Researchers with the European Space Agency say they've detected a strange spike in X-rays coming from two cosmic locations -- the Andromeda Galaxy and the Perseus Cluster. The astronomers think the strange emissions could be the signal of dark matter. If confirmed, it would be first direct evidence of dark matter.

Astronomers are confident dark matter exists, but it remains purely hypothetical. Still without it, everything scientists know about the universe falls apart -- their calculations for and modeling of various celestial behaviors wouldn't make any sense.

It's estimated that as much as 80 percent of the universe is composed of dark matter -- exerting gravitational forces on its surroundings. Because dark matter neither emits nor absorbs light, it's nearly impossible to observe.

Now researchers at the École Polytechnique Fédérale de Lausanne (EFPL), in Switzerland, claim to have fielded a dark matter signal. The signal -- "a weak, atypical photon emission" -- can't be attributed to any known particle or matter.

"The signal's distribution within the galaxy corresponds exactly to what we were expecting with dark matter -- that is, concentrated and intense in the center of objects and weaker and diffuse on the edges," researcher Oleg Ruchayskiy, a astronomy professor at Leiden University, explained in a press release.

Scientists have offered an array of theories as to the type of particles that actually make up dark matter, including weakly interacting massive particles (WIMPs) and axions. But the most popular theory involves the hypothetical "sterile neutrino," a relative of the confirmed "ordinary" neutrino -- a weakly interacting elementary subatomic particle that is without an electric charge.

It's theorized that a decaying sterile neutrino might give off photons -- thus the odd X-ray emissions detected by ESA's XMM-Newton telescope.

"Confirmation of this discovery may lead to construction of new telescopes specially designed for studying the signals from dark matter particles," Ruchayskiy's research partner, Alexey Boyarsky, said. "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."

The duo's discovery was published online this week in Cornell's open access library arXiv.