Equation of non-relativistic "heavy" gravitational field

The Einstein's postulate is discussed that the gravitational field energy itself is the source of the gravitational field. However, Einstein provided his gravitational field equation with the covariance by excluding (from the equation) the gravitational field as the source of the gravitational field. This article explores how an additional gravitational field caused by itself would change the gravitation law in the Newtonian approximation. The new equation acquired features inherent in the relativistic theory of gravity. The acceleration of gravity approached the corresponding dependence of the Schwarzschild solution. A singularity similar to the Schwarzschild singularity appeared.