Unveiling the Cosmic Mystery: China's Observatory Unravels the Origin of High-Energy Cosmic Rays
BEIJING - Scientists have made a groundbreaking discovery using China's Large High Altitude Air Shower Observatory (LHAASO). They found that black holes, by devouring material from their companion stars and producing jets, act as powerful particle accelerators, potentially playing a crucial role in the production of high-energy cosmic rays within the Milky Way.
This research, led by Cao Zhen, a principal investigator at LHAASO and an academician of the Chinese Academy of Sciences (CAS), not only sheds light on the key mechanisms behind cosmic ray origins but also deepens our understanding of the extreme physical processes within black hole systems.
Cosmic rays, primarily composed of protons, are charged particles from outer space. Their origin is a significant frontier in modern astrophysics. Past measurements have revealed a turning point in the energy spectrum around 3 PeV (peta-electron volts), known as the 'knee' due to its shape. The origin of cosmic rays in this 'knee' region has been a captivating topic in recent cosmic ray research.
The LHAASO research team discovered that microquasars, driven by accretion onto black hole systems, are potent particle accelerators in the Milky Way and are likely the sources of the 'knee'.
This study, conducted by researchers from the Institute of High Energy Physics of the CAS, Nanjing University, the University of Science and Technology of China, La Sapienza University of Rome, and other institutions, was published in the National Science Review and Science Bulletin on Sunday.
Black holes, among the most enigmatic objects in the universe, generate relativistic jets when they accrete material from companion stars in binary systems, forming 'microquasars'.
In this study, LHAASO systematically detected ultra-high-energy gamma rays from five microquasars. For instance, the analysis of the microquasar SS 433 revealed proton energies exceeding 1 PeV, with a power output per second equivalent to the energy released by 400 trillion of the most powerful hydrogen bombs.
The gamma-ray energy from the microquasar V4641 Sgr reached 0.8 PeV, indicating that the parent particles generating these gamma rays likely had energies exceeding 10 PeV. These results prove that microquasars are significant PeV particle accelerators in the Milky Way.
To fully understand the 'knee' of the cosmic-ray spectrum, precise measurements of the energy spectra of various cosmic ray species, including their respective 'knees', are essential, Cao said.
LHAASO, located on a mountain at an elevation of about 4,410 meters above sea level in Southwest China's Sichuan province, covers an area of 1.36 square kilometers and is dedicated to cosmic ray observation and research. Leveraging its world-leading ground-based cosmic-ray observation equipment, LHAASO has developed multi-parameter measurement techniques, revealing an energy spectrum structure that was entirely unexpected.
This new discovery not only marks a significant advancement in resolving the long-standing mystery of the 'knee' origin, which has puzzled the academic community for nearly 70 years, but also offers crucial observational evidence for understanding the role of black holes as the origin of cosmic rays. LHAASO, designed, constructed, and operated by Chinese scientists, has taken the lead in high-energy cosmic-ray research due to its sensitivity in both gamma ray astronomical exploration and cosmic ray precision measurements. It has achieved a series of discoveries with global impact, contributing to our understanding of the extreme physical processes in the universe.
