Astronomy and Astrophysics - An Introductory Survey, A lecture series by Prof. G. Srinivasan - Lecture 29 - Gravitational Radiation

On 25 November 1915, Einstein published the gravitational field equations of the General Theory of Relativity (GTR). Almost exactly a century later, on 14 September 2015 came the first direct detection of gravitational waves, made by an extremely sensitive instrument called the LIGO (Laser Interferometer Gravitational-Wave Observatory), providing the most direct proof of GTR. The observed gravitational waves were generated by the merger of two massive Black Holes some 1.3 billion years ago! ABOUT THE LECTURE This lecture is about the recent detections of gravitational waves. Just as Maxwell's Theory of Electromagnetism predicted the existence of transverse electromagnetic waves, Einstein's General Theory of Relativity predicted the existence of ``Gravitational Radiation". Although this should have been regarded as a `straightforward conclusion' of any `relativistic theory of gravitation', serious doubts about their existence persisted for more than forty years, with Einstein himself being one of the `doubters'. These doubts were finally laid to rest by a series of remarkable papers published in the 1950s and early 1960s. The first observational evidence for gravitational radiation came in the late 1970s. The shrinking of the orbit of the Hulse-Taylor binary pulsar agreed precisely with the prediction from General Relativity. Meanwhile, heroic efforts were underway to build a Laser Interferometer that would actually detect gravitational waves. This was an incredible symbiosis between physics, engineering, and technology. On 14 September 2015, almost exactly a hundred years after Einstein's paper, the laser interferometer detected a burst of gravitational waves from two coalescing black holes. 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