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

• Published in: Monthly notices of the Royal Astronomical Society Vol. 527; no. 3; pp. 7495 - 7514
• Main Authors: Wang, Long, Gieles, Mark, Baumgardt, Holger, Li, Chengyuan, Pang, Xiaoying, Tang, Baitian
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 01.01.2024
• Subjects: Astronomical models; Binary stars; Black holes; Density; Globular clusters; Gravitational waves; Line of sight; Stellar mass; X ray binaries; X ray stars; globular clusters: individual: Palomar 5; binaries: general; techniques: radial velocities; stars: black holes; methods: numerical
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stad3657

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 >105 d 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 104 d, 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 104–105 d in Palomar 5’s inner and tail regions to constrain BH existence.