Mysterious Quasi-Periodic Signals from Centers of External galaxies

In recent years, a new class of astrophysical transients known as Repeating Extragalactic Nuclear Transients (RENTs) has emerged. They originate from centers of galaxies and exhibit X-ray fluctuations that repeat on a few minutes to a month timescale. A leading hypothesis is that they arise from interactions between a small, gravitationally bound object and the accretion disk of a supermassive black hole (SMBH). If confirmed, such extreme mass ratio binaries could be detected with future space-based gravitational wave observatories like LISA, and would significantly advance our understanding of SMBH growth, explore dark energy, and put fundamental constraints on gravity. I will present an overview of RENTs and highlight India/AstroSAT’s role in their studies. I will end by discussing the potential of this exciting new frontier in astrophysics in the imminent era of the Rubin observatory.