HORIZON: Accelerated General Relativistic Magnetohydrodynamics

We present Horizon, a new graphics processing unit (GPU)-accelerated code to solve the equations of general relativistic magnetohydrodynamics in a given spacetime. We evaluate the code in several test cases, including magnetized Riemann problems and rapidly rotating neutron stars, and measure the performance benefits of the GPU acceleration in comparison to our CPU-based code Thor. We find substantial performance gains in comparison to a quad-core CPU both in single- and double-precision accuracy, and discuss these findings in the context of future numerical modeling efforts.