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Modelling Millisecond Pulsar Populations in Globular Clusters with NBODY6++GPU

Yuzhe Song, Debatri Chattopadhyay, Jarrod Hurley, Rainer Spurzem, Francesco Flammini Dotti, Kai Wu

TL;DR

This study extends direct $N$-body simulations of globular clusters by incorporating a realistic pulsar evolution model that includes magnetic-braking spin-down, magnetic-field decay, and accretion-driven spin-up during Roche-lobe overflow or common-envelope phases. The NBODY6++GPU framework is updated with a pulsar switch and input-driven birth distributions, and applied to a M71-like cluster to forecast MSP demographics, binary fractions, and related gravitational-wave transients. Preliminary results at 20 Myr show a large isolated MSP population with a minority in binaries, enabling forecasts of radio detectability and comparisons to $\gamma$-ray emission and LVK merger rates. The approach provides a physically grounded link between GC dynamics and MSP populations, with concrete predictions for current and future radio surveys and gravitational-wave observations.

Abstract

Millisecond pulsars (MSPs) are neutron stars with spin periods as short as a few milliseconds, formed through mass accretion from companion stars. In the dense environments of globular clusters (GCs), MSPs are likely to originate through dynamically assembled interacting binaries. Over 300 MSPs have been detected in GCs to date, more than half of the known Galactic MSP population. In this work, we model MSP populations in intermediate-mass GCs using the direct $N$-body code \textsc{NBODY6++GPU}. We update the code by implementing pulsar spin-down due to magnetic braking and spin-up through accretion, and use this framework to model the pulsar population in the globular cluster M71 to investigate the pulsar population within and the associated gravitational wave transients.

Modelling Millisecond Pulsar Populations in Globular Clusters with NBODY6++GPU

TL;DR

This study extends direct -body simulations of globular clusters by incorporating a realistic pulsar evolution model that includes magnetic-braking spin-down, magnetic-field decay, and accretion-driven spin-up during Roche-lobe overflow or common-envelope phases. The NBODY6++GPU framework is updated with a pulsar switch and input-driven birth distributions, and applied to a M71-like cluster to forecast MSP demographics, binary fractions, and related gravitational-wave transients. Preliminary results at 20 Myr show a large isolated MSP population with a minority in binaries, enabling forecasts of radio detectability and comparisons to -ray emission and LVK merger rates. The approach provides a physically grounded link between GC dynamics and MSP populations, with concrete predictions for current and future radio surveys and gravitational-wave observations.

Abstract

Millisecond pulsars (MSPs) are neutron stars with spin periods as short as a few milliseconds, formed through mass accretion from companion stars. In the dense environments of globular clusters (GCs), MSPs are likely to originate through dynamically assembled interacting binaries. Over 300 MSPs have been detected in GCs to date, more than half of the known Galactic MSP population. In this work, we model MSP populations in intermediate-mass GCs using the direct -body code \textsc{NBODY6++GPU}. We update the code by implementing pulsar spin-down due to magnetic braking and spin-up through accretion, and use this framework to model the pulsar population in the globular cluster M71 to investigate the pulsar population within and the associated gravitational wave transients.

Paper Structure

This paper contains 7 sections, 10 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Pulsar Evolution Model
  3. Evolution of Isolated Pulsars
  4. Evolution of Pulsars in Roche Lobe Overflow
  5. Evolution of Pulsars in Common Envelope
  6. N-body Simulation and Preliminary Results
  7. Follow-up

Figures (1)

  • Figure 1: Left: Spatial distribution of cluster members (gray) and pulsars (blue). The black dashed circle marks the half-mass radius, and the red dashed circle the core radius. Right: $P$–$\dot{P}$ diagram of pulsars at 20 Myr. The population includes 179 isolated pulsars and 2 pulsars in binaries.