Astrophysical Jets and Beams , Michael D. Smith, Cambridge U. Press, New York, 2012. $105.00 (228 pp.). ISBN 978-0-521-83476-6
In recent years the astrophysics community has made rapid progress in understanding the physics of cosmic jets, including those associated with active galaxies, young stars, x-ray binaries, planetary and pulsar-wind nebulae, gamma-ray bursts, comets, and the solar magnetosphere. It is commendable (and unique) that the goal of Michael Smith’s Astrophysical Jets and Beams is to assimilate the current knowledge and present astronomy students and other newcomers to the field with a timely introduction to the essentials.
The book can best be described as a collection of brief reviews accompanied by two compact chapters on radiation mechanisms and fluid dynamics, the most important common threads binding the diverse phenomena. With those two chapters in particular, Smith seems to be attempting to make the book self-contained. But given the field’s rapid developments, the diversity of jets, and the complexity of the involved physics, including molecular interactions and general-relativistic magnetohydrodynamics, the task seems almost impossible for one person to achieve, and in less than 230 pages.
Smith is a well-known astrophysicist who since the 1980s has been associated with theoretical and observational studies of cosmic jets. Early in his career he focused on jets of active galaxies. Later he turned to jets from young stars and protostars. Research on both systems enjoys the lion’s share of the coverage in the book, and observational data for them is in abundance in the literature and archives. Other types of jets are not sufficiently discussed. For example, only three pages are devoted to jets of x-ray binaries and gamma rays and only one page to jets from pulsars. As a result, their descriptions lack detail, and key results, particularly recent ones, are not even mentioned. As the author himself admits, the reviews are incomplete and serve best as a springboard to a more detailed literature search.
Perhaps a more suitable strategy to attract young researchers to the field would be to focus on the observational discoveries of the past, when different ideas on the nature of cosmic jets were in conflict and evolving in response to observational and theoretical investigations. Such a historical approach would certainly make for a more entertaining read and would prolong the book’s shelf life.
Another way to increase such an introductory book’s value would be to focus more broadly and deeply on the underpinning physical processes, which are bound to remain relevant and provide a solid foundation for many years to come. That approach is implemented successfully in Accretion Power in Astrophysics (3rd edition, Cambridge University Press, 2002) by Juhan Frank, Andrew King, and Derek Raine. In Astrophysical Jets and Beams, the attention given to gas dynamics and magnetohydrodynamics is mainly limited to basic equations and rudimentary applications.
To truly develop readers’ physical intuition and enhance their understanding of the background physics, one needs to provide derivations of solutions concerning jet dynamics and discuss them in quantitative detail. Unfortunately, the author does not do that. Even with the shock-wave solutions, which he describes as most important for understanding jet dynamics, he does not properly explain them.
On the whole, the theoretical part of the book is rather disappointing and is mostly limited to qualitative descriptions. The discussions, especially on the role of magnetic fields and relativistic models, tend to be brief and uninformative. Some important topics are completely ignored; those include the acceleration of nonthermal particles and magnetic dissipation, which is beginning to be recognized as a main mode of dissipation, and emission, in magnetized relativistic jets.
No other recent book claims to cover the whole “zoo” of cosmic jets. Instead, each tends to concentrate on some particular type of object and address it with as much rigor and detail as possible. Sophisticated readers with a particular interest would do better to consult specialized books than to work through Astrophysical Jets and Beams. Those interested in jets of active galaxies, for example, should have a look at Relativistic Jets from Active Galactic Nuclei (Wiley-VCH, 2012)—to which I contributed a chapter. That book, edited by Markus Böttcher, Daniel Harris, and Henric Krawczynski, offers a good combination of breadth and depth. Equally successful is the series of lectures on stellar jets published as several volumes under the common title Jets from Young Stars (Springer, 2007–10). I admire the author’s goal to make Astrophysical Jets and Beams a broad-based, student-friendly work. But I cannot enthusiastically recommend it as an introductory text.
