Feeding and Feedback in the Nucleus of our Galaxy

最新的望远镜和仪器为研究星系核附近超大质量黑洞（SMBHs）周围的极端环境提供了前所未有的机会。了解这些生活在大多数星系中心的奇异物体的物理特性，对于检验广义相对论以及阐明它们对星系形成和演化的影响至关重要。一个特别好的实验室是我们自己的银河系中心，在那里持续监测年轻恒星（s -星）团在SMBH内部几个光月的轨道，可以精确地推导出它的质量。尽管如此，在这些距离上的气体分布及其从邦迪半径向上到黑洞事件视界的吸积存在许多不确定性。在第一个项目中，我们建议使用s星的风作为诊断工具来推断距离SMBH几千史瓦西半径处的吸积流的特性（即密度和温度分布）（目前没有观测可以提供直接估计）。这将通过流体动力学模拟的方式来完成，这是我们小组研究气体和尘埃云G2时所采用的方法，并通过将所得的观测结果与整个电磁波谱中现有的和未来的观测结果进行彻底的比较。特别令人感兴趣的是恒星S2，它将在2018年初进行下一次（非常好观察的）近中心通道。第二个项目将包括整个s星团的模拟，以了解来自这些恒星的风如何影响内部几个月内各种气相的动力学和热力学。这将告诉我们它们对进入SMBH的吸积流是否有正反馈或负反馈作用。

The most up-to-date telescopes and instruments have offered an unprecedented opportunity to study the extreme environment surrounding supermassive black holes (SMBHs) in nearby galactic nuclei. Understanding the physics of these exotic objects, living in the center of most galaxies, is crucial to test General Relativity and to shed light on their impact on galaxy formation and evolution. A particularly good laboratory is our own Galactic Center, where continuous monitoring of the orbits of the young star (S-star) cluster in the inner few light months from the SMBH has allowed a precise derivation of its mass. Still, many uncertainties exist concerning the gas distribution at those distances and its accretion from the Bondi radius up to the black hole event horizon. In a first project, we propose to use the winds of the S-stars as diagnostic tools to infer the properties of the accretion flow (i.e., its density and temperature distributions) at a few thousand Schwarzschild radii from the SMBH (where no current observation can provide a direct estimate). This will be done by means of hydrodynamic simulations, of the type performed by our group to study the gas and dust cloud G2 and by a thorough comparison of the resulting observables with available and future observations throughout the electromagnetic spectrum. Of particular interest is the star S2 which will have its next (very well observed) peri-center passage in early 2018. The second project will consist of a simulation including the whole S-star cluster, to understand how the winds from these stars influence the dynamics and thermodynamics of the various gas phases in the inner few light months. This will tell us whether they have a positive or negative feedback effect on the accretion flow onto the SMBH.