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Exotica of Stars

Angela Olinto

Cosmic Catastrophes: Supernovae, Gamma-Ray Bursts, and Adventures in Hyperspace. J. Craig Wheeler. xv + 288 pp. Cambridge University Press, 2000. $24.95.

The unprecedented popularity of astrophysics in recent years has challenged authors of science texts for the general public to keep up with the fast pace of new discoveries. With Cosmic Catastrophes, nonexpert readers can effortlessly catch up on the most recent and exciting findings in high-energy astrophysics, such as puzzling gamma-ray bursts and hypothetical hypernovae.

Renowned astrophysicist J. Craig Wheeler skillfully relates nearly "the whole story" in a single volume. He begins with the life and death of ordinary stars, describes the current view of the origin of different types of supernovae, guides us through the formation of neutron stars and black holes and explores the frontiers of present knowledge in his discussion of topics such as wormholes and M theory.

Wheeler quickly provides readers with the basic concepts of physics necessary to understand the most powerful events in outer space. He starts by introducing the four basic forces of nature and fundamental conservation laws (the conservation of energy, momentum, angular momentum, charge, baryon number and lepton number) that are readily applied to the life and death of stars. He does not shy away from complexity, clearly describing the many ways that stellar lifestyles can vary, depending on a star's initial mass and location relative to other stars. His explanation of the basics of stellar evolution sets the stage for his discussion of the formation of compact objects (such as white dwarfs, neutron stars or black holes) through the "inexorable grip of gravity."

Very massive stars (those with a mass eight times that of the sun or greater) live a brief life ending in a catastrophic explosion known as a supernova. A single supernova can outshine a whole galaxy with the power of its explosion and is visible across the universe; it can be used to determine the distance to its host galaxy. Studies of distant supernovae have recently revealed that not only is the universe expanding, it also seems to be accelerating.

Stars that are less massive, such as our sun, may die a quieter death, unless they have partners. Stars with one companion are as common as single stars, and the evolving dynamics of a duo can also lead to cosmic fireworks. Wheeler describes the evolution of binary systems as a sophisticated dance choreographed from a number of simple steps, such as the conservation of angular momentum, the dynamics of Roche lobes, and Lagrangian points. In binary systems, mass can be transferred from a star to its companion. When compact objects are in a binary system, the very high energies involved lead to spectacular outbursts. As matter accretes onto neutron stars and black holes, the gravitational energy released generates cosmic fireworks that are observable with x-ray telescopes. Delineation of the final dance, in which gravitational radiation brings the remnants of the original stars closer and closer together, is a challenge that awaits development of the next generation of gravitational wave detectors.

Wheeler connects black holes to fascinating speculative ideas such as wormholes and time machines. He ends by discussing the search for a unifying theory of quantum gravity, a "theory of everything" that would account for both general relativity and quantum phenomena.

Cosmic Catastrophes is entertaining and dynamic, interweaving colorful personal anecdotes and historical narrative with its scientific explanations. Illustrations by Tim Jones help clarify the physical concepts, but color photographs would have been a welcome addition, as would references for readers interested in exploring topics in more depth.—Angela V. Olinto, Astronomy and Astrophysics, University of Chicago.

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