Collective excitations in neutron-star crusts

N Chamel,S Reddy,D Page

doi:10.1088/1742-6596/665/1/012065

Abstract

We explore the spectrum of low-energy collective excitations in the crust of a neutron star, especially in the inner region where neutron-proton clusters are immersed in a sea of superfluid neutrons. The speeds of the different modes are calculated systematically from the nuclear energy density functional theory using a Skyrme functional fitted to essentially all experimental atomic mass data.

Highlights

A few meters below the surface of a neutron star at densities above ∼ 104 g·cm−3, atomic nuclei are fully ionized by the pressure coexisting with a highly degenerate electron gas
Despite the absence of viscous drag, the neutron superfluid can still be strongly coupled to the crust due to nondissipative entrainment effects [3]
The collective excitations in the inner crust of a neutron star can impact the thermal evolution of the star [5]

Summary

Introduction

A few meters below the surface of a neutron star at densities above ∼ 104 g·cm−3, atomic nuclei are fully ionized by the pressure coexisting with a highly degenerate electron gas. The collective excitations in the inner crust of a neutron star can impact the thermal evolution of the star [5] These excitations have been already studied in the Wigner-Seitz approximation, using self-consistent mean-field methods with Skyrme effective interactions [6, 7]. Only high-energy collective excitations with wavelengths smaller than the size of the WignerSeitz cell can be studied in this framework This approximate treatment of the crust does not take into account entrainment effects, which arise from Bragg scattering of unbound neutrons by the Coulomb lattice. For this reason, we have recently followed a different approach by employing the band theory of solids.

Elasto-hydrodynamics of the neutron-star inner crust

Findings

Conclusions