Did European scientists find dark-matter signal buried in X-rays?

Dark matter has evaded direct detection for decades -- but scientists say they may have a found a sign

Scientists say they may have discovered a possible dark matter signal coded in the X-rays emanating from two bright objects in the sky.

The findings, set to be published next week in Physical Review Letters, could offer tangible evidence for the existence of dark matter -- and help researchers build new tools to search for and study this mysterious stuff.

When it comes to matter in the universe, dark matter is like a backroom political power broker: You never see it, but behind the scenes, it’s been throwing its weight around. The effects of its gravitational influence can be seen in the large-scale structures of the cosmos. Dark matter makes up about 84.5% of the matter in the universe while all the stuff we actually see -- stars, galaxies, planets, ourselves -- makes up the remaining 15.5%.* The enormous galaxies and clusters of galaxies that populate the universe are bantamweights compared to the massive, unseen dark matter ‘halos’ that anchor them.

Dark matter’s formidable gravitational influence is the only way it can be detected, because it’s invisible -- it does not interact with light. Physicists have no idea what it’s made of, although they’ve looked for it using a number of different methods, including building detectors in underground former gold mines and sending satellites into space.

But now, a team led by researchers at Leiden University in the Netherlands and the École Polytechnique Fédérale de Lausanne in Switzerland say they’ve discovered a signal that could be a sign of dark matter.

The scientists looked at X-ray emissions coming from the Andromeda galaxy and the Perseus galaxy cluster, collected by the European Space Agency’s XMM-Newton space telescope. After accounting for all the light particles (called photons) emanating from known sources in the Andromeda galaxy, they were left with a strange set of photons that had no known source. The found the same light signature emanating from the Perseus cluster. And when they turned their attention to the Milky Way, they found signs of this signal in our home galaxy, as well.

“It is consistent with the behavior of a line originating from the decay of dark matter particles,” the authors wrote in a pre-print of the study.

This weird light signal, they think, could be coming from the destruction of a hypothetical particle called a sterile neutrino (which, if it exists, might help explain dark matter). But it's going to take a lot of follow-up study to determine whether this signal is a scientific breakthrough or an anomalous blip.

“Future detections or non-detections of this line in multiple astrophysical targets may help to reveal its nature,” the study authors wrote.

Japan’s upcoming Astro-H mission, they said, might allow them to do just that.

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*This doesn’t include dark energy, a powerful phenomenon that’s causing the entire universe to expand but whose nature has yet to be explained. Taking normal matter, dark matter and dark energy into account, dark energy takes up a whopping 68.3% of the universe’s mass-energy density, while dark matter takes up just 26.8% and normal matter takes up a tiny 4.9%.

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