  We propose a new dynamical mechanism to account for the bar off-centering
observed in many barred galaxies. It is based on the presence of a m=1 density
wave, non-linearly excited by the strong m=2 component due to the linearly
unstable bar and by a m=3 mode. N-body simulations suggest that this mechanism
is at work in the centers of galaxies, and provide a natural explanation by
spontaneously producing bar off-centering which amounts to several tens of
parsecs.
