Linear Bimetric Gravitation Theory
  A general bimetric theory of gravitation is described as a linear in the second approximation. This is allowed due to the small experimental significance of the higher order terms. Solar System tests are satisfied. The theory allows black holes, which are physical singularities. The predicted black hole radius is equal to the one resulting from Einstein's theory, if the compatibility between the gauge conditions and the existence of gravitational waves is required (the Rosen-Fock metric). The quadrupolar gravitational radiation formula is regained. 
N. Ionescu-Pallas, M.I. Piso, S. Onofrei