Alignment and precession of a black hole misaligned with its accretion disc: Application to Low Mass X-ray Binaries

Understand

A thin viscous accretion disc around a Kerr black hole, which is warped due to the Lense-Thirring (LT) effect, was shown to cause the spin axis of the black hole to precess and align with the outer disc.

• We calculate the total LT torque acting on the black hole, and compute the alignment and precession time-scales for both persistent and transient accretors.
• In our analysis, we consider the contribution of the inner disc, as it can stay misaligned with the black hole spin for a reasonable range of parameter values.
• We find that the alignment time-scale increases with a decrease in the Kerr parameter below a critical Kerr parameter value, contrary to earlier predictions.