The effects of binary stars on inferred remnant populations in globular clusters

Abstract

Current, state-of-the-art equilibrium mass models of globular clusters assume that all stars are single, making the effects of binary systems an unknown quantity. In this thesis we develop a method to include realistic binary populations in these models. We use our method to fit three sets of models with varying binary fractions to observations of the globular cluster 47 Tuc. All three sets of models are able to reproduce all observables and differ almost exclusively in their recovered mass function slopes and black hole content while retaining consistent estimates for structural parameters. Models with binary fractions of 0%, 2% and 10% have inferred black hole populations with masses of 135⁺¹⁰⁴_−92 M⊙, 114⁺¹⁴⁴_−79 M⊙ and 81⁺¹²¹ _−81 M⊙ respectively,showing that the inferred black hole content decreases when increasing the assumed binary fraction. We show that this effect is due to binary stars filling a similar role to black holes in the central mass distribution of the cluster indicating that there exists a degeneracy between the adopted binary fraction and the inferred black hole content for some clusters. We further discuss the implications of these results for past and future works.