How physicists recreated the energy of blazars in the lab

The experiment was conducted at the Super Proton Synchrotron accelerator at CERN, and the results are published in the journal PNAS, reports the University of Oxford.

The main purpose of the study - to solve a long-standing astronomical mystery: why part of the gamma rays emanating from galaxies blazars, "lost" in space, not reaching detectors on Earth.

Blazars are supermassive black holes that emit narrow streams of particles and radiation at near-light speeds. These jets produce powerful gamma rays measured in teraelectronvolts. However, according to calculations, the collision of such rays with scattered starlight should produce cascades of electron-positron pairs that, interacting with relic microwave radiation, produce softer gamma rays. It is these secondary beams that telescopes like Fermi do not detect.

There were two hypotheses. The first is that the particles are deflected by weak intergalactic magnetic fields, so the radiation "escapes" from our field of view. The second is that the streams themselves become unstable, losing energy as they move through the intergalactic plasma.

To test the second theory, physicists from Oxford and the Centre for Laser Research STFC created in the facility HiRadMat (High-Radiation to Materials) at CERN model analogue of this process. Using an accelerator, they were able to produce a stream of electrons and positrons passing through a metre-long chamber filled with plasma. This made it possible to reproduce in miniature a phenomenon occurring on giant astronomical scales.

According to the observations, the particle beam remained stable and produced almost no magnetic fields of its own. This means that plasma instabilities are too weak to explain the disappearance of gamma rays. Consequently, a more likely explanation remains the existence of a weak intergalactic magnetic field, which may be a relic of the early Universe.

"Our experiment shows how laboratory astrophysics can combine theory and observation to help understand processes occurring over colossal distances," explained project leader Professor Gianluca Gregori from Oxford. - "This is an example of how collaboration between leading research centres is paving the way for the exploration of extreme physical regimes."

Project colleague Professor Bob Bingham from the University of Strathclyde added: "By creating analogues of relativistic plasmas in the lab, we can directly study the mechanisms of cosmic magnetic field formation and the dynamics of jets emanating from black holes."

The scientists note that their results have not only brought closer to unravelling the nature of intergalactic fields, but have also raised new questions. For example, how exactly in the young, homogeneous Universe could arise these magnetic structures. Perhaps the answer lies in physics beyond the Standard Model.