Rotating black hole

A black hole with angular momentum. In general relativity, an idealized uncharged rotating black hole is described by the Kerr solution.

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Kerr metric: An exact solution of Einstein’s field equations describing an idealized, uncharged rotating black hole. It gives the spacetime geometry around the rotating black hole.
Angular momentum: A conserved physical quantity that measures rotational motion. It is the defining extra property distinguishing a rotating black hole from a nonrotating one.
Black hole spin: A measure of a black hole’s angular momentum, commonly expressed relative to its mass. Spin controls the Kerr geometry and is inferred from astrophysical observations.
Kerr black hole uniqueness theorem: A result stating that stationary, asymptotically flat vacuum black holes are characterized by mass and angular momentum. It explains why the Kerr solution is the standard idealized rotating-black-hole model.
Frame-dragging: The relativistic effect by which rotating mass drags nearby inertial frames. The black hole’s angular momentum twists spacetime around it.
Event horizon: A boundary in spacetime beyond which events cannot influence distant observers. The rotating black hole’s horizon is shaped by its mass and spin.
X-ray reflection spectroscopy: An observational method that studies X-rays reflected from hot matter near compact objects. Relativistic distortions of iron-line spectra can constrain black-hole spin.
Black hole information paradox: The conflict between quantum-mechanical information conservation and the apparent loss of information in black hole evaporation. Rotation complicates the geometry but does not resolve the underlying quantum puzzle.
Ergosphere: The region outside a rotating black hole’s event horizon where no observer can remain stationary relative to distant stars. Frame-dragging becomes unavoidable in this region.
Einstein field equations: The equations of general relativity relating spacetime curvature to matter and energy. The Kerr solution satisfies these equations in vacuum.