WEBVTT FILE

1
00:00:01.568 --> 00:00:03.770
[Music throughout]

2
00:00:03.903 --> 00:00:06.106
Hi. My name is Judy Racusin.

3
00:00:06.106 --> 00:00:09.909
I'm the deputy project scientist
on the Fermi Gamma-ray Space Telescope.

4
00:00:10.010 --> 00:00:14.547
I'm here today to watch a video with you
of 14 years of observations

5
00:00:14.547 --> 00:00:18.218
collected by the Fermi Large Area
Telescope, or the LAT.

6
00:00:18.284 --> 00:00:20.854
This is the primary instrument
on the Fermi mission,

7
00:00:20.854 --> 00:00:24.024
and it surveys the entire sky
every few hours.

8
00:00:24.124 --> 00:00:26.659
This allows it to do a lot
of really cool things.

9
00:00:26.659 --> 00:00:29.362
It can look at sources
that vary on timescales

10
00:00:29.362 --> 00:00:32.298
from a fraction of a second
to years on end.

11
00:00:35.001 --> 00:00:37.504
There are two different kinds of maps
that we're going to look at.

12
00:00:37.504 --> 00:00:40.306
One map is in galactic coordinates.

13
00:00:40.306 --> 00:00:43.309
That means that there's a thin band
across the middle of the image,

14
00:00:43.309 --> 00:00:44.778
and that's the Milky Way.

15
00:00:44.778 --> 00:00:47.547
You've probably seen images
of the Milky Way in the optical.

16
00:00:51.951 --> 00:00:53.953
The Milky Way in the gamma rays
looks kind of similar,

17
00:00:53.953 --> 00:00:58.024
except we're looking at a number
of different types of objects.

18
00:00:58.124 --> 00:01:01.094
We'll also look at the gamma-ray sky
from another perspective,

19
00:01:01.094 --> 00:01:04.330
where we're looking up and down
out of the galaxy which gives us

20
00:01:04.330 --> 00:01:07.367
a much better view
of the extragalactic sky

21
00:01:07.534 --> 00:01:11.671
and all the sources way outside
our galaxy in the distant universe.

22
00:01:11.771 --> 00:01:15.442
In this map of the gamma ray sky,
where we have blue and red

23
00:01:15.442 --> 00:01:19.979
and yellow tones, what we're seeing
are actually intensity maps.

24
00:01:20.046 --> 00:01:23.917
Fermi isn't an imaging instrument
like you think of Hubble or Webb.

25
00:01:23.983 --> 00:01:26.586
What it is is it's actually a
photon-collecting instrument.

26
00:01:26.586 --> 00:01:28.721
It's a particle detector in space.

27
00:01:28.721 --> 00:01:32.725
And we make these maps
by adding up all of the photons we collect.

28
00:01:32.826 --> 00:01:36.563
In this case, these are over four days.

29
00:01:36.663 --> 00:01:38.998
The color scheme, blue, red, yellow.

30
00:01:38.998 --> 00:01:43.269
This is just a way for us to visualize it
because our eyes don't see gamma rays.

31
00:01:43.369 --> 00:01:46.005
Those circular sources that you see in
the galactic plane

32
00:01:46.005 --> 00:01:47.707
are actually individual objects.

33
00:01:47.707 --> 00:01:49.409
Most of those are pulsars.

34
00:01:49.409 --> 00:01:53.079
These are rapidly spinning, dense, stellar
remnants called neutron stars

35
00:01:53.279 --> 00:01:57.717
that are actually varying,
pulsing on timescales from hundreds

36
00:01:57.917 --> 00:02:01.421
of times per second to several seconds.

37
00:02:01.521 --> 00:02:03.823
We see sources above and below

38
00:02:03.823 --> 00:02:07.193
the galactic plane.
Those are largely blazars.

39
00:02:07.393 --> 00:02:11.798
What that is, is a supermassive black
hole, millions to billions of times

40
00:02:11.798 --> 00:02:15.468
the mass of our Sun,
the center of a galaxy that is active.

41
00:02:15.735 --> 00:02:19.606
That means that there's gas and stars
falling into it,

42
00:02:19.672 --> 00:02:24.611
and it produces jets of emission
And they're very chaotic systems.

43
00:02:24.711 --> 00:02:27.280
So they are turning on
and they're turning off.

44
00:02:27.280 --> 00:02:29.315
And that's actually the source
of a lot of the variability

45
00:02:29.315 --> 00:02:32.619
that we'll see throughout this movie.

46
00:02:32.719 --> 00:02:33.520
We have a team

47
00:02:33.520 --> 00:02:37.190
of dedicated scientists,
what we call the flare advocates.

48
00:02:37.290 --> 00:02:39.893
Their job is to look at data every day

49
00:02:39.893 --> 00:02:43.129
that comes from Fermi
and look for these flaring sources.

50
00:02:43.196 --> 00:02:45.131
It's not just so that we
know that they're there

51
00:02:45.131 --> 00:02:48.334
and that we catalog them,
but some sources are interesting enough

52
00:02:48.334 --> 00:02:51.571
that we want to tell our friends –
other space and ground-based telescopes –

53
00:02:51.571 --> 00:02:56.409
that they should go look at the same
place and collect multiwavelength data

54
00:02:56.609 --> 00:02:59.212
so we can better
understand these outbursts.

55
00:03:03.616 --> 00:03:04.584
You might notice

56
00:03:04.584 --> 00:03:07.587
there are a few odd
discontinuities in these images.

57
00:03:07.720 --> 00:03:11.090
This is a result of holes in the data
that we didn't want to be distracting.

58
00:03:11.291 --> 00:03:15.128
So we patched those images
using frames before or after.

59
00:03:18.231 --> 00:03:21.534
If you look carefully, you see one source
that isn't like the others.

60
00:03:21.601 --> 00:03:23.069
It's actually moving.

61
00:03:23.069 --> 00:03:25.138
And sometimes it gets brighter or fainter.

62
00:03:25.138 --> 00:03:26.940
That's actually just the Sun.

63
00:03:26.940 --> 00:03:29.075
The Sun is an interesting source
in the gamma rays.

64
00:03:29.075 --> 00:03:32.045
It's not the brightest source in the sky
like it is in the optical,

65
00:03:32.145 --> 00:03:35.248
but it's prominent
in its quiescent state

66
00:03:35.415 --> 00:03:39.118
where we're just seeing cosmic rays
interacting with the solar atmosphere.

67
00:03:39.319 --> 00:03:41.888
We also see it
when there are solar flares.

68
00:03:45.959 --> 00:03:47.293
That bright flash right there

69
00:03:47.293 --> 00:03:49.596
was a spectacular solar flare.

70
00:03:59.005 --> 00:04:02.742
You may have noticed a lot of variations
in the sky over time.

71
00:04:02.942 --> 00:04:06.412
It’s not that the galaxy itself is getting
brighter or fainter.

72
00:04:06.412 --> 00:04:11.017
It's that as Fermi surveys the sky,
it doesn't do it completely evenly.

73
00:04:11.084 --> 00:04:14.954
Over many years, we accumulate
a very nice, even exposure of the sky,

74
00:04:15.054 --> 00:04:18.258
but when we look at short timescales,
what we're seeing are variations

75
00:04:18.258 --> 00:04:21.394
in the survey, not actual
variations in the sky.

76
00:04:21.427 --> 00:04:25.231
But when you do see individual sources,
those are real variations –

77
00:04:25.431 --> 00:04:28.468
from our own solar system
out to the distant universe.

78
00:04:37.410 --> 00:04:39.912
The sky exposure pattern
seems to change a bit

79
00:04:39.912 --> 00:04:41.881
starting about 2018.

80
00:04:41.881 --> 00:04:46.319
This was due to a hardware issue where
one of our solar panels stopped rotating.

81
00:04:46.452 --> 00:04:48.955
It's still fully functional
and Fermi has enough power

82
00:04:48.955 --> 00:04:51.958
to operate both instruments
and the observatory.

83
00:04:52.091 --> 00:04:52.859
What it means, though,

84
00:04:52.859 --> 00:04:56.996
is that the way we observe the sky
and the timescales in which we survey

85
00:04:57.096 --> 00:04:58.264
have changed a bit.

86
00:05:08.341 --> 00:05:13.313
In our 14-year map there's
over 7,000 total sources.

87
00:05:13.413 --> 00:05:18.151
Almost 4,000 of those
are these active galaxies, these blazars.

88
00:05:18.217 --> 00:05:22.522
There are several hundred pulsars
and in total something like

89
00:05:22.622 --> 00:05:25.525
2.000 of these sources are variable.

90
00:05:33.299 --> 00:05:34.100
This video

91
00:05:34.100 --> 00:05:38.371
showing the first 14 years of Fermi
observations is just the beginning.

92
00:05:38.471 --> 00:05:41.507
Fermi continues to observe
the dynamic sky every day,

93
00:05:41.507 --> 00:05:44.344
and we hope it'll continue to do so
for many years into the future.

94
00:05:57.924 --> 00:06:09.335
Cumulative 14-Year Fermi Sky

95
00:06:09.902 --> 00:06:14.941
NASA