Study of the evolution of dense stellar systems by large-scale simulations on special-purpose computers

本研究的目的是通过直接的n体模拟来阐明致密恒星系统的动态演化，如球状星团，所谓的年轻和致密星团，以及星系核。这项研究的重点是这些系统中心的大质量黑洞是如何生长的。具体来说，我们设定了两个目标。(a)确定大质量恒星与其他大质量恒星逐渐合并形成超大质量恒星的合并不稳定性发生的判据；(b)确定球状星团和其他大质量星团中中心大质量黑洞的可观测特征。对于合并不稳定的条件，我们发现条件是大质量恒星的初始动力摩擦时间尺度很短（小于3Mys），初始核心半径很小。当采用King模式时，W0必须大于等于8。对于中心黑洞的观测特征，以前的观测研究寻找斜率为-7/4的尖峰，这是通过简单的单组分模型预测的。通过考虑恒星演化和恒星质量函数的n体计算，我们发现一个中心有大质量黑洞的球状星团的中心区域几乎是平核的。

The purpose of this study is to clarify the dynamical evolution of dense stellar systems, such as globular clusters, so-called young and compact clusters, and galactic nuclei, by means of direct N-body simulations. The focus of the study is how the massive black holes grow at the center of these systems. Specifically, we placed two goals. (a) To determine the criterion for the occurrence of the merging instability, in which massive stars merge with other massive stars progressively to form supermassive stars, and (b) to identify the observable signature of massive central black holes in globular clusters and other massive star clusters. As for the condition for the merging instability, we found that the condition is that the initial dynamical friction timescale of massive stars is short (less than 3Mys) and that the initial core radius is fairly small. When fitted by a King mode, W0 must be 8 or larger. For the observational signature of the central black hole, previous observational studies looked for a cusp with slope -7/4, predicted from simple single-component model. By means of N-body calculation in which stellar evolution and stellar mass function are taken into account, we found that the central region of a globular cluster with central massive black hole appears as almost flat core.