Magnetism, when extended beyond normal frameworks into cosmic space is characterized by an enormous spatial scale. Because of their large sizes the nature of magnets such as the Earth and the Sun is entirely different from the nature of a horseshoe magnet. The source of cosmic magnetism is associated with the hydrodynamic motions of a highly conductive medium. In this aspect, cosmic magnets resemble a dynamo. However, currents in the dynamo flow along properly ordered wires, while chaotic, turbulent motions are dominant inside stars and liquid planetary cores. This makes more intriguing and surprising the fact that these motions maintain a regular magnetic field. Maintenance of magnetic fields is even more impressive in huge magnets, i.e. galaxies. In fact, we are living inside a giant dynamo machine, the Milky Way galaxy. Although the idea of the global magnetic field of our Galaxy was clearly proposed almost 40 years ago, firm observational evidence and definite theoretical concepts of galactic magnetism have been developed only in the last decade. This book is the first attempt at a full and consistent presentation of this problem. We discuss both theoretical views on the origin of galactic magnetism and the methods of observational study. Previous discussions were on the level of review articles or separate chapters in monographs devoted to cosmic magnetic fields (see, e.g., H. K. Moffatt, 1978, E. N. Parker, 1979 and Zeldovich et aI., 1983).

Magnetic fields are ubiquitous in the universe and their study forms an important area of research in modern day astrophysics. Starting from planetary magnetic fields like the one of the Earth, magnetic fields are found to exist in stars like the Sun, in galaxies to clusters of galaxies. The importance of magnetic fields for our understanding of the Universe has been appreciated since mid-1950's when the advent of radio astronomy and the studies of cosmic ray propagation and confinement revealed a Universe filled with thermal and relativistic plasma whose motions are controlled by magnetic fields. Indeed, cosmic magnetic fields play a crucial role in a number of physical processes in the universe from confining cosmic rays, controlling star formation, driving turbulence in accretion discs, to the production and collimation of jets in AGN's. An extensive review of astrophysical magnetic fields incorporating recent results are in Brandenburg and Subramanian(2005a). Let us first have a quick look into the estimates of the strength and coherence scales of magnetic fields in some astrophysical objects. The magnetic field of the Sun consists of large-scale and small-scale components. The magnetic field of the Sun consists of large-scale and small-scale components. The typical length scale associated with the large-scale field is the width of the toroidal flux belts with the same polarity around the 30° latitude corresponding to about 300 Mm (1Mm = 1000 km). The pressure scale height at the bottom of the convection zone is about 50 Mm and scales smaller than this is associated with the small-scale field.

This course-tested textbook conveys the fundamentals of magnetic fields and relativistic plasma in diffuse cosmic media, with a primary focus on phenomena that have been observed at different wavelengths. Theoretical concepts are addressed wherever necessary, with derivations presented in sufficient detail to be generally accessible. In the first few chapters the authors present an introduction to various astrophysical phenomena related to cosmic magnetism, with scales ranging from molecular clouds in star-forming regions and supernova remnants in the Milky Way, to clusters of galaxies. Later chapters address the role of magnetic fields in the evolution of the interstellar medium, galaxies and galaxy clusters. The book is intended for advanced undergraduate and postgraduate students in astronomy and physics and will serve as an entry point for those starting their first research projects in the field.

This self-contained introduction to astrophysical magnetic fields provides a comprehensive review of the current state of the field and a critical discussion of the latest research. Its emphasis on results that are likely to form the basis for future progress benefits a broad audience of advanced students and active researchers.

While magnetic fields permeate the universe on all scales, the present book is dedicated to their investigation on the largest scales and affords a balanced account of both theoretical and observational aspects. Written as a set of advanced lectures and tutorial reviews that lead up to the forefront of research, this book offers both a modern source of reference for the experienced researchers as well as a high-level introductory text for postgraduate students and nonspecialist researchers working in related areas.