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[Music throughout]

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Hi. My name is Judy Racusin.

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I'm the deputy project scientist
on the Fermi Gamma-ray Space Telescope.

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I'm here today to watch a video with you
of 14 years of observations

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collected by the Fermi Large Area
Telescope, or the LAT.

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This is the primary instrument
on the Fermi mission,

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and it surveys the entire sky
every few hours.

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This allows it to do a lot 
of really cool things.

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It can look at sources
that vary on timescales

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from a fraction of a second
to years on end.

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There are two different kinds of maps
that we're going to look at.

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One map is in galactic coordinates.

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That means that there's a thin band
across the middle of the image,

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and that's the Milky Way.

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You've probably seen images
of the Milky Way in the optical.

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The Milky Way in the gamma rays 
looks kind of similar,

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except we're looking at a number
of different types of objects.

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We'll also look at the gamma-ray sky
from another perspective,

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where we're looking up and down
out of the galaxy which gives us

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a much better view
of the extragalactic sky

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and all the sources way outside
our galaxy in the distant universe.

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In this map of the gamma ray sky,
where we have blue and red

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and yellow tones, what we're seeing
are actually intensity maps.

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Fermi isn't an imaging instrument
like you think of Hubble or Webb.

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What it is is it's actually a
photon-collecting instrument.

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It's a particle detector in space.

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And we make these maps
by adding up all of the photons we collect.

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In this case, these are over four days.

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The color scheme, blue, red, yellow.

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This is just a way for us to visualize it
because our eyes don't see gamma rays.

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Those circular sources that you see in
the galactic plane

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are actually individual objects.

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Most of those are pulsars.

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These are rapidly spinning, dense, stellar
remnants called neutron stars

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that are actually varying,
pulsing on timescales from hundreds

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of times per second to several seconds.

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We see sources above and below

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the galactic plane.
Those are largely blazars.

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What that is, is a supermassive black
hole, millions to billions of times

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the mass of our Sun,
the center of a galaxy that is active.

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That means that there's gas and stars
falling into it,

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and it produces jets of emission
And they're very chaotic systems.

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So they are turning on
and they're turning off.

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And that's actually the source
of a lot of the variability

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that we'll see throughout this movie.

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We have a team

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of dedicated scientists,
what we call the flare advocates.

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Their job is to look at data every day

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that comes from Fermi
and look for these flaring sources.

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It's not just so that we
know that they're there

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and that we catalog them,
but some sources are interesting enough

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that we want to tell our friends –
other space and ground-based telescopes –

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that they should go look at the same
place and collect multiwavelength data

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so we can better 
understand these outbursts.

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You might notice

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there are a few odd
discontinuities in these images.

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This is a result of holes in the data
that we didn't want to be distracting.

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So we patched those images
using frames before or after.

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If you look carefully, you see one source
that isn't like the others.

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It's actually moving.

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And sometimes it gets brighter or fainter.

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That's actually just the Sun.

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The Sun is an interesting source
in the gamma rays.

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It's not the brightest source in the sky
like it is in the optical,

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but it's prominent
in its quiescent state

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where we're just seeing cosmic rays
interacting with the solar atmosphere.

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We also see it
when there are solar flares.

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That bright flash right there

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was a spectacular solar flare.

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You may have noticed a lot of variations
in the sky over time.

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It’s not that the galaxy itself is getting 
brighter or fainter.

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It's that as Fermi surveys the sky,
it doesn't do it completely evenly.

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Over many years, we accumulate
a very nice, even exposure of the sky,

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but when we look at short timescales,
what we're seeing are variations

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in the survey, not actual
variations in the sky.

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But when you do see individual sources,
those are real variations –

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from our own solar system
out to the distant universe.

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The sky exposure pattern
seems to change a bit

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starting about 2018.

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This was due to a hardware issue where
one of our solar panels stopped rotating.

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It's still fully functional
and Fermi has enough power

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to operate both instruments
and the observatory.

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What it means, though,

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is that the way we observe the sky
and the timescales in which we survey

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have changed a bit.

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In our 14-year map there's 
over 7,000 total sources.

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Almost 4,000 of those
are these active galaxies, these blazars.

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There are several hundred pulsars
and in total something like

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2,000 of these sources are variable.

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This video

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showing the first 14 years of Fermi
observations is just the beginning.

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Fermi continues to observe
 the dynamic sky every day,

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and we hope it'll continue to do so
for many years into the future.

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Cumulative 14-Year Fermi Sky

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NASA