Observations of the Galactic Centre show evidence of one or two disc-like structures of very young stars orbiting the central super-massive black hole within a distance of a few 0.1 pc. A number of analyses have been carried out to investigate the dynamical behaviour and consequences of these discs, including disc thickness and eccentricity growth as well as mutual interaction and warping. However, most of these studies have neglected the influence of the stellar cusp surrounding the black hole, which is believed to be 1-2 orders of magnitude more massive than the disc(s).
By means of N-body integrations using our bhint code, we study the impact of stellar cusps of different compositions. We find that although the presence of a cusp does have an important effect on the evolution of an otherwise isolated flat disc, its influence on the evolution of disc thickness and warping is rather mild in a two-disc configuration. However, we show that the creation of highly eccentric orbits strongly depends on the graininess of the cusp (i.e. the mean and maximum stellar masses): While Chang (2009) recently found that full cycles of Kozai resonance are prevented by the presence of an analytic cusp, we show that relaxation processes play an important role in such highly dense regions and support short-term resonances. We thus find that young disc stars on initially circular orbits can achieve high eccentricities by resonant effects also in the presence of a cusp of stellar remnants, yielding a mechanism to create S-stars and hyper-velocity stars.
Furthermore, we discuss the underlying initial mass function (IMF) of the young stellar discs and find no definite evidence for a non-canonical IMF.
对Sgr A $^*$（银河系中心的超大质量黑洞）周围最内部秒差距的观察揭示了多种结构，其存在和特征显然违背了动力学的基本原理。在这篇文章中，我们回顾了在过去的二十年中，银河系中心（GC）的观测所带来的动力学理论的挑战。我们概述的理论框架，已开发的理论预测和观测结果之间的差异进行调解。特别是，我们强调最近发现的子秒差距恒星盘在确定动态和解决的不一致性的作用。我们还讨论了Sgr A $^*$最近的活动的影响。
