A University of Tokyo researcher has identified a halo of high-energy gamma rays from NASA's Fermi Gamma-ray Space Telescope that matches predictions for dark matter particle annihilation. This finding, based on data from the Milky Way's center, could represent the first direct glimpse of the elusive substance proposed nearly a century ago. Professor Tomonori Totani's analysis suggests a breakthrough, though independent verification is needed.
In the 1930s, Swiss astronomer Fritz Zwicky proposed dark matter to explain why galaxies move faster than their visible mass would allow, providing the necessary gravitational pull to hold them together. For decades, scientists have inferred its existence through indirect effects, as dark matter particles do not interact with light or electromagnetic forces.
Many theories point to weakly interacting massive particles, or WIMPs, as the building blocks of dark matter. These particles, heavier than protons, are expected to annihilate upon collision, producing gamma rays among other particles. Researchers have long targeted dense dark matter regions, like the Milky Way's core, for such signals using space telescopes.
Professor Tomonori Totani of the University of Tokyo analyzed recent data from NASA's Fermi Gamma-ray Space Telescope and detected gamma rays at 20 gigaelectronvolts extending in a halo-like structure toward the galaxy's center. "We detected gamma rays with a photon energy of 20 gigaelectronvolts... extending in a halolike structure toward the center of the Milky Way galaxy. The gamma-ray emission component closely matches the shape expected from the dark matter halo," Totani stated.
The energy spectrum and intensity align with models for WIMPs around 500 times a proton's mass, and the pattern does not easily match known astrophysical sources. "If this is correct, to the extent of my knowledge, it would mark the first time humanity has 'seen' dark matter. And it turns out that dark matter is a new particle not included in the current standard model of particle physics. This signifies a major development in astronomy and physics," Totani added.
Published in the Journal of Cosmology and Astroparticle Physics in 2025, the study calls for confirmation from other teams. Future observations of dwarf galaxies could strengthen the evidence if similar signals appear. The work was funded by JSPS/MEXT KAKENHI Grant Number 18K03692.