Physics, Formation and Evolution of Rotating Stars ,

A.
Maeder
,
Springer
,
New York
, 2008. $159.00 (829 pp.). ISBN 978-3-540-76948-4

All stars rotate. For the Sun, rotation is so leisurely that the centripetal acceleration at the solar equator is less than 1% of its local gravity. Nevertheless, stellar rotation is important and interesting. For example, the rotation of the Sun, in combination with the upwelling of gas due to thermal convection, creates its magnetic field. Erupting from the surface, that field flings plasma into space as the familiar solar wind. The magnetized outflow carries off angular momentum and tamps down the star’s surface rotation.

Those and many related stellar phenomena are understood to varying degrees but remain challenging problems. So, too, is the task of presenting all such material in a single volume. André Maeder, an astrophysicist at the Observatory of Geneva, has taken up that challenge. In Physics, Formation and Evolution of Rotating Stars , he not only treats stellar rotation, but weaves it into the broader tapestry of stellar structure. There are already many books on the physics of stars, but as Maeder notes in his preface, they too often treat rotation as a minor side effect. He has sought to remedy that oversight with a comprehensive work for graduate students and researchers.

Maeder’s book is substantial and technical, as would be expected from a prolific theorist who has devoted decades to his subject—he authored or coauthored some 70 of the 640 references cited in the back. The book covers a broad range of topics associated with rotation and contains something to pique the interest of just about any theoretically inclined reader. Magnetic dynamos, meridional circulation, rotational instabilities—all those topics and more are included. The book also contains numerous high-quality figures that illustrate physical arguments and display computational results.

Yet the work as a whole is less than the sum of its parts. Ironically, given its title and the author’s explicit goal of focusing on stellar rotation, the book is too diffuse. Of the 29 chapters, 14 are designated as basic treatments, best suited for an introductory course. But 11 of those do not mention stellar rotation at all; instead, they address general aspects of structure and evolution. Only at the ends of the other three chapters is stellar rotation mentioned. Anyone using those “introductory” chapters as the basis for a course would find rotation discussed in a strictly tangential manner—exactly the problem Maeder sought to remedy.

Maeder’s expertise as a theorist is evident, and many theories discussed in the book are fascinating in themselves. After all, there is a reason why Bernhard Riemann, Henri Poincaré, and numerous others have visited the realm of rotating, self-gravitating bodies. But anyone traversing the dense forest of derivations and plots in Maeder’s book may easily lose sight of their purpose, which is to explain real objects in space.

That disconnect between theory and reality is evident in part 5 of the book, which discusses early stellar evolution. For example, figure 20.2 (page 517) shows theoretical evolutionary tracks for pre-main-sequence stars whose masses range from 0.8 to 60 times the solar value M. Although those tracks embody some interesting physics, no one has ever observed a 60-M pre-main-sequence star. The most massive known ones, those of the Herbig Be class, only reach about 10 M. The reason is that more-massive objects contract so fast that they ignite their hydrogen and thereby join the main sequence while still accumulating material from surrounding interstellar gas.

The book is strongest when it deals exclusively with rotational issues. Maeder’s inclusion of key results from helioseismology in his chapter on nonradial pulsations is especially welcome; stellar astronomers need more such exposure to important findings from the solar community. However, even the rotational sections can be tough going—the point of many of them seems to be to develop equations rather than provide physical insight. The work’s awkward English is an additional impediment. Readers will have to fend for themselves when encountering such descriptors as “the momentum of force S by volume unity” (page 339).

With its wealth of information, Maeder’s book will be useful for those seriously interested in the internal dynamics of stars. Jean-Louis Tassoul’s classic Theory of Rotating Stars (Princeton U. Press, 1979) is less ambitious in scope and, of course, lacks recent developments. However, it presents each physical idea in a more logically transparent and methodical fashion. For those seeking a unified introductory graduate text, I recommend the second edition of Stellar Interiors: Physical Principles, Structure, and Evolution (Springer, 2004), by Carl Hansen, Steven Kawaler, and Virginia Trimble.