Neutron stars and the equation of state of dense matter

Investigating constraints on the poorly understood equation of state for the dense, neutron-rich matter that makes up neutron stars could have significance both to the study of compact objects and to nuclear theory. One such constraint comes from the neutron radius in heavy nuclei. Nuclei such as 208Pb have a density similar to the central density of low mass (M ≈ 0.5 M⊙ , M⊙ = 1 solar mass) neutron stars. Thus, the low density equation of state determines both the neutron radius of the nuclei and the radius of low mass neutron stars. By using relativistic mean field theory fit to properties of symmetric and neutron-rich nuclear matter we have demonstrated a strong correlation between the neutron skin thickness in 208Pb and the radius of low mass neutron stars. Although they may not be found in nature, this research has shown that an experimental value for the skin thickness in 208Pb combined with even a single radius measurement for a neutron star can be used to constrain the high density equation of state. The equation of state of dense matter is also important in core-collapse supernova simulations where shock resuscitation may be sensitive to the radius at which neutrinos stream freely from the young, hot proto-neutron star. Consequently, it is important to investigate the sensitivity of this neutrinosphere to different equations of state including those with exotic phases or some other softening mechanism. By extending the mean field model to finite temperatures and introducing artifical softening for several equations of state, our research has demonstrated that the radius of the neutrinosphere can be varied by as much as 20 km at temperatures near 20 MeV, indicating that soft equations of state could significantly affect supernova simulations. In the future, this could be tested by running core-collapse simulations with and without softened equations of state and then comparing the results.