American scientists studied the spectrum of cosmic X-rays and found an emission line at an energy level of 3.5 kiloelectron-volts (keV). It indicates the existence of an unknown source of radiation. This was announced in a press release on Phys.org.
An emission line is an increase in the intensity of radiation in a certain region of the spectrum. Usually, the radiation intensity decreases with the frequency of the latter, but sometimes it becomes larger or, conversely, attenuates (in the latter case, we are talking about the absorption line). This is due to the transition of atoms, ions and molecules to other energy levels, as a result of which radiation is released or absorbed.
However, the nature of the 3.5 keV emission line has not yet been established, since it does not correspond to any of the known photon emissions, that is, the emission of light by an excited atom. The radiation that comes from different directions has been detected by several space telescopes - NuSTAR, XMM-Newton, Chandra and Suzaku.
Scientists believe that it is the result of the decay of sterile neutrinos - hypothetical particles that are one of the "candidates" for the role of dark matter. If the data are confirmed (the results obtained do not exclude a statistical error), then this may mean that the Milky Way is surrounded by a bubble of dark matter.