Equation of State of Neutron Stars Measured via Astronomical Observations

Abstract

The equation of state inside neutron stars is an important unsolved problem in modern physics. Astronomical observations to measure the mass and radius of neutron stars provide essential information of the high-density region that cannot be tested by ground-based nuclear experiments. In this review, we report on the current status of solving the equation of state, which has been narrowed down by the latest results from the NICER X-ray observatory, radio observations of pulsars, nuclear experiments, and gravitational wave observations.