The Galactic Supermassive Black Hole

About this book

Here, one of the world's leading astrophysicists provides the first comprehensive and logically structured overview of the many ideas and discoveries pertaining to the supermassive black hole at the galactic center known as Sagittarius A*. By far the closest galactic nucleus in the universe, Sagittarius A* alone can provide us with a realistic expectation of learning about the physics of strong gravitational fields, and the impact of such fields on the behavior of matter and radiation under severe physical conditions. Its proximity may even provide the opportunity to directly test one of general relativity's most enigmatic predictions--the existence of closed pockets of space-time hidden behind an event horizon.

The plethora of research on Sagittarius A* since its discovery in 1974 has long seemed an interwoven pattern of loose threads. No one has successfully synthesized this growing body of work into a manageable, coherent book both for professional researchers and for students taking courses focusing on black holes and galactic nuclei--until now. With Fulvio Melia's The Galactic Supermassive Black Hole, readers finally have at their disposal a one-volume crucible of essential ideas, logically streamlined but with thorough references for those wishing to explore the various topics in greater depth.

Contents

Foreword vii Preface xiii CHAPTER 1: The Galactic Center 1 1.1 Discovery of Sagittarius A* 2 1.2 Radio Morphology of the Central Region 5 1.3 X-ray Morphology of the Central Region 10 1.4 Sagittarius A East 17 CHAPTER 2: The Radio Source Sagittarius A* 25 2.1 Position of Sagittarius A* 27 2.2 Proper Motion 32 2.3 Structure as a Function of Frequency 37 CHAPTER 3: Sagittarius A*'s Spectrum 42 3.1 The Radio Spectrum 42 3.2 Linear and Circular Polarization 46 3.3 Infrared Observations 55 3.4 X-ray Observations 58 3.5 Observed High-Energy Characteristics 65 CHAPTER 4: Variability 71 4.1 Short-Term Variability in the IR and X-rays 71 4.2 Long-Term Variability in the Radio 81 CHAPTER 5: The Central Star Cluster 86 5.1 The Stellar Cusp Surrounding the Black Hole 87 5.2 Stellar Constituents and Dynamics 101 5.3 Stellar Orbits and the Enclosed Mass 109 CHAPTER 6: The Four-Dimensional Spacetime 114 6.1 The Flat Spacetime Metric 114 6.2 Relativistic Transformation of Physical Laws 126 6.3 Accelerated Frames 132 6.4 General Relativity 137 6.5 Particle Orbits and Trajectories 140 6.6 The Kerr Metric 149 CHAPTER 7: Mass Accretion and Expulsion 156 7.1 Sagittarius A*'s Gaseous Environment 158 7.2 Bondi-Hoyle Capture from Distributed Sources 162 7.3 Accretion Close to Sagittarius A* 165 7.4 Magnetic Field Dissipation 167 7.5 A Compact Magnetized Disk 176 7.6 Expulsion of Matter 204 CHAPTER 8: Flares 226 8.1 Flare Physics 226 8.2 Periodicity 234 8.3 General Relativistic Flux Modulations 240 CHAPTER 9: Strong Field Physics 245 9.1 Spin-Induced Disk Precession 246 9.2 Microlensing 251 9.3 Imaging the Shadow of the Black Hole 259 References 265 Index 287

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Biography

Fulvio Melia is Professor of Physics and Astronomy at the University of Arizona and Associate Editor of the "Astrophysical Journal Letters". His books include "The Black Hole at the Center of Our Galaxy" (Princeton), "The Edge of Infinity: Supermassive Black Holes in the Universe", and "Electrodynamics".