Dynamical mass segregation on a very short timescale

TL;DR

This paper demonstrates that star clusters can undergo rapid dynamical mass segregation due to initial substructure and cool conditions, challenging the idea that observed segregation is always primordial.

Contribution

The study shows that dynamical mass segregation can occur on very short timescales in cool, clumpy clusters, driven by dense core formation, which is a novel insight into cluster evolution.

Findings

Mass segregation occurs rapidly in simulations of cool, fractal clusters.

Dense cores form temporarily, facilitating quick mass segregation.

Observed young clusters' segregation may result from dynamical evolution, not primordial conditions.

Abstract

We discuss the observations and theory of star cluster formation to argue that clusters form dynamically cool (subvirial) and with substructure. We then perform an ensemble of simulations of cool, clumpy (fractal) clusters and show that they often dynamically mass segregate on timescales far shorter than expected from simple models. The mass segregation comes about through the production of a short-lived, but very dense core. This shows that in clusters like the Orion Nebula Cluster the stars >4 Msun can dynamically mass segregate within the current age of the cluster. Therefore, the observed mass segregation in apparently dynamically young clusters need not be primordial, but could be the result of rapid and violent early dynamical evolution.