00:39:12,983 --> 00:39:14,918
and that created more fires.
664
00:39:15,019 --> 00:39:18,054
And those fires could have
leveled forests and savannas,
665
00:39:18,155 --> 00:39:19,422
creating grasslands.
666
00:39:21,092 --> 00:39:25,195
So how could this
change/boost our intelligence?
667
00:39:25,296 --> 00:39:29,599
With their forest homes burnt,
our ancestors, early hominids,
668
00:39:29,700 --> 00:39:33,937
had to adapt to life out in the
open, which meant standing up.
669
00:39:35,072 --> 00:39:36,183
You're living in a savanna
670
00:39:36,207 --> 00:39:39,075
where there's lions and
leopards and cheetahs,
671
00:39:39,176 --> 00:39:41,244
and the savanna is
mostly grassland.
672
00:39:41,345 --> 00:39:44,214
It's a lot more efficient,
perhaps, on two feet.
673
00:39:44,315 --> 00:39:45,148
You can run.
674
00:39:45,249 --> 00:39:46,493
And moving on two
feet might have
675
00:39:46,517 --> 00:39:48,651
been the survival mechanism.
676
00:39:50,154 --> 00:39:52,956
Standing upright also
triggered the most important
677
00:39:53,057 --> 00:39:54,124
change in our history.
678
00:39:56,093 --> 00:39:57,533
Walking around on two feet
679
00:39:57,628 --> 00:40:00,864
freed our hands to be able
to start doing things.
680
00:40:00,965 --> 00:40:03,165
And as you... you know, of
course, you can imagine that,
681
00:40:03,200 --> 00:40:05,468
as you start doing things,
that drives your brain to more
682
00:40:05,569 --> 00:40:06,980
complexity as you're
trying to figure
683
00:40:07,004 --> 00:40:08,171
out how to manipulate things.
684
00:40:08,272 --> 00:40:09,939
And this is perhaps the biggest
685
00:40:10,040 --> 00:40:12,842
evolutionary leap,
because, without it, we
686
00:40:12,943 --> 00:40:13,943
don't get tool use.
687
00:40:14,044 --> 00:40:15,178
We don't get fire.
688
00:40:15,279 --> 00:40:16,780
We don't get intelligence.
689
00:40:18,749 --> 00:40:20,850
As our ancient ancestors adapted
690
00:40:20,951 --> 00:40:24,053
to their new habitat, they
took their first steps
691
00:40:24,155 --> 00:40:25,488
toward world domination.
692
00:40:27,258 --> 00:40:28,858
At least, that's the theory.
693
00:40:30,528 --> 00:40:33,830
The idea presented here
is this would be the dawn
694
00:40:33,931 --> 00:40:36,032
of modern humans as we see it.
695
00:40:36,133 --> 00:40:38,435
And we would owe
that to lightning
696
00:40:38,536 --> 00:40:40,937
created from a gamma ray burst.
697
00:40:41,038 --> 00:40:42,038
That's nuts.
698
00:40:45,509 --> 00:40:48,711
Supernovas are extraordinary.
699
00:40:48,813 --> 00:40:50,547
They launched our
journey into the cosmos.
700
00:40:51,916 --> 00:40:54,651
And in time, a
supernova may end it.
701
00:40:57,621 --> 00:41:01,658
We're searching hard to
spot which one it could be.
702
00:41:01,759 --> 00:41:04,894
But, for now, the only
way we'll know for sure
703
00:41:04,995 --> 00:41:06,596
is when it lights up our sky.
704
00:41:09,433 --> 00:41:13,570
While a supernova might appear
to be the death of a star,
705
00:41:13,671 --> 00:41:16,239
the beauty of it is
that it's really a story
706
00:41:16,340 --> 00:41:17,407
about beginnings, as well.
707
00:41:23,347 --> 00:41:26,082
Supernovae giveth,
and they taketh away.
708
00:41:26,183 --> 00:41:28,518
Without supernovae, the
Earth wouldn't exist
709
00:41:28,619 --> 00:41:29,719
and we wouldn't exist.
710
00:41:32,323 --> 00:41:35,158
I actually do imagine standing
out on a nice winter night,
711
00:41:35,259 --> 00:41:36,926
looking up at
Betelgeuse, and actually
712
00:41:37,027 --> 00:41:38,761
seeing the thing explode.
713
00:41:38,863 --> 00:41:40,864
There would be
this bright light.
714
00:41:40,965 --> 00:41:42,765
I can imagine my
face lighting up.
715
00:41:42,867 --> 00:41:44,133
I would really lose it.
716
00:41:47,438 --> 00:41:48,782
I would love to see
a supernova up close,
717
00:41:48,806 --> 00:41:49,506
Right?
718
00:41:49,607 --> 00:41:50,740
I mean, what a light show.
719
00:41:50,841 --> 00:41:52,809
But there's no way I would
want to be that close
720
00:41:52,910 --> 00:41:54,811
because I don't want to die.
721
00:41:54,835 --> 00:41:56,835
722
00:41:57,305 --> 00:42:57,864
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