My understanding is that Hawking radiation isn't really radiated from a black hole, but rather occurs when a particle anti-particle pair spontaneously pop into existence, and before they can annihilate each other, the antiparticle gets sucked into the black hole while the particle escapes. In this way it appears that matter has escaped the black hole because it has lost some mass and that amount of mass is now zipping away from it.
Is this correct? If so, wouldn't it be equally likely that the particle be trapped in the black hole and the antiparticle go zipping away, appearing as if the black hole is spontaneously growing and emitting antimatter?
How is it that this process can become unbalanced and cause a black hole to eventually emerge from its event horizon and evaporate into cosmic soup over eons?
Answer
To add to Rory's answer-
The ability to radiate particles in a random, statistical way, is in a deep sense identical to an object having the property we know as "temperature." So, black holes have a temperature. It has a particular formula that is inversely proportional to the mass of the black hole. If you set that temperature equal to the current temperature of the Cosmic Microwave Background (CMB) that is 2.725 K, then you get a mass of about 4.503 X 10^22 kg, or a little over half the mass of the Moon. Black holes above this mass will be cooler than the CMB incident upon them, so will gather mass-energy from it. Black holes below it will lose energy due to Hawking radiation faster than they gain it from the CMB, so will head towards a catastrophic, runaway "pop." Note that the CMB is also getting cooler as time goes on, so the equilibrium mass shifts upwards. No one that I know of has bothered to do any detailed "race" calculations between a black hole's Hawking radiation and the changing temperature of the CMB.
Another important mass related to Hawking radiation is the mass at which the black hole is so cool that it would have emitted negligible radiation even if had been around since the beginning of the universe. This is about 2 X 10^11 kg, roughly comparable to the total mass of all humans.
The second mass is less than the first, so if a whole range of black holes had been created at the beginning of the universe, the upshot is that some would be popping right now! Astronomers are on the lookout for these events.
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