What is Hawking radiation, and how does it relate to black hole evaporation?

• A. Hawking radiation is the gamma rays from black hole mergers.
• B. Hawking radiation is theoretical blackbody radiation caused by quantum effects near the event horizon; it leads to gradual loss of mass and evaporation of small black holes.
• C. Hawking radiation is the visible surface emission from the accretion disk.
• D. Hawking radiation is the cosmic background radiation accelerated by black holes.

Answer: (B)

Hawking radiation is theoretical blackbody radiation that arises from quantum effects near a black hole’s event horizon. In quantum field theory, particles and antiparticles constantly pop into and out of existence as fleeting pairs. Near the horizon, one member of such a pair can fall into the black hole while the other escapes to the outside universe as real radiation. To an outside observer, this looks like the black hole emitting particles, carrying away energy.

This emission means the black hole loses mass over time. For small black holes, the loss can be meaningful over long timescales, and as the hole radiates, its temperature increases, which speeds up the radiation in a feedback loop—leading to eventual evaporation of the black hole. The radiation has a blackbody-like spectrum, with a temperature inversely proportional to the black hole’s mass.

Why this is the best description: the other ideas describe different phenomena. Gamma rays from mergers come from violent dynamics and gravitational waves or high-energy processes in the accretion flow, not from quantum effects at the horizon. Emission from the accretion disk is due to heated matter orbiting the black hole, not spontaneous quantum radiation from the horizon. The cosmic background radiation is a relic of the early universe, not something accelerated by black holes. Hawking radiation, in contrast, is tied specifically to quantum effects at the horizon and the gradual mass loss that leads to evaporation.