Clusters and superclusters of galaxies are the largest objects in the Universe and are the subject of intense observational study at a variety of wavelengths, from radio to X-ray which has provoked much theoretical debate and advanced the understanding of the recent evolution of the large-scale structure the universe. The subject is reviewed in this volume by researchers who lectured at a NATO Advanced Study Institute held in Cambridge in July 1991. Much of the material is presented in a pedagogical manner and should be useful to scientists, astronomers and graduate students interested in extragalactic astronomy.

Clusters and superclusters of galaxies are the largest objects in the Universe. They have been the subject of intense observational studies at a variety of wavelengths, from radio to X-ray which has provoked much theoretical debate and advanced our understanding of the recent evolution of the large-scale structure of the Universe. The current status of the subject is reviewed in this volume by active researchers who lectured at a NATO Advanced Study Institute held in Cambridge, England in July 1991. Much of the material is presented in a pedagogical manner and will appeal to scientists, astronomers and graduate students interested in extragalactic astronomy.

X-ray astronomers discovered the diffuse gas in clusters of galaxies about 20 years ago. It was later realized that the central gas density in some clusters, and in elliptical galaxies, is so high that radiative cooling is a significant energy loss. The cooling time of the gas decreases rapidly towards the centre of the cluster or galaxy and is less than a Hubble time within the innermost few hundred kiloparsecs. This results in a cooling flow in which the gas density rises in order to maintain pressure to support the weight of the overlying gas. The rate at which mass is deposited by the flow is inferred to be several hundreds of solar masses per year in some clusters. The fraction of clusters in which cooling flows are found may exceed 50 per cent. Small flows probably occur in most normal elliptical galaxies that are not in rich clusters. The implications of this simple phenomenon are profound, for we appear to be witnessing the ongoing formation of the central galaxy. In particular, since most of the gas is undetected once it cools below about 3 million K, it appears to form dark matter. There is no reason why it should be detectable with current techniques if each cooling proton only recombines once and the matter condenses into objects of low mass.

Gas at temperatures exceeding one million degrees is common in the Universe. Indeed it is likely that most of the gas in the Universe exists in intergalactic space in this form. Such highly-ionized gas, or plasma, is not restricted to the rarefied densities of intergalactic space, but is also found in clusters of galaxies, in galaxies themselves, in the expanding remnants of exploded stars and at higher densities in stars and the collapsed remains of stars up to the highest densities known, which occur in neutron stars. The abundant lower-Z elements, at least, in such gas are completely ionized and the gas acts as a highly conducting plasma. It is therefore subject to many cooperative phenomena, which are often complicated and ill-understood. Many of these processes are, however, well-studied (if not so well-understood) in laboratory plasmas and in the near environment of the Earth. Astronomers therefore have much to learn from plasma physicists working on laboratory and space plasmas and the parameter range studied by the plasma physicists might in turn be broadened by contact with astronomers. With that in mind, a NATO Advanced Research Workshop on Physical Processes in Hot Cosmic Plasmas was organized and took place in the Eolian Hotel, Vulcano, Italy on May 29 to June 2 1989. This book contains the Proceedings of that Workshop.

Evolution is a fundamental process that cuts across boundaries of art and science and has beguiled thinkers for ages. This collection of articles about all aspects of evolution is a feast of challenging ideas, drawing together world-renowned thinkers and communicators with their own intriguing insights. This impressive cast of contributors takes on such questions as: Why and how do civilizations and societies change over time? Why do our cells develop the way they do? Why are some villages still villages while others have grown into vast cities? Can we learn from our evolutionary past to plan a better future for our health and society? Tracing the history of biological evolution, through the evolution of cultures, society, science and the universe, contributors such as Stephen Jay Gould, Freeman Dyson, and Martin Rees address these mysteries by considering parallels from all levels of life. From the evolution of the embryo to the evolution of a star, common threads emerge to tell a fascinating story with surprising implications.

We all have a natural interest in our own origins and, by extension, the origins of the world in which we live. In this volume, the first in The Darwin College Lectures Series, a distinguished team of international authorities reports on the latest research on the origins of the most fundamental features of our world. Martin Rees begins the book with a bang, the Big Bang that was the probable start of our expanding universe. The contributors then focus on the origins of the solar system, material complexity and the human species. The volume ends with essays by John Maynard Smith on social behaviour, Ernest Gellner on society and John Lyons on language. The book derives from a highly successful series of lively public lectures which have since been revised and illustrated for publication under the editorship of Professor A. C. Fabian of the Institute of Astronomy, University of Cambridge.

These contributions by recognized authorities originate from a Royal Society discussion meeting held to review the most recent results obtained from the current generation of X-ray telescope research. The launch of Chandra and XMM-Newton has revolutionized research in X-ray astronomy over the past few years, and high quality X-ray observations now being made have had a major impact on topics ranging from protostars to cosmology. This book is a valuable reference for research astronomers and graduate students.