Accreting Massive Black Holes at the Center of Galaxies and their Impact on Small Sub-pc to Large Galactic Scales

We cannot directly observe black holes as no light escapes from the event horizon. However, we can detect the light from accreting gas, which forms a dense disk around the black hole, known as an accretion disk. The accretion of material by a massive black hole at the center of its host galaxy forms an active galactic nucleus (AGN), the innermost region of which emits X-ray radiation. An AGN is energetically efficient for regulating the growth of galaxies and is crucial for the development of the Universe we see today. One of the most important tools to probe the innermost accretion flow is the detection of X-ray reverberation echoes, where the X-ray photons reflected from the accretion disk are delayed relative to the primary X-ray source. In this talk, I will first discuss how detailed measurements of the reflected X-rays from the accretion disk can be used to probe the innermost regions of accretion flow just outside the event horizon and determine the fundamental properties of the black hole, such as its spin, across the complete mass scales. Peering into the growth channels of black holes, I will discuss how we can distinguish accretion vs. merger-dominated black hole growth and probe the cosmological evolution of black hole spins in the last 10 billion years of cosmic history. Finally, I will show how enigmatic Ultra-Fast Outflows launched from the AGN accretion disk can be used to probe the feedback mechanism connecting the central black holes with their host galaxies.

Dr. Labani Mallick is a National Fellow of the Canadian Institute for Theoretical Astrophysics (CITA) hosted at the University of Manitoba, Winnipeg, Canada. She spent nearly three years in the USA for her postdoctoral research at the California Institute of Technology (Caltech) and Pennsylvania State University. She received her PhD in Astrophysics from the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in 2019. Her doctoral research addressed the complex nature of energy-dependent variability in active galactic nuclei (AGN) and the interplay between various physical processes in strong gravity. Her current research includes black hole spin measurements across mass and cosmic timescales to probe the formation channels of massive black holes and the detection advancement of relativistic winds to constrain the AGN feedback mechanisms. She develops and employs novel spectral-timing models and methods to black hole observations to extend our census of known parameters into the domains key to the black hole-galaxy co-evolution.