Stellar matter with a strong magnetic field within density-dependent relativistic models

Abstract

The effect of strong magnetic fields on the equation of state (EoS) for compact stars described with density dependent relativistic hadronic models is studied. A comparison with other mean-field relativistic models is done. It is shown that the largest differences between models occur for low densities and that the magnetic field affects the crust properties of star, namely its extension. PACS numbers: 26.60.-c 26.60.Kp 97.60.Jd 24.10.Jv I. INTRODUCTIONThe study of very asymmetric nuclear matter is presently an important issue due to the radioactive beams which will be operating in the near future and which will allow the investigation of a region of the nuclear matter phase space unaccessible till recently. Asymmetric nuclear matter is of particular interest for the description of stellar matter of compact stars.Compact star properties depend a lot on the model used to describe the hadronic equation of state (EoS). In particular relativistic nuclear mean-field models [1,2] are very popular to describe stellar matter because causality will always be satisfied. The imposition of constraints, both coming from measured star properties or from relativistic heavy ion collisions in the laboratory, is essential to test the different models [3].Magnetars are neutron stars which may have surface magnetic fields larger that 10 15 G [4-6] and which were discovered at the x-ray and γ-ray energies (for a review refer [7]). They are identified with the anomalous x-ray pulsars (AXP) and soft γ-ray repeaters. Taking as reference the critical

Magnetic susceptibility and magnetization properties of asymmetric nuclear matter in a strong magnetic field

“…Similar conclusions with respect to the effect of the magnetic field on the proton fraction have been drawn in Ref. [51], where it is shown that, for B = 4.4 × 10 18 G, the magnetic field affects mainly densities below 2ρ 0 and, instead of the usual proton fractions below 0.1, proton fractions above this value are expected. An increase of the proton fraction disfavors polarization, and, therefore, in β-equilibrium magnetized matter the proton total polarization will not occur as easily.…”

“…[43,51]. Consequently a complete description of stellar matter requires also the leptonic contribution for the description of quantities such as the total magnetization; see Ref.…”

“…A complete set of equations and description of the method can be found in the literature (e.g., Refs. [47,51,54]). For the description of the system, we need the energy density of nuclear matter, the pressure, and the baryonic density.…”

“…The density dependence of the energy of the system and its pressure, as well as its compressibility, is analyzed for different proton fractions and magnetic fields. We will not consider β-equilibrium matter in most of the results shown, but will consider a wide range of nuclear matter asymmetries of interest for stellar matter, in particular, to the study of the inner crust, where a pasta phase is expected [49], to the study of matter with trapped neutrinos where large proton fractions are expected, which may be as large as 0.4 in the presence of a magnetic field [50], and to the study of neutrino free matter in β-equilibrium where the proton fraction will increase above 0.1 at subsaturation densities for a sufficiently strong magnetic field [51]. Therefore, besides symmetric nuclear matter and neutron matter, we choose two representative proton fractions, namely Y p = 0.1 for cold β-equilibrium matter and Y p = 0.3 for warm protoneutron star matter with a fraction of 0.4 trapped leptons.…”

Magnetism in Dense Quark Matter

“…Hence, when investigating the field effects in the EoS, it is consistent to take a magnetic field that is locally constant and uniform. This is the reason why such an approximation has been systematically used in all the previous works on magnetized nuclear [1,20,25,28,29,34,35,72,79,87,115,121,124,136,140,143] and quark matter [32,33,74,104,105,120].…”