Dissertations, Theses, and Capstone Projects

Date of Degree

6-2026

Document Type

Master's Thesis

Degree Name

Master of Science

Program

Astrophysics

Advisor

Ashley J. Bransgrove

Advisor

Valentin A. Skoutnev

Subject Categories

Other Astrophysics and Astronomy | Physical Processes | Plasma and Beam Physics | Stars, Interstellar Medium and the Galaxy

Keywords

Neutron Stars, Magnetars, Magnetic Field Evolution, Magnetohydrodynamics, High Energy Astrophysics, Theory and Computational Astrophysics

Abstract

Magnetars are the most extremely magnetized objects in the universe. Their strong magnetic fields generate high-energy magnetic flares with instantaneous luminosity that can outshine their host galaxy. Previous works have explored how Hall drift in the crust affects the dynamics of magnetic field lines in the magnetosphere. This work investigates how a change in the magnetosphere, such as a flare or an outburst, can excite Hall evolution in the crust. We investigate how the twisting and untwisting of magnetic field lines in a magnetar’s magnetosphere launches Hall waves through its crust using a one-dimensional numerical model. We use the Dedalus code to solve the Hall induction equation with time-dependent boundary conditions in the context of a neutron star’s crust, where electrons are bound to magnetic field lines and move across a lattice of ’frozen’ ions. The post-flare Hall waves could produce variations in the spin-down torque, as observed after magnetar activity.

We ran a fiducial simulation with a background magnetic field strength of 10^14 G and then scanned over stronger background magnetic field strengths to analyze their effects on the Hall waves. The fiducial simulation found that it takes about 10,000 years for the first Hall waves to reach the core, after which Ohmic dissipation dissipates most of their energy. We also found that a background magnetic field of 10^14 G produces Hall waves with magnetic stress equal to 20 percent of the crust’s critical stress. Therefore, for a background magnetic field of 5 x 10^14 G and higher, the Hall waves’ magnetic energy would be strong enough to break the crust and cause a secondary magnetospheric event. We repeated the simulation for Bz = 5 × 10^14, 10^15, and 5 × 10^15 G, holding all other parameters constant. The

simulation found that at these strengths the magnetic energy from the background magnetic field is stronger then then crusts’ shear modulus for some portions. In the areas where the background magnetic field’s energy is stronger than the shear modulus, the crust will behave as a magnetized liquid. In these portions, the Hall waves’ shear magnetic stress cannot rupture the crust, as the crust behaves like a liquid and yields. However, analyzing the Hall waves’ shear magnetic energy in the portion of the crust that still behaves as a solid, these higher background magnetic values do produce Hall waves strong enough to rupture the crust and cause a secondary magnetospheric event. The timescales of the Hall waves produced with the stronger background magnetic field strengths align with our expectations and are proportional to the magnetic field strength, producing Hall waves that are 5, 10, and 50 times faster than those produced with Bz = 10^14 G, respectively.

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