The Search for Dark Matter in the Unresolved X-ray Background by Kevork N. Abazajian
Figure left: False-color image of the deep exposure of the Chandra X-ray Observatory in the southern field (CDF-S).
Figure right above: The (circled) resolved point sources and extended sources that are removed from this field to determine the spectrum of the remaining unresolved X-ray background. (Note that the two panels have different orientations.)
A candidate light particle that reduces small-scale structures is a neutrino-like particle that has no standard interactions, but can be produced in the early universe with its small coupling with the standard neutrinos, often described as a “sterile neutrino” (Dodelson & Widrow, 1994). The same coupling for its production requires a decay mode of the sterile neutrino into a photon and the standard neutrino with which it is coupled. The decay photon is mono-energetic and has X-ray energies. This has allowed the use of contemporary X-ray observatories such as NASA’s Chandra X-ray Observatory for a previously unintended purpose: the search for the signature of a dark matter candidate.