Clusterized nuclear matter in the (proto-)neutron star crust and the symmetry energy

Abstract

Though generally agreed that the symmetry energy plays a dramatic role in determining the structure of neutron stars and the evolution of core-collapsing supernovae, little is known in what concerns its value away from normal nuclear matter density and, even more important, the correct definition of this quantity in the case of unhomogeneous matter. Indeed, nuclear matter traditionally addressed by mean-field models is uniform while clusters are known to exist in the dilute baryonic matter which constitutes the main component of compact objects outer shells. In the present work we investigate the meaning of symmetry energy in the case of clusterized systems and the sensitivity of the proto-neutron star composition and equation of state to the effective interaction. To this aim an improved Nuclear Statistical Equilibrium (NSE) model is developed, where the same effective interaction is consistently used to determine the clusters and unbound particles energy functionals in the self-consistent mean-field approximation. In the same framework, in-medium modifications to the cluster energies due to the presence of the nuclear gas are evaluated. We show that the excluded volume effect does not exhaust the in-medium effects and an extra isospin and density dependent energy shift has to be considered to consistently determine the composition of subsaturation stellar matter. The symmetry energy of diluted matter is seen to depend on the isovector properties of the effective interaction, but its behavior with density and its quantitative value are strongly modified by clusterization.

A contribution to the upcoming EPJA Special Volume on Nuclear Symmetry Energy

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• Neutron skins and neutron stars
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Cited by in corpus (23)

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• Neutron star radii and crusts: uncertainties and unified equations of state
• Towards Understanding Astrophysical Effects of Nuclear Symmetry Energy
• Unified treatment of sub-saturation stellar matter at zero and finite temperature
• Nuclear Equation of state for Compact Stars and Supernovae
• Collision dynamics at medium and relativistic energies
• Constraining supernova equations of state with equilibrium constants from heavy-ion collisions
• EoS for hot neutron stars
• Connecting the nuclear EoS to the interplay between fusion and quasifission processes in low-energy nuclear reactions
• Nuclear Statistical Equilibrium Equation of State for Core Collapse
• In-medium nuclear cluster energies within the Extended Thomas-Fermi approach
• Dipole response in neutron-rich nuclei with new Skyrme interactions
• Interplay between low-lying isoscalar and isovector dipole modes: a comparative analysis between semi-classical and quantum approaches
• Low density nuclear matter with light clusters in a generalized nonlinear relativistic mean-field model
• Light clusters in dilute heavy-baryon admixed nuclear matter
• The proto-neutron star inner crust in the liquid phase
• Pre-equilibrium effects in charge-asymmetric low-energy reactions
• Pairing effects on neutrino transport in low-density stellar matter
• Finite size effects on the phase diagram of the thermodynamical cluster model
• Experimental study of the ${}^{40,48}$Ca+ ${}^{40,48}$Ca reactions at 35 MeV/nucleon
• The property difference between the neutron star PSR J0348+0432 and its proto neutron star
• Cold dilute nuclear matter with $\alpha$-particle condensation in a generalized nonlinear relativistic mean-field model
• Effects of symmetry energy and momentum dependent interaction on low-energy reaction mechanisms