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Suppose I have a Kerr black hole (rotating, uncharged) and I build a giant ring (a "Niven Ring") around it. I am interested in two related scenarios (I am confused about the second, but am also providing the first for completeness and in-case of my error):

  1. Ring lies in plane of black hole's rotation. Because frame dragging will "accelerate" a test particle from the perspective of a distant observer, I conjecture that frame dragging will "accelerate" the ring, making it match the rate of frame dragging (local observers perceive it to be at rest, however).
  2. Ring is spinning orthogonal to black hole's spin. This feels like the setup to a gyroscope problem, but I am hesitant to analyze it that way because frame dragging isn't (I think) a real force, but more a difference between reference frames (yes?).

What is the effect on the ring in this second scenario? In-particular, is there any gyroscopic precession that occurs?

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  • $\begingroup$ How far will the ring be from the black hole ? $\endgroup$ – StephenG Mar 13 '18 at 6:01
  • $\begingroup$ @StephenG I don't think the overall behavior is affected by that. But, I'd say "close enough that frame dragging is not negligible, but not so close that tidal stresses on the ring are large". A more-massive hole would be more practical in this regard. In any case, I believe "well-outside-the-ergosphere" would apply to all cases. $\endgroup$ – imallett Mar 13 '18 at 8:49

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