LHAASO Discovers First Super Cosmic Ray Accelerator in Cygnus Region

The Large High Altitude Air Shower Observatory, typically known as LHAASO, has made a groundbreaking discovery by identifying a large ultra-high-energy gamma-ray bubble within the Cygnus star-formation area. This achievement represents a pivotal moment in the pursuit of understanding cosmic rays, as it is the first time scientists have located their source of energy surpassing 10 Peta-Electronvolts (PeV).

Cosmic rays, which are high-energy charged particles predominantly comprising protons, have puzzled astrophysicists for decades regarding their origins. Previous studies indicated a distinct energy limit, known as the "knee" of the cosmic ray spectrum, highlighting that particles with energy less than this threshold typically come from sources within the Milky Way. However, the exact cause of cosmic rays in the "knee" region remains an enigma that researchers are eager to unravel.

LHAASO's discovery of the gamma-ray bubble includes multiple photons exceeding the 1 PeV mark, with the most intense reaching up to 2.5 PeV. This suggests the existence of a super cosmic ray accelerator within the structure, which is capable of accelerating cosmic ray particles to energies as high as 20 PeV, continuously sending them into the interstellar medium. Scientists believe that this bubble holds the key to understanding the origin of these high-energy particles, with indications pointing toward a massive star cluster, referred to as the "O-star association" and "B-star association," as the likely source.

This marks the identification of the first super cosmic ray accelerator to date, and as LHAASO progresses with its observations, it is anticipated that more such accelerators will be identified. This might help shed light on the puzzling origins of cosmic rays in the Milky Way galaxy. Additionally, findings from LHAASO indicate that the accelerator within the bubble contributes significantly to the cosmic ray density in the surrounding space, surpassing typical levels observed in the Milky Way. The extent of this density increase even appears to extend beyond the physical boundaries of the gamma-ray bubble, offering new explanations for diffuse gamma-ray emissions detected previously.

Professor Elena Amato, a leading astrophysicist at the Italian National Institute for Astrophysical Sciences, emphasized the significance of these findings on the understanding of cosmic rays. The results not only affect perceptions of diffuse emissions but also provide critical insights into the movement and transport of cosmic rays within our galaxy. LHAASO, situated at 4410 meters above sea level on Mount Haizi in Sichuan Province, China, is recognized as the most sensitive instrument worldwide for ultra-high-energy gamma-ray detection, having commenced its operations in July 2021.