Originally posted by twhitehead
But does it affect our measurement of the mass of the black hole using he orbit of a star?
[b]This is a variable that needs to be taken into account and you have not.
I am not convinced.
It is very relevant. I have proved what you "work out" can be wrong because the spin variable makes those calculations relative.
Relative to what?[/b]
The business of measuring or computing the mass of a star orbiting a black hole close enough to be effected by frame dragging is a valid point, if the drag is enough to effect the velocity of the star's orbit around the BH.
For instance, frame dragging is what delays the orbit of Mercury by such a tiny amount it was almost not measurable but it was one of the proof's of relativity when they first made the measurement. I think they knew about the tiny excess precession measured in 1915:
http://en.wikipedia.org/wiki/Tests_of_general_relativity#Frame-dragging_tests
Another related effect is called the Geodetic effect:
http://en.wikipedia.org/wiki/Geodetic_effect
Such effects are hard to even measure with our technology on masses like our sun but would need to be taken into account near the incredible bending of spacetime near a black hole where such effects would be extremely magnified, I suspect enough to alter the measured orbital velocity of a star unfortunate enough to get within grabbing distance of a black hole.
Space time itself is wound into a small spindle near a black hole so it makes sense such alterations of physics would have to be taken into account when trying to make such measurements as the orbital velocity of a star trapped by a black hole.