Can slow pulsars in Milky Way globular clusters form via partial recycling?

TL;DR

This paper investigates the origin of slow pulsars in globular clusters, concluding that partial recycling via binary interactions is unlikely and proposing alternative formation mechanisms like white dwarf collapse or neutron star collisions.

Contribution

The study combines analytic models and N-body simulations to demonstrate the unlikelihood of partial recycling as the formation pathway for slow pulsars in globular clusters.

Findings

Partial recycling is not feasible in typical globular cluster environments.

White dwarf collapse and neutron star collisions are more plausible formation channels.

Realistic cluster densities do not support the required mass transfer interruptions.

Abstract

Alongside the population of several hundred radio millisecond pulsars currently known in Milky Way globular clusters, a subset of six slowly spinning pulsars (spin periods $0.3-4\,$s) are also observed. With inferred magnetic fields $\gtrsim 10^{11}\,$G and characteristic ages $\lesssim10^8\,$yr, explaining the formation of these apparently young pulsars in old stellar populations poses a major challenge. One popular explanation is that these objects are not actually young but instead have been partially spun up via accretion from a binary companion. In this scenario, accretion in a typical low-mass X-ray binary is interrupted by a dynamical encounter with a neighboring object in the cluster. Instead of complete spin up to millisecond spin periods, the accretion is halted prematurely, leaving behind a ''partially recycled'' neutron star. In this Letter, we use a combination of analytic arguments motivated by low-mass X-ray binary evolution and $N$-body simulations to show that this partial-recycling mechanism is not viable. Realistic globular clusters are not sufficiently dense to interrupt mass transfer on the short timescales required to achieve such slow spin periods. We argue that collapse of massive white dwarfs and/or neutron star collisions are more promising ways to form slow pulsars in old globular clusters.