A stream of observations in the 1980-90s supported the presence of dark matter; notable, for Spirals the investigation of 967 objects by Persic, Salucci and Stel. The evidence for dark matter also included gravitational lensing of background objects by galaxy clusters, the temperature distribution of hot gas in galaxies and clusters, and the pattern of anisotropies in the cosmic microwave background. According to consensus among cosmologists, dark matter is composed primarily of a not-yet-characterized type of subatomic particle. The search for this particle, by a variety of means, is one of the major efforts in particle physics.