A Dynamical Survey of Stellar-Mass Black Holes in 50 Milky Way Globular Clusters

Abstract

Recent numerical simulations of globular clusters (GCs) have shown that stellar-mass black holes (BHs) play a fundamental role in driving cluster evolution and shaping their present-day structure. Rapidly mass-segregating to the center of GCs, BHs act as a dynamical energy source via repeated super-elastic scattering, delaying onset of core collapse and limiting mass segregation for visible stars. While recent discoveries of BH candidates in Galactic and extragalactic GCs have further piqued interest in BH-mediated cluster dynamics, numerical models show that even if significant BH populations remain in today's GCs, they are typically in configurations that are not directly detectable. We demonstrated in Weatherford et al. ( 2018) that an anti-correlation between a suitable measure of mass segregation (∆) in observable stellar populations and the number of retained BHs in GC models can be applied to indirectly probe BH populations in real GCs. Here, we estimate the number and total mass of BHs presently retained in 50 Milky Way GCs from the ACS Globular Cluster Survey by measuring ∆ between populations of main sequence stars, using correlations found between ∆ and BH retention in the CMC Cluster Catalog models. We demonstrate that the range in ∆'s distribution from our models matches that for observed GCs to a remarkable degree. Our results further provide the narrowest constraints to-date on the retained BH populations in the GCs analyzed. Of these 50 GCs, we identify NGCs 2808, 5927, 5986, 6101, and 6205 to presently contain especially large BH populations, each with total BH mass exceeding 10 3 M .

MOCCA Survey Database: Extra Galactic Globular Clusters. I. Method and first results

“…Meanwhile in Askar et al (2018) a shortlist of 29 Galactic GCs have been reported and the number of GCs shortlisted in Weatherford et al (2019) with N BH > 50 is of 28 Galactic GCs, in this paper only three have been reported. However, some of the GCs listed in Weatherford et al (2019) with N BH > 50 are actually in the "small core radii" models region. This is not completely surprising, since the author did not consider a correlation between the CSB and number of BH inside the GC.…”

“…Harris (1996Harris ( , updated 2010) catalog (name, R c and half-light radius in parsec, CRVD in km/s and CSB in L /pc 2 ) for observed Galactic GC labelled as "large core radii" in this work, that are likely to host a BHS. In bold the clusters that have been reported also in Askar et al (2018), in bold italic the clusters that have been reported also in Weatherford et al (2019).…”

“…4, we compared our "large core radii" models ( which correspond to BHS models), with the list of GCs reported in Askar et al (2018) which could contain a BHS, and the list reported in Weatherford et al (2019), considering only GCs that retain a number of BH N BH > 50. Meanwhile in Askar et al (2018) a shortlist of 29 Galactic GCs have been reported and the number of GCs shortlisted in Weatherford et al (2019) with N BH > 50 is of 28 Galactic GCs, in this paper only three have been reported. However, some of the GCs listed in Weatherford et al (2019) with N BH > 50 are actually in the "small core radii" models region.…”

Gravitational Brownian motion as inhomogeneous diffusion: black hole populations in globular clusters

“…Such a population of a significant number of BHs is believed to exist in the center of many globular clusters. Its existence is supported by numerical and theoretical developments (Merritt et al 2004;Mackey et al 2008;Morscher et al 2013;Breen & Heggie 2013;Morscher et al 2015;Wang et al 2016;Arca-Sedda 2016;Rodriguez et al 2016;Chatterjee et al 2017;Kremer et al 2018;Askar et al 2018;Arca Sedda et al 2018;Weatherford et al 2018Weatherford et al , 2019Kremer et al 2019) as well as observational evidence (Maccarone et al 2007; Barnard et al 2008;Strader et al 2012;Irwin et al 2010;Roberts et al 2012;Chomiuk et al 2013;Miller-Jones et al 2015;Taylor et al 2015;Minniti et al 2015;Bahramian et al 2017;Giesers et al 2018;Shishkovsky et al 2018;Abbate et al 2019). These recent advances are in contrast to a long time belief that globular clusters cannot retain their BHs (Spitzer 1969;Kulkarni et al 1993;Sigurdsson & Hernquist 1993).…”

Illuminating black hole subsystems in young star clusters

“…Along these lines, several groups have suggested that cluster black hole populations (or lack thereof) can be indirectly inferred from structural features, such as a large core radius and low central density (e.g., Merritt et al 2004;Chatterjee et al 2017;Askar et al 2018;Arca Sedda et al 2018;Kremer et al 2019a). Similarly, Weatherford et al (2018Weatherford et al ( , 2019 demonstrated that mass-segregation measurements can be used as a robust indicator of black hole populations in GCs.…”