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article imageGamma rays from dwarf galaxy may provide proof of dark matter

By Stephen Morgan     Mar 11, 2015 in Science
A promising new discovery by physicists at Carnegie Mellon and Brown and Cambridge Universities in the US could provide a step towards finally identifying the elusive substance called dark matter.
Until now nobody has ever seen dark matter, yet it is thought to make up the majority of the matter in the universe. In fact, astronomers believe it holds the universe together and without it the universe couldn't exist. Unfortunately, the search for it has so far only revealed its possible gravitational effects.
Consequently, it remains one of the greatest unsolved mysteries in science. Astronomers have been hunting for conclusive evidence of its existence for decades and various theories and observations have yet to solve the puzzle.
But now, mysterious gamma rays emanating from a recently discovered dwarf galaxy called Reticulum 2, have scientists speculating that they may be seeing dark matter manifesting itself in the form of radiation for the first time.
The discovery of excess gamma rays coming from Reticulum 2 may be a breakthrough. Typically, a galaxy contains ten times more dark matter than visible matter. However, scientists believe that dwarf galaxies — which have far less visible matter than usual ones — contain even larger concentrations than normal galaxies.
The New York Times describes Reticulum 2 as "one of a rare breed known as dwarf galaxies, which can have fewer than a hundred stars and are only a billionth as luminous and a millionth as massive as the Milky Way."
An email from Dr. Geringer-Sameth, the leader of the study, is quoted in ZME Science as saying, “They are very quiet systems, just containing some old stars and a lot of dark matter. If you see any excess gamma rays coming from them, something intriguing is going on.”
Astronomy Now explains the process behind this:
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.
Moreover, what makes dwarf galaxies such a favorable place for finding dark matter is that, unlike normal galaxies, they don't contain other sources of gamma rays like black holes and pulsars. Therefore, these gamma rays must be coming from something else, and dark matter is a good candidate.
“Something in the direction of this dwarf galaxy is emitting gamma rays," Geringer–Sameth said. "There’s no conventional reason this galaxy should be giving off gamma rays, so it’s potentially a signal for dark matter.”
The research team used data from NASA’s Fermi Large Area Telescope. However, they cautioned that there was still a lot of work to do before their findings could be conclusively confirmed. The study was submitted to the journal, Physical Review Letters.
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