CERN Experiment Strongly Supports Pervasive Intergalactic Magnetic Field as Solution to Missing Gamma Rays

An international team of researchers successfully recreated the extreme conditions of energetic cosmic jets in a laboratory setting, marking a significant advance in experimental astrophysics. Using the Super Proton Synchrotron (SPS) accelerator at CERN in Geneva, scientists generated plasma 'fireballs' to investigate a long-standing cosmic mystery: the unaccounted-for disappearance of high-energy gamma rays traveling across intergalactic space. This pivotal research, detailed in the Proceedings of the National Academy of Sciences (PNAS) on November 3, 2025, bridges theoretical cosmology with tangible terrestrial experimentation.

The investigation focused on blazars, which are galaxies featuring supermassive black holes that eject powerful beams of radiation and particles toward Earth at near-light speeds. These jets emit intense teraelectronvolt (TeV) gamma rays. As these rays travel through space, they are expected to interact with background light, creating electron–positron pairs. These pairs should then generate a secondary emission of lower-energy gamma rays by scattering off the cosmic microwave background. However, space-based instruments, including the Fermi satellite, consistently fail to detect this predicted secondary emission, creating a significant puzzle for astrophysicists.

Two main theories have attempted to explain this deficit: either weak magnetic fields permeate the intergalactic medium, subtly deflecting the particle pairs, or the beams themselves become unstable traversing the sparse cosmic material, generating self-reinforcing magnetic fields that dissipate energy. The research team, a collaboration involving the University of Oxford and the STFC's Central Laser Facility (CLF), utilized CERN's HiRadMat facility to test these hypotheses directly. By generating electron–positron pairs via the SPS and channeling them through a meter-long ambient plasma, they modeled the propagation of a blazar-driven cascade through intergalactic plasma.

The experimental measurements provided a clear result: the pair beam remained remarkably narrow and nearly parallel, showing minimal evidence of self-generated magnetic fields or disruptive instability. This observation strongly suggests that beam-plasma instabilities are not the primary cause for the missing GeV gamma rays, thereby lending substantial empirical support to the alternative hypothesis involving external magnetic fields. Professor Gianluca Gregori of the University of Oxford, the Lead Researcher, stated that these laboratory efforts effectively connect abstract theory with concrete observation, enhancing the understanding of distant astrophysical phenomena.

The central implication of this finding is a strong endorsement for the existence of a pervasive intergalactic magnetic field, potentially an ancient relic from the universe's earliest moments. This outcome shifts the scientific focus from merely explaining the missing gamma rays to understanding the very origin of this cosmic magnetism. The stability observed in the laboratory experiment, which implies an external magnetic scaffolding, now compels scientists to seek the initial source of that field, viewing this cosmic structure as a profound clue to the universe's initial conditions.