TAPIR Seminar

In person: 370 Cahill. To Join via Zoom: 868 5298 8404

ABSTRACT: "Classical" accretion disks are geometrically thin, radiatively efficient and mechanized by turbulent viscosity. Yet, many observational and theoretical issues challenge this paradigm. This is perhaps unsurprising, as classical disks do not take into account certain key physics, which I will highlight in two ways. Firstly, the infalling gas that eventually forms a black hole (BH) accretion disk has no prior knowledge of the black hole spin axis. Thus, most disks will be at least initially misaligned with respect to the BH spin axis. As the BH rotates, it drags the surrounding space-time, which warps the disk. I will show how strong warps dramatically alter the accretion process via the "nozzle shock" and "disk tearing" mechanisms. Such mechanisms drive rapid variability, similar to what is seen in changing-state active galactic nuclei. Secondly, realistic quasar disks may be fed from cold, highly magnetized gas complexes, which can result in magnetically dominated disks that accrete extremely quickly. I will present horizon-scale simulations of magnetically dominated disks that were self-consistently formed in a galaxy. I will show how the magnetic field evolves in surprising ways as the gas reaches the BH, and how the central engine produces emission and outflows that are qualitatively similar to what is observed in nature.