Ultrahigh-energy cosmic rays from tidally-ignited white dwarfs
  Ultra-high-energy cosmic rays (UHECRs) can be accelerated by tidal disruption
events of stars by black holes. We suggest a novel mechanism for UHECR
acceleration wherein white dwarfs (WDs) are tidally compressed by
intermediate-mass black holes (IMBHs), leading to their ignition and subsequent
explosion as a supernova. Cosmic rays accelerated by the supernova may receive
an energy boost when crossing the accretion-powered jet. The rate of encounters
between WDs and IMBHs can be relatively high, as the number of IMBHs may be
substantially augmented once account is taken of their likely presence in dwarf
galaxies. Here we show that this kind of tidal disruption event naturally
provides an intermediate composition for the observed UHECRs, and suggest that
dwarf galaxies and globular clusters are suitable sites for particle
acceleration to ultra-high energies.
