The accepted theory regarding the formation of structures in the universe stipulates that initial fluctuations in the density of the earlier universe have grown over time resulting in the setup we see today. It is the gravitational interaction of dark matter, a mysterious substance comprising about a quarter of the matter in the universe, which affected these fluctuations, creating clumps of dark matter.
Since dark matter particles interact only gravitationally, they are hard to detect. However, according to one theory, as these particles called WIMPs (weakly interacting massive particles) interact; they can annihilate each other and in the process emit gamma rays. These emissions can be detected by the Gamma-ray Large Area Space Telescope (GLAST), launched by NASA in June. Piero Madau commented: “That’s what makes this exciting; some of those clumps are so dense they will emit a lot of gamma rays if there is dark matter annihilation, and it might easily be detected by GLAST”. Juerg Diemand, a postdoctoral fellow at UCSC and first author of the Nature paper, added: “For typical WIMPs, anywhere from a handful to a few dozen clear signals should stand out from the gamma-ray background after two years of observations. That would be a big discovery for GLAST.”