From: Roger Greenway, ENN
Published July 26, 2014 07:54 AM

Astro Physics has a new mystery

Astro Physicists love to look for reasons current theories are correct. When data are obtained that do not fit a current theory, the race is on to come up with an explanation!

The Universe is a big place, full of unknowns. Astronomers using NASA's Chandra X-ray Observatory have just catalogued a new one.

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"I couldn't believe my eyes," says Esra Bulbul of the Harvard Center for Astrophysics. "What we found, at first glance, could not be explained by known physics."

Together with a team of more than a half-dozen colleagues, Bulbul has been using Chandra to explore the Perseus Cluster, a swarm of galaxies approximately 250 million light years from Earth. Imagine a cloud of gas in which each atom is a whole galaxy—that's a bit what the Perseus cluster is like. It is one of the most massive known objects in the Universe.

The cluster itself is immersed in an enormous 'atmosphere' of superheated plasma—and it is there that the mystery resides.

Bulbul explains: "The cluster's atmosphere is full of ions such as Fe XXV, Si XIV, and S XV. Each one produces a 'bump' or 'line' in the x-ray spectrum, which we can map using Chandra. These spectral lines are at well-known x-ray energies."

Yet, in 2012 when Bulbul added together 17 day's worth of Chandra data, a new line popped up where no line should be.

"A line appeared at 3.56 keV (kilo-electron volts) which does not correspond to any known atomic transition," she says. "It was a great surprise."

At first, Bulbul herself did not believe it. "It took a long time to convince myself that this line is neither a detector artifact, nor a known atomic line," she says. "I have done very careful checks. I have re-analyzed the data; split the data set into different sub groups; and checked the data from four other detectors on board two different observatories. None of these efforts made the line disappear."

In short, it appears to be real. The reality of the line was further confirmed when Bulbul's team found the same spectral signature in X-ray emissions from 73 other galaxy clusters. Those data were gathered by Europe's XMM-Newton, a completely independent X-ray telescope.

Image shows the spectral line. It appears not to come from any known type of matter, which shifts suspicion to the unknown: dark matter. Credit: NASA

Read more at Research.gov.

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