ˈshwȯrtˌshild-, ˈs(h)wȯrtsˌchīld-; ˈshvärtˌshilt- noun
Usage: usually capitalized S
Etymology: after Karl Schwarzschild died 1916 German astronomer
: the radius of the spherical boundary within which a given mass (as of a star) must collapse to become a black hole ; also : the distance of the event horizon from the center of a black hole