The formation and observational signatures of a new class of compact stellar-dynamical populations: the dark clusters

在这个提议的项目中，目标是数值研究星团的结束阶段，其中大量的恒星残骸，即中子星（NS）和黑洞（BH），在它们的祖先超新星之后被保留下来。初步研究表明，对于位于银河系内部几千秒差距内的星团来说，低质量的主序星在外部星系潮汐力的作用下从星团中剥离出来，其时间尺度相当于或短于由于相互接触而导致的黑洞耗尽时间。如此快速的恒星移动导致了引力束缚的星团残余物的形成，这些残余物由一些明亮的恒星围绕着一个BHs星团。对观测者来说，这样的天体看起来就像一个高度超虚但紧凑的星团，具有很大的质量光比。我们把这样的星团残骸称为“暗星团”，它代表了一种预测的、全新的致密恒星群。暗星团的存在和发现的可能性将对黑洞的出生冲击施加重大限制，并将星团作为黑洞之间重要动力学活动的场所，从而产生各种各样的物理现象。在这个提议的项目中，暗星团的形成和性质将使用实际模拟星团的直接n体计算进行详细和系统的研究。其目的是推断出暗星团的特性，这些特性可以很容易地被观测者用作特征，以寻找这些新预测的具有相当天体物理意义的天体。

In this proposed project the goal is to numerically study the end-phases of star clusters in which a significant number of stellar remnants, i.e., neutron stars (NS) and black holes (BH), are retained following their progenitor supernovae. Preliminary studies indicate that for star clusters residing within the inner few kiloparsec of the Galaxy, the low-mass main-sequence stars are stripped off from the cluster by the external Galactic tidal force on a timescale comparable to or shorter than the BH depletion time due to mutual encounters. Such rapid removal of stars results in the formation of gravitationally bound cluster remnants comprising a cluster of BHs orbited by a few luminous stars. To an observer, such an object would appear as a highly super-virial but compact star cluster with a large mass-to-light-ratio. We nickname such cluster remnants “dark clusters” which represent a predicted, totally new type of compact stellar population. The very existence and the probability of finding dark clusters will impose significant constraints on the natal kicks of BHs and establish star clusters as sites of significant dynamical activities among BHs which give rise to a wide variety of physical phenomena. In this proposed project, the formation and the properties of dark clusters will be studied in detail and systematically using direct N-body computations of realistically modelled star clusters. The aim is to deduce properties of dark clusters that can be readily utilized by observers as signatures, in a search of these newly predicted class of objects of considerable astrophysical significance.