Zh. K. Stoyanov

Properties of the outer crust of strongly magnetized neutron stars from Hartree-Fock-Bogoliubov atomic mass models

The equilibrium properties of the outer crust of cold nonaccreting magnetars (i.e. neutron stars endowed with very strong magnetic fields) are studied using the latest experimental atomic mass data complemented with a microscopic atomic mass model based on the Hartree-Fock-Bogoliubov method. The Landau quantization of electron motion caused by the strong magnetic field is found to have a significant impact on the composition and the equation of state of crustal matter. It is also shown that the outer crust of magnetars could be much more massive than that of ordinary neutron stars.

Effects induced by nuclear deformations and electron correlations on the ground-state energy of low and multiply charged helium like ions in high-temperature plasmas

The present work deals with the effects induced by nuclear deformations and electron correlations on the electron ground-state energies of low and multiply charged helium like ions. Numerical calculations of the ground state energies including mass corrections and polarization of the electronic system have been performed for such heliumoid ions with nuclear charge number from Z=2 to Z=118. A perturbation method has been developed based on a variational principle using explicitly correlated two-electron wave functions. The mass-polarization term accounting for correlation effects has been included for the first time in the minimization procedure. These effects have been found to be particularly pronounced for ions corresponding to nuclear magic numbers. The present method provides a general framework for high-precision calculations of plasma diagnostics.

Landau quantization and neutron emissions by nuclei in the crust of a magnetar

Magnetars are neutron stars endowed with surface magnetic fields of the order of

Landau Quantisation of Electron Motion in the Crust of Highly Magnetised Neutron Stars

10^{14}-10^{15}

Effects of Isotope Characteristics on the Electron System Ground State Energy of Helium-Like Ions

~G, and with presumably much stronger fields in their interior. As a result of Landau quantization of electron motion, the neutron-drip transition in the crust of a magnetar is shifted to either higher or lower densities depending on the magnetic field strength. The impact of nuclear uncertainties is explored considering the recent series of Brussels-Montreal microscopic nuclear mass models. All these models are based on the Hartree-Fock-Bogoliubov method with generalized Skyrme functionals. They differ in their predictions for the symmetry energy coefficient at saturation, and for the stiffness of the neutron-matter equation of state. For comparison, we have also considered the very accurate but more phenomenological model of Duflo and Zuker. Although the equilibrium composition of the crust of a magnetar and the onset of neutron emission are found to be model dependent, the quantum oscillations of the threshold density are essentially universal.

Nuclear induces effects and mass correlations in low and multiply charged helium-like ions

With observed surface magnetic fields up to \(\sim \)10\(^{15}\) G, neutron stars—the stellar remnants of gravitational core-collapse supernovae explosions—are unique cosmic laboratories for probing the properties of matter under extreme conditions. The outermost layer of a neutron star is thought to consist of a solid crust, whose atoms are fully ionised by the huge pressure. Electrons are expected to be highly degenerate and form an essentially ideal relativistic Fermi gas. With increasing depth, nuclei become progressively more neutron rich by capturing electrons until at some point, neutrons start to drip out of nuclei. At about half the density found in heavy atomic nuclei, the crust dissolves into a neutron liquid with a small admixture of protons and electrons. The composition and the equation of state of highly magnetised neutron-star crusts are shown to be significantly affected by Landau quantisation of electron motion.

Unified description of dense matter in neutron stars and magnetars

The main goal of this work is to establish a link between the energy characteristics of the ground state of helium-like ions and the isotope characteristics of the nucleus of the system. High-precision calculations of the electron ground state energies of helium-like ions require to take into account the effects associated with nuclear characteristics and electron correlations. In our previous work, we calculated ground state electron energies, mass corrections and mass polarization effects of helium-like isoelectronic ions for the main nuclides with nuclear charge from \(Z=2\) to \(Z=118\). In the present work are discussed the results for 3833 existing isotopes in the same range of nuclear charge. The results presented are without the inclusion of the mass polarization effect in the minimization procedure. The complex dependence of the ground state energy on the mass corrections and mass polarization effects as a function of charge Z and neutron number N are studied. Staggering analysis for the ground state energy dependence on Z and N helped establish the electron characteristic dependence on the nuclear magic numbers.

Role of Landau quantization on the neutron-drip transition in magnetar crusts

The ground-state electron energies, the mass correction and mass polarization of low and multiply charged helium-like ions are analytically and numerically calculated. Approximately 3500 different kinds of ions with charge Z = 2 ÷ 118 are considered. The two-electron Schrodinger equation was solved using a discrete variational-perturbation approach developed by the authors and based on explicitly correlated wave functions. This approach takes into account the motion of the nucleus and yields accurate values for the electron characteristics. The results are presented with and without the inclusion of the mass polarization in the minimization procedure. The relative importance of mass correlations and relativistic effects in the formation of the electron energy characteristics of the helium-like ions are studied for different values of Z. The role of the inclusion of the mass polarization in the minimization procedure as an instrument to present and take into account the effects induced by the nuclear properties, structure and characteristics has been shown.

Role of the symmetry energy on the neutron-drip transition in accreting and nonaccreting neutron stars

We have recently developed a set of equations of state based on the nuclear energy density functional theory providing a unified description of the different regions constituting the interior of neutron stars and magnetars. The nuclear functionals, which were constructed from generalized Skyrme effective nucleon-nucleon interactions, yield not only an excellent fit to essentially all experimental atomic mass data but were also constrained to reproduce the neutron-matter equation of state as obtained from realistic many-body calculations.