Insights into spatial mixing of multiple populations in dynamically-young globular clusters

TL;DR

This study explores how binary star interactions can influence the spatial distribution and mixing of multiple stellar populations in young globular clusters, providing insights into their dynamical evolution.

Contribution

It demonstrates that binary interactions can significantly alter the radial distributions of stellar populations, explaining observed mixing in some young globular clusters.

Findings

A single massive binary can displace P2 outward.

Multiple binaries are needed for full mixing within a few relaxation times.

Results align with observed properties of certain young GCs.

Abstract

Many galactic globular clusters (GCs) contain at least two stellar populations. Recent observational studies found that the radial distributions of the first (P1) and second population (P2) differ in dynamically-young GCs. Since P2 is conventionally assumed to form more centrally concentrated, the rapid mixing (or even inversion) in some GCs but not others is puzzling. We investigate whether dynamical processes specific to certain GCs might cause this. Specifically, we evaluate the expansion of P2 by binary-single interactions in the cluster core and whether these can mix the P1/P2 radial distributions, using a set of toy-models with varying numbers and masses of primordial binaries. We find that even one massive binary star can push the central P2 outwards, but multiple binaries are required to fully mix P1 and P2 within a few relaxation times. We also compare our results to observed properties of mixed young GCs (NGC 4590, 5053, or 5904).