Astronomers’ Observing Guides Other titles in this series The Moon and How to Observe It Peter Grego Double & Multiple Stars, and How to Observe Them James Mullaney Saturn and How to Observe it Julius Benton Jupiter and How to Observe it John McAnally Star Clusters and How to Observe Them Mark Allison Nebulae and How to Observe Them Steven Coe Galaxies and How to Observe Them Wolfgang Steinicke and Richard Jakiel Related titles Field Guide to the Deep Sky Objects Mike Inglis Deep Sky Observing Steven R. Coe The Deep-Sky Observer’s Year Grant Privett and Paul Parsons The Practical Astronomer’s Deep-Sky Companion Jess K. Gilmour Observing the Caldwell Objects David Ratledge Choosing and Using a Schmidt-Cassegrain Telescope Rod Mollise Martin Mobberley Supernovae and How to Observe Them with 167 Illustrations Martin Mobberley [email protected] Library of Congress Control Number: 2006928727 ISBN-10: 0-387-35257-0 e-ISBN-10: 0-387-46269-4 ISBN-13: 978-0387-35257-2 e-ISBN-13: 978-0387-46269-1 Printed on acid-free paper. © 2007 Springer Science+Business Media, LLC All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. 987654321 springer.com To Tom Boles, Mark Armstrong, and Ron Arbour who, together, have discovered almost 200 supernovae from the very cloudy skies of the U.K. A remarkable achievement! Preface Preface Supernova explosions, which mark the deaths of massive stars or of white dwarf stars in binary systems, are unbelievably violent events. Despite occurring in galax- ies many millions of light-years away, amateur telescopes can reveal these colossal explosions, and even discover them. In the past 25 years, the amateur astronomer’s contribution to supernova research has been staggering. Visual variable star observers with access to large-aperture amateur telescopes have contributed a steady stream of magnitude estimates of the brightest and closest supernovae. In addition, with the increasing availability of robotic telescopes and CCD technol- ogy, more and more amateurs are discovering supernovae from their backyards. Worldwide, there have been more than 400 supernovae discovered by amateur astronomers using amateur telescopes. Supernova research has never been so important. Recent professional measurements of the most distant Type Ia super- novae have revealed the staggering and unexpected discovery that the acceleration of the Universe is actually increasing! This, in turn, has led to a new phrase, dark energy, entering the astronomical vocabulary; a mysterious force, in opposition to gravity, driving the accelerated expansion. Although amateurs cannot study the farthest supernovae,their discovery and measurement of the closer examples helps to refine the science that is the hottest topic in cosmology today; that is, pinning down the history of the Universe and how much mass and energy exists within it today. As always, amateur astronomers are making a valuable contribution, and, hopefully, this book might inspire a few more to monitor and discover new supernovae. Martin Mobberley Suffolk, U.K. October 2006 vii Acknowledgments As was the case with my previous three Springer books, I am indebted to the outstanding amateur astronomers who have donated images and advice to this new work. In alphabetical surname order, the help of the following supernova experts, amateur astronomers, and observatory/science facility staff is gratefully acknowledged: Ron Arbour; Mark Armstrong; Adam Block; Tom Boles; Kathie Coil; Allan Cook; Jamie Cooper; Ray Emery; Bob Evans; Alex Fillipenko; John Fletcher; Gordon Garradd; Maurice Gavin; Robert Gendler; Sergio Gonzales; Dr. Acknowledgments Mario Hamuy; Arne Henden (AAVSO); Guy Hurst; Weidong Li; David Malin; Brian Manning; Berto Monard; Stewart Moore; Bill Patterson; Saul Perlmutter; Gary Poyner; Tim Puckett; Gordon Rogers; Michael Schwartz; Ian Sharp; Jeremy Shears; Daniel Verschatse. I am also indebted, in various ways to the following organizations: The Astronomer magazine; The British Astronomical Association (BAA); NASA; ESA; STSCI; AAO; Carnegie Supernova Project; NOAO; CBAT. I am also indebted to my father, Denys Mobberley, for his tireless help in all my observing projects. Sadly, my mother Barbara died of bowel cancer on September 8th 2006. Her support, while I was writing this book, and in all my astronomical endeavours, was always 100%. Finally,many thanks to Jenny Wolkowicki, Harry Blom, Chris Coughlin and John Watson at Springer for making this book possible. Without Jenny’s expertise and attention to detail I dare not imagine what state the final book would have ended up in! ix Contents Part I Supernovae: Physics and Statistics Chapter 1 Supernova Physics . 3 Chapter 2 Supernovae to Measure the Universe . 15 Chapter 3 Supernovae in Our Neighborhood . 25 Chapter 4 The Top 100 Extragalactic Supernovae . 37 Chapter 5 Supernovae: A Threat to Life on Earth . 49 Part II Observing and Discovering Supernovae Contents Chapter 6 Supernovae as Visual Variable Stars . 59 Chapter 7 Supernova Photometry and Light Curves . 71 Chapter 8 Supernova Spectroscopy . 101 Chapter 9 Amateur Supernova Hunting in the 21st Century . 113 Chapter 10 The Discoverers Themselves . 137 Chapter 11 Searching the Messier Galaxies . 161 Chapter 12 Searching the Caldwell Galaxies . 177 Chapter 13 Observing Supernova Remnants . 193 Appendix Useful Supernova Data and Contacts . 203 Index . 207 xi Part I Supernovae: Physics and Statistics Chapter 1 Supernova Physics Supernova Physics Introduction Even without a working knowledge of astrophysics, the term supernova conjures up a vision of an almighty stellar explosion, even amongst non-astronomers. The term was first used by Fritz Zwicky (1898–1974) and Walter Baade (1893–1960), two pioneers of the photographic era. Zwicky himself was, by all accounts, a some- what abrasive character who once stated that the other astronomers at the Mount Wilson Observatory were “spherical bastards.” When asked to explain the use of the word “spherical,” he allegedly explained that they were bastards when looked at from any angle! Abrasive or not,Zwicky was the first obsessive supernova hunter, and his vision of these events being almighty stellar explosions was accurate; indeed, an explosion on the scale of a supernova is truly beyond our capacity to comprehend. All one can do is juggle with huge numbers, containing endless zeroes, and pretend we understand the scale of events involved. But before we look at what a supernova really is, let us explain a few basic concepts here so that readers who are relatively new to astronomy will not get lost. Supernovae are stars that have reached the end of their life in a very dramatic fashion, but they are, essentially, just stars like our own sun. Okay, many potential supernovae are actually half of a binary star system and many would make our sun look very small indeed, but they are stars just the same. As our sun is not in a binary system and not a massive star, it will end its life far more peacefully. Stars exist in and around galaxies like our own Milky Way, where there is enough matter to form objects that big. Our own galaxy is approximately 100,000 light-years across (see Figure 1.1) and contains more than 100 billion stars. We are only 4.2 light-years from the nearest star, but our Milky Way Galaxy is more than 2 million light-years from the nearest big galaxy (Andromeda, or M 31). Supernovae are both rare and common events. This does sound highly contradictory, but please read on! They are rare because even stars that are destined to become supernovae may last billions of years before the final day comes, yet the flaring up and dying down of the star will last mere months. So how can they be common, too? Well, roughly 300 supernovae are discovered every year because professional astronomers and advanced amateur astronomers patrol 10,000 to 20,000 galaxies on a regular basis. With each galaxy containing a hundred billion stars, the chances of discovering a supernova rapidly improve when you scour thousands of them every clear night. Mentally grasping the size of the visible Universe is virtually impossible. Note I say visible Universe. We can only see the objects whose light has had time to reach us in the 14 billion years since the Universe formed. But, to make things simple, let 3 Supernova Physics Figure 1.1. Our own galaxy is thought to be roughly 100,000 light- years across, but recent infrared images from NASA’s Spitzer Space Tele- scope indicate that it may have a bar, 27,000 light- years long at the center. Image: Spitzer Science Centre/JPL-Caltech/NASA. us just imagine that the most distant objects we can see are 10 billion light-years away. If we pretend that this is the same as 10,000km on the earth’s surface, then a light-year becomes a millimeter and the nearest star to us is 4mm away. Our galaxy then becomes a disk 100m across, and the nearby Andromeda Galaxy is 2km away. In practice, galaxies that can be patrolled by amateurs then lie within 1,000km of us, and we are looking for the explosion of an object well under a thousandth of a millimeter across (even for a massive star).