Supermassive black holes

Hello all, I recently watched a show on Discovery about supermassive
black holes. Black holes have always fascinated me and this show what
also very interesting. I have a question though. Black holes
supposedly have such a strong gravitational pull that nothing can
escape them, not even light, so why is it that there are streams of
energy that emanate from the black hole. How can this energy escape
the gravitational pull of the black hole? Please understand that I am
not a physicist or an astronomer, this is just a passing interest, but
I am puzzled by this. Can someone explain to me how and why this
happens.

Thank you,
David

"David" wrote in message
om...
Hello all, I recently watched a show on Discovery about supermassive
black holes. Black holes have always fascinated me and this show what
also very interesting. I have a question though. Black holes
supposedly have such a strong gravitational pull that nothing can
escape them, not even light, so why is it that there are streams of
energy that emanate from the black hole. How can this energy escape
the gravitational pull of the black hole? Please understand that I am
not a physicist or an astronomer, this is just a passing interest, but
I am puzzled by this. Can someone explain to me how and why this
happens.

Nothing can escape from the black hole once it passes the "event horizon,"
but up to that point it's possible. X-rays can be emitted as gas is drawn
into the black hole and becomes superheated. Also, a small percentage of
supermassive black holes emit "jets" of material, shooting out in opposite
directions from the black hole. There are various theories about why this
happens but AFAIK it really isn't well understood.

(David) writes:

Hello all, I recently watched a show on Discovery about supermassive
black holes. Black holes have always fascinated me and this show what
also very interesting. I have a question though. Black holes
supposedly have such a strong gravitational pull that nothing can
escape them, not even light, so why is it that there are streams of
energy that emanate from the black hole. How can this energy escape
the gravitational pull of the black hole?

These so-called "jets," composed mostly of relativistic electrons
and positrons, do _not_ "emanate" from the black hole's interior ---
they are produced by the "accretion disk" of incredibly hot gas
spiraling into the hole. Several plausible mechanisms for generating
and accelerating these relativistic jets have been proposed, the two
front-runners being electrodynamic acceleration by electromagnetic fields
generated via "dynamo" action in the differentially rotating accretion
disk, and radiation-pressure acceleration by the intense X-ray and
gamma-ray radiation emitted by the incredibly hot accretion disk.

Other possible acceleration mechanisms exploit the so-called "frame-dragging"
effect (AKA the "gravitomagnetic field," a gravitational analog of magnetism)
within the "ergosphere" region just outside a rapidly rotating black hole,
which can under certain circumstances "slingshot" a fraction of the particles
spiraling into the rotating black hole up to a substantial percentage of
lightspeed.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

In article ,
(David) wrote:

Hello all, I recently watched a show on Discovery about supermassive
black holes. Black holes have always fascinated me and this show what
also very interesting. I have a question though. Black holes
supposedly have such a strong gravitational pull that nothing can
escape them, not even light

Right. But that's true only if you're sufficiently close to the black
hole. (The boundary at which not even light can escape is called the
event horizon.)

so why is it that there are streams of
energy that emanate from the black hole.

Mostly it's from the stuff that's swirling into the black hole; it's
being greatly accelerated and heated and in the process, it gives off
X-rays and other forms of radiation.

How can this energy escape the gravitational pull of the black hole?

It wasn't in the black hole to begin with. It's being emitted by stuff
outside the event horizon.

There is another form of radiation, known as Hawking radiation, that
causes the black hole to lose energy from within and eventually causes
small black holes to evaporate. But I don't think that's what you were
asking about.

HTH,
- Joe

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