  We find two families of analytic solutions to the ideal magnetohydrodynamics
(iMHD) equations, in a class of 4-dimensional (4D) curved spacetimes. The
plasma current is null, and as a result, the stress-energy tensor of the plasma
itself can be chosen to take a cosmological-constant-like form. Despite the
presence of a plasma, the force-free condition - where the electromagnetic
current is orthogonal to the Maxwell tensor - continues to be maintained.
Moreover, a special case of one of these two families leads us to a fully
self-consistent solution to the Einstein-iMHD equations: we obtain the
Vaidya-(anti-)de Sitter metric sourced by the plasma and a null electromagnetic
stress tensor. We also provide a Mathematica code that researchers may use to
readily verify analytic solutions to these iMHD equations in any curved 4D
geometry.
