Scientists Uncover Black Holes as Source of Cosmic Ray ‘Knee’

A significant breakthrough in astrophysics has emerged as scientists have linked the formation of a “knee” in the cosmic ray energy spectrum to black holes. This pivotal finding, announced on November 16, 2025, by the Large High Altitude Air Shower Observatory (LHAASO), sheds light on a mystery that has perplexed researchers for nearly seven decades.

The cosmic ray energy spectrum exhibits a sharp decrease above 3 PeV, creating a distinct knee-like shape. While the origin of this phenomenon has long been debated, recent studies published in National Science Review and Science Bulletin identify micro-quasars, formed by black holes accreting material from companion stars, as the primary accelerators of these high-energy cosmic rays.

Researchers from the Institute of High Energy Physics at the Chinese Academy of Sciences, along with teams from Nanjing University and La Sapienza University of Rome, conducted extensive investigations that revealed the role of micro-quasars in generating cosmic rays. These celestial bodies create relativistic jets, leading to the acceleration of particles to extraordinary energies.

The study 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 radiation from SS 433 was found to coincide with a significant atomic cloud, indicating that high-energy protons are accelerated by the black hole, colliding with surrounding matter. In this case, proton energies exceeded 1 PeV, with a staggering power output of approximately 10^32 joules per second—equivalent to the energy released by four trillion of the most powerful hydrogen bombs.

Further analysis revealed that V4641 Sgr achieved gamma-ray energies of 0.8 PeV, reinforcing its status as a “super PeV particle accelerator.” These findings establish micro-quasars as vital contributors to the cosmic ray “knee,” a revelation that challenges the previous belief that supernova remnants were the primary sources of cosmic rays.

Understanding the complexity of cosmic ray origins requires precise measurements of various cosmic ray species, particularly in the knee region. Historically, measuring these energies has been fraught with challenges due to the sparse nature of cosmic rays in this range. Traditional satellite detectors have faced limitations, likening detection efforts to “finding a needle in a haystack.”

Employing advanced measurement techniques, LHAASO overcame these obstacles, allowing for the selection of a large statistical sample of high-purity protons. This enabled researchers to achieve measurements of cosmic ray energy spectra with precision comparable to satellite experiments. The results revealed an unexpected structure in the energy spectrum, displaying a new “high-energy component” rather than a simple transition between spectra.

The findings from LHAASO, together with data from the AMS-02 and DArk Matter Particle Explorer (DAMPE) experiments, illustrate the existence of multiple cosmic ray accelerators within the Milky Way. Each source possesses unique acceleration capabilities and energy ranges. The knee signifies the acceleration limit of sources generating high-energy cosmic rays, suggesting that micro-quasars play a crucial role in reaching energies that exceed this threshold.

This research not only resolves a long-standing mystery regarding the origin of the cosmic ray knee but also provides vital observational evidence linking black holes to cosmic ray phenomena. For the first time, the knee structure has been connected to specific astrophysical sources, emphasizing the significance of black hole jet systems.

The hybrid detector array design employed by LHAASO has positioned it at the forefront of high-energy cosmic ray research. Its sensitivity in both gamma ray astronomical exploration and cosmic ray measurement has led to groundbreaking discoveries, enhancing our understanding of the extreme physical processes shaping the universe.

This advancement in cosmic ray science offers a clearer picture of how black holes contribute to the origins of these high-energy particles, marking a transformative moment in our comprehension of the universe’s most enigmatic objects.