Figure 13-28 Barred Spiral Galaxies As with spiral galaxies, Edwin Hubble classified barred spirals according to the tightness of their spiral arms (which correlates with the sizes of their central bulges). (a) SBa galaxies have the most tightly wound spirals and largest central bulges, (b) SBb galaxies have moderately tight spirals and medium-sized central bulges, and (c) SBc galaxies have the least tightly wound spirals and the smallest central bulges.