Neutron star matter as a dilute solution of protons in neutrons

Abstract

Neutron stars contain neutron-rich matter with around 5% protons at nuclear saturation density. In this Letter, we consider equilibrium between bulk phases of matter based on asymmetric nuclear matter calculations using chiral effective field theory interactions rather than, as has been done in the past, by interpolation between the properties of symmetric nuclear matter and pure neutron matter. Neutron drip (coexistence of nuclear matter with pure neutrons) is well established, but from earlier work it is unclear whether proton drip (equilibrium between two phases, both of which contain protons and neutrons) is possible. We find that proton drip is a robust prediction of any physically reasonable equation of state, but that it occurs over a limited region of densities and proton fractions. An analytical model based on expanding the energy in powers of the proton density, rather than the neutron excess, is able to account for these features of the phase diagram.

6 pages, 4 figures, published version

References in corpus (10)

• A unified equation of state of dense matter and neutron star structure
• Equation of state and neutron star properties constrained by nuclear physics and observation
• Constraining the Symmetry Parameters of the Nuclear Interaction
• High-quality two-nucleon potentials up to fifth order of the chiral expansion
• Chiral interactions up to next-to-next-to-next-to-leading order and nuclear saturation
• Cluster Formation and The Virial Equation of State of Low-Density Nuclear Matter
• Chiral Effective Field Theory and the High-Density Nuclear Equation of State
• Influence of light nuclei on neutrino-driven supernova outflows
• New equations of state constrained by nuclear physics, observations, and QCD calculations of high-density nuclear matter
• Nuclear equation of state for arbitrary proton fraction and temperature based on chiral effective field theory and a Gaussian process emulator

Cited by in corpus (6)

• Dense Matter in Neutron Stars with eXTP
• Probing fermionic asymmetric dark matter cores using global neutron star properties
• Connecting Relativistic Density Functional Theory to Microscopic Calculations
• Stellar modeling within regularized 4D Einstein-Gauss-Bonnet gravity in light of current astrophysical constraints
• Neutron star crust and outer core equation of state from chiral effective field theory with quantified uncertainties
• Multicomponent Fermi systems at low densities