Galaxies and the Cosmic Frontier , William H. Waller and Paul W. Hodge Harvard U. Press, Cambridge, MA, 2003. $29.95 (317 pp.). ISBN 0-674-01079-5
The layperson interested in an up-to-date overview of galaxies, their relation to our own Milky Way, and their importance in the large-scale structure and evolution of the universe has little information available. Thus the publication of Galaxies and the Cosmic Frontier by two well-known galaxy experts is a welcome, timely event that fills a niche in the popular literature. William Waller is a research associate professor of physics and astronomy at Tufts University and co-founder of NASA’s New England Space Science Initiative in Education. Paul Hodge, a seasoned author, is professor emeritus of astronomy at the University of Washington in Seattle and editor-in-chief of the Astronomical Journal.
The book covers broad ground—from color-magnitude diagrams and black bodies to grand unified theories, the inflationary universe, dark matter, and fluctuations in the cosmic microwave background. Most everything in between, especially galaxies in their various forms, is touched upon, and the authors offer occasional forays into such diverse topics as the mythology of the Amazon Indians and DNA. A related website (http://cosmos.phy.tufts.edu/cosmicfrontier/main.html), mentioned in the book’s preface, is based on a course at Tufts and provides additional technical information.
What I like about Galaxies and the Cosmic Frontier are its illustrations, which include 32 color plates and other well-chosen and appropriate black-and-white figures, especially three-dimensional ones of the local group of galaxies and the local supercluster. The book is reasonably up-to-date, especially its section on the accelerating universe. It is also an honest book in that the authors present the material without a pretense of knowing all. (For an example of the authors’ style, see the book’s section on the value of the Hubble constant.) Readers can learn and discover much during their journey through this book.
What I find disappointing, however, is the superficial and confusing manner in which much of the material is presented. The authors’ goal, “to tell this grand tale in words that can be understood by a reader with little scientific training,” could have been achieved with a little more care. For example, in chapter 1, the inverse-square law is explained verbally, but in the context of a radial decline in brightness in elliptical galaxies rather than through the more common context of a source’s distance from Earth. In chapter 2, declining brightness in ellipticals is reintroduced, but this time mathematically. Readers are told that a deprojection to “more physical units of luminosity per unit volume … yields an eightfold decrease in density.” The difference between brightness and luminosity is not explained, and the implication that light per unit volume maps directly to stellar mass per unit volume (that is, density) is completely omitted.
The authors’ treatment of the Hubble relation is equally confusing. It is introduced in chapter 12 as v r = H × d, where v r is the recessional velocity, H is a constant of proportionality usually referred to as the Hubble constant H 0, and d is the distance. Then, in chapter 14, the Hubble relation is introduced again as v r = H 0 × d, with the terms needlessly defined again, this time with some added explanation of the meaning of the recessional velocity.
Many similar examples appear in the book. In another case, supermassive black holes are first introduced in chapter 2 and are explained, in part, as being like their “stellar counter-parts” without indicating what a stellar counterpart might be. Readers finally encounter stellar-mass black holes in chapter 7, but only in the discussions of x-ray sources. Other terms, such as “self-gravity” and “partinos,” are simply introduced without definitions. The result is confusion for readers unfamiliar with the field and frustration for those who are familiar with it.
Occasionally, Galaxies and the Cosmic Frontier has some very nice sections, such as those on spiral structure (in chapter 2), the speeds of Earth and the Sun (in chapter 6), and unified models for active galactic nuclei (in chapter 11). However, for the most part, the book needs some dispassionate editing. It will work best for readers who already have some scientific and astronomical background and want to be updated about the field; and Galaxies and the Cosmic Frontier will especially serve those looking for the sense of excitement and discovery that modern galactic astronomy can evoke.
