[net.space] black holes

rrm (11/15/82)

Why don't we get into a discussion on black holes. I am interested in this
topic, but I must admit I have very little knowledge of the subject. I
believe a quite interesting and entertaining discussion could be carried
on over this net. Also, I have a specific question for anyone on the net 
who may be knowledgeable about black hole theories. I have seen reference
on the "horizon" of a black hole. What is this exactly and how (if it is
related) does this effect the Schwartzchild radius????? If anyone replies
to this, please post it on the net instead of sending me mail. Then the
rest of the world can benefit from the theory.

					Ron Meyer
					inuxa!rrm
					Bell labs - Indy

kek (11/16/82)

In response to inuxa!rrm (Ron Meyer) question on black holes:

The German astronomer Karl Schwarzschild determined the field equations
describing space-time in the vicinity of a spherical lump of matter. His
solution states that if the mass is compressed within a certain radius
(called the Schwarzschild radius) space-time is so severely distorted
that nothing, even light, is able to escape.  To put it another way,
the "local gravity" cannot be overcome.  The Schwarzschild radius (R)
for a body of mass M is:

              R = 2GM/c**2

where G is a constant of proportionality known as the universal
gravitational constant, and c is the velocity of light. Thus the
Schwarzschild equations define how compressed a body would have to
become to create a black hole. (Actually, Michell and Laplace hinted
at such a possibility nearly a century before Schwarzschild put it
all together).

A body thus compressed (e.g., a collapsing star) disappears from view
since light is unable to escape from its surface (it has become a
black hole).  The boundary of the black hole is called the "event
horizon" because nothing inside can ever pass to the outside. The
event horizon is a one-way boundary: you can check in but never out!
This boundary coincides with the Schwarzschild radius. Even if the mass
inside continues to collapse into a "singularity", the event horizon
remains the same, the Schwarzschild radius. This holds true for
simple non-rotating black holes. Rotation adds some complexity.

As a couple examples, the Schwarzschild radius for our sun is just
under 3 kilometers (it's nominal radius is about 700,000 km) and
for the Earth is a little less than one centimeter!

Three good references on the subject that I have read are:

     GRAVITY, BLACK HOLES AND THE UNIVERSE
     Iain Nicolson
     John Wiley & Sons - New York 1981

     MONSTERS IN THE SKY
     Paolo Maffei
     The MIT Press - Cambridge, Mass and London, Eng (1980)

     BLACK HOLES - THE EDGE OF SPACE, THE END OF TIME
     Walter Sullivan
     Anchor Press / Doubleday - Garden City, NY (1979)


                                         Ken Kepple
                                         Bellabs - Holmdel
                                         5941ux!kek

mcdaniel (11/17/82)

#R:inuxa:-16900:uiucdcs:12700022:000:160
uiucdcs!mcdaniel    Nov 16 19:36:00 1982

I've heard that an outside observer can determine the mass and charge 
(among other things) of a black hole.
How do the gravitrons and virtual photons get out?

REM@MIT-MC@sri-unix (11/18/82)

From: Robert Elton Maas <REM at MIT-MC>
It seems to me that there have been so many fine articles in recent
years in Scientific American and other popular journals about black
holes that there's no need to duplicate that information here.  From
recent messages I'm beginning to think most of you people on USENET
never read any scientific magazines (black holes) or watch the evening
news on TV or even read this digest (when first non-Columbia STS will
be).