  The presence of a non-zero cosmological term in Einstein field equations can
be interpreted as the physical possibility for preferred reference frames
without breaking of general covariance. This possibility is used in the process
of linearizing Einstein field equations in a de Sitter background, and in
formulating the resulting equations in the framework of
gravitoelectromagnetism. It is proposed that this set of equations only applies
to the physical vacuum and not to baryonic (normal) matter.
