From: Zardoz ®	04/11/2001 19:34:14
Subject: re: COSMOLOGY FAQ	post id: 484062
What is the critical mass of a black hole? And what happens when it is full, a big bang? Will it turn back into a sun? From: B.C. ® For a star to collapse to a black hole it must be at least three times the mass of the sun. A black hole does not become "full" and bang. It just gets bigger and bigger as long as it has mass to feed on. From: Greg L ®. There is no 'upper mass limit' on black holes. Indeed, astronomers think that black hole's of up to several billions of solar masses may reside in the hearts of some Quasars and active galaxies. On your other question, there is no way a black hole can revert back into a Sun-the object that made the black hole is effectively disconnected forever causally from the universe. The only way a black hole can decrease in size or lose mass is by 'Hawking Radiation', but this process is so slow we can effectively think of black hole's as having the same mass and 'surface area' that can only stay the same or increase in size. Why doesn't the BLACK HOLE at the centre of the galaxy swallow our galaxy? From: B.C. ® . The super-massive black hole at the centre of our galaxy and probably at the centre of most large galaxies would have already swept out an area void of any astronomical objects. They, in fact are virtually dormant black holes, only feeding on stray comets or such. Any active black holes that are residing, will probably suck in near by matter until they in turn have swept out an area void of matter.