Expert: Jayendra Upadhye - 7/6/2005

Question
Dear Jayendra,
             Despite my efforts to understand the mysteries of black holes, I am still puzzled by several aspects of these phenomena.  I understand the theory behind their formation (as far as a lay person can understand it) but I do not know anything about their life span.  How much can it vary from one black hole to another?  What, if any, factors would affect a black hole's longevity?  
             If light itself does not escape the gravity of a black hole, what happens to it?  Since light is (energy?), is it simply assimilated into the energy matrix of the black hole?  If black holes cease to exist at some point, how would you describe the process of their disintegration?  Does current thinking in astrophysics assume the existence of black holes in places other than the centers of galaxies?  Finally, what of the matter that is consumed by a black hole?  Is it immediately converted to energy or is it possible that matter could exist in some form within the black hole?
Hope I am not asking for more than my share of information.  Thank you in advance for your efforts.

Answer
Hello Jim,
To answer your question, by rights, i should myself be "uptodate" on the topic, which i am currenly not.
But anyway..for all i know..
1 - Black holes have been predicted to degenerate by loosing energy via the "hawking radiation" route.
But that takes an immense amount of time, equalling the current life of the universe.
secondly it is largely conjectural in the sense, who is going to be around for that time span and say "hey i just saw that one go off!".
2 - A black hole by definitions is a singularity.
A dimensionless "point" entity! The "known" whereabouts of which is the volume centered on it, enclosed by the "event horizon". It is the sphere of radius under which the escape velocity equals or exceeds that of light.
Perforce, the event horizon volume is infinitely greater than the black hole itself. (as it is but a point!).
We are unable to know or predict anything that enters that horizon, as conditions inside are extreme and THAT is an understatement!
3 - No one "may" describe what happens to a black hole at the end of its life, as there is no observational evidence at all.
4 - Yes! There is one orbiting around a red giant star in cygnus. The pair is a bright source of x-rays emanating from an accretion disk centered on the black hole. Matter spiralling into the hole is undergoing extreme pulverisation due to lorentz contraction and other distortions and in the process is emitting x-rays. The hole is siphoning large quantities of gas from the outlying layers of the parent star.
Mind you astrophysics does not preclude the existence of lighter black holes orbiting heavier normal stars!
5 - All stars beyond 4.3 solar masses eventually (my figure may be a bit off) end up as black holes. Depending on their starting mass, heavier ones become holes earlier.
6 - No one has ever said anything about inner conditions! As it is a dimensionless entity. only time will exist for it, but time not associated with anything "dimensional" is utterly without meaning to the entity itself!

Hope that suffices.
Pls do rate the answer.
Jayen