The birth mass function of neutron stars

TL;DR

This study constrains the birth mass distribution of neutron stars, revealing a unimodal power-law shape that informs supernova and stellar evolution theories, and suggests massive stars above 18 solar masses do not produce neutron stars.

Contribution

It provides the first probabilistic analysis of neutron star birth masses, favoring a power-law distribution over the traditional double-Gaussian model.

Findings

Neutron star birth masses follow a unimodal power-law distribution.

The distribution peaks at approximately 1.27 solar masses.

Massive stars above 18 solar masses likely do not form neutron stars.

Abstract

The birth mass function of neutron stars encodes rich information about supernova explosions, double star evolution, and properties of matter under extreme conditions. To date, it has remained poorly constrained by observations, however. Applying probabilistic corrections to account for mass accreted by recycled pulsars in binary systems to mass measurements of 90 neutron stars, we find that the birth masses of neutron stars can be described by a unimodal distribution that smoothly turns on at $1.1 M_{\odot}$, peaks at $1.27 M_{\odot}$, before declining as a steep power law. Such a ``turn-on" power-law distribution is strongly favoured against the widely-adopted empirical double-Gaussian model at the $3 \sigma$ level. The power-law shape may be inherited from the initial mass function of massive stars, but the relative dearth of massive neutron stars implies that single stars with initial masses greater than $\approx 18 M_{\odot}$ do not form neutron stars, in agreement with the absence of massive red supergiant progenitors to supernovae.