Schwarzschild radius

The Schwarzschild radius is the critical radius, according to the general theory of relativity, at which a body under the influence of its own gravitation becomes a black hole. Alternatively, it can be defined as the radius of the event horizon of a spherical black hole, from within which the strength of gravity is so strong that light cannot escape. Named after Karl Schwarzschild, it is given by Rs = 2GM/c2, where M is the mass of the body, G is the universal constant of gravitation, and c is the speed of light. For the Sun, Rs = 2.5 kilometers; for Earth Rs = 0.9 centimeter.