Counter-rotating bars within bars
  The dynamical stability and evolution of disc galaxies with different disc thickness as well as various fraction and concentration of stellar counter-rotation is investigated with self-consistent numerical simulations. In particular, systems of nested, counter-rotating, stable bars are presented. As for the direct case, the nuclear secondary bar rotates faster than the primary bar. Contrary to the direct case, the presence of significant amount of gas is not necessary to produce such system. Observed bars within bars in lenticular (i.e. gas-poor) galaxies could thus be explained by counter-rotating bars. This hypothesis can easily be tested since the retrograde case produces distinct kinematical signatures from the direct one. Moreover, the best morphological similarities between numerical models and typical SB0's are found in the models with significant amount of stellar nuclear counter-rotation. 
D. Friedli