On Sun, 12 May 2002, Glen  wrote:

> Anybody,
> 	I don't know if this address is directed to the person(s) who can
> answer my question but I suppose I'll give it a shot anyway.
> I have grasp the fundamental idea of blackholes. I understand that the force
> of gravity is so strong that nothing can escape. but one thing confuses me.
> When matter is sucked in and compressed it emits high amounts of x-ray/gamma
> energy how is it possible for that to escape?  Is it because the x-ray is a
> wave not a particle, therefor it has nothing to "grab a hold of" ?   All of
> that sqeezing and pulling on matter has to generate heat can that heat
> escape?

It is true, Glen, that a black hole can pull
in objects and never let them escape.  But, that "point
of no return" occurs only at a certain distance from the
black hole.  We call this distance the "event horizon".
Now, you are right on: when matter is sucked in, it gets
hot and radiates.  This is actually how scientists can detect
black holes.  Both light (x-rays) and matter are affected by
this.  At a certain point, neither photons nor particles
could escape.

So, how do we see the x-rays?

Well, the matter starts getting hot and radiating
*before* it reaches the event horizon.  Even farther away, the
stuff getting sucked in emits x-rays.  The x-rays escape,
and the matter getting trapped *could* escape if you gave
it a push.  It is just falling, however, so even though it
could possibly escape, it does not since it is receiving no
propulsion in the opposite direction.  The photons escape
because they are "born with" natural propulsion which makes
them travel at the same speed always.

But, at the event horizon, both the matter and photons get
trapped.  By then, though, the falling mass has emitted
a large amount of radiation.

Hope this helps,
Scott Funkhouser
UCBerkeley