Neutron Star Equation of State from Crust to Core

With recent advances in neutron star observations, major progress has been made in determining the pressure of neutron star matter at high density. This pressure is constrained by the neutron star deformability, determined from gravitational waves emitted in a neutron-star merger, and measurements of radii of two neutron stars, using a new X-ray observatory on the International Space Station. Alongside these observations, significant constraints are also coming from nuclear experiments, which serve as crucial terrestrial messengers.

 

Previous studies have relied on nuclear theory calculations to provide the equation of state at low density. However, constraints on neutron-rich nuclear matter at higher densities are now beginning to emerge with the advancement of rare-isotopes beam facilities. The current status of nuclear experiments relevant to neutron star physics will be discussed. An example of combining constraints from astronomical observations and nuclear experiments will be presented, and the results will be compared to chiral effective field theory. Its implications on the composition of neutron stars and their cooling via neutrino radiation will also be discussed.