A systematic analysis of star cluster disruption by tidal shocks -- I. Controlled N-body simulations and a new theoretical model

Abstract

Understanding the evolution of stellar clusters in an evolving tidal field is critical for studying the disruption of stellar clusters in a cosmological context. We systematically characterise the response of stellar clusters to tidal shocks using controlled \(N\)-body simulations of clusters with various properties that are subjected to different types of shocks. We find that the strength of the shock and the density of the cluster within the half-mass radius are the dominant properties that drive the amount of mass lost by the cluster, with the shape of the cluster profile being of minor influence. When the shock is applied as two separate sub-shocks, the amount of mass loss during the second sub-shock is sensitive to the gap time between them. Clusters that experience successive sub-shocks separated by less than their crossing time attain the same masses and sizes at the end of the simulation. However, clusters subjected to sub-shocks separated by more than a crossing time experience different evolutionary histories. The amount of mass lost in the \(N\)-body models and its scaling with shock and cluster properties differs from that predicted by classical tidal disruption theory. We demonstrate that the discrepancy is alleviated by including a dependence on the escape time-scale of unbound stars, analogously to mass loss driven by two-body relaxation. With our new theoretical model for shock-driven mass loss, the predicted relative amounts of mass loss agree with the results of the \(N\)-body simulations to \(\sim0.3 \ \rm{dex}\) across the full suite of simulations.