Galaxies in Turmoil: The Active and Starburst Galaxies and the Black Holes That Drive Them : Chris Kitchin , Springer, New York, 2007. $29.95 (298 pp.). ISBN 978-1-84628-670-4
Stars are the primary energy source of normal galaxies. Hundreds of billions of them account for most of the light that can be detected from a typical galaxy. In contrast, accretion of material onto a supermassive black hole at the galactic center is the energy source for active galaxies; the resulting radiation often outshines all the stars in the galaxy. The exceptional feeding monsters at the centers of active galaxies are called active galactic nuclei, or AGNs. Active galaxies, and the extremely luminous starburst galaxies, which exhibit unusually high rates of star formation, are the subject of Galaxies in Turmoil: The Active and Starburst Galaxies and the Black Holes That Drive Them, by Chris Kitchin.
Although they are distinct phenomena, AGNs and the intense star formation of starbursts together make a coherent subject for a topical book. Recently measured relationships between the mass of a central black hole and the total stellar mass in its host galaxy indicate that black hole accretion and star formation may be physically related and fundamental to galaxy evolution.
The text is written at a level appropriate for undergraduate students, and its intended audience also includes amateur astronomers. Kitchin, professor emeritus of astronomy at the University of Hertfordshire in the UK, is the author of several practical and technical observing guides. After lucidly explaining the physical processes of the tumultuous galaxies featured in his book, he devotes a chapter to observations that can be made with binoculars or a small telescope. His account of beaming in AGN jets and the apparent superluminal motion of jet particles proceeds from the aberration of starlight, a phenomenon that is familiar to observers.
A great contribution of the book is its clear description of the many types of AGNs. Both the text and an appendix set out the defining features of the multiple and often overlapping classifications astronomers use. Despite the common underlying nature of AGN activity as described in unified models, differences in intensity and viewing geometry lead to a variety of observational characteristics. A central feature of the models is the presence of a toroidal distribution of dust in the nuclear region. Although the text makes it clear that differing views relative to the torus are responsible for many of the observational distinctions, the corresponding figures erroneously suggest that the torus is necessarily aligned with the disk of the host galaxy.
Overall, the text is direct. A few stories of key episodes in understanding galaxies reveal the path of scientific discovery. For example, the book’s first chapter tells of Edwin Hubble’s confirmation that there exist galaxies outside the Milky Way. Unfortunately, the development of main ideas is sometimes lost when the straightforward writing becomes choppy. Even before the reader has learned the significance of Hubble’s discovery, the text is diverted for a seven-page box on spectroscopy. More significantly, the connections between chapters are often weak. For example, some outstanding problems in the field are identified, but with no indication of likely solutions. Other chapters, though, describe recent developments that may answer those very questions. The book’s coherence would be further strengthened if the author more deeply explored the relationship between starburst and accretion activity, a subject occasionally hinted at in the text.
The scarcity of equations is intentional, but a few more would be helpful, particularly for use in a college course—even one geared toward non-scientists. Equations could succinctly describe the quantitative information that is listed in tables, such as the aberration angle as a function of velocity or the Schwarzschild radius as a function of black hole mass. The topics covered are of interest to students, and to the best of my knowledge, no other book provides a similar focus at a comparable level. Although the concepts may be familiar to amateur observers, university students need an explicit introduction to angular sizes and the relationships between angular and physical dimensions.
AGNs and starbursts are areas of vigorous ongoing research, and Kitchin’s book contains current results. Many controversies and questions, however, are not yet resolved conclusively, so more information about the latest work would be useful. In a general-interest book, references to professional publications are not necessarily appropriate, but identifying the key researchers by name would allow the reader to keep up with their results. Graduate students are not Kitchin’s intended audience, but with the addition of specific supplemental references, Galaxies in Turmoil would make an excellent introduction for beginning research students.
