China’s Large High Altitude Air Shower Observatory (LHAASO) aims to catch the air showers associated with the highest energy gamma rays, which in turn correspond to the highest energy cosmic rays. LHAASO is a cluster of detectors spanning more than 1 square kilometer on Haizi Mountain, 4410 meters above sea level in Sichuan province. More than 5000 detectors spread across the site capture particles associated with the highest energy strikes, while more than 1000 muon detectors, buried underground, help rule out particle showers associated with unrelated cosmic rays that constantly pepper Earth. Before LHAASO began operations in 2019, most detectors worked in much lower energy bands. But the new results show the universe is capable of far higher accelerations.
Using data from LHAASO’s first year of operation, Cao Zhen from the Institute of High Energy Physics of the Chinese Academy of Sciences and his colleagues detected more than 530 photons with energies greater than 0.1 PeV, they reported yesterday in Nature. The photons were traced to 12 cosmic ray factories capable of PeV accelerations—100 times more energetic than collisions at the world’s most powerful atom smasher, the Large Hadron Collider. The sources, which the team calls “PeVatrons,” include long-suspected accelerators, such as the Crab nebula, the site of an ancient supernova, the final explosion of a dying star, and home to a powerful pulsar, a dense neutron star. But the highest energy photons came from a surprising source: the Cygnus Cocoon, a stellar nursery 4600 light-years from the Sun. “PeVatrons are basically everywhere in our galaxy,” Cao says.