There are no constraints in this graph. This is what happens if you use CoLa as a drop-in replacement for D3 Force layout. You should notice that compared to D3 Force layout, CoLa has much nicer convergence properties. That is, it glides smoothly to a local minimum in the layout objective function with no "jitter".
To be precise, it monotonically reduces the "stress" of the layout. The improved stability is also noticable when you drag nodes around interactively.