Cosmological Enigmas This page intentionally left blank Cosmological Enigmas Pulsars, Quasars & Other Deep-Space Questions mark kidger the johns hopkins university press Baltimore © 2007 The Johns Hopkins University Press All rights reserved. Published 2007 Printed in the United States of America on acid-free paper 987654321 The Johns Hopkins University Press 2715 North Charles Street Baltimore, Maryland 21218-4363 www.press.jhu.edu Library of Congress Cataloging-in-Publication Data Kidger, Mark R. (Mark Richard), 1960– Cosmological enigmas : pulsars, quasars, and other deep-space questions / Mark Kidger. p. cm. Includes bibliographical references and index. ISBN-13: 978-0-8018-8460-3 (hardcover : acid-free paper) ISBN-10: 0-8018-8460-8 (hardcover : acid-free paper) 1. Cosmology—Popular works. I. Title. QB982.K53 2007 523.1—dc22 2007014811 A catalog record for this book is available from the British Library. Page 225 constitutes an extension of this copyright page. 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To Sir Patrick Moore For opening the author’s eyes to the wonders of the Universe as a young child with his BBC program The Sky at Night This page intentionally left blank Contents Acknowledgments ix Introduction 1 chapter 1 How Are Stars Born and How Do They Die? 5 chapter 2 How Do We Know That Black Holes Exist? 24 chapter 3 Who Is the Strangest in the Cosmic Zoo? 39 chapter 4 How Far Is It to the Stars and Will We Ever Be Able to Travel to Them? 61 chapter 5 How Old Is the Universe? 80 chapter 6 Is Anybody There? 96 chapter 7 How Will the Universe End? 117 chapter 8 Why Is the Sky Dark at Night? 136 chapter 9 How Do We Know There Was a Big Bang? 154 chapter 10 What Is There Outside the Universe? 174 Notes 193 Index 217 Color galleries follow pages 84 and 116. viii Contents Acknowledgments any people have contributed directly or indirectly to this book and its sister volume. In most cases, the help has been Manonymous or “E Pluribus”; in other cases, it has been so direct and important that it would be churlish not to acknowledge it. The team at Johns Hopkins University Press has been extremely sup- portive and professional, starting with my editor, Trevor Lipscombe. Most people do not realize how important an editor’s role is in a suc- cessful book project: ideas, encouragement, suggestions, corrections, and modifications all have come from Trevor and his encyclopedic knowl- edge. Other staff at JHUP, in particular Juliana McCarthy and Bronwyn Madeo, have also gone well above and beyond the call of duty. I have also been privileged to work with two eagle-eyed copy editors who have done far more than just correct spelling mistakes and bad grammar. Fi- nally, a vote of thanks to supportive colleagues, both former ones in Tenerife and the amazing Herschel team in Madrid—the best team in the world. This page intentionally left blank Cosmological Enigmas This page intentionally left blank Introduction hy study the Universe? A few years ago the president of the British Astronomical Association entitled his presidential Wlecture, “Let’s Be Useless,” a whimsical nod to the many people who think that astronomy is a harmless, entertaining, but to- tally useless pursuit. What is the point in studying the Universe when millions in the world are starving? Should we be spending huge sums on new telescopes to study the distant confines of the Universe, or could that money be better used close to home? This book does not try to an- swer directly why we study the Universe. Instead of justifying why we study, its purpose is to explain how we find out the things we think we know. With such information, the reader may (or may not!) be persuaded that my fellow astronomers and myself, far from being a useless luxury, actually do serve some purpose. Some time after this volume is published, the Spanish Gran Tele- scopio CANARIAS (Canaries Large Telescope, usually known as the GTC) will enter service. It will be the second-largest single-mirror tel- escope in the world with a largest diameter of 11.4 meters,1 and a surface area equivalent to a full 10-meter diameter, surpassing the two Keck tele- scopes atop Mauna Kea in Hawai’i. This monster is probably the largest scien- tific project that Spain has ever undertaken and comes with an impressive price tag that, when the project was approved, was estimated at 13 billion pesetas (about $90 million). This may sound like a lot of money, but it is less than a third of the cost of a new A380 airliner, and about the same as a new Typhoon Eurofighter, or two (now obsolete) F-14 Tomcats. The GTC has cost the average Spaniard about 30 cents a year over the course of the project, less than a quarter of what the average Spaniard spends on midmorning coffee. The cost of astronomy, even the large, ambitious projects that are sometimes called “big astronomy,” is a lot less than most people think. What do you get for your dollars? Part of the answer is technology: solving scientific and engineering problems almost always turns out to be profitable in the end because it challenges industry to test itself and find its limits. This new tech- nology may later find hundreds of unexpected uses (telescope construction, for example, poses big challenges in precision engineering, electronics, and optics, to say nothing of computing and heavy engineering). More than anything, though, what we are buying is knowledge, and that is something that will never go away. A navigator called Christopher Columbus had this crazy idea that you can cut the time taken to travel to the Indies by going west instead of struggling around Africa to get there. He hawked his idea around the royal courts of Italy, Spain, and Portugal, where most people just laughed at the idea because they knew that the Earth was flat and that, by sailing west, Columbus would fall off the edge of the world. Should he have given up because his voyage seemed silly and irrele- vant? Just imagine what would have happened had Columbus lacked the temerity to persist with his “ridiculous” question about what would happen if he sailed west and not east. We learn by asking ridiculous questions and challenging existing knowledge and facts. For 1,000 years after the fall of Rome, the human race stopped asking questions, seeking answers, and pushing itself to new heights; the result of this period of stagnation was the Dark Ages and later the Middle Ages, when the qual- ity of human life dropped abysmally. Sanitation, medicine, communications, and culture in general dropped to a frightening degree, and most people lived in mis- ery—even the richest and best-off had a poor diet and poor sanitation and, as a result, were prone to diseases. The Black Death, for example, eradicated perhaps one-third of the entire population of Europe (in Venice 60 percent of the popu- 2 Cosmological Enigmas lation died in just 18 months). I am not saying that the Black Death would have been avoided if our ancestors had built a few 10-meter telescopes, but had they re- tained even a fraction of the accumulated knowledge of the Greeks and Romans, an awful lot of misery could have been avoided. Scientific knowledge, even abstract knowledge, is a part of human culture, and its accumulation over 4 million years of human evolution fuels our advance. Its beginnings have been immortalized in the scene in 2001: A Space Odyssey in which the man-ape Moon-watcher discovered that using a bone as a weapon lengthened his reach, strengthened his blow, allowed him to feed his family better, and thus avoid the extinction of the line that would lead to Homo sapiens. When Moon- watcher throws the bone into the air in triumph it changes into a spacecraft; Stan- ley Kubrick shows, brilliantly in this flash forward, how a tiny discovery for a man- ape would eventually lead to modern man and spaceflight. With each grain of knowledge added to our store, we have advanced a little further along the evolutionary course. What appeared to be abstract and useless research on “animal electricity” by the English bookbinder Michael Faraday in the early nineteenth century led to the development of the dynamo. When combined with the independent discovery that crude oil, when refined, gives highly com- bustible products, dynamos could power motors, which in turn would bring cheap light and power to the entire world. Scientific research has many blind alleys and dead ends, but even the most abstract research can pay off in a way that could never be imagined. The peaceful uses of radioactivity in medicine and engineering, for example, would have struck its nineteenth-century discoverers almost as witchcraft. Research to counteract a possible Nazi death ray led, directly, to radar (making air traffic control and thus mass transport by air possible) and also to high-capacity long-distance communications. It even made microwave ovens possible. While attempting to explain electricity to the then prime minister Sir Robert Peel, Faraday was asked, “What good is it?” Faraday replied with feeling, “What good is a new-born baby?” According to the legend, Faraday added, “Rest assured, one day you will tax it.” Numerous attempts have been made by different govern- ments to fund only “useful” practical research; these have been doomed to failure and have rarely produced great results, while cutting off other lines of progress.