What compact object has gravity so strong that light cannot escape?

A black hole is a compact object whose gravity is so strong that light cannot escape. In general relativity, its boundary of no return is called the event horizon.

A black hole forms when enough mass is compressed into a sufficiently small region, making spacetime curvature extreme. Once an object crosses the event horizon, it cannot send a signal back to a distant observer. The horizon is not a solid surface; it is a causal boundary in spacetime.

Black holes can arise from the collapse of massive stars, and supermassive black holes occupy the centers of galaxies. They can also be detected indirectly through effects on nearby stars, glowing accretion disks, jets, and gravitational waves from mergers.

A neutron star is also extremely dense, but its surface can emit light and matter. A quasar is a brilliantly active galactic nucleus powered by material falling toward a supermassive black hole; it is not itself the compact object’s name. White dwarfs are dense stellar remnants that remain visible.