An international research consortium, led by the University of Oxford, achieved a significant milestone in experimental astrophysics by successfully generating plasma 'fireballs' inside CERN's Super Proton Synchrotron (SPS) accelerator near Geneva. This development, detailed in the November 3, 2025, issue of the Proceedings of the National Academy of Sciences (PNAS), directly addresses a long-standing cosmic mystery: the apparent disappearance of low-energy gamma rays.
The investigation centers on energetic emissions from blazars, which launch powerful jets of radiation peaking at several tera-electron volts (TeV). Current theory posits that these TeV rays should interact with ambient light in the intergalactic medium, creating electron-positron pairs that subsequently generate secondary, lower-energy gamma rays in the giga-electron volt (GeV) range. The persistent failure of sensitive instruments, such as the Fermi space telescope, to detect these predicted GeV signals has created a significant observational discrepancy.
To test this cosmic accounting issue, the team utilized CERN's HiRadMat facility. They employed the SPS beam to create a torrent of electron-positron pairs, channeling this energy through a meter-long plasma. This controlled laboratory setup served as a terrestrial analogue for the cascade process believed to occur over light-years in space. The initial simulation was designed to determine if internal beam instability could account for the missing energy.
The laboratory findings indicated that the observed instability within the generated beam was insufficient to explain the magnitude of the missing GeV radiation. This result strongly suggests that a more pervasive, external mechanism is responsible for the phenomenon. The leading hypothesis now focuses on the influence of ancient, large-scale magnetic fields permeating the intergalactic void, which may be deflecting the predicted particles away from direct observation.
This controlled recreation of a high-energy cosmic event marks a major advance in the capacity to test astrophysical models previously confined to theory. The precision offered by the SPS and HiRadMat apparatus provides a unique means to examine fundamental interactions governing the universe's highest-energy phenomena. Related research on cosmic ray propagation reinforces this conclusion, as intergalactic magnetic fields are known to steer charged particles over vast distances, shifting the scientific focus toward mapping these unseen cosmic structures.