Cosmic Catastrophes: Exploding Stars, Black Holes, and Mappi the Universe

Wheeler begins his book by describing how stars form, how they evolve in response to gravity, how they ignite, how they burn, and eventually how they die. This is a logical introduction, since virtually all the examples of cosmic catastrophes involve stars in one form or another. Like people, though, the life of each star is unique - and the end times are very different. Wheeler does an excellent job of describing the negative feedback process that stabilizes solar activity. If the star generates too much heat it expands. This expansion reduces the temperature, and throttles back on the rate of nuclear fusion. If the star cools down it contracts, and the contraction heats it up again, keeping the rate of fusion at a remarkably constant level for long periods of time during the stars life.

Much of Wheeler's text is actually about how stars evolve. This is important because to understand their deaths, you need to understand how they are born and how they evolve over their lifetimes. Their deaths are frequently the most interesting parts of the story because they are often involved with the catastrophes that are the book's principal thesis. While I bought the book because of its discussion about cosmic catastrophes, I found it valuable for its descriptions of stellar evolution alone. This includes a nice description of the "solar-neutrino" problem as well as a nice explanation of the red-giant phase, and especially the last stages during the life of a massive star that explodes in a super nova.

The foundational understanding of the basics of stellar evolution makes it easier to follower Wheeler as he takes the reader on a tour of the major players in cosmic catastrophes: white dwarfs, super novae (of many different types), neutron stars, black holes, and gamma-ray bursts. Wheeler's descriptions of these phenomena (to the extent that modern science understands them) are among the best I've seen in a popular science textbook. There is also a smattering of discussion about the origin of the universe in the Big Bang, and some interesting speculation about time (and space) travel using black holes.

In any book dealing with modern cosmology and astronomy there are inevitable discussions about the nature of space and time and how they fit together with Einstein's theory of general relativity. Most such books have at least one figure showing a funnel-shaped construct with grid lines converging as they swoop into the tapering end where the black hole resides. Wheeler uses lots of such diagrams. However, I think he does a better job than most at helping the reader understand what the diagrams illustrate. More importantly, he helps the reader understand what the diagrams do not illustrate, and their limitations (he dispels some common misperceptions about these sorts of figures). I especially enjoyed Wheeler's explanations about how one might (with the application of the appropriate mental acrobatics) use the diagrams to actually envision what is really going on in our multi-dimensional world.

Another thing I liked about Wheeler's book is the clear and frequent illustrations. For the most part the author has anticipated those places where prose just cannot quite complete the mental picture. When this happens there is inevitably a well-constructed diagram that finishes the concept and makes things clear. There was one exception, however. Figure 7.3 really needs to have an arrow or circle marking the location of SN 1987A. [I'm pretty sure I found it, but the exposure changes between the photographs, and so I'm not quite sure. It would have been nice to have the author's help in preventing a false identification.]

Reading this book one gets the sense that even though it is a qualitative description of astronomy (there are no equations) Wheeler is not over simplifying. His discussion of super novae, for example, lists many classes and describes theoretical uncertainties that other authors gloss over or ignore all together. Of course there is much more detail to super novae than what is in Wheeler's book. But at the qualitative level Wheeler leaves the reader understanding that there are many classifications of super novae, that some of the boundaries between classifications are not always so clear cut, and that we still don't know a lot about how some types form, and how other types explode. These are concepts that other popular science textbooks don't always convey. I think the only thing missing from the chapters on super novae is a table that summarizes all the different types and some of their descriptive identifiers.

Unlike some popular science texts, Wheeler devotes quite a bit of time describing the evolution of binary stars, which play an important role in some of the greatest cosmic catastrophes. I think he does an especially good job of qualitatively describing accretion disks, and how they fit in the context of mass transfer in binary systems. It's this mass transfer that is ultimately involved in some of the most spectacular catastrophes in the sky.

Overall, this is a great book. If you enjoy astronomy I'm sure you will find it satisfying and informative. It's just the sort of book to enjoy on a vacation, or after a grueling day at the office.
October 06, 2000