星系核中心黑洞的漂移及黑洞质量与核球质量的关联
Wandering of the central black hole in a galactic nucleus and correlation of the black hole mass with the bulge mass
摘要：
我们研究了一个位于星系中心的超大质量黑洞在星系核区域内游荡的机制。假设中心黑洞在核球中受到附近分子云的引力吸引而移动，但通过周围恒星的动力学摩擦而制动。我们估计的近似动能的黑洞之间的平衡的能量增益率通过引力吸引和能量损失率通过动力学摩擦，在一个核球组成的一个核恒星盘和一个核星团从我们的银河系观察。当黑洞质量相对较小时，黑洞在核球引力势中的漂移距离估计为几十pc。然而，随着黑洞质量的增加，距离缩小，当黑洞质量超过一个上限时，能量增益和损失之间的平衡解消失。结果表明，黑洞质量的演化过程是这样的：当黑洞质量小于上限时，环核区域星际物质的质量吸积导致活动星系核的活动，使黑洞质量增大。然而，当质量达到上限时，黑洞失去了对抗动力学摩擦的平衡力，并开始螺旋下降到重心。通过简单的参数标度，我们发现黑洞的质量上限与黑洞的核团质量成正比，这可以解释观测到的黑洞质量与核团质量的相关性。
英文摘要：
We investigate a mechanism for a super-massive black hole at the center of a galaxy to wander in the nucleus region. A situation is supposed in which the central black hole tends to move by the gravitational attractions from the nearby molecular clouds in a nuclear bulge but is braked via the dynamical frictions by the ambient stars there. We estimate the approximate kinetic energy of the black hole in an equilibrium between the energy gain rate through the gravitational attractions and the energy loss rate through the dynamical frictions, in a nuclear bulge composed of a nuclear stellar disk and a nuclear stellar cluster as observed from our Galaxy. The wandering distance of the black hole in the gravitational potential of the nuclear bulge is evaluated to get as large as several 10 pc, when the black hole mass is relatively small. The distance, however, shrinks as the black hole mass increases and the equilibrium solution between the energy gain and loss disappears when the black hole mass exceeds an upper limit. As a result, we can expect the following scenario for the evolution of the black hole mass: When the black hole mass is smaller than the upper limit, mass accretion of the interstellar matter in the circum-nuclear region, causing the AGN activities, makes the black hole mass larger. However, when the mass gets to the upper limit, the black hole loses the balancing force against the dynamical friction and starts spiraling downward to the gravity center. From simple parameter scaling, the upper mass limit of the black hole is found to be proportional to the bulge mass and this could explain the observed correlation of the black hole mass with the bulge mass.
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