翘曲吸积盘中黑洞排列过程中质量和自旋的共同演化
Mass and spin coevolution during the alignment of a black hole in a warped accretion disc
摘要：
本文研究了黑洞与未对准吸积盘的重磁相互作用，并在假设吸积盘的外部区域不断地被角动量固定的物质馈送的条件下，研究了黑洞自旋的进动和对准以及黑洞质量和自旋参数的演化.我们发展了一个基于绝热近似的迭代方案来研究BH-盘的协同演化：在这种方法中，吸积盘通过一系列准定态翘曲态（Bardeen-Petterson效应）与BH相互作用，直到BH自旋与外角动量方向对齐.对于与同向旋转盘对准的BH，质量的分数增加通常小于百分之几，而自旋模量可以增加高达百分之几十。最大旋转黑洞以爱丁顿速率吸积的时间尺度在10万年到100万年之间。由于克尔度规中的不对称性，与镜面同向旋转的情况相比，从最初反向旋转的盘对准BH盘往往更有效：反向旋转的物质在穿过最内部的稳定轨道时携带更大和相反的角动量，因此自旋模量下降得更快，相对倾角也更快。
英文摘要：
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 and spin parameter 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 coevolution: 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 BH spin aligns with the outer angular momentum direction. For a BH aligning with a co-rotating disc, the fractional increase in mass is typically less than a few percent, while the spin modulus can increase up to a few tens of percent. The alignment timescale is between ~ 100 thousands and ~ 1 millions years 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 co-rotating 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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