Prior probability distributions of neutron star crust models

Abstract

To make best use of multi-faceted data sets in the age of multi-messenger astronomy and the results of nuclear experimental and theoretical studies, probability distributions of neutron star models that can be used to propagate errors from one domain to another are required. In this paper we prepare two ensembles of neutron star crust models that can be used as prior distributions in Bayesian studies. The ensembles are generated by input distributions of the first three coefficients of the expansion of the nuclear symmetry energy at saturation density J, L and K sym . The first ensemble uses a uniform distribution, within which all experimental constraints comfortably fall, and the second is derived from general considerations about the pure neutron matter EOS informed by the results of chiral effective field theory calculations. We use an extended Skyrme model to consistently model nuclear matter, finite nuclei and crustal matter.The compressible liquid drop model (CLDM) is used to compute crust models. We present a unique fit of the surface parameters of the CLDM to quantum 3D Hartree-Fock calculations of nuclei in a neutron gas near the spherical nuclei-nuclear pasta transition. We present the resulting distributions of crust-core transition properties, and, for the first time, the properties of the crust layer where pasta first appears and the relative mass (column depth) and thickness fractions of the pasta layers. All models predict more than 50% of the crust by mass and 15% of the crust by thickness comprises pasta; 95% of models predict relative masses of pasta of 62 +8 −10 % and 62 +3 −4 % for uniform and pure neutron matter distributions respectively and relative thicknesses of pasta of 30 +13 −13 % and 29 +4 −9 %. We also present 68% and 95% ranges for the crust composition, shear modulus, melting temperature and frozen-composition adiabatic index as a function of density.We examine the relationships between crust-core boundary and pasta transition properties, the thickness of the pasta layers, the symmetry energy at saturation and sub-saturation densities and the neutron skins of 208 Pb and 48 Ca. We quantify the correlations using the maximal information coefficient, which can effectively characterizes non-linear relationships. Future measurements of 208 Pb and 48 Ca from the PREX/CREX and MREX experiments, information from nuclear masses and giant resonances, and constraints on pure neutron matter from ab-initio theoretical methods will be able to place strong constraints on the location of the pasta layers, the crust-core boundary and the amount of pasta in the crust.

Superconducting phases in a two-component microscale model of neutron star cores

“…First, the transition between the neutron star crust and the core is not a sharp one, but covers a density range, which is dependent on the specific Skyrme model considered. 64 How the magnetic flux distribution changes from the innermost crustal layer, through this extended transition into the core is not known and these lower density regions likely impact on the ground state of the superconducting protons, making our predictions less robust. Second, the physical parameters (in particular the neutron coherence length, ξ n ) that influence the phases of the superconductor vary significantly in the region close to the crust-core interface, and so the concept of a local ground state becomes less meaningful.…”

Glassy quantum nuclear pasta in neutron star crusts

“…In Figure 20 we plot the pressure (Figure 20a) and chemical potential (Figure 20b) at which we perform each of our calculations as a function of the densities of each local minimum as blue diamonds. We compare this with the pressure and neutron chemical potential as calculated with the compressible liquid drop model (CLDM) using the surface parameters that give closest agreement to 3DHF results (as described in [53]). First, we note that spurious shell effects caused by the discretization of the neutron energy spectrum and corresponding change in the density of states means we don't expect the pressure and neutron chemical potential to match exactly the CLDM results.…”

“…Pasta could account for 50% of the crust by mass [52,53], so there are observational consequences to the microscopic organization of pasta. The increased resistivity of disordered pasta could lead to potentially observable effects on the cooling curves of X-ray binaries [54] and the evolution of pulsar magnetic fields [55].…”

Resonant shattering flares as multimessenger probes of the nuclear symmetry energy

“…We use an extended Skyrme mean field model for the uniform matter EOS . Three parameters of the model affect only the pure neutron matter EOS, and can be written in terms of 𝐽, 𝐿 and 𝐾 sym (Newton & Crocombe 2020;Balliet et al 2020). This way, a given set of values {𝐽, 𝐿, 𝐾 sym } can be converted into a set of Skyrme models (each of which labeled by the 3 symmetry energy parameters) and corresponding crust models and equations of state.…”