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The Question

(Submitted October 22, 1997)

I read in a book about black holes that their singularities could be circular if the black hole had spin, if it rotated. Besides that book, everything I've read said that singularities are points of infinite density etc., but none of them said it had spin. In the book it said black holes can be defined by charge, spin, and something else. Is this false information?

Sincerely,

a mixed up 7th grader.

The Answer

Properties of black holes are indeed be defined by its mass, charge, and spin.

The simplest type of black holes are the known as Schwarzschild black holes, named after the scientist who discovered this solution of General Relativity. Schwarzschild black holes have 0 spin (they are not rotating) and 0 charge. It is possible that some books describe only this type of black holes, without saying so.

Rotating black holes are known as Kerr black holes, which can indeed have ring-shaped singularity.

Hope this has cleared things up a bit.

Koji Mukai
for Ask an Astrophysicist

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