Recent studies published in National Science Review and Science Bulletin reveal that micro-quasars powered by black hole accretion serve as major particle accelerators in the Milky Way and are responsible for producing the knee. Scientists from the Institute of High Energy Physics of the Chinese Academy of Sciences (CAS), Nanjing University, University of Science and Technology of China, La Sapienza University of Rome, and additional institutions contributed to this research.
Black holes in binary star systems form micro-quasars when material from a companion star is accreted, generating relativistic jets. LHAASO observed ultra-high-energy gamma rays from five micro-quasars: SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070, and Cygnus X-1. Ultra-high-energy radiation from SS 433 overlapped with a large atomic cloud, indicating that energetic protons accelerated by the black hole collided with surrounding matter. The system's protons reached over 1 PeV, producing power comparable to the energy released by four trillion hydrogen bombs per second. V4641 Sgr exhibited gamma ray energies up to 0.8 PeV, indicating its role as another PeV particle accelerator, with parent particles exceeding 10 PeV.
These data demonstrate that micro-quasars are significant PeV accelerators, a role previously attributed to supernova remnants. However, both modeling and observations have shown that supernova remnants cannot reach such energies.
Precise measurement of proton energy spectra, especially in the knee region, requires advanced techniques. Cosmic rays in this range are rare, and atmospheric interference complicates ground-based detection. LHAASO used multi-parameter approaches to isolate a large, high-purity proton sample, enabling satellite-level measurement accuracy. The observed spectra deviated from expected power-law transitions, revealing a distinct high-energy component.
Combining LHAASO findings with data from AMS-02 and DAMPE space experiments, researchers identified multiple sources of cosmic ray acceleration in the Milky Way. Each source displays unique energy capabilities, with micro-quasars surpassing supernova remnants in acceleration limits. The knee marks this limit for the highest energy component.
LHAASO's hybrid detector system enables detection of cosmic ray sources via ultra-high-energy gamma rays and provides detailed particle measurements around the solar system. The knee is now directly linked to black hole jet systems, a first in observational astrophysics.
The LHAASO facility, designed and operated by Chinese scientists, has advanced high-energy cosmic ray research worldwide thanks to its sensitivity and precision. Its discoveries are reshaping understanding of extreme physical processes in the universe.
Research Report: Precise measurements of the cosmic ray proton energy spectrum in the "knee" region
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