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Effects of Strong Magnetic Fields on the Crust and Entrainment in Neutron Stars

Authors: Sagar Dipak Silva Pratapsi

Supervisors: Contança Providência

MSc thesis, Mestrado em Física, Universidade de Coimbra (2017)

Abstract: Pulsars are magnetized neutron stars that rotate at exceptionally stable rates. Nevertheless, younger pulsars exhibit sporadic events called glitches, in which the rotation frequency suddenly increases and then steadily decreases. It is believed that the glitches are a consequence of angular momentum transfer between the crust and superfluids in the star’s interior. The crust, however, may not be able to store enough momentum of inertia to validate this model. Magnetic fields of high intensity significantly affect the properties of neutron stars, which may indicate they play a role in the glitch mechanism. However, their intensity must be of the order of 1018 G to significantly alter the equation of state of stellar matter. As a result, such effects are not usually considered when performing magnetohydrodynamic calculations in stars. Recently, however, a possible effect on the crust’s equation of state has been discovered which, under a strong magnetic field, results in the increase of the crust’s extension. The goal of this thesis is to study the effects of magnetic fields on the stellar matter’s equation of state, particularly those that are most directly related to pulsar glitches. We analyze two problems: • How strong must a magnetic field be to significantly alter the crust’s dimensions? • How does the magnetic field affect the entrainment between superfluid neutrons and the crust? For the first problem, we use the dynamical spinodal method in order to determine the crust’s size under strong magnetic fields. For the second, we study the effect of the magnetic field on the relativistic entrainment matrix for a mixture of protons and neutrons, using a relativistic Landau Fermi liquid theory, generalized to include superfluidity.