Astronomy and Astrophysics - An Introductory Survey, A lecture series by Prof. G. Srinivasan - Lecture 23 - Black Holes II

Chandrasekhar once remarked - The black holes of nature are the most perfect macroscopic objects there are in the universe: the only elements in their construction are our concepts of space and time.'' Very appropriately, one of the most remarkable developments in physics in the later part of the twentieth century, the formulation of the theory of black holes, has depended entirely upon considerations of theoretical physics and abstract mathematics, without hardly any observational corroboration. This lecture describes the path to the most important milestones of this theory in simple terms. ABOUT THE LECTURE As we saw in Lecture 21, in 1939 Oppenheimer and his student, Snyder, made the spectacular discovery that if a star contracts to the critical radius, and becomes BLACK, it will continue to collapse till it disappears - all that will be left is a Black HOLE! This raised the following fundamental question, ``What is inside a black hole?"" This question was answered emphatically by Sir Roger Penrose in 1965. He showed in a mathematically exact manner that if a black hole forms, there must be a space-time singularity inside it. He was awarded the Nobel Prize in 2020 for this profound discovery. This was followed by a series of spectacular theorems - the ``No Hair Theorems"" - concerning the attributes of black holes. And then came, in 1974, the great discovery by Stephen Hawking that black holes will emit radiation, after all! This lecture will attempt to describe these great discoveries in simple terms. Lecture 24: Binary Neutron Stars Lecture 25: Recycled Pulsars 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