What is the defining feature of a black hole?

A black hole is defined primarily by its extremely strong gravitational pull, which is so intense that not even light can escape from it. This characteristic arises from the collapse of a massive star at the end of its life cycle, where the core collapses under the influence of gravity. The boundary surrounding a black hole, known as the event horizon, marks the point beyond which no information or matter can return once crossed, which underscores why light, the fastest entity in the universe, also cannot escape.

The nature of black holes means they are invisible against the backdrop of space, but they can often be inferred through their interaction with nearby matter, such as stars or gas clouds. Their strong gravitational forces can warp space-time, leading to various observable effects, such as gravitational lensing, where the light from objects behind a black hole is bent.

The other options do not accurately reflect the defining characteristics of a black hole. For example, a region of space with negligible gravity does not relate to the overwhelming gravity of a black hole, and stating that an area where only light can escape contradicts the very nature of black holes. Additionally, while a collapsed star may lead to the formation of a black hole, high luminosity is not a feature of black holes themselves;