Which object can evaporate due to Hawking radiation, has an event horizon defined by the Schwarzschild radius, and not even light can escape?

• A. White dwarf
• B. Quasar
• C. Black hole
• D. Neutron star

Answer: (C)

Hawking radiation is a quantum effect that sits at the boundary called the event horizon, which for a simple black hole is the Schwarzschild radius. Inside this boundary, escape is impossible because the escape speed exceeds light, so nothing can get out, not even light. Yet near the horizon, quantum fluctuations can create particle pairs, and one particle can escape while the other falls in, causing the black hole to lose mass and, in principle, gradually evaporate over enormous timescales. Among the options, only a black hole has this horizon and the associated evaporation mechanism. White dwarfs and neutron stars are compact stars without an event horizon, so Hawking radiation is negligible for them and they don’t evaporate in this sense. A quasar is a bright active galactic nucleus powered mainly by accretion onto a black hole, with its luminosity governed by that accretion rather than Hawking evaporation. So the object that fits all parts is the black hole.