2020/02/28 by P. Haensel, Haensel, P., J. L. Zdunik +1
Physics and Astronomy · #Astro and Planetary Science #FOS: Physical sciences #Gamma-ray bursts and supernovae #High Energy Astrophysical Phenomena (astro-ph.HE) #Nuclear Theory (nucl-th) #Pulsars and Gravitational Waves Research #astro-ph.HE #nucl-th
paper · pdf · doi:10.48550/arxiv.2002.12827
To be submitted for publication. Remarks and comments on the present paper will be welcome by the authors
arxiv created 2020/02/28 · openalex publication_date 2020/02/28 · arxiv updated 2020/03/02 · openalex created_date 2022/10/02 · openalex updated_date 2026/07/28
Using a Wigner-Seitz approximation with spherical cells, we re-analyze a widely used single nucleus model of accreting neutron star crust. We calculate beta disequilibrium within the crust, which is sizable, and implies that neutron and baryon chemical potentials, μn and μ\rm b, are not equal. We include also non-equilibrium reactions, driven by matter compression, and proceeding in the reaction layers. The constancy of eΦμn, where the spacetime metric component g00=e2Φ, in the shells between the reaction layers is not applicable, because single electron captures are blocked, so that the neutron fraction is fixed, and therefore neutrons are not an independent component of the crust matter. The absence of neutron diffusion in the shells between the reaction layers, stems from the constancy of the neutron fraction (concentration) in these shells. In the reaction layers, the outward force resulting from neutron fraction gradient is balanced by the inward gravitational force acting on unbound neutrons. Neglecting the thickness of the reaction layers compared to the shell thickness, we obtain condition eΦ(r)fQ(r)g(r)=constant, where g is Gibbs energy per nucleon, undergoing discontinuous drops on the reaction surfaces, and fQ(r)g(r)=\widetildeg(r) is a continuous function, due to the factor fQ(r) canceling the discontinuities (drops) in g(r). The function fQ(r) is calculated using the Tolman-Oppenheimer-Volkov equations from fQ(P) and g(P) obtained from the equation of state (EOS) with discontinuites. The constancy of of eΦ(r)\widetildeg(r) is an extension of the standard relation eΦ(r)μ\rm b(r)=constant, valid in hydrostatic equilibrium for catalyzed crust.