Seeing as the star is in close proximity to a blackhole it would likely be similar to the Kerr-Metric [1] (as we _should_ assume the black hole as some spin).
The white star has non-trivial mass of its own which greatly complicates the curvature of the local space-time region and render the Kerr-Metric equations lacking.
Unless the hole is rotating extremely rapidly (which I don't see mentioned), the difference between the Kerr metric and the Schwarzschild metric (which is what I used for the formula I posted upthread) is too small to matter unless you are really close to the hole's horizon.
You got me curious, and I wanted to put numbers around this. It's worth noting that the actual paper claims only this is a black hole candidate, and is not certain it's a black hole (despite the Science alert headline).
The paper guesses that the black hole is ~ 1 solar mass, so the Schwarzschild radius would be about 3 km.
The distance is about 2.5x the earth-moon, which is about 10^6 km.
See also [1].
[1] http://www.edu-observatory.org/physics-faq/Relativity/SR/clo...