QuoteThe cold spot in question is an unexplained anomaly in the map of the cosmic microwave background (CMB) created by NASA’s WMAP satellite. The photons of the CMB coming from a region of the sky in the direction of the constellation Eridanus are colder than expected. Rudnick’s team started looking for radio sources such as radio galaxies and quasars in the direction of the cold spot. "Radio sources track the distribution of mass in the universe," says Rudnick. "They are the signposts for galaxies, clusters of galaxies and dark matter."