Few things in the universe are as puzzling as dark matter — the invisible substance thought to make up most of the matter in galaxies. Scientists infer its existence from gravitational effects because it neither emits nor absorbs light, but detecting it directly has proved elusive for nearly a century.
A Japanese astrophysicist, Tomonori Totani of the University of Tokyo, says he may have found the first direct evidence: extended gamma-ray emissions forming a halo-like pattern near the center of the Milky Way. Totani’s analysis of data from NASA’s Fermi Gamma-ray Space Telescope, which detects high-energy gamma rays, revealed intense emissions spread over a large, roughly spherical region rather than concentrated at a point. He described the signal as having a unique energy spectrum and spherical symmetry not seen in known astrophysical sources.
Dark matter was first proposed in the 1930s when Fritz Zwicky observed that galaxies in the Coma Cluster moved as if extra, unseen mass were present. Today, dark matter is estimated to make up about 27% of the universe while ordinary matter accounts for roughly 5%. One popular theoretical candidate is a class of hypothetical particles called WIMPs (weakly interacting massive particles). If WIMPs collide and annihilate, they could produce gamma rays — a possible signature Totani sought.
The gamma-ray emissions Totani reports are about one-millionth the brightness of the entire Milky Way and appear as a diffuse halo across a wide swath of sky. To avoid contamination from the plane of the galaxy, his analysis excluded that region, focusing on the spherical component extending outward from the galactic center. Totani said no known cosmic-ray or stellar process he is aware of produces both the observed spherical symmetry and the particular energy spectrum of the signal.
Totani’s findings, published in the Journal of Cosmology and Astroparticle Physics, are striking but have met with skepticism from other researchers. David Kaplan of Johns Hopkins University cautioned that we do not yet know all the sources of gamma rays in the universe; fast-spinning neutron stars, black holes that emit jets, or other energetic processes could produce similar emissions. Eric Charles of SLAC at Stanford noted that the complexity of gamma-ray production makes interpretation difficult. Dillon Brout of Boston University emphasized that the galactic center is among the hardest regions to model, so extraordinary claims require extraordinary evidence.
Kaplan called the work interesting and worth following but stopped short of endorsement, saying further analyses will be needed to confirm whether this is truly a dark matter signal. Totani himself urged independent replication and further study, acknowledging the potential impact if the result holds.
If confirmed, a direct detection of dark matter through gamma-ray signatures would transform our understanding of the universe — explaining how galaxies formed and influencing models of cosmic evolution. For now, Totani’s claim remains a tantalizing possibility that the community will scrutinize carefully.
