Early dynamics and violent relaxation of multimass rotating star clusters

Alexander Livernois,Enrico Vesperini,Maria Tiongco,Anna Lisa Varri,Emanuele Dalessandro

doi:10.1093/mnras/stab2119

Abstract

ABSTRACT We present the results of a study aimed at exploring, by means of N-body simulations, the evolution of rotating multimass 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.

Highlights

Many recent observational studies have significantly improved our understanding of the dynamical properties of star clusters and provided key constraints for the study of the dynamical evolution of these systems and the role played by different dynamical processes
Studies of clusters’ formation and very early evolution have shown that clusters can emerge from these evolutionary phases with dynamical properties characterized by mass segregation, internal rotation, and radial anisotropy in the velocity distribution; the detailed role of different dynamical processes acting during these phases and the variety of different dynamical paths resulting in these dynamical properties are still matter of intense investigation
We present the results of a suite of N-body simulations aimed at exploring the dynamics of rotating clusters during the violent relaxation phase, in the presence of a weak external tidal field

Summary

Introduction

Many recent observational studies have significantly improved our understanding of the dynamical properties of star clusters and provided key constraints for the study of the dynamical evolution of these systems and the role played by different dynamical processes. The observational study of young star clusters has received growing interest in the last several years (see e.g. Kuhn et al 2013, 2014, 2015a, 2015b, Getman et al 2018), and thanks to data from the Gaia mission, significant progress has been made in the study of their internal kinematic properties Studies of clusters’ formation and very early evolution have shown that clusters can emerge from these evolutionary phases with dynamical properties characterized by mass segregation, internal rotation, and radial anisotropy in the velocity distribution; the detailed role of different dynamical processes acting during these phases and the variety of different dynamical paths resulting in these dynamical properties are still matter of intense investigation Studies of clusters’ formation and very early evolution have shown that clusters can emerge from these evolutionary phases with dynamical properties characterized by mass segregation, internal rotation, and radial anisotropy in the velocity distribution; the detailed role of different dynamical processes acting during these phases and the variety of different dynamical paths resulting in these dynamical properties are still matter of intense investigation (see e.g. Goodwin & Whitworth 2004, McMillan et al 2007, Allison et al 2009, 2010, Moeckel & Bonnell 2009, Fujii et al 2012, Fujii & Portegies Zwart 2016, Vesperini et al 2014, Parker et al 2016, Domínguez et al 2017, Mapelli 2017, Banerjee & Kroupa 2014, 2017, 2018, Sills et al 2018, Daffern-Powell & Parker 2020, Ballone et al 2020, Ballone et al 2021)

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Conclusion