Rip the Macho Era (1974-2004)

This article reviews the life and death of a scientific theory 1. The MACHO Ideology 1.1. The Dawn of Dark Matter The hypothesis of dark matter is often ascribed to Fritz Zwicky. Certainly, Zwicky 1 in his book " Morphological Astronomy " noted the discrepancy between masses of clusters inferred from the virial theorem and masses inferred from the visible constituent galaxies. He suggests five possible explanations. The fifth (and most tentative) — after propositions that the clusters may not be in equilibrium or that light may tire on traversal of enormous distances — is: " Finally, attention must be called to the recent discovery of luminous and of dark intergalactic matter. The existence of this dark matter may seriously affect all previous estimates concerning the distribution of mass in the Universe ". The focus of this conference is on the direct and indirect detection of dark matter in the Milky Way galaxy and other nearby galaxies. Even if Zwicky was the first to hypothesise the existence of dark matter in clusters, he did not believe that there was appreciable dark matter in galaxies (in " Morphological Astronomy " , he advocated Keplerian fitting to rotation curves to estimate the masses of galaxies). The realisation that galaxies are surrounded by dark matter haloes only came much later. Dark matter on the scales of galaxies became widely accepted after the publication of the rotation curve of the nearby galaxies M31, M81 and M101 by Roberts and collaborators 2. In an influential paper, Ostriker, Peebles & Yahil 3 brought together a number of lines of evidence to suggest that: " There