- the radius at which a gravitationally collapsing celestial body becomes a black hole.
- astronomy the radius of a sphere (Schwarzschild sphere) surrounding a non-rotating uncharged black hole, from within which no information can escape because of gravitational forces
- A radius defined for a body of a given mass and proportional to that mass, such that if the body is smaller than that radius, the force of gravity is strong enough to prevent matter and energy to escape from within that radius. The Earth is much larger than its Schwarzschild radius, which is approximately 7 mm (0.28 inches).Black holes are examples of objects smaller than their Schwarzschild radius, which defines the radius of their event horizon. The Schwarzschild radius is a consequence of Einstein’s General Relativity theory. It is named after the German astronomer Karl Schwarzschild (1873-1916).