Particle acceleration by electrostatic polarization fields that arise in plasmas streaming across magnetic fields is discussed as a possible acceleration mechanism of highest energy $\left(\gtrsim {10}^{20}\mathrm{eV}\right)$ cosmic rays. Specifically, plasmoids arising in planetoid impacts onto neutron star magnetospheres are considered. We find that such impacts at plausible rates may account for the observed flux and energy spectrum of the highest energy cosmic rays.

• Received 6 April 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.4745