Disc tearing and Bardeen–Petterson alignment in GRMHD simulations of highly tilted thin accretion discs
Disc tearing and Bardeen–Petterson alignment in GRMHD simulations of highly tilted thin accretion discs
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DOI：
10.1093/mnras/staa099
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发表时间：
2019-04
影响因子：
4.8
通讯作者：
M. Liska;M. Liska;C. Hesp;A. Tchekhovskoy;A. Ingram;M. Klis;S. Markoff;M. V. Moer
中科院分区：
文献类型：
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作者：
M. Liska;M. Liska;C. Hesp;A. Tchekhovskoy;A. Ingram;M. Klis;S. Markoff;M. V. Moer
明亮的活动星系核和X射线双星通常包含几何薄，辐射冷却的吸积盘。根据理论，在许多情况下，这些粒子最初与黑洞赤道高度错位。在这项工作中，我们提出了第一个广义相对论磁流体动力学模拟非常薄的（h/r = 0.015-0.05）吸积盘周围的快速旋转（a = 0.9）黑洞和倾斜45°-65°。我们表明，内部区域的磁盘与h/r <$0.03与黑洞赤道对齐，虽然比分析工作预测的半径更小。内部对准和外部未对准的盘区域由倾斜角的急剧中断分离，伴随着密度的急剧下降。我们发现，帧拖动的旋转黑洞压倒了磁盘的粘度，这是自洽产生的磁化湍流，撕裂光盘分开，形成一个快速旋进内子盘周围的一个缓慢旋进外子盘。我们发现，该系统产生一对相对论射流的所有初始倾斜值。在小距离处，黑洞发射的喷流与内子盘一起快速进动，而在大距离处，它们与外子盘部分对齐，进动较慢。如果撕裂半径可以在未来的工作中准确建模，基于进动驱动的准周期振荡的黑洞自旋的发射模型独立的测量可能成为可能。
Luminous active galactic nuclei and X-ray binaries often contain geometrically thin, radiatively cooled accretion discs. According to theory, these are – in many cases – initially highly misaligned with the black hole equator. In this work, we present the first general relativistic magnetohydrodynamic simulations of very thin (h/r ∼ 0.015–0.05) accretion discs around rapidly spinning (a ∼ 0.9) black holes and tilted by 45°–65°. We show that the inner regions of the discs with h/r ≲ 0.03 align with the black hole equator, though out to smaller radii than predicted by analytic work. The inner aligned and outer misaligned disc regions are separated by a sharp break in tilt angle accompanied by a sharp drop in density. We find that frame dragging by the spinning black hole overpowers the disc viscosity, which is self-consistently produced by magnetized turbulence, tearing the disc apart and forming a rapidly precessing inner sub-disc surrounded by a slowly precessing outer sub-disc. We find that the system produces a pair of relativistic jets for all initial tilt values. At small distances, the black hole launched jets precess rapidly together with the inner sub-disc, whereas at large distances they partially align with the outer sub-disc and precess more slowly. If the tearing radius can be modeled accurately in future work, emission model independent measurements of black hole spin based on precession-driven quasi-periodic oscillations may become possible.