Mass loss from massive globular clusters in tidal fields

TL;DR

This study uses N-body simulations to analyze star loss mechanisms in massive globular clusters under tidal influences, revealing that external tidal interactions dominate over internal processes, with clusters surviving for cosmological timescales.

Contribution

It provides a comparative analysis of different N-body codes and identifies the dominant star escape processes in globular clusters within tidal fields.

Findings

Sweeps are more common than kicks in star escape.

Mass loss rates are low, allowing clusters to survive for tens of Hubble times.

Numerical artifacts depend on the N-body code parameters.

Abstract

Massive globular clusters lose stars via internal and external processes. Internal processes include mainly two-body relaxation, while external processes include interactions with the Galactic tidal field. We perform a suite of N-body simulations of such massive clusters using three different direct-summation N-body codes, exploring different Galactic orbits and particle numbers. By inspecting the rate at which a star's energy changes as it becomes energetically unbound from the cluster, we can neatly identify two populations we call kicks and sweeps, that escape through two-body encounters internal to the cluster and the external tidal field, respectively. We find that for a typical halo globular cluster on a moderately eccentric orbit, sweeps are far more common than kicks but the total mass loss rate is so low that these clusters can survive for tens of Hubble times. The different N-body codes give largely consistent results, but we find that numerical artifacts may arise in relation to the time step parameter of the Hermite integration scheme, namely that the value required for convergent results is sensitive to the number of particles.