Stellar Alchemy: The Celestial Origin of Atoms

  • Michel Cassé
(transl. Stephen Lyle) Cambridge University Press: 2003. 256 pp. $30, £19.99 0521821827 | ISBN: 0-521-82182-7
The ancestral home? We are made up of atoms that were created inside distant stars. Credit: NASA/JPL/CALTECH

Have you ever wondered how humans fit into the cosmos, what our relationship is to the stars, or how the elements were formed? If so, you should enjoy Stellar Alchemy. Michel Cassé, a French astrophysicist, takes the reader on an idiosyncratic journey through the intricacies of modern astrophysics to show how the stars, galaxies, the Universe and humans are interrelated. The book, published in French and now translated into English by Stephen Lyle, is designed for general, but scientifically literate, readers.

The book's focus is on nucleosynthesis, the formation of the elements. The Big Bang created hydrogen, helium and some lithium. Two other light elements, beryllium and boron, are made in interstellar space from interactions between cosmic rays and gas atoms. Over the 14-billion-year lifetime of the Universe, all the other elements have been synthesized inside stars and ejected into space to make new stars, planets and even us. In this process a common element, such as iron, could be transformed into gold — the alchemists' dream.

To explain this requires an understanding of the births, evolution and particularly deaths of stars. Cassé draws colourful comparisons between stellar and human life cycles, although he notes that stars are not alive in the same sense as humans. As stars are the primary components of galaxies, which are strewn across the Universe, the formation of galaxies and the origin and fate of the Universe are also described in great and interesting detail, as are the requisite and related physics: the nature of light, the spectra and atomic physics we use to detect elements in stars, and the various aspects of nuclear physics involved in making the elements.

If the focus is on nucleosynthesis, the book's theme is that we are stardust — the atoms in our bodies were once in stars, making stars our distant ancestors. This idea, popularized by the late Carl Sagan, emphasizes the connections between life on Earth and the formation of elements such as carbon and oxygen in stars. In a personal and reflective manner, Cassé places humanity's origins and future squarely in the cosmos. He includes a nice discussion of the death of our Sun, the Earth and the Solar System, and speculates on humans emigrating from Earth before it is too late. Cassé's optimism shines through as he guarantees we will have mastered space flight by that time, assuming we survive as a species.

The book addresses many of the topical questions in astrophysics. There are lengthy discussions and speculations concerning the dark matter that composes more than 90% of the Universe but cannot be seen, and the recently discovered dark energy, an apparent antigravitational effect that is causing an accelerating expansion of the Universe. Although these topics are still mysterious, Cassé remains the optimist, noting that their explanations may be “unknown but not unknowable”.

Cassé's writing style, flowery and poetic and full of historical references, makes even the more technical material accessible to the general reader. The book is also filled with delightful aphorisms, such as “patience is a virtue in the hunt for the invisible” and “the best way of finding a needle in a haystack is to burn the hay”. His organization and chapter titles are whimsical, but work — “The Sociology of Stars and Clouds”, for example. Another nice touch is a glossary of technical terms at the beginning of each chapter. Even with those, however, parts of the book may require effort for those without a background in physics and astronomy.

Some of the figures also seem to be more appropriate for, and have come from, researchers in the field, and some of the tables and appendices are for specialists only. Cassé also stresses the individual and national contributions from French astronomers. While no doubt deserved, their frequent mention seems somewhat out of place. But these are minor quibbles, and Cassé's interesting story about the relations between the stars and humans, and his joy in the subject, carry the reader along on a pleasant journey.