What astronomical objects have gravitational singularities from which light cannot escape and may lose mass through Hawking radiation?

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

Answer: (D)

Objects with a boundary surrounding a region where light cannot escape are black holes. The key idea is the event horizon, the point beyond which the gravitational pull is so intense that nothing, not even light, can break free. Inside sits a central singularity in the classical view, where density would become infinite, though the full physics there is still a frontier. Hawking radiation describes a theoretical quantum process where particle-antiparticle pairs form near the horizon; one particle falls in while the other escapes, causing the black hole to lose a little mass over incredibly long timescales.

Neutron stars and white dwarfs are incredibly dense, but their gravity isn’t enough to trap light entirely—the escape velocity at their surfaces is below the speed of light—so light can still escape. Quasars, on the other hand, are extremely bright sources powered by matter falling into supermassive black holes, not singularities themselves.