Scientists Link Black Holes to Cosmic Ray ‘Knee’ Formation

A significant breakthrough in astrophysics has emerged as researchers have connected the formation of a peculiar feature in the cosmic ray energy spectrum—known as the “knee”—to black hole systems. Findings released by the Large High Altitude Air Shower Observatory (LHAASO) on November 16, 2025, explain that micro-quasars, which are powered by black holes, play a crucial role in this phenomenon.

The “knee” in the cosmic ray spectrum is characterized by a sharp decline in cosmic rays above 3 PeV, a mystery that has perplexed scientists for nearly seven decades. Previous theories suggested this decline might indicate a transition in the energy spectrum of cosmic rays due to limitations in their acceleration sources. However, two recent studies published in the National Science Review and Science Bulletin have shifted this understanding, identifying micro-quasars as the primary drivers behind the knee formation.

Micro-Quasars as Cosmic Accelerators

Micro-quasars, which are binary systems where black holes consume material from companion stars, generate powerful jets that accelerate particles to extreme energies. The LHAASO’s observations have revealed ultra-high-energy gamma rays from five identified micro-quasars: SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070, and Cygnus X-1. Notably, in the case of SS 433, the radiation overlaps with a massive atomic cloud, suggesting that high-energy protons are being accelerated by the black hole, leading to collisions with surrounding matter.

In this cosmic environment, proton energies have exceeded 1 PeV, with an output of approximately 10^32 joules per second. This is equivalent to the energy released by four trillion hydrogen bombs each second. Moreover, the gamma-ray emissions from V4641 Sgr reached 0.8 PeV, confirming it as another potent particle accelerator within our galaxy.

These discoveries highlight a significant shift in the understanding of cosmic ray origins. Historically, supernova remnants were believed to be the primary sources of cosmic rays. However, both observational data and theoretical analysis have shown that they fall short when it comes to producing cosmic rays with energies that correspond to the knee and beyond.

Challenges and New Measurement Techniques

To fully understand the knee and its implications, precise measurements of the energy spectra of various cosmic ray species are vital. The initial focus has been on the lightest nuclei, primarily protons. Yet, measuring cosmic rays in the knee region is notably challenging due to their sparsity and the limitations of satellite detectors.

Ground-based observations, like those conducted by LHAASO, have now employed advanced multi-parameter measurement techniques to address these challenges. By selecting a large statistical sample of high-purity protons, researchers have achieved measurements with precision comparable to satellite experiments. This effort has uncovered an unexpected energy spectrum structure, revealing a new “high-energy component” instead of a straightforward transition between power-law spectra.

The findings from LHAASO, combined with low-energy data from the AMS-02 experiment and intermediate-energy findings from the DArk Matter Particle Explorer (DAMPE) experiment, indicate the presence of multiple cosmic ray accelerators within the Milky Way. Each of these sources possesses distinct acceleration capabilities and energy ranges, with the knee representing the limit of acceleration for the sources generating the high-energy component.

The research underscores the importance of micro-quasars as “new sources” of cosmic rays, capable of accelerating particles beyond the knee threshold. This understanding not only addresses a long-standing scientific mystery but also enhances our comprehension of the extreme physical processes occurring in black hole systems.

The observational connection between the knee structure and black hole jet systems marks a significant advancement in astrophysics. LHAASO’s innovative hybrid detector array has set new standards in high-energy cosmic ray research, enabling the detection of cosmic ray sources through ultra-high-energy gamma rays while simultaneously measuring cosmic ray particles with unprecedented accuracy.

These findings contribute to a broader understanding of the universe’s most extreme phenomena, highlighting the intricate relationship between black holes and cosmic rays. As scientists continue to unravel these cosmic mysteries, the implications of this research may reshape fundamental concepts in astrophysics and enhance our grasp of the cosmos.