Extremal graphs for weights

Given a graph G = (V,E) and α ∈ R, we write wα(G)=∑xyϵEdG(x)αdG(y)α, and study the function wα(m) = max {wα(G): e(G) = m}. Answering a question from Bollobás and Erdös (Graphs of external weights, to appear), we determine wi(m) for every m, and we also give bounds for the case α ≠ 1