Bars and rings
Galaxies with bars
Galaxies with rings
Bars and rings in the disks of galaxies
The disks of lenticular and spiral galaxies often host a bar, and sometimes one or more rings.
Like spiral arms, the bars and rings are waves of matter, caused by the movement of gas and stars within the disk of a galaxy.
Bars and rings are sporadic in the history of a galaxy, and modify its appearance with the passing of the billion years.