Abstract
Neutron stars host the strongest magnetic fields that we know of in the Universe. Their magnetic fields are the main means of generating their radiation, either magnetospheric or through the crust. Moreover, the evolution of the magnetic field has been intimately related to explosive events of magnetars, which host strong magnetic fields, and their persistent thermal emission. The evolution of the magnetic field in the crusts of neutron stars has been described within the framework of the Hall effect and Ohmic dissipation. Yet, this description is limited by the fact that the Maxwell stresses exerted on the crusts of strongly magnetised neutron stars may lead to failure and temperature variations. In the former case, a failed crust does not completely fulfil the necessary conditions for the Hall effect. In the latter, the variations of temperature are strongly related to the magnetic field evolution. Finally, sharp gradients of the star’s temperature may activate battery terms and alter the magnetic field structure, especially in weakly magnetised neutron stars. In this review, we discuss the recent progress made on these effects. We argue that these phenomena are likely to provide novel insight into our understanding of neutron stars and their observable properties.
Highlights
The magnetic field evolution has been a central topic in the study of the physics of neutron stars (NS)
Hall drift is related to the presence of free electrons in the crust which carry the electric current while the ion lattice remains rigid, any Lorentz force remains in equilibrium due to crust elasticity
When the crucial role of the magnetic field in the physics of NSs was assessed, it was modelled as a dipolar field, unchanged for the entire life of the star
Summary
The magnetic field evolution has been a central topic in the study of the physics of neutron stars (NS) Even before their observational discovery [1] it had been proposed that NSs host strong magnetic fields which lead to energy emission [2]. Apart from the isotropic conductivity of the lattice, pasta phases such as rods, slabs, tubes and bubbles, appearing at the base of the crust, where the nuclear forces and charge screening play an important role lead to enhancements of the resistivity and changes to its overall properties [51,52] These models have successfully addressed observational properties of NSs and they have revealed, rich effects in terms of magnetohydrodynamical evolution, arising from the non-linear nature of the equations.
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