Accumulation of Elastic Strain toward Crustal Fracture in Magnetized Neutron Stars
Abstract
This study investigates elastic deformation driven by the Hall drift in a magnetized neutron-star crust. Although the dynamic equilibrium initially holds without elastic displacement, the magnetic-field evolution changes the Lorentz force over a secular timescale, which inevitably causes the elastic deformation to settle in a new force balance. Accordingly, elastic energy is accumulated, and the crust is eventually fractured beyond a particular threshold. We assume that the magnetic field is axially symmetric, and we explicitly calculate the breakup time, maximum elastic energy stored in the crust, and spatial shear-stress distribution. For the barotropic equilibrium of a poloidal dipole field expelled from the interior core without a toroidal field, the breakup time corresponds to a few years for the magnetars with a magnetic-field strength of ~1015 G; however, it exceeds 1 Myr for normal radio pulsars. The elastic energy stored in the crust before the fracture ranges from 1041 to 1045 erg, depending on the spatial-energy distribution. Generally, a large amount of energy is deposited in a deep crust. The energy released at a fracture is typically ~1041 erg when the rearrangement of elastic displacements occurs only in the fragile shallow crust. The amount of energy is comparable to the outburst energy on the magnetars.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2022
- DOI:
- 10.3847/1538-4357/ac9184
- arXiv:
- arXiv:2209.04136
- Bibcode:
- 2022ApJ...938...91K
- Keywords:
-
- Neutron stars;
- Magnetars;
- Compact objects;
- High energy astrophysics;
- Magnetic fields;
- Soft gamma-ray repeaters;
- 1108;
- 992;
- 288;
- 739;
- 994;
- 1471;
- Astrophysics - High Energy Astrophysical Phenomena;
- General Relativity and Quantum Cosmology
- E-Print:
- 14 pages, 5 figures