Magnetic Field Evolution in Neutron Star Crusts: Beyond the Hall Effect

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.

Spin Evolution of Neutron Stars

“…[244] and references therein), to poorly known topology and evolution of the magnetic field (see the reviews in Refs. [4,245]) and to many uncertainties in plasma-magnetic field interaction (see Refs. [246,247]).…”

Magnetic Field Evolution in the Crust of Neutron Stars: Crust Failure and Plastic Flow

“…This wide exploration of the effect of plastic flow in the crusts of neutron stars has demonstrated an additional evolutionary channel for the magnetic field beyond the Hall effect that has been central in such studies so far (Gourgouliatos et al 2022). The impact of plastic flow has started to receive significant attention recently focusing on applications such as the role global flows within the star, the limits of crust elasticity and the evolution of crustal fractures (Suvorov and Kokkotas 2019;Giliberti et al 2020;Kojima and Suzuki 2020;Kojima et al 2021a;Kuan et al 2021;Kojima et al 2021bKojima et al , 2022.…”

Heating of millisecond pulsars by magnetic field decay

“…The hotter area certainly is the polar cap surface where strong and small-scale field components must be necessarily present. Otherwise, no radio emission can be produced (Gil et al 2003). For the larger area, the heating mechanism discussed above may work.…”

“…Different heating mechanisms that may be responsible for a surface temperature T s ≳ 10 5 K have been discussed by Gonzalez & Reisenegger (2010). These are (besides some more exotic ones) frictional motion of superfluid vortices, rotochemical heating, magnetic field decay, and crust cracking.…”