Giovanni Carraro - Astrophysics of the Interstellar Medium

UNITEXT for Physics series publishes textbooks in physics and astronomy, characterized by a didactic style and comprehensiveness. The books are addressed to upper-undergraduate and graduate students, but also to scientists and researchers as important resources for their education, knowledge, and teaching.

More information about this series at http://www.springer.com/series/13351

This Springer imprint is published by the registered company Springer Nature Switzerland AG

The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

This book collects the material of the course of Astrophysics of the Inter-Stellar Medium for the master degree in Astrophysics and Cosmology at Padova University. It has been translated and adapted from the original hardcopy paper-notes in Italian of the course of Mezzo Inter-stellare given by Prof. Guido Barbaro until the academic year 20122013. The course (of 48 hours) has been retaken with the same syllabus after a few years hiatus by this writer in the academic year 20182019. Several chapters have been largely improved with the inclusion of new, modern material. As such, this publication effort is heart-fully dedicated to the memory of Prof. Guido Barbaro.

As brilliantly and effectively iconised by Donald Osterbrok, a pioneer of Inter-Stellar Medium (ISM) studies and author of numerous papers and books on the subject, the ISM is everything not in stars.

The modern picture of the ISM is of a multi-component, multi-phase, turbulent, and magneto-hydro-dynamic system. Each component is characterized by a different particle number density and mean temperature. From the cold molecular phase, where stars and planetary systems form, to the very hot coronal gas which surrounds galaxies and galaxy clusters, the ISM is everywhere. Studying the properties of the ISM is vital for the exploration of virtually any field of modern research in Astronomy and Cosmology.

The ISM is a violent system, where energy is generated in spectacular events like Supernovae explosions, spiral density wave shocks and galaxy mergers or pumped in the medium by strong UV flux and stellar winds from massive stars and/or Active Galactic Nuclei.

These notes bring the student through all this with a coherent and accurate mathematical and physical approach, with continuous references to the real ISM in galaxies.

The course (and the book) is naturally divided into three parts.

Part I (Chaps. ) describes the ISM neglecting electrical and magnetic fields. Being the ISM a hydro-dynamic system, this part starts setting the scene by introducing the equations of the fluid dynamics (the conservation equations) for a system at rest. Then, acoustic waves are introduced, which represent the main avenue to the study of instabilities and out-of-equilibrium situations. The real ISM is then described by exploring the role of thermal conduction and viscosity. This first part is concluded by discussing shock waves and turbulence, two ubiquitous and essential ingredients of the thermal balance of the ISM.

In Part II (Chaps. ), the electro-magnetic field is switched on and its role in modulating shock waves and contrasting gravity is studied.

The third and last part (Chaps. is dedicated to molecular clouds. Eventually, star formation is presented in the last Chapter.

This preface cannot end without mentioning the continuous contribution of the students who over the years attended this course. Two students in particular have provided an essential help for the preparation of this book: Nicola Gaspari, and Martina Lai, to whom much gratitude is expressed. Finally, nobody more than my old friend Butler Burton instilled interest for the ISM in me.

The properties of matter in its different states of aggregation depend on the entity of intermolecular forces, on density, and on the degree of thermal agitation. Let us analyze the dependence of such forces on intermolecular distance, as illustrated in Fig.. Forces are repulsive when , attractive when