Reassessing The Fundamentals: New Constraints on the Evolution, Ages and Masses of Neutron Stars

TL;DR

This paper provides new constraints on neutron star ages and masses, highlighting discrepancies with standard models and proposing a modified age estimate, supported by analysis of pulsar demographics and mass distributions.

Contribution

It introduces a modified spin-down age for millisecond pulsars and refines neutron star mass distribution estimates, incorporating binary evolution constraints.

Findings

Observed pulsar demographics are more diverse than standard models predict.

A modified spin-down age aligns better with true neutron star ages.

Mass distribution peaks at 1.35 and 1.50 solar masses, with a 2 solar mass cutoff.

Abstract

The ages and masses of neutron stars (NSs) are two fundamental threads that make pulsars accessible to other sub-disciplines of astronomy and physics. A realistic and accurate determination of these two derived parameters play an important role in understanding of advanced stages of stellar evolution and the physics that govern relevant processes. Here I summarize new constraints on the ages and masses of NSs with an evolutionary perspective. I show that the observed P-Pdot demographics is more diverse than what is theoretically predicted for the standard evolutionary channel. In particular, standard recycling followed by dipole spin-down fails to reproduce the population of millisecond pulsars with higher magnetic fields (B > 4 x 10^{8} G) at rates deduced from observations. A proper inclusion of constraints arising from binary evolution and mass accretion offers a more realistic insight into the age distribution. By analytically implementing these constraints, I propose a "modified" spin-down age for millisecond pulsars that gives estimates closer to the true age. Finally, I independently analyze the peak, skewness and cutoff values of the underlying mass distribution from a comprehensive list of radio pulsars for which secure mass measurements are available. The inferred mass distribution shows clear peaks at 1.35 Msun and 1.50 Msun for NSs in double neutron star (DNS) and neutron star-white dwarf (NS-WD) systems respectively. I find a mass cutoff at 2 Msun for NSs with WD companions, which establishes a firm lower bound for the maximum mass of NSs.