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arXiv 1011.0002astro-ph.HEastro-ph.GAgr-qc
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双黑洞周围的吸积盘:一个准稳态模型

Accretion Disks Around Binary Black Holes: A Quasistationary Model

Yuk Tung Liu, Stuart L. Shapiro

摘要:

潮汐力矩作用在双黑洞周围的气体吸积盘上,可以在靠近轨道半径的盘上产生一个间隙。在后期,当双星因引力波发射而产生的螺旋时间尺度变得比盘中的粘性时间尺度更短时,双星从盘中分离并最终合并。在解耦之前,潮汐力矩和粘性力矩之间的平衡将盘驱动到准稳态平衡态,由间隙边缘发出的小振幅螺旋密度波略微扰动。我们考虑一个黑洞二与同伴的质量较小,并建立一个简单的牛顿模型的几何薄,开普勒盘在轨道平面的二。我们解决了磁盘演化方程在稳定状态下,以确定准静态,(轨道平均)表面密度分布之前去耦。我们使用我们的解决方案,这是解析到简单的求积,计算在这个时代的电磁通量和近似辐射谱。一个单一的无量纲参数Td/Tvis,等于在轨道半径的潮汐粘性扭矩的比率,确定磁盘结构,包括表面密度分布,差距的程度,存在的内部磁盘,和吸积率。在小Td/Tvis的极限下,该解退化为单个黑洞周围静止吸积盘的Shakura-Sunyaev轮廓.我们的解决方案可能是有用的物理参数的选择和建立准静态磁盘初始数据的详细数值模拟,开始前去耦和跟踪随后的演变的黑洞双盘系统。

英文摘要:

Tidal torques acting on a gaseous accretion disk around a binary black hole can create a gap in the disk near the orbital radius. At late times, when the binary inspiral timescale due to gravitational wave emission becomes shorter than the viscous timescale in the disk, the binary decouples from the disk and eventually merges. Prior to decoupling the balance between tidal and viscous torques drives the disk to a quasistationary equilibrium state, perturbed slightly by small amplitude, spiral density waves emanating from the edges of the gap. We consider a black hole binary with a companion of smaller mass and construct a simple Newtonian model for a geometrically thin, Keplerian disk in the orbital plane of the binary. We solve the disk evolution equations in steady state to determine the quasistationary, (orbit-averaged) surface density profile prior to decoupling. We use our solution, which is analytic up to simple quadratures, to compute the electromagnetic flux and approximate radiation spectrum during this epoch. A single nondimensional parameter Td/Tvis, equal to the ratio of the tidal to viscous torque at the orbital radius, determines the disk structure, including the surface density profile, the extent of the gap, the existence of an inner disk, and the accretion rate. The solution reduces to the Shakura-Sunyaev profile for a stationary accretion disk around a single black hole in the limit of small Td/Tvis. Our solution may be useful for choosing physical parameters and setting up quasistationary disk initial data for detailed numerical simulations that begin prior to decoupling and track the subsequent evolution of a black hole binary-disk system.

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