Events, Seminars, Talks

Abstract
Gaia, developed and operated by the European Space Agency, was launched in 2013, and operated until January 2025. It's creating a revolutionary six-dimensional map of our Galaxy by measuring the accurate distances and space motions of some three billion stars. While the measurement of star positions has a very long history, stretching back more than 2000 years, Gaia's accuracies exploit the numerous advantages of measurements made from above the Earth's atmosphere. Absolute positional accuracies of order 10 micro-arcsec can register stellar motions that would require more than 10,000 years to be discerned on the ground.  This is providing a major advance in understanding stellar evolution, and in unravelling the composition, structure, and history of our Galaxy's formation. I will not focus on the technical details, but provide a "big picture" of Gaia's scientific advances.

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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. To arrange a visit with the speaker during the visit, please contact their host: Haochang Jiang

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