A mysterious X-ray signal is emitting from the Perseus galaxy cluster, leaving astronomers scratching their heads. There are several exciting possibilities of what could be causing this, including the decay of dark matter factors called "sterile neutrinos."

The ray in question is an X-ray emission line - a spike of intensity in a very specific wavelength of X-ray light, as observed by NASA's Chandra X-ray Observatory and European Space Association's XMM-Newton. The emission line was first discovered during a detailed study of 73 galaxy clusters, including 17 days of observing the Perseus Cluster over 10 years.

Researchers have now theorized that the most likely explanation for this mysterious observation is that the X-ray emission is the result of decaying sterile neutrinos - a hypothetical type of neutrino particle that interacts with normal matter only via gravity, making it a huge part of dark matter theories.

"We know that the dark matter explanation is a long shot, but the pay-off would be huge if we're right," Esra Bulbul, a Harvard-Smithsonian astrophysicist and author of the study, said in a statement. "So we're going to keep testing this interpretation and see where it takes us."

Even as a long shot, most experts believe that this is the most plausible explanation as to why the Perseus Cluster is emitting this incredibly specific X-ray line.

According to the researchers, other explanations could involve more traditional matter interactions, but Bulbul's team concluded that all of them would have to involve unlikely changes to the galaxy cluster's physical structure - changes that have not been detected.

"There are lots of ideas out there about what these data could represent," said co-author Adam Foster. "We may not know for certain until Astro-H launches, with a new type of X-ray detector that will be able to measure the line with more precision than currently possible."

Astro-H is the sixth of NASA's X-ray observation satellites dedicated to observing the "extreme universe," including high plasma galaxies and black holes. Its wide range X-ray imaging systems and X-ray spectroscopy system will help reassure Bulbul's team that their observations weren't simply an instrument malfunction. NASA plans to launch this latest satellite into space in 2015.

Interestingly, a public access paper published by a Netherlands team this week reports a similar finding - supporting Bulbul's claims.

The Bulbul study was published in The Astrophysical Journal on June 20.