What Does a Black Hole Look Like?,
Early in his book What Does a Black Hole Look Like?, Charles Bailyn points out the paradox of the book’s subject matter: Since by its very definition a black hole is an object from which no light can escape, how can we see one? And yet, black holes and methods for observing them have a central place in modern astrophysics.
Bailyn’s short book unravels the seeming contradiction of “seeing” black holes. Its 10 chapters cover topics ranging from the accretion physics of x-ray binaries to the taxonomy of active galactic nuclei. Recent observations—by modern x-ray telescopes such as NASA’s Chandra X-Ray Observatory and NuSTAR (Nuclear Spectroscopic Telescope Array) and the European Space Agency’s XMM-Newton—have underpinned the many successes and exposed remaining shortcomings in the theories that describe physical processes near black holes. The author’s discussion of the open questions and controversies in interpreting data with current theory is timely; it also highlights the opportunity for discoveries still to be made in the field.
What Does a Black Hole Look Like? is the latest in the Princeton Frontiers in Physics series. The stated goal of the series is to have leading specialists provide short introductions to the most exciting areas of physics research today. Indeed, Bailyn is an authority on identifying and measuring the properties of astrophysical black holes; he has authored numerous papers on the subject. He writes clearly and engagingly about observational results and the history of discovery of astrophysical black holes.
The first chapter of the book introduces black holes; the next two cover the bare bones of the theory of accretion physics, radiation, and jets. These early chapters establish the foundation for the remainder of the text. The next six chapters focus on how actual observations are used in conjunction with theory to identify black holes and understand their environment. They cover all types of black holes, from stellar-mass to supermassive black holes. These chapters are the core of the book and offer a lightning introduction to nearly all aspects of modern research on astrophysical black holes. A short chapter on gravitational waves is a welcome and timely addition to the end of this section of the book, considering that the Advanced LIGO detectors are poised to begin their first observational campaign. The 10th and final chapter focuses on quantum and speculative aspects of black holes. Bailyn’s discussion in that chapter of Hawking radiation and primordial black holes is valuable, but there are many popular, entertaining science books that discuss those and other issues in cosmology—predominant among them Stephen Hawking’s own still-relevant classic A Brief History of Time (Bantam Books, 1988).
Unfortunately, the introductory theory section is relatively weak. That may not be too surprising, since it’s unclear who the book’s target audience is. The mathematics is kept at a basic undergraduate level, but the physical ideas are often complex. The book is too basic to serve as a topical review for researchers, and the author does not shy away from technical jargon (though he provides a helpful glossary). And some typographical errors early on may confuse the serious student attempting to follow the derivations.
What Does a Black Hole Look Like? would not serve well as a textbook. Although possibly useful as a resource for an undergraduate survey course, the book is too short and too complex to be a main text. Advanced students would be better served by reaching for Bradley Carroll and Dale Ostlie’s An Introduction to Modern Astrophysics (2nd edition, Addison-Wesley, 2006). Bailyn’s book does improve over Carroll and Ostlie’s text by incorporating up-to-date observational results and discussing open problems.
The book’s best audience would appear to be technically minded nonspecialists who are intrigued by black holes. For them, the author provides a fascinating glimpse into how astronomers study those exotic objects and how the same data set can lead to a variety of interpretations. As an introduction for the growing population of scientifically passionate nonscientists, this brief work is a success.
Aaron Zimmerman is a postdoctoral fellow at the Canadian Institute for Theoretical Astrophysics in Toronto. His research focuses on the perturbations of black holes, gravitational waves emitted from black holes, and the visualization of spacetime.