Radius inside which the gravitational attraction between a body's particles must cause its irreversible gravitational collapse, named for Karl Schwarzschild. This is thought to be the final fate of the most massive stars (see black hole). The gravitational radius (math.R_math.g) of an object of mass math.M is given by math.R_math.g = 2math.Gmath.M/math.c², where math.G is the universal gravitational constant and math.c the speed of light. For a star like the Sun, the Schwarzschild radius would be about 1.8 mi (3 km).

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