Astronomers have identified an unexplained gamma ray glow in the outer regions of the Milky Way that may hint at dark matter particles. Using 15 years of data from NASA's Fermi Gamma-ray Space Telescope, researcher Tomonori Totani found a signal that fits predictions for weakly interacting massive particles, or WIMPs. Experts caution that more verification is needed before confirming the discovery.
Dark matter, which constitutes about 85 percent of the universe's mass, remains elusive despite decades of searches. Physicists hypothesize it could consist of WIMPs, particles that rarely interact with ordinary matter but might self-annihilate, releasing gamma rays.
For over a decade, scientists have debated whether excess gamma rays from the Milky Way's center indicate such annihilations, but results have been inconclusive. Now, Tomonori Totani at the University of Tokyo reports a potential signal from the galaxy's outer halo.
Totani analyzed 15 years of observations from the Fermi Gamma-ray Space Telescope. He modeled expected gamma ray emissions from known sources, including stars, cosmic rays, and large radiation bubbles above and below the galaxy. Subtracting these left an excess glow at around 20 gigaelectronvolts, matching the energy range predicted for WIMP annihilations.
"The signal is the most promising candidate radiation from dark matter known to date," Totani said. He described his initial skepticism: "Even though the research began with the aim of detecting dark matter signals, I thought it was like playing the lottery. So when I first spotted what seemed like a signal, I was sceptical. But when I took the time to check it meticulously and felt confident it was correct, I got goosebumps."
However, the finding requires further scrutiny. Francesca Calore at the French National Centre for Scientific Research noted that modeling all non-dark-matter gamma ray sources is challenging, and Totani's models need more stress-testing. Silvia Manconi at Sorbonne University pointed out the lack of similar signals from dwarf galaxies and called for advanced models. Anthony Brown at the University of Durham emphasized the need for data across wavelengths, like radio waves and neutrinos, to rule out other explanations.
While promising, the result is preliminary and demands additional observations to confirm.