Neutron Stars and Black Holes (Lecture -13: The Realm of the Supermassive Black... by G. Srinivasan

Colloquium The Realm of the Supermassive Black Holes Speaker: G. Srinivasan (Raman Research Institute (Retired), Bangalore ) Date: Wed, 26 June 2019, 10:00 to 11:30 Venue: Madhava Lecture Hall, ICTS Campus Bangalore Abstract One of the most momentous discoveries in the history of astronomy was the discovery of QUASARS in 1963. Their incredible luminosity - more than million, million times the luminosity of the Sun - implied that their masses must be in excess of a billion solar mass. Another unexpected discovery was that their flux was 'variable'. It soon emerged that the 'central engines' that powered the Quasars must be supermassive black holes. A parallel discovery was that of radio galaxies with their powerful relativeistic jets. Various observations led to the conclusion that all types of Active Galactic Nuclei are also powered by supermassive black holes. In the subsequent decades, X-ray observations revealed that all galaxies, and not just the more 'active' ones, have massive black holes in their centres. This talk will review the evolution of our understanding of the realm of the supermassive black holes. It will be pedagogic in nature and will not assume any prior knowledge. The main thrust of the talk will be towards an understanding of the very recent result from the Event Horizon Telescope - an image of the shadow of the black hole at the centre of the giant galaxy M87. Table of Contents (powered by https://videoken.com) 0:00:00 Neutron Stars and Black Holes (Lecture -13: The Realm of the Supermassive Black Holes) 0:00:19 Realm of the Supermassive Black Holes 0:01:20 The Radio Galaxy Cygnus A 0:02:28 Cliff top Interferometer 0:04:53 Intensity Interferometer 0:04:59 Hanbury-Brown & Twiss Intensity Interferometer 0:06:52 Michelson Interferometer 0:07:04 Intensity Interferometer of Hanbury-Brown 0:08:48 The Radio Galaxy Cygnus A 0:09:37 Quest for high angular resolution 0:11:12 Origin of the radio lobes 0:13:19 Jets discovered in Cygnus A 0:13:54 Very Long Baseline Interferometry 0:14:04 The Global VLBI-Array 0:16:10 CYGNUS A 0:17:15 One sided jets 0:17:23 M 87 The giant elliptical 0:18:00 NGC 6251 0:19:40 Proper time: 0:20:04 Doppler Shift 0:23:49 Doppler favoritism 0:25:31 Imagine a black hole at position A ejecting a blob in direction making an angle theta to the observer. Let the blob be moving with velocity v. 0:26:58 Superluminal motion 0:27:32 Apparent transverse velocity as a function of beta and theta 0:28:26 Superluminal Motion in the M87 Jet 0:28:47 To achieve sub-milli arc second resolution one uses intercontinental baseline interferometry. 0:28:51 Relativistic jets 0:29:39 Energy content in the radio lobes 0:29:49 Energy content 0:32:07 The central engines 0:33:09 Eddington Luminosity Limit 0:34:26 Thompson scattering cross section: 0:36:48 Variability of Quasars 0:38:05 Supermassive Black Holes 0:39:47 Accretion onto Supermassive Black Holes 0:45:19 Evidence for supermassive Black Holes 0:45:33 NGC 4258 0:45:52 Mega MASERS in NGC 4258 0:47:11 Stars orbiting the Galactic Centre Black Hole 0:47:57 Black Hole at the centre of Milky Way 0:48:18 The giant black hole at the center of M 87 0:49:41 M87 Base of Jet 0:50:19 Angular resolution required to resolve the event horizon of the central BH 0:51:39 VLBI at 1.3 mm 0:55:38 Event Horizon Telescope 0:56:00 VLBI at 1.3 mm with the EHT 0:57:51 Environment of the Black Hole 1:03:06 What does one expect to see with the EHT? 1:03:11 Motion of light near a nonrotating BH 1:06:56 What does one expect to see? 1:11:56 Comparison with simulations suggests that the torus is rotating CLOCKWISE around the spin axis of the BH 1:12:14 Summary of the conclusions 1:13:08 Has General Relativity finally been verified to a satisfactory extent? 1:14:05 S. Chandrasekhar: 1:18:15 X-Ray interferometry - in the near future - and, to a lesser extent, space based GW detectors hold out tantalizing prospects 1:18:37 Formation of supermassive black holes 1:18:45 Mergers 1:19:09 How did the original BHs form? 1:21:26 Supermassive stars 1:22:15 Stability of Matter 1:23:13 Stability of a star in General Relativity 1:26:31 Stability of a supermassive star in General Relativity 1:28:11 Next Lecture - Universe or Multiverse?! 1:28:18 Q&A