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Title: Symmetry energy at subnuclear densities and nuclei in neutron star crusts

Abstract

We examine how the properties of inhomogeneous nuclear matter at subnuclear densities depend on the density dependence of the symmetry energy. Using a macroscopic nuclear model we calculate the size and shape of nuclei in neutron star matter at zero temperature in a way dependent on the density dependence of the symmetry energy. We find that for smaller symmetry energy at subnuclear densities, corresponding to the larger density symmetry coefficient L, the charge number of nuclei is smaller and the critical density at which matter with nuclei or bubbles becomes uniform is lower. The decrease in the charge number is associated with the dependence of the surface tension on the nuclear density and the density of a sea of neutrons, whereas the decrease in the critical density can be generally understood in terms of proton clustering instability in uniform matter.

Authors:
 [1];  [2];  [3];  [4];  [5]
  1. Department of Media Theories and Production, Aichi Shukutoku University, Nagakute, Nagakute-cho, Aichi-gun, Aichi 480-1197 (Japan)
  2. (RIKEN), Hirosawa, Wako, Saitama 351-0198 (Japan)
  3. The Institute of Physical and Chemical Research (RIKEN), Hirosawa, Wako, Saitama 351-0198 (Japan)
  4. (United States)
  5. (Japan)
Publication Date:
OSTI Identifier:
20990978
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 75; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevC.75.015801; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; BUBBLES; DENSITY; NEUTRON STARS; NEUTRONS; NUCLEAR MATTER; NUCLEAR MODELS; NUCLEI; PROTONS; SHAPE; SURFACE TENSION; SYMMETRY

Citation Formats

Oyamatsu, Kazuhiro, The Institute of Physical and Chemical Research, Iida, Kei, RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973-5000, and Department of Materials Science, Kochi University, Akebono-cho, Kochi 780-8520. Symmetry energy at subnuclear densities and nuclei in neutron star crusts. United States: N. p., 2007. Web. doi:10.1103/PHYSREVC.75.015801.
Oyamatsu, Kazuhiro, The Institute of Physical and Chemical Research, Iida, Kei, RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973-5000, & Department of Materials Science, Kochi University, Akebono-cho, Kochi 780-8520. Symmetry energy at subnuclear densities and nuclei in neutron star crusts. United States. doi:10.1103/PHYSREVC.75.015801.
Oyamatsu, Kazuhiro, The Institute of Physical and Chemical Research, Iida, Kei, RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973-5000, and Department of Materials Science, Kochi University, Akebono-cho, Kochi 780-8520. Mon . "Symmetry energy at subnuclear densities and nuclei in neutron star crusts". United States. doi:10.1103/PHYSREVC.75.015801.
@article{osti_20990978,
title = {Symmetry energy at subnuclear densities and nuclei in neutron star crusts},
author = {Oyamatsu, Kazuhiro and The Institute of Physical and Chemical Research and Iida, Kei and RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973-5000 and Department of Materials Science, Kochi University, Akebono-cho, Kochi 780-8520},
abstractNote = {We examine how the properties of inhomogeneous nuclear matter at subnuclear densities depend on the density dependence of the symmetry energy. Using a macroscopic nuclear model we calculate the size and shape of nuclei in neutron star matter at zero temperature in a way dependent on the density dependence of the symmetry energy. We find that for smaller symmetry energy at subnuclear densities, corresponding to the larger density symmetry coefficient L, the charge number of nuclei is smaller and the critical density at which matter with nuclei or bubbles becomes uniform is lower. The decrease in the charge number is associated with the dependence of the surface tension on the nuclear density and the density of a sea of neutrons, whereas the decrease in the critical density can be generally understood in terms of proton clustering instability in uniform matter.},
doi = {10.1103/PHYSREVC.75.015801},
journal = {Physical Review. C, Nuclear Physics},
number = 1,
volume = 75,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • We examine how nuclear masses are related to the density dependence of the symmetry energy. Using a macroscopic nuclear model we calculate nuclear masses in a way dependent on the equation of state of asymmetric nuclear matter. We find by comparison with empirical two-proton separation energies that a smaller symmetry energy at subnuclear densities, corresponding to a larger density symmetry coefficient L, is favored. This tendency, which is clearly seen for nuclei that are neutron-rich, nondeformed, and light, can be understood from the property of the surface symmetry energy in a compressible liquid-drop picture.
  • The transition density n{sub t} and pressure P{sub t} at the inner edge between the liquid core and the solid crust of a neutron star are analyzed using the thermodynamical method and the framework of relativistic nuclear energy density functionals. Starting from a functional that has been carefully adjusted to experimental binding energies of finite nuclei, and varying the density dependence of the corresponding symmetry energy within the limits determined by isovector properties of finite nuclei, we estimate the constraints on the core-crust transition density and pressure of neutron stars: 0.086 fm{sup -3}<=n{sub t}<0.090 fm{sup -3} and 0.3 MeV fm{supmore » -3}<P{sub t}<=0.76 MeV fm{sup -3}.« less
  • We investigate the specific heat of superfluid neutrons in the region of the crust of a neutron star characterized by unusual nuclear shapes, whose possible existence has been recently proposed. To describe pairing properties the results from Reid soft-core potential for nucleon-nucleon interaction are used. It is found that the presence of unusual nuclei causes a sizable increase in the specific heat. The results can have consequences in the study of thermal evolution of young neutron stars.