Dark matter is known to make up roughly 85% of all mass in the universe, as evidenced by the way galaxies spin and how galaxy clusters are held together under gravity. Yet despite decades of searching, physicists have never managed to detect the elusive substance directly.
In new research published in Physical Review Letters, a team led by Yi-Zhong Fan at the Chinese Academy of Sciences claims to have spotted a strong gamma-ray signal coming from a group of galaxy clusters, which could be among the most compelling evidence yet for a leading dark matter candidate known as WIMPs.
Elusive particles
WIMPs, or weakly interacting massive particles, are hypothetical particles that barely interact with normal matter or light but would still exert a gravitational pull. For decades, physicists have favored WIMPs because of their mathematical convenience: Particles with roughly the right mass and interaction strength would naturally exist in about the right abundance to account for all that missing mass.
WIMP collisions and annihilations are predicted to produce particles across a broad energy spectrum that would be nearly impossible to distinguish from ordinary cosmic noise. In contrast, a clean, sharp energy spike would be far more difficult to explain using existing physics, making it a far more convincing signature of dark matter.
Matching signal
In their study, Fan’s team discovered a signal that closely matched these criteria. After searching through more than 15 years of data from the Fermi Gamma-ray Space Telescope and examining signals from 13 nearby massive galaxy clusters, they picked out a narrow gamma-ray line at an energy of around 43 billion electron volts. The signal showed up most strongly in three clusters (Virgo, Fornax and Ophiuchus) that are expected to hold the densest concentrations of dark matter.
According to the team’s calculations, this kind of sharp spike is difficult to produce through any known astrophysical process but is precisely the kind of signal WIMP annihilation would be expected to produce. They also checked the center of our own galaxy, where a similar signal caused by telescope error was famously mistaken for dark matter a decade ago. This time, they found no equivalent glitch, lowering the likelihood of a simple instrumental mistake.
Guide for future observations
Despite this promising evidence, Fan’s team is still cautious. Since the signal’s strength has fluctuated over the years, dipping around 2016 before climbing again, the researchers stopped short of calling it a confirmed detection. Rather, they viewed it as a strong enough hint to warrant a closer look.
If the striking signal really was produced by WIMPs, the researchers now hope it could be confirmed by an as-yet-theoretical Very Large Area Gamma-ray Space Telescope, first proposed by Fan’s team. In turn, this observation could potentially turn a promising signal into the first real look at the elusive particles that make up most of our universe’s mass.
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Publication details
Yi-Zhong Fan et al, Evidence for a ∼43 GeV 𝛾-ray Line Signal in a Stacking Analysis of the Virgo, Fornax, and Ophiuchus Galaxy Clusters, Physical Review Letters (2026). DOI: 10.1103/lq5r-sjp7. On arXiv: arxiv.org/html/2407.11737
Key concepts
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Gamma-ray signal could be long awaited evidence for WIMPs (2026, August 25)
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