Figure 21-22: Hawking Radiation and Evaporation of a Black Hole This illustration shows two pairs of virtual particles—an electron (e⁻) and a positron (e⁺), and a pair of virtual photons (γ)—appearing just outside the event horizon of a black hole. If one member of the pair becomes real and escapes, it carries a little energy away from the black hole, the black hole decreases in mass and the event horizon shrinks. The real particles radiating away are referred to as Hawking radiation, and the process is described as black hole evaporation.