A huge complex of telescopes in Tibet has found the first evidence of ultra-high-energy gamma-ray propagation through the Milky Way. They come from unknown naturally occurring stellar accelerators that have been orbiting the galaxy for millions of years. This is reported in an article published in the journal Physical Review Letters.
Scientists have recorded 23 events of cosmic gamma radiation, while the energy of one of them broke the world record and amounted to almost one petaelectronvolt. This is three orders of magnitude more than the energy of any other known gamma radiation caused by cosmic rays, or particles dispersed in accelerator laboratories.
High-energy gamma rays are produced by nuclear interactions between high-energy cosmic rays emitted by powerful galactic sources and interstellar gas in the Milky Way galaxy. Cosmic rays are generated by enigmatic PeVatrons, which can be supernova explosions, star-forming regions, or a supermassive black hole at the center of the galaxy. However, so far not a single active pewatron has been found, although the discovery for the first time indicates their existence.