Standalone Validation of a Pulsar Evolution Subroutine for NBODY6++GPU: Seven Test Scenarios

Abstract

Pulsars in globular clusters provide critical constraints on the evolution of compact objects. However, the treatment of neutron stars in standard N-body codes is outdated, and requires a better implementation of magnetic field decay, spin evolution, and accretion driven recycling that shape their observable properties. We present a standalone validation of a pulsar evolution subroutine for NBODY6++GPU, systematically tested across seven controlled scenarios prior to integration into full cluster simulations. These scenarios isolate distinct evolutionary regimes, including young pulsar spin down, millisecond pulsar weak torque evolution, accretion driven recycling in X-ray binaries, environmental torques in dense cores, wide binary systems, and compact binaries in the dipole spin-down regime. Through two separate numerical implementations, we achieve cross validation demonstrating better than 0.1% agreement across all physical quantities and timescales. Our validation confirms that analytical solutions are reproduced with high precision for isolated pulsars, gigayear scale evolution (tau_c ~ 1.0 Gyr) matches observations of millisecond pulsars in clusters like 47 Tucanae, and accretion driven recycling operates with physically realistic timescales, yielding a final period of 1.0 ms and a period derivative of approximately -5.9e-19 s/s, with accretion dominance by a factor of about 14. We demonstrate that environmental torques remain negligible even in the densest cluster environments, while compact binary spin down is validated; gravitational wave orbital decay is deferred to future work. All validation codes, test suites, and integration instructions are publicly available to support future applications.

arXiv commentAccepted for publication in Research in Astronomy and Astrophysics (RAA). 22 pages, 15 figures

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