BH2 - Theoretical and observational studies of astrophysical black holes |
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Speaker |
Banerjee, Srimanta |
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Coauthors |
Chakraborty, Chandrachur; Bhattacharyya, Sudip |
| Talk Title |
Alignment and precession of a black hole misaligned with its accretion disk |
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Abstract |
We consider a thin accretion disk around a spinning black hole where the outer disk is misaligned with the spin direction of the black hole. For such a scenario, the inner part of the accretion disk was predicted to become aligned with the spin axis of the black hole by the well known Bardeen-Petterson effect. However, in our recent work, where we have considered the contribution of the inner disk and torque at the inner boundary, we have shown that for certain reasonable range of the parameter values, the inner disk may not be aligned at all with the spin axis of the black hole. As the black hole exerts a torque on the accretion disk due to Lense-Thirring precession and tries to align the inner disk with its own spin direction, same torque is also applied on it due to the conservation of angular momentum. As a result of which the black hole ultimately aligns itself with the outer disk. In this work, we compute the torque on the black hole due to Lense-Thirring precession taking the contribution from the entire disk. Thus, we obtain the alignment timescale and precession timescale of the black hole and study the timescales as a function of several parameters of the system. We consider the dynamical evolution of the disk during the alignment process and explore how it affects both the timescales in persistent as well as transient accretion. We also discuss the observational implications of our results in the context of microquasars. |
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