The Composition of Dense Matter from Neutron Star Observations

Neutron stars are unique probes of the physics of hot and dense matter. Neutron star observations have begun to provide important constraints on the dense matter equation of state, e.g. the relationship between pressure and energy density. While, there are few previous constraints on the composition of dense matter, we show that, presuming a model of dense matter which does not contain any exotic particles, observations of neutron star cooling constrain the number of protons per baryon to exceed than ten percent at twice the density in the center of a nucleus. We discuss briefly the importance of combining different equations of state in the Modular Unified Solver of the Equation of State framework. Finally, we offer a short overview of how machine learning based estimators could be utilized in the field of nuclear astrophysics.