Single Millisecond Pulsars from Dynamical Interaction Processes in Dense Star Clusters

TL;DR

This study uses N-body models to explain the high ratio of single to binary millisecond pulsars in dense globular clusters, highlighting the roles of tidal disruption and white-dwarf mergers.

Contribution

The paper introduces novel N-body simulations that identify two key dynamical processes responsible for the prevalence of single pulsars in dense star clusters.

Findings

Binary disruption is ineffective in dense clusters.

Tidal disruption of main-sequence stars by neutron stars is significant.

White-dwarf merger remnants may be linked to fast radio bursts.

Abstract

Globular clusters (GCs) are particularly efficient at forming millisecond pulsars. Among these pulsars, about half lack a companion star, a significantly higher fraction than in the Galactic field. This fraction increases further in some of the densest GCs, especially those that have undergone core collapse, suggesting that dynamical interaction processes play a key role. For the first time, we create N-body models that reproduce the ratio of single-to-binary pulsars in Milky-Way-like GCs. We focus especially on NGC 6752, a typical core-collapsed cluster with many observed millisecond pulsars. Previous studies suggested that an increased rate of neutron star binary disruption in the densest clusters could explain the overabundance of single pulsars in these systems. Here, we demonstrate that binary disruption is ineffective and instead we propose that two additional dynamical processes play the dominant role: (1) tidal disruption of main-sequence stars by neutron stars; and (2) gravitational collapse of heavy white-dwarf-binary merger remnants. Neutron stars formed through these processes may also be associated with fast radio bursts similar to those observed recently in an extragalactic GC.