We study relationships between the neutron-rich skin of a heavy nucleus and the properties of neutron-star crusts. Relativistic effective field theories with a thicker neutron skin in 208 Pb have a larger electron fraction and a lower liquid-to-solid transition density for neutron-rich matter. These properties are determined by the density dependence of the symmetry energy which we vary by adding nonlinear couplings between isoscalar and isovector mesons. An accurate measurement of the neutron radius in 208 Pb-via parity violating electron scattering-may have important implications for the structure of neutron stars.It is an extrapolation of 18 orders of magnitude from the neutron radius of a heavy nucleus-such as 208 Pb with R n ≈ 5.5 fm-to the approximately 10 km radius of a neutron star. Yet both radii depend on our incomplete knowledge of the equation of state of neutron-rich matter. Therefore, an accurate measurement of the neutron radius in 208 Pb may have important implications for the structure of neutron stars.Heavy nuclei are expected to have a neutron-rich skin. This important feature of nuclear structure arises because of the large neutron excess and because the Coulomb barrier reduces the proton density at the surface. The thickness of the neutron skin depends on the pressure of neutron-rich matter: the greater the pressure, the thicker the skin as neutrons are pushed out against surface tension. The same pressure supports a neutron star against gravity [1]. Thus models with thicker neutron skins often produce neutron stars with larger radii.Neutron stars are expected to have a solid crust of nonuniform neutron-rich matter above a liquid mantle. The phase transition from solid to liquid depends on the properties of neutron-rich matter. Indeed, a high pressure implies a rapid rise of the energy with density making it energetically unfavorable to separate uniform matter into regions of high and low densities. Thus a high pressure typically implies a low transition density from a solid crust to a liquid mantle. This suggests an inverse relationship: the thicker the neutron-rich skin of a heavy nucleus, the thinner the solid crust of a neutron star.In this letter we study possible "data-to-data" relations between the neutron-rich skin of a heavy nucleus and the crust of a neutron star. These relations may impact neutron star observables. Indeed, properties of the crust are important for models of glitches in the rotational period of pulsars [2,3], for the shape and gravitational radiation of non-spherical rotating stars [4] and for neutron-star cooling [5]. Note that the skin of a heavy nucleus and the crust of a neutron star are composed of the same material: neutron-rich matter at similar densities.The Parity Radius Experiment (PREX) at the Jefferson Laboratory aims to measure the neutron radius in 208 Pb via parity violating electron scattering [6,7]. Parity violation is sensitive to the neutron density because the Z 0 boson couples primarily to neutrons. The result of this purely electroweak experim...

An accurately calibrated relativistic parametrization is introduced to compute the ground state properties of finite nuclei, their linear response, and the structure of neutron stars. While similar in spirit to the successful NL3 parameter set, it produces an equation of state that is considerably softer--both for symmetric nuclear matter and for the symmetry energy. This softening appears to be required for an accurate description of several collective modes having different neutron-to-proton ratios. Among the predictions of this model are a symmetric nuclear-matter incompressibility of K=230 MeV and a neutron skin thickness in 208 Pb of Rn-Rp=0.21 fm. The impact of such a softening on various neutron-star properties is also examined.

The historical first detection of a binary neutron star merger by the LIGO-Virgo Collaboration [B. P. Abbott et al., Phys. Rev. Lett. 119, 161101 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.161101] is providing fundamental new insights into the astrophysical site for the r process and on the nature of dense matter. A set of realistic models of the equation of state (EOS) that yield an accurate description of the properties of finite nuclei, support neutron stars of two solar masses, and provide a Lorentz covariant extrapolation to dense matter are used to confront its predictions against tidal polarizabilities extracted from the gravitational-wave data. Given the sensitivity of the gravitational-wave signal to the underlying EOS, limits on the tidal polarizability inferred from the observation translate into constraints on the neutron-star radius. Based on these constraints, models that predict a stiff symmetry energy, and thus large stellar radii, can be ruled out. Indeed, we deduce an upper limit on the radius of a 1.4M_{⊙} neutron star of R_{⋆}^{1.4}<13.76  km. Given the sensitivity of the neutron-skin thickness of ^{208}Pb to the symmetry energy, albeit at a lower density, we infer a corresponding upper limit of about R_{skin}^{208}≲0.25  fm. However, if the upcoming PREX-II experiment measures a significantly thicker skin, this may be evidence of a softening of the symmetry energy at high densities-likely indicative of a phase transition in the interior of neutron stars.

Neutron-rich matter at subnuclear densities may involve complex structures displaying a variety of shapes, such as spherical, slablike, and/or rodlike shapes. These phases of the nuclear pasta are expected to exist in the crust of neutron stars and in core-collapse supernovae. The dynamics of core-collapse supernovae is very sensitive to the interactions between neutrinos and nucleons/nuclei. Indeed, neutrino excitation of the low-energy modes of the pasta may allow for a significant energy transfer to the nuclear medium, thereby reviving the stalled supernovae shock. The linear response of the nuclear pasta to neutrinos is modeled via a simple semi-classical simulation. The transport mean-free path for µ and τ neutrinos (and antineutrinos) is expressed in terms of the static structure factor of the pasta, which is evaluated using Metropolis Monte Carlo simulations.

Nuclear effective interactions are useful tools in astrophysical applications especially if one can guide the extrapolations to the extremes regions of isospin and density that are required to simulate dense, neutron-rich systems. Isospin extrapolations may be constrained in the laboratory by measuring the neutron skin thickness of a heavy nucleus, such as 208 Pb. Similarly, future observations of massive neutron stars will constrain the extrapolations to the high-density domain. In this contribution we introduce a new relativistic effective interaction that is simultaneously constrained by the properties of finite nuclei, their collective excitations, and neutron-star properties. By adjusting two of the empirical parameters of the theory, one can efficiently tune the neutron skin thickness of 208 Pb and the maximum neutron star mass. We illustrate this procedure in response to the recent interpretation of X-ray observations by Steiner, Lattimer, and Brown that suggests that the FSUGold effective interaction predicts neutron star radii that are too large and a maximum stellar mass that is too small. The new effective interaction is fitted to a neutron skin thickness in 208 Pb of only Rn −Rp = 0.16 fm and a moderately large maximum neutron star mass of 1.94 M .