Astronomy and Astrophysics - An Introductory Survey, A lecture series by Prof. G. Srinivasan - Lecture 22 - Black Holes I

There are two kinds of black holes. The first is formed in supernovae, as the evolutionary end products of the most massive stars. The stellar black holes can be as heavy as a few tens of solar masses. Then there are the super-massive black holes, such as the one sitting at the center of the Milky Way and most other galaxies, which can be more than a million times more massive than the Sun. On 10 April 2019, eighty years after Oppenheimer & Snyder predicted the existence of black holes, scientists of the ‘Event Horizon Telescope (EHT) released the first-ever image of a black hole - the super-massive object at the heart of the M87 galaxy. This impressive image is a rather remarkable indication of our technological prowess as well as the capability of our scientists to form and work in gigantic collaborations. ABOUT THE LECTURE The idea that light may not be able to escape from sufficiently dense bodies dates back to 1783 when the English Pastor John Michell first advanced this notion. This found a prominent mention in the great treatise by the French mathematician Laplace (1798). This conclusion was within the premise of Newton's theory of gravity. Einstein published his new theory of gravity in 1915. Within a couple of months, the great German Polymath obtained an exact solution to Einstein's equations for the gravitational field. This solution, describing the geometry of space-time around a non-rotating star, clearly showed that when a star contracts to a critical radius, no signal would be able to escape from it. Many decades later, the New Zealand mathematician Roy Kerr obtained an exact solution to Einstein's equations describing the geometry of space-time outside a rotating star. This lecture is a historical account of these monumental discoveries and explains several of the spectacular consequences of Einstein's theory of gravity. Lecture 23: Black Holes II Lecture 24: Binary Neutron Stars 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