GPU-Enabled General Relativistic Simulations of Misaligned Black Hole Accretion Systems

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A black hole accretion disk is a structure formed by diffused materials in orbital motion around a black hole (BH). From observations, the presence of tilted accretion disks around a BH is detected in some systems. However, the physics of accretion disks is poorly understood. This project will run very large scale simulations on the Blue Waters supercomputer to improve our fundamental understanding of BH accretion disks. Results of the proposed simulations will address long-standing questions in the way supermassive black holes consume and expel gas, and thereby exert feedback on their environment. These results will allow the physics community to gain first-principles understanding of disk physics in typical tilted BH accretion systems.Gas falling into a BH from large distances is unaware of BH spin direction, and misalignment between the accretion disk and BH spin is expected to be common. However, the physics of tilted disks is poorly understood, even for the "standard", geometrically thin, radiatively efficient accretion disks that power active galactic nuclei known as quasars and thought to provide the best observational tests of general relativity and disk physics. In particular, it is still not understood how the curved space-time of a spinning black hole imprints itself on the structure of the tilted disks. This project will make use of the fact that, at their core, BH accretion disks are well-described by the general relativistic magnetohydrodynamics (GRMHD) equations of motion. By carrying out direct GRMHD simulations of tilted thin and thick disks, the project will obtain the first-principles understanding of disk physics in typical, tilted BH accretion systems. To surmount the prohibitively expensive nature of these simulations, the project has constructed the first GPU-accelerated GRMHD code, H-AMR, which is capable of adaptive mesh refinement and is ideally suited for the Blue Waters supercomputer.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.