A newly discovered dwarf galaxy orbiting our own Milky Way has offered up a surprise — it appears to be radiating gamma rays, according to an analysis by physicists at Carnegie Mellon, Brown, and Cambridge universities. The exact source of this high-energy light is uncertain at this point, but it just might be a signal of dark matter lurking at the galaxy’s center. Credit: NASA/DOE/Fermi-LAT Collaboration/Geringer-Sameth & Walker/Carnegie Mellon University/Koushiappas/Brown University
A newly discovered dwarf galaxy orbiting our own Milky Way has offered up a surprise – it appears to be radiating gamma rays, according to an analysis by physicists. The exact source of this high-energy light is uncertain at this point, but it just might be a signal of dark matter lurking at the galaxy’s center.
The galaxy, named Reticulum 2, was discovered earlier this year in the data of the Dark Energy Survey, an experiment that maps the southern sky to understand the accelerated expansion of the universe. At approximately 98,000 light-years from Earth, Reticulum 2 is one of the nearest dwarf galaxies yet detected. Using publicly available data from NASA’s Fermi Gamma-ray Space Telescope, CMU’s Geringer-Sameth and Matthew Walker and Brown’s Savvas Koushiappas have shown gamma rays coming from the direction of the galaxy in excess of what would be expected from normal background.
“In the search for dark matter, gamma rays from a dwarf galaxy have long been considered a very strong signature,” said Koushiappas “It seems like we may now be detecting such a thing for the first time.”
A leading theory suggests that dark matter particles are WIMPs — Weakly Interacting Massive Particles. When pairs of WIMPs meet, they annihilate one another, giving off high-energy gamma rays. If that’s true, then there should be a lot of gamma rays emanating from places where WIMPs are thought to be plentiful, like the dense centers of galaxies. The trouble is, the high-energy rays also originate from many other sources, including black holes and pulsars, which makes it difficult to untangle a dark matter signal from the background noise.
That’s why dwarf galaxies are important in the hunt for the dark matter particle. Dwarfs are thought to lack other gamma-ray-producing sources, so a gamma ray flux from a dwarf galaxy would make a very strong case for dark matter.
Further study of this dwarf galaxy’s attributes could reveal hidden sources that may be emitting gamma rays, but the researchers are cautiously optimistic.
“The fact that there are gamma rays and also a clump of dark matter in the same direction makes it quite interesting,” Walker said. https://news.brown.edu/articles/2015/08/gammarays
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