NASA | NASA's Fermi Shows How Active Galaxies Can Be

Uploaded by NASAexplorer on 08.09.2011

Hi, I'm Elizabeth Hayes, a scientist working on NASA's
Fermi Gamma-ray Space Telescope. Every 3 hours, the
Large Area Telescope onboard Fermi builds up a picture of the sky in gamma-rays,
the most energetic form of light. One thing it sees a lot of is
blazars, active galaxies whose emissions are powered by supermassive black
holes. Blazars are extremely active objects.
Here's one of the most extreme Fermi has seen. It's been known to flare up so brightly
that, for a few days, it outshines every other gamma-ray source.
Considering that it's more than 7 billion light-years away, this is an immense
energy output. At the core of an active galaxy is a supermassive
black hole that powers jets of particles moving near the speed of light.
We call it a blazar when one of the jets is pointed in our direction.
This offers us the best view for seeing dramatic flares when there are changes along
the jet. Fermi has found about a thousand gamma-ray blazars so far.
Every day, the gamma-ray sky changes depending on which galaxies are
in outburst and which are in a quiet phase. Because we're watching them all the time,
we can track their activity and alert other telescopes to new flare-ups.
As Fermi continues to watch the sky, it builds a more complete picture of the
daily lives of these powerful objects. Some of the flares we
see announce the presence of blazars we've never seen before. And sometimes
we find a gamma-ray flare that is not from a blazar, which is very exciting.
We hope to discover new types of gamma-ray-emitting objects that we don't yet know
about. Right now, nearly one third of Fermi sources cannot be connected
to any known type of gamma-ray source. Out there in the dark,
what new discoveries await us?
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