You have to estimate the mass of the star. In this case it is tiny compared to the black hole, which fortunately helps simplify things. The rest is a standard formula or two. No doubt because of relativity the velocity numbers you get from the formulas for this kind of extreme case are too high. But it does give a ballpark figure. Incidentally working the same formulas backwards is how they estimate the size of the black hole.
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Date: 2008-12-12 01:05 pm (UTC)