[Music throughout] Announcer: Liftoff of the Delta rocket carrying a gamma-ray
telescope searching for unseen...[Fades out] Narrator: I'm Julie Mcenery, Fermi
Project Scientist. Since its launch in 2008, 
the Fermi Gamma-ray Space Telescope has revolutionized our understanding of
powerful events and objects in the cosmos. Fermi observes the universe using
gamma rays, the highest-energy form of light, more energetic than even X-rays.
Gamma rays are emitted by objects with extreme gravity and magnetic fields.
Many of the gamma rays Fermi sees are produced by black holes,
and incredibly dense, rapidly spinning stars called pulsars.
Fermi's predecessor, the Compton Gamma Ray Observatory, collected data
from 1991 to 2000, which was used to create this all-sky map.
Over the past decade, Fermi has
refined our view and fundamentally changed our understanding of the cosmos.
In celebration of its 10th anniversary, here are just a few
of its transformative discoveries. In its very first
year of observations, Fermi spotted a short, powerful gamma-ray burst
called GRB 090510. This burst
provided proof that space-time works the way Einstein predicted.
Gamma-ray bursts are the most luminous events Fermi sees.
Scientists think they are caused when stars collapse, or when neutron stars or black holes
merge. These events drive jets of particles at nearly the speed of light.
The material in the jets collides, generating shock waves that produce the 
gamma rays that we see. In the last decade, Fermi has detected over
2,300 bursts. Fermi detected two gamma rays
with different energies from GRB 090510. Although
they traveled over 7 billion light-years, both reached Fermi at nearly the same
instant. This supports Einstein's theory that all light
no matter its energy, moves at the same speed because space-time is smooth.
In 2017, Fermi spotted a gamma-ray burst
coming from the constellation Hydra, which coincided with the detection 
of ripples in space-time. The burst came from the merger of
two superdense neutron stars. Ground-based observatories
detected gravitational waves at nearly the same instant Fermi detected gamma rays.
This was the first time light and gravitational waves were detected 
from the same source. Early in Fermi's mission,
scientists noticed odd structures emerging from above and below the 
Milky Way. These Fermi "bubbles" have become more prominent with each passing year
of data. The bubbles extend 25,000 light-years
above and below the galactic plane. They were probably produced only
a few million years ago by the supermassive black hole at the center of the Milky Way.
This means our galaxy was extremely active a very
short time ago, in astronomical terms.
Over the last 10 years, Fermi has also placed new limits on
theories about dark matter by looking at tiny, faint galaxies called dwarf spheroidals.
Almost 85 percent of the universe's matter is dark matter,
but scientists don't know exactly what dark matter is.
One theory is that it's made of Weakly Interacting Massive Particles,
or WIMPs. WIMPs don't produce light, or interact with
other particles. When two WIMPs meet, though, scientists think
they annihilate and produce gamma rays with unique signatures.
Dwarf spheroidals have high concentrations of dark matter.
Fermi has observed several of these galaxies, but seen no sign of
WIMP-produced gamma rays. This sets strong limits on the properties
of dark matter. The universe is a sea of
charged particles called cosmic rays, moving at nearly the speed of light.
Fermi observations of two supernova remnants shed new light on their origins.
Thousands of cosmic rays hit every square meter of Earth's atmosphere
every second. And Fermi's Large Area Telescope
detects only one gamma ray for every thousand cosmic rays. Despite their
abundance, the origins of cosmic rays were a longstanding mystery.
In 1949, Enrico Fermi, the satellite's
namesake, proposed that they might be generated in the shock waves of supernovas.
But cosmic ray paths are hard to trace. They veer off course each time
they encounter a magnetic field. In 2013,
Fermi observed gamma rays coming from two supernova remnants.
The gamma rays' properties told scientists they were created by cosmic rays propelled by
supernova shock waves, just as Enrico Fermi predicted.
While the atmosphere is pelted by cosmic rays from above, thunderstorms
generate gamma rays from below. Fermi observes these
terrestrial gamma-ray flashes, or TGFs, using its Gamma-ray Burst Monitor.
Under the right conditions, a lightning flash triggers a flood
of electrons that rush to the top of the cloud at nearly the speed of light.
These electrons produce gamma rays when they run into air molecules.
Fermi has spotted 5,000 TGFs over
10 years, but scientists estimate more than a thousand of them occur every day.
From Earth's atmosphere, to the farthest reaches
of the cosmos, Fermi's first ten years have fundamentally altered how
we look at the universe. The gamma-ray sky changes every day,
who knows what new, exciting await us
in the future?
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