振荡黑洞环的形成
Ring Formation from an Oscillating Black Hole
摘要：
大规模的黑洞（BH）合并会导致合并后的残余物受到200 km/s $^{-1}$或更大的“反冲”，这将导致残余物围绕星系中心振荡。在这里，我们分析的情况下，BH振荡通过星系中心垂直或平行于星系的平面的模型星系组成的指数盘，普卢默模型隆起，和等温暗物质晕。对于垂直运动，我们发现在接近但略小于“共振半径”$r_R$的地方，BH振荡频率等于二分之一、四分之一、（1/6等），圆盘径向运动存在一个强的共振强迫。在圆盘平面内的径向周转频率。在共振半径附近，径向流和盘密度会有很大的增强，这会导致激波的形成。反过来，冲击波可能会触发$r_R$附近恒星环的形成。作为一个例子，对于BH质量为$10^8 M_\odot$和反冲速度为150 km/s $^{-1}$，我们发现共振半径在0.2和1 kpc之间。对于BH运动平行于平面的星系，我们发现，BH留下了一个超音速尾流，恒星形成可能会被触发。计算了尾流的形状以及BH的减速时间。圆盘的差速旋转将尾流拉伸成环状段。
英文摘要：
Massive black hole (BH) mergers can result in the merger remnant receiving a "kick", of order 200 km s$^{-1}$ or more, which will cause the remnant to oscillate about the galaxy centre. Here we analyze the case where the BH oscillates through the galaxy centre perpendicular or parallel to the plane of the galaxy for a model galaxy consisting of an exponential disk, a Plummer model bulge, and an isothermal dark matter halo. For the perpendicular motion we find that there is a strong resonant forcing of the disk radial motion near but somewhat less than the "resonant radii" $r_R$ where the BH oscillation frequency is equal one-half, one-fourth, (1/6, etc.) of the radial epicyclic frequency in the plane of the disk. Near the resonant radii there can be a strong enhancement of the radial flow and disk density which can lead to shock formation. In turn the shock may trigger the formation of a ring of stars near $r_R$. As an example, for a BH mass of $10^8 M_\odot$ and a kick velocity of 150 km s$^{-1}$, we find that the resonant radii lie between 0.2 and 1 kpc. For BH motion parallel to the plane of the galaxy we find that the BH leaves behind it a supersonic wake where star formation may be triggered. The shape of the wake is calculated as well as the slow-down time of the BH. The differential rotation of the disk stretches the wake into ring-like segments.
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