Overview: Gas falling into a black hole (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, we still do not understand how the curved space-time of a spinning black hole imprints itself on the structure of the tilted disks. In this proposal we make use of the fact that, at their core, black hole accretion disks and jets are well-described by the general relativistic magnetohydrodynamics (GRMHD) equations of motion. By carrying out direct GRMHD simulations of tilted thin and thick disks, we will obtain the first-principles understanding of disk physics in typical, tilted BH accretion systems. To surmount the prohibitively expensive nature of these simulations, we have 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. Intellectual Merit: By studying magnetic fields, accretion, and jets near the black hole event horizon, this proposal probes strong-field gravity. The proposed simulations will provide answers to several long-standing questions in the BH accretion community: Do tilted thick disks undergo rigid-body precession and does this depend on whether they are externally fed (e.g., via gas infall from large distances or by a tidal disruption of a star)? Do the inner parts of thin disks align with the midplane of the BH due to the Bardeen-Petterson effect as was predicted more than 40 years ago but has never been seen in a GRMHD simulation? Do tilted disks break apart into several misaligned annuli as suggested by recent non-relativistic hydrodynamical simulations? Do thin disks drag in large-scale magnetic flux, allowing them produce relativistic jets as thick disks do, and, if so, how? Understanding these issues will allow the scientific community to meaningfully and quantitatively interpret black hole accretion in a wide range of astrophysical contexts. Broader Impacts: Impact on Astrophysics: This project elucidates the basic physics of tilted accretion disks and their jets that is applicable to a range of sources including quasars, black hole binaries, binary neutron star mergers, ultra-luminous X-ray sources, and tidal disruption events. The 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. Relevance to Fundamental Physics: The proposed simulations will study, from first principles and for the first time, the behavior of the standard thin disks when they are misaligned relative to the central BH. Research Experience for High Schoolers: The PI will bring experiments into a local high-school and will involve high-school students into data analysis and visualization, and they will gain experience in working with Big Data, black hole accretion and jet physics, presenting their results at conferences, and publishing their work in peer-reviewed journals. The PI has has worked with 14 students (1 high-school, 2 undergraduate, and 11 graduate students), which has led to 10 peer-reviewed publications. Public Outreach: Black holes consuming gas and producing relativistic jets offer some of the most fascina
|Effective start/end date||8/1/20 → 7/31/23|
- National Science Foundation (AST-2009884)
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