Accretion-Powered Galactic Nuclei: Extreme Variability and Transient Phenomena

In some galaxies, the accretion of matter onto their central supermassive black holes (SMBHs) generates substantial radiation. These objects, known as active galactic nuclei (AGNs), are generally persistent. Recent observations have unveiled fascinating categories of galactic nuclei that exhibit extreme variability, such as quasi-periodic eruptions, and changing-look AGNs. Additionally, the tidal disruption of stars by an SMBH can trigger accretion, leading to transient phenomena in otherwise quiescent galactic nuclei. Multi-wavelength observations of these objects are providing new information, offering valuable insights and posing significant challenges. The speaker will present an overview of galactic nuclear activity and discuss recent findings, particularly those derived from AstroSat.