Rapid dynamical mass segregation and properties of fractal star clusters

TL;DR

This study uses N-body simulations to show that young star clusters rapidly undergo mass segregation influenced by initial conditions, with some stars escaping and exhibiting inverse mass segregation in velocity space.

Contribution

It introduces a modified MST method for measuring mass segregation and highlights the effects of initial velocity distribution and star escape on cluster evolution.

Findings

Mass segregation occurs within 0.5 Myr in fractal clusters.

Stars escaping influence the degree of mass segregation over time.

Massive stars have higher velocity dispersions than lower-mass stars.

Abstract

We investigate the evolution of young star clusters using N-body simulations. We confirm that subvirial and fractal-structured clusters will dynamically mass segregate on a short timescale (within 0.5 Myr). We adopt a modified minimum-spanning-tree (MST) method to measure the degree of mass segregation, demonstrating that the stars escaping from a cluster's potential are important for the temporal dependence of mass segregation in the cluster. The form of the initial velocity distribution will also affect the degree of mass segregation. If it depends on radius, the outer parts of the cluster would expand without undergoing collapse. In velocity space, we find 'inverse mass segregation,' which indicates that massive stars have higher velocity dispersions than their lower-mass counterparts.