The population of highly magnetized neutron stars

Abstract

Abstract. In this work, we study the effects of strong magnetic field configurations on the population of neutron stars. The stellar matter is described within a relativistic mean field formalism which considers many-body force contributions in the scalar couplings. We choose the parametrization of the model that reproduces nuclear matter properties at saturation and also describes massive hyperon stars. Hadronic matter is modeled at zero temperature, in betaequilibrium, charge neutral and populated by the baryonic octet, electrons and muons. Magnetic effects are taken into account in the structure of stars by the solution of the Einstein-Maxwell equations with the assumption of a poloidal magnetic field distribution. Our results show that magnetic neutron stars are populated essencialy by nucleons and leptons, due to the fact that strong magnetic fields decrease the central density of stars and, hence, supress the appearance of exotic particles. IntroductionThe topic of strong magnetic fields in neutron stars have been extensively studied in the literature. Magnetic field effects have been explored both on the equation of state [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17] and on the strucuture of magnetic neutron stars [18,19,20,21,22], in order to identify their impact on the global properties of neutron stars, such as masses and radii. In particular, Refs. [21,22] have shown that magnetic effects in the equation of state are not strongly significant for the determination of global properties of stars (i.e., mass and radius), although magnetic field dependence on microscopic processess as neutrino emission and consequently the cooling are still important [23].Another relevant effect of strong magnetic fields in neutron stars is their equatorial radius enhancement and the consequent decrease of the central baryon densities [22]. Such effect can have a severe impact on the population of highly magnetized neutron stars. The decrease of the central chemical potential, related to the baryon density, can prevent the appearance of phase transitions [22,24] as well as the existence of exotic degrees of freedom. In this work, we show for a particular parametrization of the many-body forces model (MBF model) that the hyperon population of neutron stars is completely supressed in the presence of central magnetic fields B c ∼ 10 18 G.

Magnetic field distribution in magnetars

“…While such observations only probe the surface magnetic field, there is no way to measure directly the maximum magnetic field in the interior. Using the simple virial theorem, one may estimate the maximum interior magnetic field to be as high as 10 18 G. If such large fields exist in the interior, they may strongly affect the energy of the charged particles by confining their motion to quantized Landau levels and consequently modify the particle population, transport properties as well as the global structure [2][3][4][5][6][7][8][9][10][11][12][13][14]. However, it is necessary to know the magnetic field amplitude at a given location in the star, i.e.…”