Vector displacements expressed in spherical coordinates are proposed. They correspond to electromagnetic fields in vacuum that globally rotate about an axis and display many circular patterns on the surface of a sphere. The fields basically satisfy the set of Maxwell's equations, but enjoy further properties that allow them to be suitably interpreted as solutions of a plasma model that combines electrodynamics with the Euler's equation for fluids. Connection with magnetohydrodynamics can also be established. The fields are extended with continuity outside the sphere in a very peculiar manner. In order to avoid peripheral velocities of arbitrary magnitude, as it may happen for a rigid rotating body, they are organized to form successive encapsulated shells, with substructures recalling successive ball-bearing assemblies. A recipe for the construction of these solutions is provided by playing with the eigenfunctions of the vector Laplace operator. Some applications relative to astronomy are finally discussed.
Categories: physics.class-ph physics.plasm-ph