Thermal conductivity and phase separation of the crust of accreting neutron stars

Abstract

Recently, crust cooling times have been measured for neutron stars after extended outbursts. These observations are very sensitive to the thermal conductivity $\kappa$ of the crust and strongly suggest that $\kappa$ is large. We perform molecular dynamics simulations of the structure of the crust of an accreting neutron star using a complex composition that includes many impurities. The composition comes from simulations of rapid proton capture nucleosynthesys followed by electron captures. We find that the thermal conductivity is reduced by impurity scattering. In addition, we find phase separation. Some impurities with low atomic number $Z$ are concentrated in a subregion of the simulation volume. For our composition, the solid crust must separate into regions of different compositions. This could lead to an asymmetric star with a quadrupole deformation that radiates gravitational waves. Observations of crust cooling can constrain impurity concentrations.

8 pages, 8 figures, minor changes, PRE in press

References in corpus (5)

• Fusion reactions in multicomponent dense matter
• Cooling of the quasi-persistent neutron star X-ray transients KS 1731-260 and MXB 1659-29
• Phase separation in the crust of accreting neutron stars
• Fusion of neutron rich oxygen isotopes in the crust of accreting neutron stars
• The Shear Viscosity and Thermal Conductivity of Nuclear Pasta

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• Structure of Multicomponent Coulomb Crystals
• Constraining the properties of dense neutron star cores: The case of the low-mass X-ray binary HETE J1900.1-2455
• Stochastic Dynamics and Bound States of Heavy Impurities in a Fermi Bath