Multimass modelling of milky way globular clusters – II. Present-day black hole populations

Abstract

Populations of stellar-mass black holes (BHs) in globular clusters (GCs) influence their dynamical evolution and have importantimplications on one of the main formation channels for gravitational wave sources. Inferring the size of these populationsremains difficult, however. In this work, multimass models of 34 Milky Way GCs, first presented in Dickson et al., are used toexplore the present-day BH populations. Direct constraints on both the total and visible mass components provided by severalobservables allow these models to accurately determine the distribution of the dark mass (including BHs) within clusters, aswe demonstrate in a proof-of-concept fitting of the models to mock observations extracted from Monte Carlo cluster models.New constraints on the BH population retained to the present-day in each cluster are inferred from our models. We find thatBH mass fractions ranging from 0 to 1 per cent of the total mass are typically required to explain the observations, except forω Cen, for which we infer a mass fraction above 5 per cent, in agreement with previous works. Relationships between the darkremnant populations and other cluster parameters are examined, demonstrating a clear anticorrelation between the amount ofBHs and mass segregation between visible stars, as well as a correlation between remnant mass fractions and the dynamical ageof clusters. Our inferred BH populations are in good agreement overall with other recent studies using different methodologies,but with notable discrepancies for individual clusters.