The most energetic form of light (electromagnetic radiation) is gamma radiation. This form of radiation tends to be caused by certain nuclear reactions as well as the energetic processes that occur near black holes and neutron stars. It’s a good idea to avoid gamma rays as they can do a lot of damage to living tissue. Fortunately, the Earth’s atmosphere protects us from most of such radiation coming from space.
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There is quite a bit of gamma radiation in interstellar and intergalactic space. In the past few decades, a field of astronomy devoted to observing the source of gamma rays has been born and is flourishing. This new field is how certain cosmic sources of gamma rays have been definitively identified.
A new study, soon to be published in Physical Review Letters, presents the results of a survey of “background” gamma radiation and speculates what its source might be. The gamma ray background was identified by subtracting gamma rays from identified sources known to produce it. The resulting map showed a coincidence between regions in the universe that are gamma ray sources, and regions that are believed to have enough dark matter to cause image distortion of light sources behind them due to the warping of space. This coincidence raises the possibility that the dark matter is actually the source of this background gamma radiation.
After decades of speculation and hypotheses being proved wrong, it’s still anybody’s guess as to what dark matter is made of. We only know for sure that, in order to explain the observed behavior of stars in galaxies, 85 % of matter must be the dark stuff, which doesn’t interact with light, but which affects the motion of ordinary observable matter through its gravitational influence. If dark matter is emitting gamma rays, this suggests that either it is decaying, or undergoing some other process, wherein it is transforming into something else. This could provide a clue regarding what dark matter, thus far completely inscrutable, may actually be.
Don’t get too excited, though. This suggestion is only a little firmer than speculation. There are a number of assumptions that went into the work that could prove wrong, and eliminate this possibility. However, if it is true, we could be a little closer to understanding what this mysterious material consists of.
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