Early dynamics and violent relaxation of multi-mass rotating star clusters

TL;DR

This study uses N-body simulations to investigate how rotating multi-mass star clusters evolve during violent relaxation, revealing mass segregation, energy equipartition, and differential rotation among stars.

Contribution

It provides new insights into the impact of initial rotation and mass spectrum on the violent relaxation process and the resulting cluster properties.

Findings

Massive stars rotate faster than low-mass stars.

Massive stars tend to segregate into orbits aligned with cluster rotation.

Clusters evolve towards spatial mass segregation and energy equipartition.

Abstract

We present the results of a study aimed at exploring, by means of N-body simulations, the evolution of rotating multi-mass star clusters during the violent relaxation phase, in the presence of a weak external tidal field. We study the implications of the initial rotation and the presence of a mass spectrum for the violent relaxation dynamics and the final properties of the equilibria emerging at the end of this stage. Our simulations show a clear manifestation of the evolution towards spatial mass segregation and evolution towards energy equipartition during and at the end of the violent relaxation phase. We study the final rotational kinematics and show that massive stars tend to rotate more rapidly than low-mass stars around the axis of cluster rotation. Our analysis also reveals that during the violent relaxation phase, massive stars tend to preferentially segregate into orbits with angular momentum aligned with the cluster's angular momentum, an effect previously found in the context of the long-term evolution of star clusters driven by two-body relaxation.