Galactic Dynamics , James Binney and Scott Tremaine
Princeton U. Press, Princeton, NJ, 2008. 2nd ed. $110.00, $60.00 paper (885 pp.). ISBN 978-0-691-13026-2, ISBN 978-0-691-13027-9 paper
The first edition of James Binney and Scott Tremaine’s Galactic Dynamics is the bible of its field. Written by two of the world’s leading dynamicists, it educated a generation of graduate students and serves as a reference book for researchers of all specialties who work on the subject. Since the book’s publication in 1987, galactic dynamics has witnessed major developments and shifts in perspective, and new dynamical techniques have emerged for modeling and interpreting observations. Nowadays galaxies are not considered in isolation; astrophysicists recognize that their evolution cannot be separated from their formation in the broader cosmological context. Dark matter, an immature concept in 1987, is now seen as the dominant element in the formation and dynamics of galaxies. It is a good time for a second edition.
The new edition incorporates several changes. It expands on the use of Lagrangian and Hamiltonian mechanics and more strongly emphasizes orbit-based methods for constructing stellar systems. In response to increasingly sophisticated N-body simulations, the new edition includes more on numerical methods for evaluating gravitational fields and following orbits. Discussions of dark matter are integrated into the other chapters. Moreover, Galactic Dynamics now has an introductory section to set the cosmological context. The final chapter on galaxy formation and cosmological structure formation includes a short section on star formation and feedback. The topic is far from mature, but it is an appropriate one with which to end the book because it is potentially so important for galactic dynamics. Back in 1987 the community’s understanding of dark matter—the concluding topic for the first edition—was similarly undeveloped.
Galactic Dynamics begins with an observational introduction that is broader in scope than its predecessor. As one who frequently teaches galactic dynamics to students who had somehow missed out on basic astrophysics, I find the new introduction very useful. It provides a comprehensive overview of essential stellar astrophysics, galaxies, star clusters, clusters and groups of galaxies, and the basic concepts of collisionless dynamics and cosmology.
In the 20 years since the first edition was published, astronomers have developed powerful new numerical orbit-based techniques for constructing stellar systems, each of which is tailor made to match the observational constraints on a system’s structure and kinematics. We have learned much about massive black holes at the centers of galaxies and about how those black holes affect the dynamics of their host galaxy. The use of stellar kinematics as a mass detector has advanced greatly, both for central black holes and for application to more general problems in galaxies. The halos of dark matter that envelop galaxies are affected by adiabatic compression as stellar disks grow slowly in the halos’ inner regions, and the halos in turn influence the behavior of the disks. Those and other topics appear in the chapters on potential theory, orbits, and the equilibrium of stellar systems.
Dynamicists have changed their perspectives concerning spiral structure in galaxies, and there is now more interest in how transient spiral structure and the central bars in galaxies can affect the stars of the disk by transporting angular momentum and inducing observable resonant effects. Nonetheless, the more classical theory of spiral waves remains interesting and is still thoroughly presented. The chapter on kinetic theory includes the dynamics of binary interaction, the statistical mechanics of gravitating systems, the gravothermal catastrophe, and the evolution of stellar systems as they are affected by those processes. Much of the chapter pertains more to the dynamics of star clusters than to galaxies, but the dynamics is nonetheless interesting and important because it is essential for understanding the star-cluster populations observed in galaxies.
In the current cold-dark-matter cosmology, galaxies are built from the merging of smaller entities. For that reason, the encounters, merging, and destruction of galaxies are important topics in dynamics. Dynamical friction, tides, and high-speed encounters are all relevant, and the new edition contains an expanded discussion of those topics. It also includes new material on the evolution of binary black holes and additional information on the evolution of tidal tails and streamers.
The book ends with an expanded and useful set of technical appendices. A new feature, the use of boxes, highlights special points of interest. Those boxes are not detailed in the table of contents; it would be helpful to list them in a future reprinting.
The second edition of Galactic Dynamics is a successful revision of its 1987 predecessor and will long be a reference for those working on galaxies. Astronomers teaching advanced courses in galactic dynamics will also use it widely, in part because it includes an expanded collection of interesting and demanding problems for teaching and consolidation of the wealth of material presented in the book.
