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.
They have a chaotic, irregular appearance. Some have bars, but no arms. Sites of active star formation with young stars and luminous gas clouds. Some very old stars are present in globular clusters. Examples of irregular galaxies are the Small Magellanic Cloud and the Large Magellanic Cloud.