Astronomers Discover a Supermassive Black Hole Rotating at Half Speed of Light

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16 points·petethomas··5 comments

I don't understand why they don't all rotate at very nearly the speed of light. Isn't all matter that crosses the event horizon going that fast, by definition?

I understand that matter does not necessarily enter at very close to a tangential angle, and only the tangential component would contribute to rotation, but it seems like most of it must, in practice.

Clue?

Is there a 1:1 relationship between the rotational speed of the black hole itself and the speed of the matter falling into it? If matter would fall straight (with 0 angular momentum) towards a rotating black hole, would its matter fall in straight, or would the black hole drag the matter into rotation?

pure speculation but I would assume space around that black hole would act like a vortex, like water going down the drain. so anything get close will be dragged I guess.

The latter. Unlike Schwarzschild black holes, a Kerr black hole drags spacetime with it as it rotates.

The black hole in Interstellar was a Kerr black hole.

https://en.wikipedia.org/wiki/Kerr_metric

I have a theoretical question: Since events horizon is not a real object, can the tangencial speed at the equator be greater than the speed of light?

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