The time-scale of escape from star clusters

Abstract

In this paper a cluster is modelled as a smooth potential (due to the cluster stars) plus the steady tidal field of the Galaxy. In this model there is a minimum energy below which stars cannot escape. Above this energy, however, the time‐scale on which a star escapes varies with the orbital parameters of the star (mainly its energy) in a way which we attempt to quantify, with both theoretical arguments and computer simulations. Within the limitations of the model we show that the time‐scale is long enough to complicate the interpretation of full N‐body simulations of clusters, and that stars above the escape energy may remain bound to the cluster for about a Hubble time.

The M 4 Core Project with HST: I. Overview and first epoch

“…In addition to the features of the old version, it incorporates the direct Fewbody integrator (Fregeau et al 2004) for three and four-body interactions and a new treatment of the escape process based on Fukushige & Heggie (2000). With the addition of the Fewbody integrator the code can follow all interaction channels that are important for the rate of creation of various types of objects and binaries observed in star clusters, and it ensures that energy generation by binaries nearly matches that in an N-body model.…”

Fractal basins of escape and the formation of spiral arms in a galactic potential with a bar

“…These consist of orbits which approach the unstable periodic Lyapunov orbits around L1/L2 asymptotically for t → +∞ or t → −∞. A few of these asymptotic orbits are shown in Figure 8 of Fukushige & Heggie (2000).…”

The early evolution of star clusters in compressive and extensive tidal fields

“…During this phase the cluster loses mass due to the evolution of massive stars; the effects of mass loss due to stellar evolution have been explored in detail for clusters evolving in an extensive tidal field and have been shown to lead to an early cluster expansion and in some cases to a rapid dissolution (see e.g. Chernoff & Weinberg 1990;Fukushige & Heggie 1995; see also Vesperini 2010 and references therein). Given the possibility that a cluster's early evolution occurs in a compressive tidal field it is important to explore how this field can affect the cluster's response to early evolutionary processes and how the properties set in the primordial tidal field determine the cluster's subsequent evolution after its transition to an extensive tidal field.…”