I follow a bar from its formation, via its evolution, to its destruction and,
perhaps, regeneration. I discuss the main features at each stage and
particularly the role of the halo. Bars can form even in sub-maximum discs. In
fact, such bars can be stronger than bars which have grown in maximum discs.
This is due to the response of the halo and, in particular, to the exchange of
energy and angular momentum between the disc particles constituting the bar and
the halo particles at resonance with it. The bar slowdown depends on the
initial central concentration of the halo and the initial value of the disc Q.
Contrary to the halo mass distribution, the disc changes its radial density
profile considerably during the evolution. Applying the Sackett criterion, I
thus find that discs become maximum in many simulations in which they have
started off as sub-maximum. I briefly discuss the evolution if a gaseous
component is present, as well as the destruction and regeneration of bars.Comment: 12 pages, 8 figures, includes gh2001-asp.sty, invited review paper
for the 4th Guillermo Haro conference on "Disks of Galaxies: Kinematics,
Dynamics and Perturbations" at Puebla, Mexico, ASP Conf. Series 275, eds. E.
Athanassoula, A. Bosma & R. Mujic