GRay2: A General Purpose Geodesic Integrator for Kerr Spacetimes

Abstract

Fast and accurate integration of geodesics in Kerr spacetimes is an important tool in modeling the orbits of stars and the transport of radiation in the vicinities of black holes. Most existing integration algorithms employ Boyer-Lindquist coordinates, which have coordinate singularities at the event horizon and along the poles. Handling the singularities requires special numerical treatment in these regions, often slows down the calculations, and may lead to inaccurate geodesics. We present here a new general-purpose geodesic integrator, GRay2, that overcomes these issues by employing the Cartesian form of Kerr-Schild coordinates. By performing particular mathematical manipulations of the geodesic equations and several optimizations, we develop an implementation of the Cartesian Kerr-Schild coordinates that outperforms calculations that use the seemingly simpler equations in Boyer-Lindquist coordinates. We also employ the OpenCL framework, which allows GRay2 to run on multi-core CPUs as well as on a wide range of GPU hardware accelerators, making the algorithm more versatile. We report numerous convergence tests and benchmark results for GRay2 for both time-like (particle) and null (photon) geodesics.

11 pages, 9 figures, 3 tables; submitted to ApJ

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• GRMHD Simulations and Modeling for Jet Formation and Acceleration Region in AGNs
• Observing supermassive black holes in virtual reality
• Shadow Geometry of Kerr Naked Singularities
• Blacklight: A General-Relativistic Ray-Tracing and Analysis Tool
• Strong gravitational lens image of the M87 black hole with a simple accreting matter model
• FANTASY: User-Friendly Symplectic Geodesic Integrator for Arbitrary Metrics with Automatic Differentiation
• Not all spacetime coordinates for general-relativistic ray tracing are created equal
• Synthetic gravitational lens image of the Sagittarius A${}^{\ast }$ black hole with a thin disk model
• ipole - semianalytic scheme for relativistic polarized radiative transport
• All analytic solutions for geodesic motion in axially symmetric space-times
• PATOKA: Simulating Electromagnetic Observables of Black Hole Accretion