Scientists Link Cosmic Ray 'Knee' to Black Holes, Solving Long‑Standing Puzzle
On November 16, researchers at the Large High‑Altitude Air Shower Observatory (LHAASO) announced results that appear to resolve a decades‑old mystery in astrophysics. The data show a clear connection between the long‑observed ‘knee’—a sudden steepening in the cosmic‑ray energy spectrum around 3 petaelectronvolts—and the influence of black‑hole‑driven particle acceleration. The announcement marks a significant milestone for the international community studying high‑energy cosmic phenomena.
The ‘knee’ has been a focal point of research since it was first identified in the 1950s, because it signals a change in the origin or propagation of cosmic rays reaching Earth. Over the years, scientists proposed a variety of explanations, ranging from limits in supernova‑remnant acceleration to interactions with interstellar magnetic fields. However, none of these models could fully account for the abrupt drop in flux observed across multiple experiments.
Using LHAASO’s array of more than 5,000 scintillator detectors and its wide‑field gamma‑ray telescopes, the team measured the composition and arrival directions of ultra‑high‑energy particles with unprecedented precision. The analysis revealed a statistical excess of particles that align with regions of the sky where active galactic nuclei host rapidly accreting black holes. The researchers interpret this pattern as evidence that shock fronts near black‑hole jets can boost particles to energies that produce the observed knee feature.
Experts unaffiliated with the project have welcomed the findings, noting that they provide a coherent framework that links cosmic‑ray physics with high‑energy astrophysical sources. The results are expected to guide future observations by next‑generation facilities such as the Cherenkov Telescope Array and space‑based detectors. While the study does not close all questions about cosmic‑ray origins, it narrows the field of viable theories and underscores the role of black holes as powerful accelerators in the universe.
