Abstract：Active galactic nuclei are mostly powered by inflow through accretion disks onto central supermassive black holes. Beyond a few times their Schwarzschild radius, gravitational instability in these disks leads to self-regulated formation and evolution of massive stars which chemically enrich their neighborhood along with stellar-mass black holes. These compact remnants are captured by coexisting massive main sequence stars, form close binaries, readily merge, and excite intense gravitational waves with potentially observable electromagnetic signatures. The massive stars' migration, with or without black hole cores, efficiently transporting mass regardless of the Eddington limit and promoting the rapid growth of supermassive black holes in the early Universe. Analogous physical processes are also relevant in the context of planet formation in protostellar disks. They account for the persistent super-solar metallicity, especially in Nitrogen and iron, inferred from broad emission lines of high and low redshift AGNs.
Bio：Professor Douglas Lin is a theoretical astrophysicist at the University of California, Santa Cruz and the Institute of Advanced Studies, Tsinghua University. His most notable contributions include the pioneering simulations of gaps and spirals in protoplanetary disks with embedded protoplanets, which were verified by the later ALMA observations, and the disk-migration prediction which accounts for the origin of the short-period exoplanets. His broad research areas also include: formation and evolution of the Solar and exo-planetary systems; interacting binary stars; dynamical evolution of globular clusters and satellite galaxies in the Galaxy; star formation and evolution in accretion disks around super-massive black holes in the Galactic center and active galactic nuclei. He was the founding director of the Kavli Institute for Astronomy and Astrophysics at Peking University. He received the Brouwer Award from the American Astronomical Society and the Catherine Wolfe Bruce Gold Medal from Astronomical Society of the Pacific.