Researchers at CERN may be on the verge of explaining the universe’s missing gamma rays and hidden magnetic fields, after creating the first-ever plasma fireballs within the facility’s Super Proton Synchrotron accelerator.
The new research, presented in Proceedings of the National Academy of Sciences, was designed to study how plasma jets emanate from blazers. However, instead of a simple explanation, the researchers have uncovered something at CERN that may challenge the Standard Model of physics.
Blazars and Gamma Rays
Surrounded by supermassive black holes, blazers are galaxies that emit beams of particles and radiation traveling close to the speed of light. The jets from this activity produce gamma-ray emissions observable from Earth.
As those gamma-rays traverse the cosmos, they scatter off the stellar background light to produce electron-positron pairs. In turn, those pairs should scatter off the microwave background radiation to reform as lower-energy gamma rays, but such activity has never been observed. Researchers have long debated why this was the case, but now, the recent work at CERN may have finally provided an answer.
Two major hypotheses have been proposed to explain the issue. One is that weak intergalactic magnetic fields deflect the lower-energy gamma rays out of our line of sight. Another idea is that, because matter is so sparse in the regions of space through which the beams are traveling, they lose stability. If that were to happen, it would produce small beam current fluctuations, which would serve to further destabilize and dissipate the beam’s energy.
Creating Plasma Fireballs At CERN
Behind the recent tests was a collaboration of researchers between the University of Oxford and the Science and Technology Facilities Council’s Central Laser Facility, operating out of CERN’s HiRadMat facility. After generating the electron-positron pairs using the Super Proton Synchrotron, the researchers pushed them through a meter-long ambient plasma to produce a laboratory-scale model of a blazer-driven pair moving through intergalactic plasma. This allowed the scientists to keep a close eye on what was occurring by measuring the beam profile and magnetic field signatures to see how they affected the beam-plasma instabilities.
The results were completely different from what the team expected. The beam was remarkably resilient, maintaining a narrow, parallel path without significant disruption or self-generated magnetic fields. From this result, the team suggests that the beam-plasma instabilities are too weak to account for the missing gamma rays, indicating that a magnetic field left over from the early universe is hiding in the intergalactic medium.
“Our study demonstrates how laboratory experiments can help bridge the gap between theory and observation, enhancing our understanding of astrophysical objects from satellite and ground-based telescopes,” said lead author Professor Gianluca Gregori of the University of Oxford. “It also highlights the importance of collaboration between experimental facilities around the world, especially in breaking new ground in accessing increasingly extreme physical regimes.”
Reconsidering the Early Universe
“If there is indeed an intergalactic magnetic field of sufficient strength, then circular rings of emission (“pair halos”) should be detectable around the blazars being observed by the Cherenkov Telescope Array Observatory (CATO), now nearing completion at sites in Chile and the Canary Islands,” Gregori told The Debrief in an email.
The result has implications far beyond this single phenomenon; it also challenges the prevailing view that the early universe was highly uniform, leaving little room for such a magnetic field to seed. Upending such expectations would require new physics outside of the standard model, and the team hopes that the next generation of observatories will provide better confirmation of their findings.
“If future CTAO observations confirm our findings, the only possibility is that the magnetic field is primordial in origin,” Gregori explained. “However, having magnetic fields implies currents, and currents require inhomogeneities which are hard to create in the early Universe. So new physics may be needed.”
“For example, the random fluctuation of dark matter and ordinary matter densities may not sync together if the dark matter is made of hypothetical particles called axions,” Gregori added. “This could give rise to the equivalent of the thermoelectric effect (temperature and electron density fluctuations produce a current).”
Continuing to Explore the Universe at CERN
“Another important topic to study is how cosmic rays are produced,” Gregori said. “One theory is that relativistic jets are one of the main engines for the acceleration of cosmic rays. But most mechanisms for particle acceleration require magnetic fields. In future experiments, we will look in more detail at how cosmic rays may be accelerated in these systems.”
Gregori and his colleagues still see a great deal of information remaining to be learned from such ongoing experiments at CERN, which will provide researchers with a greater depth of insight into the fundamental processes underlying our universe.
“It was a lot of fun to be part of an innovative experiment like this that adds a novel dimension to the frontier research being done at CERN,” said Professor Subir Sarkar (Department of Physics, University of Oxford. “Hopefully, our striking result will arouse interest in the plasma (astro)physics community to the possibilities for probing fundamental cosmic questions in a terrestrial high energy physics laboratory.”
The paper, “Suppression of Pair Beam Instabilities in a Laboratory Analogue of Blazar Pair Cascades,” will appear in Proceedings of the National Academy of Scienceson November 7, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.