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Imagine a universe
with no stars...
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00:00:09,410 --> 00:00:12,011
a dark, endless night.
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00:00:14,081 --> 00:00:17,961
This is not some
Sci-Fi nightmare.
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00:00:17,985 --> 00:00:20,931
This is our future.
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00:00:20,955 --> 00:00:24,668
There will definitely be a point
in the future when, you look up,
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00:00:24,692 --> 00:00:27,137
you will no longer
be able to see stars.
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00:00:27,161 --> 00:00:29,606
Things really will get
darker and darker,
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00:00:29,630 --> 00:00:33,844
until there will be almost
no memory of light left.
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00:00:33,868 --> 00:00:39,016
For billions of years, stars
brought life to the universe.
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00:00:39,040 --> 00:00:45,355
The fact that you exist at all
is because of stars.
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00:00:45,379 --> 00:00:50,694
Now, they're dying out
in a star apocalypse.
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00:00:50,718 --> 00:00:53,096
The effect could be tremendous.
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00:00:53,120 --> 00:00:56,299
It can permeate
throughout the universe.
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00:00:56,323 --> 00:00:58,802
What's causing the die-off,
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00:00:58,826 --> 00:01:03,874
and what happens to life
when the lights go out?
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00:01:03,898 --> 00:01:06,143
Eventually, the whole
entire universe
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00:01:06,167 --> 00:01:09,368
starts to get
a little bit weird.
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00:01:15,543 --> 00:01:18,522
Captions by vitac...
www.vitac.com
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00:01:18,546 --> 00:01:21,580
captions paid for by
discovery communications
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for over 4.5 billion years,
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the sun has bathed
our home planet with light.
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Its bright, stable glow
helps life flourish,
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00:01:36,397 --> 00:01:38,475
but hidden in the night sky,
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00:01:38,499 --> 00:01:43,213
other planetary systems
haven't been so lucky.
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00:01:43,237 --> 00:01:45,315
Hanging right above
your head every night,
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00:01:45,339 --> 00:01:49,853
we see up there
these dead corpses of stars.
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400 light-years from earth
lies a system called SDSSJ1228.
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A disk of debris orbits
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00:01:59,220 --> 00:02:03,967
the faintly glowing leftovers
of a dead star.
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00:02:03,991 --> 00:02:06,303
J1228 is a dead star.
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00:02:06,327 --> 00:02:08,972
It is a core of a star
that had aged,
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00:02:08,996 --> 00:02:11,908
blown off its outer layers,
revealed the core...
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00:02:11,932 --> 00:02:13,643
which is about
the size of the earth,
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00:02:13,667 --> 00:02:15,812
but has about half
the mass of the star in it.
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00:02:15,836 --> 00:02:17,636
And we call these
"white dwarfs."
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May, 2018.
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00:02:27,882 --> 00:02:30,894
Astronomers investigated J1228
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00:02:30,918 --> 00:02:34,397
using the world's largest
optical telescope...
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00:02:34,421 --> 00:02:38,468
the Gran Telescopio Canarias.
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00:02:38,492 --> 00:02:42,038
They discovered what appears
to be a ball of iron
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00:02:42,062 --> 00:02:44,641
orbiting the white dwarf.
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00:02:44,665 --> 00:02:48,545
The lump of metal,
less than 400 miles across,
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00:02:48,569 --> 00:02:52,916
could be the exposed core
of a destroyed planet.
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00:02:52,940 --> 00:02:56,853
It's a clue to
this system's past.
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00:02:56,877 --> 00:02:58,221
It's always a little poignant
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00:02:58,245 --> 00:03:01,424
when you see evidence
of a planet around a dead star.
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00:03:01,448 --> 00:03:03,493
You know, you think back of
when that star was shining,
48
00:03:03,517 --> 00:03:05,996
and could there have been life
in that solar system?
49
00:03:06,020 --> 00:03:11,067
The J1228 system
is a cosmic graveyard.
50
00:03:11,091 --> 00:03:14,471
It might look different
than our solar system,
51
00:03:14,495 --> 00:03:18,041
but this is our future.
52
00:03:18,065 --> 00:03:22,512
This discovery of a dead planet
orbiting a dead star
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00:03:22,536 --> 00:03:24,848
is like looking into
a crystal ball.
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00:03:24,872 --> 00:03:28,018
And is it the future
of our own solar system?
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00:03:28,042 --> 00:03:29,352
Yep.
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00:03:29,376 --> 00:03:31,188
For a glimpse into your future,
you know,
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00:03:31,212 --> 00:03:33,278
all you need to do is look up.
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00:03:37,484 --> 00:03:42,732
Just like J1228,
our sun will die,
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00:03:42,756 --> 00:03:46,002
killing off earth
in the process.
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00:03:46,026 --> 00:03:50,240
This terrifying fate
will play out across the galaxy
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00:03:50,264 --> 00:03:53,343
in a star apocalypse.
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00:03:53,367 --> 00:03:56,780
Our sun is a fairly common type
of star in the milky way,
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00:03:56,804 --> 00:03:59,316
and so, other stars
in the milky way
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00:03:59,340 --> 00:04:01,551
will undergo the same sort
of fate as the sun.
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00:04:01,575 --> 00:04:03,086
They will end up
as white dwarfs.
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00:04:03,110 --> 00:04:06,223
And so, any other planets out
there orbiting sun-like stars
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00:04:06,247 --> 00:04:08,046
will undergo a similar fate.
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00:04:10,951 --> 00:04:12,996
Once the stars like our sun
have died out,
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00:04:13,020 --> 00:04:14,164
what's gonna happen?
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00:04:14,188 --> 00:04:18,602
Could life still survive
around white dwarfs?
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00:04:18,626 --> 00:04:21,504
To understand the fate
of sun-like stars,
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00:04:21,528 --> 00:04:23,340
we have to look inside them.
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00:04:23,364 --> 00:04:28,578
Buried within are clues to how
they live, and why they die.
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00:04:28,602 --> 00:04:31,414
The core, the very center,
that's where the action is.
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00:04:31,438 --> 00:04:34,484
That's where the star
is fusing light elements
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00:04:34,508 --> 00:04:36,686
into heavier elements.
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00:04:36,710 --> 00:04:38,321
And that works like
a hydrogen bomb.
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00:04:38,345 --> 00:04:39,956
It's the same thing.
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00:04:39,980 --> 00:04:43,193
If you compress hydrogen enough,
it gets very hot,
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00:04:43,217 --> 00:04:44,828
and the pressure gets very high,
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00:04:44,852 --> 00:04:49,032
and if fuses into helium,
and generates energy... heat.
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00:04:49,056 --> 00:04:52,435
And that's what's happening
in the core of every star.
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00:04:52,459 --> 00:04:54,271
Because of their enormous mass,
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00:04:54,295 --> 00:04:57,507
stars have huge
amounts of gravity.
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00:04:57,531 --> 00:05:02,746
This gravity pushes inwards,
trying to collapse the star,
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00:05:02,770 --> 00:05:07,951
but fusion energy from the core
stops that from happening.
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00:05:07,975 --> 00:05:11,054
It's really this sort of
very balanced dance
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00:05:11,078 --> 00:05:14,858
between gravity pushing in,
fusion energy pushing out.
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00:05:14,882 --> 00:05:18,962
You can think of a star
as losing energy,
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00:05:18,986 --> 00:05:20,764
continuously,
to the outside world/
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00:05:20,788 --> 00:05:23,366
and gravity is saying,
"yes, I'm gonna take over."
92
00:05:23,390 --> 00:05:27,637
But, no, the nuclear reactions
inside a star
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00:05:27,661 --> 00:05:30,407
replenish the energy
that's lost,
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00:05:30,431 --> 00:05:33,943
and keep the star hot
and pressurized inside,
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00:05:33,967 --> 00:05:40,216
so that the pressure-gravity
balance can be maintained.
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00:05:40,240 --> 00:05:43,653
This balance
keeps sun-like stars alive
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00:05:43,677 --> 00:05:46,823
for up to 10 billion years,
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00:05:46,847 --> 00:05:51,661
until the star's gas tank
runs dry.
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00:05:51,685 --> 00:05:53,396
It's gonna run out of fuel.
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00:05:53,420 --> 00:05:56,132
And when that happens,
it's going to die.
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00:05:56,156 --> 00:05:57,367
But what is that
gonna look like?
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How is this gonna happen?
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One hundred million years ago,
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00:06:02,763 --> 00:06:08,778
things in the J1228 system
started to get ugly.
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00:06:08,802 --> 00:06:14,384
First, the star grew large...
really large.
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00:06:14,408 --> 00:06:17,487
Once the center starts
fusing heavier elements,
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00:06:17,511 --> 00:06:19,022
the outside will swell
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00:06:19,046 --> 00:06:22,826
into what will eventually be
a red giant star.
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00:06:22,850 --> 00:06:28,131
J1228 transformed
into a red giant.
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00:06:28,155 --> 00:06:29,799
Its outer layers blew off,
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extending out
over 40 million miles.
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00:06:34,528 --> 00:06:37,941
When stars like our sun die,
it's not a quiet affair.
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00:06:37,965 --> 00:06:41,077
It's very violent,
and ugly, and messy.
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They turn into red giants,
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00:06:42,770 --> 00:06:44,981
and they turn themselves
inside out,
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00:06:45,005 --> 00:06:49,152
and vomit
all over the solar system.
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00:06:49,176 --> 00:06:52,756
When J1228 swelled
into a red giant,
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00:06:52,780 --> 00:06:58,261
nearby planets
were stuck in a kill zone.
119
00:06:58,285 --> 00:07:01,765
The dying star engulfed them,
or fried them
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00:07:01,789 --> 00:07:05,635
with temperatures of over
1,200 degrees Fahrenheit.
121
00:07:05,659 --> 00:07:08,338
Atmospheres disappeared.
122
00:07:08,362 --> 00:07:10,940
Oceans boiled away,
123
00:07:10,964 --> 00:07:15,678
but one planet survived
J1228's death throes.
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00:07:15,702 --> 00:07:20,350
Here's a case where a planet
survived, in some sense,
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00:07:20,374 --> 00:07:23,653
the death of its own star,
and it's still hanging around,
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00:07:23,677 --> 00:07:27,991
still hanging on,
hoping for something new.
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00:07:28,015 --> 00:07:30,427
The red giant's
expanding outer layers
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00:07:30,451 --> 00:07:32,951
separated from the star's core.
129
00:07:34,955 --> 00:07:41,738
With no active fusion, the core
collapsed into a white dwarf.
130
00:07:41,762 --> 00:07:43,807
The white dwarf's dense gravity
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00:07:43,831 --> 00:07:48,411
then went to work
on the one surviving planet.
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00:07:48,435 --> 00:07:51,981
The planet that might've been
orbiting the normal star
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00:07:52,005 --> 00:07:55,752
can gradually spiral in
toward the white dwarf,
134
00:07:55,776 --> 00:07:58,755
and then, eventually, the
gravity of the white dwarf pulls
135
00:07:58,779 --> 00:08:02,158
on the near side of the planet
more than on the far side,
136
00:08:02,182 --> 00:08:04,461
and that tears it apart.
137
00:08:04,485 --> 00:08:07,063
What we're seeing here
is a dead star
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00:08:07,087 --> 00:08:10,188
dining on its own solar system.
139
00:08:11,925 --> 00:08:14,993
That's what is in the future
for the sun.
140
00:08:17,998 --> 00:08:23,146
J1228 feasted on the
remains of its rocky worlds,
141
00:08:23,170 --> 00:08:29,486
leaving behind a disk of debris
and the planetary core.
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00:08:29,510 --> 00:08:33,590
It's a glimpse
of earth's future.
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00:08:33,614 --> 00:08:35,892
What happened here
around this white dwarf
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00:08:35,916 --> 00:08:37,227
is gonna happen to earth.
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00:08:37,251 --> 00:08:39,596
It's gonna be stripped
of its atmosphere,
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00:08:39,620 --> 00:08:41,731
its crust, and its mantle,
147
00:08:41,755 --> 00:08:46,469
and the only thing that
will remain will be the core.
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00:08:46,493 --> 00:08:49,639
Fried and ripped apart
by a dying star...
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not a good way to go.
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00:08:52,199 --> 00:08:54,310
Fortunately, for life on earth,
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00:08:54,334 --> 00:08:58,014
our own sun
isn't dying just yet.
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00:08:58,038 --> 00:08:59,849
The sun is middle-aged.
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00:08:59,873 --> 00:09:01,518
It's 4.5 billion years old,
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00:09:01,542 --> 00:09:04,821
and it's going to go on for
another 5 or 6 billion years.
155
00:09:04,845 --> 00:09:06,356
We've got a little bit of time
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00:09:06,380 --> 00:09:11,094
before our sun pukes
all over the solar system.
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00:09:11,118 --> 00:09:13,596
Our home planet
may be safe for now,
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00:09:13,620 --> 00:09:16,733
but systems like J1228 show us
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00:09:16,757 --> 00:09:20,870
that sun-like stars
are destined to die,
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00:09:20,894 --> 00:09:24,707
killing off any life
orbiting them.
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00:09:24,731 --> 00:09:27,911
But sun-like stars
aren't the only stars
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00:09:27,935 --> 00:09:30,446
dying across the cosmos.
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00:09:30,470 --> 00:09:35,285
There are others out there,
and they're all doomed.
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00:09:35,309 --> 00:09:38,354
There's a wonderful
rainbow of stars
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out there,
of all different shapes,
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00:09:40,180 --> 00:09:43,159
all different sizes,
and all different colors.
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00:09:43,183 --> 00:09:44,894
We're talking down to, you know,
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00:09:44,918 --> 00:09:46,796
fractions of the mass
of the sun,
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up to hundreds of times
the mass of the sun.
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00:09:50,057 --> 00:09:53,937
When it comes to the star
apocalypse, size matters.
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00:09:53,961 --> 00:09:57,862
The bigger and brighter
the star, the faster it dies.
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00:10:17,517 --> 00:10:21,786
Our universe is a vast expanse
of death and destruction.
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00:10:23,924 --> 00:10:29,327
All of the stars are destined
to die, but not all at once.
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00:10:30,964 --> 00:10:33,176
There's not going to be
one particular point
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where all the lights turn off
at the same time.
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00:10:35,869 --> 00:10:38,481
It's more like a power outage,
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00:10:38,505 --> 00:10:42,085
where different grids go off
at different times, until,
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00:10:42,109 --> 00:10:46,456
like, there's the one last
light bulb that'll just go off.
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00:10:46,480 --> 00:10:51,461
This is because stars
come in different sizes.
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00:10:51,485 --> 00:10:53,930
The way a star dies
has everything to do with
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00:10:53,954 --> 00:10:55,898
the amount of mass
it started life with.
182
00:10:55,922 --> 00:10:59,769
It carries that all the way
through its lifetime.
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00:10:59,793 --> 00:11:02,672
The sun is a medium-sized star
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00:11:02,696 --> 00:11:06,909
living a stable existence
for billions of years.
185
00:11:06,933 --> 00:11:09,746
Giant stars are different.
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00:11:09,770 --> 00:11:13,549
They live fast, and die young.
187
00:11:13,573 --> 00:11:17,220
A star like the sun,
which is a medium-sized star,
188
00:11:17,244 --> 00:11:19,656
it lives about 10 billion years.
189
00:11:19,680 --> 00:11:21,457
The really massive stars,
190
00:11:21,481 --> 00:11:25,328
they live maybe
10 million years.
191
00:11:25,352 --> 00:11:28,731
Massive stars can be tens
or even hundreds of times
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00:11:28,755 --> 00:11:31,734
more massive than the sun.
193
00:11:31,758 --> 00:11:35,905
When it comes to life span,
that's a problem.
194
00:11:35,929 --> 00:11:40,743
A massive star has more fuel
to burn, in a nuclear sense.
195
00:11:40,767 --> 00:11:43,446
So, you might naively think
that it lasts longer,
196
00:11:43,470 --> 00:11:45,948
but it's the exact opposite.
197
00:11:45,972 --> 00:11:51,521
Massive stars can only access
hydrogen fuel in their core.
198
00:11:51,545 --> 00:11:54,490
The rest is trapped
in the outer layers,
199
00:11:54,514 --> 00:11:57,393
and can't be used as fuel.
200
00:11:57,417 --> 00:11:59,729
If there's hydrogen
in the core, you're good.
201
00:11:59,753 --> 00:12:03,199
If there's hydrogen outside
of the core, it can't be used.
202
00:12:03,223 --> 00:12:06,357
If it's not in your fuel tank,
it's not doing you any good.
203
00:12:07,994 --> 00:12:13,643
Massive stars also have
more gravity than smaller stars,
204
00:12:13,667 --> 00:12:17,413
so they have to burn
their hydrogen fuel faster
205
00:12:17,437 --> 00:12:19,704
to prevent the star
from collapsing.
206
00:12:21,708 --> 00:12:23,786
They burn their candle
on both ends.
207
00:12:23,810 --> 00:12:25,688
Because of
their incredible mass,
208
00:12:25,712 --> 00:12:27,790
their fusion reactions
in the core
209
00:12:27,814 --> 00:12:30,326
happen at an incredible rate.
210
00:12:30,350 --> 00:12:32,929
Giant stars are
kind of fast and furious.
211
00:12:32,953 --> 00:12:34,697
They are bright.
212
00:12:34,721 --> 00:12:37,856
They live their life,
and they die very quickly.
213
00:12:40,026 --> 00:12:42,605
When a giant star's
fuel runs out,
214
00:12:42,629 --> 00:12:44,907
the core collapses
catastrophically
215
00:12:44,931 --> 00:12:48,377
under the overwhelming
force of gravity.
216
00:12:48,401 --> 00:12:51,536
And then, boom, supernova.
217
00:12:58,512 --> 00:13:00,189
The death of a giant star
218
00:13:00,213 --> 00:13:03,081
triggers one of the biggest
bangs in the universe.
219
00:13:07,220 --> 00:13:11,156
The blast would instantly
vaporize nearby planets.
220
00:13:14,995 --> 00:13:19,876
But these star deaths
are also critical for life.
221
00:13:19,900 --> 00:13:22,912
When massive stars die,
they release heavy elements
222
00:13:22,936 --> 00:13:25,882
they've been making through
the course of their lives.
223
00:13:25,906 --> 00:13:27,884
And sometimes,
they even make new ones.
224
00:13:27,908 --> 00:13:32,922
And it's these heavier elements
that are essential for life.
225
00:13:32,946 --> 00:13:35,458
We owe our existence to stars
226
00:13:35,482 --> 00:13:38,316
that formed
billions of years ago.
227
00:13:42,789 --> 00:13:47,870
In may of 2018, we spotted
evidence of ancient stars
228
00:13:47,894 --> 00:13:50,373
creating the stuff of life.
229
00:13:50,397 --> 00:13:53,009
We picked up
an infrared light signal
230
00:13:53,033 --> 00:13:59,304
from a distant galaxy
named MACS1149-JD1.
231
00:14:01,141 --> 00:14:04,142
The signal was ionized oxygen.
232
00:14:06,613 --> 00:14:10,459
It's been traveling
for 13.3 billion years,
233
00:14:10,483 --> 00:14:15,097
so the oxygen formed when
the universe was very young...
234
00:14:15,121 --> 00:14:20,770
just 500 million years
after the big bang.
235
00:14:20,794 --> 00:14:26,709
This oxygen formed
in the hearts of massive stars.
236
00:14:26,733 --> 00:14:28,277
The presence of oxygen tells us
237
00:14:28,301 --> 00:14:31,581
that there needed to be massive
stars in the early universe
238
00:14:31,605 --> 00:14:34,016
in order to synthesize
hydrogen and helium
239
00:14:34,040 --> 00:14:36,352
into heavier elements,
like oxygen,
240
00:14:36,376 --> 00:14:38,988
and then explode
to eject that oxygen
241
00:14:39,012 --> 00:14:42,814
back into the interstellar
and intergalactic medium.
242
00:14:44,918 --> 00:14:49,220
Extreme pressure in the cores
of the stars produces oxygen...
243
00:14:51,524 --> 00:14:55,905
...and other elements,
like carbon and nitrogen.
244
00:14:55,929 --> 00:15:00,142
Supernova blasts spread these
elements across the universe,
245
00:15:00,166 --> 00:15:04,513
helping to create
new generations of stars,
246
00:15:04,537 --> 00:15:08,784
and, most importantly, us.
247
00:15:08,808 --> 00:15:11,787
If there is one single fact
that you should care about
248
00:15:11,811 --> 00:15:15,391
in all of science...
and this is my favorite fact...
249
00:15:15,415 --> 00:15:18,683
is that you and I
are a consequence of star death.
250
00:15:22,455 --> 00:15:24,400
Before you can have
life, you need to have
251
00:15:24,424 --> 00:15:27,303
the kind of elements
out of which life forms.
252
00:15:27,327 --> 00:15:29,272
You need carbon.
You need nitrogen.
253
00:15:29,296 --> 00:15:30,640
You need oxygen.
254
00:15:30,664 --> 00:15:32,508
You need the elements
that are the backbone
255
00:15:32,532 --> 00:15:36,112
to the biology
that makes us possible.
256
00:15:36,136 --> 00:15:37,580
Where did those elements
come from?
257
00:15:37,604 --> 00:15:38,881
Well, they came from stars.
258
00:15:38,905 --> 00:15:41,350
They came from stars that formed
in the early universe,
259
00:15:41,374 --> 00:15:44,153
before even the sun existed.
260
00:15:44,177 --> 00:15:46,555
The huge size of massive stars
261
00:15:46,579 --> 00:15:49,525
quickly signs
their death warrants.
262
00:15:49,549 --> 00:15:55,998
Their explosive ends help create
new stars, and even life.
263
00:15:56,022 --> 00:16:01,225
The fact that you exist at all
is because of stars.
264
00:16:02,562 --> 00:16:05,808
But, probing galaxies
across the universe,
265
00:16:05,832 --> 00:16:08,477
we've discovered something else.
266
00:16:08,501 --> 00:16:12,381
The star apocalypse
isn't just killing stars.
267
00:16:12,405 --> 00:16:15,751
It's stopping them
from ever being born.
268
00:16:15,775 --> 00:16:17,486
Star formation is dying.
269
00:16:17,510 --> 00:16:19,956
And in fact,
it's dying rather quickly.
270
00:16:19,980 --> 00:16:22,058
The universe,
right before our eyes,
271
00:16:22,082 --> 00:16:24,093
is becoming a darker place.
272
00:16:24,117 --> 00:16:25,828
It's running out of fuel.
273
00:16:25,852 --> 00:16:29,153
And eventually, no more stars
will be made at all.
274
00:16:51,044 --> 00:16:55,491
Life on earth follows
a series of regular patterns.
275
00:16:55,515 --> 00:16:59,128
Day after day, the sun rises...
276
00:16:59,152 --> 00:17:02,198
And sets,
277
00:17:02,222 --> 00:17:06,902
and stars light up the darkness
of the night sky.
278
00:17:06,926 --> 00:17:09,872
The reason I got into astronomy
to begin with
279
00:17:09,896 --> 00:17:12,341
was because I grew up
in a rural part of the country,
280
00:17:12,365 --> 00:17:13,809
and the sky
was beautiful and dark.
281
00:17:13,833 --> 00:17:15,611
You go outside at night,
and you look up,
282
00:17:15,635 --> 00:17:18,381
and you could see
thousands of stars.
283
00:17:18,405 --> 00:17:20,805
But it won't be
that way forever.
284
00:17:23,309 --> 00:17:27,757
2016, a network
of telescopes across the world
285
00:17:27,781 --> 00:17:32,495
measured the energy outputs
of over 200,000 galaxies.
286
00:17:34,521 --> 00:17:37,566
They discovered that
in the past 2 billion years,
287
00:17:37,590 --> 00:17:40,958
the universe has lost
half its brightness.
288
00:17:42,429 --> 00:17:44,907
The night sky is getting darker
289
00:17:44,931 --> 00:17:49,211
as stars flicker
out of existence.
290
00:17:49,235 --> 00:17:50,746
About 10 billion years ago,
291
00:17:50,770 --> 00:17:52,815
the universe
kind of hit its peak,
292
00:17:52,839 --> 00:17:55,251
and lots of stars were shining.
293
00:17:55,275 --> 00:17:58,187
It was an incredibly
bright place,
294
00:17:58,211 --> 00:18:00,756
but in the last
couple billion years,
295
00:18:00,780 --> 00:18:04,593
it's really, overall,
become a less bright place.
296
00:18:04,617 --> 00:18:07,463
The darkening universe
isn't just a sign
297
00:18:07,487 --> 00:18:09,899
that stars are dying.
298
00:18:09,923 --> 00:18:15,438
It seems there's a problem
with star birth as well.
299
00:18:15,462 --> 00:18:17,573
When we look
into the universe's past,
300
00:18:17,597 --> 00:18:19,175
what we find is that long ago,
301
00:18:19,199 --> 00:18:21,777
stars were forming
at a much higher rate.
302
00:18:21,801 --> 00:18:24,146
Right now what we see is
that really,
303
00:18:24,170 --> 00:18:27,950
stars are dying off faster
than they're being born.
304
00:18:27,974 --> 00:18:30,352
A milky way-type galaxy, today,
305
00:18:30,376 --> 00:18:32,788
produces about
seven stars per year.
306
00:18:32,812 --> 00:18:35,291
However, 11 billion years ago,
307
00:18:35,315 --> 00:18:38,850
a galaxy like our own would've
produced 10 times more stars.
308
00:18:40,453 --> 00:18:43,299
In the early universe,
old stars died,
309
00:18:43,323 --> 00:18:46,268
and new ones formed
in their place
310
00:18:46,292 --> 00:18:48,504
from the material left over.
311
00:18:48,528 --> 00:18:51,696
It was a cycle that kept
the cosmos bright.
312
00:18:52,665 --> 00:18:54,777
Not anymore.
313
00:18:54,801 --> 00:18:58,781
It kind of sucks for us.
We like a bright universe.
314
00:18:58,805 --> 00:19:01,383
We like all this energy and life
315
00:19:01,407 --> 00:19:03,719
that's vibrating
through the universe,
316
00:19:03,743 --> 00:19:06,589
but that's just not always
going to be the case.
317
00:19:06,613 --> 00:19:09,892
The universe is already
winding down.
318
00:19:12,485 --> 00:19:15,631
One of the biggest
mysteries in galaxy evolution
319
00:19:15,655 --> 00:19:18,968
is figuring out how galaxies
stop forming their stars.
320
00:19:18,992 --> 00:19:21,070
And we really don't know
the answer yet,
321
00:19:21,094 --> 00:19:23,572
and it's really important
for us to figure out why
322
00:19:23,596 --> 00:19:27,343
because in the end,
stars really equal life.
323
00:19:29,969 --> 00:19:33,115
To find out what is
shutting off the stars,
324
00:19:33,139 --> 00:19:35,751
we study galaxy clusters.
325
00:19:38,978 --> 00:19:41,090
These giant regions of space
326
00:19:41,114 --> 00:19:45,816
contain hundreds of galaxies
bound together by gravity.
327
00:19:46,953 --> 00:19:51,233
Slowly, the clusters
pull new galaxies into them,
328
00:19:51,257 --> 00:19:55,504
causing something
strange to happen.
329
00:19:55,528 --> 00:19:59,408
What we see happening when
a galaxy falls into a cluster
330
00:19:59,432 --> 00:20:01,343
is that its star formation
is quenched.
331
00:20:01,367 --> 00:20:03,712
It's shut off.
332
00:20:03,736 --> 00:20:06,215
The cause of this
quenching effect
333
00:20:06,239 --> 00:20:09,985
has baffled scientists
for decades.
334
00:20:10,009 --> 00:20:13,222
Then in October of 2018,
335
00:20:13,246 --> 00:20:15,858
an international team
of astronomers
336
00:20:15,882 --> 00:20:18,761
investigated this
long-standing mystery.
337
00:20:20,653 --> 00:20:23,365
They tracked variations
in quenching
338
00:20:23,389 --> 00:20:25,134
across 14 galaxy clusters
339
00:20:25,158 --> 00:20:29,104
and found
a possible explanation.
340
00:20:29,128 --> 00:20:32,041
The ability a galaxy
has to make new stars
341
00:20:32,065 --> 00:20:35,377
is related to the larger
environment it finds itself in.
342
00:20:35,401 --> 00:20:38,147
In clusters of galaxies
where many galaxies
343
00:20:38,171 --> 00:20:39,748
are orbiting around each other,
344
00:20:39,772 --> 00:20:44,687
we see interactions that strip
gas and dust away from galaxies.
345
00:20:44,711 --> 00:20:46,555
The stuff that makes up stars
346
00:20:46,579 --> 00:20:49,046
literally just thrown off
into space.
347
00:20:50,917 --> 00:20:54,363
Stars formed from
dense parcels of cold gas,
348
00:20:54,387 --> 00:20:56,254
something galaxies
are filled with.
349
00:20:58,091 --> 00:21:01,070
But when a galaxy is dragged
into a cluster,
350
00:21:01,094 --> 00:21:03,405
everything changes.
351
00:21:03,429 --> 00:21:06,675
Clusters of galaxies contain
a lot of hot gas,
352
00:21:06,699 --> 00:21:09,245
whereas you need cold gas
inside of a galaxy
353
00:21:09,269 --> 00:21:10,879
in order to form stars,
354
00:21:10,903 --> 00:21:14,149
and when a galaxy is moving
through this hot gas,
355
00:21:14,173 --> 00:21:17,742
then the cold gas inside
is stripped away.
356
00:21:19,178 --> 00:21:20,889
If this new study is right,
357
00:21:20,913 --> 00:21:25,160
and galaxy clusters are
stripping away star-forming gas,
358
00:21:25,184 --> 00:21:28,486
new starlight will become rare.
359
00:21:29,656 --> 00:21:32,034
Looking over the history
of the universe
360
00:21:32,058 --> 00:21:35,337
and how much gas was out there
and how much is still left,
361
00:21:35,361 --> 00:21:38,173
I think it's fair to say
that most of the stars
362
00:21:38,197 --> 00:21:41,277
that will ever be made
already have been made.
363
00:21:41,301 --> 00:21:43,100
They've already been born.
364
00:21:44,504 --> 00:21:47,316
Thanks to the shortage
of star-forming gas,
365
00:21:47,340 --> 00:21:50,953
stars won't just be dying
in the universe.
366
00:21:50,977 --> 00:21:52,955
They'll go extinct,
367
00:21:52,979 --> 00:21:56,792
and the first to go
will be the largest.
368
00:21:56,816 --> 00:21:58,994
As the universe runs out of gas
369
00:21:59,018 --> 00:22:01,196
and fewer of these stars
are being made,
370
00:22:01,220 --> 00:22:03,365
eventually sometime
in the future,
371
00:22:03,389 --> 00:22:06,635
all the high-mass and even
medium-mass stars like the sun,
372
00:22:06,659 --> 00:22:08,137
they'll be gone.
373
00:22:08,161 --> 00:22:10,606
What does that mean for life?
374
00:22:13,800 --> 00:22:16,045
Some of the brightest stars
375
00:22:16,069 --> 00:22:17,446
will disappear forever,
376
00:22:17,470 --> 00:22:20,549
begging the question,
can life survive
377
00:22:20,573 --> 00:22:23,874
the monsters
that dead stars leave behind?
378
00:22:24,911 --> 00:22:29,958
The long-term fate of the
universe is not a pretty sight.
379
00:22:29,982 --> 00:22:34,263
Some very interesting creatures
can start to appear.
380
00:22:50,870 --> 00:22:52,614
In the star apocalypse,
381
00:22:52,638 --> 00:22:56,018
the first stars to fade away
will be the brightest...
382
00:22:56,042 --> 00:23:01,679
the giant stars,
followed by the mid-sized suns.
383
00:23:02,849 --> 00:23:07,196
The universe will become
unrecognizable.
384
00:23:07,220 --> 00:23:09,832
The far future will be
a very dim universe,
385
00:23:09,856 --> 00:23:11,934
especially for creatures
like us.
386
00:23:11,958 --> 00:23:16,093
If there's no more gas,
no more new stars, it gets dark.
387
00:23:17,630 --> 00:23:19,108
Scared of the dark?
388
00:23:19,132 --> 00:23:21,643
You will be...
389
00:23:21,667 --> 00:23:24,113
Because 100 billion years
from now,
390
00:23:24,137 --> 00:23:27,216
in the shadows
of this new universe,
391
00:23:27,240 --> 00:23:30,486
monsters will come out to play.
392
00:23:30,510 --> 00:23:34,223
Now we find ourselves in the era
of stars and starlight.
393
00:23:34,247 --> 00:23:36,291
What comes after
you can think of
394
00:23:36,315 --> 00:23:38,916
as the era of the dead corpses
of old stars.
395
00:23:40,420 --> 00:23:43,132
We already see
the corpses of dead stars
396
00:23:43,156 --> 00:23:46,235
scattered
throughout the cosmos...
397
00:23:46,259 --> 00:23:52,107
black holes,
pulsars, white dwarfs.
398
00:23:52,131 --> 00:23:57,713
What happens when more stars die
out and the dead take over?
399
00:23:57,737 --> 00:23:59,982
Can life survive?
400
00:24:00,006 --> 00:24:03,385
It's actually possible that life
in the universe will survive,
401
00:24:03,409 --> 00:24:05,576
but we're going to have
to get more creative.
402
00:24:06,913 --> 00:24:09,958
January 2019.
403
00:24:09,982 --> 00:24:14,830
The Gaia satellite studied
15,000 white dwarfs
404
00:24:14,854 --> 00:24:18,066
within 300 light-years of earth.
405
00:24:18,090 --> 00:24:22,571
These are the corpses
of sunlight stars.
406
00:24:22,595 --> 00:24:25,140
White dwarfs are
the remnants, the cores,
407
00:24:25,164 --> 00:24:27,242
of stars like the sun
after they die.
408
00:24:27,266 --> 00:24:30,212
There's no more fusion going on
inside of a white dwarf.
409
00:24:30,236 --> 00:24:32,781
So it's just kind of
sitting there cooling off,
410
00:24:32,805 --> 00:24:36,240
but it turns out
there's a slight reprieve.
411
00:24:37,543 --> 00:24:41,490
The white dwarf
corpses usually cool off and dim
412
00:24:41,514 --> 00:24:44,092
over tens of billions of years.
413
00:24:44,116 --> 00:24:47,596
Gaia's data showed something
different,
414
00:24:47,620 --> 00:24:50,599
something
we've never seen before.
415
00:24:50,623 --> 00:24:54,558
Some of the older dead stars
aren't dimming at all.
416
00:24:56,395 --> 00:24:57,873
We used to think
that white dwarfs
417
00:24:57,897 --> 00:24:59,741
could really only dim over time.
418
00:24:59,765 --> 00:25:02,211
After all, there's no source
of fusion,
419
00:25:02,235 --> 00:25:04,646
no source of energy
in their interiors,
420
00:25:04,670 --> 00:25:07,950
but new studies with
the Gaia satellite have shown
421
00:25:07,974 --> 00:25:10,886
that there must be
some other energy source
422
00:25:10,910 --> 00:25:14,056
keeping those older
white dwarfs shining bright.
423
00:25:16,082 --> 00:25:19,828
Something is giving these
white dwarf corpses a spark,
424
00:25:19,852 --> 00:25:24,399
bringing them back from the dead
as zombies.
425
00:25:24,423 --> 00:25:25,767
The leading contender
426
00:25:25,791 --> 00:25:28,570
is that the insides of
white dwarfs
427
00:25:28,594 --> 00:25:30,794
actually crystallize.
428
00:25:32,331 --> 00:25:35,177
Up to 6 billion years
after dying,
429
00:25:35,201 --> 00:25:38,881
the hot carbon and oxygen matter
inside the white dwarf
430
00:25:38,905 --> 00:25:42,751
cools and crystallizes,
becoming solid,
431
00:25:42,775 --> 00:25:46,421
giving the dead star a lifeline.
432
00:25:46,445 --> 00:25:49,525
This actually releases energy.
433
00:25:49,549 --> 00:25:51,693
As the star cools,
it winds up releasing
434
00:25:51,717 --> 00:25:54,229
a little bit more energy
than it otherwise would.
435
00:25:54,253 --> 00:25:59,801
This unusual heat source could
warm up a nearby frozen planet,
436
00:25:59,825 --> 00:26:03,272
giving life a second chance.
437
00:26:03,296 --> 00:26:07,042
There will be some extra energy
available from these objects.
438
00:26:07,066 --> 00:26:08,744
So this is the time that we have
439
00:26:08,768 --> 00:26:10,834
to cuddle up
close to the zombies.
440
00:26:12,338 --> 00:26:16,785
Crystallization
can rejuvenate old white dwarfs,
441
00:26:16,809 --> 00:26:19,021
and the process
could even provide
442
00:26:19,045 --> 00:26:22,691
a spectacular setting
for an orbiting planet.
443
00:26:22,715 --> 00:26:24,693
We have a special name
444
00:26:24,717 --> 00:26:27,496
for cooled-down crystallized
carbon and oxygen.
445
00:26:27,520 --> 00:26:29,398
We call them diamonds.
446
00:26:29,422 --> 00:26:32,067
The long-term fate
of our universe
447
00:26:32,091 --> 00:26:35,960
will be sprinkled with
all these glittering diamonds.
448
00:26:37,930 --> 00:26:41,376
A zombie that comes to life
and shines like a diamond
449
00:26:41,400 --> 00:26:43,211
might be pretty to look at,
450
00:26:43,235 --> 00:26:47,338
but it's still no guarantee
that life could survive here.
451
00:26:48,841 --> 00:26:51,820
You can kind of think
of these white dwarfs
452
00:26:51,844 --> 00:26:55,457
as maybe making a little
more energy for the universe,
453
00:26:55,481 --> 00:26:58,060
but even that's going
to eventually run out.
454
00:26:58,084 --> 00:27:01,863
The whole thing becomes
a gigantic crystal and, again,
455
00:27:01,887 --> 00:27:04,755
it's just going to
start cooling and fading away.
456
00:27:05,891 --> 00:27:09,137
The zombie fizzles out
into a dark cinder,
457
00:27:09,161 --> 00:27:12,941
giving off almost
no light at all,
458
00:27:12,965 --> 00:27:17,401
but there's another monster
lurking in the cosmos.
459
00:27:20,673 --> 00:27:23,785
When a star that's much
more massive than the sun dies,
460
00:27:23,809 --> 00:27:24,987
it explodes violently,
461
00:27:25,011 --> 00:27:27,723
and during that explosion,
the core collapses
462
00:27:27,747 --> 00:27:30,993
and becomes an incredibly dense,
small object,
463
00:27:31,017 --> 00:27:35,419
one of the most wonderful
real monsters in the universe.
464
00:27:37,123 --> 00:27:39,434
This is a pulsar...
465
00:27:39,458 --> 00:27:44,239
PSR B0329+54,
466
00:27:44,263 --> 00:27:47,342
3,000 light-years away from us.
467
00:27:47,366 --> 00:27:50,012
The pulsar has the mass
of the sun,
468
00:27:50,036 --> 00:27:52,414
but is just 12 miles across.
469
00:27:52,438 --> 00:27:57,352
Its rapid spin generates beams
of radiation from its poles,
470
00:27:57,376 --> 00:28:00,477
bringing the zombie to life.
471
00:28:01,714 --> 00:28:07,829
Now, we've discovered an alien
world orbiting this zombie star.
472
00:28:07,853 --> 00:28:10,565
In 2017, a new planet
473
00:28:10,589 --> 00:28:12,868
was discovered around a pulsar.
474
00:28:12,892 --> 00:28:15,904
They're about twice
the mass of the earth,
475
00:28:15,928 --> 00:28:18,407
and that's really incredible.
476
00:28:18,431 --> 00:28:21,677
The pulsar planet
sounds intriguing,
477
00:28:21,701 --> 00:28:24,980
but the prospects
for life aren't good.
478
00:28:25,004 --> 00:28:29,785
Orbiting a pulsar would be
a brutal environment for life.
479
00:28:29,809 --> 00:28:32,721
It's highly unlikely
that there's life
480
00:28:32,745 --> 00:28:35,924
because the radiation from this
system would be overwhelming
481
00:28:35,948 --> 00:28:39,116
and likely blow away
the atmosphere.
482
00:28:40,186 --> 00:28:42,798
As for sustaining life
in the universe,
483
00:28:42,822 --> 00:28:47,135
none of these options
is what you'd call a safe bet.
484
00:28:49,228 --> 00:28:52,774
These are momentary reprieves
from the inevitable.
485
00:28:52,798 --> 00:28:55,010
No matter what you do,
eventually,
486
00:28:55,034 --> 00:28:57,579
you're going to run out
of these gimmes.
487
00:28:57,603 --> 00:29:00,382
You're going to run out of the
get-of-jail-free cards.
488
00:29:00,406 --> 00:29:04,486
Inevitably, everything is going
to cool and fade away.
489
00:29:07,246 --> 00:29:09,891
This might be
game over for stars
490
00:29:09,915 --> 00:29:12,828
and even for life.
491
00:29:12,852 --> 00:29:17,599
But there is still a glimmer
of hope hidden in the cosmos,
492
00:29:17,623 --> 00:29:20,769
a star that isn't dying.
493
00:29:20,793 --> 00:29:24,573
It appears blessed
with eternal life,
494
00:29:24,597 --> 00:29:27,175
and its color is red.
495
00:29:27,199 --> 00:29:31,012
Red dwarfs... we are literally
surrounded by them,
496
00:29:31,036 --> 00:29:33,237
but they are largely
invisible to us.
497
00:29:46,685 --> 00:29:49,765
Illuminating
every corner of our night sky
498
00:29:49,789 --> 00:29:52,934
is the light of stars...
499
00:29:52,958 --> 00:29:58,039
But what we see with a naked eye
doesn't tell the whole story.
500
00:30:00,199 --> 00:30:03,345
The stars that you're seeing
are mainly stars like the sun
501
00:30:03,369 --> 00:30:05,714
or even more massive
and even hotter than the sun.
502
00:30:05,738 --> 00:30:08,617
They're bright. You can see them
from a distance,
503
00:30:08,641 --> 00:30:11,286
but amazingly, the most
common form of star,
504
00:30:11,310 --> 00:30:14,322
by far, are the red dwarf stars.
505
00:30:14,346 --> 00:30:16,491
They're up there right now
in the sky,
506
00:30:16,515 --> 00:30:19,594
but they're just too small
and too faint to see.
507
00:30:19,618 --> 00:30:23,365
Red dwarfs are up to
10 times smaller than the sun,
508
00:30:23,389 --> 00:30:26,101
and they burn less brightly.
509
00:30:26,125 --> 00:30:29,070
Right now,
hidden in the night sky,
510
00:30:29,094 --> 00:30:33,542
over three-quarters of the stars
in our galaxy are red dwarfs...
511
00:30:33,566 --> 00:30:38,313
And while the larger stars
are dying out,
512
00:30:38,337 --> 00:30:41,316
we've never seen
a red dwarf die,
513
00:30:41,340 --> 00:30:44,119
making them
the best bet for life
514
00:30:44,143 --> 00:30:47,189
to survive the star apocalypse.
515
00:30:47,213 --> 00:30:51,293
When the most massive stars
eventually go out
516
00:30:51,317 --> 00:30:54,129
and are not replaced,
what will be left
517
00:30:54,153 --> 00:30:58,400
are much, much dimmer stars
like red dwarf stars.
518
00:30:58,424 --> 00:31:01,903
We've seen star death
across the universe,
519
00:31:01,927 --> 00:31:04,272
so why not red dwarfs?
520
00:31:04,296 --> 00:31:06,675
Turns out their size
521
00:31:06,699 --> 00:31:10,378
gives them a crucial advantage
over larger stars.
522
00:31:10,402 --> 00:31:13,248
The more massive a star
is, the hotter it burns.
523
00:31:13,272 --> 00:31:15,650
A red dwarf star burns
at a lower temperature.
524
00:31:15,674 --> 00:31:17,552
So it doesn't burn through
it's fuel
525
00:31:17,576 --> 00:31:19,688
quite as quickly
as a mid-mass star does.
526
00:31:19,712 --> 00:31:22,691
These are like the economy
cars of the universe.
527
00:31:22,715 --> 00:31:25,427
They're just sipping
on their nuclear fuel,
528
00:31:25,451 --> 00:31:28,163
and they can coast along.
529
00:31:28,187 --> 00:31:31,333
Not only that,
despite being smaller,
530
00:31:31,357 --> 00:31:34,057
they have access to more fuel.
531
00:31:35,327 --> 00:31:38,573
Our mid-size sun
is split into three layers...
532
00:31:38,597 --> 00:31:41,309
a core, a radiation zone,
533
00:31:41,333 --> 00:31:43,478
and a convective layer.
534
00:31:43,502 --> 00:31:47,282
The radiation zone prevents
hydrogen in the top layer
535
00:31:47,306 --> 00:31:50,685
from ever becoming available
for the core to burn.
536
00:31:50,709 --> 00:31:52,954
So the sun can only access
537
00:31:52,978 --> 00:31:57,092
about 10 percent
of its total hydrogen fuel.
538
00:31:57,116 --> 00:32:01,229
Once the hydrogen
in our sun's core runs out,
539
00:32:01,253 --> 00:32:04,232
its days are numbered.
540
00:32:04,256 --> 00:32:06,468
In some ways,
these mid-sized stars
541
00:32:06,492 --> 00:32:08,136
end up starving themselves.
542
00:32:08,160 --> 00:32:11,539
The smaller red dwarfs
are different.
543
00:32:11,563 --> 00:32:15,043
They can access all
the hydrogen they want.
544
00:32:15,067 --> 00:32:18,546
In low-mass stars,
outside of the core,
545
00:32:18,570 --> 00:32:21,483
this outer layer
is fully convective.
546
00:32:21,507 --> 00:32:25,353
What that means is, stuff near
the core rises to the surface
547
00:32:25,377 --> 00:32:28,290
and then drops back down
all the way to the core,
548
00:32:28,314 --> 00:32:30,492
and that means if you have
hydrogen somewhere
549
00:32:30,516 --> 00:32:33,128
outside of the core,
eventually, it's going to make
550
00:32:33,152 --> 00:32:35,597
its way down there,
and it can be used for fuel.
551
00:32:35,621 --> 00:32:37,832
The red dwarf has
access to everything
552
00:32:37,856 --> 00:32:39,167
at the all-you-can-eat buffet.
553
00:32:39,191 --> 00:32:41,736
It can grab stuff from
the distant regions
554
00:32:41,760 --> 00:32:44,773
at the surface of the star
and bring it all the way
555
00:32:44,797 --> 00:32:48,098
down the gullet
to the heart of the star.
556
00:32:49,201 --> 00:32:52,414
This all-you-can-eat
hydrogen buffet
557
00:32:52,438 --> 00:32:56,518
extends the life span of red
dwarfs to incredible lengths.
558
00:32:56,542 --> 00:33:00,322
The universe is over 13 billion
years old,
559
00:33:00,346 --> 00:33:04,114
but any red dwarf
that age is a toddler.
560
00:33:05,517 --> 00:33:07,362
A red dwarf, even if it was born
561
00:33:07,386 --> 00:33:09,297
at the very beginning
of the universe
562
00:33:09,321 --> 00:33:11,032
when red dwarfs
could first form,
563
00:33:11,056 --> 00:33:14,703
even today, it's just
a tiny fraction of its lifespan.
564
00:33:14,727 --> 00:33:17,272
They can last for trillions
of years,
565
00:33:17,296 --> 00:33:20,542
thousands of times
the current age of the universe.
566
00:33:20,566 --> 00:33:22,610
Thirteen billion years old...
567
00:33:22,634 --> 00:33:24,779
that seems like a long time,
568
00:33:24,803 --> 00:33:26,581
but a small red dwarf,
569
00:33:26,605 --> 00:33:28,783
it's barely out of diapers.
570
00:33:30,609 --> 00:33:33,021
Red dwarf stars will not die out
571
00:33:33,045 --> 00:33:36,558
for 10 trillion years or more...
572
00:33:36,582 --> 00:33:40,462
And we're discovering
they have another trump card
573
00:33:40,486 --> 00:33:42,230
that's good news for life.
574
00:33:46,425 --> 00:33:48,737
February 2017.
575
00:33:48,761 --> 00:33:51,473
NASA announced
the discovery of a system
576
00:33:51,497 --> 00:33:55,143
in the Aquarius constellation
called Trappist-1
577
00:33:55,167 --> 00:34:00,570
where seven earth-sized
planets orbit a red dwarf star.
578
00:34:01,707 --> 00:34:04,953
It turns out that red
dwarfs, apparently,
579
00:34:04,977 --> 00:34:07,422
are really good
at making planets,
580
00:34:07,446 --> 00:34:10,725
including planets that are
roughly the size of the earth.
581
00:34:10,749 --> 00:34:16,164
That's really cool because
these stars last a long time.
582
00:34:16,188 --> 00:34:18,666
If they have planets
orbiting them with life,
583
00:34:18,690 --> 00:34:22,692
they could outlast our solar
system by trillions of years.
584
00:34:23,762 --> 00:34:28,465
Sounds promising, but
red dwarfs have an ugly side.
585
00:34:30,235 --> 00:34:32,547
In October 2018,
586
00:34:32,571 --> 00:34:35,283
astronomers turned
the Hubble space telescope
587
00:34:35,307 --> 00:34:38,586
to a series of young
red dwarf stars
588
00:34:38,610 --> 00:34:41,823
in the Tucana-Horologium
association.
589
00:34:41,847 --> 00:34:47,829
They witnessed these infants
throwing daily stellar tantrums.
590
00:34:47,853 --> 00:34:49,898
Even though they're
the smallest stars,
591
00:34:49,922 --> 00:34:52,367
they actually have
some of the strongest flares
592
00:34:52,391 --> 00:34:54,335
and storms on them.
593
00:34:54,359 --> 00:34:56,871
Red dwarfs can emit flares
594
00:34:56,895 --> 00:35:00,575
10,000 times more powerful
than the sun.
595
00:35:00,599 --> 00:35:04,634
These flares would cook
any nearby planets.
596
00:35:05,637 --> 00:35:07,348
When a red dwarf star forms,
597
00:35:07,372 --> 00:35:08,983
they're rotating very rapidly,
598
00:35:09,007 --> 00:35:11,386
and this creates
a lot of magnetic activity
599
00:35:11,410 --> 00:35:14,556
which creates flares
and mass ejections.
600
00:35:14,580 --> 00:35:16,925
For life to exist,
601
00:35:16,949 --> 00:35:21,251
it would have to wait for infant
red dwarfs to grow up.
602
00:35:22,754 --> 00:35:24,799
As a red dwarf gets older,
603
00:35:24,823 --> 00:35:27,435
there's drag between
the magnetic fields
604
00:35:27,459 --> 00:35:30,105
in space as it rotates,
and that has the effect
605
00:35:30,129 --> 00:35:32,107
of slowing down
its rate of rotation.
606
00:35:32,131 --> 00:35:34,409
And so this means
the activity settles down.
607
00:35:34,433 --> 00:35:38,012
So maybe later, in this life
of a red dwarf star,
608
00:35:38,036 --> 00:35:40,570
they can support
planets with life.
609
00:35:42,908 --> 00:35:47,155
Red dwarf stars will
dominate the future universe
610
00:35:47,179 --> 00:35:50,892
and may give life
a chance to survive.
611
00:35:50,916 --> 00:35:55,096
These small red stars
are extremely long-lived,
612
00:35:55,120 --> 00:35:57,732
but no star is immortal.
613
00:35:57,756 --> 00:36:01,302
Even though they're really going
through their nuclear fuel
614
00:36:01,326 --> 00:36:06,329
very slowly, there's just not
enough fuel to last forever.
615
00:36:07,599 --> 00:36:10,778
These little stars
will die out eventually.
616
00:36:10,802 --> 00:36:16,084
Unlike their larger stellar
siblings, they'll go quietly.
617
00:36:16,108 --> 00:36:18,219
Well, it actually just gets
hotter,
618
00:36:18,243 --> 00:36:21,156
and the color of a star
depends on its temperature.
619
00:36:21,180 --> 00:36:24,192
So as the red dwarf gets hotter,
it turns bluer.
620
00:36:24,216 --> 00:36:27,128
So sometime
in the very distant future,
621
00:36:27,152 --> 00:36:28,463
some of these red dwarfs
622
00:36:28,487 --> 00:36:31,232
are actually going
to become blue dwarfs.
623
00:36:31,256 --> 00:36:35,703
The universe isn't old enough
for blue dwarfs to exist yet.
624
00:36:35,727 --> 00:36:38,206
But trillions of years from now,
625
00:36:38,230 --> 00:36:43,133
a dim blue glow will
complete the star apocalypse.
626
00:36:44,236 --> 00:36:48,183
There will be a last star,
one last red dwarf,
627
00:36:48,207 --> 00:36:51,586
maybe now turning blue
as it warms up,
628
00:36:51,610 --> 00:36:55,712
but it too will eventually
cool off, fade away.
629
00:36:56,848 --> 00:36:59,394
And there will be no more stars
in the universe.
630
00:36:59,418 --> 00:37:01,396
It is inevitable.
631
00:37:03,455 --> 00:37:06,534
In this dark, starless universe,
632
00:37:06,558 --> 00:37:09,804
prospects for life
seem impossible.
633
00:37:09,828 --> 00:37:14,042
But will something else
take the place of stars?
634
00:37:14,066 --> 00:37:16,678
As we get to the end of
the universe,
635
00:37:16,702 --> 00:37:19,869
things get really cold,
but they also get really weird.
636
00:37:35,854 --> 00:37:39,133
Trillions of years
from now, the star apocalypse
637
00:37:39,157 --> 00:37:42,670
will leave the universe
empty and dark,
638
00:37:42,694 --> 00:37:45,295
a never-ending night.
639
00:37:46,331 --> 00:37:47,942
The universe at this time
640
00:37:47,966 --> 00:37:49,844
is nothing like
the universe of today.
641
00:37:49,868 --> 00:37:55,350
There's no light, and it's
really cold and very lonely.
642
00:37:55,374 --> 00:37:59,187
When all of the stars die
and the light goes away,
643
00:37:59,211 --> 00:38:01,189
anything that relies on the heat
644
00:38:01,213 --> 00:38:04,392
and the processes from
these stars will start to die.
645
00:38:06,285 --> 00:38:08,563
Once all the lights go out,
646
00:38:08,587 --> 00:38:12,367
the only things that will remain
will be the leftovers.
647
00:38:12,391 --> 00:38:15,169
With stars as we know
them long gone,
648
00:38:15,193 --> 00:38:17,939
could something else
spark into existence
649
00:38:17,963 --> 00:38:20,341
in this cosmic wasteland?
650
00:38:20,365 --> 00:38:23,278
You'd think that's it,
no more star formation.
651
00:38:23,302 --> 00:38:27,181
But the universe still
has a few tricks up its sleeve.
652
00:38:27,205 --> 00:38:29,851
Over the history
of the universe,
653
00:38:29,875 --> 00:38:32,620
generations of stars
have lived and died.
654
00:38:32,644 --> 00:38:36,090
They released heavy metal
elements into the universe,
655
00:38:36,114 --> 00:38:39,727
building materials
for a new kind of star,
656
00:38:39,751 --> 00:38:42,263
and stars born from these
new materials
657
00:38:42,287 --> 00:38:46,801
can do things
their ancestors could not.
658
00:38:46,825 --> 00:38:50,872
As you enrich the universe,
as more and more metals
659
00:38:50,896 --> 00:38:52,607
get produced over time,
660
00:38:52,631 --> 00:38:56,311
you can lower
the temperature needed
661
00:38:56,335 --> 00:38:58,913
for fusion reactions in a star.
662
00:38:58,937 --> 00:39:02,617
With lower
temperatures needed for fusion,
663
00:39:02,641 --> 00:39:06,354
stars have
become smaller and smaller.
664
00:39:06,378 --> 00:39:08,956
Currently, the smallest
possible star
665
00:39:08,980 --> 00:39:11,626
is a little under 10 percent
the sun's mass.
666
00:39:11,650 --> 00:39:14,062
But eventually it may
be possible to form stars
667
00:39:14,086 --> 00:39:16,686
that have around 4 percent
the sun's mass.
668
00:39:18,256 --> 00:39:21,703
Hundreds of trillions
of years in the future,
669
00:39:21,727 --> 00:39:24,439
a new star may dominate
the universe,
670
00:39:24,463 --> 00:39:30,545
built from scraps left over
from generations of dead stars,
671
00:39:30,569 --> 00:39:32,647
a star so small
672
00:39:32,671 --> 00:39:36,039
that it burns cold
instead of hot.
673
00:39:37,476 --> 00:39:39,320
One of the weirdest types
of stars
674
00:39:39,344 --> 00:39:42,156
that scientists hypothesize
might exist in the far future
675
00:39:42,180 --> 00:39:43,880
is the frozen star.
676
00:39:45,417 --> 00:39:49,564
You can start forming
stars that are very, very small
677
00:39:49,588 --> 00:39:52,900
and very cold,
where nuclear fusion
678
00:39:52,924 --> 00:39:57,472
is happening in the core,
but the surfaces are cold.
679
00:40:00,832 --> 00:40:02,844
These small, cold objects
680
00:40:02,868 --> 00:40:04,946
will be thousands of times
dimmer
681
00:40:04,970 --> 00:40:08,449
than the faintest star
we see today.
682
00:40:08,473 --> 00:40:11,853
So cold, the temperatures
on the surface
683
00:40:11,877 --> 00:40:15,456
could reach just 32 degrees
Fahrenheit...
684
00:40:15,480 --> 00:40:19,761
And ice clouds may form
in the star's atmosphere.
685
00:40:19,785 --> 00:40:23,398
They are so much cooler
than stars now.
686
00:40:23,422 --> 00:40:27,902
They could actually have ice,
water ice, on their surface,
687
00:40:27,926 --> 00:40:31,472
even though
they are technically stars.
688
00:40:31,496 --> 00:40:36,077
It's literal water-ice
covering the surface of a star,
689
00:40:36,101 --> 00:40:39,580
the same ice that you can use
for ice-skating
690
00:40:39,604 --> 00:40:41,549
or ice racing or curling.
691
00:40:41,573 --> 00:40:43,284
You could do all of this
692
00:40:43,308 --> 00:40:46,476
on the surface of a star
in the far future.
693
00:40:47,646 --> 00:40:50,024
It's hard to predict
if life could arise
694
00:40:50,048 --> 00:40:53,316
on planets
orbiting frozen stars.
695
00:40:55,454 --> 00:40:59,667
We won't know
until one appears...
696
00:40:59,691 --> 00:41:03,827
And that
won't be for a very long time.
697
00:41:05,497 --> 00:41:07,308
The universe is far too young
698
00:41:07,332 --> 00:41:09,610
for even the first one
of these things
699
00:41:09,634 --> 00:41:11,446
to even be a glimmer of an idea.
700
00:41:11,470 --> 00:41:14,081
So if you want to wait,
you know, a quadrillion years,
701
00:41:14,105 --> 00:41:15,917
then we can find out.
702
00:41:15,941 --> 00:41:18,753
Stars helped create us,
703
00:41:18,777 --> 00:41:21,055
building and spreading
the ingredients
704
00:41:21,079 --> 00:41:23,124
for life to develop,
705
00:41:23,148 --> 00:41:25,159
but the coming star apocalypse
706
00:41:25,183 --> 00:41:27,829
may mean the end of life,
707
00:41:27,853 --> 00:41:30,186
just not for a while.
708
00:41:31,656 --> 00:41:36,337
Small red stars will continue
to illuminate the darkness...
709
00:41:36,361 --> 00:41:41,042
Safe havens for life to survive
and even flourish.
710
00:41:41,066 --> 00:41:42,777
As for us on earth,
711
00:41:42,801 --> 00:41:46,214
we should be
most thankful for one star
712
00:41:46,238 --> 00:41:50,451
because without it,
we simply wouldn't exist.
713
00:41:50,475 --> 00:41:53,621
I really want you to never
experience a sunny day again
714
00:41:53,645 --> 00:41:54,989
and not think about this.
715
00:41:55,013 --> 00:41:57,358
The sun, someday, will burn out,
716
00:41:57,382 --> 00:41:59,527
and so will all of
the other stars.
717
00:41:59,551 --> 00:42:03,598
We are in this wonderful era
of light and warmth
718
00:42:03,622 --> 00:42:05,132
coming out of the sky,
719
00:42:05,156 --> 00:42:09,036
and everything is going to go
dark, absolutely everything,
720
00:42:09,060 --> 00:42:11,138
everywhere in the universe.
721
00:42:11,162 --> 00:42:14,408
So for the time being, you know,
enjoy the light.
722
00:42:14,432 --> 00:42:16,511
Step outside, enjoy the sun,
723
00:42:16,535 --> 00:42:19,647
and think about how lucky we are
to live in this time.
58125
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