Search

The effect of isospin-dependent nuclear forces on the inner crust of neutron stars is modeled within the framework of Quantum Molecular Dynamics (QMD). To successfully control the density dependence of the symmetry energy of neutron-star matter below nuclear saturation density, a mixed vector-isovector potential is introduced. This approach is inspired by the baryon density and isospin density-dependent repulsive Skyrme force of asymmetric nuclear matter. In isospin-asymmetric nuclear matter, the system shows nucleation, as nucleons are arranged into shapes resembling nuclear pasta. The dependence of clusterization in the system on the isospin properties is also explored by calculating two-point correlation functions. We show that, as compared to previous results that did not involve such mixed interaction terms, the energy symmetry slope L is successfully controlled by varying the corresponding coupling strength. Nevertheless, the effect of changing the slope of the nuclear symmetry energy L on the crust-core transition density does not seem significant. To the knowledge of the authors, this is the first implementation of such a coupling in a QMD model for isospin asymmetric matter, which is relevant to the inner crust of neutron and proto-neutron stars. [ABSTRACT FROM AUTHOR]

The effect of isospin-dependent nuclear forces on the inner crust of neutron stars is modeled within the framework of Quantum Molecular Dynamics (QMD). To successfully control the density dependence of the symmetry energy of neutron-star matter below nuclear saturation density, a mixed vector-isovector potential is introduced. This approach is inspired by the baryon density and isospin density-dependent repulsive Skyrme force of asymmetric nuclear matter. In isospin-asymmetric nuclear matter, the system shows nucleation, as nucleons are arranged into shapes resembling nuclear pasta. The dependence of clusterization in the system on the isospin properties is also explored by calculating two-point correlation functions. We show that, as compared to previous results that did not involve such mixed interaction terms, the energy symmetry slope L is successfully controlled by varying the corresponding coupling strength. Nevertheless, the effect of changing the slope of the nuclear symmetry energy L on the crust-core transition density does not seem significant. To the knowledge of the authors, this is the first implementation of such a coupling in a QMD model for isospin asymmetric matter, which is relevant to the inner crust of neutron and proto-neutron stars.

At very high densities, electrons react with protons to form neutron-rich matter. This material is central to many fundamental questions in nuclear physics and astrophysics. Moreover, neutron-rich matter is being studied with an extraordinary variety of new tools such as Facility for Rare Isotope Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that uses parity violating electron scattering to measure the neutron radius in 208Pb. This has important implications for neutron stars and their crusts. We discuss X-ray observations of neutron star radii. These also have important implications for neutron-rich matter. Gravitational waves (GW) open a new window on neutron-rich matter. They come from sources such as neutron star mergers, rotating neutron star mountains, and collective r-mode oscillations. Using large scale molecular dynamics simulations, we find neutron star crust to be very strong. It can support mountains on rotating neutron stars large enough to generate detectable gravitational waves. Finally, neutrinos from core collapse supernovae (SN) provide another, qualitatively different probe of neutron-rich matter. Neutrinos escape from the surface of last scattering known as the neutrino-sphere. This is a low density warm gas of neutron-rich matter. Neutrino-sphere conditions can be simulated in the laboratory with heavy ion collisions. Observations of neutrinos can probe nucleosyntheses in SN. Simulations of SN depend on the equation of state (EOS) of neutron-rich matter. We discuss a new EOS based on virial and relativistic mean field calculations. We believe that combing astronomical observations using photons, GW, and neutrinos, with laboratory experiments on nuclei, heavy ion collisions, and radioactive beams will fundamentally advance our knowledge of compact objects in the heavens, the dense phases of QCD, the origin of the elements, and of neutron-rich matter. [ABSTRACT FROM AUTHOR]

We address the description of neutron-proton-electron degenerate matter in beta equilibrium subjected to compression both in the case of confined nucleons into a nucleus as well as in the case of deconfined nucleons. We follow a step-by-step generalization of the classical Thomas-Fermi model to special and general relativistic regimes, which leads to a unified treatment of beta equilibrated neutron-proton-electron degenerate matter applicable from the case of nuclei all the way up to the case of white-dwarfs and neutron stars. New gravito-electrodynamical effects, missed in the traditional approach for the description of neutron star configurations, are found as a consequence of the new set of general relativistic equilibrium equations. [ABSTRACT FROM AUTHOR]

To account for pulsar frequency glitches, it is necessary to use a neutron star crust model allowing not only for neutron superfluidity but also for elastic solidity. These features have been treated separately in previous treatments of crust matter, but are combined here in a unified treatment that is based on the use of a Lagrangian master functon, so that the system is ensured coherence by the relevant Noether identities. Besides the model obtained directly from the variation principle, the same master function can provide other conservative alternatives, allowing in particular for the effect of perfect vortex pinning. It is also shown how such models can be generalized to allow for dissipative effects, including that of imperfect pinning, meaning vortex drag or creep. [ABSTRACT FROM AUTHOR]

Phenomena such as pulsar frequency glitches are believed to be attributable to differential rotation of a current of "free" superfluid neutrons at densities above the "drip" threshold in the ionic crust of a neutron star. Such relative flow is shown to be locally describable by adaption of a canonical two-fluid treatment that emphasizes the role of the momentum covectors constructed by differentiation of action with respect to the currents, with allowance for stratification whereby the ionic number current may be conserved even when the ionic charge number Z is altered by beta processes. It is demonstrated that the gauge freedom to make different choices of the chemical basis determining which neutrons are counted as "free" does not affect their "superfluid" momentum covector, which must locally have the form of a gradient (though it does affect the "normal" momentum covector characterizing the protons and those neutrons that are considered to be "confined" in the nuclei). It is shown how the effect of "entrainment" (whereby the momentum directions deviate from those of the currents) is controlled by the (gauge-independent) mobility coefficient $\mathcal{K}$, estimated in recent microscopical quantum mechanical investigations, which suggest that the corresponding (gauge-dependent) "effective mass" m⋆ of the free neutrons can become very large in some layers. The relation between this treatment of the crust layers and related work (using different definitions of "effective mass") intended for the deeper core layers is discussed. [ABSTRACT FROM AUTHOR]

The physics of neutron star crusts is vast, involving many different research fields, from nuclear and condensed matter physics to general relativity. This review summarizes the progress, which has been achieved over the last few years, in modeling neutron star crusts, both at the microscopic and macroscopic levels. The confrontation of these theoretical models with observations is also briefly discussed.

Abstract: The crust of a neutron star is of special interest because of the phase transition from a gas of nuclei to homogeneous asymmetric nuclear matter. Several efforts have been made to explore the nuclear matter in this region of the neutron star. These calculations have been done mostly in spherical Wigner–Seitz-cells using Skyrme Hartree–Fock (HF) or relativistic mean field (RMF) calculations. We apply both approaches in a Cartesian Wigner–Seitz-cell and get a smooth transition from nuclei to homogeneous matter showing various shapes. In this article we pay special attention to the relativistic mean field. Pairing is included in the BCS approximation. [Copyright &y& Elsevier]

In cold atoms and in the crust of neutron stars, the pairing gap can reach values comparable with the Fermi energy. While in nuclei the neutron gap is smaller, it is still of the order of a few percent of the Fermi energy. The pairing mechanism in these systems is due to short range attractive interactions between fermions and the size of the Cooper pair is either comparable to the inter‐particle separation or it can be as big as a nucleus, which is still relatively small in size. Such a strong pairing gap is the result of the superposition of a very large number of particle–particle configurations, which contribute to the formation of the Cooper pairs. These systems have been shown to be the host of a large number of remarkable phenomena, in which the large magnitude of the pairing gap plays an essential role: quantum shock waves, quantum turbulence, Anderson–Bogoliubov–Higgs mode, vortex rings, domain walls, soliton vortices, vortex pinning in neutron star crust, unexpected dynamics of fragmented condensates and role of pairing correlations in collisions on heavy‐ions, Larkin–Ovchinnikov phase as an example of a Fermi supersolid, role of pairing correlations in controlling the dynamics of fissioning nuclei. [ABSTRACT FROM AUTHOR]