Uncertainties in the pasta-phase properties of catalysed neutron stars

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.

1S0 Pairing Gaps, Chemical Potentials and Entrainment Matrix in Superfluid Neutron-Star Cores for the Brussels–Montreal Functionals

“…Together with the results published in [19][20][21][22] for the composition and the equation of state, our calculations provide consistent microscopic inputs for modeling the global structure and dynamics of superfluid neutron stars. Although we have considered the specific functional BSk24 because it has been shown to be in excellent agreement with existing nuclear data and astrophysical observations [23,44], we have also derived all the necessary equations to evaluate superfluid properties for any other functional of the Brussels-Montreal type (this includes all the functionals based on standard Skyrme effective nucleon-nucleon interactions). Extension of the TDHFB theory to account for 3 PF 2 neutron superfluidity in the inner core of massive neutron stars is left for future studies.…”

“…and ε Λ is a cutoff above the Fermi level to regularize the ultraviolet divergences (see Section 3.1). Expressing the hyperbolic functions in terms of the exponential function, we can alternatively rewrite (43) and (44) as…”

A Bayesian analysis of the properties of hybrid stars with the NJL model

“…In order to explore consistently the current theoretical uncertainty on the nuclear equation of state, we use at low densities a meta-model of nuclear matter [27,28] extended to include surface terms [29][30][31] such as to allow a consistent and unified description of the crust. This approach is based on the hypothesis that the total baryonic density n B can be simply written as the sum of the neutron n n and proton n p densities, n B = n p + n n .…”

“…( 1). We use a compressible liquid drop model (CLDM) to describe the mass of a finite nucleus with Z protons and A = N + Z nucleons as [29,30]:…”

“…The very large nuclear sample is motivated by the fact that stringent theoretical constraints exist on the behavior of the energy per particle of pure neutron matter from many-body perturbation theory using chiral effective interactions [65,66]. We will include these constraints as a pass-band filter following previous works [29][30][31] which will sensibly reduce the size of our sample to about 10000 models, the minimum statistics needed for a convergence of the results presented in this paper. On the other side, we have checked that the limited number of quark EoS is sufficient to cover all the possible behaviors of the quark branch within the reduced set of parameters of the NJL model.…”