Buchdahl compactness limit and gravitational field energy

The main aim of this paper is essentially to point out that the Buchdahl compactness limit of a static object is given by gravitational field energy being less than or equal to half of its non-gravitational matter energy. It is thus entirely determined without any reference to interior distribution by the unique exterior solutions, the Schwarzschild for neutral and the Reissner-Nordstrom for charged object. In terms of surface potential, it reads as Phi(R) = (M - Q(2)/2R)/R <= 4/9 which translates to surface red-shift being less than or equal to 3. It also prescribes an upper bound on charge an object could have, Q(2)/M-2 <= 9/8 > 1.