A mysterious X-ray sign from clusters of galaxies recently caused some excitement among astronomers: Does it perhaps originate from dark matter,which makes up around 80 percent of the matter in the universe, but which scientists have not yet been able to detect? In order to succor answering this question, or physicists at the Max Planck Institute for Nuclear Physics in Heidelberg checked an alternative explanation. Accordingly,the search for this form of matter, which is difficult to detect, or must proceed on,as the mysterious X-ray sign seems to originate from highly charged sulfur ions that capture electrons from hydrogen atoms.
Source: phys.org