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).