Ultra-High-Energy Particles at the Border of Kerr Black Holes Triggered by Magnetocentrifugal Winds

Abstract

The source, origin, and acceleration mechanisms of ultra-high-energy cosmic rays (UHECR) (E>1020 eV, beyond the GZK limit) remain uncertain and unclear. The main explanations are associated with particular mechanisms, such as the Fermi mechanism, in which charged particles could be accelerated by clouds of magnetized gas moving within our Galaxy, or by the magnetic reconnection of field lines at, e.g., the core of high-energy astrophysical sources, where the topology of the magnetic field is rearranged and magnetic energy is converted into kinetic energy. However, the recent observation of extragalactic neutrinos may suggest that the source of UHECRs is likely an extragalactic supermassive black hole. In the present work, we propose that charged particles can be accelerated to ultrahigh energies in marginally bound orbits near extreme rotating black holes and could be triggered by collisions of magnetocentrifugal winds; the accretion disk surrounding the black hole would provide such winds. The ultra-high-energy process is governed by the frame-dragging effects of the black hole spacetime.