Long-term evolution of multimass rotating star clusters

TL;DR

This study uses N-body simulations to explore the long-term dynamical evolution of rotating, multimass star clusters, revealing how rotation, energy equipartition, and anisotropy develop over time with respect to stellar mass and spatial distribution.

Contribution

It provides new insights into the evolution of internal kinematics, including rotation, energy equipartition, and anisotropy, in multimass rotating star clusters through detailed simulations.

Findings

Massive stars rotate faster and peak closer to the center.

Energy equipartition evolves faster in the rotational direction for rapid rotators.

Velocity distribution anisotropy is stronger among massive stars.

Abstract

We investigate the long-term dynamical evolution of the internal kinematics of multimass rotating star clusters. We have performed a set of N-body simulations to follow the internal evolution of clusters with different degrees of initial rotation and have explored the evolution of the rotational velocity, the degree of energy equipartition, and anisotropy in the velocity distribution. Our simulations show that: 1) as the cluster evolves, the rotational velocity develops a dependence on the stellar mass with more massive stars characterised by a more rapid rotation and a peak in the rotation curve closer to the cluster centre than low-mass stars; 2) the degree of energy equipartition in the cluster's intermediate and outer regions depends on the component of the velocity dispersion measured; for more rapidly rotating clusters, the evolution towards energy equipartition is more rapid in the direction of the rotational velocity; 3) the anisotropy in the velocity distribution is stronger for massive stars; 4) both the degree of mass segregation and energy equipartition are characterised by spatial anisotropy; they have a dependence on both $R$ and $z$, correlated with the flattening in the spatial variation of the cluster's density and velocity dispersion, as shown by 2D maps of the mass segregation and energy equipartition on the ($R$-$z$) meridional plane.