Symmetry energy at subnuclear densities and nuclei in neutron star crusts

Department of Materials Science, Kochi University, Akebono-cho, Kochi 780-8520, Japan(Dated: February 9, 2008)We examine how the properties of inhomogeneous nuclear matter at subnuclear densities dependon the density dependence of the symmetry energy. Using a macroscopic nuclear model we calculatethe size and shape of nuclei in neutron star matter at zero temperature in a way dependent onthe density dependence of the symmetry energy. We find that for smaller symmetry energy atsubnuclear densities, corresponding to larger density symmetry coefficient L, the charge number ofnuclei is smaller, and the critical density at which matter with nuclei or bubbles becomes uniform islower. The decrease in the charge number is associated with the dependence of the surface tensionon the nuclear density and the density of a sea of neutrons, while the decrease in the critical densitycan be generally understood in terms of proton clustering instability in uniform matter.