Princeton University Gravity Initiative Seminar

Abstract: Classical" accretion disks are geometrically thin, radiatively efficient and mechanized by turbulent viscosity. Yet, many observational and theoretical issues challenge this standard model, suggesting that we are missing essential-but-overlooked physics, such as warped **accretion. When black holes rotate, they twist up the surrounding space-time, torquing any matter that lives nearby. If an accretion disk is tilted with respect to the black hole spin, it becomes twisted up, developing a warp. Warps dramatically alter the accretion process and the resulting observables. I will discuss the internal hydrodynamic mechanisms that allow strong warps to drive the rapid inflow of gas to the black hole — far quicker than in classical thin disks. Strong enough warps also tear the disk apart into multiple, individually precessing “sub-disks”. These sub-disks lead short, violent lives as they crash into each other. I will present synthetic observations of disk tearing events and draw connections to poorly-understood ``changing-look'' events in active galactic nuclei. In particular, I will propose a method to measure accretion disk tearing in active galactic nuclei, allowing us to detect strong warps in real systems.