A Nuclear Equation of State Inferred from Stellar r-process Abundances

Binary neutron star mergers (NSMs) have been confirmed as one source of the heaviest observable elements made by the rapid neutron-capture (r-) process. However, modeling NSM outflows---from the total ejecta masses to their elemental yields---depends on the unknown nuclear equation of state (EOS) that governs neutron-star structure. In this work, we derive a phenomenological EOS by assuming that NSMs are the dominant sources of the heavy-element material in metal-poor stars that display r-process abundance patterns. We start with a population synthesis model to obtain a set of merging neutron-star binaries and calculate their EOS-dependent elemental yields. We then find the EOS such that the yields calculated from these mergers reproduces the abundances of r-process elements derived from observations of metal-poor stars. This EOS therefore represents our best prediction for what neutron stars should look like if they are to be the main progenitors of r-process material in the early universe. We present this EOS and comment on how it compares to both existing EOS models and results from the Neutron Star Interior Composition Explorer.