# Optimal neutron-star mass ranges to constrain the equation of state of nuclear matter with electromagnetic and gravitational-wave observations

## TL;DR

This study uses a vast library of neutron star models to determine which mass ranges for radius measurements best constrain the nuclear matter equation of state, highlighting the importance of different mass regimes.

## Contribution

It provides a quantitative analysis of how electromagnetic radius measurements at specific neutron star masses can optimize constraints on the nuclear matter EOS.

## Key findings

- Radius measurements of neutron stars with 1.7-1.85 M_sun best constrain low-density EOS.
- Massive neutron stars (>2.1 M_sun) are less effective for EOS constraints.
- Future observations can significantly improve understanding of nuclear matter at high densities.

## Abstract

Exploiting a very large library of physically plausible equations of state (EOSs) containing more than $10^{7}$ members and yielding more than $10^{9}$ stellar models, we conduct a survey of the impact that a neutron-star radius measurement via electromagnetic observations can have on the EOS of nuclear matter. Such measurements are soon to be expected from the ongoing \textit{Neutron Star Interior Composition Explorer} mission and will complement the constraints on the EOS from gravitational-wave detections. Thanks to the large statistical range of our EOS library, we can obtain a first quantitative estimate of the commonly made assumption that the high-density part of the EOS is best constrained when measuring the radius of the most massive, albeit rare, neutron stars with masses $M\gtrsim2.1\,M_\odot$. At the same time, we find that radius measurements of neutron stars with masses $M\simeq1.7-1.85\,M_\odot$ can provide the strongest constraints on the low-density part of the EOS. Finally, we quantify how radius measurements by future missions can further improve our understanding of the EOS of matter at nuclear densities.