Lecture Notes in Physics Editorial Board R. Beig, Wien, Austria W. Beiglböck, Heidelberg, Germany W. Domcke, Garching, Germany B.-G. Englert, Singapore U. Frisch, Nice, France P. Hänggi, Augsburg, Germany G. Hasinger, Garching, Germany K. Hepp, Zürich, Switzerland W. Hillebrandt, Garching, Germany D. Imboden, Zürich, Switzerland R. L. Jaffe, Cambridge, MA, USA R. Lipowsky, Golm, Germany H. v. Löhneysen, Karlsruhe, Germany I. Ojima, Kyoto, Japan D. Sornette, Nice, France, and Los Angeles, CA, USA S. Theisen, Golm, Germany W. Weise, Garching, Germany J. Wess, München, Germany J. Zittartz, Köln, Germany The Lecture Notes in Physics The series Lecture Notes in Physics (LNP), founded in 1969, reports new developments in physics research and teaching – quickly and informally, but with a high quality and the explicit aim to summarize and communicate current knowledge in an accessible way. Books published in this series are conceived as bridging material between advanced grad- uate textbooks and the forefront of research to serve the following purposes: • to be a compact and modern up-to-date source of reference on a well-defined topic; • to serve as an accessible introduction to the field to postgraduate students and nonspe- cialist researchers from related areas; • to be a source of advanced teaching material for specialized seminars, courses and schools. Both monographs and multi-author volumes will be considered for publication. Edited volumes should, however, consist of a very limited number of contributions only. Pro- ceedings will not be considered for LNP. Volumes published in LNP are disseminated both in print and in electronic formats, the electronic archive is available at springerlink.com. The series content is indexed, abstracted and referenced by many abstracting and information services, bibliographic networks, subscription agencies, library networks, and consortia. Proposals should be sent to a member of the Editorial Board, or directly to the managing editor at Springer: Dr. Christian Caron Springer Heidelberg Physics Editorial Department I Tiergartenstrasse 17 69121 Heidelberg/Germany [email protected] Richard Wielebinski Rainer Beck (Eds.) Cosmic Magnetic Fields ABC Editors Richard Wielebinski Rainer Beck Max-Planck-Institut für Radioastronomie Auf dem Hügel 69 53121 Bonn Germany E-mail: [email protected] E-mail: [email protected] Richard Wielebinski and Rainer Beck, Cosmic Magnetic Fields, Lect. Notes Phys. 664 (Springer, Berlin Heidelberg 2005), DOI 10.1007/b104621 Library of Congress Control Number: 2005930474 ISSN 0075-8450 ISBN-10 3-540-24175-2 Springer Berlin Heidelberg New York ISBN-13 978-3-540-24175-1 Springer Berlin Heidelberg New York This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable for prosecution under the German Copyright Law. Springer is a part of Springer Science+Business Media springeronline.com c Springer-Verlag Berlin Heidelberg 2005 Printed in The Netherlands The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Typesetting: by the author using a Springer LATEX macro package Printed on acid-free paper SPIN: 11369875 55/Techbooks 543210 Preface Recent years have seen great progress in the field of cosmic magnetic fields, both in the available observational data and in the theoretical interpretations. Now we have extensive data on magnetic fields in virtually all types of cosmic objects: the Earth, the Sun, the Milky Way, out to magnetic fields in the most distant reaches of the Universe. The first detection of a magnetic field outside the Earth was made by G.E. Hale, who made optical Zeeman effect observations of magnetic fields in the Sun, nearly 100 years ago. The detection of the Zeeman effect in stars by H.W. Babcock followed some 40 years later. Optical starlight polariza- tion observations were made in 1949 and, when combined with the Davis– Greenstein effect interpretation, suggested that magnetic fields were present in our Milky Way. Radio polarization measurements confirmed this deduc- tion in 1962. With developing sensitivity of radio and optical observations magnetic fields have been shown to be present practically everywhere. We know that the Sun is driven by magnetic fields. Supernova remnants show us the evolution of the magnetic field in shock fronts that follow a stellar explo- sion. Pulsars and X-ray sources have been shown to possess extremely intense magnetic fields. The Milky Way is a magnetic laboratory, with complex mag- netic field structures, worthy of exploration. Regular patterns of large-scale magnetic fields are observed in nearby galaxies and radio galaxies. Also clus- ters of galaxies were shown to be permeated with detectable magnetic fields. In spite of this mounting evidence about the presence of magnetic fields in the cosmic Universe only a few attempts have been made to interpret the situations taking into account all the relevant parameters, in particular those resulting from the presence of magnetic fields. In many publications elaborate numerical investigations are carried out but without the consideration of the action of a magnetic field. Only recently did we get magneto-hydrodynamic codes. These developments show us that the inclusion of magnetic fields is indeed necessary. Possibly the whole approach to the interpretation of obser- vational data will change as a result of magnetic effects. The next decade in astrophysics will shed more light on the role of magnetic fields in the Uni- verse. We should soon find out if the magnetic fields are only a consequence of gas motion, or are they at the heart of the matter? VI Preface The scheme of this book is to start with the most distant magnetic fields in the Universe and then make our way back to our Galaxy. Contributions based on observational data will describe magnetic fields in clusters of galax- ies, in radio galaxies, nearby galaxies and in the Milky Way. Contributions on various theoretical effects and considerations of the magnetic fields in the Uni- verse are interspersed between the observational chapters where appropriate. The review articles in this book do not cover all aspects of cosmic magnetic fields. In particular no contribution on solar magnetic fields has been included since in recent years numerous reviews and books have covered this subject adequately. In the first contribution Martin Rees considers the magnetic fields in the early Universe. A substantial magnetic field could have been generated in the early Universe, however no relevant physics to this early stage of our development has been proposed do far. It is argued that the first significant magnetic fields must have been formed in the course of formation of the early non-linear structures giving the needed seed fields needed for the dynamo action. The build-up of the magnetic fields is an important aspect of the cosmogonic process. The second contribution by Philipp Kronberg deals with the magnetic fields in galaxy systems, clusters of galaxies and beyond. The history of the realization that cosmic rays and magnetic fields are essential for the observed radio emission is given. This chapter focuses on the possible role of stars, black holes and supernovae, in injecting magnetic energy into the intergalactic medium. These two broad categories of energy output from galaxies have been recognized for some time. The discussion begins with the environment of galaxies out to a distance of the local Supercluster of galaxies and proceeds all the way back to the formation of first stars and galaxies. The magnetic effect in radio galaxies are also considered. Rainer Beck’s contribution describes the magnetic fields in nearby galax- ies. There has been a tremendous progress in this field in recent years. This progress in observations reveals a wide range of large-scale magnetic phenom- ena. Spiral fields exist in grand-design and flocculent galaxies, and even some dwarf galaxies host ordered fields. Regular magnetic fields trace the gas flow in barred galaxies. Vertical magnetic fields observed above disks of edge-on galaxies indicate strong galactic winds into the halos. Magnetic fields possi- bly help to feed the active galactic nuclei, which may solve a long-standing problem. A contribution by Russel Kulsrud on the origin of Galactic magnetic field follows. From considerations of the origin of cosmic rays the existence of magnetic field became obvious. Assuming that a magnetic field did exist there is no problem in sustaining it. On the other hand there are problems to create such a magnetic field. The discussion touches on the well known alpha–omega disc dynamo as well as evolution of primordial magnetic fields. Arguments for and against either interpretation are clearly given, pointing Preface VII out that the question of the origin of the galactic magnetic fields remains open. In the fifth contribution Richard Wielebinski describes the present knowl- edge about the magnetic fields of the Milky Way, derived from radio contin- uum and Faraday effect observations. The basics of the synchrotron emission theory are sketched showing their application to the observations of magnetic fields. The development of radio observations is given and the latest results described. A combination of radio polarization surveys and Faraday Rotation Measure studies of pulsars and extragalactic radio sources are expected to lead to a ‘tomography’, a three-dimensional description of the magnetic field of the Milky Way.