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 \it{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 exterior unique solutions, the Schwarzschild for neutral and the Reissner-Nordstr{$\ddot{o}$}m for charged object. In terms of surface potential, it reads as $\mathrm{\Phi }(R)=(M-Q^2\mathrm{/}2R)\mathrm{/}R\le 4\mathrm{/}9$ 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, $Q^2\mathrm{/}{M}^2\le 9\mathrm{/}8>1$.