Constraints on physics of neutron stars from X-ray observations

TL;DR

This paper reviews how X-ray observations of neutron stars' surfaces provide constraints on their internal physics, including mass, radius, and matter properties, through spectral analysis and cooling measurements.

Contribution

It synthesizes recent observational data and models to improve understanding of neutron star structure and dense matter physics.

Findings

Neutron star mass and radius constraints inform dense matter equations of state.

X-ray spectral lines and pulsation profiles reveal surface and magnetic field properties.

Cooling measurements constrain superfluidity and neutrino emission in neutron star cores.

Abstract

I summarize some constraints on the physics of neutron stars arising from X-ray observations of the surfaces of neutron stars, focusing on using models of low-magnetic-field neutron star atmospheres to interpret their X-ray spectra. I discuss observations of spectral lines, pulsation profiles, X-ray bursts, radius measurements of transiently accreting neutron stars in quiescence, crust and core cooling measurements of transiently accreting neutron stars, and cooling of young neutron stars. These observations have constrained the neutron star mass and radius (and thus the internal composition, and dense matter equation of state), the superfluidity and neutrino emissivity properties of the core, and the composition and superfluid state of the crust.