Schwarzschild radius

Summary

The Schwarzschild radius of a mass $M$ is the length $r_s = 2GM/c^2$. It is the radius of the event horizon of the Schwarzschild metric of mass $M$. A spherical, non-rotating, uncharged body that is compressed inside its Schwarzschild radius becomes a black hole. It sets the natural length scale of strong gravity for a given mass.