Properties of Kerr Spacetime

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Kerr spacetime describes a rotating black hole. The line element in Boyer–Lindquist coordinates is given by


with and . is the mass of the black hole and is the angular momentum.

The roots of the function define the event horizon and the inner horizon , where . The region between the event horizon and the static limit is called the ergosphere.

The two marginally stable timelike circular geodesics are defined by the radii , where and . An object on the smaller radius rotates with the Kerr black hole, whereas an object on the larger radius rotates in the opposite direction.

The direct (-) and retrograde (+) photon orbits are defined via .

Here, the mass of the black hole is taken as .


Contributed by: Thomas Müller (March 2011)
Open content licensed under CC BY-NC-SA



A detailed discussion of the parameters is given in:

J. M. Bardeen, W. H. Press, and S. A. Teukolsky, "Rotating Black Holes: Locally Nonrotating Frames, Energy Extraction, and Scalar Synchrotron Radiation," The Astrophysical Journal, 178, 1972 pp. 347–369.

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