Dust clouds and messy physicists

The Chemically Controlled Cosmos
February 7, 1997

What a shame the recent spectacular Hubble space telescope images of the giant dust pillars in the Eagle nebulae did not find their way on to the cover of this splendid book - they summarise more dramatically than words ever could the abundance of interstellar matter and remind us of the need to understand the vital chemical role played by molecular clouds in the formation of stars, planets and ourselves.

T. W. Hartquist and D. A. Williams provide a clear nonmathematical description of how the chemistry of simple molecules acts to regulate a number of important astro-environmental variables such as temperature, density and radiation fields that allow galaxies, stars and planetary systems to form. Although hardly a pop-science book on astronomy, neither is The Chemically Controlled Cosmos a heavyweight textbook, it instead occupies a middle ground that should cater for scientifically literate lay persons and junior undergraduates alike. With 12 self-contained chapters, the book starts by introducing the reader to a brief history of the grandiose sounding topic of molecular astrophysics, highlighting the seminal role played by Arthur Eddington in the chemistry of interstellar gas and dust that set the scene for all further inquiry. Interestingly, in the pre-supernovae universe, with no known process available to generate molecules at rates high enough to keep their abundances constant, Eddington was reluctant to conclude that interstellar clouds harboured even the simplest of molecules. Confirmation of their existence would have to wait until observational evidence from radio and infrared telescopes during the 1960s and 1970s that have so far revealed more than 80 molecular species in astronomical sources, from the ubiquitous H2 to the exotic HC11N (cyano-decapenta-yne). After a brief but useful review of cosmic timescales to get the mind into astronomical gear, the real work starts with a look at how energy states at the atomic level permit molecules to absorb and emit radiation at set frequencies, and how this electromagnetic information can be used to unravel the physical conditions of interstellar gas and dust clouds, and even look inside regions of active star formation.

Throughout this wide-ranging book, which covers galaxy and star formation, supernovae, comets, stellar winds and the birth of the solar system, the reader is left in no doubt as to the importance of astrochemistry in shaping some of the most powerful objects in the universe. So much so that it left me wondering if, in writing this book, the authors were not motivated in part by the overwhelming perception that physics and physicists alone hold the keys to the inner workings of the universe. As if to confirm my suspicion, I even found the smoking gun - a quote from Frederick Soddy at the start of chapter three: "Chemistry has been termed by the physicist as the messy part of physics, but that is no reason why the physicists should be permitted to make a mess of chemistry when they invade it". Does physics ultimately run the show? Maybe. But if astrochemistry has been the Cinderella of astronomy in recent years, this book is the ticket to the ball.

Nick Petford is senior lecturer in the school of geological sciences, Kingston University.

The Chemically Controlled Cosmos: Astronomical Molecules from the Big Bang to Exploding Stars

Author - T. W. Hartquist and D. A. Williams
ISBN - 0 521 41983 2
Publisher - Cambridge University Press
Price - £19.95
Pages - 169

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