ASTRO-110 Chapter Notes - Chapter 8: Elliptical Galaxy, Spiral Galaxy, Irregular Galaxy
Document Summary
We se galaxies at different stages of their evolution by looking at various look back times. Close to us are old, the farther back you look, the older the star/galaxy. Spiral galaxies are most common outside of galaxy clusters, and elliptical galaxies are most common within galaxy clusters irregular galaxies were much more common in the past. We see galaxies colliding with other galaxies the oldest stars formed before a galaxy has fully coalesced, creating a population of stars in random orbits. These are population i stars and these disk stars orbit around the galaxy in a common direction. Elliptical galaxies have little to no dust and gas and contain only population ii stars. At least three ways we can see that elliptical galaxies can be formed instead of spiral galaxies: if the material in the protogalactic cloud has little angular momentum, it might never have a disk.
