Reply #13: Indeed they are. [View All]

But my point was that the cosmic rays (which are atomic nuclei) must be interacting with other matter in the vicinity of the black hole. More specifically, the interaction must be with electromagnetic fields generated by the other matter.

What is observed on the ground is a shower of secondary particles resulting from the impact of the primary cosmic ray on the upper atmosphere. The geometry of the measurements indicates the approximate direction of the primary cosmic ray. The correlation of these directions with known active galactic nuclei is evidence that supermassive black holes are involved.

As you said, the exact mechanism of acceleration is unknown.