Lequeux James - The interstellar medium

Author : Lequeux James
Title : The interstellar medium With the collaboration of Edith falgarone and Charles Ryter with 151 figures including 32 color plates
Year : 2005

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Foreword. In spite of its generally low density, the medium between the stars plays a very important role in astrophysics. Stars are born from this interstellar matter when it undergoes gravitational collapse. During their lifetime and in particular in the final stages of their evolution, the stars return matter to the interstellar medium. This material is enriched in heavy elements arising from the thermonuclear processes that occurred inside the stars. New stars form from the interstellar matter that has been enriched by previous stellar generations. The evolution of the Universe is thus characterized by a continual mass exchange between stars and the surrounding medium. Mass exchange also takes place between the interstellar medium of galaxies and the intergalactic medium. The interstellar matter consists of atomic, molecular and ionized gas at various temperatures, and also of dust grains which contain a large fraction of the elements heavier than hydrogen and helium. These grains are formed in the circumstellar shells around stars at the end of their lifetime. They are also continuously destroyed, altered and reformed in interstellar space. Interstellar grains play two important roles. Firstly, they absorb a large fraction of the photons emitted by stars and reemit the corresponding energy thermally as mid- and far-infrared photons. Secondly, molecules form on the surfaces of interstellar grains, in particular the most abundant hydrogen molecule H2. Interstellar physics and chemistry differ markedly from those of terrestrial laboratories due to the very different conditions. The elementary processes are often more visible in interstellar space because of the low densities. The study of the interstellar medium is thus of fundamental interest for understanding and elucidating these basic processes. The purpose of this book is to describe interstellar matter in our Galaxy in all of its various forms, and to consider the physical and chemical processes that are occuring within this matter. Like the authors, the reader will come up with difficulties related to the extreme complexity of the interstellar medium, which makes impossible a linear description. Moreover, our very conception of this medium experiences a deep evolution at the time of writing, as we progressively realise that it is most often turbulent and out of equilibrium. However, we do not yet know enough on this to find it necessary to abandon the relatively simple concepts that have governed its study up to now. These concepts stay at the basis of this book, and their pedagogical value will stand for a long time. ...

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