# Magnetic Field-Decay-Induced Electron Captures: a Strong Heat Source in Magnetar Crusts

## TL;DR

This paper introduces a novel heating mechanism in magnetar crusts where magnetic field decay induces electron captures, releasing heat comparable to the magnetic energy and potentially powering magnetars' X-ray emissions.

## Contribution

It proposes a new process where magnetic decay causes electron captures that significantly heat the crust, a mechanism not previously considered as a primary energy source.

## Key findings

- Field-decay electron captures release heat comparable to magnetic energy.
- This mechanism can explain the soft X-ray emission in magnetars.
- The process is driven by magnetic pressure loss and increased electron Fermi energy.

## Abstract

We propose a new heating mechanism in magnetar crusts. Magnetars' crustal magnetic fields are much stronger than their surface fields; therefore, magnetic pressure partially supports the crust against gravity. The crust loses magnetic pressure support as the field decays and must compensate by increasing the electron degeneracy pressure; the accompanying increase in the electron Fermi energy induces nonequilibrium, exothermic electron captures. The total heat released via field-decay electron captures is comparable to the total magnetic energy in the crust. Thus, field-decay electron captures are an important, if not the primary, mechanism powering magnetars' soft X-ray emission.