Secular evolution of Milky Way-type galaxies
  The internal evolution of disk galaxies like the Milky Way are driven by
non-axisymmetries (bars) and the implied angular momentum transfer of the
matter; baryons are essentially driven inwards to build a more concentrated
disk. This mass concentration may lead to the decoupling of a secondary bar,
since the orbit precessing frequency is then much enhanced. Vertical resonances
with the bar will form a box/peanut bulge in a Gyr time-scale. Gas flows due to
gravity torques can lead to a young nuclear disk forming stars, revealed by a
sigma-drop in velocity dispersion. These gas flows moderated by feedback
produce intermittent accretion of the super-massive black hole, and cycles of
AGN activity. The fountain effect due to nuclear star formation may lead to
inclined, and even polar nuclear disks.
