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  1. How are non-rotating black holes formed?

I guess that non-rotating black holes are formed from non-rotating stars but I couldn't find any proof that such a star exists on the internet. If this is true can you also put up an example of such a star?

  1. Does the matter absorption of a non-rotating black hole differ from a rotating black hole?
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  • $\begingroup$ Also, one question per question please... $\endgroup$ – Lightness Races with Monica Aug 24 '15 at 18:40
  • $\begingroup$ @LightnessRacesinOrbit Sometimes it makes sense to ask two questions in the same post because they are quite related that they cannot live independently, IMO. $\endgroup$ – user2216 Aug 26 '15 at 20:01
  • $\begingroup$ @Axl: Sometimes, when they are conjunct parts of the same question, but I don't see that this is really the case here? Granted, I'm no astrophysicist :) $\endgroup$ – Lightness Races with Monica Aug 26 '15 at 20:10
  • $\begingroup$ @LightnessRacesinOrbit My observation was not particularly referred to this post, but for a general case. I also think actually that these two questions should deserve their own separate post... $\endgroup$ – user2216 Aug 26 '15 at 21:24
  • $\begingroup$ @Axl alright noted for the future, thanks guys! $\endgroup$ – CipherBot Aug 26 '15 at 23:27
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All stars have some angular momentum. Conservation of angular momentum when the core of a star collapses means that it is very likely that most black holes are rapidly rotating, just as newly-born neutron stars are observed to be extremely fast-rotating.

Even if one were to have a star with a non-rotating core as it collapsed, the subsequent accretion of material with angular momentum would give the black hole that angular momentum.

Non-spinning black holes are a theoretical ideal that is unlikely to be found in nature.

The details of the accretion of material onto a black hole are complex and still the subject of theoretical and observational research. But yes, the details of accretion in spacetime governed by the Kerr metric appropriate for rotating black holes will differ from those of a non-rotating Schwarzschild black hole. Kerr black holes have an "ergosphere", outside their event horizons, where material is force to co-rotate with the black hole.

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  • $\begingroup$ Sounds like an accretion disc inside ergosphere would act to spin up a non-rotating black hole. $\endgroup$ – Wayfaring Stranger Aug 24 '15 at 13:59
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    $\begingroup$ @WayfaringStranger A non-rotating black hole doesn't have an ergosphere. $\endgroup$ – Rob Jeffries Aug 24 '15 at 14:16
  • $\begingroup$ Now I think, of course not. Seems an accretion disk might still spin the thing up, even wo material necessarily crossing event horizon. $\endgroup$ – Wayfaring Stranger Aug 24 '15 at 14:19
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For the first part of your question: A real black hole is formed from a collapsing start is likely to have angular momentum. In theory a non-spinning black hole could be formed by collapse of a non-rotating star. In theory, you could potentially also realize a non-rotating black hole if angular momentum were extracted from a rotating black hole via the Penrose process.

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

For the second part of your question, I think it's not quite clear what you mean. The best that I can understand your question, I would say that matter is "absorbed" the same, although the path taken into the black hole may depend on its spin.

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  • $\begingroup$ This begs the question, if we find a non-rotating black hole in the future, was it more likely created by natural processes or aliens extracting the energy via Penrose process? :) $\endgroup$ – joseph.hainline Sep 19 '16 at 1:54
  • $\begingroup$ I wonder if a kugelblitz would be non rotating. $\endgroup$ – Howard Miller Jan 6 '17 at 20:28

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