New simulations suggest that past collisions reshaped the Milky Way's dark matter core, potentially explaining a mysterious gamma-ray excess long attributed to pulsars. Led by researchers from the Leibniz Institute for Astrophysics Potsdam, the study revives dark matter as a key suspect in this astronomical puzzle. The findings, published in Physical Review Letters, highlight how the galaxy's chaotic history could match observations from NASA's Fermi telescope.
For over a decade, astronomers have puzzled over the Galactic Center Excess, an unexpected surge of gamma rays emanating from the Milky Way's heart, first detected by NASA's Fermi Gamma-ray Space Telescope. Initial theories pointed to dark matter particles annihilating each other to produce the radiation, but the gamma-ray pattern did not align with expected dark matter distributions, leading many to propose millisecond pulsars—fast-spinning neutron stars—as the source.
A new study challenges this shift by incorporating the Milky Way's turbulent early history. Using the Hestia simulations, which model galaxy formation in realistic cosmic environments, researchers traced how ancient mergers and collisions distorted the dark matter core into a nonspherical structure. This configuration naturally reproduces the observed gamma-ray spread without requiring numerous pulsars.
The research, led by Dr. Moorits Muru with Dr. Noam Libeskind and Dr. Stefan Gottlöber from the Leibniz Institute for Astrophysics Potsdam (AIP), alongside Professor Yehuda Hoffman from the Hebrew University of Jerusalem's Racah Institute of Physics and Professor Joseph Silk from Oxford University, appears in Physical Review Letters (2025; 135 (16)). "The Milky Way's history of collisions and growth leaves clear fingerprints on how dark matter is arranged at its core," the researchers explained. "When we account for that, the gamma-ray signal looks a lot more like something dark matter could explain."
While the study does not resolve the debate, it reestablishes dark matter as a viable explanation. Future observations from the Cherenkov Telescope Array could test these ideas by detecting higher-energy gamma rays, potentially confirming dark matter's role or revealing new insights into the galaxy.