X-ray Spectra Could Help Reveal Dark Matter in Galaxy Clusters

The XRISM Collaboration combined nearly three months of high-resolution X-ray spectra to search galaxy clusters for unidentified emission lines that could indicate decaying dark matter; sterile neutrinos are cited as one candidate for such lines.

Researchers in the international XRISM Collaboration used high-resolution X-ray spectra to search for signs of decaying dark matter in galaxy clusters. Decaying dark matter models predict faint X-ray lines when hypothetical particles break down over long timescales. XRISM's Resolve instrument provides higher energy resolution than traditional CCD detectors, and the team combined nearly three months of XRISM observations for the search. Their work follows a 2014 study that reported a weak unidentified X-ray line in 73 galaxy clusters. Key points: - XRISM is a space X-ray observatory developed by JAXA and NASA with support from ESA. - The Resolve spectra resolve many known atomic lines from elements such as iron, silicon, sulfur, and nickel. - Emission lines that do not match known atomic positions are treated as candidates for dark-matter decay signals. - Sterile neutrinos are discussed as a theoretical candidate; models predict they could decay into two photons of the same energy, producing a narrow X-ray line. - Galaxy clusters contain about 85% of their mass as dark matter and are therefore considered strong targets for this search. - Because any decay signals are expected to be very weak, the team combined nearly three months of XRISM data for the analysis. Summary: The high-resolution XRISM spectra allow researchers to separate known atomic emission from unexplained lines and provide new observational constraints on decaying dark-matter scenarios. The results help narrow the range of particle properties that are consistent with the data, and the researchers note further study of alternative candidate particles is important. Undetermined at this time.