Mystery X-Ray Signal Probably Not Dark Matter After All | Motherboard
http://motherboard.vice.com/read/mystery-x-ray-signal-probably-not-dark-matter-after-all
A couple of years ago, astronomers took note of a curious x-ray signal in data from both NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton Observatory.
First, it was seen in observations of the Perseus galaxy gathered by both instruments, and, then, it was all over the place. XMM-Newton found the same signal present in 73 other
galaxies: an x-ray emission line at a frequency where there shouldn't be one. Thoughts quickly turned to a dark matter explanation.
Of course, dark matter being dark and all sort of precludes it from spitting out x-rays. Instead, the idea is that as certain dark matter particles decay, they might emit x-rays.
This is the case for one potential dark matter explanation: sterile neutrinos. These hypothesized particles interact only via gravity, a la dark matter, but as they decay, they
should emit an x-ray glow. We haven't actually detected sterile neutrinos yet owing to the extreme sensitivities required. Indeed, the x-ray signals observed by Chandra and XMM-
Newton were at the upper limits of their observational powers.
So, as it turns out, the signals may not be so dark or mysterious. According to researchers at the Max Planck Institute for Nuclear Physics in Heidelberg, they are likely
the product of highly-charged sulfur ions being devious. This is all described in a paper posted recently to the arXiv pre-print server and slated for publication in
the Astrophysical Journal.