Measuring energy equipartition in globular clusters

Bianchini, P, Van De Ven, G, Norris, Mark orcid iconORCID: 0000-0002-7001-805X, Schinnerer, E and Varri, A.L (2016) Measuring energy equipartition in globular clusters. In: 2016 Cosmic-Lab Conference: Star Clusters as Cosmic Laboratories for Astrophysics, Dynamics and Fundamental Physics, MODEST 2016, 18 April 2016 through 22 April 2016, Bologna; Italy.

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Globular clusters (GCs) evolve toward a state of partial energy equipartition over their long-term evolution, due to relaxation processes that induce exchange of energy between stars. This establishes a mass-dependent internal kinematics: more-massive stars lose kinetic energy and sink toward the center while less-massive stars gain kinetic energy and move outward. In this contribution, we show how the mass-dependence of the velocity dispersion can be efficiently described, both in simulations and observations, with an exponential function characterized by one parameter indicating how close to full energy equipartition a system is. Moreover, we show that the degree of equipartition reached by a GC tightly correlates with its dynamical state and therefore we propose this equipartition-dynamical state relation as a tool to characterize the relaxation condition of a cluster, based on kinematic measurements.

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