CHINA’S Large High Altitude Air Shower Observatory (LHAASO) has detected the most energetic photons ever recorded from Cygnus X-3, a violent binary star system in the constellation Cygnus. The gamma-ray signals reached at least 4 petaelectronvolts — hundreds of times more energetic than the protons in the world’s most powerful human-built accelerator — far exceeding current theoretical predictions. This discovery not only challenges existing models of particle acceleration but also reveals a natural cosmic accelerator operating at energies previously thought impossible.

The study, published in National Science Review on July 22, was conducted by an international team led by the Institute of High Energy Physics of the Chinese Academy of Sciences, in collaboration with researchers from Shanghai Jiao Tong University and the Max-Planck-Institute for Nuclear Physics in Germany.

Cygnus X-3 consists of a compact object feeding on a massive companion star, generating powerful stellar winds that accelerate particles to extreme energies. The LHAASO data reveal that these ultra-high-energy photons originate directly from this violent feeding process.

The signals appeared in bursts that precisely matched flares detected at lower energies by NASA’s Fermi Gamma-ray Space Telescope, confirming Cygnus X-3 as the definitive source. This lockstep behavior ties the highest-energy particles directly to the system’s feeding frenzy, ruling out alternative explanations. The signals also exhibited a 4.8-hour periodicity, corresponding to the orbital motion of the two stars, pinpointing the accelerator to a region roughly three times the size of the sun — the highest localization precision ever achieved for such a cosmic accelerator.

By establishing Cygnus X-3 as the first ultra-high-energy gamma-ray source with time-variable characteristics, LHAASO has opened a new frontier in ultra-high-energy time-domain astronomy, creating new pathways for studying extreme physics around black holes. The findings have already attracted significant attention in the astrophysics community, becoming one of the most intensely discussed topics at international conferences.

Located 4,410 meters above sea level in Daocheng county, Sichuan Province, LHAASO is the world’s most sensitive detector for ultra-high-energy gamma rays. (SD-Agencies)