Fr.: rayon de Schwarzschild
The critical radius at which a massive body becomes a → black hole, i.e., at which light is unable to escape to infinity: Rs = 2GM / c2, where G is the → gravitational constant, M is the mass, and c the → speed of light. The fomula can be approximated to Rs≅ 3 x (M/Msun), in km. Therefore, the Schwarzschild radius for Sun is about 3 km and for Earth about 1 cm.