AI research reinforces dark matter as a likely source of excess gamma rays at the center of the Milky Way
New scientific discoveries shake up the astrophysics scene by rekindling the possibility that dark matter, an enigmatic and invisible substance, is responsible for an excessive emission of gamma rays in the heart of the Milky Way. An international team of researchers, including scientists from the University of Vienna, used machine learning to re-examine crucial data, challenging previous conclusions that ruled out this hypothesis. The study, detailed in the academic journal “Physical Review Letters”, brings new life to the debate about the composition of our universe.
The mystery of excess gamma rays at the galactic center
For many years, astronomers have observed a spherical concentration of gamma rays, called GCE (Galactic Center Excess), in the central region of the Milky Way. The origin of this radiation has been the subject of intense debate, with two main theories in conflict. One suggests that GCE is the result of the annihilation of dark matter particles, while the other attributes the phenomenon to a myriad of compact celestial objects, such as millisecond pulsars. To date, statistical analysis has tended to favor the pulsar explanation.
Dark matter, which is estimated to be five to six times more abundant than ordinary matter in the universe, remains one of science’s biggest enigmas, given its undetectability through electromagnetic waves. Understanding their nature and interactions could revolutionize our view of the cosmos.
Machine learning uncovers patterns in gamma rays
The team of researchers, led by Florian List of the University of Vienna and Nick Rodd of Lawrence Berkeley National Laboratory, introduced an innovative approach to investigating the source of gamma rays. They argued that conventional methodologies did not fully exploit the energetic information of each individual photon.
- To overcome this limitation, scientists:
- They trained a machine learning model (neural network) using more than a million simulation data points.
- They simultaneously evaluated spatial and spectral information of gamma rays, including intensity distribution by wavelength.
This in-depth analysis revealed that if the GCE were truly caused by point sources, the center of the Milky Way would require more than 35,000 extremely faint sources. This number substantially exceeds previous estimates, which ranged from hundreds to thousands. According to Rodd, the radiation emitted by such a vast array of point sources would be practically indistinguishable from the scattering expected from the annihilation of dark matter. These findings led the team to reconsider the dark matter hypothesis, stating that “it is still too early to rule it out.”
Divergent studies reveal complexity of dark matter
While the research by List et al. reignites the GCE debate, a parallel study, published in 2025 by Professor Tomonori Totani of the University of Tokyo, offers a contrasting perspective. Using data from NASA’s Fermi satellite, Totani identified a halo-like emission component extending symmetrically from the center of the Milky Way, after excluding regions with a high density of celestial objects.
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- The gamma rays observed by Totani had an energy peak around 20 GeV (gigaelectronvolts), consistent with theoretical predictions for the annihilation of dark matter particles with approximately 500 GeV in mass. This finding, while also pointing to dark matter, highlights a crucial discrepancy:
- GCE emission peak (List et al.):Around 2-3 GeV.
- Halo emission peak (Totani):Around 20 GeV.
This order of magnitude difference in energy ranges, coupled with distinctions in assumed density distributions, suggests that GCE and halo radiation may have distinct origins. If both phenomena are indeed traces of dark matter, the implication is that their particles would have significantly different masses and interaction properties (annihilation cross section).
Next steps in elucidating cosmic secrets
Recent discoveries, both those that corroborate the dark matter hypothesis for the GCE and those that reveal the halo phenomenon with distinct characteristics, impose new “tensions” on scientific understanding. Theoretically, these tensions raise fundamental questions for astrophysics: is one of the phenomena of conventional astronomical origin and the other related to dark matter? Or would dark matter not be a single entity, but rather a set of particles with more complex and varied properties than previously imagined?
The accumulation of more observational data, combined with independent verification by different research teams, will be fundamental to unraveling these mysteries. As technology advances and analytical capabilities improve, the scientific community hopes to take decisive steps toward understanding the true nature of dark matter, one of the greatest challenges and secrets of the universe.
