A black hole is a place in space where gravity is so strong that it pulls so much. Even electromagnetic radiation such as light cannot escape it; because no light can get out, people can’t see black holes.
The gravity is so strong because matter has been squeezed into a tiny space. This compression happens when a star is dying. The death of a massive star can form a black hole.
Black holes were predicted by Einstein’s most famous theory of general relativity, which showed that when a massive star dies, it leaves behind a small, dense remnant core. If the core’s mass is more than about three times the mass of the Sun, the equations show that the force of gravity overwhelms all other forces and creates a black hole.
