Magnetized Moving Mesh Merger of a Carbon-Oxygen White Dwarf Binary

TL;DR

This study simulates magnetic field evolution during a white dwarf binary merger, revealing exponential magnetic growth and complex field structures that could influence remnant evolution and ignition processes.

Contribution

It introduces the first magnetohydrodynamic moving mesh simulations of white dwarf mergers, demonstrating significant magnetic field amplification during coalescence.

Findings

Magnetic fields grow exponentially during merger.

Final magnetic field strength exceeds 10^{10} G.

Magnetic energy constitutes about 0.2% of the remnant's total energy.

Abstract

White dwarf (WD) binary mergers are possible progenitors to a number of unusual stars and transient phenomena, including type Ia supernovae. To date, simulations of mergers have not included magnetic fields, even though they are believed to play a significant role in the evolution of the merger remnant. We simulated a 0.625 - 0.65 $M_{\odot}$ carbon-oxygen WD binary merger in the magnetohydrodynamic moving mesh code Arepo. Each WD was given an initial dipole field with a surface value of $\sim10^3$ G. As in simulations of merging double neutron star binaries, we find exponential field growth within Kelvin-Helmholtz instability-generated vortices during the coalescence of the two stars. The final field has complex geometry, and a strength $>10^{10}$ G at the center of the merger remnant. Its energy is $\sim2\times10^{47}$ ergs, $\sim0.2$% of the remnant's total energy. The strong field likely influences further evolution of the merger remnant by providing a mechanism for angular momentum transfer and additional heating, potentially helping to ignite carbon fusion.