On the masses of neutron stars

TL;DR

This paper re-evaluates neutron star masses using X-ray binary observations, emphasizing realistic uncertainty assessments, but finds current data insufficient to constrain the neutron star equation of state.

Contribution

It provides a consistent analysis of observational data with improved uncertainty estimates, highlighting the need for better optical measurements to advance understanding.

Findings

Confidence limits are less optimistic than previous estimates.

Current data do not firmly constrain the neutron star equation of state.

No firm upper mass limit for neutron stars can be established yet.

Abstract

We analyze the currently available observations of X-ray binaries in a consistent way, to re-determine the masses of the neutron stars in these systems. In particular, our attention is focussed on a realistic and consistent assessment of observational uncertainties and sources of systematic error. Confidence limits for these new mass estimates are generally less optimistic than previously assumed. The available observations, including data on six radio pulsars, do not firmly constrain the equation of state of neutron star matter. In particular, a firm upper mass limit cannot yet be established. An improvement of the accuracy of optical data holds the key to further progress.