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Billions of dollars have been spent running dozens of experiments for decades in the hope of finding elusive dark matter.

And now a detection may have been made in the form of a mysterious X-ray signal originating in the Perseus galaxy cluster 240 million light years away.

If confirmed, the discovery, made by a combination of Nasa's Chandra X-ray Observatory and Esa's XMM-Newton, could be the best evidence of dark matter yet.

A mysterious X-ray signal has been spotted in the Perseus Cluster (pictured) by two space observatories. The signal comes in the form of a spike of intensity in an emission from the galaxy (inset), and it could be a sign of 'sterile neutrinos' - a possible component of dark matter

Astronomers think dark matter constitutes 85 per cent of the matter in the universe, but does not emit or absorb light like 'normal' matter, such as protons, neutrons and electrons.

These are known to make up the familiar elements observed in planets, stars, and galaxies.

Because of this, scientists must use indirect methods to search for clues about dark matter.

The latest results from Chandra and XMM-Newton consist of an unidentified spike of X-ray intensity coming from the Perseus Cluster.

The researchers suggest this emission line could be a signature from the decay of a 'sterile neutrino'.

Sterile neutrinos are a hypothetical type of neutrino predicted to interact with normal matter only, via gravity.

Some scientists have proposed that sterile neutrinos may at least partially explain dark matter.

But while holding exciting potential, these results must be confirmed with additional data to rule out other explanations and determine whether it is plausible that dark matter has been observed.

'We know that the dark matter explanation is a long shot, but the pay-off would be huge if we're right,' said Esra Bulbul of the Harvard-Smithsonian Center for Astrophysics, who led the study.

'So we're going to keep testing this interpretation and see where it takes us.'

The detection was made jointly with Esa's XMM-Newton space telescope and Nasa's Chandra X-ray Observatory (pictured), both of which are telescopes that observe the distant reaches of the universe in X-ray wavelengths. The observation pushes the capabilities of the telescopes, meaning there is room for error

One source of uncertainty is that the detection of this signal is pushing the capabilities of the two observatories in terms of sensitivity - suggesting there may be room for error.

Also, there may be explanations other than sterile neutrinos if this signal is deemed to be real.

There are ways that normal matter in the cluster could have produced the signal, although the team's analysis suggested that all of these would involve unlikely changes to the understanding of physical conditions in the galaxy cluster.

And, the researchers add, even if the sterile neutrino interpretation is correct their detection does not necessarily imply that all of dark matter is composed of these particles.

The next step will be to combine these results with data from other observatories to see if the same signal can be found before it can truly be identified.