Scientists searching for elusive and invisible dark matter thought to make up most of the mass in the universe say they may have detected a signal of its existence buried in X-ray signals from two bright objects in the cosmos.
Although dark matter can be inferred from gravitational effects observed affecting the universe's visible matter, tangible evidence has been scarce.
Now, a group of French and Dutch researchers says they believe they've detected a signal given off by decaying particles of dark matter.
The evidence is buried in X-rays emitted by two celestial objects, they say; the Perseus cluster of galaxies situated around 250 million light years distant from Earth, and our nearby "sister" Andromeda galaxy, just 2.5 million light years away.
Analysis of data gathered by a European Space Agency X-ray space telescope has uncovered a strange "anomaly" that cannot have been emitted by any known particle or atom, the researchers report in the journal Physical Review Letters.
After eliminating observations of light particles, or photons, from all known sources in the Perseus Cluster and Andromeda, they were left with a mysterious kind of photon with no known source.
A hypothetical particle dubbed a sterile neutrino, which would be just 1/100th the size of an electron -- and which, if it exists, could help explain dark matter -- could be emitting the strange photons as it decays, they said.
"This tiny (several hundred extra photons) excess has been interpreted as originating from very rare decays of dark matter particles," says lead researcher Alexey Boyarsky, a professor of physics and astronomy at Leiden University in the Netherlands.
"Although the signal is very weak, it has passed several 'sanity checks' that one expects from a decaying dark matter signal."
Whether this mysterious anomaly in the X-ray data represents a breakthrough in the search for dark matter or remains an anomaly -- just a statistical "blip" -- will take significant follow-up studies to confirm, the researchers at Leiden University and the École Polytechnique Fédérale de Lausanne in Switzerland noted.
"Future detections or non-detections of this line in multiple astrophysical targets may help to reveal its nature," the study authors wrote.
The detection of the mysterious photon in X-ray signals could spur the development of new technologies to further the hunt for dark matter, Boyarsky says.
"Confirmation of this discovery may lead to construction of new telescopes specially designed for studying the signals from dark matter particles," he says. "We will know where to look in order to trace dark structures in space and will be able to reconstruct how the Universe has formed."
