If nothing can escape a black hole, why do they still emit x-rays?
It is true that once matter or energy passes within the so-called Event
Horizon of a black hole, that it can never turn around and get back
out. However, in the real world, a lot can happen to matter as it approaches
the Event Horizon. Commonly, matter falls into what is called an
accretion disk which orbits the black hole. Material orbits the black hole
within this disk, but if it happens to be gas and dust, this matter
experiences friction and the disk heats up as some of the orbital
energy of the gas is converted into heat. The closer the disk material is
to the black hole, the more rapidly it orbits so that the greater is the
heating effect. Just before it reaches the Event Horizon, this disk matter can
be heated by friction to thousands of degrees which is enough to produce
X-rays. Even higher temperatures approaching a million degrees can occur
which can produce gamma rays.
This disk radiation, being outside the black hole, is what we detect as we
look at black holes.
Copyright 1997 Dr. Sten Odenwald
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