Mysterious feature seen in X-ray spectrum may arise from dark matter annihilation
Credit: N. Cappelluti et al.; NASA

Light from Dark Matter?

It's back - a controversial signal from deep space that may resolve the 80-year old mystery of dark matter, the stuff that provides nearly all of the gravity that holds the Universe together. Just to recap, a few years ago astronomers seemed to have found a strange emission line in the X-ray spectra of 70 galaxy clusters, appearing at an energy of 3.5 kilo-electron volts (keV), an energy where no known X-ray feature should exist. An exciting suggestion was that this emission line is really a cosmic signal produced by the decay of dark matter. If so, this would identify subatomic particles called sterile neutrinos (a proposed cousin of the 3 known types of neutrinos) as the source of dark matter. However, this emission line is weak and thus difficult to detect, and could be nothing more than a previously unidentified instrumental artifact. Other observations using the IceCube Antarctic neutrino observatory failed to find evidence of sterile neutrinos. A high-resolution X-ray spectrum of the Perseus cluster of galaxies obtained by the Hitomi X-ray observatory (just before its tragic, untimely demise) did not find any evidence of this emission line either, casting further doubt. But now a new study of a 10 million second deep field observations with the Chandra X-ray observatory has once again found evidence of the mysterious 3.5 keV X-ray feature. The Chandra X-ray spectra are shown above (along with models of the data shown by the solid lines). The feature is the bump shown within the shaded area in the upper plot. Astronomers believe this line is not produced by any known instrumental effect, and the strength of the line is consistent with the previous X-ray analysis. Future X-ray observatories like the Athena X-ray Observatory may help finally resolve this controversy.
Published: February 13, 2017

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Page Author: Dr. Michael F. Corcoran
Last modified Monday, 13-Feb-2017 08:24:54 EST