1999MNRAS.307..491B

Considerations of the collision losses for protons traversing the 2.7-K blackbody microwave radiation field have led to the conclusion that the highest energy cosmic rays, those observed at ≥10²⁰eV, must come from sources within the present epoch. In light of this constraint, it is here suggested that these particles may be accelerated near the event horizons of spinning supermassive black holes associated with presently inactive quasar remnants. The required emf is generated by the black hole induced rotation of externally supplied magnetic field lines threading the horizon. Producing the observed flux of the highest energy cosmic rays would constitute a negligible drain on the black hole dynamo. Observations with upcoming air shower arrays and space missions may lead to the identification of candidate dormant galaxies that harbour such black holes. Although the highest energy events observed so far are accounted for within the context of this scenario, a spectral upper bound at ∼10²¹eV is expected since the acceleration to higher energies appears to be precluded, on general grounds.