A black hole, defined by an event horizon from which not even light can escape, is not perfectly black. Quantum field theory predicts that empty space around that horizon seethes with particle–antiparticle pairs. Normally these virtual pairs annihilate almost instantly, leaving no net effect on the surrounding vacuum.
Near the event horizon, gravity becomes strong enough to separate some of these pairs. One particle falls inward with negative energy relative to the black hole, while its partner escapes to infinity as real radiation. This outward flow is known as Hawking radiation. By absorbing negative energy, the black hole loses mass, in line with mass–energy equivalence.
As the mass decreases, the surface gravity and Hawking temperature rise, so the emission becomes more intense. The process respects the second law of thermodynamics because the loss of black hole entropy is balanced, and eventually outweighed, by the radiation’s entropy. Left undisturbed, the black hole can evaporate completely, leaving only a faint relic of information in the surrounding quantum fields.
