Milestones achieved by the **Large High Altitude Air Shower Observatory** (LHAASO) on **November 16, 2025**, have provided clarity on a long-standing mystery regarding the cosmic ray energy spectrum. This spectrum exhibits a notable decline in cosmic rays above **3 PeV**, creating a distinctive knee-like shape that has puzzled scientists since its discovery nearly seventy years ago.
The cause of this “knee” has been a subject of speculation, with suggestions that it relates to the acceleration limits of cosmic ray sources and indicates a transition between different power-law distributions in the cosmic ray energy spectrum. Recent studies have shifted this perspective, revealing that micro-quasars powered by black hole systems are likely responsible for this phenomenon.
New Research Highlights Role of Micro-Quasars
Research published in **National Science Review** and **Science Bulletin** underscores the role of micro-quasars as potent particle accelerators within the **Milky Way**. The studies, conducted by teams from the **Institute of High Energy Physics of the Chinese Academy of Sciences** (CAS), **Nanjing University**, and **La Sapienza University of Rome**, detail how these black holes, which create relativistic jets while accreting material from companion stars, contribute to cosmic ray acceleration.
LHAASO’s observations marked the first systematic detection of ultra-high-energy gamma rays from five micro-quasars: **SS 433**, **V4641 Sgr**, **GRS 1915+105**, **MAXI J1820+070**, and **Cygnus X-1**. Notably, the high-energy radiation from **SS 433** was found to overlap with a massive atomic cloud, indicating that protons accelerated by the black hole are colliding with surrounding matter. The energy of protons in this system exceeded **1 PeV**, producing a power output of around **10^32 joules per second**, equivalent to the energy released by four trillion powerful hydrogen bombs.
The gamma-ray energy measured from **V4641 Sgr** reached **0.8 PeV**, reinforcing its status as a “super PeV particle accelerator.” The parent particles responsible for these gamma rays possessed energies exceeding **10 PeV**, confirming the significance of micro-quasars in the cosmic ray landscape of the Milky Way.
Advancements in Cosmic Ray Measurement Techniques
Understanding cosmic ray origins requires precise measurements of energy spectra across various cosmic ray species, particularly the lightest nuclei—protons. However, cosmic rays in the “knee” region are rare, presenting challenges in detection due to atmospheric interference, which complicates the differentiation between protons and other nuclei.
Traditionally, measuring these spectra has been deemed nearly impossible. Yet, LHAASO’s advanced ground-based cosmic ray observational technologies have enabled the development of multi-parameter measurement techniques. By analyzing a large statistical sample of high-purity protons, researchers achieved energy spectrum measurements with precision comparable to satellite experiments.
These measurements unveiled a previously unexpected energy spectrum structure, displaying a new “high-energy component” rather than a simple transition between power-law spectra. Together with findings from the **AMS-02** and **DArk Matter Particle Explorer (DAMPE)** experiments, LHAASO’s results reveal multiple cosmic ray accelerators within the Milky Way, each with distinct acceleration capabilities and energy ranges.
The knee in the spectrum signifies the acceleration limits of the sources responsible for the high-energy component, suggesting that cosmic ray protons in the PeV energy range primarily originate from “new sources” like micro-quasars. These systems can generate high-energy cosmic rays that exceed the knee, advancing our understanding of cosmic ray origins significantly.
In conclusion, the connection between black holes and cosmic rays established by these studies marks a pivotal advancement in astrophysical research. LHAASO’s innovative design allows for the detection of cosmic ray sources through ultra-high-energy gamma rays and facilitates precise measurements of cosmic ray particles near the solar system. This work not only resolves the mystery of the knee’s origin but also enhances our comprehension of the extreme physical processes associated with black hole systems, contributing significantly to the global scientific community’s understanding of the universe.
