The Effects of Internal Rotation, Pressure Anisotropy, and Tides on the Dynamics of Globular Clusters

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Abstract

To fully understand the internal dynamics of globular clusters, a number of important physical ingredients, in particular the three-dimensional effects of external tides, internal rotation, and anisotropy in velocity space, should be added to the traditional paradigm that primarily relies on spherical non-rotating models of quasi-relaxed stellar systems. In fact, the acquisition of high-quality structural and kinematical data is rapidly bringing us well beyond such simple dynamical interpretation. Driven by these motivations, I will present a family of triaxial models that incorporate in a self-consistent way the tidal effects of the host galaxy. I will also discuss the effects of the presence of internal rotation and pressure anisotropy, studied by means of two new families of axisymmetric equilibria, flattened by either solid-body or differential rotation. The results of an extensive survey of N-body simulations designed to investigate the dynamical stability and the long-term evolution of the rotating models will then be described. Configurations in the moderate rotation regime are found to be dynamically stable; a first application to the interpretation of the kinematics and morphology of selected Galactic globular clusters is shown to lead to some important conclusions on their internal structure. In turn, a new dynamical instability is observed in models characterized by strong differential rotation, in striking analogy with recent stability analyses of differentially rotating fluid polytropes. Curiously, there also exists an intermediate rotation regime in which systems exhibit a central toroidal structure and are dynamically stable. Within this new dynamical framework, several observational and theoretical issues will be addressed, including the study of the role of angular momentum in the early stages of star cluster formation, the dynamical interplay between angular momentum trasport and two-body relaxation processes, and the kinematical characterization of globular clusters with multiple stellar populations.
Original languageEnglish
Publication statusPublished - 1 Jan 2013

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