Speaker
Description
Sagittarius A has been investigated for years and is one of the most interesting sources in the Galactic Center, a region enriched by strong magnetic fields, dense gas and enhanced cosmic-ray activity. The black hole’s shadow was imaged for the very first time in 2022 by the Event Horizon Telescope at a frequency of 230 GHz, demonstrating a characteristic ring morphology and a significantly small horizon-scale variability within the accretion flow. On the other hand, Sagittarius A exhibits bright flaring events in the Near Infrared (GRAVITY, Very Large Telescope Interferometer) and X-ray bands (Chandra X-ray Observatory) several times a day, with several bright flares tracing an orbit in the vicinity of the supermassive black hole. One of the most effective ways to investigate these phenomena is through General Relativistic Magnetohydrodynamic (GRMHD) simulations of the magnetized accretion disk coupled with General Relativistic Radiative Transfer (GRRT) calculations to create synthetic observables of the accretion flow near the horizon. A recent breakthrough in GRMHD simulations has been the implementation of resistivity within the accretion flow, providing a natural mechanism for magnetic field dissipation and describing its interaction with the disk plasma in the framework of General Relativity. We present the most recent code developments in resistive GRMHD and GRRT calculations and their implementation in state-of-the-art codes (BHAC and BHOSS, respectively). We show the first images of a resistive accretion flow in the vicinity of a black hole and discuss the effect of magnetic field dissipation on the highly variable MAD accretion state. Furthermore, we generate synthetic observables of resistive accretion disks for direct comparison with the horizon-scale images of Sagittarius A* and investigation of the observed accretion flow variability. These numerical advances pave the way for a more physical description of the intricate mechanisms that occur in the vicinity of an accreting black hole, providing a promising framework for understanding the vast spectrum of multi-messenger observations and characteristics of the supermassive black hole in the Galactic Center.
