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Warped accretion discs are common around black holes and stars. There is growing indirect observational evidence for warped circumstellar discs around young stars, indicated by shadows cast by the warps. I will briefly review the rich warped disc dynamics, including warp diffusion, bending wave propagation and disc breaking. I will focus on a hydrodynamic instability due to resonance between pairs of inertial waves and warp induced shear flow. The ensuing turbulence, captured for the first time in a global simulation, damps relative orbital inclinations and leads to a decrease in the angular momentum deficit. As a result, the warp undergoes significant damping within one bending-wave crossing time. Observed protoplanetary disc warps are likely maintained by companions or aftermath of disc breaking.

Host: Xuening Bai