Estimating magnetar radii with an empirical meta-model

Abstract

The presence of strong magnetic fields in neutron stars, such as in magnetars, may significantly affect their crust-core transition properties and the crust size. This knowledge is crucial in the correct interpretation of astrophysical phenomena involving magnetars, such as glitches in observed rotation frequencies, cooling, bursts and possibly tidal polarizabilities. A recently developed metamodelling technique allows exploring the model dependence of density functional theory equation of state calculations. In this work, we extend this metamodel to investigate the effect of strong magnetic fields on spinodal instabilities of neutron star matter and the associated crust-core properties. Both Tolman-Oppenheimer-Volkov and a full self-consistent numerical calculations are performed for the neutron star structure, the results being quantitatively different for strong magnetic fields. * dchatterjee@lpccaen.in2p3.fr

Gravitational wave signatures of highly magnetized neutron stars

“…There is no doubt that the ideal situation is to use the LORENE code [27], which performs a numerical computation of the neutron star by taking into account the Einstein-Maxwell equations and equilibrium solutions self-consistently with a densitydependent magnetic field. Unfortunately, this calculation is not always feasible for all purposes and it gives some estimates that may not be correct, as the case of the neutron star crust thickness discussed in [28]. However, the latter work shows clearly that although not too strong magnetic fields have a negligible effect on the EOS itself, it strongly affects properties related to the crust, as the cases discussed next.…”

Analytical determination of the structure of the outer crust of a cold nonaccreted neutron star: Extension to strongly quantizing magnetic fields

“…In principle, the global structure of a highly magnetized neutron star should be calculated solving simultaneously Einstein's and Maxwell's equations. However, the influence of the magnetic field on the crust size was shown to lie below about 1-2% for B 10 4 [28][29][30][31]. We shall thus employ the same analytical formulas as those derived for unmagnetized neutron stars in Ref.…”

“…Having found the composition, the crustal properties could thus be refined in a second stage by solving numerically Eqs. ( 29) and (30). The overall procedure will still remain much faster than the full minimization.…”

A Neutron Star Is Born

“…From the theoretical point of view, there is no reason to believe that the structure of the magnetars differs from the ones I have mentioned in this article. Thus, they can also be described as hadronic objects [81,[154][155][156][157][158], as quark stars [138,139,[157][158][159][160] or as hybrid stars [155,157].…”

“…However, at least two important points involving matter subject to strong magnetic fields can be dealt with even without the LORENE code. The first one is the crust core transition density discussed in [156,162]. Although the magnetic fields at the surface of magnetars are not stronger than 10 15 G, if the crust is as large as expected (about 10% of the size of the star), at the transition region the magnetic field can reach 10 17 G. The transition density can then be estimated by computing the spinodal sections, both dynamically and thermodynamically.…”