Essentially, when spinning a black hole doesn't have a point at it's center but a ring (a point can't rotate).
Theoretically a black hole can spin faster than the speed of light since the event horizon is just space, not matter, and space can certainly exceed the speed of light (see expansion of the universe).
IIRC from relevant literature, the event horizon shrinks with increasing speed until it vanishes once the speed of light is exceeded and leaves behind a naked singularity; a black hole with no event horizon.
What is a black hole with no event horizon? Does that mean that once crossing, you are instantly subject to a great gravity? So there's a gravity gradient? How is that possible?
It means that the black hole is close to extremal. This means that the space near them is deformed in even more interesting ways than around a boring old non-spinning spherically-symmetrical hole.
I think it's often assumed that most black holes in the universe would have relatively low spin, compared to their mass. The research here is saying that, perhaps, the way that stars collapse would produce near-extremal holes in most cases, so they would be common in the universe.
I recommend reading up on black hole geometry ad Kerr(-Newman) holes; it's likely that any description that fits in a HN comment will leave you knowing less than when you started.
I am confused by this as well. The only thing I can imagine is "the matter falling into the hole at the event horizon moves at near the speed of light, relative to the center of the black hole". But I'm not 100% sure.
The angular momentum inside the black hole should then also reflect this, but I don't know if physicists are too confident about what the matter inside a black hole looks like.
chupa-chups|6 years ago
But this appears to be more complicated:
https://physics.stackexchange.com/questions/183832/typical-r...
https://physics.stackexchange.com/questions/174247/is-there-...
Taken from one of the stackexchange posts, this is quite interesting: http://www.nature.com/news/spin-rate-of-black-holes-pinned-d...
zaarn|6 years ago
Theoretically a black hole can spin faster than the speed of light since the event horizon is just space, not matter, and space can certainly exceed the speed of light (see expansion of the universe).
IIRC from relevant literature, the event horizon shrinks with increasing speed until it vanishes once the speed of light is exceeded and leaves behind a naked singularity; a black hole with no event horizon.
emilfihlman|6 years ago
chupa-chups|6 years ago
wiml|6 years ago
I think it's often assumed that most black holes in the universe would have relatively low spin, compared to their mass. The research here is saying that, perhaps, the way that stars collapse would produce near-extremal holes in most cases, so they would be common in the universe.
I recommend reading up on black hole geometry ad Kerr(-Newman) holes; it's likely that any description that fits in a HN comment will leave you knowing less than when you started.
lalaithion|6 years ago
fragsworth|6 years ago
The angular momentum inside the black hole should then also reflect this, but I don't know if physicists are too confident about what the matter inside a black hole looks like.
unknown|6 years ago
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