Abstract
Context. The interior of a neutron star is expected to exhibit different states of matter. In particular, complex non-spherical configurations known as ‘pasta’ phases may exist at the highest densities in the inner crust, potentially having an impact on different neutron-star phenomena. Aims. We study the properties of the pasta phase and the uncertainties in the pasta observables which are due to our incomplete knowledge of the nuclear energy functional. Methods. To this aim, we employed a compressible liquid-drop model approach with surface parameters optimised either on experimental nuclear masses or theoretical calculations. To assess the model uncertainties, we performed a Bayesian analysis by largely varying the model parameters using uniform priors, and generating posterior distributions with filters accounting for both our present low-density nuclear physics knowledge and high-density neutron-star physics constraints. Results. Our results show that the nuclear physics constraints, such as the neutron-matter equation of state at very low density and the experimental mass measurements, are crucial in determining the crustal and pasta observables. Accounting for all constraints, we demonstrate that the presence of pasta phases is robustly predicted in an important fraction of the inner crust. We estimate the relative crustal thickness associated with pasta phases as Rpasta/Rcrust = 0.128 ± 0.047 and the relative moment of inertia as Ipasta/Icrust = 0.480 ± 0.137. Conclusions. Our findings indicate that the surface and curvature parameters are more influential than the bulk parameters for the description of the pasta observables. We also show that using a surface tension that is inconsistent with the bulk functional leads to an underestimation of both the average values and the uncertainties in the pasta properties, thus highlighting the importance of a consistent calculation of the nuclear functional.
Highlights
The interior of a cold neutron star (NS) is predicted to be made of various phases of matter, from a solid crust to a liquid core
The outer crust is thought to be made of ions arranged in a lattice, embedded in an electron gas, while in the inner crust the neutron-proton clusters, neutralised by the electron gas, coexist with a neutron gas, until, at about half the saturation density, nuclei dissolve into homogeneous matter, marking the transition to the liquid core (Haensel et al 2007)
We presented a study of the properties of pasta phases in cold catalysed NSs, extending the work of Carreau et al (2019a, 2020b)
Summary
The interior of a cold neutron star (NS) is predicted to be made of various phases of matter, from a solid crust to a liquid core. We studied the properties of the pasta phases in cold, non-accreting NSs under the so-called ‘catalysed matter hypothesis’, that is matter in its absolute ground state at zero temperature To this aim, we extended the CLD model of Carreau et al (2019a, 2020b) to account for non-spherical pasta structures in the inner crust. To obtain quantitative predictions of the uncertainties in the pasta observables, we performed a Bayesian analysis using flat uniform priors to generate posteriors with filters accounting for both our current knowledge of low-density nuclear physics and constraints at high density from general and NS physics
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