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What Is Rotating Black Hole (BH) Singularity Size?

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Posted by Alexander on March 7, 2001 17:29:45 UTC

If to assume that a rotating BH has a ring singularity, then can we estimate radius of this singularity as follows?:

Let's assume that if a star's angular momentum is of the order of plank value h, then the singularity ring radius is also of the order of plank value (plankl length 1.6x10^-35 m). If the angular momentum of a BH is L, then there are L/h spin quanta there, so you have L/h of them over area of singularity ring circle, thus the radius of singularity ring has to be of the order of (L/h)1/2lplank.

h is hbar here = 1.06x10^-34 J sec.

For the Sun collapsed in BH (with the Schwarzschild radius being 2.97 km), I got a singularity ring radius to be about 950 m (from the above equation and ssuming no loss of angular momentum during collapse - with loss, ring is correspondingly smaller.)

Interesting, that if a BH rotates with the equatorial speed close to speed of light c,then the ring radius approaches the Schwarzscild one (ring merges with the event horizon on the equator). What does it mean?

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