[IanCal]

Armchair Physicist here, not a real one.

There are two reasons why you'd say black holes emit radiation. An interesting one and a very interesting one (warning, other peoples scales may be calibrated differently to mine).

1) Black holes accelerate things massively, so they're travelling at an astonishing speed before they "enter". This can result in huge amounts of x-rays being emitted due to heating things to millions of degrees (well beyond white hot!). It's not the black hole itself, but the black hole is certainly to blame. http://hyperphysics.phy-astr.gsu.edu/hbase/astro/blkbin.html

2) The weirder one. Hawking radiation: http://en.wikipedia.org/wiki/Hawking_radiation

Hawking radiation happens when a pair of virtual particles "pop" into existence near the event horizon. Normally these pairs annihilate quickly, but if it happens near the event horizon it's possible for one of the particles to fall in and the other to escape. This results in a loss of mass of the black hole (told you it was weird) so could be considered to be the black hole emitting radiation.

[jjoonathan]

> one of the particles to fall in and the other to escape. This results in a loss of mass of the black hole (told you it was weird)

How does the energy to create the virtual particles come from the black hole (which it has to in order for the accounting to work: -2+1=-1)? Is it a "Quantum Field Theory doesn't care about the event horizon" type thing?

[pdonis]

It doesn't take any energy to create virtual particles; virtual particle pairs are constantly being created and destroyed everywhere, according to Quantum Field Theory, but when they're created, on average, they have zero net energy: one has positive energy and one has negative energy. (Note that this is a heuristic description and not every quantum field theorist would agree with it. The only really unambiguous way to describe the process is using math; but translating math into everyday language is often difficult because our intuitions don't really match up with what the math is telling us. I'm doing the best I can.)

However, if a virtual particle pair happens to be created just outside a black hole's horizon, the hole's tidal gravity can pull the negative energy particle inside the horizon before it can be annihilated by the positive energy particle. The positive energy particle can then escape. Effectively, this means the positive energy particle's energy is taken from the hole's mass, so the hole's mass decreases slightly.

[Ygg2]

Also some particles might travel faster than speed of light by tunneling or similar quantum mechanisms.