Predictions for triple stars with and without a pulsar in star clusters

Abstract

Though about 80 pulsar binaries have been detected in globular clusters so far, no pulsar has been found in a triple system in which all three objects are of comparable mass. Here, we present predictions for the abundance of such triple systems, and for the most likely characteristics of these systems. Our predictions are based on an extensive set of more than 500 direct simulations of star clusters with primordial binaries, and a number of additional runs containing primordial triples. Our simulations employ a number Ntot of equal-mass stars from Ntot = 512 to 19 661 and a primordial binary fraction from 0 to 50 per cent. In addition, we validate our results against simulations with N = 19 661 that include a mass spectrum with a turn-off mass at 0.8 M⊙, appropriate to describe the old stellar populations of Galactic globular clusters. Based on our simulations, we expect that typical triple abundances in the core of a dense cluster are two orders of magnitude lower than the binary abundances, which in itself already suggests that we do not have to wait too long for the first comparable-mass triple with a pulsar to be detected. © 2008 The Authors.