On the mass distribution of neutron stars

TL;DR

This paper uses Bayesian inference to analyze neutron star mass data, revealing a likely bimodal distribution with peaks around 1.37 and 1.73 solar masses, challenging single-mass models and exploring potential low-mass subgroups.

Contribution

It provides the first Bayesian analysis indicating a bimodal mass distribution of neutron stars, supporting different evolutionary origins for the peaks.

Findings

Evidence for a bimodal mass distribution with peaks at 1.37 and 1.73 solar masses.

Weak evidence for a low-mass subgroup around 1.25 solar masses.

Supports the idea of different evolutionary histories for neutron star populations.

Abstract

The distribution of masses for neutron stars is analyzed using the Bayesian statistical inference, evaluating the likelihood of proposed gaussian peaks by using fifty-four measured points obtained in a variety of systems. The results strongly suggest the existence of a bimodal distribution of the masses, with the first peak around $1.37 {M_{\odot}}$, and a much wider second peak at $1.73 {M_{\odot}}$. The results support earlier views related to the different evolutionary histories of the members for the first two peaks, which produces a natural separation (even if no attempt to "label" the systems has been made here), and argues against the single-mass scale viewpoint. The bimodal distribution can also accommodate the recent findings of $\sim M_{\odot}$ masses quite naturally. Finally, we explore the existence of a subgroup around $1.25 {M_{\odot}}$, finding weak, if any, evidence for it. This recently claimed low-mass subgroup, possibly related to $O-Mg-Ne$ core collapse events, has a monotonically decreasing likelihood and does not stand out clearly from the rest of the sample.