I was reading an article on black hole spin
(http://www.space.com/scienceastronomy/061120_mm_blackhole_spin.html) and
noted the article speaking about a theoretical limit of 1150 hz.

Anthony Garcia wrote:
I was reading an article on black hole spin
(http://www.space.com/scienceastronomy/061120_mm_blackhole_spin.html)
and noted the article speaking about a theoretical limit of 1150 hz.

The author is probably confusing black holes with pulsars. Evidence for
black hole rotation exists, but rate has yet to be determined.

First Direct Evidence of Black Hole Rotation
http://www.aip.org/pnu/2001/538.html

I was reading an article on black hole spin
(http://www.space.com/scienceastronomy/061120_mm_blackhole_spin.html) and
noted the article speaking about a theoretical limit of 1150 hz.

Conceptually I have no difficulty with a limit on stars spinning; spin too
fast and if flies apart. However what is it that limits a black hole's
spin?

On Feb 21, 4:10 am, "Anthony Garcia" <agarcia...@sbcglobal.net> wrote:
I was reading an article on black hole spin
(http://www.space.com/scienceastronomy/061120_mm_blackhole_spin.html) and
noted the article speaking about a theoretical limit of 1150 hz.

Conceptually I have no difficulty with a limit on stars spinning; spin
too
fast and if flies apart. However what is it that limits a black hole's
spin?

Almost the same thing - but the black hole cannot physically fall
apart, but it could lose its opaque event horizon(s) if it spins too
fast. The limit avoids us being able to see a naked singularity at the
centre of the spinning black hole.

In crude vaguely classical terms the frame dragging of the black hole
cannot cause the event horizon at the equator to move faster that the
speed of light. This puts a limit on the total amount of angular
momentum a given mass black hole can have (and by implication for a
given mass and angular momentum the radius and period of the fastest
innermost stable orbit going with and against the spin - they are
seriously different).

Modern X-ray telescopes with spectrographs can now follow the
emissions of material going down the gravitaional plughole and so
infer a spin/mass ratio for a spinning BH.

There isn't an easy explanation I know of that avoids heavy maths.
Wikipedia isn't bad on this:

http://en.wikipedia.org/wiki/Rotating_black_hole

It is intimately link to the strong cosmic censorship hypothesis

http://en.wikipedia.org/wiki/Cosmic_censorship_hypothesis

Regards,
Martin Brown

I was reading an article on black hole spin...

I was reading an article on black hole spin
(http://www.space.com/scienceastronomy/061120_mm_blackhole_spin.html) and
noted the article speaking about a theoretical limit of 1150 hz.

Conceptually I have no difficulty with a limit on stars spinning; spin too
fast and if flies apart. However what is it that limits a black hole's
spin?

Once matter goes past the event horizon is it still limited by the speed of
light or can it accelerate past this limit due to time slowing down within
the black hole.

Please excuse my ignorance but I dont have a physics education just a
curiosity about black holes.