Gamma-Ray Hints of Dark Matter Seen at Galaxy’s Center

Astronomers have perhaps their best lead to date about the nature of dark matter, the strange and invisible stuff that dominates the material universe.

The center of our Milky Way galaxy generates more high-energy gamma rays than can be explained by conventional sources such as supernova remnants and fast-spinning, super-dense neutron stars known as pulsars, a new study suggests. The "excess" may be produced by the annihilation of colliding dark matter particles. This NASA video explains the tantalizing dark matter find.

"This is a very exciting signal, and while the case is not yet closed, in the future we might well look back and say this was where we saw dark matter annihilation for the first time," co-author Tracy Slatyer, a theoretical physicist at the Massachusetts Institute of Technology in Cambridge, said in a statement. [The Hunt for Dark Matter: Images and Photos]

Image: Gamma-ray map
At left is a map of gamma rays with energies between 1 and 3.16 GeV detected in the galactic center by the Fermi Gamma-ray Space Telescope's Large Area Telescope. Red indicates the greatest number. Prominent pulsars are labeled. Removing all known gamma-ray sources (right) reveals the excess emission that may arise from dark matter annihilations. T. Linden / Univ. of Chicago

Dark matter— which is thought to make up more than 80 percent of the matter in the universe — is so named because it apparently neither absorbs nor emits light, making it impossible to observe directly with telescopes. But its gravity does affect the "normal" stuff we can see and touch, providing one way to hunt dark matter down.

Gamma rays — the most energetic light in the universe — also provide another potential detection method.

Many scientists think dark matter is primarily composed of weakly interacting massive particles, or WIMPs. Theory suggests that some types of WIMPs annihilate when they collide with each other, while others generate a fast-decaying secondary particle when they interact. In either case, the idea goes, gamma rays are produced.

In the new study, researchers used data from NASA's Fermi Gamma-ray Space Telescope to make maps of the Milky Way's center in gamma-ray light. The maps reveal an "excess" of gamma-ray emissions extending outward at least 5,000 light-years from the Milky Way's core, researchers said.

They said the excess can be explained by annihilations of dark matter particles with a mass between 31 and 40 billion electron volts.

The new study has been submitted to the journal Physical Review D.

— Mike Wall,

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