An excess of gamma rays detected coming from a recently discovered dwarf galaxy named Reticulum 2, which is 98,000 light years from Earth, could provide researchers with clues about dark matter, which is the mysterious stuff that makes up most of the Universe.
The existence of theoretical particles known as WIMPS, or Weakly Interacting Massive Particles, is a leading theory on what comprises dark matter. The theory describes how, when these particles meet, they annihilate one another. This interaction leads to the release of high-energy gamma rays and is thus a potential signpost marking the spot where dark matter might be lurking.
However, lots of objects give off gamma rays such as pulsars and black holes and separating these sources from gamma rays that might have been produced from dark matter is a tricky task. In a bid to minimise any confusion and limit unwanted background noise, researchers have identified dwarf galaxies as potential objects in which to search for dark matter. Dwarf galaxies appear ideal as they are considered quiet systems that possess no known astrophysical gamma-ray sources. They are also thought to contain large amounts of dark matter, as studies have shown that their individual stars’ motions cannot be fully explained by their gravity of their visible matter alone. Because dark matter does not absorb, reflect or emit light, it is through its gravitational effect on visible matter that researchers infer its existence. Scientists have been looking for gamma rays from dark matter annihilation in dwarf galaxies for a number of years now, but without much success. The detection of gamma rays from Reticulum 2 by a team of physicists at Carnegie Mellon, Brown and Cambridge universities, suggests this may now be changing.
“Something in the direction of this dwarf galaxy is emitting gamma rays. There’s no conventional reason this galaxy should be giving off gamma rays, so it’s potentially a signal for dark matter”, says Alex Geringer–Sameth, a postdoctoral research associate at Carnegie Mellon University’s and the lead scientist behind the observations. The team are eager to point out that while these results are very exciting, further observations are required to rule out other hidden source that may be emitting the gamma rays instead.