|MadSci Network: Astronomy|
Very insightful question. The short answer is, it's not the black hole emitting radiation. It's the _event horizon_! To grasp this, you have to understand a quirk of quantum mechanics; to wit, even the vacuum can produce pairs of particles spontaneously. If the particles violate energy conservation, they're called "virtual particles" and they have to annihilate each other before a time delta_t = h / delta_E. To do that, they have to be anti-particles. This random creation and destruction is disturbing but it happens all the time ... including near black holes. Let's zoom into near the horizon. If that happens, sometimes one of the particles pops into being headed towards the black hole and falls in. In doing so, it gives up gravitational potential energy. This allows the other particle to _gain_ the energy, giving it postive energy and become "real". The first particle, of course, disappears from the Universe. But the second, freed from the Uncertainty Principle restrictions, goes on forever. Since it was created _outside_ the horizon, it's possible for it to escape, if its energy is big enough. To an outside observer, the black hole seems to 'radiate' this particle. Interesting sidebar: The particle has picked up energy, enough to make it real. Where did that come from? The gravity of the black hole, of course, and since the source of gravity is mass, the black hole loses mass. It appears to evaporate as it radiates.
Try the links in the MadSci Library for more information on Astronomy.