Spiral Structure in Galaxies: A Density Wave Theory(The MIT Press)

How does it happen that billions of stars can cooperate to produce the beautiful spirals that characterize so many galaxies, including ours? This book presents a theory of spiral structure that has been developed over the past three decades under the continuous stimulus of new observational studies. The theory unfolds in a way that can be grasped by any reader with an undergraduate science background who is interested in astronomy, as well as by graduate students and scientists actively involved in astronomy or related subjects who want to see the "backbone" and the physical content of the theory. The foundations of this theoretical framework were laid in the early 1960s, following the pioneering work of B. Lindblad. C.C. Lin had already contributed significantly to the field of fluid mechanics when he turned his attention to spiral structures, and he has focused on the problem ever since. Guiseppe Bertin joined this research effort when he first visited at MIT in 1975, bringing to the project knowledge from his work on elliptical galaxies and plasma astrophysics. Together, Bertin and Lin have contributed to the exciting developments on spiral structure of the last few decades, working closely with many observers and other theorists. In this book they describe the density-wave theory with the goal of making the key concepts and astrophysical implications explicit and accessible. The essence of the solution Bertin and Lin present is that the spirals are wave rather than material phenomena and generally trace intrinsic characteristics of the individual galaxies. The book is in three parts - physical concepts, observational studies, and dynamical mechanisms - with most of the technical details confined to the last part.

Table of Contents:
Introduction - morphology and semiempirical approach; co-existence of small- and large-scale structures; excitation of spiral structure; three "persistence" problems and main-tenance of spiral structure; roles of the cold, dissipative gas component; the dynamical window; prevalence of two-armed grand designs; barred spirals; scales of motion; viability of the model approach for normal spirals; a physical per-spective; future developments. Part 1 Physical concepts: physical and morphological characteristics of galaxies - hubble classification, overall characteristics of spiral galaxies, morphology of spiral arms, major issues addressed in this monograph, relation to other astrophysical themes of general interest; the concept of density waves - density waves versus material arms, tendency for the formation of spiral waves, collective behaviour, a preliminary formulation of the hypothesis of quasi-stationary spiral structure; density waves, interstellar medium, and star formation - processes of star formation, sketch of the large-scale shock scenario, direct simple evidence of density waves, mechanisms of self-regulation; regularity, morphological classification, and the concept of spiral modes - global modes as intrinsic characteristics of the galaxy, excitation mechanisms, linearly growing modes, moderately growing modes, nonlinear equilibration, the hypothesis of quasi-stationary spiral structure, morphology of modes - normal spirals versus barred spirals, grand design versus flocculent galaxies, a tentative interpretation of the hubble sequence, tides and well-developed bars. Part 2 Observational studies: external galaxies - in search of a unifying framework for ob-servations, morphology, luminosity classification and star formation, kinematics, modeling; the milky way - a unique case, spiral arms and spiral features, kinematics, modeling the solar neighbourhood. Part 3 Dynamical mechanisms: basic models and relevant parameter regimes - modeling of the basic state, zero-thickness dynamical models, kinematics of a differentially rotating disk; geometry of wave patterns - density maxima, potential minima, and number of arms, pattern frequency, pitch angle of spiral structure, trailing and leading, normal spiral structure, barred spiral structure, and oval distortions, trapping of orbits at resonances and self-consistency. (Part contents).

About the Author :
G. Bertin is Professor in the Department of Physics at the University of Milan. C. C. Lin was Institute Professor Emeritus in Applied Mathematics at MIT and Distinguished Professor at Tsinghua University in China.