Study Plan
Just as stars vary based on their mass or on their stage of evolution, galaxies also come in many forms. After realizing that galaxies are huge collections of stars and dust, astronomers have found ways to classify these galaxies into various types and make sense of the differences among them. By the end of this chapter you should be able to:
- Classify galaxies according to the basic types on the Hubble tuning fork diagram
- Determine a galaxy's type, given information about the orbits of the stars it contains.
- Explain why the arms of spiral galaxies, which form whenever the disk of a spiral galaxy is disturbed, are sites of star formation
- Describe the known properties of dark matter and the evidence for its existence
- Explain the evidence that shows that most, perhaps all, large galaxies have supermassive black holes at their centers
- Describe the unified model of active galactic nuclei and how the direction of view explains the different observations of these objects
- Describe the grouping of galaxies and the large scale structure of our Universe, beginning with the Local Group and proceeding through the hierarchy galaxy clusters to superclusters