The extremes of AGN variability: changing-look AGN and supermassive binary black holes
Stefanie Komossa (Max Planck Institute for Radio Astronomy)
Thursday 23/11/2023 @ 11:30, Sala Antonio Sollima (IV piano Battiferro) + remoto
Highly variable and transient active galactic nuclei (AGN) provide us with important insights into the physics of accretion of matter onto their central supermassive black holes (SMBHs). This talk discusses some of the most extreme cases of variability so far observed among AGN, including the highest-amplitude X-ray--optical outbursts, deep-minima states, and exceptional optical emission-line changes, and their interpretation, based on observations taken at mutiple wavebands from radio to the X-ray regime. A fraction of AGN harbor binary SMBHs at their centers. Upon final coalescence, these are the loudest sources of gravitational waves in the universe. After a brief introduction of the topic, I will then discuss the best-known case of a compact binary SMBH candidate, hosted by the blazar OJ 287. In the course of the project MOMO, we have carried out the densest, longest, multi-wavelength monitoring project of OJ 287 done so far from radio to high energies, and I will highlight key results and implications for binary SMBH scenarios.