Spiral galaxies are flat disks with a nuclear bulge, a halo of old stars, and spiral arms with young stars. Arms emerge fromt he ends of the bar. Dust is readily visible as dark streaks . The Milky Way galaxy is a spiral galaxy. Globular clusters encircle spiral galaxies.
Old stars are dominant.
There is no prominent internal structure. They are circled by a halo of globular clusters. Little or no gas and dust are present. Almost all has been converted into stars. Irregular galaxies are ot disk-like or spheroidal and have no nucleus.