What are the regions of space with gravity so strong that light cannot escape, predicted to evaporate over time via Hawking radiation?

• A. Neutron stars
• B. White dwarfs
• C. Quasars
• D. Black holes

Answer: (D)

Light cannot escape only in regions where gravity is so intense that nothing, not even light, can break free—this boundary is called an event horizon, and the object that creates it is a black hole. The idea that such regions can slowly lose mass over time comes from Hawking radiation, a quantum effect near the horizon. In this picture, particle-antiparticle pairs pop into existence at the horizon; one falls in while the other escapes, producing radiation and causing the black hole to lose mass gradually. Over very long times, this leads to evaporation, especially for small black holes; large ones would take far longer than the age of the universe to vanish.

Other dense objects like neutron stars and white dwarfs don’t trap all light—light can escape their strong gravity, so they aren’t regions from which light cannot escape. Quasars are extremely bright centers of distant galaxies powered by matter spiraling into black holes, but the region that traps light is the black hole itself, not the emitting accretion disk around it.