Micro-quasars have been confirmed as major engines of extreme cosmic rays, resolving the long-puzzling “knee” in the energy spectrum. Credit: Shutterstock Milestone results released by the Large High Altitude Air Shower Observatory (LHAASO) on November 16 have finally clarified a decades-old puzzle in astrophysics: the unusual drop in cosmic ray counts above 3 PeV that produces what scientists call the "knee" in the cosmic ray energy spectrum. The cause of this steep decline has remained