For almost a century, dark matter has been inferred only from its gravitational pull. Tomonori Totani of the University of Tokyo has reported a candidate for something far more direct: analysing data from NASA's Fermi Gamma-ray Space Telescope, he identified gamma rays with energies of 20 gigaelectronvolts extending in a halo-like structure towards the centre of the Milky Way, just where dark matter is expected to be densest.
The measured energy spectrum matches what theorists predict from the annihilation of weakly interacting massive particles, or WIMPs, with masses around 500 times that of the proton. WIMPs have been the leading dark matter candidate for decades, yet direct-detection experiments deep underground have so far returned nothing, making an astrophysical signature of annihilation an enticing alternative route.
The analysis, published in the Journal of Cosmology and Astroparticle Physics, is explicitly provisional. Totani himself stresses that the result must be verified through independent analysis, and other astrophysical processes could yet explain the emission. But if the halo survives scrutiny, it would mark the first observation of dark matter announcing itself through anything other than gravity.