1
00:00:00,000 --> 00:00:03,427
"Hubble Science"

2
00:00:03,427 --> 00:00:07,298
"Galaxy Mergers, Past and Present"

3
00:00:07,298 --> 00:00:11,511
One of the surprises that the Hubble Space
Telescope has given us over

4
00:00:11,511 --> 00:00:17,392
its decades of observation
is that galaxies have not always

5
00:00:17,392 --> 00:00:21,000
simply existed as independent entities,

6
00:00:21,021 --> 00:00:25,233
one from another, forming separately
and remaining separate, that in fact

7
00:00:25,233 --> 00:00:31,156
galaxies typically merge
with other galaxies during cosmic history.

8
00:00:31,156 --> 00:00:35,326
Now, this is a little counterintuitive
because we know the universe is expanding,

9
00:00:35,326 --> 00:00:37,120
so we would expect that galaxies

10
00:00:37,120 --> 00:00:40,123
are moving apart from each other,
which they generally are.

11
00:00:40,123 --> 00:00:43,543
But what we know
is that when galaxies are close enough

12
00:00:43,543 --> 00:00:47,547
to each other, their mutual gravitational
pull can dominate

13
00:00:47,547 --> 00:00:52,343
and draw these galaxies together as one.
We call that a merger.

14
00:00:52,343 --> 00:00:57,098
And Hubble revealed for the first time
in such detail

15
00:00:57,098 --> 00:01:01,728
many of these cases where galaxies,
particularly in the distant universe,

16
00:01:01,728 --> 00:01:05,940
were in the process of merging
with a neighbor galaxy.

17
00:01:05,940 --> 00:01:08,735
These dramatic mergers are not unusual.

18
00:01:08,735 --> 00:01:13,323
In fact, we believe now, thanks to Hubble
and subsequent observations

19
00:01:13,323 --> 00:01:17,202
that all galaxies
typically go through at least one merger

20
00:01:17,202 --> 00:01:20,497
in the process
to becoming what they are today.

21
00:01:26,002 --> 00:01:26,711
So here's some

22
00:01:26,711 --> 00:01:30,507
examples of what Hubble
has seen in terms of galaxies

23
00:01:30,507 --> 00:01:35,345
in the process of merging
or in the aftermath of merging.

24
00:01:35,345 --> 00:01:40,100
So here you can see some examples
of distorted shapes of galaxies.

25
00:01:40,100 --> 00:01:44,062
You can see here and here
none of these look like your typical

26
00:01:44,062 --> 00:01:49,567
beautiful spiral
or even spherical or elliptical shape.

27
00:01:49,567 --> 00:01:54,280
They all have some irregularities to them,
which are telltale signs

28
00:01:54,280 --> 00:01:58,409
that they are either currently merging
with another galaxy or are right

29
00:01:58,409 --> 00:02:02,122
in the aftermath of merging
with another galaxy.

30
00:02:02,122 --> 00:02:04,874
One of those telltale signs are long tails.

31
00:02:04,874 --> 00:02:08,002
So in some of these
you see these interesting long

32
00:02:08,002 --> 00:02:12,048
tail structures
coming out from the galaxy itself.

33
00:02:12,048 --> 00:02:17,345
That's often an aftereffect
or an impact of galaxies gravitationally

34
00:02:17,345 --> 00:02:21,850
interacting with each other
and creating these long tail structures.

35
00:02:21,850 --> 00:02:26,229
Another telltale sign is that you can
sometimes see two nuclei

36
00:02:26,229 --> 00:02:29,566
visible in the cores
of some of these structures.

37
00:02:29,566 --> 00:02:33,486
That means that there’s still two bright
cores of the originally separate

38
00:02:33,486 --> 00:02:37,448
galaxies that haven't quite completed
merging together.

39
00:02:37,448 --> 00:02:42,579
An irregular structure, as all of these
have, is always a sign that something

40
00:02:42,579 --> 00:02:47,167
has disrupted the original more symmetric
structure of these galaxies.

41
00:02:47,167 --> 00:02:50,670
And it's typically the interaction
with a neighboring galaxy during

42
00:02:50,670 --> 00:02:52,297
the process of merging,

43
00:02:52,297 --> 00:02:55,300
"Galaxy Merger Simulations"

44
00:02:55,300 --> 00:02:57,343
Mergers can take millions of years.

45
00:02:57,343 --> 00:03:00,513
So these are not quick processes
and in fact,

46
00:03:00,513 --> 00:03:04,434
sometimes they are very interesting
little dances where the galaxies

47
00:03:04,434 --> 00:03:07,812
can come close to each other
and then begin to rotate around one

48
00:03:07,812 --> 00:03:12,275
another before they eventually merge,
or they can actually pass through one

49
00:03:12,275 --> 00:03:17,447
another and then be pulled back again
and again before they eventually merge.

50
00:03:17,447 --> 00:03:19,699
So this can take a long time.

51
00:03:25,580 --> 00:03:26,706
So we now know that

52
00:03:26,706 --> 00:03:29,751
most galaxies have gone through mergers

53
00:03:29,751 --> 00:03:33,755
and some galaxies are still on the path
toward a future merger.

54
00:03:33,755 --> 00:03:38,343
We know that our own Milky Way
has a whole little swarm of dwarf galaxies

55
00:03:38,343 --> 00:03:42,305
orbiting around that will eventually
be swallowed into the Milky Way.

56
00:03:42,305 --> 00:03:47,018
But we have a more traditional merger
in line with the Andromeda

57
00:03:47,018 --> 00:03:50,438
Galaxy, our nearest neighbor,
a big spiral galaxy.

58
00:03:50,438 --> 00:03:54,025
It's on a head on collision course
with the Milky Way.

59
00:03:54,025 --> 00:03:55,944
Hubble has ascertained

60
00:03:55,944 --> 00:03:59,197
that this is going to happen
probably in a few billion years.

61
00:03:59,197 --> 00:04:01,282
So we don't need to think about it
too soon.

62
00:04:01,282 --> 00:04:04,577
But it is interesting
that our universe is not finished.

63
00:04:04,577 --> 00:04:09,249
We're still in the dynamics of forming
and growing galaxies, even today.

64
00:04:09,249 --> 00:04:17,840
"Follow us on social media @NASAHubble"