Enhanced activity of massive black holes by stellar capture assisted by a self-gravitating accretion disc
Enhanced activity of massive black holes by stellar capture assisted by a self-gravitating accretion disc
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DOI：
10.1051/0004-6361:20066068
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发表时间：
2007-04
影响因子：
6.5
通讯作者：
V. Karas;L. Šubr
中科院分区：
文献类型：
--
作者：
V. Karas;L. Šubr
目标。研究了核团中的恒星与大质量黑洞（10 4 MM· 10 8 M�）近距离相遇的概率。系统的引力场由在其影响范围内的黑洞支配。它是进一步修改的集群平均场（球形项）和气体盘/环面（轴对称项），通过Kozai振荡造成长期的恒星轨道演化。间歇性的高离心率阶段增加了恒星在中央黑洞潮汐半径内受损的机会。这些事件可能产生碎片，导致不断发生的增强的吸积活动。方法.我们引入了一个有效的损失锥，并将其与潮汐中断在高偏心率阶段的Kozai周期。通过数值积分的轨迹形成的边界的损失锥，我们确定其形状和体积。我们还包括近心点的相对论性推进的影响。结果盘的潜力有扩大损失锥的效果，因此，预测的潮汐破坏恒星的数量应该增加到10 2倍。另一方面，星系团平均势的影响，以及相对论近心推进，对偏心率振荡的作用。最后，我们预计潮汐扰动事件的频率约为10倍，与模型相比，其中的三个影响-集群平均场，相对论近心点的进步，和Kozai机制-都被忽略。随着黑洞质量的增加，不同影响因素的竞争抑制了预测的恒星破裂率。因此，所考虑的过程对中等质量黑洞M·10 4 M·更重要。
Aims. We study the probability of close encounters between stars from a nuclear cluster and a massive black hole (10 4 MM• 10 8 M� ). The gravitational field of the system is dominated by the black hole in its sphere of influence. It is further modified by the cluster mean field (a spherical term) and a gaseous disc/torus (an axially symmetric term) causing a secular evolution of stellar orbits via Kozai oscillations. Intermittent phases of high eccentricity increase the chance that stars become damaged inside the tidal radius of the central hole. Such events can produce debris and lead to recurring episodes of enhanced accretion activity. Methods. We introduce an effective loss cone and associate it with tidal disruptions during the high-eccentricity phases of the Kozai cycle. By numerical integration of the trajectories forming the boundary of the loss cone, we determine its shape and volume. We also include the effect of a relativistic advance of the pericentre. Results. The potential of the disc has the efffect of enlarging the loss cone, therefore, the predicted number of tidally disrupted stars should grow by factor of � 10 2 . On the other hand, the effect of the cluster mean potential, together with the relativistic pericentre advance, act against the eccentricity oscillations. In the end we expect the tidal disruption events to be approximately ten times more frequent in comparison with the model in which the three effects - the cluster mean field, the relativistic pericentre advance, and the Kozai mechanism - are all ignored. The competition of different influences suppresses the predicted star-disruption rate as the black hole mass increases. Hence, the process under consideration is more important for intermediate-mass black holes, M• � 10 4 M� .