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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 a High-Energy Astronomer
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