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Søren Ragsdale asked the Naked Scientists: I've heard that black holes spin, which causes frame dragging. I'm not sure what that means, though. If we talk about a bicycle wheel, its "rotations per minute" measure how fast the tire travels around its axle. But a singularity inside the event horizon of a black hole is a point, it has zero radius. How can we say how fast a black hole's singularity is spinning if it has zero radius?What do you think?

It is not possible (or necessary) to measure the angular velocity of the singularity.