Three Types of Galaxies

Irregular galaxies are more related to spirals, because of the presence of disks and bulges some of its parts. Unless a galaxy is perfectly spherical, it will have a different appearance according to the direction from which we observe it. All spiral galaxy labels begin with the prefix "S", and usually is followed by a lower case letter, which describes the "style" or overall appearance of the particular object. The class of spiral type Sa has very tightly wound spiral arms, and large central nuclei. Small red patches found in this class are glowing clouds of gas and dust, heated by nearby stars to form nebulae, and in some of these, stars are being formed, like they are in our own galaxy (The Milky Way). These galaxies some times can be regarded as "primitive". Astronomers predict that they will eventually collide with the Milky Way and be incorporated into our own galaxy. The next class of spiral, Sb, has bright central regions that contain most of the galaxy's young stars, so regions further from the middle hold the older objects. They have very small amounts of "heavy" elements (elements more dense than helium). These galaxies also have a lot of dust and gas. Some have cores that emit a lot of the radio waves of the light spectrum, and using instruments like the Hubble Space Telescope show that this is correct and that they have a central region that is powered by material such as stars and gas falling into a black hole. These are often referred to as the "Grand Design". Excluding that, the similarity ends, since the disks of irregular galaxies don't show a sign of the spiral structure, and the bulges are not even located at the center. It's likely that Irregular galaxies have been distorted by collisions with other galaxies at some time in their history. Most of spiral galaxies are "b" type spirals.