ALIEN SKIES A Travelogue of the Universe First Edition By Mario Mateo University of Michigan - Ann Arbor cognellcf JSSKs Bassim Hamadeh, CEO and Publisher Kassie Graves, Director of Acquisitions Jamie Giganti, Senior Managing Editor Jess Estrella, Senior Graphic Designer Sean Adams, Project Editor Luiz Ferreira, Senior Licensing Specialist Chelsey Schmid, Associate Editor Copyright © 2017 by Cognella, Inc. All rights reserved. No part of this publication may be reprinted, reproduced, trans­ mitted, or utilized in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information retrieval system without the written permission of Cognella, Inc. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. 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Printed in the United States of America ISBN: 978-1-5165-0632-3 (pbk) / 978-1-5165-0633-0 (br) cognella CONTENTS ACKNOWLEDGMENTS XI FOREWORD XIII DESTINATION 1 : THE MOON: OUR FIRST STEP OFF EARTH 1.1 In Search of Alien Skies 1 1.2 The Sky from Home 3 1.3 Our First Step 11 DESTINATION 2: THE VIEW FROM MARS 2.1 Terror and Fear in the Sky of Mars 21 2.2 The Riddle of Planetary Motion 28 2.3 Kepler’s Third Law: The Triumph of Simplicity 34 DESTINATION 3: THE SKY FROM EARTH: A LAST LOOK FROM HOME 3.1 Preparations for a Long Voyage 43 3.2 Navigating in the Sky 44 3.3 The Distances of Stars: Stellar Parallax 53 DESTINATION 4: THE SKY FROM a CENTAURI 4.1 A Familiar Light in an Alien Sky 61 4.2 An Alien Light in an Alien Sky 67 4.3 A Faint Light in an Alien Sky 73 DESTINATION 5: THE 'EMPTY' SKY OF DEEP SPACE: AT ‘ANTI-CENTAURI’ 5.1 No Place in Particular 81 5.2 The Matter of'Empty Space' 83 5.3 Seeing the Invisible: Neutral Hydrogen and 21-cm Radiation 91 5.4 Hot Matter in Cold Space 98 DESTINATION 6: THE ORION NEBULA 6.1 Secrets of a Celestial Hunter 103 6.2 The Bright Sky of the Orion Nebula 106 6.3 The Dark Clouds of the Orion Nebula 115 6.4 The Stars of the Orion Nebula 127 DESTINATION 7: EXTRASOLAR PLANETARY SYSTEMS: 51 PEGASI 7.1 A Star in Pegasus 137 7.2 What We Really Came to See 140 7.3 The Properties and Formation of Planetary Systems 149 7.4 Do Planets Imply Life? 154 DESTINATION 8: THE PLEIADES 8.1 A Sky Without Night 163 8.2 The Stars of the Pleiades Cluster 167 8.3 The Spectra of Stars 172 8.4 Why Do Stars Shine? 180 DESTINATION 9: EXPLORING THE MILKY WAY 9.1 Our Home’s Home 193 9.2 Rising up from the Milky Way 197 9.3 The Galactic Disk 202 9.4 Through the Galactic Plane 207 9.5 Rotation of the Galaxy 211 9.6 A Summary of a Fantastic Journey 219 DESTINATION 10: INWARD BOUND: THE GALACTIC CENTER 10.1 To the Galactic Center: Through the Inner Galactic Disk 227 10.2 To the Galactic Center: From the Disk to the Bulge 233 10.3 A Strange New World: The Galactic Center 238 DESTINATION 11: A BLAZING SKY OF STARS: THE GLOBULAR CLUSTER M 92 11.1 Summer in Paris 251 11.2 The Sky Ablaze: The View from M 92 254 11.3 Stellar Death 261 11.4 White Dwarfs: The Corpses of Low-Mass Stars 266 11.5 A Window to an Ancient Past 272 11.6 A Different Way to Stay Together 274 DESTINATION 12: THE MAGELLANIC CLOUDS: THE NEAREST GALAXIES 12.1 The Magellanic Clouds: Beyond the Galaxy 281 12.2 The Case of the Missing White Dwarfs 286 12.3 The Evolution of High-Mass Stars 290 12.4 Witnessing High-Mass Stellar Evolution 296 12.5 Victory of a Relentless Force 303 DESTINATION 13: THROUGH THE HEART OF DARKNESS: THE GALACTIC HALO 13.1 The Lonely Outskirts of the Galaxy 311 13.2 Dark Matter in the Galactic Halo 317 13.3 The Structure of the Galactic Halo 325 DESTINATION 14: THE NEARBY SPIRAL GALAXIES M 31 AND M 33 14.1 Leaving Our Galaxy Behind 335 14.2 Cepheid Variable Stars: A New Way to Estimate Extragalactic Distances 339 14.3 The Galaxy, M 31, and M 33: The Closest Spiral Galaxies 344 14.4 What Are Spiral Arms? 348 14.5 The Peculiar Role of Dark Matter 352 14.6 The Local Group 354 DESTINATION 15: THE GIANT ELLIPTICAL GALAXY MAFFEI 1 15.1 Beyond the Local Group 363 15.2 Maffei 1: A Giant Elliptical Galaxy 368 15.3 Classifying Galaxies: The Hubble Sequence 377 DESTINATION 16: THE VIRGO CLUSTER: A SKY OF GALAXIES 16.1 The Virgo Cluster of Galaxies 389 16.2 Galaxies in Collision 394 16.3 The Hubble Law 402 16.4 The Dark Matter of the Virgo Cluster 408 DESTINATION 17: THERE’S SOMETHING STRANGE HERE: THE SEYFERT GALAXY M 77 17.1 The Monster in the Middle 417 17.2 The Two Faces of the Monster 424 17.3 The Name of the Monster 427 17.4 Einstein's Legacy: An Introduction 433 17.5 Einstein's Legacy: Getting Personal 438 17.6 The Maw of the Monster 442 17.7 In Memoriam 444 DESTINATION 18: THE BOOTES VOID 18.1 Mapping the Distribution of Galaxies 449 18.2 The Dark, Lumpy Universe 456 18.3 'Light' in the Darkness: The Cosmic Microwave Background 463 DESTINATION 19: BACK IN TIME TO A DISTANT GALAXY CLUSTER 19.1 Navigating Space and Time 471 19.2 Telling Time in the Universe 473 19.3 What Kind of Universe Do We Inhabit? 483 19.4 MS1054-0321: A Galaxy Cluster at z = 0.8 490 DESTINATION 20: HIGH REDSHIFT GALAXIES: THE YOUNG AND RESTLESS UNIVERSE 20.1 The Galaxies of the Early Universe 499 20.2 The Golden Era of Galaxy Formation 504 DESTINATION 21: QUASARS AT THE DAWN OF GALAXY FORMATION 21.1 Young Galaxies and 'False Stars’ 513 21.2 Quasars: Extreme Active Galactic Nuclei 516 21.3 Quasars in the Early Universe: Implications for Galaxy Formation 530 DESTINATION 22: THE DARK AGES 22.1 A Simpler Universe 537 22.2 The Problem with Being Smooth, Part 1: Why So Lumpy Now? 541 22.3 The Problem with Being Smooth, Part 2: Why Is the CMB So Uniform? 545 DESTINATION 23: THE ERA OF RECOMBINATION 23.1 Into the Fog 553 23.2 Lifting the Veil: The Era of ‘Re’-combination 558 23.3 The Seeds of Creation 565 DESTINATION 24: THE FIRST ELEMENTS IN THE UNIVERSE 24.1 The Evolution of the Chemical Elements: Getting Started 573 24.2 Fusion in an Expanding Universe 579 DESTINATION 25: TO A TIME BEFORE TIME 25.1 The Genesis of Matter 587 25.2 The Genesis of Physical Forces and the Inflation Era 596 25.3 As Far as We Can Go: The Planck Time 602 APPENDICES Appendix A Summary of Destinations 611 Appendix B Units, Symbols, and Conversion Factors 621 Appendix C Constants 627 Appendix D Mathematical Formulae 629 Appendix E Basic Data for Selected Planets and Dwarf Planets of the Solar System 641 Appendix F The Constellations of Earth's Sky 643 Appendix G The Natural Chemical Elements 649 FIGURE CREDITS 653 INDEX 669