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It is conjectured that a rotating black hole has at its center a ring-shaped singularity.

Thus, at the center of the ring-shaped singularity the gravitational field must be zero (similar to gravitational field at center of dense object), and gravity must be minimized along the rotational axis. At the rotational axis, the gravitional field will be oriented towards the center from both sides, which will cause matter and eventually spacetime to flow towards the center.

Therefore, it seems plausible that the event horizon is a flattened ellipsoid that has upper and lower inward bulges that are rotationally symmetric around the rotational axis.

Also, for a very large black hole, the event horizon might open up around the rotational axis, such that the event horizon becomes toroidal (donut-shaped). Is that possible?

Halfdan Faber
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    Please break this up into multiple questions. – Zo the Relativist Apr 08 '16 at 22:17
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    I think its best to keep as one question at least initially. Note that questions are simple derivations that provide context from the underlying question of whether matter can pass through the center of a ring-shaped singularity along the rotational axis, where the gravitational field points towards the center. – Halfdan Faber Apr 08 '16 at 22:54
  • Interestingly, frame dragging would likely be very signifant in central disc inside ring-shaped singularity. For any beam going through the center, this should tend to produce a rotation around the rotational axis. This could be consistent with rotation that is appearant in some relativistic jets. – Halfdan Faber Apr 08 '16 at 23:01
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    No, the answers to these things are all radically different and have nothing to do with each other. – Zo the Relativist Apr 08 '16 at 23:05
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    It isn't 'conjectured': there is an exact solution whose properties have been extensively investigated. –  Apr 09 '16 at 08:34
  • Yes, the the Kerr and Kerr-Newman metrics are exact solutions to Einsteins field equations, which both have a ring singularity. It is therefore conjectured that actual black holes have a ring singularity. This could be true if you believe there are singularities in the physical world. Personally, I believe there are no continous structures nor singularities in the physical multiverse. My belief would be that the inner region of a rotating black hole from a distance can be approximated by a torus with a compressed boundary. That is just a belief, however. – Halfdan Faber Apr 09 '16 at 17:16
  • I will split up the question, starting with the torus-shaped event horizon... – Halfdan Faber Apr 09 '16 at 17:27
  • Related: http://physics.stackexchange.com/q/78803/2451 – Qmechanic Apr 09 '16 at 17:50
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    Can someone reopen? – Halfdan Faber Apr 09 '16 at 18:07

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