X-ray signals reaching Earth from a giant group of galaxies around 250 million light years way could be evidence of the so-far mysterious constituent of the universe known as dark matter, astronomers say.
Scientists believe dark matter may make up 85 percent of all matter existing in the universe, although they suspect it cannot be observed directly because it neither emits nor absorbs light.
However, its gravitational effect on stars and galaxies throughout the universe may be a detectable sign of its presence, they say.
One such sign could be the detected X-ray signal, researchers say, possibly the result of the decay one candidate component of dark matter, so-called sterile neutrinos.
Both the Chandra X-ray observatory of NASA and the European Space Agency's XMM-Newton instrument in space have picked up the signal from a giant collection of more than 70 separate galaxy clusters.
"We know that the dark matter explanation is a long shot, but the pay-off would be huge if we're right," study leader Esra Bulbul of the Harvard-Smithsonian Center for Astrophysics says. "So we're going to keep testing this interpretation and see where it takes us."
The researchers say they're staying cautious about what they've detected, explaining that there are possibilities involving normal, not dark, matter, but add they would require "unlikely changes to our understanding of physical conditions in the galaxy cluster or the details of the atomic physics of extremely hot gases."
They hope to see if similar signals can be detected being emitted from other massive galaxy clusters.
"Our next step is to combine data from Chandra and JAXA's [the Japanese Aerospace Exploration Agency's] Suzaku mission for a large number of galaxy clusters to see if we find the same X-ray signal," said study co-author Adam Foster, also at the Harvard-Smithsonian center.
A collection of mysterious particles have been put forward as candidates for being a dark matter component, including weakly interacting massive particles, or WIMPs, axions or sterile neutrons.
Sterile neutrons are a hypothetical variety of neutrinos that could emit X-rays as it decays, astrophysicists say.
"We have a lot of work to do before we can claim, with any confidence, that we've found sterile neutrinos," study co-author Maxim Markevitch at NASA's Goddard Space Flight Center in Greenbelt, Md., said. "But just the possibility of finding them has us very excited."
The planned launch of a new kind of X-ray detector dubbed Astro-H could probe the signal with more precision than current instruments, the researchers said.
The researchers have published a report of their findings in The Astrophysical Journal.
