The origin of cosmic rays has been a century-old open question in astrophysics. On July 22, 2026, *National Science Review* published a China-led study in which the Large High Altitude Air Shower Observatory (LHAASO) certified the binary system Cygnus X-3 as the highest-energy particle accelerator yet observed.
Cygnus X-3 consists of a compact object (a black hole or neutron star) and a massive companion star. As the compact object violently accretes the intense stellar wind blown off by its companion, it can accelerate particles to extreme energies. LHAASO's precise timing measurements, ultra-high gamma-ray energies, and energy spectrum together confirm it as a cosmic-ray source, with particle energies reaching at least 30 PeV (1 PeV = 10¹⁵ eV). Mainstream theory had generally placed the upper limit for charged-particle acceleration in the Milky Way at around 1 PeV—meaning the observed 30 PeV raises that theoretical ceiling by roughly 30 times.
The key evidence: time variability plus localization
The most valuable result is the combination of variability and localization:
- LHAASO detected clear burst behavior in ultra-high-energy (>10¹⁴ eV) gamma-ray signals.
- These bursts showed a clean temporal correlation with GeV-band observations a million times lower in energy: during GeV flares, both the Fermi Gamma-ray Space Telescope and LHAASO saw significant signals simultaneously; during GeV-quiet periods, LHAASO saw nothing.
- The signal carried a 4.8-hour periodicity—the binary's orbital period. Using this, the team localized the particle acceleration site to within roughly 3 solar radii, the highest localization precision achieved for an ultra-high-energy cosmic accelerator.
- Whether the compact object is a black hole or a neutron star remains an open "or" in the paper.
- 30 PeV is a lower bound ("at least"); the true peak may be higher, but event counts at even higher energies are scarce and statistical significance still accumulating.
- This is a deep certification of a single source; whether it generalizes to other similar binary systems awaits future surveys.
Physical mechanism
Protons from the base of the Cygnus X-3 jet interact with photons from the companion star, producing high-energy photons and neutrinos—the origin of the ultra-high-energy gamma-ray signals LHAASO captured.
Caveats
Why it matters
The result changes two things:
1. Physics: It lifts the assumed Galactic particle-acceleration ceiling from ~1 PeV to 30 PeV, forcing existing shock-acceleration theory to be reworked. 2. Method: Using ultra-high-energy gamma-ray temporal correlations plus orbital periodicity to infer the size of the acceleration region provides a new tool for studying extreme physics near compact objects such as black holes and neutron stars.
Where cosmic-ray sources were previously portrayed mostly through static snapshots, this work turns variability and periodicity into probes—inaugurating the field of "ultra-high-energy time-domain astronomy." LHAASO, perched at 4,410 meters on the Tibetan Plateau, has once again written Chinese instrumentation into the key evidence chain for the origin of cosmic rays.