China's observatory detects record-breaking gamma rays from Cygnus X-3

China's Large High Altitude Air Shower Observatory, or LHAASO, has spotted the most energetic photons ever recorded from a violent stellar system in the constellation Cygnus, or the Swan, revealing a natural particle accelerator that smashes through theoretical limits and opens a new window into the extreme physics around black holes.

The binary star system, Cygnus X-3, produces gamma-ray signals reaching at least 4 petaelectronvolts — one petaelectronvolt equals 10 to the power of 15 electron volts — far exceeding current theoretical predictions. To put that in perspective, it is hundreds of times more energetic than the protons circulating in the world's most powerful human-built accelerator.

The study was conducted by an international team from the Institute of High Energy Physics of the Chinese Academy of Sciences, the Tsung-Dao Lee Institute at Shanghai Jiao Tong University, the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, and Max-Planck-Institute for Nuclear Physics in Germany, and was published in the journal National Science Review on July 22.

Cygnus X-3 is a binary system in which a compact object — either a black hole or a neutron star — devours material from a massive companion star, generating powerful stellar winds. The LHAASO data reveal that these ultra-high-energy photons originate from this violent feeding process.

LHAASO found that ultra-high-energy gamma signals appear in bursts which match the timing of flares seen at much lower energies by NASA's Fermi Gamma-ray Space Telescope. When Fermi detected bright flares, LHAASO also picked up strong signals. When Fermi saw nothing, LHAASO detected nothing either.

This lockstep behavior is the smoking gun that ties the highest-energy particles directly to the feeding frenzy in Cygnus X-3, ruling out alternative explanations and confirming the system as the source.

The signals also exhibit 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 an ultra-high-energy 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 and created new pathways for studying extreme physical processes near compact objects such as black holes, according to the study.

The findings have attracted significant attention in the astrophysics community, becoming one of the most intensely discussed topics at international conferences.

LHAASO is a major national scientific facility located 4,410 meters above sea level in Daocheng county, Southwest China's Sichuan province. It is the world's most sensitive detector for ultra-high-energy gamma rays, with the core scientific goal to explore the origin of high-energy cosmic rays — high-speed particles constantly bombarding Earth from deep space — and conduct cutting-edge research in high-energy astrophysics and related fields.