[1][2][3] There are four known, exact, black hole solutions to the Einstein field equations, which describe gravity in general relativity.
[1][2] Since observed astronomical objects do not possess an appreciable net electric charge, only the Kerr solution has astrophysical relevance.
The formation of a rotating black hole by a collapsar is thought to be observed as the emission of gamma ray bursts.
[11] A complete mathematical description for how light bends around the equatorial plane of a Kerr black hole was published in 2021.
[13] Rotating black holes have two temperature states they can exist in: heating (losing energy) and cooling.
[14] Kerr black holes are featured extensively in the 2009 visual novel Steins;Gate (also TV / manga), for their possibilities in time travelling.
The boundaries of a Kerr black hole relevant to astrophysics. Note that there are no physical "surfaces" as such. The boundaries are mathematical surfaces, or sets of points in spacetime, relevant to analysis of the black hole's properties and interactions.
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While from an infalling observer's perspective the plunge into a rotating black hole occurs in a finite proper time and with very high
rapidity
(left), from the perspective of a coordinate observer at infinity they
slow down
, approaching zero velocity at the horizon relative to a stationary probe on site while being whirled around forever by the black hole's
frame-dragging
effect (right).
Prograde bound orbit around a black hole rotating with a
spin parameter
of a/M=0.9.
Rotating black hole from the perspective of the distant observer. The different frames show the black hole from different angles.
