On the disruption of pulsar and X-ray binaries in globular clusters

¹ Department of Astrophysics/IMAPPRadboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
e-mail: F.Verbunt@astro.ru.nl
² SRON Netherlands Institute for Space Research, Utrecht, The Netherlands
³ Max-Planck-Institut für Radioastronomie, auf dem Hügel 69, 53121 Bonn, Germany
e-mail: pfreire@mpifr-bonn.mpg.de

Received: 28 January 2013
Accepted: 17 October 2013

Abstract

The stellar encounter rate Γ has been shown to be strongly correlated with the number of X-ray binaries in globular clusters (GCs) and also to the number of radio pulsars. However, the pulsar populations in different GCs show remarkably different characteristics: in some GCs the population is dominated by binary systems, in others by single pulsars and exotic systems that result from exchange encounters. In this paper, we describe a second dynamical parameter for GCs, the encounter rate for a single binary, γ. We find that this parameter provides a good characterization of the differences between the pulsar populations of different GCs. The higher γ is for any particular GC, the more isolated pulsars and products of exchange interactions are observed. Furthermore, we also find that slow and “young” pulsars are found almost exclusively in clusters with a high γ; this suggests that these kinds of objects are formed by the disruption of X-ray binaries, thus halting the recycling of a previously dead neutron star. We discuss the implications of this for the nature of young pulsars and for the formation of neutron stars in GCs.