Knowra Schwarzschild radius Schwarzschild radius The radius of the event horizon of a nonrotating, uncharged black hole. It equals twice the black hole’s mass times the gravitational constant divided by the speed of light squared.
Schwarzschild metric : An exact solution to Einstein’s field equations describing spacetime outside a spherical, nonrotating, uncharged mass. Its horizon occurs at the Schwarzschild radius.
Gravitational constant : The fundamental constant setting the strength of gravity in Newtonian gravity and general relativity. It makes the radius increase in direct proportion to mass.
Kerr metric : An exact solution of Einstein’s field equations describing the spacetime around a rotating, uncharged black hole. Rotation gives its horizon a different radius from the Schwarzschild value.
Stellar-mass black hole : A black hole formed from the collapse of a massive star, typically with a mass of a few to hundreds of solar masses. Its Schwarzschild radius is only a few to hundreds of kilometers.
Event horizon : A boundary in spacetime beyond which events cannot influence distant observers. The Schwarzschild radius locates this boundary for a Schwarzschild black hole.
Speed of light : The speed at which light propagates in vacuum and the invariant limiting speed in relativity. Its square appears in the denominator, setting the relativistic length scale.
Reissner–Nordström metric : An exact solution describing the spacetime around a static, electrically charged, spherically symmetric object. Charge changes the horizon radii, unlike the uncharged case.
Supermassive black hole : A black hole with millions to billions of solar masses, commonly found at the centers of galaxies. Its radius scales linearly with mass and can span millions or billions of kilometers.
Escape velocity : The minimum speed needed for an object to escape a gravitational field without further propulsion. A Newtonian calculation gives the same radius by setting escape velocity equal to light speed, though general relativity supplies the correct account.
Mass–energy equivalence : The relation between mass and energy expressed by Einstein’s equation E = mc². It connects a black hole’s mass to the energy scale represented by its horizon.
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