Detecting Dark Matter’s Violent End
Dark matter is a mysterious substance that is thought to make up 23 percent of matter in the universe, and it lives up to its name—it doesn’t emit any electromagnetic radiation, so it’s very difficult to detect, and we can only see it through its gravitational influence on visible matter, radiation and the structure of the universe. However, one of the leading candidates for the dark matter particle is a WIMP (weakly interacting massive particle), and when a WIMP and its anti-particle collide, they annihilate and produce a shower of radiation—including gamma rays. NASA’s Fermi Gamma-ray Telescope has been searching for excess gamma rays near the heart of our galaxy where it’s thought dark matter will be concentrated. In 2010, physicist Dan Hooper at Fermilab, Illinois, reported possibly finding dark matter particles with a mass of 10 gigaelectron volts (GeV). (Masses of elementary particles are often expressed in terms of electron volts, which are both units of energy and units of mass, thanks to energy-mass equivalence.) This report has met controversy, partly because it’s a smaller mass than previous predictions, and partly because the data could easily be skewed by the violent galactic region that contains newborn stars, hot gas, supernovae and a black hole that could all be emitting gamma rays. But in follow up studies, Hooper and his colleagues have shown that their signal is significantly far enough away from the galactic core to make interference unlikely, and at the same time, particle detectors here on earth have shown hints of 10 GeV dark matter. Researchers are now looking further to confirm these signals. Dwarf galaxies (pictured above) are handy places to look, because they’re much calmer than our turbulent galaxy’s heart and so it should be much easier to spot dark matter annihilation. Finding 10 GeV signals elsewhere could transform Hooper’s curious discovery into a plausible theory—but such dwarf galaxies are faint, so it may be several more years before the results are clear.
Image Credit: NASA/DOE/Fermi-LAT Collaboration