Despite the fact that it is believed to make up around eighty per cent of the matter in the universe, so-called "dark matter" remains an enigma to scientists. It is totally invisible as it neither absorbs or emits light, and its presence has so far been determined only via its gravitational interaction with visible matter.

But now astronomers believe that sensors on the International Space Station (ISS) may have finally detected its unique signal; in a new study that examined data collated from the European Space Agency’s XMM-Newton spacecraft, a team of researchers noticed an unusual X-ray signal being emitted from the Andromeda galaxy and the Perseus galaxy cluster.The mysterious signal cannot be linked to any known particle or atom, leading scientists to assume that it must have been produced by dark 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," said study co-author Oleg Ruchayskiy, of the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland, said in a statement.

"With the goal of verifying our findings, we then looked at data from our own galaxy, the Milky Way, and made the same observations," added lead author Alexey Boyarsky, of EPFL and Leiden University in the Netherlands.

It is not known what the constituents of dark matter are, but various peculiar particles have been suggested, such as weakly interacting massive particles (WIMPs), axions and sterile neutrinos. Sterile neutrinos are the hypothetical cousins of "ordinary" neutrinos (confirmed particles that resemble electrons but lack an electrical charge), and when sterile neutrinos decay that X-rays are believed to be formed. If these odd particles are constituents of dark matter, this could explain the mysterious signals detected by the ISS.

The results of the study are to be published in the journal Physical Review Letters, and it is hoped that the findings could pave the way for a whole new field of astronomy that could finally unravel the mystery of dark matter:

"Confirmation of this discovery may lead to construction of new telescopes specially designed for studying the signals from dark matter particles," 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."

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