Globular clusters and pulsars

Abstract

Globular clusters are the oldest known stellar system in our Galaxy. It is therefore surprising that they are found to contain relatively large numbers of millisecond pulsars, since these pulsars have a limited active lifetime. Globular cluster pulsars are preferentially found in clusters with massive and dense cores and are often binary with another star. These properties suggest that they are neutron stars which have been captured by a cluster star or binary system and ‘‘recycled,’’ that is, spun up to their present short periods by accretion of mass from the companion. Based on the observed sample of 30 or so pulsars, it is estimated that the total number of pulsars in globular clusters is about 1000. This is about two orders of magnitude greater than the observed number of low‐mass X‐ray binary systems, which places limits on the lifetime of these systems if they are the progenitors of millisecond pulsars. Some pulsars lying close to the core of dense clusters are observed to be accelerated in the clu...