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The clusterization of nuclear matter in a Neutron star under strong magnetic fields

Authors: Jianjun Fang

Ref.: PhD Thesis in Physics, University of Coimbra, Supervisors: Constança Providência and Helena Pais (December 2017) (2017)

Abstract: We study of the stability of stellar matter in the inner crust of neutron stars under the effect of strong external magnetic fields, as the ones that may occur in magnetars. Quantizing magnetic fields with inten- sities in the range of 2 × 1015 < B < 5 × 1016G are considered. We use relativistic mean-field models to describe nuclear matter coupled to the magnetic field. The anomalous magnetic moment of neutrons and protons are explicitlely included in the study and their effect anal- ysed. The stability of the ground state is then examined with respect to longitudinal modes using the relativistic Vlasov formalism, and the explicite calculation of the dynamical spinodal. We find that the strong magnetic field introduces additional heterogeneity into the structure of the inner crust with significant fluctuations in the cluster size with density. It can extend the crust-core transition density by 0.01 fm−3 or even more, and would result in a significant increase in the mass and moment of inertia of the crust and, perhaps most interestingly, at high enough field strength, we obtain layers of homogeneous nuclear matter sandwiched in-between clustered matter in the deep layers of the inner crust. The simultaneous effects of the magnetic field intensity and both the symmetry energy and the temperature on the crust-core transition of a magnetar are also discussed. Under strong magnetic fields, the crust extension is very sensitive to the density dependence of the sym- metry energy, and the properties that depend on the crust thickness could set a constraint on the equation of state. The thermodynami- cal spinodals are used to study the stability of stellar matter at finite temperature. It is shown that the effect on the extension of the crust- core transition is washed out for temperatures above 109 K. However, for temperatures below that value, a noticeable effect exists that grows as the temperature decreases and which should be taken into account when the evolution of magnetars is studied.