Evolution of Binary Stars in Multiple-Population Globular Clusters - II. Compact Binaries

TL;DR

This study uses N-body simulations to investigate how the binary star populations evolve differently in multiple-generation globular clusters, revealing that second-generation binaries decrease faster and are more centrally concentrated over time.

Contribution

It provides new insights into the dynamical evolution of compact binaries in multiple-population clusters, highlighting the effects of initial structural differences and dynamical processes.

Findings

SG binary fraction decreases faster than FG

Inner binary fraction increases over time due to segregation

Simulation results align with observational data on binary fractions

Abstract

We present the results of a survey of N-body simulations aimed at exploring the evolution of compact binaries in multiple-population globular clusters.We show that as a consequence of the initial differences in the structural properties of the first-generation (FG) and the second-generation (SG) populations and the effects of dynamical processes on binary stars, the SG binary fraction decreases more rapidly than that of the FG population. The difference between the FG and SG binary fraction is qualitatively similar to but quantitatively smaller than that found for wider binaries in our previous investigations.The evolution of the radial variation of the binary fraction is driven by the interplay between binary segregation, ionization and ejection. Ionization and ejection counteract in part the effects of mass segregation but for compact binaries the effects of segregation dominate and the inner binary fraction increases during the cluster evolution. We explore the variation of the difference between the FG and the SG binary fraction with the distance from the cluster centre and its dependence on the binary binding energy and cluster structural parameters. The difference between the binary fraction in the FG and the SG populations found in our simulations is consistent with the results of observational studies finding a smaller binary fraction in the SG population.