The evolution of a central depression of density in stellar discs of galaxies.

A numerical simulation of a three-dimensional collisionless disk by a large number of particles in the field of a static spherical component (the halo) is presented. It is shown that the density depression disappears after two-to-three rotations of the disk if, in the depression region, the ratio of the spherical to the disk component masses is less than about 0.75. The formation of a central density depression in the disks of some galaxies not having a massive bulge appears to be associated with the presence of a bar-mode structure.