Classification results on purely electric or magnetic perfect fluids

Abstract

Non-conformally flat, non-vacuum perfect fluid models for which the magnetic, resp. electric, part of the Weyl tensor w.r.t. the fluid congruence vanishes, are called purely electric (PE), resp. purely magnetic (PM), perfect fluids. Their Petrov type is necessarily I or D. They are of particular interest, since the electric part is the relativistic generalization of the tidal tensor in Newtonian theory, whereas the magnetic part has no Newtonian analogue. A survey of recent classification results is presented, with focus on Petrov type D and on the Petrov type I non-accelerating subclass. Important known universe models are naturally embedded in the analysis, while new and physically interesting PE and PM families emerge.