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|Re: Smallest Event Horison Possible
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Posted by David Tate/">David Tate on January 31, 1998 03:20:05 UTC
: : : :How small can a singularity be? How small is the smallest mass? What is "one" quanta of mass? Damned if I know, but it can't be all that difficult to find out. Ask those blokes at the birthplace of the web. : : : : :
: : : : Well that is not the same thing, you need Enough mass to generate gravity strongenough to hold light to have an event horizon...
: : : :No you don't. Mass has nothing to do with it. ANY mass that becomes a singularity has no dimension. Since it has mass but no dimension then it figures that its gravitational pull is at some point from the centre of the singularity strong enough to form a black hole. Albeit very very tiny indeed. The real question I suppose is how small a mass can a singularity be. Or to be precise, a fragment of a singularity, since a small one could not form all by itself. Either in the context of how small an object can form a singularity or how small can it be before the ordinary laws of physics of a larger body be compromised.Is it possible to have a really really small singularity. Particle sized fragments? If it is possible, then it goes without saying that that singularity will have a really really small event horizon - but it will have one.
: : The event horison has everything to do with the gravitional pull, unless I misunderstand what an event horison is.
: : The event horison is the point at which, as you travel towards the singularity, you must exceed the speed of light to escape its gravitational attraction. The reason you have to exceed the speed of light is to escape the gravatitional pull. If there is little mass, there is no, or little gravitational pull and thus you can easily escape it. and if the gravitational pull can not contain light (such as the gravitational pull of the earth) then there is no event horison. Even if you compressed teh earth into a singularity, you would not have an event horison around it. : :
: There are 2 ways in which a singularity with less : than 1.4 solar masses can form:
: the first is by compression, which may have : occurred under the conditions of the big bang
: the second is by radiating energy. You see, black : holes radiate energy and lose mass in the process. : The smaller they are, the faster they radiate. If : they are not fed new matter, over time any black : hole will shrink below the 1.4 solar mass limit. : This is an extremely long process for larger : black holes (something like 10^67 years), but : smaller black holes radiate more and have : lifespans comparable to the age of the universe.
: However,it would seem that if a singularity of : "small" mass is formed, it is cut off from the rest of the : universe by an event horizon that has some non-zero : dimension, and will not decompress into "normal" : matter. At least that's the theory.
I think the Hawkings radiation theory you mention predicts that as a black hole radiates energy, and thus reduces its size, an thus looses the mass necessiary to maintain the strength of gravitational pull needed to maintain the black hole, and thus has the fate of exploding.
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