When Disks Break: A GRMHD Study of Tilted Accretion Flows around Kerr Black Holes

The Bardeen-Petterson effect, arising from a misaligned black hole spin, can cause an accretion disk to either warp smoothly or violently tear into precessing rings. The conditions governing this transition remain a major unsolved problem in accretion disk physics. This project will develop a new General Relativistic Magnetohydrodynamics (GRMHD) module within the exascale code IDEFIX, built at IPAG. The PhD student will implement, validate, and then use this tool to run a suite of 3D simulations systematically exploring the parameter space — black hole spin, tilt angle, disk aspect ratio, and magnetic field geometry. The core scientific goals are to determine under which conditions a magnetized, tilted disk breaks into distinct sub-rings, and to connect this dynamics to observable signatures: low- and high-frequency Quasi-Periodic Oscillations (QPOs) in X-ray binaries, jet precession in AGN and XRBs, and changing-look AGN behavior. The new GRMHD module will be released publicly, providing the community with a high-performance GPU-ready tool for next-generation black hole accretion studies.