The original theory of black holes appeared in Einstein's General Theory of Relativity, but Einstein did not name this celestial body. In the General Theory of Relativity, he said: If the mass of a celestial body is very large, its gravity is so strong that even light cannot escape its gravity, but this celestial body will never appear in nature.

Later observation found that the problem that Einstein avoided was proved to be real, and it was a black hole.

a Black hole is an ultra-high-density celestial body existing in space in modern general relativity. It is named as a black hole because it is similar to a thermodynamically black body that does not reflect light at all.

A black hole is a celestial body in curvature of spacetime that is too big for light to escape from its horizon. Black holes are caused by gravitational collapse of stars with sufficient mass after the fuel of nuclear fusion reaction is exhausted and "dead".