Revealing the Galaxy’s Dark Side

Physicist Neal Weiner of NYU says that just because the galactic center "is a tricky place to study, to be sure, that doesn't mean one can brush a signal like this aside. This feature has a dramatic cutoff in its spectrum and a rapid falloff as a function of radius. I don't know of a population of astrophysical objects that has that distribution."

Nonetheless, Weiner cautions, "we need to be careful before making strong claims" that the signal comes from dark matter.

Ritz notes that he and his Fermi collaborators—Hooper and Goodenough are not on the Fermi team—are still hard at work trying to better estimate uncertainties in the distribution and identity of ordinary gamma-ray-emitting sources before weighing in on the dark matter issue.

"If you want to claim new physics, the burden of proof is very high; you have to exclude actively all the standard astrophysical interpretations," says Ritz.

Complicating the task, says Fermi researcher Simona Murgia of the SLAC National Accelerator Laboratory in Menlo Park, Calif., the gamma rays that Fermi observes "are produced not only in the galactic center but also in the line of sight between us and the galactic center and beyond."

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