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DOE Pulse
  • Number 411  |
  • April 14, 2014

Scientists find signal that may come from dark matter

The map at left shows gamma rays detected in the galactic center. Removing all known gamma-ray sources, the map at right reveals excess emission that may arise from dark matter annihilations. Credit: T. Linden, Univ. of Chicago

The map at left shows gamma rays detected
in the galactic center. Removing all known
gamma-ray sources, the map at right reveals
excess emission that may arise from dark
matter annihilations. Credit: T. Linden, Univ.
of Chicago

Since early in the mission of the Fermi Gamma-ray Space Telescope, a number of scientists have noticed a fairly bright spot of gamma-ray light coming from the center of our galaxy, the Milky Way.

Using publicly available data from the telescope, a team of scientists at DOE’s Fermilab, the Harvard-Smithsonian Center for Astrophysics, the Massachusetts Institute of Technology and the University of Chicago now confirmed that the spectrum and spatial shape of the gamma-ray signal seems to match that predicted to come from annihilating dark-matter particles. The team developed maps showing that the galactic center produces more high-energy gamma rays than can be explained by known sources and that this excess emission is consistent with some forms of dark matter.

In many theories of dark matter, when pairs of dark-matter particles interact, they can annihilate each other, producing other kinds of energetic particles in their place. Given the large densities of dark matter that must be present around our galactic center, dark-matter particles are expected to annihilate there at a high rate, producing large fluxes of energetic gamma rays that can be detected by gamma-ray telescopes.

In their analysis, submitted to the journal Physical Review D for publication, the team of scientists—including Fermilab’s Dan Hooper as the leading author—found that the signal from the galactic center looked, in every respect the team could measure, like the signal one would expect from the annihilation of dark-matter particles.

The shape of the observed gamma-ray spectrum was in excellent agreement with what they expected from dark matter particles with a mass of about 35 GeV/c2. The spatial distribution of the photons also looked very much like what they calculate based on numerical simulations. And the overall brightness of the gamma-ray signal implied a dark matter annihilation cross section (times relative velocity) of about 2x10-26 cm3/s, which is almost exactly the value predicted for a generic dark matter species produced in the big bang.

“This gamma-ray signal does look remarkably like annihilating dark matter,” Hooper said. “If so, it would represent the first detection of dark matter particles. It is an exciting time to be hunting for dark matter.”

[Andre Salles, 630.840.3351,
media@fnal.gov]