Dynamics and Radiation of Accretion Flows in Complex Geometries: From Tilted Disks to Binary Black Holes

The era of multi-messenger astrophysics demands precise theoretical models for accretion flows in complex environments. In this talk, I will present results from high-fidelity General Relativistic Magnetohydrodynamic (GRMHD) simulations addressing two extreme scenarios: tilted accretion disks and binary black holes (BBHs). First, I will discuss the dynamics of misaligned accretion flows around single black holes, highlighting a novel magnetically driven retrograde precession mechanism. Second, I will introduce a newly developed GPU-accelerated GRMHD framework based on AthenaK, implemented with a superimposed Kerr-Schild metric. I apply this tool to simulate large-mass-ratio binary systems, investigating the complex interaction between the secondary black hole and the primary’s accretion disk. I will discuss the resulting electromagnetic signatures calculated via General Relativistic Radiative Transfer (GRRT), specifically focusing on shock-driven flares and periodic relativistic self-lensing events, which offer unique diagnostic probes for future time-domain and LISA observations.