Can a non rotating black hole start rotating? Intuitively it is not possible, but intuition often leads to wrong conclusions.
I have only basic physic knowledge, however I like to wonder about relativity, quantum mechanics e.t.c, so even not comprehensive answer would be great for me.
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Qmechanic
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Jakub Pawlak
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2What do you think will happen to the conservation of angular momentum if a spinning ball falls into a black hole? ;) – Jun 24 '20 at 16:31
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1I'm curious as to why you say, "Intuitively it is not possible". – probably_someone Jun 24 '20 at 16:35
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Is not black hole infinitesimally small small? It would have to rotate infinitesimally fast in order to preserve angular momentum while some rotating objects fall into it, unless some forces stopped the rotation of falling object. – Jakub Pawlak Jun 24 '20 at 16:42
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How can a singularity in a black hole rotate if it's just a point? – G. Smith Jun 24 '20 at 17:20
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A black hole is characterised by its mass, angular momentum and charge.
If a black hole accretes material that has angular momentum, then that gets added to the angular momentum of the black hole.
Just because there is a singularity at the centre does not mean it cannot possess mass, angular momentum and charge. An electron is point-like and also has all three.
You might object that electron spin is a consequence of relativistic quantum theory, whilst General Relativity is classical. Note though, that the singularity in a rotating (Kerr) black hole is not a point, it is more like a ring, so there is no need to invoke any weird quantum effects to ascribe it an angular momentum.
ProfRob
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