1
00:00:03,044 --> 00:00:07,180
Space -- a maelstrom
of chaos and violence.

2
00:00:07,182 --> 00:00:10,316
Stars gobbling up other stars.

3
00:00:10,318 --> 00:00:13,519
Black holes eating up
entire star systems.

4
00:00:13,521 --> 00:00:16,422
Galaxies colliding
with other galaxies.

5
00:00:17,223 --> 00:00:20,058
The Universe
is a hostile place.

6
00:00:20,060 --> 00:00:23,127
You are blowing up a star.

7
00:00:23,129 --> 00:00:26,664
There's no way to describe
that kind of energy.

8
00:00:26,666 --> 00:00:30,167
The hidden mechanism
controlling these phenomenon --

9
00:00:30,169 --> 00:00:31,902
orbits.

10
00:00:31,904 --> 00:00:34,704
If you understand
all possible orbits,

11
00:00:34,706 --> 00:00:38,040
you understand the dynamics
driving the Universe.

12
00:00:38,042 --> 00:00:42,311
Orbits hold everything
together and tear it all apart.

13
00:00:42,313 --> 00:00:44,946
Extreme orbits mean
colliding galaxies,

14
00:00:44,948 --> 00:00:48,249
collapsing dust clouds,
the very creation of life,

15
00:00:48,251 --> 00:00:49,384
as well as destruction.

16
00:00:50,819 --> 00:00:52,953
Extreme orbits --

17
00:00:52,955 --> 00:00:55,689
Masters of life and death
in our Universe.

18
00:01:09,903 --> 00:01:12,437
This is our solar system.

19
00:01:12,439 --> 00:01:16,607
8 planets, more than 150 moons,

20
00:01:16,609 --> 00:01:22,312
billions of space rocks,
dust, and gas

21
00:01:22,314 --> 00:01:25,215
all orbit a single star

22
00:01:25,217 --> 00:01:31,487
in a giant whirling disk
10 billion miles across.

23
00:01:31,489 --> 00:01:34,656
It's been this way
for 4 billion years.

24
00:01:34,658 --> 00:01:37,859
Everything moves around
in an orderly fashion,

25
00:01:37,861 --> 00:01:40,428
serene and stable.

26
00:01:44,066 --> 00:01:46,367
But our solar system is unusual.

27
00:01:48,203 --> 00:01:52,972
Elsewhere in our Universe,
orbits are nothing like this.

28
00:01:52,974 --> 00:01:58,544
They're unstable, chaotic,
even destructive.

29
00:02:02,115 --> 00:02:03,615
Even in the nearby Universe,

30
00:02:03,617 --> 00:02:07,084
we see incredibly violent
examples of orbits --

31
00:02:07,086 --> 00:02:10,120
giant planets that hurtle in
toward their stars.

32
00:02:10,122 --> 00:02:12,189
We see shock waves
of thousands of degrees

33
00:02:12,191 --> 00:02:13,857
perpetuate
through the atmosphere.

34
00:02:13,859 --> 00:02:15,292
There are planets that dip

35
00:02:15,294 --> 00:02:17,527
right over the surfaces
of other stars,

36
00:02:17,529 --> 00:02:20,630
huge stars orbiting each other,
multiple orbital systems,

37
00:02:20,632 --> 00:02:22,498
where there's just chaos,

38
00:02:22,500 --> 00:02:24,834
and entire objects can be kicked
out of the system.

39
00:02:24,836 --> 00:02:27,236
Stars gobbling up other stars.

40
00:02:27,238 --> 00:02:30,672
Black holes eating up
entire star systems.

41
00:02:30,674 --> 00:02:34,008
Galaxies colliding
with other galaxies.

42
00:02:34,010 --> 00:02:35,209
That's the norm.

43
00:02:38,342 --> 00:02:42,478
Earth is an oasis
of water and warmth.

44
00:02:42,480 --> 00:02:48,550
Life flourishes because
of how we orbit the Sun.

45
00:02:48,552 --> 00:02:53,087
Earth's orbit
is almost circular.

46
00:02:53,089 --> 00:02:57,090
We stay about the same distance
from the Sun all year round.

47
00:03:00,161 --> 00:03:03,262
The temperature here
is relatively constant.

48
00:03:03,264 --> 00:03:05,731
And Earth's orbit
has been stable

49
00:03:05,733 --> 00:03:09,401
for the past
4 1/2 billion years.

50
00:03:10,970 --> 00:03:14,339
Without this stability,
we would not exist.

51
00:03:14,341 --> 00:03:19,009
To create DNA out of the oceans
takes hundreds of millions,

52
00:03:19,011 --> 00:03:20,944
perhaps even a billion years.

53
00:03:20,946 --> 00:03:24,247
And for that stability,
you need circular orbits.

54
00:03:24,249 --> 00:03:27,217
And so without the stability
of the solar system

55
00:03:27,219 --> 00:03:30,186
and the Earth's orbit,
there's no life on Earth.

56
00:03:34,925 --> 00:03:37,159
We owe everything
to Earth's orbit.

57
00:03:37,161 --> 00:03:39,261
We get a gentle ride.

58
00:03:39,263 --> 00:03:42,664
In an otherwise
violent Universe,

59
00:03:42,666 --> 00:03:46,333
we've hit the orbital jackpot.

60
00:03:46,335 --> 00:03:50,337
Yet, chaos is never far away.

61
00:03:50,339 --> 00:03:52,372
Even within our solar system,

62
00:03:52,374 --> 00:03:55,174
there are extreme
and violent orbits,

63
00:03:55,176 --> 00:03:58,978
where life could never survive.

64
00:03:58,980 --> 00:04:02,547
Mercury --
the closest rock to the Sun

65
00:04:02,549 --> 00:04:06,551
and the smallest planet
in the solar system.

66
00:04:06,553 --> 00:04:10,121
Its orbit stretches
into an oval shape.

67
00:04:10,123 --> 00:04:11,522
At its furthest point,

68
00:04:11,524 --> 00:04:15,359
Mercury is 43 million miles
from the Sun.

69
00:04:15,361 --> 00:04:20,430
But at its closest point,
it's just 28 million.

70
00:04:20,432 --> 00:04:24,000
This close in, it's hot.

71
00:04:24,002 --> 00:04:27,469
800 degrees Fahrenheit,
hotter than a baker's oven.

72
00:04:27,471 --> 00:04:30,906
Also, because there's very
little atmosphere on Mercury,

73
00:04:30,908 --> 00:04:32,107
you'd choke.

74
00:04:32,109 --> 00:04:34,275
And because
there's no air to speak of,

75
00:04:34,277 --> 00:04:36,644
the blood in your body
would boil

76
00:04:36,646 --> 00:04:38,579
and it would burst your skin.

77
00:04:38,581 --> 00:04:41,682
You would literally explode
on the surface of Mercury.

78
00:04:45,319 --> 00:04:47,454
But the temperature
can also fall

79
00:04:47,456 --> 00:04:50,890
to 300 degrees below zero,

80
00:04:50,892 --> 00:04:54,994
three times colder than
the coldest place on Earth.

81
00:04:56,429 --> 00:05:00,131
Mercury has the most extreme
temperature variations

82
00:05:00,133 --> 00:05:03,001
of any planet
in the solar system.

83
00:05:03,003 --> 00:05:07,104
But it's also proof
that orbits don't just loop.

84
00:05:07,106 --> 00:05:12,142
With each revolution around
the Sun, Mercury's path shifts.

85
00:05:12,144 --> 00:05:16,879
Over thousands of years, the
planet follows a daisy pattern.

86
00:05:18,682 --> 00:05:20,649
At the other end
of the solar system,

87
00:05:20,651 --> 00:05:24,686
there's Pluto,
4 billion miles from the Sun.

88
00:05:24,688 --> 00:05:30,191
The further away an object is,
the slower its orbit.

89
00:05:30,793 --> 00:05:37,130
Pluto takes 248 years
to complete a single loop.

90
00:05:37,132 --> 00:05:40,066
And Pluto is an anomaly.

91
00:05:40,068 --> 00:05:42,468
Its stretched orbit

92
00:05:42,470 --> 00:05:46,104
is on a completely different
plane from the major planets,

93
00:05:46,106 --> 00:05:50,642
and it creates
an amazing spectacle.

94
00:05:50,644 --> 00:05:52,310
During most of its orbit,

95
00:05:52,312 --> 00:05:56,280
Pluto is a frozen block of ice
and rock.

96
00:05:56,282 --> 00:06:00,117
But as it gets closer
to the Sun, summer begins.

97
00:06:01,652 --> 00:06:07,456
When Pluto warms up, the frozen
ices on the surface of Pluto --

98
00:06:07,458 --> 00:06:10,259
these are water ices,
carbon dioxide,

99
00:06:10,261 --> 00:06:15,096
even some carbon monoxide, maybe
methane ices -- they evaporate.

100
00:06:15,098 --> 00:06:17,632
And you get a fog,
and the fog gets thicker.

101
00:06:17,634 --> 00:06:19,200
And then you get thick clouds,

102
00:06:19,202 --> 00:06:22,136
and, suddenly, you have an
actual atmosphere around Pluto

103
00:06:22,138 --> 00:06:25,606
that wasn't there before.

104
00:06:25,608 --> 00:06:27,207
This atmosphere

105
00:06:27,209 --> 00:06:30,110
is thickest when Pluto
is closest to the Sun.

106
00:06:30,112 --> 00:06:34,080
But as the planet
heads back into deep space,

107
00:06:34,082 --> 00:06:38,150
the temperature plummets
to 400 degrees below zero.

108
00:06:40,120 --> 00:06:44,756
It begins to snow flakes
of frozen nitrogen and methane.

109
00:06:47,326 --> 00:06:49,093
As winter comes,

110
00:06:49,095 --> 00:06:52,563
these gases slowly begin
to freeze out of the atmosphere.

111
00:06:52,565 --> 00:06:54,965
They may rain down
in a snow-like way,

112
00:06:54,967 --> 00:06:56,833
but, gradually, they accumulate

113
00:06:56,835 --> 00:06:59,335
sort of a glassy,
semitransparent layer,

114
00:06:59,337 --> 00:07:02,137
a frozen atmosphere
on the surface of Pluto.

115
00:07:02,139 --> 00:07:07,242
After a bitter winter,
Pluto drifts closer to the Sun,

116
00:07:07,244 --> 00:07:11,712
and the 248-year cycle
begins again.

117
00:07:11,714 --> 00:07:16,850
Extreme changes like these
remind us how lucky we are

118
00:07:16,852 --> 00:07:19,619
that earth's orbit is stable
and benign.

119
00:07:23,056 --> 00:07:25,056
But it's a delicate balance.

120
00:07:25,058 --> 00:07:28,293
The smallest change
could kill us all.

121
00:07:28,295 --> 00:07:32,029
If Earth's orbit were closer
to the Sun,

122
00:07:32,031 --> 00:07:35,699
we would be like
our closest neighbor, Venus.

123
00:07:35,701 --> 00:07:37,067
Venus is a pretty good example

124
00:07:37,069 --> 00:07:38,735
of what might happen
to the Earth

125
00:07:38,737 --> 00:07:41,303
if our orbit shifted a little
bit in from where we are now.

126
00:07:41,305 --> 00:07:43,605
Venus has this hugely
thick atmosphere

127
00:07:43,607 --> 00:07:45,173
that traps all of the heat,

128
00:07:45,175 --> 00:07:47,575
and the surface is close
to 900 degrees.

129
00:07:47,577 --> 00:07:50,545
If we moved even just
a little bit closer to the Sun,

130
00:07:50,547 --> 00:07:52,179
we would become more like Venus.

131
00:07:52,181 --> 00:07:56,550
Oceans would boil away.

132
00:07:56,552 --> 00:07:58,718
Our planet would become
a desert.

133
00:07:58,720 --> 00:08:01,520
Life would be destroyed.

134
00:08:03,723 --> 00:08:07,225
A small shift
in the opposite direction,

135
00:08:07,227 --> 00:08:11,829
and instead of boiling,
we'd freeze.

136
00:08:11,831 --> 00:08:13,964
You would have snowball Earth,

137
00:08:13,966 --> 00:08:16,733
the Earth completely encased
in ice.

138
00:08:16,735 --> 00:08:19,035
And that's only by moving
the Earth

139
00:08:19,037 --> 00:08:21,571
a fraction of its distance
from the Sun.

140
00:08:27,344 --> 00:08:30,445
The polar ice caps would expand.

141
00:08:30,447 --> 00:08:34,481
Oceans would freeze.

142
00:08:34,483 --> 00:08:37,651
A permanent ice age would begin.

143
00:08:37,653 --> 00:08:40,553
The smallest shift
in Earth's orbit,

144
00:08:40,555 --> 00:08:43,322
and we'd die by fire or ice.

145
00:08:44,491 --> 00:08:47,292
Orbits allow life to flourish.

146
00:08:50,596 --> 00:08:53,331
But they can also cause chaos.

147
00:08:55,667 --> 00:08:59,569
Orbits are even capable
of destroying entire stars.

148
00:09:08,263 --> 00:09:12,771
Our planet's orbit
makes life possible.

149
00:09:12,773 --> 00:09:16,213
But most orbits are violent.

150
00:09:20,491 --> 00:09:26,296
Space is a cosmic freeway.
Nothing stands still.

151
00:09:26,298 --> 00:09:30,402
Everything moves
around everything else,

152
00:09:30,404 --> 00:09:33,404
thanks to a single force --
gravity.

153
00:09:36,108 --> 00:09:39,048
Gravity is the universal force
of attraction

154
00:09:39,050 --> 00:09:41,951
that spreads throughout
the Universe itself.

155
00:09:41,953 --> 00:09:44,256
It's the force
that holds stars together.

156
00:09:44,258 --> 00:09:47,467
It's the force that binds
the solar system together.

157
00:09:47,469 --> 00:09:50,946
All objects have gravity,

158
00:09:50,948 --> 00:09:53,761
so all objects
attract each other.

159
00:09:53,763 --> 00:09:58,036
The more mass an object has,
the stronger its attraction.

160
00:09:58,038 --> 00:10:01,772
That's why falling apples
are pulled toward Earth.

161
00:10:04,443 --> 00:10:08,578
In our solar system,
the biggest object is the Sun.

162
00:10:11,849 --> 00:10:17,190
It's 700 times more massive than
all the planets put together.

163
00:10:17,192 --> 00:10:20,493
The titanic force
of the Sun's gravity

164
00:10:20,495 --> 00:10:22,862
pulls all the planets inward.

165
00:10:22,864 --> 00:10:26,698
But something stops them
from falling in.

166
00:10:26,700 --> 00:10:30,134
The planets
are in constant motion.

167
00:10:30,136 --> 00:10:34,336
They fly through space
at incredible speed --

168
00:10:34,338 --> 00:10:38,273
not directly toward the sun
but sideways,

169
00:10:38,275 --> 00:10:40,208
creating a tug-of-war

170
00:10:40,210 --> 00:10:44,479
between the Sun's gravity
and the planets' speed.

171
00:10:44,481 --> 00:10:49,257
When the two balance out,
the planet loops around the Sun.

172
00:10:49,259 --> 00:10:51,960
We call this an orbit.

173
00:10:51,962 --> 00:10:55,430
An orbit is simply the motion,

174
00:10:55,432 --> 00:10:59,667
the path of an object around
another object due to gravity.

175
00:10:59,669 --> 00:11:02,870
So you can have circular orbits.
You can have elliptical orbits.

176
00:11:02,872 --> 00:11:05,606
Even if I were to take a ball
and throw it in the air

177
00:11:05,608 --> 00:11:07,208
and catch it, very briefly,

178
00:11:07,210 --> 00:11:10,343
that ball is an orbit around
the center of the Earth.

179
00:11:10,345 --> 00:11:12,709
It's just motion
affected by gravity.

180
00:11:12,711 --> 00:11:16,807
Imagine what would happen

181
00:11:16,809 --> 00:11:19,943
if the Sun had no gravity.

182
00:11:19,945 --> 00:11:23,480
The planets' speed would
shoot them out into space.

183
00:11:25,082 --> 00:11:28,785
On the other hand,
if the planets stopped moving,

184
00:11:28,787 --> 00:11:31,254
gravity would pull them
into the Sun.

185
00:11:37,660 --> 00:11:42,364
All orbits are a balance
between gravity and motion.

186
00:11:46,768 --> 00:11:50,537
We like to think the Universe
runs like clockwork,

187
00:11:50,539 --> 00:11:52,638
everything neat and orderly,

188
00:11:52,640 --> 00:11:58,009
the planets moving
in cosmic harmony.

189
00:11:58,011 --> 00:11:59,243
But that's wrong.

190
00:11:59,245 --> 00:12:03,914
Orbits can be wild
and unpredictable.

191
00:12:03,916 --> 00:12:06,883
And the more objects there are,

192
00:12:06,885 --> 00:12:11,188
the more unpredictable
their orbits become.

193
00:12:11,190 --> 00:12:14,391
Things can get complicated when
you have more than two objects

194
00:12:14,393 --> 00:12:16,059
all trying to orbit
around each other.

195
00:12:16,061 --> 00:12:19,929
Then an orbit can actually loop
between one object and another.

196
00:12:19,931 --> 00:12:22,197
Speeds can get faster
and slower.

197
00:12:22,199 --> 00:12:25,100
An orbit doesn't have to be
just one regular path.

198
00:12:28,937 --> 00:12:31,338
The Universe's creativity

199
00:12:31,340 --> 00:12:32,840
defies the imagination.

200
00:12:32,842 --> 00:12:38,644
Travel out beyond Pluto,
halfway to the nearest star,

201
00:12:38,646 --> 00:12:44,916
and you find these --
comets, chunks of ice and rock.

202
00:12:44,918 --> 00:12:47,652
They float in vast clouds,

203
00:12:47,654 --> 00:12:53,124
frozen remnants from the dawn
of our solar system.

204
00:12:53,126 --> 00:12:57,494
Every so often,
one falls towards the Sun.

205
00:12:57,496 --> 00:12:59,729
They can start
a trillion miles out

206
00:12:59,731 --> 00:13:02,432
and fall right above the surface
of the Sun.

207
00:13:02,434 --> 00:13:05,668
So when they're really far away,
they're hardly moving at all.

208
00:13:05,670 --> 00:13:07,636
When they're whipping
past the Sun,

209
00:13:07,638 --> 00:13:09,605
they're moving really,
really fast.

210
00:13:09,607 --> 00:13:11,907
And so, these can be some
of the most extreme orbits

211
00:13:11,909 --> 00:13:13,275
in the solar system.

212
00:13:13,277 --> 00:13:16,611
They can be so elongated,
they're almost a straight line.

213
00:13:18,247 --> 00:13:23,350
Comets travel at
up to a million miles an hour.

214
00:13:23,352 --> 00:13:29,723
They're cosmic missiles
guided by gravity and speed.

215
00:13:29,725 --> 00:13:34,960
Comets show us how
destructive orbits can be.

216
00:13:34,962 --> 00:13:37,262
Many plunge into the Sun...

217
00:13:39,799 --> 00:13:43,167
...or crash into planets.

218
00:13:43,169 --> 00:13:44,802
If a comet were
to hit the Earth,

219
00:13:44,804 --> 00:13:48,672
perhaps 5, 6 miles across...

220
00:13:48,674 --> 00:13:52,008
Watch out.
It would be a planet-buster.

221
00:13:52,010 --> 00:13:53,509
It would be an object

222
00:13:53,511 --> 00:13:57,479
sufficient to wipe out all life
as we know it on the planet.

223
00:13:57,481 --> 00:14:02,150
But most comets miss.

224
00:14:02,152 --> 00:14:04,686
They fly in from deep space

225
00:14:04,688 --> 00:14:08,357
and out again
on million-year orbits.

226
00:14:11,862 --> 00:14:14,763
But move beyond
our solar system,

227
00:14:14,765 --> 00:14:18,833
and orbits become
even more violent.

228
00:14:18,835 --> 00:14:23,203
Death spirals rip apart
entire planets...

229
00:14:24,438 --> 00:14:29,475
...shred stars, and even
tear holes in space.

230
00:14:48,034 --> 00:14:51,299
The Universe
is unimaginably big,

231
00:14:51,300 --> 00:14:54,365
so there should be other
Earth-like worlds out there.

232
00:14:54,367 --> 00:14:54,713
Scientists looking
for habitable planets

233
00:14:54,714 --> 00:14:57,548
thought they would find orbits
just like ours.

234
00:14:58,232 --> 00:14:59,691
They were wrong.

235
00:14:59,716 --> 00:15:02,548
Now we're on HD 154088.

236
00:15:02,549 --> 00:15:04,615
They were wrong.

237
00:15:04,617 --> 00:15:08,485
Now we're on HD 154088.

238
00:15:08,487 --> 00:15:11,954
And there it is.
Looks good.

239
00:15:11,956 --> 00:15:14,590
We have discovered
hundreds of planets

240
00:15:14,592 --> 00:15:18,527
outside our solar system, but
they're not like Earth at all.

241
00:15:18,529 --> 00:15:25,265
These are strange, alien worlds
with unfamiliar orbits.

242
00:15:25,267 --> 00:15:28,401
What we're finding
among extra-solar planets

243
00:15:28,403 --> 00:15:33,672
is an incredible diversity of
these orbital shapes and sizes.

244
00:15:33,674 --> 00:15:37,643
Some of the orbits are extremely
tight around their host star,

245
00:15:37,645 --> 00:15:40,746
the planet going around
in just hours or days.

246
00:15:40,748 --> 00:15:44,716
So we're seeing interactions
and shapes and sizes of orbits

247
00:15:44,718 --> 00:15:46,618
that are like nothing
we ever imagined.

248
00:15:50,757 --> 00:15:53,092
Some worlds are so hostile,

249
00:15:53,094 --> 00:15:56,395
life as we know it
would be impossible.

250
00:15:56,397 --> 00:16:00,899
This is WASP-18b.

251
00:16:00,901 --> 00:16:02,601
It's a hot Jupiter,

252
00:16:02,603 --> 00:16:07,238
a class of huge planets
that closely orbit their stars.

253
00:16:10,308 --> 00:16:16,913
WASP-18b is 50 times closer to
its star than we are to the Sun.

254
00:16:16,915 --> 00:16:21,384
It's so close, it orbits
in less than one day.

255
00:16:23,753 --> 00:16:27,389
If you had said, "What's
the weirdest, least-likely orbit

256
00:16:27,391 --> 00:16:29,157
you could possibly imagine?"

257
00:16:29,159 --> 00:16:31,660
I would have said,
"take something like Jupiter

258
00:16:31,662 --> 00:16:35,129
and plop it down right next to
a star, 5 million miles away."

259
00:16:35,131 --> 00:16:37,732
And it turns out,
I would be totally wrong.

260
00:16:37,734 --> 00:16:39,806
That is an extremely
common thing

261
00:16:39,808 --> 00:16:41,475
that we see in the Universe.

262
00:16:41,477 --> 00:16:43,110
In fact, most of the planets

263
00:16:43,112 --> 00:16:44,811
that we're discovering
around other stars

264
00:16:44,813 --> 00:16:46,246
appear to be in orbits
like that.

265
00:16:46,248 --> 00:16:49,114
This cosmic duel

266
00:16:49,116 --> 00:16:53,318
produces incredibly powerful
physical effects.

267
00:16:53,320 --> 00:16:58,156
WASP-18b burns at 4,000 degrees.

268
00:16:58,158 --> 00:17:02,059
Thermal hurricanes
blast across its surface.

269
00:17:02,061 --> 00:17:04,227
And both star and planet

270
00:17:04,229 --> 00:17:08,030
are distorted by vast
gravitational forces,

271
00:17:08,032 --> 00:17:12,500
the same forces that cause
the tides on Earth.

272
00:17:12,502 --> 00:17:15,103
Everybody is familiar
with the idea of tides.

273
00:17:15,105 --> 00:17:16,404
In the course of a day,

274
00:17:16,406 --> 00:17:18,439
the level of the oceans
get higher and then lower.

275
00:17:18,441 --> 00:17:21,075
Well, that's from the influence
of the Sun and the Moon,

276
00:17:21,077 --> 00:17:23,944
from the influence of orbits,
things that are going around us

277
00:17:23,946 --> 00:17:25,245
or that we're going around.

278
00:17:25,247 --> 00:17:27,647
If you bring things
closer together,

279
00:17:27,649 --> 00:17:29,282
tides become more extreme.

280
00:17:29,284 --> 00:17:31,984
Planets can actually get pulled
into different shapes.

281
00:17:35,188 --> 00:17:39,124
WASP-18b was formed
in a cold region of space

282
00:17:39,126 --> 00:17:41,726
far away from its star.

283
00:17:41,728 --> 00:17:44,095
Over millions of years,

284
00:17:44,097 --> 00:17:48,031
it spiraled
into its present position.

285
00:17:48,033 --> 00:17:50,834
It's locked
in a gravitational battle

286
00:17:50,836 --> 00:17:53,035
that can only end one way.

287
00:17:56,539 --> 00:17:59,140
Less than a million years
from now,

288
00:17:59,142 --> 00:18:01,075
it will be consumed by fire.

289
00:18:08,949 --> 00:18:12,051
The key conclusion
you have to draw is --

290
00:18:12,053 --> 00:18:16,487
when you see the Universe today,
it won't be that way tomorrow

291
00:18:16,489 --> 00:18:19,190
and it won't be that way
the week or the millennium

292
00:18:19,192 --> 00:18:22,159
or a billion years later
because of gravity.

293
00:18:24,495 --> 00:18:27,797
Our search
for Earth-like planets

294
00:18:27,799 --> 00:18:30,099
reveals a destructive Universe,

295
00:18:30,101 --> 00:18:33,236
from the deadly missile-like
orbits of comets

296
00:18:33,238 --> 00:18:35,838
to the searing paths
of hot Jupiters.

297
00:18:35,840 --> 00:18:39,174
There are even planets

298
00:18:39,176 --> 00:18:42,210
that don't seem to orbit
anything at all.

299
00:18:42,212 --> 00:18:45,879
Scientists have recently
detected tiny fluctuations

300
00:18:45,881 --> 00:18:48,581
in the light from distant stars.

301
00:18:48,583 --> 00:18:50,482
The only explanation?

302
00:18:50,484 --> 00:18:54,686
A massive object
between us and them.

303
00:18:54,688 --> 00:18:59,123
These rogue planets
don't orbit a parent star.

304
00:18:59,125 --> 00:19:04,428
They are planetary orphans,
all alone in space.

305
00:19:04,430 --> 00:19:08,098
Planets, by definition,
go around stars,

306
00:19:08,100 --> 00:19:11,768
so, boy, were we shocked
to find rogue planets.

307
00:19:11,770 --> 00:19:15,204
Rogue planets are
a contradiction in terms --

308
00:19:15,206 --> 00:19:17,439
planets without a mother star.

309
00:19:17,441 --> 00:19:19,707
Scientists think

310
00:19:19,709 --> 00:19:23,277
every rogue planet
did once orbit a star

311
00:19:23,279 --> 00:19:25,913
until gravity hurled them away.

312
00:19:28,116 --> 00:19:31,651
New solar systems
are chaotic places.

313
00:19:31,653 --> 00:19:36,354
Planets tug on each other
and dramatically change course.

314
00:19:36,356 --> 00:19:43,927
Some planets even spiral out
to wander the galaxy alone.

315
00:19:43,929 --> 00:19:45,696
The presence of rogue planets

316
00:19:45,698 --> 00:19:49,098
shows us that gravity is not
just this attractive force

317
00:19:49,100 --> 00:19:51,734
which binds the solar system
together.

318
00:19:51,736 --> 00:19:55,069
It can also fling entire planets
into outer space.

319
00:19:55,071 --> 00:19:58,739
A recent sky survey suggests

320
00:19:58,741 --> 00:20:03,309
our galaxy contains more
rogue planets than stars.

321
00:20:03,311 --> 00:20:07,914
We've discovered orbits we
didn't even know were possible.

322
00:20:10,517 --> 00:20:14,452
Gravity and motion keep our
Universe in constant turmoil.

323
00:20:16,488 --> 00:20:20,824
Vast orbiting suns
cannibalize each other.

324
00:20:20,826 --> 00:20:24,628
Violent vortexes
distort space itself.

325
00:20:24,630 --> 00:20:30,298
And powerful forces flick a star
like a spinning top.

326
00:20:36,987 --> 00:20:41,090
Gravity causes chaos
on an epic scale...

327
00:20:43,727 --> 00:20:46,762
...hurling planets
to their destruction

328
00:20:46,764 --> 00:20:48,964
or firing them off into space.

329
00:20:50,333 --> 00:20:55,570
But the cosmic roller coaster
gets even more extreme.

330
00:20:55,572 --> 00:21:01,975
Orbits become so violent,
they rip chunks out of stars.

331
00:21:06,713 --> 00:21:08,981
This is HM Cancri,

332
00:21:08,983 --> 00:21:13,985
a binary star system
16,000 light-years from Earth.

333
00:21:13,987 --> 00:21:18,756
They're white dwarfs --
small but incredibly dense.

334
00:21:18,758 --> 00:21:23,593
One teaspoon of white-dwarf
matter can weigh 5 tons.

335
00:21:23,595 --> 00:21:27,096
The stars are just
50,000 miles apart,

336
00:21:27,098 --> 00:21:30,866
five times closer than we are
to the Moon.

337
00:21:30,868 --> 00:21:36,804
They orbit at more than
a million miles an hour.

338
00:21:36,806 --> 00:21:41,175
We have two white dwarves
an infinitesimal distance apart,

339
00:21:41,177 --> 00:21:44,612
rotating around each other
in 5 1/2 minutes.

340
00:21:44,614 --> 00:21:49,121
This is a world's record for
an astronomical body in space.

341
00:21:51,791 --> 00:21:54,959
The forces are immense.

342
00:21:54,961 --> 00:21:58,929
Gravity rips superheated gas
out of one star

343
00:21:58,931 --> 00:22:02,566
and slams it into the other.

344
00:22:02,568 --> 00:22:06,235
Scientists believe
this orbit is so violent,

345
00:22:06,237 --> 00:22:09,338
it warps the fabric of space
itself.

346
00:22:09,340 --> 00:22:15,143
In the process, the stars lose
energy, falling even closer.

347
00:22:17,379 --> 00:22:19,848
Eventually, they'll collide...

348
00:22:21,651 --> 00:22:23,985
...creating a supernova.

349
00:22:30,991 --> 00:22:35,127
A supernova is one
of the most violent,

350
00:22:35,129 --> 00:22:38,430
energetic events
in the Universe today.

351
00:22:38,432 --> 00:22:41,966
You are blowing up a star.

352
00:22:41,968 --> 00:22:44,534
There's no way to describe
that kind of energy.

353
00:22:48,638 --> 00:22:51,339
Some supernovae
are so powerful,

354
00:22:51,341 --> 00:22:54,375
they are second only
to the Big Bang itself

355
00:22:54,377 --> 00:22:56,944
for energy and sheer power.

356
00:22:56,946 --> 00:22:59,279
They are so magnificent,

357
00:22:59,281 --> 00:23:04,584
they can outshine an entire
galaxy of 200 billion stars.

358
00:23:07,020 --> 00:23:09,087
Supernovas can create

359
00:23:09,089 --> 00:23:13,591
one of the weirdest objects
in the Universe...

360
00:23:13,593 --> 00:23:15,426
a pulsar.

361
00:23:15,428 --> 00:23:18,528
Pulsars are intensely
magnetic stars.

362
00:23:18,530 --> 00:23:22,332
They fire out beams
of electromagnetic radiation

363
00:23:22,334 --> 00:23:24,634
that sweep across space.

364
00:23:24,636 --> 00:23:26,537
There are few things
in the Universe

365
00:23:26,539 --> 00:23:27,905
more dramatic than a pulsar.

366
00:23:27,907 --> 00:23:30,407
Imagine a ball
about 10 miles across

367
00:23:30,409 --> 00:23:32,876
rotating hundreds of times
a second

368
00:23:32,878 --> 00:23:35,477
with a density
that's almost unimaginable.

369
00:23:35,479 --> 00:23:37,576
1 cubic centimeter
of this material

370
00:23:37,578 --> 00:23:40,810
would have as much mass
as Mount Everest.

371
00:23:40,812 --> 00:23:45,247
You would feel a gravity that is
millions, millions of times

372
00:23:45,249 --> 00:23:47,983
what you're feeling sitting
on the surface of the Earth.

373
00:23:47,985 --> 00:23:50,152
You wouldn't just be
crushed flat by this.

374
00:23:50,154 --> 00:23:52,587
You would be crushed
into a paste

375
00:23:52,589 --> 00:23:54,689
that is only a few atoms thick.

376
00:23:54,691 --> 00:23:59,727
Anything that orbits
a pulsar too closely

377
00:23:59,729 --> 00:24:02,396
risks being torn to shreds.

378
00:24:04,899 --> 00:24:08,267
This is the black widow pulsar.

379
00:24:08,269 --> 00:24:12,904
It rips through our galaxy
at 600,000 miles an hour.

380
00:24:15,841 --> 00:24:18,443
The shock wave is so vast,

381
00:24:18,445 --> 00:24:22,880
our telescopes can't detect it
5,000 light-years away.

382
00:24:22,882 --> 00:24:25,182
Traveling alongside it,

383
00:24:25,184 --> 00:24:30,520
a brown dwarf bigger than
a planet, smaller than a star.

384
00:24:30,522 --> 00:24:34,757
The pair are locked
in an orbital dance of death.

385
00:24:34,759 --> 00:24:38,359
The black widow, in some sense,
is like a vampire,

386
00:24:38,361 --> 00:24:41,929
sucking the lifeblood
from this brown dwarf star,

387
00:24:41,931 --> 00:24:44,931
eating away at its hydrogen
and helium fuel.

388
00:24:48,068 --> 00:24:52,370
Radiation blasts the
brown dwarf's gases into space.

389
00:24:54,339 --> 00:24:56,606
A pulsar just 10 miles wide

390
00:24:56,608 --> 00:25:00,343
is destroying an object
bigger than Jupiter.

391
00:25:00,345 --> 00:25:05,248
Eventually, the brown dwarf
will evaporate.

392
00:25:07,117 --> 00:25:12,054
A single pulsar has immense
destructive power.

393
00:25:14,891 --> 00:25:16,925
But two pulsars together

394
00:25:16,927 --> 00:25:20,194
can change the shape
of the Universe.

395
00:25:20,196 --> 00:25:23,863
This is the only known
double-pulsar system

396
00:25:23,865 --> 00:25:26,498
in our galaxy.

397
00:25:26,500 --> 00:25:30,402
Orbiting at 700,000 miles
an hour,

398
00:25:30,404 --> 00:25:35,573
their speed and mass
make them spin chaotically.

399
00:25:38,843 --> 00:25:41,044
It's incredible to think

400
00:25:41,046 --> 00:25:44,013
of the enormous forces,
gravitationally,

401
00:25:44,015 --> 00:25:46,382
that these two stars exert
on each other,

402
00:25:46,384 --> 00:25:49,585
causing the whole geometry,
the architecture of the system

403
00:25:49,587 --> 00:25:53,555
to change and spin around
like a top on the table.

404
00:25:57,559 --> 00:25:59,527
The gravity
of the heavier pulsar

405
00:25:59,529 --> 00:26:03,363
makes the smaller one
wobble erratically.

406
00:26:03,365 --> 00:26:05,899
It whips around so violently

407
00:26:05,901 --> 00:26:10,970
that the whole star almost tips
over, just like a spinning top.

408
00:26:12,372 --> 00:26:15,339
It can't last forever.

409
00:26:15,341 --> 00:26:19,610
85 million years from now,
the two pulsars will merge

410
00:26:19,612 --> 00:26:22,779
to form a vast
gravitational abyss...

411
00:26:27,550 --> 00:26:32,587
...the Universe's ultimate
monster -- a black hole.

412
00:26:50,922 --> 00:26:53,789
A black hole --

413
00:26:53,791 --> 00:26:57,793
the most extreme object
in the Universe.

414
00:26:57,795 --> 00:27:03,097
At its center, the laws
of physics break down.

415
00:27:05,232 --> 00:27:08,568
Time comes to an end.

416
00:27:08,570 --> 00:27:12,072
Gravity is infinite.

417
00:27:12,074 --> 00:27:14,941
A black hole is a bottomless pit
of gravity

418
00:27:14,943 --> 00:27:16,476
caused by the death of a star.

419
00:27:16,478 --> 00:27:19,011
There is nothing in the Universe
more mysterious

420
00:27:19,013 --> 00:27:20,379
than how black holes work.

421
00:27:20,381 --> 00:27:21,546
If you want to talk about

422
00:27:21,548 --> 00:27:23,281
extreme orbits
and extreme gravity,

423
00:27:23,283 --> 00:27:24,549
you're talking black holes.

424
00:27:24,551 --> 00:27:26,252
That is at the top of the list.

425
00:27:26,254 --> 00:27:29,455
Nothing has stronger gravity
than a black hole.

426
00:27:29,457 --> 00:27:32,957
It is the mass of something
like the Sun or more

427
00:27:32,959 --> 00:27:34,892
compressed down into a ball

428
00:27:34,894 --> 00:27:37,694
that's only a couple of miles
across.

429
00:27:37,696 --> 00:27:39,462
50 years ago,

430
00:27:39,464 --> 00:27:42,932
black holes were dismissed
as science fiction,

431
00:27:42,934 --> 00:27:45,334
but not anymore.

432
00:27:48,171 --> 00:27:51,873
Now we see them
at the center of galaxies,

433
00:27:51,875 --> 00:27:53,841
wandering through outer space.

434
00:27:53,843 --> 00:27:55,509
Black holes, we now know,

435
00:27:55,511 --> 00:27:58,512
are central to the evolution
of the Universe.

436
00:28:02,149 --> 00:28:05,684
We now think there may
be 100 million black holes

437
00:28:05,686 --> 00:28:08,120
in our galaxy alone.

438
00:28:08,122 --> 00:28:13,423
An encounter with any of them
leads to oblivion.

439
00:28:17,461 --> 00:28:21,531
This is one of the largest and
hottest stars in the Universe.

440
00:28:21,533 --> 00:28:27,836
It's 20 times more massive than
our Sun and 10 times hotter.

441
00:28:34,476 --> 00:28:37,611
Stars like this never live long,

442
00:28:37,613 --> 00:28:42,281
but this one is locked
in a diabolic waltz,

443
00:28:42,283 --> 00:28:45,417
trapped in the grip
of a black hole.

444
00:28:45,419 --> 00:28:48,352
The gravity here is so powerful,

445
00:28:48,354 --> 00:28:52,223
the star orbits at
half a million miles an hour.

446
00:28:56,160 --> 00:28:59,996
The black hole sucks
the star's outer layers

447
00:28:59,998 --> 00:29:02,298
into a vast, swirling disk,

448
00:29:02,300 --> 00:29:06,434
a disk so hot
it blasts out X-rays

449
00:29:06,436 --> 00:29:11,472
a million times more powerful
than our Sun.

450
00:29:17,778 --> 00:29:19,211
This configuration --

451
00:29:19,213 --> 00:29:21,246
a star orbiting around
a black hole --

452
00:29:21,248 --> 00:29:23,282
is extreme and it's unstable.

453
00:29:23,284 --> 00:29:25,283
First of all, the black hole

454
00:29:25,285 --> 00:29:29,120
is eating away at the atmosphere
of its companion star,

455
00:29:29,122 --> 00:29:31,756
but the star itself is unstable.

456
00:29:31,758 --> 00:29:34,926
It will one day undergo
a supernova

457
00:29:34,928 --> 00:29:37,595
and perhaps leave a black hole
in its wake.

458
00:29:37,597 --> 00:29:39,963
And then it will have
two black holes

459
00:29:39,965 --> 00:29:42,098
rotating around each other,

460
00:29:42,100 --> 00:29:45,467
one of the rarest sights
in the Universe.

461
00:29:45,469 --> 00:29:49,904
Eventually,
these black holes will merge

462
00:29:49,906 --> 00:29:53,140
to create a new, larger monster,

463
00:29:53,142 --> 00:29:57,944
and the cycle of destruction
will continue.

464
00:29:57,946 --> 00:30:00,780
But this black hole is small.

465
00:30:00,782 --> 00:30:06,118
Other black holes take violence
to a whole new level.

466
00:30:06,120 --> 00:30:09,120
In 2011, astronomers witnessed

467
00:30:09,122 --> 00:30:13,690
one of the biggest explosions
ever recorded,

468
00:30:13,692 --> 00:30:18,528
a flash of radiation brighter
than 100 billion suns --

469
00:30:18,530 --> 00:30:22,031
a gamma-ray burst.

470
00:30:22,033 --> 00:30:24,400
It was a spectacular event.

471
00:30:29,539 --> 00:30:33,575
The burst came from
a supermassive black hole

472
00:30:33,577 --> 00:30:36,177
at the center
of a distant galaxy.

473
00:30:38,980 --> 00:30:40,516
It had been dormant,

474
00:30:40,518 --> 00:30:43,619
but something had shocked it
back to life.

475
00:30:46,823 --> 00:30:49,457
If you pass by
the event horizon,

476
00:30:49,459 --> 00:30:52,560
an imaginary sphere
surrounding the black hole,

477
00:30:52,562 --> 00:30:54,561
that's the point of no return.

478
00:30:54,563 --> 00:30:57,230
It's like the ultimate
roach motel --

479
00:30:57,232 --> 00:30:59,999
everything checks in,
nothing checks out.

480
00:31:07,975 --> 00:31:11,944
Several stars
were orbiting the black hole

481
00:31:11,946 --> 00:31:13,512
at a safe distance.

482
00:31:13,514 --> 00:31:15,881
Then one of them got too close.

483
00:31:15,883 --> 00:31:19,517
The sleeping giant
suddenly awoke.

484
00:31:19,519 --> 00:31:22,220
Immense gravitational forces

485
00:31:22,222 --> 00:31:26,290
stretched the star
to its breaking point

486
00:31:26,292 --> 00:31:29,827
until, finally,
it was torn apart.

487
00:31:29,829 --> 00:31:32,796
Debris swirled around
the black hole,

488
00:31:32,798 --> 00:31:35,866
heated to millions of degrees.

489
00:31:35,868 --> 00:31:40,169
Two giant jets of gamma rays

490
00:31:40,171 --> 00:31:43,105
blasted into space
at the speed of light.

491
00:31:46,676 --> 00:31:49,143
A black hole has torn
a star apart,

492
00:31:49,145 --> 00:31:52,246
swallowed up half
of the material of the star,

493
00:31:52,248 --> 00:31:54,414
and ejected the other half
in an event

494
00:31:54,416 --> 00:31:57,350
that is among the most violent
things we have ever seen

495
00:31:57,352 --> 00:31:58,918
in the history of astronomy.

496
00:31:58,920 --> 00:32:02,021
The event was so violent,

497
00:32:02,023 --> 00:32:05,724
we saw it from Earth,
3 billion light-years away.

498
00:32:09,662 --> 00:32:15,467
Black holes can suck in planets
and rip apart stars.

499
00:32:15,469 --> 00:32:18,668
But gravity doesn't always
pull things in.

500
00:32:20,003 --> 00:32:22,737
Any high-school student knows
that gravity sucks.

501
00:32:22,739 --> 00:32:24,205
It pulls. It never pushes.

502
00:32:24,207 --> 00:32:26,273
But it's actually
more complicated.

503
00:32:26,275 --> 00:32:28,442
That's true when you
just have two objects.

504
00:32:28,444 --> 00:32:30,744
But the minute you have
more than two objects,

505
00:32:30,746 --> 00:32:32,679
strange things can happen,

506
00:32:32,681 --> 00:32:35,715
and gravity can actually
push you away.

507
00:32:35,717 --> 00:32:37,384
You can get very close
to a body,

508
00:32:37,386 --> 00:32:39,420
but if you come in
at just the right angle

509
00:32:39,422 --> 00:32:42,656
and just the right speed,
instead of colliding together,

510
00:32:42,658 --> 00:32:45,092
one object can slingshot
the other one away.

511
00:32:45,094 --> 00:32:49,263
Recently,
scientists discovered stars

512
00:32:49,265 --> 00:32:53,634
hurtling away from our galaxy
at incredible speed.

513
00:32:53,636 --> 00:32:56,636
Normal stars don't do this.

514
00:32:56,638 --> 00:33:02,641
So what could accelerate
a star to hypervelocity?

515
00:33:02,643 --> 00:33:05,610
The answer was a surprise.

516
00:33:05,612 --> 00:33:09,313
You can only eject stars at
these very, very high velocity,

517
00:33:09,315 --> 00:33:12,416
so close to 700, 800,
1,000 kilometers a second.

518
00:33:12,418 --> 00:33:13,884
You could only eject these

519
00:33:13,886 --> 00:33:16,620
with interactions
with a supermassive black hole.

520
00:33:16,622 --> 00:33:20,490
Each hypervelocity
star was originally

521
00:33:20,492 --> 00:33:25,828
one of a pair of stars orbiting
a supermassive black hole.

522
00:33:25,830 --> 00:33:29,898
When they got too close,
gravity pulled them apart.

523
00:33:29,900 --> 00:33:31,933
The black hole catapulted

524
00:33:31,935 --> 00:33:36,604
one star out of the galaxy
at 2 million miles an hour.

525
00:33:36,606 --> 00:33:41,709
Eventually, the other was
sucked in and destroyed.

526
00:33:41,711 --> 00:33:43,143
The interesting thing here is

527
00:33:43,145 --> 00:33:45,813
that you can get a complete
redistribution of stars,

528
00:33:45,815 --> 00:33:48,615
so you have stars that are
in the center of the galaxy,

529
00:33:48,617 --> 00:33:51,618
and, suddenly, they're ejected
out into intergalactic space.

530
00:33:51,620 --> 00:33:54,988
And it's out here,
in deep space,

531
00:33:54,990 --> 00:33:58,091
that orbits are
at their most powerful,

532
00:33:58,093 --> 00:34:00,927
smashing entire galaxies
together

533
00:34:00,929 --> 00:34:04,696
to create the structure
of the Universe itself.

534
00:34:17,937 --> 00:34:20,172
Across the Universe,

535
00:34:20,174 --> 00:34:24,609
extreme gravity
is a force of destruction.

536
00:34:24,611 --> 00:34:26,644
The orbits of planets and stars

537
00:34:26,646 --> 00:34:29,614
can be chaotic,
unpredictable, and violent.

538
00:34:29,616 --> 00:34:33,551
But on a truly cosmic scale,

539
00:34:33,553 --> 00:34:36,621
gravity is no longer
just a destroyer.

540
00:34:40,492 --> 00:34:43,160
It also creates new worlds.

541
00:34:43,162 --> 00:34:47,330
These are galaxies --
giant spinning clusters

542
00:34:47,332 --> 00:34:52,968
of stars, gas, and dust
100,000 light-years across.

543
00:34:54,471 --> 00:34:56,605
Galaxies orbit each other

544
00:34:56,607 --> 00:34:59,841
in the same way
planets orbit stars.

545
00:34:59,843 --> 00:35:02,376
Gravity pulls them together.

546
00:35:02,378 --> 00:35:04,978
Their speed keeps them apart.

547
00:35:04,980 --> 00:35:08,715
But, ultimately,
gravity always wins.

548
00:35:08,717 --> 00:35:10,951
Entire galaxies smash together.

549
00:35:10,953 --> 00:35:15,521
One of the most spectacular
events in the Universe

550
00:35:15,523 --> 00:35:17,256
is when galaxies collide.

551
00:35:17,258 --> 00:35:20,658
You're talking about hundreds
of billions of stars

552
00:35:20,660 --> 00:35:22,426
100,000 light-years across,

553
00:35:22,428 --> 00:35:25,328
two of these things slamming
into each other.

554
00:35:29,267 --> 00:35:31,334
Collisions
between orbiting galaxies

555
00:35:31,336 --> 00:35:35,671
take place
over millions of years.

556
00:35:35,673 --> 00:35:39,342
Gravity slowly
pulls them together.

557
00:35:44,480 --> 00:35:45,847
And you get these two galaxies

558
00:35:45,849 --> 00:35:48,950
that merge like two fluids
mixing together.

559
00:35:48,952 --> 00:35:53,119
And you get long tidal tails
as they pass through each other,

560
00:35:53,121 --> 00:35:55,254
but then gravity brings them
back together again.

561
00:35:55,256 --> 00:35:57,923
And in the end,
you get a full-fledged,

562
00:35:57,925 --> 00:36:01,260
more mature, larger galaxy
than you had originally.

563
00:36:07,432 --> 00:36:09,366
On this intergalactic scale,

564
00:36:09,368 --> 00:36:14,137
gravity and motion are
no longer destructive forces.

565
00:36:14,139 --> 00:36:18,173
Now they trigger
the creation of life itself.

566
00:36:18,175 --> 00:36:21,409
You would think
a galactic collision

567
00:36:21,411 --> 00:36:23,211
would be incredibly destructive,

568
00:36:23,213 --> 00:36:24,612
and in one sense, it is,

569
00:36:24,614 --> 00:36:27,415
but in another sense,
it's a very creative force.

570
00:36:30,592 --> 00:36:35,264
Colliding galaxies
smash vast gas clouds together.

571
00:36:35,266 --> 00:36:39,768
Huge shock waves rip
through them, squeezing the gas.

572
00:36:42,271 --> 00:36:45,740
Then something amazing
happens --

573
00:36:45,742 --> 00:36:48,542
the birth of countless stars.

574
00:36:50,511 --> 00:36:53,313
It's incredible to think
about two galaxies

575
00:36:53,315 --> 00:36:56,381
that gravitationally attract
each other and collide.

576
00:36:56,383 --> 00:36:58,182
What could be more destructive?

577
00:36:58,184 --> 00:37:02,719
But, in fact, there is a power
of construction in such mergers,

578
00:37:02,721 --> 00:37:05,655
because as two galaxies
come together,

579
00:37:05,657 --> 00:37:08,357
the gases are compressed,
and sometimes,

580
00:37:08,359 --> 00:37:12,361
the gases are compressed so much
that you get the birth of stars

581
00:37:12,363 --> 00:37:16,098
and the associated planets
around those stars.

582
00:37:16,100 --> 00:37:19,701
And so, in the titanic collision
between two galaxies,

583
00:37:19,703 --> 00:37:22,604
you can get the birth of stars
and planets

584
00:37:22,606 --> 00:37:25,606
and perhaps eventually
life on those planets.

585
00:37:30,377 --> 00:37:32,445
Sometimes,
these collisions

586
00:37:32,447 --> 00:37:34,780
trigger a chain reaction...

587
00:37:39,654 --> 00:37:42,689
...two spiral galaxies
in mid-collision

588
00:37:42,691 --> 00:37:46,192
creating stars and planets.

589
00:37:49,329 --> 00:37:51,796
But this time,
there's a difference.

590
00:37:58,503 --> 00:38:00,436
Some of these new stars

591
00:38:00,438 --> 00:38:03,773
are massive, unstable,
and short-lived.

592
00:38:03,775 --> 00:38:05,541
They explode.

593
00:38:05,543 --> 00:38:10,513
Each explosion blasts out
new shock waves

594
00:38:10,515 --> 00:38:14,449
and triggers the birth
of even more stars.

595
00:38:14,451 --> 00:38:17,619
Astronomers call this
a starburst.

596
00:38:20,556 --> 00:38:24,725
It's the ultimate example
of gravity's creative power.

597
00:38:26,394 --> 00:38:28,895
A starburst galaxy is one

598
00:38:28,897 --> 00:38:31,798
that is creating stars
at a much higher rate

599
00:38:31,800 --> 00:38:34,400
than we usually see
in normal galaxies.

600
00:38:34,402 --> 00:38:35,735
And so, it's amazing

601
00:38:35,737 --> 00:38:38,370
that you can have such
a beautiful, creative process

602
00:38:38,372 --> 00:38:41,139
coming out of something
so violent and destructive.

603
00:38:43,976 --> 00:38:46,277
Gravity and motion,

604
00:38:46,279 --> 00:38:50,079
the two forces that give birth
to every new star,

605
00:38:50,081 --> 00:38:54,249
also weave together the fabric
of the Universe itself.

606
00:38:57,420 --> 00:39:02,089
Our cosmos is not random.
It has structure.

607
00:39:02,091 --> 00:39:07,860
The Universe is a vast
three-dimensional tapestry.

608
00:39:07,862 --> 00:39:11,397
Each of these threads
and filaments

609
00:39:11,399 --> 00:39:14,267
contains billions of galaxies.

610
00:39:14,269 --> 00:39:17,603
It's the scaffolding that holds
everything together,

611
00:39:17,605 --> 00:39:21,607
the cosmic web.

612
00:39:21,609 --> 00:39:23,876
And we think about scaffolding
of a building,

613
00:39:23,878 --> 00:39:25,544
it's just sitting there, static.

614
00:39:25,546 --> 00:39:27,111
But, in fact, this scaffolding

615
00:39:27,113 --> 00:39:29,046
is quite dynamic
and quite amazing

616
00:39:29,048 --> 00:39:30,681
because all of the constituents

617
00:39:30,683 --> 00:39:33,149
are moving around
at very high speeds,

618
00:39:33,151 --> 00:39:34,917
crashing into one another --

619
00:39:34,919 --> 00:39:37,652
galaxies, stars,
black holes, supernovae --

620
00:39:37,654 --> 00:39:40,555
all in this tremendous
cosmic dance.

621
00:39:40,557 --> 00:39:46,160
The cosmic web
is incomprehensibly vast.

622
00:39:46,162 --> 00:39:48,929
Each thread is full of motion.

623
00:39:48,931 --> 00:39:52,332
Galaxies form, orbit,
and collide,

624
00:39:52,334 --> 00:39:56,936
countless billions
in a constant stream.

625
00:39:56,938 --> 00:39:59,203
Every filament
is a galactic freeway

626
00:39:59,205 --> 00:40:05,667
with an endless flow of traffic,
each point of light a galaxy.

627
00:40:07,665 --> 00:40:14,161
It's rush hour 24/7, and
sometimes, there's gridlock.

628
00:40:14,163 --> 00:40:16,497
Every billion light-years,

629
00:40:16,499 --> 00:40:20,034
several filaments join
to form a knot.

630
00:40:22,170 --> 00:40:25,472
Whole clusters collide to form

631
00:40:25,474 --> 00:40:30,075
some of the largest structures
we know of -- superclusters.

632
00:40:30,077 --> 00:40:36,615
This is one of them --
Abell 2744.

633
00:40:38,884 --> 00:40:42,754
Five orbiting galaxy clusters
crashed together

634
00:40:42,756 --> 00:40:46,657
in the single biggest
cosmic pile-up ever discovered.

635
00:40:52,396 --> 00:40:56,967
Gradually, the five clusters
merged and fused

636
00:40:56,969 --> 00:41:00,270
to form a single giant
supercluster

637
00:41:00,272 --> 00:41:02,405
6 million light-years across.

638
00:41:04,508 --> 00:41:06,642
The incredible power of orbits

639
00:41:06,644 --> 00:41:11,479
can literally tie the universe
in knots.

640
00:41:11,481 --> 00:41:14,515
Structures in the Universe have
evolved over billions of years

641
00:41:14,517 --> 00:41:18,051
through their orbits and their
mutual gravitational attraction,

642
00:41:18,053 --> 00:41:20,987
and they've built up into larger
and larger structures.

643
00:41:20,989 --> 00:41:23,823
And it's all thanks to these
same attractive forces

644
00:41:23,825 --> 00:41:26,825
that bring them together
but can also tear them apart.

645
00:41:35,633 --> 00:41:37,801
Again and again,

646
00:41:37,803 --> 00:41:41,270
we discover orbits
dominating the cosmos.

647
00:41:42,405 --> 00:41:45,040
The atom is the basic unit
of chemistry.

648
00:41:45,042 --> 00:41:46,408
In the same way,

649
00:41:46,410 --> 00:41:50,246
the orbit is the basic unit
of the Universe itself.

650
00:41:50,248 --> 00:41:52,981
If you understand
all possible orbits,

651
00:41:52,983 --> 00:41:56,351
you understand the dynamics
driving the Universe.

652
00:41:56,353 --> 00:42:00,688
Orbits have created a cosmos

653
00:42:00,690 --> 00:42:03,591
full of richness and complexity.

654
00:42:03,593 --> 00:42:06,260
Orbits are changeable.
They're chaotic.

655
00:42:06,262 --> 00:42:08,696
Things that we never thought
were possible

656
00:42:08,698 --> 00:42:09,931
are, in fact, possible.

657
00:42:09,933 --> 00:42:12,601
From the smallest scale
to the largest scale,

658
00:42:12,603 --> 00:42:15,503
it's the gravitational
interactions and collisions

659
00:42:15,505 --> 00:42:19,072
that actually make our Universe
the beautiful place that it is.

660
00:42:19,074 --> 00:42:24,911
And behind it all
is a curious paradox.

661
00:42:24,913 --> 00:42:28,047
Extreme orbits mean variations,
collisions.

662
00:42:28,049 --> 00:42:30,082
That seems very destructive.

663
00:42:30,084 --> 00:42:32,948
But, also, extreme orbits
mean colliding galaxies,

664
00:42:32,950 --> 00:42:36,352
collapsing dust clouds,
the very creation of life,

665
00:42:36,354 --> 00:42:37,419
as well as destruction.

666
00:42:37,421 --> 00:42:42,391
Orbits are the driving force

667
00:42:42,393 --> 00:42:47,762
behind this never-ending cycle
of creation and destruction.

668
00:42:47,764 --> 00:42:52,633
They're at the very heart
of how the Universe works.