Phase Mixing in Stellar Systems and the Nucleus of M31

ast -9900316恒星系统中的相混合和m31的核心。Tremaine正在研究星系和星团等恒星系统动力学的两个方面。第一种是相混合，即由无碰撞等离子体组成的恒星系统达到平衡的过程。相位混合是一个渐进的过程，在这个过程中，系统形成时出现的不规则性越来越紧密地包裹在许多轨道上，因此宏观上恒星系统变得越来越平滑。这些不规则性的持续存在导致了几个重要的效应被研究：星系内部盘和暗晕之间的引力耦合，可能会旋转并使内晕变平；在星系中心附近增强的松弛可能使恒星分布函数各向同性；在恒星的相空间分布中存在着突出的非束缚结构。第二个是偏心星盘的动力学，比如据信存在于附近星系M31中心的那个。这样的圆盘可以在接近开普勒引力势的情况下自然产生，例如靠近被认为位于附近星系中心的大质量中央黑洞。特里梅因博士正在研究接近开普勒势的轴对称恒星盘的稳定性和正常模式，以确定偏心恒星盘是否自然产生，并在星系的年龄中持续存在。

AST-9900316Phase mixing in stellar systems and the nucleus of M31Scott TremaineDr. Tremaine is studying two aspects of the dynamics of systems of stars such as galaxies and star clusters. The first is phase mixing, the process by which a stellar system of collisionless plasma reaches equilibrium. Phase mixing is a gradual process, in which irregularities present at the formation of the system become more and more tightly wrapped over many orbits so that macroscopically the stellar system becomes smoother and smoother. The persistence of these irregularities leads to several important effects that are investigated: gravitational coupling between the disk and dark halo in the inner parts of galaxies, that may spin up and flatten the inner halo; enhanced relaxation near the centers of galaxies that may isotropize the stellar distribution function; and the presence of prominent unbound structures in the phase space distribution of stars. The second is the dynamics of eccentric stellar disks such as the one believed to be present in the center of the nearby galaxy M31. Such disks can arise naturally in a nearly Keplerian gravitational potential, for example close to the massive central black hole that is believed to sit in the centers of nearby galaxies. Dr. Tremaine is studying the stability and normal modes of axisymmetric stellar disks in nearly Keplerian potentials, to determine whether eccentric stellar disks arise naturally and persist for the age of the galaxy.