Astronomy and Astrophysics - An Introductory Survey, A lecture series by Prof. G. Srinivasan - Lecture 27 - Supermassive Black Holes

"Black Holes are macroscopic objects with masses varying from a few solar masses to millions of solar masses. Macroscopic objects are governed by a variety of forces derived from a variety of approximations to a variety of physical theories. In contrast, the only elements in the construction of Black Holes are our basic concepts of space and time. They are, thus, almost by definition, the most perfect macroscopic objects there are in the universe. - S. Chandrasekhar" ABOUT THE LECTURE The compact sources at the centre of radio galaxies have incredible luminosities. Invoking the "Eddington Luminosity Limit", astronomers concluded that the central engine must have a mass of the order of a billion solar masses. The time variability of the compact central source led one to conclude that it must be a very compact object. Thus emerged the paradigm that the central engines of Quasars and Radio Galaxies must be supermassive black holes. In April 2019, a stunning image was made of the shadow of the giant black hole at the centre of the giant elliptical galaxy M 87. This was done using the "Event Horizon Telescope" - an intercontinental baseline radio interferometer. This Lecture describes the technical advances that were needed to make such an image and explains how one might understand the morphology of the image. Lecture 28: The case of the missing neutrinos Lecture 29: Gravitational Radiation ABOUT THE LECTURE SERIES This lecture series is organized by the Astronomical Society of India as a part of its Golden Jubilee celebrations. Aimed at undergraduate and graduate students, this series of talks by renowned astrophysicist and teacher, Prof G. Srinivasan, starts from the first principles of Physics and builds up the subject rigorously to the present state of our understanding. Series website: https://astron-soc.in/srini-ana The website hosts a question bank as well as a list of suggested reading for each lecture (prepared by Dr Sushan Konar) ABOUT THE SPEAKER Professor G. Srinivasan In a research career spanning more than five decades, his interests have spanned many aspects of physics and astrophysics. He is a passionate teacher and has authored two outstanding Astronomy texts titled ‘What Are The Stars?’ and ‘Can Stars Find Peace?’ He is a Past President of the Astronomical Society of India, and a Past President of the Division on Space and High Energy Astrophysics of the International Astronomical Union. In his distinguished career he has worked at the University of Chicago, USA; the IBM Research Laboratory in Zurich, Switzerland; Chalmers University of Technology, Goteborg, Sweden; the Cavendish Laboratory, University of Cambridge, England and the Raman Research Institute, Bengaluru Follow us on social media at https://twitter.com/asipoec https://www.facebook.com/asi.poec/ This series is also supported by the IAU OAE Centre in India https://twitter.com/astro4edu_India https://www.facebook.com/OAE-Center-India-105698322030674