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The Question
(Submitted June 08, 1998)
I have absolutely no experience in astrophysics but a friend of mine
did a a thesis on AGN. She could not explain it to me because she is
Polish and I am an American. so my question comes in two parts. What
is AGN exactly? What implications does it have for understanding how
the universe works?
The Answer
An AGN is short for "Active Galactic Nucleus."
Some galaxies have nuclei (centers) that are 'active', meaning they emit
large amounts of radiation (radio, optical, X-rays, gamma-rays, particle
jets, etc.), and/or are highly variable. (For example, a galactic nucleus
starting at 30 billion times as bright as the Sun, then growing to 45
billion times as bright as the Sun in just half an hour).
Since they vary so rapidly, the important region must be small, no larger
than the inner solar system (since the time over which something can vary
is limited to the time it takes light to get from one side to the other).
Since they are so bright, that small region must have unbelievable energies
in it.
Gigantic black holes, billions of times as massive as the Sun, swallowing
stars and gas clouds, are the only reasonable theories that seem to fit the
data.
Do a search on our website for 'active' to find more information
David Palmer
for Ask a High-Energy Astronomer
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