Researchers Find Massive Gamma-Ray Bubble, Shedding Light on Cosmic Ray Origins
TEHRAN (Tasnim) – Chinese researchers have uncovered a significant breakthrough in astrophysics, revealing the origin of cosmic rays through the discovery of a colossal ultra-high-energy gamma-ray bubble structure within the Milky Way.
This discovery marks the first time the origin of cosmic rays with energy exceeding 10 Peta-Electronvolt (PeV) has been revealed, as detailed in a study published in the journal Science Bulletin on Monday.
Cosmic rays, comprised of charged particles from outer space, pose one of the most significant scientific challenges in contemporary astrophysics due to their elusive origins.
Utilizing the Large High Altitude Air Shower Observatory (LHAASO) of the Institute of High Energy Physics at the Chinese Academy of Sciences (CAS), the researchers identified the colossal bubble structure within the Cygnus star-forming region.
Inside this bubble, researchers detected numerous photons with energies surpassing 1 PeV, with the highest reaching 2.5 PeV. According to the researchers, this indicates the presence of a "super cosmic ray accelerator" inside the bubble, continuously boosting high-energy cosmic ray particles up to 20 PeV and releasing them into interstellar space.
In their investigation, the researchers pinpointed a massive star cluster near the bubble's core, dubbed Cygnus OB2, as the most likely candidate for the super cosmic ray accelerator.
Cygnus OB2 comprises several young, hot, massive stars with surface temperatures ranging from about 15,000 to 35,000 degrees Celsius. These stars emit radiation luminosity hundreds to millions of times that of the sun. Their intense radiation pressure can expel material from their surfaces, creating a potent stellar wind that can travel at speeds of up to 3,000 kilometers per second.
The researchers note that the collision between these stellar winds and the surrounding interstellar medium, as well as the violent interactions between stellar winds, have generated "ideal sites for efficient particle acceleration."
"This is the first super cosmic ray accelerator identified to date," stated Cao Chen, chief scientist of LHAASO and academician at the CAS, in an interview with CGTN. He emphasized that this discovery would have been inconceivable without LHAASO's exceptional sensitivity, which enables it to trace the origins of cosmic rays and study their behavior.
Situated at an elevation of 4,410 meters in Daocheng County, southwest China's Sichuan Province, LHAASO stands as a key national scientific and technological facility dedicated to cosmic ray research.
Comprising a ground-based shower particle detector array of 5,216 electromagnetic particle detectors and 1,188 muon detectors, a 78,000-square-meter water Cherenkov detector array, and 18 wide-angle Cherenkov telescopes, LHAASO boasts the world's most sensitive ultra-high-energy gamma-ray detection system.
In June of last year, the observatory made headlines by detecting the "brightest-of-all-time" gamma-ray burst.
Looking ahead, Cao expressed optimism, stating, "In time, LHAASO is expected to detect more super cosmic ray accelerators and hopefully solve the mystery of the origin of cosmic rays in the Milky Way."