Can we determine the rotation speed of a black hole?

[cosmicpencil]

Is it possible to calculate the rotation speed of a black hole? Idid not find anything on this on google.

thanks

 

[Chronos]

A Kerr black hole has a theoretical rotation component due to conservation of angular momentum. It cannot be measured directly as we cannot observe anything occurring inside the event horizon. I doubt it's meaningful to talk about rotataion with respect to the event horizon. For discussion, see
http://science.howstuffworks.com/black-hole.htm/printable

 

[cosmicpencil]

I heard in class of a theorie that would use the light emmited from the black hole surroundings to calculate the rotation speed, anyone familiar with these theories?
thanks

 

[Maria76]

I heard about that. In an x-ray binary in which a black hole is believed to be the compact object, it has been suggested that the strength of an ultrasoft x-ray component is directly related to the black hole's spin.
Check out section 8.2 of the following:
http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.astro.44.051905.092532

 

[Chronos]

Good link, maria, but, I am unconvinced the authors have derived an effective way to derive the intrinsic spin of a black hole.

 

[cosmicpencil]

thank you for this link.