High energy astrophysics is one of the most important and exciting areas of contemporary astronomy, involving the most energetic phenomena in the universe. The highly acclaimed first and second editions of Professor Longair’s series immediately established themselves as essential text books on high energy astrophysics. In this third edition, the subject matter is brought up to date and consolidated into a single volume covering Galactic, extragalactic and cosmological aspects of High Energy Astrophysics. The material is presented in four parts. The first provides the necessary astronomical background for understanding the con- text of high energy astrophysical phenomena. The second provides a thorough treatment the physical processes that govern the behaviour of particles and radiation in astrophysical environments such as interstellar gas, neutron stars, and black holes. The third part applies these tools to a wide range of high energy astrophysical phenomena in our own Galaxy, while the fourth and final part deals with extragalactic and cosmological aspects of high energy astrophysics. This book assumes that readers have some knowledge of physics and mathematics at the undergraduate level, but no prior knowledge of astronomy is required. The new third edition of the book covers all aspects of modern high energy astrophysics to the point at which the key concerns of current research can be understood. High Energy Astrophysics Third Edition Malcolm S. Longair Emeritus Jacksonian Professor of Natural Philosophy, Cavendish Laboratory, University of Cambridge, Cambridge PUBLISHED BY THE PRESS SYNDICATE OF THE UNIVERSITY OF CAMBRIDGE The Pitt Building, Trumpington Street, Cambridge, United Kingdom CAMBRIDGE UNIVERSITY PRESS The Edinburgh Building, Cambridge CB2 2RU, UK 40 West 20th Street, New York, NY 10011-4211, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia Ruiz de Alarcon´ 13, 28014 Madrid, Spain Dock House, The Waterfront, Cape Town 8001, South Africa http://www.cambridge.org c Cambridge University Press 1981, 1992, 1994, 1997, 2000, 2002, 2004 First published 1981 Second edition in two volumes 1992, 1994, reprinted with corrections 1997, 2000, 2002, 2004 British Library cataloguing in publication data Longair, M. S. (Malcolm S.) High energy astrophysics. I. Title XXX.YYYYY ISBN 0 XXX YYYYY Z hardback Transferred to digital printing 2004 For Deborah Contents Preface page ii Acknowledgements v Part I. Astronomical background 1 1 High energy astrophysics – an introduction 3 1.1 High energy astrophysics and modern physics and astronomy 3 1.2 The sky in different astronomical wavebands 5 1.3 Optical waveband 7 1.4 Infrared waveband 10 1.5 Millimetre and submillimetre waveband 14 1.6 Radio waveband 19 1.7 Ultraviolet waveband 23 1.8 X-ray waveband 25 1.9 γ-ray waveband 27 1.10 Cosmic ray astrophysics 29 1.11 Other non-electromagnetic astronomies 34 1.12 Concluding remarks 36 2 The stars and stellar evolution 39 2.1 Introduction 39 2.2 Basic observations 39 2.3 Stellar structure 43 2.4 The equations of energy generation and energy transport 48 2.5 The equations of stellar structure 53 2.6 The Sun as a star 56 2.7 Evolution of high and low mass stars 66 2.8 Stellar evolution on the colour-magnitude diagram 76 2.9 Mass loss 77 2.10 Conclusion 84 vii viii Contents 3 The galaxies 85 3.1 Introduction 85 3.2 The Hubble sequence 86 3.3 The red and blue sequences 89 3.4 Further correlations among the properties of galaxies 95 3.5 The masses of galaxies 98 3.6 The luminosity function of galaxies 104 4 Clusters of galaxies 109 4.1 The morphologies of rich clusters of galaxies 109 4.2 Clusters of galaxies and isothermal gas spheres 113 4.3 The Coma cluster of galaxies 117 4.4 Mass distribution of hot gas and dark matter in clusters 119 4.5 Cooling flows in clusters of galaxies 123 4.6 The Sunyaev-Zeldovich effect in hot intracluster gas 125 4.7 Gravitational lensing by galaxies and clusters of galaxies 129 4.8 Dark matter in galaxies and clusters of galaxies 135 Part II. Physical processes 141 5 Ionisation losses 143 5.1 Introduction 143 5.2 Ionisation losses – non-relativistic treatment 144 5.3 The relativistic case 149 5.4 Practical forms of the ionisation loss formulae 154 5.5 Ionisation losses of electrons 158 5.6 Nuclear emulsions, plastics and meteorites 159 5.7 Dynamical friction 165 6 Radiation of accelerated charged particles and bremsstrahlung of electrons 169 6.1 Introduction 169 6.2 The radiation of accelerated charged particles 169 6.3 Bremsstrahlung 178 6.4 Non-relativistic bremsstrahlung energy loss rate 182 6.5 Thermal bremsstrahlung 183 6.6 Relativistic bremsstrahlung 189 7 The dynamics of charged particles in magnetic fields 195 7.1 A uniform static magnetic field 195 7.2 A time-varying magnetic field 197 7.3 The scattering of charged particles by irregularities in the magnetic field 202 7.4 The scattering of high energy particles by Alfven´ and hydromagnetic waves 205 7.5 The diffusion-loss equation for high energy particles 207 Contents ix 8 Synchrotron radiation 213 8.1 The total energy loss rate 213 8.2 Non-relativistic gyroradiation and cyclotron radiation 216 8.3 The spectrum of synchrotron radiation – physical arguments 219 8.4 The spectrum of synchrotron radiation - a fuller version 223 8.5 The synchrotron radiation of a power law distribution of electron energies 233 8.6 The polarisation of synchrotron radiation 235 8.7 Synchrotron self-absorption 239 8.8 Useful numerical results 244 8.9 The radio emission of the Galaxy 246 9 Interactions of high energy photons 251 9.1 Photoelectric absorption 251 9.2 Thomson and Compton scattering 255 9.3 Inverse Compton scattering 261 9.4 Comptonisation 267 9.5 The Sunyaev-Zeldovich effect 282 9.6 Synchrotron–self Compton radiation 286 9.7 Cherenkov radiation 291 9.8 Electron–positron pair production 297 9.9 Electromagnetic showers 299 9.10 Electron-positron annihilation and positron production mechanisms 302 10 Nuclear interactions 307 10.1 Nuclear interactions and high energy astrophysics 307 10.2 Spallation cross-sections 310 10.3 Nuclear emission lines 315 10.4 Cosmic rays in the atmosphere 321 11 Aspects of plasma physics and magnetohydrodynamics 327 11.1 Elementary concepts in plasma physics 327 11.2 Magnetic flux freezing 334 11.3 Shock waves 344 11.4 The Earth’s magnetosphere 349 11.5 Magnetic buoyancy 352 11.6 Reconnection of magnetic lines of force 354 Part III. High Energy Astrophysics in our Galaxy 361 12 Interstellar gas and magnetic fields 363 12.1 The interstellar medium in the life cycle of stars 363 12.2 Diagnostic tools - neutral interstellar gas 363 12.3 Ionised interstellar gas 370 12.4 Interstellar dust 378 x Contents 12.5 An overall picture of the interstellar gas 387 12.6 Star formation 393 12.7 The Galactic magnetic field 402 13 Dead stars 413 13.1 Supernovae 414 13.2 White dwarfs, neutron stars and the Chandrasekhar limit 431 13.3 White dwarfs 438 13.4 Neutron stars 439 13.5 The discovery of neutron stars 444 13.6 The galactic population of neutron stars 458 13.7 Thermal emission of neutron stars 460 13.8 Pulsar glitches 461 13.9 The pulsar magnetosphere 464 13.10 The radio and high energy emission of pulsars 467 13.11 Black holes 469 14 Accretion power in astrophysics 483 14.1 Introduction 483 14.2 Accretion - general considerations 483 14.3 Thin accretion discs 491 14.4 Thick discs and advective flows 504 14.5 Accretion in binary systems 506 14.6 Accreting binary systems 516 14.7 Black holes in X-ray binaries 531 14.8 Final thoughts 537 15 Cosmic rays 539 15.1 The energy spectra of cosmic ray protons and nuclei 539 15.2 The abundances of the elements in the cosmic rays 543 15.3 The isotropy and energy density of cosmic rays 549 15.4 Gamma ray observations of the Galaxy 550 15.5 The origin of the light elements in the cosmic rays 554 15.6 The confinement time of cosmic rays in the Galaxy and cosmic ray clocks 563 15.7 The confinement volume for cosmic rays 565 15.8 The Galactic halo 568 15.9 The highest energy cosmic rays and extensive air-showers 571 15.10 Observations of the highest energy cosmic rays 573 15.11 The isotropy of ultra-high energy cosmic rays 578 15.12 The Greisen-Kuzmin-Zatsepin (GKZ) cut-off 581 16 The origin of cosmic rays in our Galaxy 585 16.1 Introduction 585 16.2 Energy loss processes for high energy electrons 585 Contents xi 16.3 diffusion-loss equation for high energy electrons 590 16.4 Supernova remnants as sources of high energy particles 594 16.5 The minimum energy requirements for synchrotron radiation 599 16.6 Supernova remnants as sources of high energy electrons 603 16.7 The evolution of supernova remnants 604 16.8 The adiabatic loss problem and the acceleration of high energy particles 607 17 The acceleration of high energy particles 613 17.1 General principles of acceleration 613 17.2 The acceleration of particles in solar flares 614 17.3 Fermi acceleration - original version 616 17.4 Diffusive shock acceleration in strong shock waves 621 17.5 Beyond the standard model 627 17.6 The highest energy cosmic rays 635 Part IV. Extragalactic High Energy Astrophysics 637 18 Active galaxies 639 18.1 Introduction 639 18.2 Radio galaxies and high energy astrophysics 639 18.3 The quasars 641 18.4 Seyfert galaxies 648 18.5 Blazars, superluminal sources and γ-ray sources 651 18.6 Low Ionisation Nuclear Emission Regions – LINERS 653 18.7 Ultra-Luminous Infrared Galaxies – ULIRGs 654 18.8 X-ray Surveys of Active Galaxies 656 18.9 Unification Schemes for Active Galaxies 658 19 Black Holes in the Nuclei of Galaxies 667 19.1 The Properties