Speaker
Description
General Relativistic MagnetoHydroDynamic (GRMHD) simulations solve the time-dependent electro- and hydrodynamic partial differential equations in arbitrary spacetimes. They usually employ conservative integration routines to advance the solution in the time domain, which are known to produce mostly numerically stable results. The most common one is the Finite Volume Method, which accurately evolves the conserved quantities in time, but in return requires the precise recovery of the primitive variables (pressure, velocity and density) in each time step and every grid cell, by solving a complex system of algebraic equations. This procedure is known for its numerical difficulty, especially in the context of GRMHD simulations. Although the currently used Newton- Raphson solvers prove to be very useful, they fail to provide accurate solutions in highly magnetized, low-density, or high Lorentz factor regions. There regions, that are commonly found in highly energetic astrophysical environments such as black hole accretion systems, require advanced techniques for primitive variable recovery, which often rely on approximations. In our work, we employ the robust method proposed in Kastaun et al. 2021 and implement it in the Black Hole Accretion Code (BHAC). The novelty of this approach is to transform the system of equations to a single equation and provide a bisection bracketing interval for accurate convergence in numerically unstable domains. We apply our implementation in high-resolution GRMHD simulations of magnetically arrested disks, whose variable accretion flow creates quasiperiodic flux eruptions and strongly magnetized regions within the disk and funnel.
