What are barred spiral galaxies and normal spiral galaxies?

   Two subsets of spiral galaxies can be found in the universe in approximately equal numbers: barred and normal (unbarred). In barred spirals, a thick band of bright stars lies across the center of the galaxy. An arm emerges from each end of the bar and arches back toward the other end, forming a semi-circle above and below the nucleus. In normal spirals the arms emerge directly from the spherical nucleus. Both barred and normal spiral galaxies exist in numerous forms. In some cases the arms are just thin strands, tightly coiled around a large nucleus. In other cases large arms loosely surround a small nucleus.