Galactic leftovers reheated

Cold dark matter, a key collisionless constituent of the universe, contains about 30 per cent of the total cosmic energy density and played a pivotal role in the formation of individual galaxies and of galactic clusters. We now realise that only a small fraction of the universe is visible. Unfortunately, we do not know what the rest of the universe consists of.

In 1987, the Fourth Jerusalem Winter School for Theoretical Physics discussed this mysterious missing dark matter. The assembled experts wrote up their lectures, producing a first-class introduction to the subject. Essays were written on the distribution of dark matter in spiral galaxies and galactic clusters, the effect of dark matter on globular clusters, the effect of the localised injection of energy on the expansion of the universe, gravitational lenses as a probe of the early universe, the dark matter that is needed to ensure that Omega (the cosmological density parameter) is unity, weakly interacting massive particles (Wimps), cosmic strings and the theory that Newtonian gravitation fails at low accelerations.

Almost two decades on, the book is reissued. Do the authors revise their chapters in the light of advances in this fast-moving field? Are new ideas evaluated? Are references updated and detection frontiers reviewed? The short answer is "no". Only two changes have been made. An essay on dark matter in the Milky Way is omitted, and Anthony Aguirre has provided 15 pages on dark matter's role in theoretical cosmology.

The justification of the chief editor is that "most of what we have learnt since 1986 is what dark matter is not; discovering what the dark matter really is remains an exciting challenge". When it comes to this second edition of Dark Matter in the Universe , save your money. If you want an "exciting challenge", try buying the first edition second-hand.

David Hughes is professor of astronomy, Sheffield University.