The influence of black holes on the binary population of the globular cluster Palomar 5

TL;DR

This study uses N-body simulations to explore how black holes influence binary populations and cluster dynamics in Palomar 5, revealing that black holes significantly affect binary disruption and mass function, with implications for future observations.

Contribution

It provides the first detailed simulation-based analysis of black hole effects on binary populations in Palomar 5, incorporating primordial binaries and predicting observable signatures.

Findings

Primordial binaries have minimal impact on long-term evolution.

Black holes decrease the fraction of wide binaries with periods >10^5 days.

Multi-epoch spectroscopy can detect most bright binaries with periods below 10^4 days.

Abstract

The discovery of stellar-mass black holes (BHs) in globular clusters (GCs) raises the possibility of long-term retention of BHs within GCs. These BHs influence various astrophysical processes, including merger-driven gravitational waves and the formation of X-ray binaries. They also impact cluster dynamics by heating and creating low-density cores. Previous N-body models suggested that Palomar 5, a low-density GC with long tidal tails, may contain more than 100 BHs. To test this scenario, we conduct N-body simulations of Palomar 5 with primordial binaries to explore the influence of BHs on binary populations and the stellar mass function. Our results show that primordial binaries have minimal effect on the long-term evolution. In dense clusters with BHs, the fraction of wide binaries with periods >$10^5$ days decreases, and the disruption rate is independent of the initial period distribution. Multi-epoch spectroscopic observations of line-of-sight velocity changes can detect most bright binaries with periods below $10^4$ days, significantly improving velocity dispersion measurements. Four BH-MS binaries in the model with BHs suggests their possible detection through the same observation method. Including primordial binaries leads to a flatter inferred mass function because of spatially unresolved binaries, leading to a better match of the observations than models without binaries, particularly in Palomar 5's inner region. Future observations should focus on the cluster velocity dispersion and binaries with periods of $10^4-10^5$ days in Palomar 5's inner and tail regions to constrain BH existence.