Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated:
1
00:00:01,543 --> 00:00:04,000
ln the beginning,
there was darkness...
2
00:00:04,042 --> 00:00:06,125
and then, bang...
3
00:00:06,167 --> 00:00:09,332
giving birth to an endless
expanding existence...
4
00:00:09,375 --> 00:00:11,915
of time, space, and matter.
5
00:00:11,958 --> 00:00:14,206
Now, see further
than we've ever imagined...
6
00:00:14,249 --> 00:00:16,124
beyond the limits of our existence...
7
00:00:16,165 --> 00:00:18,998
in a place we call "The Universe."
8
00:00:21,707 --> 00:00:26,039
lt's a crucible
of creation and destruction.
9
00:00:26,082 --> 00:00:27,579
The name "Milky Way"
sounds like something...
10
00:00:27,622 --> 00:00:28,997
kind of comforting and sweet.
11
00:00:29,039 --> 00:00:31,621
But the Milky Way galaxy
is a monster.
12
00:00:31,664 --> 00:00:36,870
lt'sjust one galaxy among billions,
and we're living on the edge.
13
00:00:36,913 --> 00:00:39,495
Just recently, we've discovered
that there are two small galaxies...
14
00:00:39,538 --> 00:00:42,161
colliding
with the Milky Way right now.
15
00:00:42,204 --> 00:00:46,703
lt's a tapestry of brilliant
suns and blinding dust.
16
00:00:46,745 --> 00:00:48,743
lt's surprising
how little of the light...
17
00:00:48,786 --> 00:00:51,785
from our rather luminous
Milky Way galaxy reaches us.
18
00:00:52,495 --> 00:00:56,451
lt's a place of extremes,
where stars can drift lazily...
19
00:00:56,494 --> 00:01:00,993
or be flung out at more
than a million miles per hour.
20
00:01:01,035 --> 00:01:05,158
Now scientists have pierced
the galaxy's heart of darkness...
21
00:01:05,201 --> 00:01:07,992
to find ourway
through the Milky Way.
22
00:01:21,199 --> 00:01:24,532
lt's 100,000 light-years in diameter...
23
00:01:25,865 --> 00:01:28,863
has a trillion times
more mass than our Sun.
24
00:01:31,489 --> 00:01:34,363
lt began about
thirteen billion years ago...
25
00:01:36,697 --> 00:01:39,487
and is still under construction.
26
00:01:42,363 --> 00:01:46,112
lt's our galaxy, the Milky Way.
27
00:01:47,445 --> 00:01:50,486
The Milky Way galaxy
is an extremely active place.
28
00:01:50,529 --> 00:01:52,319
lt's like a construction project.
29
00:01:52,362 --> 00:01:54,444
There's things going on
all the time.
30
00:01:55,695 --> 00:01:58,068
You have old stars
dying and torn down...
31
00:01:59,028 --> 00:02:02,776
and then that material gets used
to build brand-new stars.
32
00:02:06,026 --> 00:02:07,900
ln the midst of this work zone...
33
00:02:07,943 --> 00:02:11,692
lies our little solar system
and a whole lot more.
34
00:02:12,734 --> 00:02:14,900
l suppose the best way to think
ofthe Milky Way galaxy...
35
00:02:14,943 --> 00:02:16,400
is ourfamily of stars.
36
00:02:16,441 --> 00:02:19,565
These are the stars that
we travel through the universe with...
37
00:02:19,608 --> 00:02:22,649
in a clump,
all orbiting a common center.
38
00:02:24,524 --> 00:02:27,231
Within its far-reaching spiral arms...
39
00:02:27,273 --> 00:02:29,648
lie clues to where we started...
40
00:02:31,148 --> 00:02:33,398
and how it all will end.
41
00:02:37,023 --> 00:02:40,854
On a clear summer night,
the stars of the Milky Way...
42
00:02:40,897 --> 00:02:44,854
unfurl like a shimmering banner
across the sky.
43
00:02:44,897 --> 00:02:47,853
Ancient Egyptians
saw this river of stars...
44
00:02:47,896 --> 00:02:50,312
as a pathway to the afterlife...
45
00:02:50,354 --> 00:02:53,478
but the Greeks
were the first to name it.
46
00:02:53,521 --> 00:02:56,978
The Milky Way comes
from the word "galacos"...
47
00:02:57,020 --> 00:02:58,977
which is Greek for milk.
48
00:03:00,395 --> 00:03:04,060
And though we once believed
we lived at the center of the universe...
49
00:03:04,103 --> 00:03:06,434
we now know
that we don't even live...
50
00:03:06,477 --> 00:03:08,810
in the center
of our own galaxy.
51
00:03:10,769 --> 00:03:12,059
When we look up
into the night sky...
52
00:03:12,102 --> 00:03:14,266
and we see
this milky swath of stars...
53
00:03:14,309 --> 00:03:15,392
that we call the Milky Way...
54
00:03:15,434 --> 00:03:19,058
what we're actually seeing
is a spiral arm of the galaxy...
55
00:03:19,101 --> 00:03:21,475
that's closer to the center
of the galaxy than we are.
56
00:03:21,518 --> 00:03:24,307
We can't really see the center
of the galaxy from here...
57
00:03:24,350 --> 00:03:27,598
but what we can see is
one of the spiral arms...
58
00:03:27,641 --> 00:03:31,640
that's a few thousand light-years
closer to the center than we are.
59
00:03:33,848 --> 00:03:37,931
As we gaze at the Milky Way
from our earthbound position...
60
00:03:37,974 --> 00:03:40,639
it's like looking
at the edge of a coin.
61
00:03:40,682 --> 00:03:43,680
We get no sense
of the galaxy's real shape.
62
00:03:45,847 --> 00:03:48,887
lf, however, you look
at a galaxy from the top down...
63
00:03:48,930 --> 00:03:50,346
it's a disk, remember...
64
00:03:50,389 --> 00:03:53,054
and it's like looking
at a Frisbee from the top down.
65
00:03:53,097 --> 00:03:55,095
You can see its full glory.
66
00:03:56,137 --> 00:03:58,470
Even though it's thin,
you don't see how thin it is...
67
00:03:58,513 --> 00:04:00,511
but you see its full structure.
68
00:04:02,844 --> 00:04:04,302
You can make the analogy
ofthe Milky Way...
69
00:04:04,345 --> 00:04:05,927
as being very much like a city.
70
00:04:07,803 --> 00:04:08,927
There's a central region...
71
00:04:10,760 --> 00:04:11,927
there's big buildings...
72
00:04:13,468 --> 00:04:15,009
there's a lot of action
in the middle...
73
00:04:16,510 --> 00:04:18,384
and that's certainly true
of our galaxy.
74
00:04:20,510 --> 00:04:22,175
Then you move out
to the suburbs...
75
00:04:23,342 --> 00:04:24,675
where life is a little bit
more comfortable...
76
00:04:24,717 --> 00:04:25,800
a little more relaxing.
77
00:04:25,842 --> 00:04:27,800
lt's a better place
to raise a family.
78
00:04:29,758 --> 00:04:32,465
This is where we reside.
79
00:04:32,508 --> 00:04:36,881
Our solar system is among
the Milky Way's spiral arms...
80
00:04:36,924 --> 00:04:40,923
26,000 light-years
from the bustling center.
81
00:04:40,966 --> 00:04:43,089
Our galaxy is so large...
82
00:04:43,131 --> 00:04:47,463
that it takes Earth more than
200 million years to make one lap.
83
00:04:48,422 --> 00:04:49,630
The Sun is located
in what would be...
84
00:04:49,673 --> 00:04:53,253
just an average neighborhood
around the city center.
85
00:04:53,296 --> 00:04:55,962
But, again, ifyou stand
in the middle of this neighborhood...
86
00:04:56,004 --> 00:04:57,046
you don't really know
what the neighborhood...
87
00:04:57,089 --> 00:04:59,003
on the opposite side
of the city looks like...
88
00:04:59,046 --> 00:05:00,670
because you can't see it directly.
89
00:05:04,087 --> 00:05:07,252
As we move outward
beyond the suburbs...
90
00:05:07,295 --> 00:05:10,752
the population
becomes more sparse.
91
00:05:10,795 --> 00:05:13,335
And, yeah, you've even got
sort ofthe boondocks.
92
00:05:13,378 --> 00:05:15,460
ln our galaxy,
you've got the halo...
93
00:05:15,503 --> 00:05:17,126
where you have very old stars...
94
00:05:17,168 --> 00:05:19,751
in sort ofwide orbits
around the galaxy.
95
00:05:20,627 --> 00:05:22,292
The galactic sprawl doesn't stop...
96
00:05:22,335 --> 00:05:26,167
at the Milky Way's
loose and undefined halo.
97
00:05:26,210 --> 00:05:28,959
lt reaches far beyond
our neighborhood...
98
00:05:29,001 --> 00:05:32,666
and out to a group of galaxies
called the Local Group.
99
00:05:34,042 --> 00:05:35,957
lfyou think
of the Milky Way galaxy...
100
00:05:35,999 --> 00:05:37,666
as a city like Los Angeles...
101
00:05:38,624 --> 00:05:43,373
then you can think of these as counties
all within the state of California.
102
00:05:43,415 --> 00:05:46,747
And together, this Local Group
makes up the entire state.
103
00:05:51,373 --> 00:05:53,871
Besides our huge Milky Way...
104
00:05:53,914 --> 00:05:57,621
and the even larger
Andromeda galaxy...
105
00:05:57,664 --> 00:06:01,371
the Local Group consists of close
to fifty smaller galaxies...
106
00:06:01,413 --> 00:06:05,495
the closest ofwhich are roughly
40,000 light-years away.
107
00:06:06,704 --> 00:06:09,578
There are two relatively
nearby dwarf galaxies...
108
00:06:09,621 --> 00:06:12,327
the Large and Small
Clouds of Magellan...
109
00:06:12,370 --> 00:06:14,911
that orbit
our Milky Way galaxy...
110
00:06:14,954 --> 00:06:17,660
and are easily seen
in the southern hemisphere.
111
00:06:17,702 --> 00:06:19,410
They're small, little galaxies.
112
00:06:19,453 --> 00:06:23,201
But our Local Group has
several dozen such galaxies...
113
00:06:23,243 --> 00:06:25,409
sort ofwandering around inside it.
114
00:06:25,452 --> 00:06:27,700
The big galaxies are the minority.
115
00:06:29,451 --> 00:06:32,533
One advantage of actually being
in the outer edges of our galaxy...
116
00:06:32,576 --> 00:06:35,950
we have a clearer view
of outside of our Milky Way.
117
00:06:35,992 --> 00:06:38,282
We're able to see
the rest of the universe...
118
00:06:38,325 --> 00:06:40,532
our neighboring galaxies
and galaxy clusters...
119
00:06:40,575 --> 00:06:43,407
beyond our own
Local Group of galaxies.
120
00:06:46,658 --> 00:06:51,656
lnside the Milky Way's halo
lie massive globular clusters.
121
00:06:51,698 --> 00:06:55,280
Globular clusters are densely
packed regions of stars...
122
00:06:55,323 --> 00:06:57,405
that are all of similar composition.
123
00:07:00,988 --> 00:07:04,655
These are like the ethnic neighborhoods
of the Milky Way galaxy.
124
00:07:06,154 --> 00:07:10,071
lndeed, these globular clusters formed
when the galaxy was very young.
125
00:07:10,113 --> 00:07:12,278
They are among the first stars
to have formed.
126
00:07:12,321 --> 00:07:16,653
Some globular clusters are
twelve or thirteen billion years old.
127
00:07:16,695 --> 00:07:20,069
They contain a hundred thousand
or even a million stars.
128
00:07:20,986 --> 00:07:25,026
Globular clusters,
almost as old as the universe itself...
129
00:07:25,069 --> 00:07:28,734
gave us the first clue
to our place in the galaxy.
130
00:07:30,027 --> 00:07:32,442
We saw these globular
clusters in the sky...
131
00:07:32,485 --> 00:07:36,150
but their centerwas somewhere
far away from us.
132
00:07:36,193 --> 00:07:37,650
And that was one
of ourfirst measurements...
133
00:07:37,692 --> 00:07:39,483
ofwhere the middle
of the galaxy should be.
134
00:07:40,567 --> 00:07:41,983
They weren't orbiting around us...
135
00:07:42,025 --> 00:07:45,815
but around an area somewhere
about 27,000 light-years away.
136
00:07:48,483 --> 00:07:51,522
We can never get far enough
away from our own galaxy...
137
00:07:51,565 --> 00:07:52,940
to actually see it.
138
00:07:54,231 --> 00:07:56,189
But by looking at other galaxies...
139
00:07:56,231 --> 00:07:58,813
and comparing what we know
about our own galaxy...
140
00:07:58,856 --> 00:08:02,188
we've got a pretty good picture
ofthe Milky Way.
141
00:08:03,564 --> 00:08:06,271
The very first time we saw
galaxies through telescopes...
142
00:08:06,314 --> 00:08:08,146
we didn't even know
they were galaxies.
143
00:08:09,605 --> 00:08:12,354
We thought they werejust
nebulae in our own galaxy...
144
00:08:12,396 --> 00:08:15,145
and we werejust amazed
by the beautiful spiral shape.
145
00:08:16,229 --> 00:08:18,269
So it was sort of natural
for astronomers...
146
00:08:18,312 --> 00:08:21,519
to classify galaxies according
to their shape, what we see.
147
00:08:22,811 --> 00:08:26,977
Astronomers recognize
four basic galactic shapes:
148
00:08:27,020 --> 00:08:31,184
Elliptical, built of old stars
and which doesn't spin...
149
00:08:31,226 --> 00:08:34,142
lenticular, consisting
of a bulge and a disc...
150
00:08:34,185 --> 00:08:36,516
and little
or no new starformation...
151
00:08:37,477 --> 00:08:40,434
irregular, which
has no real shape at all...
152
00:08:40,477 --> 00:08:43,308
like the Magellanic Clouds
in our own Local Group...
153
00:08:43,351 --> 00:08:47,891
and spiral,
which includes our Milky Way.
154
00:08:47,934 --> 00:08:50,766
lt's a pinwheel
ofyoung and old stars...
155
00:08:50,808 --> 00:08:54,349
spinning gracefully
through space.
156
00:08:54,391 --> 00:08:56,473
A long time ago, people thought
that maybe an elliptical galaxy
157
00:08:56,515 --> 00:08:58,890
eventually
collapses down into a spiral...
158
00:09:00,307 --> 00:09:02,972
or maybe eventually
spirals all come together...
159
00:09:03,015 --> 00:09:04,348
and form an elliptical.
160
00:09:05,514 --> 00:09:08,804
And it was sort of hard to figure out
exactlywhat the sequence is.
161
00:09:08,847 --> 00:09:13,304
One thing we know is that elliptical
galaxies tend to be very large.
162
00:09:15,888 --> 00:09:19,386
Centaurus A,
a misshapen elliptical galaxy...
163
00:09:19,429 --> 00:09:21,844
about thirteen million
light-years away...
164
00:09:21,887 --> 00:09:25,345
suggests why
elliptical galaxies get so big.
165
00:09:27,053 --> 00:09:30,677
There's a lot of evidence that there's
a spiral galaxy in there somewhere...
166
00:09:30,720 --> 00:09:32,927
that got absorbed
by a larger galaxy.
167
00:09:32,969 --> 00:09:35,092
So, right now, it's possible...
168
00:09:35,135 --> 00:09:38,760
that these really big
elliptical galaxies we see...
169
00:09:38,802 --> 00:09:42,759
may be the mergers of several spirals
and other types of galaxies.
170
00:09:46,551 --> 00:09:50,549
Our Milky Way isn't in danger
of being absorbed any time soon.
171
00:09:51,634 --> 00:09:56,298
But the heart of our spiral galaxy
has revealed a secret of its own.
172
00:09:57,467 --> 00:09:59,590
Only recently, we discovered
that the Milky Way...
173
00:09:59,633 --> 00:10:03,173
is not a classic spiral,
but a barred spiral.
174
00:10:03,215 --> 00:10:05,423
There's a bar of stars
going through the center...
175
00:10:05,466 --> 00:10:08,339
and the spiral arms sort of
attach offfrom that bar.
176
00:10:09,589 --> 00:10:12,755
Spanning 27,000 light-years...
177
00:10:12,797 --> 00:10:16,254
it's the most popular bar
in the galaxy.
178
00:10:16,297 --> 00:10:18,837
Thirty million stars gravitate to it.
179
00:10:20,254 --> 00:10:23,378
The bar of our galaxy is
a natural result of gravity...
180
00:10:23,421 --> 00:10:26,961
the mutual gravitational interactions
of the individual stars...
181
00:10:27,004 --> 00:10:31,753
that form the disk of our galaxy
and the bulge of our galaxy.
182
00:10:31,795 --> 00:10:35,252
lt causes sometimes the stars
to sort of bunch up...
183
00:10:35,295 --> 00:10:38,126
into this bar configuration.
184
00:10:38,169 --> 00:10:40,668
Surrounding the middle
ofthe Milky Way...
185
00:10:40,711 --> 00:10:43,417
is a huge central bulge.
186
00:10:43,460 --> 00:10:48,001
lt's mostly composed of stars between
ten and eleven billion years old.
187
00:10:49,500 --> 00:10:50,709
The size of the bulge...
188
00:10:50,751 --> 00:10:54,541
is linked to the Milky Way's
most gripping feature of all...
189
00:10:54,584 --> 00:10:56,957
a supermassive black hole.
190
00:10:58,000 --> 00:10:59,291
Though it would easily fit...
191
00:10:59,334 --> 00:11:02,040
in the space
between the Earth and our Sun...
192
00:11:02,082 --> 00:11:05,456
it's four million times
more massive than our Sun.
193
00:11:06,541 --> 00:11:07,956
Now, that sounds like a lot...
194
00:11:07,998 --> 00:11:10,122
but other galaxies
have central black holes...
195
00:11:10,165 --> 00:11:13,538
which extend up to a billion
times the mass of our Sun.
196
00:11:13,581 --> 00:11:17,622
So, whereas we call
our black hole...
197
00:11:17,664 --> 00:11:21,246
at the center of our Milky Way
a supermassive black hole...
198
00:11:21,288 --> 00:11:24,203
among supermassive black holes,
it's kind of a runt.
199
00:11:27,413 --> 00:11:31,745
Black holes can't be seen directly
because light can't escape them.
200
00:11:32,662 --> 00:11:35,202
Astronomers have located
galactic ground zero...
201
00:11:35,245 --> 00:11:38,453
through a radio source
in the constellation Sagittarius...
202
00:11:38,495 --> 00:11:41,910
known as Sagittarius A star.
203
00:11:41,952 --> 00:11:43,993
lt's creating quite a stir.
204
00:11:44,952 --> 00:11:47,992
The black hole in the middle
of our galaxy is spinning...
205
00:11:48,035 --> 00:11:49,701
and it appears to be spinning...
206
00:11:49,744 --> 00:11:53,617
at a rate of about one spin
per eleven minutes.
207
00:11:55,659 --> 00:11:59,491
As it spins, central region stars
caught in its gravity...
208
00:11:59,534 --> 00:12:01,824
get swept along for the ride...
209
00:12:01,867 --> 00:12:05,324
orbiting it at about
three million miles per hour.
210
00:12:07,533 --> 00:12:10,531
The black hole affects
the central region the most.
211
00:12:11,948 --> 00:12:14,197
But we can't feel
its tug on Earth...
212
00:12:14,240 --> 00:12:17,572
since we orbit the galaxy
far away from the center.
213
00:12:18,656 --> 00:12:21,405
The colossal forces
at the galaxy's heart...
214
00:12:21,448 --> 00:12:25,321
are negated by the Milky Way's
unimaginable size.
215
00:12:26,281 --> 00:12:27,945
To me, the name "Milky Way"
sounds like something...
216
00:12:27,988 --> 00:12:29,862
kind of comforting,
sweet, you know...
217
00:12:29,905 --> 00:12:31,237
a candy bar,
that sort of thing.
218
00:12:31,280 --> 00:12:33,612
But the Milky Way galaxy
is a monster.
219
00:12:34,613 --> 00:12:36,486
lt is incredibly huge.
220
00:12:36,529 --> 00:12:39,403
So, when you think about
howvast our solar system is...
221
00:12:39,446 --> 00:12:41,235
the fact that it takes years...
222
00:12:41,278 --> 00:12:44,861
for the fastest spacecraft to get
out to Saturn or Jupiter...
223
00:12:44,904 --> 00:12:47,527
if the entire solar system
were the size of a CD...
224
00:12:47,570 --> 00:12:50,110
the Earth would be comparable
to the Milky Way.
225
00:12:50,153 --> 00:12:51,484
That's huge.
226
00:12:51,527 --> 00:12:54,525
That's absolutely mind-blowing,
and it never ceases to amaze me.
227
00:12:56,318 --> 00:12:59,233
And the amazement
goes on and on.
228
00:12:59,276 --> 00:13:01,442
The galaxy's bustle
and commotion...
229
00:13:01,484 --> 00:13:03,275
may be concentrated
in the center...
230
00:13:03,318 --> 00:13:07,940
but the spectacular spiral arms
have action of their own.
231
00:13:07,983 --> 00:13:10,857
lt's here that stellar
neighborhoods are being built...
232
00:13:10,900 --> 00:13:13,440
and stars are being born.
233
00:13:16,608 --> 00:13:18,814
This is our galaxy.
234
00:13:18,857 --> 00:13:20,230
lt's a lot to take in...
235
00:13:20,273 --> 00:13:23,063
and we'rejust beginning
to probe its depths.
236
00:13:25,023 --> 00:13:28,688
Our suburban location makes
it difficult to get the big picture...
237
00:13:29,439 --> 00:13:33,479
and the hazy clouds of cosmic dust
only block our view.
238
00:13:34,688 --> 00:13:37,270
Even the most powerful
optical telescope...
239
00:13:37,313 --> 00:13:39,728
can't pierce the darkness.
240
00:13:39,770 --> 00:13:42,227
So, ifwe want to learn more
about the Milky Way...
241
00:13:42,270 --> 00:13:45,185
we need to look beyond
what our eyes can see.
242
00:13:49,186 --> 00:13:51,727
For all its vastness
and empty space...
243
00:13:51,769 --> 00:13:54,435
the Milky Way is
tremendously active...
244
00:13:54,477 --> 00:13:57,517
and populated with some
astonishing phenomena:
245
00:13:58,768 --> 00:14:00,018
Star clusters...
246
00:14:00,060 --> 00:14:01,726
nebulas...
247
00:14:01,768 --> 00:14:05,017
blazing invaders
from other galaxies.
248
00:14:05,934 --> 00:14:09,391
Technology is making us
rethink old beliefs...
249
00:14:09,434 --> 00:14:13,724
and is showing us things
we've never even considered before.
250
00:14:13,766 --> 00:14:15,724
We have ignition...
and liftoff.
251
00:14:19,932 --> 00:14:21,681
T-plus fifteen seconds.
252
00:14:21,724 --> 00:14:24,306
We're sending
the New Horizon spacecraft...
253
00:14:24,348 --> 00:14:27,264
on its way to the very edge
of our solar system.
254
00:14:30,472 --> 00:14:34,054
We live on a dusty planet
in a dusty galaxy...
255
00:14:34,097 --> 00:14:36,305
in a dusty universe.
256
00:14:36,347 --> 00:14:38,596
Empty space isn't so empty.
257
00:14:40,054 --> 00:14:44,387
Optical telescopes can see
only as far as the nearest dust cloud...
258
00:14:45,596 --> 00:14:47,095
which isn't far at all.
259
00:14:48,470 --> 00:14:50,677
Most of our galaxy
is invisible to us, however...
260
00:14:50,720 --> 00:14:53,427
and that's because the galaxy
is full of dust...
261
00:14:53,469 --> 00:14:54,886
dust clouds, ifyou will...
262
00:14:54,928 --> 00:14:57,051
and these dust clouds
block the light...
263
00:14:57,094 --> 00:14:59,509
from most of the stars
in our galaxy.
264
00:14:59,552 --> 00:15:01,593
lt's surprising
how little of the light...
265
00:15:01,635 --> 00:15:05,884
from our rather luminous
Milky Way galaxy reaches us.
266
00:15:05,926 --> 00:15:08,884
The reason for that is simply
because the dust blocks it.
267
00:15:09,801 --> 00:15:14,049
But visible light isjust a small sliver
of the energy spectrum...
268
00:15:14,092 --> 00:15:19,091
and radio waves rush in where
visible light beams fear to tread.
269
00:15:20,091 --> 00:15:23,256
On a foggy day, you might
not be able to see very far...
270
00:15:23,299 --> 00:15:25,881
at visible wavelengths,
which your eye can see...
271
00:15:25,923 --> 00:15:30,089
but you can still listen
to your radio orwatch your TV.
272
00:15:31,048 --> 00:15:34,130
The ability of radio waves
to penetrate space dust...
273
00:15:34,172 --> 00:15:37,380
is crucial
to the study of the stars...
274
00:15:37,423 --> 00:15:40,421
but that use
was discovered by accident.
275
00:15:42,422 --> 00:15:47,962
ln 1933, Karl Jansky, an engineer
at Bell Labs in New Jersey...
276
00:15:48,005 --> 00:15:51,128
built an antenna to track down
the source of static...
277
00:15:51,170 --> 00:15:53,711
on transatlantic
telephone lines.
278
00:15:53,753 --> 00:15:56,460
He was surprised to discover
the interference...
279
00:15:56,503 --> 00:15:59,003
was raining down
from the center of our galaxy...
280
00:15:59,044 --> 00:16:01,460
the constellation Sagittarius.
281
00:16:01,503 --> 00:16:03,167
lt took several decades...
282
00:16:03,210 --> 00:16:06,710
for scientists to realize
that Jansky was on to something.
283
00:16:06,752 --> 00:16:10,542
Celestial bodies emit
electromagnetic radiation...
284
00:16:10,585 --> 00:16:14,208
and, thus,
radio astronomy was born.
285
00:16:14,251 --> 00:16:17,584
But radio waves
werejust the beginning.
286
00:16:17,626 --> 00:16:20,541
Because the human eye can't
see all the light that's available...
287
00:16:20,584 --> 00:16:22,416
we have to resort
to technology.
288
00:16:22,458 --> 00:16:24,373
And one of the best ways
of seeing the universe...
289
00:16:24,416 --> 00:16:27,373
in a very different way
is with an infrared camera.
290
00:16:27,416 --> 00:16:31,706
An infrared camera sees only
the wavelengths generated by heat...
291
00:16:31,748 --> 00:16:35,080
then converts it to something
the human eye can see.
292
00:16:36,540 --> 00:16:38,122
There actually is
no visible light at all...
293
00:16:38,164 --> 00:16:39,414
that passes through this lens.
294
00:16:39,456 --> 00:16:41,414
This lens only lets
heat light through.
295
00:16:41,456 --> 00:16:42,496
And then you can see...
296
00:16:42,539 --> 00:16:44,580
what everything looks like
in infrared light.
297
00:16:45,414 --> 00:16:47,371
Three, two...
298
00:16:47,414 --> 00:16:48,453
main engine start...
299
00:16:48,496 --> 00:16:51,662
ln 2003,
the Spitzer Space Telescope...
300
00:16:51,705 --> 00:16:54,203
equipped with a battery
of infrared cameras...
301
00:16:54,246 --> 00:16:55,786
was launched into space.
302
00:16:55,829 --> 00:16:57,870
...and the evolution
of our universe.
303
00:16:57,912 --> 00:17:01,119
lts mission is to explore
some of the youngest stars...
304
00:17:01,161 --> 00:17:04,035
and farthest galaxies
in the universe.
305
00:17:05,120 --> 00:17:06,368
The instruments
that Spitzer has on it...
306
00:17:06,411 --> 00:17:07,577
are actually many times...
307
00:17:07,619 --> 00:17:10,660
millions of times more sensitive
than these cameras...
308
00:17:10,703 --> 00:17:13,285
but they're basically
the same thing.
309
00:17:13,327 --> 00:17:15,659
This camera doesn't
peer into the heavens...
310
00:17:18,243 --> 00:17:22,241
but is used by firefighters
to save lives right here on Earth.
311
00:17:26,534 --> 00:17:29,032
The camera can see
through a smoke-filled room...
312
00:17:29,075 --> 00:17:32,865
to read the body heat from
an unconscious or immobilized victim.
313
00:17:36,740 --> 00:17:40,573
This same technology has enabled
astronomer Susan Stolovy...
314
00:17:40,615 --> 00:17:43,905
to see 26,000 light-years away...
315
00:17:43,948 --> 00:17:48,488
visualizing the center of
the galaxy as never before.
316
00:17:48,531 --> 00:17:50,530
This high-resolution mosaic...
317
00:17:50,573 --> 00:17:54,653
was assembled from roughly
12,000 individual images...
318
00:17:54,696 --> 00:17:56,404
taken from the Spitzer
Space Telescope.
319
00:17:57,445 --> 00:18:00,152
Even though that sounds like
a lot of data, and it is...
320
00:18:00,195 --> 00:18:03,194
it only took about sixteen hours
of telescope time.
321
00:18:03,237 --> 00:18:05,694
This particular region
of the galactic center...
322
00:18:05,736 --> 00:18:09,111
spans an area of the sky
that's equivalent to fourfull Moons...
323
00:18:09,153 --> 00:18:11,652
in one direction
and three full Moons in the other.
324
00:18:13,402 --> 00:18:18,567
That's the equivalent of 900 light-years
across by 700 light-years high...
325
00:18:19,735 --> 00:18:22,276
a small fraction
ofwhat's out there to see...
326
00:18:22,318 --> 00:18:24,900
but a phenomenal achievement
nonetheless.
327
00:18:26,025 --> 00:18:27,358
Just a few decades ago...
328
00:18:27,401 --> 00:18:30,358
the galactic center
was not a subject of study...
329
00:18:30,401 --> 00:18:32,065
because you couldn't see it.
330
00:18:32,108 --> 00:18:33,607
Visually, nothing gets through.
331
00:18:33,650 --> 00:18:37,273
Only one light wave in a trillion
can penetrate the dust.
332
00:18:37,315 --> 00:18:40,481
But ifyou go into the infrared...
333
00:18:40,524 --> 00:18:43,648
or use radio astronomy
or X-ray astronomy...
334
00:18:43,691 --> 00:18:45,313
you can see
what's going on there.
335
00:18:46,565 --> 00:18:49,230
Different wavelengths of
the electromagnetic spectrum...
336
00:18:49,273 --> 00:18:52,521
can reveal different aspects
ofthe galaxy...
337
00:18:52,564 --> 00:18:55,563
because they penetrate
celestial objects differently.
338
00:18:58,646 --> 00:19:02,687
Radio waves have the lowest energy
or longest wavelength...
339
00:19:02,729 --> 00:19:04,728
but most celestial objects
emit them.
340
00:19:06,062 --> 00:19:10,644
Then comes infrared,
visible light, ultraviolet.
341
00:19:11,520 --> 00:19:15,686
High energy X-rays with wavelengths
about the size of an atom...
342
00:19:15,727 --> 00:19:18,935
are emitted by black holes
and supernovas.
343
00:19:18,978 --> 00:19:20,893
The highest energy, gamma rays...
344
00:19:20,936 --> 00:19:24,976
come from the collision or decay
of subatomic particles...
345
00:19:25,017 --> 00:19:28,141
like when stars explode
at billions of degrees.
346
00:19:29,268 --> 00:19:31,559
Together, these waves
give astronomers...
347
00:19:31,601 --> 00:19:35,599
a more complete picture of the activity
and shape of our galaxy.
348
00:19:38,183 --> 00:19:39,932
Many, if not all,
of the wavelengths...
349
00:19:39,975 --> 00:19:41,974
are needed to study the cosmos.
350
00:19:42,974 --> 00:19:45,848
The various wavelengths
of the electromagnetic spectrum...
351
00:19:45,890 --> 00:19:48,347
are similar
to the strings on a violin.
352
00:19:53,098 --> 00:19:55,347
ln music,
many wavelengths of sound...
353
00:19:55,390 --> 00:19:58,222
are used to communicate
a musical idea.
354
00:19:58,264 --> 00:19:59,887
This piece
has a very large range...
355
00:19:59,930 --> 00:20:01,887
from a low note
to a high note.
356
00:20:09,096 --> 00:20:12,344
lfwe were to restrict ourselves
to the visible light spectrum...
357
00:20:12,387 --> 00:20:14,678
it's almost as ifwe
were only to hear two notes...
358
00:20:14,720 --> 00:20:16,302
in the middle of that piece.
359
00:20:20,719 --> 00:20:22,510
Using alternate wavelengths...
360
00:20:22,553 --> 00:20:25,218
the more we look,
the more we're discovering.
361
00:20:28,094 --> 00:20:30,634
Just recently, we've discovered
that there are two small galaxies...
362
00:20:30,677 --> 00:20:33,133
colliding with the Milky Way
right now...
363
00:20:33,176 --> 00:20:35,384
and the only reason
we didn't know they were there...
364
00:20:35,426 --> 00:20:37,341
is because
there was so much dust...
365
00:20:37,384 --> 00:20:39,674
in the disk of our galaxy,
we couldn't see them.
366
00:20:39,716 --> 00:20:42,340
We're living
inside this cloud...
367
00:20:42,383 --> 00:20:43,674
and it's something
we're not aware of.
368
00:20:43,716 --> 00:20:47,048
But with infrared light,
you can cut through that dust.
369
00:20:47,841 --> 00:20:50,673
And the minute we turned
infrared telescopes to the sky...
370
00:20:50,715 --> 00:20:54,089
we saw these little galaxies
up there, coming right at us.
371
00:20:57,714 --> 00:21:00,255
From our cockeyed position
in the Milky Way...
372
00:21:00,297 --> 00:21:03,629
it's difficult to gauge
what our galaxy really looks like.
373
00:21:05,130 --> 00:21:09,087
Radio and optical astronomy
give us a glimpse of its features...
374
00:21:09,129 --> 00:21:12,920
but to get the big picture,
we need to look outward.
375
00:21:14,337 --> 00:21:16,877
So the waywe gain some
understanding of our own galaxy...
376
00:21:16,920 --> 00:21:19,044
is, first of all,
by looking at other galaxies...
377
00:21:19,087 --> 00:21:22,585
and seeing what they look like
and seeing things in other galaxies...
378
00:21:22,628 --> 00:21:26,168
that correspond to things
that we see in our own galaxy...
379
00:21:26,211 --> 00:21:28,585
like clouds of gas
that are kind of lined up...
380
00:21:28,627 --> 00:21:30,751
along what looks
like a spiral arm.
381
00:21:30,794 --> 00:21:33,543
You know, we can see parts
of spiral arms in our own galaxy...
382
00:21:33,585 --> 00:21:35,542
and we figure
that they're all connected...
383
00:21:35,584 --> 00:21:37,916
kind of like the spiral arms
of other galaxies...
384
00:21:37,959 --> 00:21:39,708
that we can see
from the outside.
385
00:21:41,042 --> 00:21:44,500
We know that the Milky Way's
four main spiral arms...
386
00:21:44,542 --> 00:21:48,957
swing out from the downtown
center like wide streets.
387
00:21:48,999 --> 00:21:53,832
From the inside out,
they're named Norma...
388
00:21:53,873 --> 00:21:54,873
Scutum-Crux...
389
00:21:55,791 --> 00:21:57,039
Sagittarius...
390
00:21:58,040 --> 00:21:59,205
and Perseus.
391
00:22:02,581 --> 00:22:05,163
lfthe arms
are the galaxy's suburbs...
392
00:22:05,206 --> 00:22:08,746
then our solar system lives
on a quiet, dead-end street...
393
00:22:08,789 --> 00:22:13,704
between Sagittarius and Perseus
on what's called the Orion Spur.
394
00:22:15,371 --> 00:22:16,995
All the stars in the Milky Way...
395
00:22:17,038 --> 00:22:21,286
add up to a community
of about 200 to 400 billion...
396
00:22:21,329 --> 00:22:23,661
and they're on the move.
397
00:22:23,703 --> 00:22:25,285
We are orbiting
around the galaxy.
398
00:22:25,328 --> 00:22:26,661
We change our position.
399
00:22:26,703 --> 00:22:28,493
So far, we think
the Sun has always been...
400
00:22:28,536 --> 00:22:30,618
about the same distance
away from the center...
401
00:22:30,661 --> 00:22:31,660
but we've been in and out...
402
00:22:31,702 --> 00:22:34,326
of pretty much every spiral arm
that there is.
403
00:22:36,202 --> 00:22:39,116
The spirals
are called density waves...
404
00:22:39,159 --> 00:22:42,158
areas where the stars and gas
get pushed together.
405
00:22:43,409 --> 00:22:45,866
As the density waves
spiral around...
406
00:22:45,909 --> 00:22:48,908
the billions of stars ride
over and through them.
407
00:22:50,951 --> 00:22:52,824
When you think about watching
the Tour de France...
408
00:22:52,866 --> 00:22:54,323
and you see
all of these bicycles.
409
00:22:54,366 --> 00:22:55,657
They're all moving forward.
410
00:22:55,699 --> 00:22:58,615
Sometimes they kind of clump up
around one bicyclist.
411
00:22:58,658 --> 00:23:00,364
And sometimes
they're stretched out.
412
00:23:00,406 --> 00:23:02,156
That's sort ofwhat
the spiral arms are like...
413
00:23:02,199 --> 00:23:04,823
that the stars are going around
like the bicyclists...
414
00:23:04,865 --> 00:23:06,280
sometimes in clumpy areas...
415
00:23:06,323 --> 00:23:08,488
and sometimes
in more spread-out areas...
416
00:23:08,531 --> 00:23:10,530
but they keep going
around the center.
417
00:23:12,988 --> 00:23:16,196
Stars don't
usually travel alone.
418
00:23:16,238 --> 00:23:20,487
While giant globular clusters
populate the galaxy's halo...
419
00:23:20,530 --> 00:23:24,653
the galactic disk has open
or galactic clusters.
420
00:23:24,695 --> 00:23:26,361
These bundles ofyoung stars...
421
00:23:26,403 --> 00:23:29,527
are barely held together
by their mutual gravity.
422
00:23:30,695 --> 00:23:34,819
Now, "open cluster" implies that
the stars are actually free to go.
423
00:23:34,860 --> 00:23:35,902
lt is open.
424
00:23:35,945 --> 00:23:37,276
So this is a cluster, usually...
425
00:23:37,319 --> 00:23:39,485
of many stars
that have formed together...
426
00:23:39,527 --> 00:23:42,526
all from one of these
giant clouds of dust and gas.
427
00:23:42,568 --> 00:23:45,234
Over time, they're going
to move away from each other...
428
00:23:45,276 --> 00:23:46,942
distribute themselves
around the galaxy.
429
00:23:48,984 --> 00:23:53,857
Astronomers have counted about
20,000 open clusters in the galaxy.
430
00:23:54,442 --> 00:23:57,649
The Pleiades is the one
found nearest to the Earth.
431
00:23:57,691 --> 00:24:00,315
lt formed
a hundred million years ago...
432
00:24:00,358 --> 00:24:02,815
and will be around
at least twice that long...
433
00:24:02,857 --> 00:24:06,105
before the galaxy's spiral arms
tear it apart.
434
00:24:08,232 --> 00:24:11,730
Closer to home, our own Sun,
orbiting in solitude...
435
00:24:11,773 --> 00:24:14,813
may have once been part
of an open-cluster star...
436
00:24:14,855 --> 00:24:16,688
that struck out on its own.
437
00:24:17,605 --> 00:24:21,562
The Sun, the star clusters,
our own planet...
438
00:24:21,605 --> 00:24:25,394
in fact, the entire galaxy
and the universe beyond...
439
00:24:25,437 --> 00:24:27,978
are built of dust and gases.
440
00:24:28,813 --> 00:24:31,770
These particles
that now block ourview...
441
00:24:31,813 --> 00:24:34,769
are what got us here
in the first place...
442
00:24:34,812 --> 00:24:38,851
and the star-making machinery
is still cranking.
443
00:24:48,851 --> 00:24:52,683
Nothing beats the spectacle
of a glorious sunset...
444
00:24:54,017 --> 00:24:57,557
but we owe it all
to dust and gas.
445
00:24:58,642 --> 00:25:03,307
The setting Sun appears yellow,
orange, or even red for two reasons.
446
00:25:03,350 --> 00:25:06,390
First of all, the molecules of air
in the atmosphere...
447
00:25:06,433 --> 00:25:09,306
are scattering the violet,
blue, and green light...
448
00:25:09,349 --> 00:25:10,972
out of our line of sight...
449
00:25:11,015 --> 00:25:14,972
leaving the yellows, oranges,
and reds to reach our eyes.
450
00:25:15,015 --> 00:25:17,971
And second of all,
particles like dust or smoke...
451
00:25:18,014 --> 00:25:21,638
or smog in the atmosphere
absorb blue light...
452
00:25:21,680 --> 00:25:23,387
more than they do red light.
453
00:25:24,972 --> 00:25:30,970
Even the grandeur of a blue sky
is really an optical illusion.
454
00:25:31,013 --> 00:25:32,303
Why is the sky blue?
455
00:25:32,346 --> 00:25:35,011
There's nothing blue about
the gases of our atmosphere...
456
00:25:35,054 --> 00:25:38,011
but as sunlight comes
through our atmosphere...
457
00:25:38,054 --> 00:25:40,385
the shorterwavelengths,
the blue light...
458
00:25:40,428 --> 00:25:43,177
get scattered more
than the longerwavelengths do.
459
00:25:43,220 --> 00:25:45,134
So ifyou look
at any particular part of the sky...
460
00:25:45,177 --> 00:25:46,635
you're more
likely to see blue light...
461
00:25:46,677 --> 00:25:48,426
being scattered
towards your eye.
462
00:25:54,177 --> 00:25:58,258
Space is dark because there aren't
enough gas or dust particles...
463
00:25:58,301 --> 00:26:00,841
to reflect the light
of a billion stars.
464
00:26:02,509 --> 00:26:06,216
And though space may be
a vacuum, it's not perfect.
465
00:26:07,758 --> 00:26:11,714
The galactic disk,
the largest portion of the Milky Way...
466
00:26:11,757 --> 00:26:16,006
owes about fifteen percent
of its mass to dust and gas.
467
00:26:17,423 --> 00:26:22,005
Gas clouds can span hundreds
or even thousands of light-years...
468
00:26:22,048 --> 00:26:25,797
providing the raw material
that fires the galaxy.
469
00:26:25,839 --> 00:26:30,129
These regions of cosmic dust
and gas are called nebulae...
470
00:26:30,172 --> 00:26:33,879
and they produce effects
rivaling anything seen on Earth.
471
00:26:36,921 --> 00:26:39,128
A good example
is the Orion Nebula...
472
00:26:39,171 --> 00:26:41,461
in the constellation Orion.
473
00:26:41,504 --> 00:26:44,586
This region is active
with stellarformation...
474
00:26:44,629 --> 00:26:47,668
which makes the gas
around the stars glow.
475
00:26:48,753 --> 00:26:51,502
lt's literally fluorescing
in response to the light...
476
00:26:51,543 --> 00:26:55,376
coming out of the massive stars
that are near the nebula...
477
00:26:55,419 --> 00:26:58,917
and this nebula literally
glows and can be seen.
478
00:26:58,959 --> 00:27:00,709
You can see it
with your naked eye.
479
00:27:02,250 --> 00:27:03,792
When you see
the Orion Nebula...
480
00:27:03,834 --> 00:27:07,166
in a real way, those are
baby pictures for us.
481
00:27:07,209 --> 00:27:10,207
Five billion years ago,
we were in a glowing hot nebula...
482
00:27:10,249 --> 00:27:12,624
and the Sun and the planets
were forming together...
483
00:27:12,666 --> 00:27:13,916
under the influence of gravity.
484
00:27:16,249 --> 00:27:18,539
Orion,
which contains hot stars...
485
00:27:18,582 --> 00:27:21,831
ionizing its gases
with ultraviolet light...
486
00:27:21,874 --> 00:27:24,664
is called a diffuse
or emission nebula.
487
00:27:26,414 --> 00:27:30,913
Astronomers classify
two other categories of nebulae.
488
00:27:30,955 --> 00:27:33,954
Some nebulae are what are
called reflection nebulae.
489
00:27:33,997 --> 00:27:36,370
They're simply--
the dust in these nebulae...
490
00:27:36,413 --> 00:27:39,787
is simply reflecting the starlight
from the bright star nearby.
491
00:27:42,412 --> 00:27:46,952
The Witch Head Nebula
is an example of a reflection nebula...
492
00:27:46,995 --> 00:27:49,328
borrowing light
from the star Rigel.
493
00:27:50,328 --> 00:27:55,243
Reflection nebulae appear blue
for the same reason our sky does.
494
00:27:55,286 --> 00:27:57,951
Blue light is
more easily reflected than red.
495
00:27:59,161 --> 00:28:02,992
And last there are dark nebulae
like the Horsehead.
496
00:28:06,868 --> 00:28:09,742
When low-mass stars
like our Sun die...
497
00:28:09,785 --> 00:28:14,282
they form another kind of nebula
called a planetary nebula.
498
00:28:16,657 --> 00:28:20,573
These dim, short-lived nebulae,
like the Cat's Eye Nebula...
499
00:28:20,616 --> 00:28:23,823
spew elements
back into the galaxy.
500
00:28:23,866 --> 00:28:28,781
These may become raw materials
for new suns and new planets.
501
00:28:34,323 --> 00:28:37,987
Just as dying stars spew out
clouds of dust and gas...
502
00:28:38,822 --> 00:28:42,321
dust and gas can come together
to form stars.
503
00:28:45,321 --> 00:28:49,695
At a construction site, you have
old buildings being torn down...
504
00:28:49,738 --> 00:28:51,611
and new buildings going up.
505
00:28:51,653 --> 00:28:55,194
And it's very much the same
in the Milky Way galaxy.
506
00:28:55,236 --> 00:28:57,319
You have old stars explode...
507
00:28:57,361 --> 00:29:00,068
and they cast out new material,
raw material...
508
00:29:00,111 --> 00:29:03,318
gas and dust that can be used
to form new stars.
509
00:29:07,068 --> 00:29:10,776
Nebulae are the galaxy's
recycling centers...
510
00:29:10,818 --> 00:29:13,275
where old becomes new again.
511
00:29:14,318 --> 00:29:16,775
Recycling is notjust
a good idea here on Earth.
512
00:29:16,817 --> 00:29:20,690
lt's a natural cosmic law.
513
00:29:20,733 --> 00:29:24,107
ln fact, our own bodies
are made out of recycled material...
514
00:29:24,150 --> 00:29:26,231
from earlier generations of stars...
515
00:29:26,274 --> 00:29:29,023
that had dispersed material
into the interstellar medium...
516
00:29:29,065 --> 00:29:31,022
before our own
solar system formed.
517
00:29:32,774 --> 00:29:36,521
Each generation of stars
creates heavier elements...
518
00:29:36,564 --> 00:29:39,563
which become the ingredients
for everything in the universe.
519
00:29:40,647 --> 00:29:43,146
Most of the galaxy's
hot, young stars...
520
00:29:43,189 --> 00:29:45,854
get built in the Milky Way's
spiral arms.
521
00:29:47,897 --> 00:29:51,312
As gas clouds orbit the center
of the galaxy like the stars do...
522
00:29:52,312 --> 00:29:55,478
they get squeezed as they go
through a spiral arm.
523
00:29:56,395 --> 00:30:01,478
Remember, a spiral arm is simply
a wave in the pattern of stars.
524
00:30:01,520 --> 00:30:03,935
And because stars
are denser there...
525
00:30:03,978 --> 00:30:07,435
the gas clouds that orbit through it
tend to get compressed.
526
00:30:07,478 --> 00:30:12,143
That compression allows gravity
to get a hold of that gas...
527
00:30:12,186 --> 00:30:14,392
and cause it to collapse
to form stars...
528
00:30:14,435 --> 00:30:16,433
more readily there
than anywhere else.
529
00:30:19,100 --> 00:30:21,599
Stars often die
in the spiral arms...
530
00:30:21,641 --> 00:30:24,099
because they are formed here
more frequently...
531
00:30:24,142 --> 00:30:26,973
victims of
their own enormous mass.
532
00:30:28,141 --> 00:30:30,806
The more massive stars
are extremely powerful...
533
00:30:30,849 --> 00:30:32,222
extremely luminous.
534
00:30:32,265 --> 00:30:33,432
And to be that luminous...
535
00:30:33,474 --> 00:30:37,930
they have to use up
their energy source very quickly.
536
00:30:37,973 --> 00:30:41,680
So massive stars
live only short lives...
537
00:30:41,723 --> 00:30:48,179
and they are thus found in or near
their birthplaces, the spiral arms...
538
00:30:48,221 --> 00:30:50,596
because they simply
don't have enough time...
539
00:30:50,638 --> 00:30:53,803
to wander away from the places
where they were born.
540
00:30:56,471 --> 00:30:59,428
Although we can anticipate
the future of some stars...
541
00:30:59,471 --> 00:31:01,927
it's often difficult
to learn their history.
542
00:31:02,887 --> 00:31:05,136
But new techniques
are revealing new secrets...
543
00:31:05,179 --> 00:31:09,593
about a well-studied star
in the Milky Way called Mira A.
544
00:31:10,470 --> 00:31:13,926
Mira has actually been a favorite star
of astronomers for 400 years.
545
00:31:13,969 --> 00:31:16,384
lt's a very easily visible star
in the night sky.
546
00:31:17,426 --> 00:31:22,049
Recently, the GALEX spacecraft,
the Galaxy Evolution Explorer...
547
00:31:22,092 --> 00:31:26,216
photographed Mira
in invisible ultraviolet light...
548
00:31:26,259 --> 00:31:32,132
and revealed that it's leaving a trail
thirteen light-years long behind it.
549
00:31:32,175 --> 00:31:33,715
We think that's actually
caused by the fact...
550
00:31:33,758 --> 00:31:36,506
that as the star plows
through the gas...
551
00:31:36,549 --> 00:31:38,756
the gas heats up
in a bow shock...
552
00:31:38,798 --> 00:31:41,672
very much like waves
breaking up against a boat.
553
00:31:41,715 --> 00:31:45,422
And then that streams out
into a wake of hot material.
554
00:31:45,465 --> 00:31:47,797
You're actually looking at Mira
acting very much like a boat...
555
00:31:47,840 --> 00:31:49,629
plowing through the water.
556
00:31:49,672 --> 00:31:51,671
When you look at howfast
Mira's going right now...
557
00:31:51,714 --> 00:31:54,087
about 291,000 miles an hour...
558
00:31:54,130 --> 00:31:55,546
and you do the calculations...
559
00:31:55,589 --> 00:31:59,170
that long tail is its path
the last 30,000 years.
560
00:31:59,212 --> 00:32:01,836
We can't predict exactly
where the Sun will go...
561
00:32:01,879 --> 00:32:03,336
in its orbit
around the Milky Way.
562
00:32:03,379 --> 00:32:05,753
There's all kinds of things
it could interact with.
563
00:32:05,795 --> 00:32:07,419
But here we have
the history of one star.
564
00:32:07,462 --> 00:32:09,753
We know this is the path it took.
565
00:32:09,795 --> 00:32:12,419
And that'll help us model
how the galaxyworks...
566
00:32:12,461 --> 00:32:14,960
and how all the stars move
around the middle of the galaxy.
567
00:32:17,294 --> 00:32:20,667
Within the Milky Way's
suburban spiral arms...
568
00:32:20,710 --> 00:32:23,833
young stars enjoy plenty
of space to move around.
569
00:32:24,793 --> 00:32:27,083
As we move
into the galactic bulge...
570
00:32:27,126 --> 00:32:30,416
conditions get much more
crowded and urban.
571
00:32:31,292 --> 00:32:32,750
The closest star to the Sun...
572
00:32:32,792 --> 00:32:35,124
is a little more
than four light-years away.
573
00:32:35,167 --> 00:32:37,123
And when we look up
into the night sky...
574
00:32:37,166 --> 00:32:40,498
even on a perfectly clear night
with no lights around...
575
00:32:40,541 --> 00:32:43,914
you can't see more than
about 2,000 or 3,000 stars.
576
00:32:45,874 --> 00:32:50,413
But if our planet was down
in the middle of the galaxy...
577
00:32:50,456 --> 00:32:53,830
there would be a million stars
in the night sky...
578
00:32:53,873 --> 00:32:57,413
as bright as the brightest star
that we've ever seen in our sky.
579
00:32:57,456 --> 00:32:59,996
And it would be so bright that, in fact,
it wouldn't be nighttime.
580
00:33:00,038 --> 00:33:01,829
lt would be daytime
all the time.
581
00:33:03,620 --> 00:33:06,995
Life, as we know it,
would be completely different.
582
00:33:07,037 --> 00:33:09,411
So what do we owe
our position to?
583
00:33:10,370 --> 00:33:14,161
Scientists believe that gravity
has a lot to do with it.
584
00:33:18,703 --> 00:33:22,951
Gravity is the power
that drives the galaxy...
585
00:33:22,994 --> 00:33:27,075
and at the galaxy's center,
churns the engine it feeds.
586
00:33:28,118 --> 00:33:32,742
Galaxies are like a city
in that they are ever-changing...
587
00:33:32,784 --> 00:33:36,116
and you're constantly being
rebuilt and reinvigorated.
588
00:33:37,908 --> 00:33:40,198
There's no question
that the Milky Way...
589
00:33:40,241 --> 00:33:41,282
a few billion years ago...
590
00:33:41,324 --> 00:33:43,656
looked a lot different
than it does today.
591
00:33:44,700 --> 00:33:46,740
lt probably was smaller.
592
00:33:46,782 --> 00:33:48,905
lt probably didn't have
the beautiful spiral shape...
593
00:33:48,948 --> 00:33:50,281
that we see today.
594
00:33:51,198 --> 00:33:55,197
As things collapse under gravity,
you tend to naturally form a disk.
595
00:33:55,240 --> 00:33:57,071
You'll notice
there are disks everywhere.
596
00:33:57,114 --> 00:34:00,280
Our solar system is a disk,
our galaxy is a disk.
597
00:34:00,322 --> 00:34:03,071
So the stars all start rotating
in the same direction.
598
00:34:06,447 --> 00:34:11,320
Just as in a city, not all of
the stars in the galaxy are natives.
599
00:34:11,363 --> 00:34:14,111
Some stars,
born beyond the Milky Way...
600
00:34:14,154 --> 00:34:17,527
settle here
and begin to make their mark.
601
00:34:18,153 --> 00:34:20,485
But then,
if another galaxy comes by...
602
00:34:20,528 --> 00:34:23,068
the gravity affects the way
the stars move...
603
00:34:23,111 --> 00:34:25,443
and this may initiate
the spiral arms.
604
00:34:26,360 --> 00:34:30,276
So, in fact, our spiral shape
may be some evidence...
605
00:34:30,318 --> 00:34:33,067
that the Milky Way is composed
of more than one small galaxy...
606
00:34:33,110 --> 00:34:35,483
that came together
a long time ago.
607
00:34:37,609 --> 00:34:39,774
Historically,
the center of the galaxy...
608
00:34:39,817 --> 00:34:42,607
has been
an impenetrable mystery...
609
00:34:42,650 --> 00:34:46,107
until we developed
X-ray vision.
610
00:34:46,941 --> 00:34:48,773
One of the first ways
we really identified...
611
00:34:48,816 --> 00:34:50,773
where the exact center
ofthe galaxywas...
612
00:34:50,816 --> 00:34:52,689
was with an X-ray telescope.
613
00:34:52,732 --> 00:34:54,897
Well, the X-rays were
able to pass through...
614
00:34:54,940 --> 00:34:57,897
all ofthe dust and gas
in the disk of our galaxy.
615
00:34:57,939 --> 00:35:01,896
And so, even though we can't really
see this bright center to the galaxy...
616
00:35:01,939 --> 00:35:05,063
in X-rays, there's this giant,
glowing hot source...
617
00:35:05,106 --> 00:35:06,730
right in the middle.
618
00:35:06,772 --> 00:35:09,855
The X-ray emitter,
Sagittarius A star...
619
00:35:09,896 --> 00:35:12,937
is associated with
the supermassive black hole...
620
00:35:12,980 --> 00:35:14,770
in the Milky Way's center.
621
00:35:16,104 --> 00:35:18,728
By definition, a black hole
doesn't allow light...
622
00:35:18,770 --> 00:35:21,394
or even X-rays to escape.
623
00:35:21,437 --> 00:35:24,935
The radiation comes from gas
caught in its gravity...
624
00:35:24,978 --> 00:35:28,601
spun and heated
to millions of degrees.
625
00:35:30,060 --> 00:35:33,518
They're moving
at extremely high velocities.
626
00:35:33,561 --> 00:35:37,642
For example, the more extreme cases
that we've been able to observe...
627
00:35:37,685 --> 00:35:41,517
the stars are moving
as they pass by the black hole...
628
00:35:41,560 --> 00:35:45,349
at a speed of10,000
kilometers per second.
629
00:35:46,517 --> 00:35:49,516
That's like going around
the world in four seconds.
630
00:35:50,808 --> 00:35:54,473
And we're talking about a whole star
moving at that speed.
631
00:35:55,765 --> 00:35:58,931
When we watch stars orbiting
the very center of our galaxy...
632
00:35:58,974 --> 00:36:01,722
it's obvious that there's
some sort of invisible monster there.
633
00:36:03,764 --> 00:36:05,930
They're orbiting
around a giant mass.
634
00:36:05,973 --> 00:36:08,222
And the orbits of the stars
imply that there's about...
635
00:36:08,265 --> 00:36:11,263
three to four million times
the mass ofthe Sun...
636
00:36:11,305 --> 00:36:13,388
in the very center of our galaxy.
637
00:36:13,431 --> 00:36:16,721
We're not sure which came first,
the galaxy or the black hole...
638
00:36:16,763 --> 00:36:20,178
but we know that it's there,
and it's tremendous.
639
00:36:21,929 --> 00:36:25,802
For all its power and weirdness,
the supermassive black hole...
640
00:36:25,845 --> 00:36:29,844
is pretty typical for a galaxy
the size of the Milky Way.
641
00:36:31,302 --> 00:36:34,510
Other spiral galaxies
and big elliptical galaxies...
642
00:36:34,553 --> 00:36:38,509
also seem to have supermassive
black holes in their middle...
643
00:36:38,552 --> 00:36:41,551
ranging from a million times
the mass of our Sun...
644
00:36:41,592 --> 00:36:44,925
up to several billion times
the mass of our Sun.
645
00:36:47,259 --> 00:36:50,550
The stars surrounding
the black hole are ancient.
646
00:36:50,592 --> 00:36:54,590
Many are red giants, hundreds
oftimes bigger than our Sun.
647
00:36:55,883 --> 00:36:58,549
The galactic center
is crowded with them...
648
00:36:58,591 --> 00:37:01,881
like an urban downtown
crowded with people.
649
00:37:02,757 --> 00:37:05,964
And stars, like people,
can be pushy.
650
00:37:06,923 --> 00:37:08,296
Most stars
in the galactic center...
651
00:37:08,339 --> 00:37:11,171
simplyjust keep orbiting
the central black hole.
652
00:37:11,214 --> 00:37:12,338
But in the galactic center...
653
00:37:12,381 --> 00:37:14,463
there are so many stars
packed so close together...
654
00:37:14,506 --> 00:37:16,879
that stars are constantly
nudging each other...
655
00:37:16,922 --> 00:37:18,295
a little bit gravitationally.
656
00:37:18,338 --> 00:37:21,129
And their orbits
are being perturbed...
657
00:37:21,171 --> 00:37:22,212
changed a little bit.
658
00:37:24,129 --> 00:37:27,211
A bumped star can get
stripped of its atmosphere...
659
00:37:27,254 --> 00:37:29,669
leaving just its orbiting core.
660
00:37:29,712 --> 00:37:34,252
Or, rarely, it can tumble
into the black hole and vanish.
661
00:37:36,211 --> 00:37:39,210
But something else is happening
around the black hole.
662
00:37:40,085 --> 00:37:42,209
This turbulent,
dangerous neighborhood...
663
00:37:42,252 --> 00:37:44,875
is also a stellar nursery.
664
00:37:46,085 --> 00:37:47,875
The stars that we're observing...
665
00:37:47,918 --> 00:37:49,917
moving fastest
around the black hole...
666
00:37:49,960 --> 00:37:54,291
are the young stars
that have very recently formed.
667
00:37:54,334 --> 00:37:57,125
And it's something we call
the paradox ofyouth...
668
00:37:57,167 --> 00:37:59,374
because it's hard to imagine
how to form...
669
00:37:59,417 --> 00:38:02,665
these massive young stars
in the presence of a black hole...
670
00:38:02,708 --> 00:38:03,997
and yet there they are.
671
00:38:06,249 --> 00:38:08,206
Recently,
astronomers discovered...
672
00:38:08,249 --> 00:38:11,372
that not all stars caught
in the black hole's grip...
673
00:38:11,415 --> 00:38:13,081
are doomed to stay there.
674
00:38:14,415 --> 00:38:18,579
A few manage to break away
and see the universe.
675
00:38:22,038 --> 00:38:23,371
Barreling through the universe...
676
00:38:23,414 --> 00:38:26,829
at one and a half million
miles per hour...
677
00:38:26,871 --> 00:38:30,828
hyper-velocity stars
are the escapees of the galaxy.
678
00:38:32,246 --> 00:38:34,577
And what's interesting
about high-velocity stars...
679
00:38:34,620 --> 00:38:37,036
is the only way to explain
their extreme velocities...
680
00:38:37,079 --> 00:38:39,868
is that they were ejected
by a supermassive black hole.
681
00:38:41,536 --> 00:38:43,035
For a star to go ballistic...
682
00:38:43,078 --> 00:38:46,867
takes a very specific
set of circumstances...
683
00:38:46,910 --> 00:38:49,534
and, in fact,
it requires two stars.
684
00:38:50,868 --> 00:38:52,826
Most ofthe stars
you see in the sky...
685
00:38:52,868 --> 00:38:57,700
are not single stars,
but pairs or binary stars.
686
00:39:00,409 --> 00:39:04,366
They orbit around each other,
linked by gravity's embrace.
687
00:39:05,241 --> 00:39:07,657
But a star pair
in the galactic center...
688
00:39:07,700 --> 00:39:10,365
might getjostled
by surrounding stars...
689
00:39:10,407 --> 00:39:12,906
and stray too close
to the black hole.
690
00:39:14,448 --> 00:39:15,698
When that happens...
691
00:39:15,739 --> 00:39:19,030
the moment that the gravitational
pull ofthe black hole...
692
00:39:19,073 --> 00:39:22,655
exceeds the gravity that's
binding the two stars together...
693
00:39:22,698 --> 00:39:25,488
the pair of stars is broken apart.
694
00:39:25,531 --> 00:39:28,279
One ofthe stars will be
captured by the black hole...
695
00:39:28,322 --> 00:39:30,904
usually into a very tight orbit
around the black hole...
696
00:39:30,947 --> 00:39:32,028
and the other star
will then gain...
697
00:39:32,071 --> 00:39:33,529
all the energy of that system
and it'll be ejected...
698
00:39:33,571 --> 00:39:35,237
with this incredible velocity.
699
00:39:36,362 --> 00:39:38,569
lf the galaxy were a city...
700
00:39:38,612 --> 00:39:42,194
where most of the stars
would be cars or pedestrians...
701
00:39:42,237 --> 00:39:45,360
a high-velocity star
would be more like an airplane...
702
00:39:45,403 --> 00:39:48,402
or a high-speed train
rushing out of the country.
703
00:39:49,902 --> 00:39:54,734
lfyou were on a high-velocity star,
the ride would be quite amazing.
704
00:39:54,777 --> 00:39:56,693
The sky would be covered
with stars...
705
00:39:56,735 --> 00:39:59,025
as bright as the full Moon
in every direction.
706
00:39:59,068 --> 00:40:00,692
But that view
would quickly change...
707
00:40:00,734 --> 00:40:03,358
'cause the high-velocity star
moves so quickly out of the galaxy...
708
00:40:03,401 --> 00:40:05,982
the stars would appear
fewer and fewer in the night sky.
709
00:40:07,775 --> 00:40:10,440
The galaxy is
constantly in motion...
710
00:40:10,483 --> 00:40:13,898
like a giant wheel
or a sprawling metropolis.
711
00:40:15,857 --> 00:40:17,189
ln the heart of town...
712
00:40:17,232 --> 00:40:20,356
the supermassive black hole's gravity
whips stars around...
713
00:40:20,399 --> 00:40:22,980
in an orbit
of around eleven minutes.
714
00:40:24,897 --> 00:40:28,938
Where the Earth sits, two-thirds
of the way out on a spiral arm...
715
00:40:28,980 --> 00:40:33,979
we traverse the Milky Way
once every 250 million years.
716
00:40:35,646 --> 00:40:37,770
Our solar system
has been around the block...
717
00:40:37,813 --> 00:40:40,936
only eighteen times
since it formed.
718
00:40:41,813 --> 00:40:44,769
The Milky Way's
incomprehensible size...
719
00:40:44,812 --> 00:40:48,477
makes it easy to forget
it'sjust one small part...
720
00:40:48,520 --> 00:40:50,519
of an expanding universe.
721
00:40:51,394 --> 00:40:53,143
When people hear
about the expanding universe...
722
00:40:53,186 --> 00:40:56,018
a common misconception is
that everything is expanding.
723
00:40:56,060 --> 00:40:58,643
And in fact,
l'm not expanding right now.
724
00:40:58,686 --> 00:41:00,351
My atoms are the same size.
725
00:41:00,394 --> 00:41:01,892
My cells are the same size.
726
00:41:02,893 --> 00:41:06,058
The Earth is not getting
farther away from the Sun.
727
00:41:06,101 --> 00:41:09,516
The expansion ofthe universe
only applies to celestial objects...
728
00:41:09,558 --> 00:41:11,557
that aren't bound together
by gravity.
729
00:41:12,891 --> 00:41:14,932
Since the planets
within the Milky Way...
730
00:41:14,974 --> 00:41:16,890
have stronger gravitational pulls...
731
00:41:16,933 --> 00:41:20,306
than the expanding forces
outside our galaxy...
732
00:41:20,349 --> 00:41:24,306
the expansion ofthe universe
doesn't affect our solar system.
733
00:41:26,098 --> 00:41:28,721
Our own Milky Way,
a spiral galaxy...
734
00:41:28,764 --> 00:41:32,055
is on a collision course
with another spiral galaxy...
735
00:41:32,098 --> 00:41:33,554
the largest spiral near us...
736
00:41:33,597 --> 00:41:35,471
and that is
the Andromeda galaxy.
737
00:41:35,514 --> 00:41:39,303
We think that in maybe three
orfour billion years...
738
00:41:39,346 --> 00:41:42,011
our two galaxies
may merge together.
739
00:41:42,054 --> 00:41:43,804
lt will be very interesting
to see what happens.
740
00:41:45,429 --> 00:41:48,428
What probably won't happen
is a collision of stars.
741
00:41:49,470 --> 00:41:53,052
Even though both galaxies
contain billions of stars...
742
00:41:53,095 --> 00:41:55,094
the space between them
is enormous.
743
00:41:57,219 --> 00:41:59,385
They will
gravitationally interact...
744
00:41:59,427 --> 00:42:02,176
changing
their direction and motion.
745
00:42:02,219 --> 00:42:05,634
Eventually, the merged spirals
will settle down...
746
00:42:05,677 --> 00:42:07,966
to become an elliptical galaxy.
747
00:42:09,051 --> 00:42:13,216
Essentially, all ofthe several
dozen galaxies in our local group...
748
00:42:13,258 --> 00:42:16,341
will be part of one supergalaxy.
749
00:42:17,384 --> 00:42:20,965
And then, gradually, that supergalaxy
will start losing stars...
750
00:42:21,008 --> 00:42:25,590
because of gravitational interactions
among the stars within that galaxy.
751
00:42:25,633 --> 00:42:29,880
Some will get flung away
into intergalactic space.
752
00:42:31,964 --> 00:42:36,630
When it first formed, the Milky Way
built stars at a rapid pace...
753
00:42:36,673 --> 00:42:41,129
using raw materials that were
ejected in space from the Big Bang.
754
00:42:41,172 --> 00:42:42,837
As the galaxy aged...
755
00:42:42,880 --> 00:42:46,420
the star production slowed down
from a few hundred a year...
756
00:42:46,463 --> 00:42:50,461
to about four to six new stars
each year today.
757
00:42:50,504 --> 00:42:53,252
Over time, the Milky Way galaxy
has changed dramatically...
758
00:42:53,295 --> 00:42:55,835
and we don't know exactly
what it looked like long ago.
759
00:42:55,878 --> 00:42:59,210
But probably early on,
there was a lot more gas and dust...
760
00:42:59,252 --> 00:43:00,585
and probably fewer stars.
761
00:43:00,628 --> 00:43:03,668
And you had a lot ofvery large,
very massive stars...
762
00:43:03,710 --> 00:43:05,126
that would've formed early on.
763
00:43:05,169 --> 00:43:09,209
And these early stars
exploded fantastically...
764
00:43:09,251 --> 00:43:12,833
and spat out new material,
heavier metals...
765
00:43:12,876 --> 00:43:16,291
that could be used to form
smaller second-generation...
766
00:43:16,334 --> 00:43:18,083
and then third-generation stars.
767
00:43:20,541 --> 00:43:24,874
Some younger galaxies are still
enjoying that kind of building boom.
768
00:43:26,750 --> 00:43:27,873
We can see some galaxies...
769
00:43:27,916 --> 00:43:30,997
where the rate of star
formation is very high...
770
00:43:31,040 --> 00:43:32,165
compared to our galaxy.
771
00:43:32,207 --> 00:43:34,665
Those are called
starburst galaxies.
772
00:43:34,707 --> 00:43:36,580
The rate of starformation
there can be anywhere...
773
00:43:36,623 --> 00:43:39,622
from ten to a hundred times
what it is now in our galaxy.
774
00:43:40,830 --> 00:43:45,163
With every generation,
star production slows down...
775
00:43:45,206 --> 00:43:49,037
and the Milky Way has been
in business for thirteen billion years.
776
00:43:49,954 --> 00:43:53,204
One of the reasons that the rate
of star formation in our galaxy...
777
00:43:53,246 --> 00:43:56,161
has changed over time,
going from a very high rate...
778
00:43:56,204 --> 00:43:58,662
to the current modest rate
of star formation...
779
00:43:58,704 --> 00:44:01,619
is because the gas
is being used up.
780
00:44:01,662 --> 00:44:04,243
Gas is used up to form stars.
781
00:44:04,286 --> 00:44:06,577
And we're running out of gas,
literally.
782
00:44:07,452 --> 00:44:13,284
Eventually, over trillions ofyears,
starformation will stop completely.
783
00:44:14,535 --> 00:44:18,200
The great galactic construction
project will shut down...
784
00:44:19,368 --> 00:44:25,158
and one by one,
the twinkling stars will fade away.
9999
00:00:0,500 --> 00:00:2,00
www.tvsubtitles.net
67384
Can't find what you're looking for?
Get subtitles in any language from opensubtitles.com, and translate them here.
Afrikaans
Akan
Albanian
Amharic
Arabic
Armenian
Azerbaijani
Basque
Belarusian
Bemba
Bengali
Bihari
Bosnian
Breton
Bulgarian
Cambodian
Catalan
Cebuano
Cherokee
Chichewa
Chinese (Simplified)
Chinese (Traditional)
Corsican
Croatian
Czech
Danish
Dutch
English
Esperanto
Estonian
Faroese
Finnish
Galician
Georgian
German
Greek
Guarani
Haitian Creole
Hausa
Hawaiian
Hebrew
Hmong
Hungarian
Icelandic
Indonesian
Irish
Italian
Japanese
Kazakh
Kinyarwanda
Kirundi
Kongo
Korean
Krio (Sierra Leone)
Kurdish
Kyrgyz
Laothian
Latin
Latvian
Lithuanian
Luganda
Luo
Luxembourgish
Macedonian
Malagasy
Malay
Maltese
Maori
Mauritian Creole
Moldavian
Mongolian
Myanmar (Burmese)
Montenegrin
Nepali
Norwegian
Pashto
Persian
Polish
Portuguese (Portugal)
Quechua
Romanian
Romansh
Russian
Samoan
Scots Gaelic
Serbian
Sesotho
Setswana
Seychellois Creole
Shona
Sindhi
Sinhalese
Slovak
Slovenian
Somali
Spanish
Swedish
Tajik
Thai
Tigrinya
Tonga
Turkish
Turkmen
Ukrainian
Uzbek
Vietnamese
Welsh
Wolof