1
00:00:02,634 --> 00:00:03,936
The milky way...
2
00:00:06,005 --> 00:00:10,274
...an empire
of over 200 billion stars.
3
00:00:10,275 --> 00:00:13,411
The earth is our home.
The sun is our star.
4
00:00:13,412 --> 00:00:14,812
And the milky way is
our galaxy.
5
00:00:14,813 --> 00:00:17,583
It's us.
It's our home.
6
00:00:17,584 --> 00:00:20,519
But where did it all come from?
7
00:00:20,520 --> 00:00:22,953
Why do galaxies form at all?
8
00:00:22,954 --> 00:00:25,392
Something has to happen.
Something has to mix things up.
9
00:00:26,794 --> 00:00:29,831
So what sparked
our galaxy into life?
10
00:00:33,133 --> 00:00:37,202
New research suggests
an unlikely hero.
11
00:00:37,203 --> 00:00:40,873
At the center of our
galaxy is a massive black hole.
12
00:00:40,874 --> 00:00:42,741
And by massive,
i mean really massive.
13
00:00:42,742 --> 00:00:45,845
Even though this thing
is terrifying,
14
00:00:45,846 --> 00:00:47,046
our galaxy depends on it.
15
00:00:47,047 --> 00:00:49,516
Could this monster,
16
00:00:49,517 --> 00:00:52,251
the great destroyer
of the universe,
17
00:00:52,252 --> 00:00:55,787
actually be a great creator?
18
00:00:55,788 --> 00:00:59,759
Could a black hole have built
our home, the milky way?
19
00:00:59,760 --> 00:01:01,494
The black hole
may be responsible
20
00:01:01,495 --> 00:01:02,995
for the beginning of our galaxy,
21
00:01:02,996 --> 00:01:06,000
and it'll definitely ultimately
be responsible for its death.
22
00:01:18,013 --> 00:01:20,780
look around the universe,
23
00:01:20,781 --> 00:01:24,283
and you'll see galaxies
of every kind,
24
00:01:24,284 --> 00:01:28,556
a kaleidoscopic array
of unique shapes and sizes.
25
00:01:29,992 --> 00:01:34,194
These grand galactic structures
fill the cosmos.
26
00:01:34,195 --> 00:01:38,432
The basic building block
of the universe is the galaxy,
27
00:01:38,433 --> 00:01:41,670
and there are hundreds
of billions of galaxies
28
00:01:41,671 --> 00:01:43,537
in the universe.
29
00:01:43,538 --> 00:01:45,640
The same way that cells make up
your body
30
00:01:45,641 --> 00:01:47,141
or bricks make up a building,
31
00:01:47,142 --> 00:01:49,078
galaxies make up the universe.
32
00:01:51,412 --> 00:01:54,982
We should thank
our lucky stars for galaxies.
33
00:01:54,983 --> 00:01:57,986
Galaxies are the only
place in the universe
34
00:01:57,987 --> 00:01:59,622
where stars and planets form.
35
00:01:59,623 --> 00:02:02,723
We don't see stars
out between the galaxies.
36
00:02:02,724 --> 00:02:03,992
This is the only place
37
00:02:03,993 --> 00:02:06,260
where the hydrogen is
brought together,
38
00:02:06,261 --> 00:02:08,865
heated up, and a generation
of life can begin.
39
00:02:10,698 --> 00:02:14,469
There are hundreds of billions
of galaxies in the universe,
40
00:02:14,470 --> 00:02:17,905
but only one gave birth to us.
41
00:02:17,906 --> 00:02:22,844
I sometimes ask my students
to identify where they live.
42
00:02:22,845 --> 00:02:27,582
Well, you would say,
for example, "new york city,"
43
00:02:27,583 --> 00:02:31,153
the us of a, "planet earth,"
44
00:02:31,154 --> 00:02:33,855
third planet from the sun.
45
00:02:33,856 --> 00:02:37,359
And then, you would say
the milky way galaxy.
46
00:02:39,963 --> 00:02:42,300
The milky way galaxy is
our home.
47
00:02:44,535 --> 00:02:46,470
Because we see it from within,
48
00:02:46,471 --> 00:02:51,373
all we see is a band of stars
stretched across the sky.
49
00:02:51,374 --> 00:02:54,210
But viewed from outside,
50
00:02:54,211 --> 00:02:58,514
we'd see a spectacular
giant spiral galaxy
51
00:02:58,515 --> 00:03:01,952
made up
of over 200 billion stars.
52
00:03:02,953 --> 00:03:07,557
Our sun is just a dot
within one of its enormous arms.
53
00:03:07,558 --> 00:03:11,395
Our milky way galaxy is huge.
54
00:03:11,396 --> 00:03:14,564
It's actually one of the biggest galaxies
in the universe, as a matter of fact.
55
00:03:14,565 --> 00:03:17,166
I'd probably put it
in the top 10% certainly.
56
00:03:17,167 --> 00:03:21,904
Massive, magnificent.
57
00:03:21,905 --> 00:03:26,643
Our galaxy has long hidden
its secrets at its heart.
58
00:03:26,644 --> 00:03:30,713
The greatest question
how did it form?
59
00:03:30,714 --> 00:03:35,086
At stake is not just the answer
to the origins of our galaxy,
60
00:03:35,087 --> 00:03:38,289
but the origins
of our solar system,
61
00:03:38,290 --> 00:03:43,125
our star, the sun,
and ultimately, us.
62
00:03:43,126 --> 00:03:46,563
The milky way's past
and the whole story
63
00:03:46,564 --> 00:03:49,233
leads us to where we are now
and who we are now.
64
00:03:50,302 --> 00:03:53,070
So what created the milky way,
65
00:03:53,071 --> 00:03:54,571
and how did it grow
66
00:03:54,572 --> 00:03:57,743
into the majestic galaxy
we see today?
67
00:04:01,313 --> 00:04:02,546
To answer that,
68
00:04:02,547 --> 00:04:05,984
we have to travel back
to the infant universe,
69
00:04:05,985 --> 00:04:08,453
to just after the big bang.
70
00:04:13,992 --> 00:04:17,529
13.6 billion years ago,
71
00:04:17,530 --> 00:04:21,366
There are no stars,
no planets...
72
00:04:21,367 --> 00:04:23,734
And no galaxies.
73
00:04:23,735 --> 00:04:27,005
How do we go
from that early universe
74
00:04:27,006 --> 00:04:29,173
that's almost perfectly,
perfectly featureless
75
00:04:29,174 --> 00:04:31,209
to this complex
and very interesting universe
76
00:04:31,210 --> 00:04:32,477
that we see around us today?
77
00:04:33,579 --> 00:04:37,750
The early universe is
a thick, uniform soup of gas
78
00:04:37,751 --> 00:04:40,419
with some tiny irregularities.
79
00:04:40,420 --> 00:04:46,292
But it's enough to set gravity
to work, pulling gas together.
80
00:04:47,961 --> 00:04:51,197
Gravity keeps on compressing
the gas down to a point.
81
00:04:51,198 --> 00:04:54,233
And that's when temperatures
rise dramatically
82
00:04:54,234 --> 00:04:56,601
to 50-to 100-million degrees.
83
00:04:56,602 --> 00:04:58,904
At that point, you get ignition.
84
00:04:58,905 --> 00:05:04,008
At that point, hydrogen fuses
into helium, and we get a star.
85
00:05:04,009 --> 00:05:08,014
A star is born.
86
00:05:08,749 --> 00:05:10,918
In this theory,
87
00:05:10,919 --> 00:05:15,290
not one, but millions of stars
burst into life.
88
00:05:17,591 --> 00:05:20,993
Slowly,
gravity brings them together.
89
00:05:20,994 --> 00:05:24,198
After a few million years,
90
00:05:24,199 --> 00:05:28,267
they form a rotating sphere
of stars,
91
00:05:28,268 --> 00:05:31,238
and a galaxy is born.
92
00:05:31,239 --> 00:05:35,075
There's a problem, though.
93
00:05:35,076 --> 00:05:37,678
There's too much gravity.
94
00:05:37,679 --> 00:05:40,647
Something other
than just the stars
95
00:05:40,648 --> 00:05:43,116
must be holding them together.
96
00:05:43,117 --> 00:05:45,786
But what is it?
97
00:05:45,787 --> 00:05:52,126
Turns out, the answer lies at
the center of our own galaxy.
98
00:05:52,994 --> 00:05:54,663
At the very heart
of the milky way,
99
00:05:54,664 --> 00:05:57,565
you see stars orbiting
something that isn't there.
100
00:05:57,566 --> 00:05:59,901
And if you do the calculations,
101
00:05:59,902 --> 00:06:02,805
the amount of mass needed
at the very center
102
00:06:02,806 --> 00:06:06,707
is about four million times
the mass of our sun.
103
00:06:06,708 --> 00:06:09,344
So stars are basically orbiting
like planets
104
00:06:09,345 --> 00:06:11,579
around this empty object
105
00:06:11,580 --> 00:06:13,650
with four million times
the mass of the sun.
106
00:06:16,186 --> 00:06:19,086
This object must be colossal.
107
00:06:19,087 --> 00:06:22,457
It must be unimaginably dense.
108
00:06:22,458 --> 00:06:26,161
It could only be one thing
109
00:06:26,162 --> 00:06:28,930
a black hole,
110
00:06:28,931 --> 00:06:31,768
a supermassive black hole.
111
00:06:34,003 --> 00:06:36,070
if the moon
goes around the earth,
112
00:06:36,071 --> 00:06:38,841
and the earth
goes around the sun,
113
00:06:38,842 --> 00:06:41,877
then what does the sun
go around?
114
00:06:41,878 --> 00:06:44,615
The sun goes around
a massive black hole
115
00:06:44,616 --> 00:06:47,248
at the center of the galaxy.
116
00:06:47,249 --> 00:06:48,817
Within the milky way,
117
00:06:48,818 --> 00:06:53,356
scientists find their
first supermassive black hole.
118
00:06:53,357 --> 00:06:55,991
But it wasn't the last.
119
00:06:55,992 --> 00:06:59,396
Turns out, they're everywhere.
120
00:06:59,397 --> 00:07:02,764
We know that most big galaxies
121
00:07:02,765 --> 00:07:05,801
have a supermassive black hole
right in their center.
122
00:07:05,802 --> 00:07:08,437
That's telling us that
these two things are related.
123
00:07:08,438 --> 00:07:10,940
They come as a pair.
124
00:07:10,941 --> 00:07:15,611
Somehow, the black holes
and the galaxies
125
00:07:15,612 --> 00:07:17,681
and their origin and evolution
are tied together.
126
00:07:20,217 --> 00:07:22,418
Amazingly, the milky way,
127
00:07:22,419 --> 00:07:25,889
this sparkling expanse of stars,
128
00:07:25,890 --> 00:07:27,957
is all intrinsically linked
129
00:07:27,958 --> 00:07:29,625
to the darkest
130
00:07:29,626 --> 00:07:33,296
and most enigmatic entity
in the universe
131
00:07:33,297 --> 00:07:36,199
a supermassive black hole.
132
00:07:36,200 --> 00:07:38,901
It is an object of tremendous
fascination and mystery.
133
00:07:38,902 --> 00:07:40,370
How did it get there?
134
00:07:40,371 --> 00:07:42,339
How did it grow to be so large?
135
00:07:42,340 --> 00:07:44,707
Is it gonna continue to grow?
136
00:07:44,708 --> 00:07:48,577
To figure out
the origins of our galaxy,
137
00:07:48,578 --> 00:07:52,449
we must first find out
how it got its black hole.
138
00:07:58,590 --> 00:08:03,095
In the early universe,
the first stars burst into life.
139
00:08:06,965 --> 00:08:11,269
But these stars,
they're nothing like our sun.
140
00:08:11,270 --> 00:08:14,704
Those first stars were
very, very massive.
141
00:08:14,705 --> 00:08:17,740
And one of the things
that happens with massive stars
142
00:08:17,741 --> 00:08:19,110
is they explode quickly.
143
00:08:22,614 --> 00:08:25,049
In just
a few hundred million years,
144
00:08:25,050 --> 00:08:29,252
the biggest burn through
their hydrogen fuel...
145
00:08:29,253 --> 00:08:31,289
And die.
146
00:08:35,728 --> 00:08:37,429
They would've exploded
147
00:08:37,430 --> 00:08:40,665
as incredibly powerful
supernovae, exploding stars.
148
00:08:40,666 --> 00:08:43,535
Their cores would've collapsed
to form black holes,
149
00:08:43,536 --> 00:08:44,902
and this may have been
150
00:08:44,903 --> 00:08:47,239
the very first black holes
that formed in the universe.
151
00:08:50,709 --> 00:08:53,344
These black holes
would start small.
152
00:08:53,345 --> 00:08:55,848
Over billions of years,
153
00:08:55,849 --> 00:08:59,084
one would eat
and grow into the monster
154
00:08:59,085 --> 00:09:02,888
that now sits at the heart
of our galaxy.
155
00:09:05,191 --> 00:09:09,560
It's a solid theory,
but there's a problem.
156
00:09:09,561 --> 00:09:12,964
Astronomers
find super-bright lights
157
00:09:12,965 --> 00:09:15,801
in the very early universe.
158
00:09:19,373 --> 00:09:22,474
These aren't stars.
159
00:09:22,475 --> 00:09:25,110
They're called quasars.
160
00:09:25,111 --> 00:09:29,781
Quasars are the bad boys
of astronomy.
161
00:09:29,782 --> 00:09:32,117
When we first found them,
we were puzzled,
162
00:09:32,118 --> 00:09:35,720
because how can an object emit
so much energy?
163
00:09:35,721 --> 00:09:42,028
The energy output is sufficient
to light up the entire universe.
164
00:09:44,797 --> 00:09:46,266
These quasars,
165
00:09:46,267 --> 00:09:48,767
though smaller
than our solar system,
166
00:09:48,768 --> 00:09:53,106
somehow outshine
100 galaxies put together.
167
00:09:58,778 --> 00:10:02,648
The energy emitted vastly
exceeds the energy in a star.
168
00:10:02,649 --> 00:10:05,551
The only process we know
169
00:10:05,552 --> 00:10:07,588
that would produce
that kind of energy
170
00:10:07,589 --> 00:10:10,089
is the collapse
of huge amounts of matter
171
00:10:10,090 --> 00:10:11,426
into a massive black hole.
172
00:10:14,295 --> 00:10:17,229
We realized, "oh, my god.
173
00:10:17,230 --> 00:10:21,602
These are, in fact,
huge, raging black holes."
174
00:10:21,603 --> 00:10:23,369
they're much bigger
175
00:10:23,370 --> 00:10:27,175
than those made at the end
of a star's life.
176
00:10:27,176 --> 00:10:29,609
We're not just talking about
a stellar mass black hole,
177
00:10:29,610 --> 00:10:33,013
which might have 5 or 10 or 20
times the mass of the sun.
178
00:10:33,014 --> 00:10:34,916
We're talking
about a true monster
179
00:10:34,917 --> 00:10:38,387
that has millions or billions
of times the mass of the sun.
180
00:10:40,955 --> 00:10:43,158
So where do
these black holes come from?
181
00:10:45,194 --> 00:10:51,031
They're way too big to be the
result of early exploding stars.
182
00:10:51,032 --> 00:10:54,701
They have to be formed
in another way.
183
00:10:54,702 --> 00:10:57,604
The theory
that stars formed first,
184
00:10:57,605 --> 00:11:00,306
converging to build galaxies,
185
00:11:00,307 --> 00:11:03,377
needs a radical overhaul.
186
00:11:03,378 --> 00:11:07,714
Instead,
does the black hole come first?
187
00:11:07,715 --> 00:11:11,585
is it the mother
Of all creation,
188
00:11:11,586 --> 00:11:17,527
giving birth to the milky way,
the stars, and us?
189
00:11:24,935 --> 00:11:26,902
The milky way,
190
00:11:26,903 --> 00:11:32,074
our vast, incandescent galaxy,
has a heart of darkness.
191
00:11:32,075 --> 00:11:37,446
But which came first
the light or the dark?
192
00:11:37,447 --> 00:11:40,783
It's almost sort of
like a chicken and an egg.
193
00:11:40,784 --> 00:11:42,985
Which came first,
the galaxy or the black hole?
194
00:11:42,986 --> 00:11:46,223
Do you need a black hole
to make a galaxy,
195
00:11:46,224 --> 00:11:48,791
or do you need a large galaxy
to make a large black hole?
196
00:11:48,792 --> 00:11:51,261
Did the black hole come first?
197
00:11:51,262 --> 00:11:54,465
Or did the stars and the galaxy
come first?
198
00:11:57,234 --> 00:11:59,704
In one theory, stars come first.
199
00:11:59,705 --> 00:12:02,672
The biggest die,
200
00:12:02,673 --> 00:12:06,345
creating a black hole
during their death throes.
201
00:12:10,415 --> 00:12:13,950
But the discovery of quasars
challenges this.
202
00:12:13,951 --> 00:12:16,454
There are
supermassive black holes
203
00:12:16,455 --> 00:12:18,388
at the very start
of the universe,
204
00:12:18,389 --> 00:12:22,827
far too large to be the remnants
of the first stars.
205
00:12:23,830 --> 00:12:26,598
So where do they come from?
206
00:12:26,599 --> 00:12:30,302
And could they go on
to create galaxies?
207
00:12:35,106 --> 00:12:39,445
Enter the new theory
of direct collapse.
208
00:12:39,446 --> 00:12:43,047
In this theory,
in the very early universe,
209
00:12:43,048 --> 00:12:44,882
you have a giant gas cloud
210
00:12:44,883 --> 00:12:47,720
that collapses
straight into a black hole.
211
00:12:49,689 --> 00:12:52,156
It's just like
the birth of a star,
212
00:12:52,157 --> 00:12:56,161
but the star dies
before it's born.
213
00:12:56,162 --> 00:12:58,897
The theory goes like this.
214
00:12:58,898 --> 00:13:02,533
Clouds of gas clump together.
215
00:13:02,534 --> 00:13:06,304
They spiral
into a central point,
216
00:13:06,305 --> 00:13:08,339
becoming incredibly dense.
217
00:13:08,340 --> 00:13:12,545
At this point in star formation,
the core would ignite.
218
00:13:12,546 --> 00:13:16,214
But here, too much gas and dust
is piled in.
219
00:13:16,215 --> 00:13:19,319
The mass of it all is so great
220
00:13:19,320 --> 00:13:22,489
that gravity becomes
unstoppable.
221
00:13:24,624 --> 00:13:29,094
It crushes the gas,
making it denser and denser,
222
00:13:29,095 --> 00:13:32,297
until it reaches
its breaking point.
223
00:13:32,298 --> 00:13:37,737
Finally, the gas collapses...
224
00:13:37,738 --> 00:13:43,608
So violently, it rips through
the fabric of space.
225
00:13:43,609 --> 00:13:46,480
A massive black hole is born.
226
00:13:47,481 --> 00:13:49,583
I'm talking about making
a black hole that's way bigger
227
00:13:49,584 --> 00:13:50,717
than any kind of black hole
228
00:13:50,718 --> 00:13:52,421
that would form at the end
of a star's life.
229
00:13:54,723 --> 00:13:57,791
This could explain
how the black holes and quasars
230
00:13:57,792 --> 00:14:01,530
are so huge
so early on in the universe.
231
00:14:03,498 --> 00:14:08,837
If true, then it might be black
holes come first, before stars.
232
00:14:10,772 --> 00:14:13,874
But for now, it's just a theory.
233
00:14:18,845 --> 00:14:23,451
The jury is still out as to
how our galaxy first forms.
234
00:14:25,521 --> 00:14:27,722
The chicken-and-egg question is,
235
00:14:27,723 --> 00:14:30,157
do black holes cause
the galaxies
236
00:14:30,158 --> 00:14:32,093
to coil us around them,
237
00:14:32,094 --> 00:14:36,531
or do the galaxies build up and
hit some crucial, critical size,
238
00:14:36,532 --> 00:14:39,700
beyond which black holes
must form at their center?
239
00:14:39,701 --> 00:14:40,901
And we want to learn about that.
240
00:14:40,902 --> 00:14:42,302
And the only way to learn about
241
00:14:42,303 --> 00:14:44,306
that is to look out in the
universe and try and find out.
242
00:14:46,341 --> 00:14:47,742
To prove one of our theories,
243
00:14:47,743 --> 00:14:51,579
we need observational evidence.
244
00:14:51,580 --> 00:14:55,349
And a small dwarf galaxy
might provide it.
245
00:14:55,350 --> 00:14:58,551
Henize 2-10 is young.
246
00:14:58,552 --> 00:15:02,690
Many of its stars are
just a few million years old.
247
00:15:02,691 --> 00:15:05,126
It might provide us a look back
248
00:15:05,127 --> 00:15:08,997
at our milky way
in its infant years.
249
00:15:08,998 --> 00:15:13,501
Henize 2-10 is a very
interesting, tiny dwarf galaxy.
250
00:15:13,502 --> 00:15:16,805
Originally,
i was studying this galaxy
251
00:15:16,806 --> 00:15:19,208
because it has all
this star formation going on.
252
00:15:19,209 --> 00:15:21,943
But when i started looking
at all of the data,
253
00:15:21,944 --> 00:15:24,712
i was sort of shocked
and very excited.
254
00:15:24,713 --> 00:15:27,616
I found
a supermassive black hole
255
00:15:27,617 --> 00:15:29,152
at the center
of this little galaxy.
256
00:15:30,888 --> 00:15:34,555
Finding a black hole
in a galaxy is nothing new,
257
00:15:34,556 --> 00:15:37,325
but the real discovery
258
00:15:37,326 --> 00:15:41,164
is the size
of this monster black hole.
259
00:15:42,801 --> 00:15:46,469
Our best estimate for the mass
of the black hole in henize 2-10
260
00:15:46,470 --> 00:15:49,539
is a million or two
solar masses.
261
00:15:49,540 --> 00:15:52,675
Now, this is comparable
to the mass of the black hole
262
00:15:52,676 --> 00:15:54,377
in our own milky way galaxy.
263
00:15:54,378 --> 00:15:57,513
But the milky way is
100,000 light-years across,
264
00:15:57,514 --> 00:16:01,417
whereas henize 2-10 is only a
few thousand light-years across.
265
00:16:01,418 --> 00:16:05,055
It's amazing to find
a black hole
266
00:16:05,056 --> 00:16:08,157
that is so massive
in a small dwarf galaxy.
267
00:16:08,158 --> 00:16:10,427
Before this discovery,
268
00:16:10,428 --> 00:16:13,531
scientists didn't think
such a tiny galaxy
269
00:16:13,532 --> 00:16:16,367
could contain such a colossus.
270
00:16:16,368 --> 00:16:19,637
This is completely unexpected.
271
00:16:19,638 --> 00:16:21,805
Usually, supermassive
black holes are found
272
00:16:21,806 --> 00:16:24,708
in much larger,
much more massive galaxies.
273
00:16:24,709 --> 00:16:28,845
Amy's discovery
is groundbreaking.
274
00:16:28,846 --> 00:16:31,882
In henize 2-10,
275
00:16:31,883 --> 00:16:35,853
the black hole is more developed
than the galaxy.
276
00:16:35,854 --> 00:16:40,390
It's evidence suggesting
the black hole is older,
277
00:16:40,391 --> 00:16:43,994
that it came first.
278
00:16:43,995 --> 00:16:47,799
Could this be the same
for other galaxies?
279
00:16:47,800 --> 00:16:51,735
How many dwarf galaxies
host massive black holes?
280
00:16:51,736 --> 00:16:54,204
Is henize 2-10 a unique case,
281
00:16:54,205 --> 00:16:56,840
or are there lots
of other examples?
282
00:16:56,841 --> 00:16:59,210
We've searched through
the sloan digital sky survey
283
00:16:59,211 --> 00:17:02,413
and found over
100 more dwarf galaxies
284
00:17:02,414 --> 00:17:04,850
that have
supermassive black holes.
285
00:17:05,784 --> 00:17:09,186
Henize 2-10 could be
a blueprint
286
00:17:09,187 --> 00:17:11,956
for how all galaxies
first formed,
287
00:17:11,957 --> 00:17:16,329
including our own galaxy,
the milky way.
288
00:17:18,497 --> 00:17:21,532
It's fascinating, because it
could be the evidence that
289
00:17:21,533 --> 00:17:23,268
the big black holes form first,
290
00:17:23,269 --> 00:17:25,272
and then, the galaxies form
around them.
291
00:17:26,706 --> 00:17:28,875
Everything we see in our sky
292
00:17:28,876 --> 00:17:33,012
the stars, our sun,
293
00:17:33,013 --> 00:17:37,116
the planets, our whole galaxy
294
00:17:37,117 --> 00:17:41,721
might all have started
as a supermassive black hole.
295
00:17:41,722 --> 00:17:45,825
But how do you go from this
296
00:17:45,826 --> 00:17:51,697
to something as glorious
as the milky way we see today?
297
00:17:51,698 --> 00:17:54,634
Where do the stars come from?
298
00:18:03,677 --> 00:18:05,679
13 billion years ago,
299
00:18:05,680 --> 00:18:07,982
The milky way
may have started life
300
00:18:07,983 --> 00:18:11,585
as a supermassive black hole,
301
00:18:11,586 --> 00:18:14,987
a huge sphere of black
302
00:18:14,988 --> 00:18:18,658
surrounded by a maelstrom
of gas and dust.
303
00:18:18,659 --> 00:18:22,096
This is our galaxy.
304
00:18:22,097 --> 00:18:25,433
But how do you go from this
305
00:18:25,434 --> 00:18:29,104
to the shimmering sweep of stars
we see today?
306
00:18:32,107 --> 00:18:33,643
People think of black holes
307
00:18:33,644 --> 00:18:35,944
as being gigantic
cosmic vacuum cleaners
308
00:18:35,945 --> 00:18:37,412
that suck everything down.
309
00:18:37,413 --> 00:18:38,748
That's not really true.
310
00:18:38,749 --> 00:18:40,348
If you get too close to one,
311
00:18:40,349 --> 00:18:42,849
yeah, you can fall in,
and you'll never get back out.
312
00:18:42,850 --> 00:18:45,619
But they can be a force
for creation, as well.
313
00:18:45,620 --> 00:18:50,258
How can a black hole
be creative?
314
00:18:50,259 --> 00:18:54,463
One clue black holes aren't
just black.
315
00:18:54,464 --> 00:18:56,598
Far from it.
316
00:18:56,599 --> 00:18:58,500
You can think of black holes
317
00:18:58,501 --> 00:19:00,868
as one of the biggest paradoxes
in the universe.
318
00:19:00,869 --> 00:19:02,971
They're black,
so they don't emit any light.
319
00:19:02,972 --> 00:19:04,304
But they can cause
320
00:19:04,305 --> 00:19:06,341
some of the brightest things
in the entire universe.
321
00:19:08,578 --> 00:19:11,812
Quasars prove
that these massive black holes
322
00:19:11,813 --> 00:19:15,284
throw out more light
than whole galaxies.
323
00:19:16,786 --> 00:19:20,054
Black holes don't just
swallow matter.
324
00:19:20,055 --> 00:19:22,590
They also spit it out.
325
00:19:22,591 --> 00:19:26,628
A supermassive
black hole is a messy eater.
326
00:19:26,629 --> 00:19:28,397
It's trying to suck matter in,
327
00:19:28,398 --> 00:19:31,333
but it ends up superheating
matter and expelling matter,
328
00:19:31,334 --> 00:19:34,468
and sometimes, it will
even belch during its meal
329
00:19:34,469 --> 00:19:35,905
and have an outburst.
330
00:19:38,140 --> 00:19:39,541
In the early universe,
331
00:19:39,542 --> 00:19:43,913
the supermassive black hole,
the beginnings of the milky way,
332
00:19:43,914 --> 00:19:48,283
is surrounded by gas and dust.
333
00:19:48,284 --> 00:19:53,188
The black holes feast
on the matter.
334
00:19:53,189 --> 00:19:57,225
But not all of it is doomed.
335
00:19:57,226 --> 00:20:00,530
When it eats too much
too quickly,
336
00:20:00,531 --> 00:20:02,664
it generates so much energy
337
00:20:02,665 --> 00:20:05,869
that even the black hole's
gravity can't contain it.
338
00:20:08,471 --> 00:20:11,773
Suddenly, the milky way
fires off
339
00:20:11,774 --> 00:20:15,478
highly energized atoms and light
from the core...
340
00:20:20,318 --> 00:20:24,955
...pumping out up to a trillion
Times more energy than our sun.
341
00:20:24,991 --> 00:20:29,958
If you were to have a close encounter
with a supermassive black hole,
342
00:20:29,959 --> 00:20:32,229
you're gonna have to go through
a very dangerous environment.
343
00:20:32,230 --> 00:20:36,066
You'd have to survive
the intense radiation.
344
00:20:36,067 --> 00:20:37,902
You'd have to survive the jet.
345
00:20:40,571 --> 00:20:43,939
So how do stars form
around such violence?
346
00:20:43,940 --> 00:20:48,377
Astronomers find a black hole
which might hold the key
347
00:20:48,378 --> 00:20:52,080
to how the milky way got
its first stars.
348
00:20:52,081 --> 00:20:54,618
There's
a really exciting discovery
349
00:20:54,619 --> 00:20:56,351
of a supermassive black hole,
350
00:20:56,352 --> 00:20:59,022
the kind we normally only find
at the hearts of galaxies,
351
00:20:59,023 --> 00:21:02,024
sitting out there by itself
with no galaxy around it.
352
00:21:02,025 --> 00:21:07,196
This thing's shining like crazy,
so we know it's gobbling up gas.
353
00:21:07,197 --> 00:21:11,702
He0450-2958
354
00:21:11,703 --> 00:21:14,539
sits 5 billion light-years
from earth,
355
00:21:14,540 --> 00:21:17,076
a black hole with a huge jet.
356
00:21:18,976 --> 00:21:21,980
This jet is smashing
into dust and gas
357
00:21:21,981 --> 00:21:24,181
and its neighboring galaxy.
358
00:21:24,182 --> 00:21:26,518
You'd think
it would destroy the galaxy,
359
00:21:26,519 --> 00:21:29,019
but instead,
it's helping to build it.
360
00:21:29,020 --> 00:21:32,290
It's next to a big galaxy,
361
00:21:32,291 --> 00:21:36,060
and this big galaxy is
forming stars like crazy.
362
00:21:36,061 --> 00:21:38,662
So we think what's going on is,
because of the stuff
363
00:21:38,663 --> 00:21:41,031
coming off of the black hole
as it's growing,
364
00:21:41,032 --> 00:21:43,335
there are stars being triggered
to form
365
00:21:43,336 --> 00:21:44,836
in this galaxy next to it.
366
00:21:47,240 --> 00:21:49,374
The black hole's colossal jet
367
00:21:49,375 --> 00:21:53,511
is the spark needed to create
a star factory.
368
00:21:53,512 --> 00:21:57,148
The black hole is
emitting radiation.
369
00:21:57,149 --> 00:22:00,551
And when this radiation runs
into all the gas in the galaxy,
370
00:22:00,552 --> 00:22:02,521
this causes the gas
to clump together,
371
00:22:02,522 --> 00:22:03,723
and new stars get made.
372
00:22:04,891 --> 00:22:09,428
Direct evidence that
black holes can create stars.
373
00:22:09,429 --> 00:22:18,305
He0450-2958 might be a look back
into the milky way's past.
374
00:22:20,240 --> 00:22:22,908
Our galaxy's
supermassive black hole's
375
00:22:22,909 --> 00:22:26,744
violent feasting sparks
stars into life.
376
00:22:26,745 --> 00:22:29,648
These stars are drawn
377
00:22:29,649 --> 00:22:32,518
by the black hole's
huge gravity and orbit,
378
00:22:32,519 --> 00:22:34,687
building the galaxy.
379
00:22:34,688 --> 00:22:36,022
Well, the black hole
380
00:22:36,023 --> 00:22:39,458
could actually stimulate
star formation.
381
00:22:39,459 --> 00:22:42,529
So some people believe that the
very fact that we have galaxies
382
00:22:42,530 --> 00:22:43,797
is due to the fact
383
00:22:43,798 --> 00:22:46,232
that we have a raging black hole
at the center
384
00:22:46,233 --> 00:22:49,169
which helps to initiate
star formation.
385
00:22:51,238 --> 00:22:53,741
It's possible
that the black hole
386
00:22:53,742 --> 00:22:57,912
could have created many of the
stars we see in our sky today,
387
00:22:57,913 --> 00:23:02,515
including the one star
we can't live without,
388
00:23:02,516 --> 00:23:05,284
our sun.
389
00:23:05,285 --> 00:23:07,454
It's kind of amazing
390
00:23:07,455 --> 00:23:10,323
that black holes existed
as theoretical constructs
391
00:23:10,324 --> 00:23:11,992
that many of the physicists
who were involved
392
00:23:11,993 --> 00:23:13,761
in developing those constructs
didn't believe in.
393
00:23:13,762 --> 00:23:16,297
Now, we understand
that even perhaps
394
00:23:16,298 --> 00:23:18,865
our very existence
depends upon them.
395
00:23:18,866 --> 00:23:22,403
They've gone from objects
in our imagination
396
00:23:22,404 --> 00:23:25,173
to objects
on which our life depends.
397
00:23:28,443 --> 00:23:31,078
Even though this black
hole in the center
398
00:23:31,079 --> 00:23:32,646
is terrifying to conceive of,
399
00:23:32,647 --> 00:23:35,249
in fact,
our galaxy depends on it.
400
00:23:35,250 --> 00:23:37,149
And our own planet and star
401
00:23:37,150 --> 00:23:40,087
may have formed
because of this system.
402
00:23:46,761 --> 00:23:48,794
13 billion years ago,
403
00:23:48,795 --> 00:23:54,001
The first stars of the milky way
spark into life.
404
00:23:54,002 --> 00:23:58,504
The galaxy starts to take shape.
405
00:23:58,505 --> 00:24:03,711
The milky way is now big enough
to throw its weight around.
406
00:24:04,847 --> 00:24:09,216
And in the early universe,
the milky way is not alone.
407
00:24:09,217 --> 00:24:13,954
Its cosmic neighbors become
its prey.
408
00:24:13,955 --> 00:24:17,894
The milky way becomes
a cannibal.
409
00:24:26,936 --> 00:24:29,638
The young milky way is growing.
410
00:24:29,639 --> 00:24:33,208
It already contains
millions of stars.
411
00:24:33,209 --> 00:24:38,780
Now, it's big enough to enter
its next stage of evolution.
412
00:24:38,781 --> 00:24:42,118
It's time to get violent.
413
00:24:42,119 --> 00:24:46,388
Our galaxy turns
on its cosmic siblings.
414
00:24:46,389 --> 00:24:49,525
Galaxies are gorgeous,
415
00:24:49,526 --> 00:24:50,926
huge pinwheels
416
00:24:50,927 --> 00:24:53,696
spiraling elegantly
throughout the universe.
417
00:24:53,697 --> 00:24:55,933
But there's a dark side
to these galaxies.
418
00:24:55,934 --> 00:24:59,502
The process of building up
galaxies is one of cannibalism.
419
00:24:59,503 --> 00:25:02,806
The galaxies don't form en masse
as large objects.
420
00:25:02,807 --> 00:25:05,140
What they do, like many things,
421
00:25:05,141 --> 00:25:08,545
is form by
eating smaller objects.
422
00:25:10,148 --> 00:25:12,683
If we could view
the infant universe,
423
00:25:12,684 --> 00:25:15,686
we would see a battle raging.
424
00:25:15,687 --> 00:25:19,089
Dwarf galaxies collide
and merge.
425
00:25:19,090 --> 00:25:23,829
And in this arena, size matters.
426
00:25:28,100 --> 00:25:31,736
It's a cosmic
roller-derby match.
427
00:25:34,139 --> 00:25:36,807
The players represent
dwarf galaxies
428
00:25:36,808 --> 00:25:39,577
which populate
the early universe.
429
00:25:39,578 --> 00:25:42,446
If you look
at a roller-derby match,
430
00:25:42,447 --> 00:25:44,949
you might get a better idea about
what galaxy formation's like.
431
00:25:49,487 --> 00:25:52,824
You've got people skating around
the middle of a rink.
432
00:25:56,795 --> 00:25:58,696
There's people slamming
all over the place.
433
00:25:58,697 --> 00:26:03,135
It's a very violent process,
really chaotic.
434
00:26:03,136 --> 00:26:06,306
And it's exactly the same way
around the galaxy.
435
00:26:11,744 --> 00:26:13,512
In a galaxy,
you've got this middle
436
00:26:13,513 --> 00:26:15,013
that's attracting everything,
437
00:26:15,014 --> 00:26:17,249
and stuff is swimming around it.
438
00:26:17,250 --> 00:26:21,019
Dwarf galaxies
smash into one another.
439
00:26:21,020 --> 00:26:24,089
The larger always get
the upper hand.
440
00:26:24,090 --> 00:26:26,424
You've got all
this stuff slamming together.
441
00:26:26,425 --> 00:26:28,426
Stars are getting thrown
all over the place.
442
00:26:28,427 --> 00:26:32,196
They strip mass from each other.
They collide.
443
00:26:32,197 --> 00:26:34,433
And if there are
any smaller objects in-between,
444
00:26:34,434 --> 00:26:36,167
they get eaten up.
445
00:26:36,168 --> 00:26:40,906
It's billions of years
of destructive mayhem.
446
00:26:40,907 --> 00:26:43,575
It's just this crazy,
violent dance
447
00:26:43,576 --> 00:26:45,245
that just goes on
over and over again.
448
00:26:47,848 --> 00:26:50,082
In the chaos of collisions,
449
00:26:50,083 --> 00:26:52,786
the milky way grows bigger.
450
00:26:56,823 --> 00:27:02,361
Today, our galaxy dominates
our part of the universe.
451
00:27:02,362 --> 00:27:06,833
And even now, it's still
devouring other galaxies.
452
00:27:07,836 --> 00:27:10,172
There is a galaxy called
sagittarius
453
00:27:10,173 --> 00:27:13,607
which has left a huge trail
of stars around the milky way
454
00:27:13,608 --> 00:27:16,743
and is essentially in
the process of being devoured.
455
00:27:16,744 --> 00:27:20,446
There's a giant stream
of stars coming off of it.
456
00:27:20,447 --> 00:27:22,349
So it's totally
just being ripped apart
457
00:27:22,350 --> 00:27:23,483
by the milky way itself.
458
00:27:23,484 --> 00:27:25,919
But in this battle,
459
00:27:25,920 --> 00:27:29,589
the milky way
doesn't go unscathed.
460
00:27:29,590 --> 00:27:32,393
This collision
could've triggered the formation
461
00:27:32,394 --> 00:27:34,528
of the spiral arms
of the milky way itself.
462
00:27:34,529 --> 00:27:37,065
So the reason why the milky way
is a spiral galaxy
463
00:27:37,066 --> 00:27:40,900
might be because
it's eating up sagittarius.
464
00:27:40,901 --> 00:27:46,339
Violence doesn't
just build our galaxy.
465
00:27:46,340 --> 00:27:48,176
It sculpts it...
466
00:27:49,579 --> 00:27:52,313
...smashing the milky way
Into shape
467
00:27:52,314 --> 00:27:56,684
and rearranging the positions
of the stars,
468
00:27:56,685 --> 00:27:59,454
perhaps even our sun.
469
00:27:59,455 --> 00:28:03,291
It's possible that the sun
was actually born
470
00:28:03,292 --> 00:28:05,359
much closer to the middle
of the galaxy,
471
00:28:05,360 --> 00:28:07,294
and it's migrated out here
to the suburbs
472
00:28:07,295 --> 00:28:09,563
over the course of the last
couple billion years.
473
00:28:09,564 --> 00:28:12,400
And it's possible that
when sagittarius hit the disk,
474
00:28:12,401 --> 00:28:14,301
it created some spiral arms
475
00:28:14,302 --> 00:28:17,306
that then allowed the sun
to migrate out.
476
00:28:18,542 --> 00:28:20,643
The sun and our solar system
477
00:28:20,644 --> 00:28:25,348
are now about 26,000 light-years
from the galaxy's center.
478
00:28:25,349 --> 00:28:29,051
For life on earth,
that's good news.
479
00:28:29,052 --> 00:28:31,686
If you're too close to the big
black hole in the center,
480
00:28:31,687 --> 00:28:34,022
there's a lot going on
that can actually hurt life.
481
00:28:34,023 --> 00:28:35,925
There's high-energy radiation.
482
00:28:35,926 --> 00:28:39,395
There are bursts of star
formation, supernova explosions.
483
00:28:39,396 --> 00:28:42,764
We're in a quieter, kind of
outlying suburb of the galaxy.
484
00:28:42,765 --> 00:28:45,435
And things there are
much more conducive to life.
485
00:28:45,436 --> 00:28:48,736
Our galaxy's cannibalism
486
00:28:48,737 --> 00:28:52,107
proves essential
for life on earth.
487
00:28:52,108 --> 00:28:55,278
Through violence,
we're able to live,
488
00:28:55,279 --> 00:28:58,949
and our galaxy
continues to grow.
489
00:29:00,517 --> 00:29:02,019
But can anything stop
490
00:29:02,020 --> 00:29:05,523
the juggernaut
of our cannibal galaxy?
491
00:29:07,692 --> 00:29:09,527
Looking out at the milky way,
492
00:29:09,528 --> 00:29:13,163
astronomers find
hardly any new stars.
493
00:29:13,164 --> 00:29:18,068
Turns out, something is shutting
our galaxy's growth down,
494
00:29:18,069 --> 00:29:21,438
the biggest flamethrower
in the universe.
495
00:29:30,948 --> 00:29:33,717
The milky way started small.
496
00:29:33,718 --> 00:29:37,821
Over billions of years,
it has grown huge,
497
00:29:37,822 --> 00:29:41,858
spawning over 200 billion stars
and counting.
498
00:29:41,859 --> 00:29:45,396
But the count is slowing.
499
00:29:45,397 --> 00:29:46,630
So, in the milky way right now,
500
00:29:46,631 --> 00:29:48,165
there are stars
that are being born.
501
00:29:48,166 --> 00:29:49,666
And there's about one star
per year
502
00:29:49,667 --> 00:29:52,137
somewhere in our giant galaxy
that's being born.
503
00:29:52,138 --> 00:29:54,239
Star formation's not done
in the milky way,
504
00:29:54,240 --> 00:29:55,373
but it's settled down.
505
00:29:57,408 --> 00:29:59,377
In its past, the milky way
506
00:29:59,378 --> 00:30:02,012
was bursting
with star formation.
507
00:30:02,013 --> 00:30:03,882
So what's changed?
508
00:30:04,783 --> 00:30:07,653
So, one of the big questions
in galaxy formation today is,
509
00:30:07,654 --> 00:30:09,588
why isn't more gas
turning into stars?
510
00:30:09,589 --> 00:30:11,356
Well, one clue
is that black holes
511
00:30:11,357 --> 00:30:13,393
actually might be limiting
this process.
512
00:30:16,596 --> 00:30:18,163
In the early universe,
513
00:30:18,164 --> 00:30:22,399
our black hole may have sparked
stars into life.
514
00:30:22,400 --> 00:30:26,504
Now, it might be stopping stars
from forming.
515
00:30:26,505 --> 00:30:29,575
To find out why, we need to look
516
00:30:29,576 --> 00:30:33,413
at the milky way's supermassive
black hole in detail.
517
00:30:36,581 --> 00:30:39,751
And for the first time, we can,
518
00:30:39,752 --> 00:30:44,056
thanks to one of nasa's
newest space telescopes, nustar.
519
00:30:44,057 --> 00:30:48,393
Fiona harrison runs
the nustar mission.
520
00:30:48,394 --> 00:30:50,463
Its first target
521
00:30:50,464 --> 00:30:53,332
the black hole at the center
of our galaxy.
522
00:30:53,801 --> 00:30:56,903
Nustar can see
the very highest-energy x-rays
523
00:30:56,904 --> 00:30:59,272
that can penetrate
through dust and gas.
524
00:30:59,273 --> 00:31:02,776
It enables us to have this view
of this black hole.
525
00:31:04,677 --> 00:31:06,713
Nustar's x-ray vision
526
00:31:06,714 --> 00:31:10,448
sees only the most violent
events.
527
00:31:10,449 --> 00:31:17,122
Black hole tantrums are rare,
but nustar got lucky.
528
00:31:17,123 --> 00:31:18,925
We looked.
529
00:31:18,926 --> 00:31:20,792
And about six hours
after we looked,
530
00:31:20,793 --> 00:31:25,898
we saw the black hole get
a hundred times brighter.
531
00:31:25,899 --> 00:31:29,034
How long did that last?
Only a few hours.
532
00:31:29,035 --> 00:31:31,037
Then it faded away
back into oblivion.
533
00:31:31,038 --> 00:31:35,774
But this event was
what we were looking for.
534
00:31:35,775 --> 00:31:38,477
We were all just amazed.
535
00:31:38,478 --> 00:31:40,378
There were cheers in the room.
536
00:31:40,379 --> 00:31:42,715
It was just one
of the most exciting moments,
537
00:31:42,716 --> 00:31:44,717
and so early on
in the mission, too.
538
00:31:44,718 --> 00:31:47,654
It's direct evidence
539
00:31:47,655 --> 00:31:50,156
our black hole is still active
540
00:31:50,157 --> 00:31:53,561
and still has the muscle
to control the galaxy.
541
00:31:57,098 --> 00:31:59,567
The black hole's power
is revealed
542
00:31:59,568 --> 00:32:05,638
when it lights up a disk of gas
and dust which spins around it.
543
00:32:05,639 --> 00:32:08,842
As this material is swirling
around the black hole in a disk,
544
00:32:08,843 --> 00:32:10,310
it rubs against each other.
545
00:32:10,311 --> 00:32:12,980
And there's also magnetic fields
and other forces.
546
00:32:12,981 --> 00:32:16,885
All of this heats that disk to
much hotter, even, than the sun.
547
00:32:19,021 --> 00:32:22,022
Nustar detects
that gas around the black hole
548
00:32:22,023 --> 00:32:26,060
is heating up to
180 million degrees fahrenheit.
549
00:32:26,061 --> 00:32:30,265
That's 18,000 times hotter
than the surface of the sun.
550
00:32:32,301 --> 00:32:36,804
This superheated gas is bad news
for star formation.
551
00:32:36,805 --> 00:32:41,376
The gas has to get cold in order
for it to eventually form stars.
552
00:32:41,377 --> 00:32:43,677
And that's because the gas has
to get very, very dense
553
00:32:43,678 --> 00:32:45,679
so that, eventually,
the gas can collapse
554
00:32:45,680 --> 00:32:48,416
into something that's gonna have
nuclear fusion in its core.
555
00:32:48,417 --> 00:32:50,685
So in regions
around black holes,
556
00:32:50,686 --> 00:32:52,186
because they're so hot,
557
00:32:52,187 --> 00:32:53,789
they heat up
the gas around them.
558
00:32:53,790 --> 00:32:55,490
And that totally limits
the ability
559
00:32:55,491 --> 00:32:56,926
for that gas to turn into stars.
560
00:32:58,528 --> 00:33:01,297
Massive amounts of energy
are emitted.
561
00:33:01,298 --> 00:33:04,166
And that actually can
not only destroy stars,
562
00:33:04,167 --> 00:33:07,937
it can blow the gas away
that would later on form stars.
563
00:33:10,639 --> 00:33:13,444
Star birth shuts down.
564
00:33:16,413 --> 00:33:17,914
Over our galaxy's life,
565
00:33:17,915 --> 00:33:22,151
our supermassive black hole
drags gas and dust towards it,
566
00:33:22,152 --> 00:33:25,254
the ingredients needed
for star formation.
567
00:33:25,255 --> 00:33:27,256
In its infancy,
568
00:33:27,257 --> 00:33:30,392
its power slams
these gas clouds together,
569
00:33:30,393 --> 00:33:33,129
sparking stars into life.
570
00:33:33,130 --> 00:33:37,533
Now, it blows them apart
with its extreme heat,
571
00:33:37,534 --> 00:33:41,637
regulating the population
of stars in the galaxy.
572
00:33:41,638 --> 00:33:45,207
The black hole in the center
acts a little bit like a valve,
573
00:33:45,208 --> 00:33:48,075
controlling how stars form
in the galaxy itself.
574
00:33:48,076 --> 00:33:51,046
There is a remarkable
symbiotic relationship
575
00:33:51,047 --> 00:33:52,716
between black holes
and galaxies.
576
00:33:52,717 --> 00:33:56,687
Black holes act like
cosmic regulators,
577
00:33:56,688 --> 00:33:59,289
increasing, at certain times,
star formation
578
00:33:59,290 --> 00:34:02,225
and governing the rate
at which galaxies evolve.
579
00:34:02,226 --> 00:34:05,595
We're not sure why
our black hole
580
00:34:05,596 --> 00:34:10,267
stops some star formation
and sparks others.
581
00:34:10,268 --> 00:34:12,403
All we do know
582
00:34:12,404 --> 00:34:16,238
is that this regulation might be
essential for us.
583
00:34:16,239 --> 00:34:18,274
When it made stars,
584
00:34:18,275 --> 00:34:22,211
the black hole might have
also helped create our sun.
585
00:34:22,212 --> 00:34:26,015
Now, it limits star formation,
586
00:34:26,016 --> 00:34:29,354
which could bring lethal
radiation near planet earth.
587
00:34:29,355 --> 00:34:31,622
If we were living
in an area where there were
588
00:34:31,623 --> 00:34:33,591
lots of young stars
and supernovae blowing up,
589
00:34:33,592 --> 00:34:36,227
that would not be so good
for life on earth.
590
00:34:36,228 --> 00:34:41,533
Now the conditions
for life are perfect.
591
00:34:41,534 --> 00:34:47,907
Looking up at our night sky,
it looks unchanging, eternal.
592
00:34:50,109 --> 00:34:53,511
But in the universe,
nothing lasts forever.
593
00:34:55,547 --> 00:34:59,850
Our galaxy is gearing up
for its next big change.
594
00:34:59,851 --> 00:35:04,588
So what does the future hold?
595
00:35:04,589 --> 00:35:07,624
The answer is that we won't be
a spiral galaxy for much longer.
596
00:35:07,625 --> 00:35:09,928
Our lifetime as a spiral galaxy
597
00:35:09,929 --> 00:35:13,232
is about two-thirds of the way
into its final death throes.
598
00:35:14,333 --> 00:35:17,035
The milky way has
a giant sister out there,
599
00:35:17,036 --> 00:35:19,872
too close for comfort.
600
00:35:19,873 --> 00:35:24,344
Their sibling rivalry will set
the night on fire
601
00:35:26,846 --> 00:35:30,448
and pit two of the biggest
heavyweights in the cosmos
602
00:35:30,449 --> 00:35:33,085
in a fight to the death.
603
00:35:41,462 --> 00:35:43,528
Around 13 billion years ago,
604
00:35:43,529 --> 00:35:48,301
the milky way forms around
a supermassive black hole.
605
00:35:48,302 --> 00:35:52,205
It adds hundreds of billions
of stars,
606
00:35:52,206 --> 00:35:59,111
settles into a flat disk
and is sculpted into a spiral.
607
00:35:59,112 --> 00:36:02,849
Our galaxy has
constantly evolved.
608
00:36:02,850 --> 00:36:06,151
Its future is no different.
609
00:36:06,152 --> 00:36:10,423
And it's going to get violent.
610
00:36:10,424 --> 00:36:12,291
Go out tonight
and look at the night sky
611
00:36:12,292 --> 00:36:13,494
with a pair of binoculars,
612
00:36:13,495 --> 00:36:17,229
and you can see
the andromeda galaxy.
613
00:36:17,230 --> 00:36:20,533
That is our future.
614
00:36:20,534 --> 00:36:23,769
Perhaps 4 or 5 billion years
from now,
615
00:36:23,770 --> 00:36:27,539
we will be on a collision course
with our next-door neighbor.
616
00:36:27,540 --> 00:36:30,677
And it could be like
a hostile takeover.
617
00:36:31,779 --> 00:36:35,115
Andromeda is heading
straight for us.
618
00:36:35,116 --> 00:36:38,551
Collisions are, of course,
nothing new.
619
00:36:38,552 --> 00:36:40,720
In its infancy,
620
00:36:40,721 --> 00:36:45,492
our galaxy grew by colliding
and eating other galaxies.
621
00:36:45,493 --> 00:36:48,930
But this time, it's different.
622
00:36:48,931 --> 00:36:53,769
The original schoolyard bully
is going to meet its match.
623
00:36:55,237 --> 00:36:57,405
The milky way has always been
the biggest thing around.
624
00:36:57,406 --> 00:36:59,573
So any little dwarf galaxy
that's gotten near
625
00:36:59,574 --> 00:37:00,707
has gotten torn apart,
626
00:37:00,708 --> 00:37:02,810
but the milky way
just keeps right on going.
627
00:37:02,811 --> 00:37:05,146
Now, there's
another really big galaxy
628
00:37:05,147 --> 00:37:07,182
that's actually headed
right for us right now.
629
00:37:07,183 --> 00:37:09,484
That's andromeda.
It's another disk.
630
00:37:09,485 --> 00:37:11,687
And when these two big disks
come together,
631
00:37:11,688 --> 00:37:13,021
there's not gonna be
a disk left.
632
00:37:13,022 --> 00:37:15,555
Neither of those disks is
gonna win.
633
00:37:15,556 --> 00:37:18,026
As the collision nears,
634
00:37:18,027 --> 00:37:21,162
our night sky will change
completely.
635
00:37:21,163 --> 00:37:24,298
Today, if you look out
when it's really dark,
636
00:37:24,299 --> 00:37:27,001
you see the big band
of the milky way.
637
00:37:27,002 --> 00:37:28,602
It's a beautiful thing.
638
00:37:28,603 --> 00:37:29,870
A few billion years from now,
639
00:37:29,871 --> 00:37:32,073
what you would see
is not just one band of stars,
640
00:37:32,074 --> 00:37:35,577
but another band of stars
that crisscrosses like this.
641
00:37:35,578 --> 00:37:38,379
As it nears,
642
00:37:38,380 --> 00:37:42,783
andromeda grows
larger and larger in our sky.
643
00:37:42,784 --> 00:37:47,189
Finally, the galaxies
smash into one another.
644
00:37:47,190 --> 00:37:51,227
Stars are torn
from their orbits.
645
00:37:51,228 --> 00:37:53,095
The stars
don't actually collide.
646
00:37:53,096 --> 00:37:54,463
Stars are extremely small
647
00:37:54,464 --> 00:37:56,566
compared to the space
in-between them.
648
00:37:56,567 --> 00:37:58,568
But that's not true
for gas clouds.
649
00:37:58,569 --> 00:38:00,002
Gas clouds are very large.
650
00:38:00,003 --> 00:38:01,736
They can actually
slam into each other.
651
00:38:01,737 --> 00:38:04,474
When they collide,
that creates new star formation.
652
00:38:04,475 --> 00:38:09,745
This gas and dust
is gonna get set on fire.
653
00:38:09,746 --> 00:38:11,513
There will be a crazy thing
going on,
654
00:38:11,514 --> 00:38:13,816
and maybe even begin to look
like fireworks in the sky
655
00:38:13,817 --> 00:38:14,783
as stars are born.
656
00:38:14,784 --> 00:38:17,852
Huge gas clouds
blazing out light
657
00:38:17,853 --> 00:38:19,754
from the mass of stars
forming in them.
658
00:38:19,755 --> 00:38:20,958
It would be magnificent.
659
00:38:24,561 --> 00:38:27,465
This is our swan song.
660
00:38:29,935 --> 00:38:34,906
This burst of star formation
marks the end for our galaxy.
661
00:38:39,210 --> 00:38:44,347
The milky way and andromeda
rip each other to shreds.
662
00:38:44,348 --> 00:38:48,017
When these two
beautiful structured spirals
663
00:38:48,018 --> 00:38:49,352
smack into each other,
664
00:38:49,353 --> 00:38:54,191
that really orderly shape
is going to be destroyed.
665
00:38:54,192 --> 00:38:56,727
And what's probably
gonna be left is sort
666
00:38:56,728 --> 00:38:59,930
of a big blob of stars that's
called an elliptical galaxy.
667
00:38:59,931 --> 00:39:02,198
Those two galaxies are
gonna turn into a ball of stars.
668
00:39:02,199 --> 00:39:04,867
You won't see any bands at all.
669
00:39:04,868 --> 00:39:08,305
It'll just be stars
spread across the sky.
670
00:39:09,442 --> 00:39:12,843
The milky way
and andromeda are gone.
671
00:39:12,844 --> 00:39:18,850
In their place,
a new galaxy, milkomeda.
672
00:39:21,853 --> 00:39:24,421
But it's not over.
673
00:39:24,422 --> 00:39:29,861
Their two supermassive black
holes hurtle towards each other.
674
00:39:29,862 --> 00:39:33,765
Those black holes are
gonna be hunting for each other.
675
00:39:33,766 --> 00:39:35,600
So you've got
two giant black holes,
676
00:39:35,601 --> 00:39:38,002
both more than a million times
the mass of the sun,
677
00:39:38,003 --> 00:39:39,502
spiraling in towards each other.
678
00:39:39,503 --> 00:39:40,705
As this is happening,
679
00:39:40,706 --> 00:39:42,874
both of them will probably start
gobbling up gas
680
00:39:42,875 --> 00:39:44,309
that happens to be around them.
681
00:39:44,310 --> 00:39:46,443
They're both trying to eat
all the gas that's around them,
682
00:39:46,444 --> 00:39:48,678
and they're gonna get bright,
so it's gonna be a crazy event.
683
00:39:48,679 --> 00:39:50,747
It will be fantastic.
684
00:39:50,748 --> 00:39:55,086
Two fireballs
rotating around each other
685
00:39:55,087 --> 00:39:57,921
until the black holes
at the center of them
686
00:39:57,922 --> 00:40:01,024
finally coalesce.
687
00:40:01,025 --> 00:40:02,926
The black holes merge,
688
00:40:02,927 --> 00:40:06,397
forming an even larger
supermassive black hole,
689
00:40:06,398 --> 00:40:11,636
a new king to rule
over a new galaxy.
690
00:40:13,706 --> 00:40:16,675
But this new galaxy is
already dying.
691
00:40:16,676 --> 00:40:20,513
Over billions of years,
the stars slowly die out.
692
00:40:20,514 --> 00:40:24,783
There's no fuel left to create
new stars and replace them.
693
00:40:24,784 --> 00:40:28,088
What you're left with is
basically a dark galaxy.
694
00:40:28,089 --> 00:40:31,089
It's not generating
any energy, any heat, any light.
695
00:40:31,090 --> 00:40:33,124
It's just black.
696
00:40:33,125 --> 00:40:36,495
One hundred trillion years
697
00:40:36,496 --> 00:40:40,731
after it was formed in the
darkness of the early universe,
698
00:40:40,732 --> 00:40:44,635
the voracious black hole
returns to darkness.
699
00:40:44,636 --> 00:40:48,939
Here, it's left to feast
on the galaxy it built,
700
00:40:48,940 --> 00:40:53,211
eating the dead remains
of stars and planets.
701
00:40:53,212 --> 00:40:55,580
The orbits of the stars decay,
702
00:40:55,581 --> 00:40:58,352
and they fall in toward
the supermassive black hole.
703
00:40:58,353 --> 00:41:01,252
And it ultimately it's thought
galaxies like the milky way
704
00:41:01,253 --> 00:41:04,056
will just form
one supermassive black hole.
705
00:41:05,259 --> 00:41:06,658
In literature,
706
00:41:06,659 --> 00:41:08,595
beginnings and endings
are always tied together,
707
00:41:08,596 --> 00:41:11,196
but the same is true
for our galaxy's black hole.
708
00:41:11,197 --> 00:41:12,531
It is quite possible that,
709
00:41:12,532 --> 00:41:15,200
without the formation
of the black hole at its center,
710
00:41:15,201 --> 00:41:17,602
our galaxy would not
have coalesced around it
711
00:41:17,603 --> 00:41:19,205
and have the properties it has.
712
00:41:19,206 --> 00:41:21,008
But the ultimate future
of our galaxy
713
00:41:21,009 --> 00:41:23,508
is to collapse
into a massive black hole.
714
00:41:23,509 --> 00:41:26,312
So, in that sense, the black
hole may be responsible
715
00:41:26,313 --> 00:41:28,013
for the beginning of our galaxy,
716
00:41:28,014 --> 00:41:31,252
and it'll definitely ultimately
be responsible for its death.
717
00:41:32,621 --> 00:41:36,224
Our galaxy is magnificent.
718
00:41:36,225 --> 00:41:40,461
All this, everything we see
in our night sky,
719
00:41:40,462 --> 00:41:41,829
could be the result
720
00:41:41,830 --> 00:41:45,564
of one of the most fearsome
objects in the universe
721
00:41:45,565 --> 00:41:50,104
a supermassive black hole
that could've been our creator
722
00:41:50,105 --> 00:41:53,541
and will be the destroyer
of our galaxy
723
00:41:53,542 --> 00:41:57,246
and all the galaxies
in the universe.
724
00:41:57,296 --> 00:42:01,846
Repair and Synchronization by
Easy Subtitles Synchronizer 1.0.0.0