What is the process by which black holes emit particles and slowly lose mass?

Hawking radiation is the process by which black holes emit particles and slowly lose mass. Stephen Hawking predicted the effect in 1974 by applying quantum field theory to the curved spacetime around an event horizon. In this picture, quantum effects make a black hole behave as though it has a temperature and emits near-thermal radiation.

When energy escapes as radiation, the black hole loses an equivalent amount of mass through Einstein’s mass–energy relation. Over an extraordinarily long period, an isolated black hole could therefore shrink and eventually evaporate. The effect is far too weak to observe from ordinary stellar or supermassive black holes with current technology.

A key detail is that Hawking radiation does not mean ordinary objects escape from inside the event horizon. The radiation is associated with quantum processes outside or near the horizon. Smaller black holes are hotter and lose mass faster, while larger black holes are colder. Accretion is matter falling into a black hole, the Penrose process extracts energy from a rotating black hole, and the Blandford–Znajek process extracts rotational energy electromagnetically; none is the name of this evaporation process.