The evidence for electrical currents in cosmic plasma

With the advent of fully three-dimensional, fully electromagnetic, particle-in-cell simulations, investigations of Birkeland currents and magnetic-field-aligned electric fields have become possible in plasmas not accessible to in situ measurement, i.e. in plasmas having the dimensions of galaxies or systems of galaxies. The necessity for a three-dimensional electromagnetic approach derives from the fact that the evolution of magnetized plasmas involves complex geometries, intense self-fields, nonlinearities, and explicit time-dependence. A comparison of the synchrotron radiation properties of simulated currents to those of extragalactic sources provides observational evidence for galactic-dimensional Birkeland currents