Damping of the Milky Way bar by manifold-driven spirals
  We describe a new phenomenon of `bar damping' that may have played an
important role in shaping the Milky Way bar and bulge as well as its spiral
structure. We use a collisionless N-body simulation of a Milky Way-like galaxy
initially composed of a dark matter halo and an exponential disk with Toomre
parameter slightly above unity. In this configuration, dominated by the disk in
the center, a bar forms relatively quickly, after 1 Gyr of evolution. This is
immediately followed by the formation of two manifold-driven spiral arms and
the outflow of stars that modifies the potential in the vicinity of the bar,
apparently shifting the position of the L_1/L_2 Lagrange points. This
modification leads to the shortening of the bar and the creation of a next
generation of manifold-driven spiral arms at a smaller radius. The process
repeats itself a few times over the next 0.5 Gyr resulting in further
substantial weakening and shortening of the bar. The time when the damping
comes to an end coincides with the first buckling episode in the bar which
rebuilds the orbital structure so that no more new spiral arms are formed. The
morphology of the bar and the spiral structure at this time show remarkable
similarity to the present properties of the Milky Way. Later on, the bar starts
to grow rather steadily again, weakened only by subsequent buckling episodes
occurring at more distant parts of the disk.
