Abstract
The post-merger evolution of binary white dwarfs is a complex process that relies heavily on understanding the interplay between fluid dynamics, magnetic fields, and gravitational forces. In particular, magnetic fields and magnetorotational instability play critical roles in determining the thermal structure and angular momentum transport of the post-merger configuration. In this work, we introduce a novel multiwave approximate Riemann solver for ideal MHD simulations, implemented in the massively parallel astrophysical framework, FLASH. Building upon the work of Bouchut et al., our solver is adapted to incorporate the Helmholtz equation of state and multispecies transport advection equations, alongside steepening and flattening algorithms that preserve the integrity of magnetized shocks. Through a series of standard tests involving self-similar solutions, we demonstrate the solver’s accuracy and stability, laying the groundwork for future magnetized compact binary merger simulations that include both white dwarfs and neutron stars, with suitable extensions to the equation of state. Because the magnetic field is understood to play a central role in many astrophysical processes, this new computational approach can be applied both to white dwarf mergers, as well as a wide range of astrophysical applications.