Astronomers using NASA’s Chandra X-ray Observatory to explore the Perseus Cluster, a swarm of galaxies approximately 250 million light years from Earth, have observed the spectral line that appears not to come from any known type of matter. The signal is not explained by known physics.
The Perseus Cluster is a collection of galaxies and one of the most massive known objects in the Universe, immersed in an enormous ‘atmosphere’ of superheated plasma. It is approximately 768 000 light years across. "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."
"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. It took a long time to convince myself that this line is neither a detector artifact, nor a known atomic line," Bulbul said. "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."