Black holes bend light so strongly that nothing escapes past the event horizon.

The longer version

Extreme gravity warps space and time around a black hole, bending the paths of passing light rays. Closer in, the curvature becomes so steep that every possible route leads inward. The event horizon marks that boundary; crossing it means no light or matter can climb back out. From outside, a distant observer would see infalling material appear to slow.

Nothing about the object is solid in the usual sense. What lies at the center is hidden behind the horizon, and the physics there is not fully understood. Matter falling in often forms a hot accretion disk that radiates strongly before disappearing from view.

Where this entry sits

The night sky looks calm, yet almost everything up there is moving, burning, or slowly changing. These facts cover planets, stars, the Moon, gravity, black holes, comets, and the story of how people began exploring beyond Earth. The full list sits on the Space and Sky page, where every entry is listed in order.