Mass and spin co-evolution during the alignment of a black hole in a warped accretion disc |
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Authors: | A Perego M Dotti M Colpi M Volonteri |
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Institution: | Department of Physics, University of Basel, Klingelbergstr. 82, 4056 Basel, Switzerland;Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA;Dipartimento di Fisica, Universitàdegli Studi di Milano-Bicocca, Piazza Della Scienza 3, 20126 Milano, Italy |
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Abstract: | In this paper, we explore the gravitomagnetic interaction of a black hole (BH) with a misaligned accretion disc to study BH spin precession and alignment jointly with BH mass M BH and spin parameter a evolution, under the assumption that the disc is continually fed, in its outer region, by matter with angular momentum fixed on a given direction . We develop an iterative scheme based on the adiabatic approximation to study the BH–disc co-evolution: in this approach, the accretion disc transits through a sequence of quasi-steady warped states (Bardeen–Petterson effect) and interacts with the BH until the spin J BH aligns with . For a BH aligning with a corotating disc, the fractional increase in mass is typically less than a few per cent, while the spin modulus can increase up to a few tens of per cent. The alignment time-scale is of ∼105–106 yr for a maximally rotating BH accreting at the Eddington rate. BH–disc alignment from an initially counter-rotating disc tends to be more efficient compared to the specular corotating case due to the asymmetry seeded in the Kerr metric: counter-rotating matter carries a larger and opposite angular momentum when crossing the innermost stable orbit, so that the spin modulus decreases faster and so the relative inclination angle. |
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Keywords: | accretion accretion discs black hole physics galaxies: active galaxies: evolution quasars: general |
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