Neutron drip transition in accreting and nonaccreting neutron star crusts

Abstract

The neutron-drip transition in the dense matter constituting the interior of neutron stars generally refers to the appearance of unbound neutrons as the matter density reaches some threshold density ${\rho }_{\text{drip}}$. This transition has been mainly studied under the cold catalyzed matter hypothesis. However, this assumption is unrealistic for accreting neutron stars. After examining the physical processes that are thought to be allowed in both accreting and nonaccreting neutron stars, suitable conditions for the onset of neutron drip are derived and general analytical expressions for the neutron drip density and pressure are obtained. Moreover, we show that the neutron-drip transition occurs at lower density and pressure than those predicted within the mean-nucleus approximation. This transition is studied numerically for various initial composition of the ashes from X-ray bursts and superbursts using microscopic nuclear mass models.

24 pages, accepted for publication in Physical Review C

References in corpus (4)

• Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. XII: Stiffness and stability of neutron-star matter
• Models of crustal heating in accreting neutron stars
• Tests of the nuclear equation of state and superfluid and superconducting gaps using the Cassiopeia A neutron star
• On the validity of the Wigner-Seitz approximation in neutron star crust

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