Predictions for Triple Stars with and without a Pulsar in Star Clusters

TL;DR

This paper predicts the occurrence and characteristics of triple star systems with pulsars in globular clusters using extensive simulations, suggesting such systems are rare but likely detectable soon.

Contribution

It provides the first detailed predictions for the abundance and properties of triple systems with pulsars in star clusters based on large-scale simulations.

Findings

Triple systems with pulsars are predicted to be two orders of magnitude rarer than binaries.

Simulations show the expected abundance of such triples in dense cluster cores.

Results are validated against models with realistic stellar mass spectra.

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 N_{tot} of equal mass stars from N_{tot}=512 to N_{tot}=19661 and a primordial binary fraction from 0-50%. In addition, we validate our results against simulations with N=19661 that include a mass spectrum with a turn-off mass at 0.8 M_{sun}, 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 don't have to wait too long for the first comparable-mass triple with a pulsar to be detected.