What happens if one black hole collides with another?

[niky]

I think that rather depends on the mass of the black hole. Black holes evaporate due to energy loss but I don't see a supermassive black hole evaporating as it swallows more energy then it loses...


As I've read...

Even supermassive blackholes will evaporate over time. It just takes a lot longer for it to happen than anybody can even begin to understand except as a really, really big and ludicrously large number. A time scale that makes the current age of the universe seem insignificant, in fact.

While I can't pretend to know why they evaporate, it apparently has to do with heat. Black holes, through some bizarre quantum interaction, radiate heat back into the universe... a neat solution to the apparent violation of thermodynamic law that perpetual black holes would represent.

There's also something about the weakening of gravity over time, but that's even more arcane an idea than this.

Some futurists see this as one way for a civilization "downtime" to survive the heat death of the Universe, at least for a while... by living off the radiation emitted by dying supermassive black holes... wouldn't be much of a life, though.