Chapter 18: Galaxies

Study Plan

As humans it is difficult for us to comprehend the scale of even a single star such as our Sun; yet there are as many stars in the universe as there are grains of sand on all the world's beaches. Stars are not spread uniformly through space, but are instead grouped into what Kant referred to as "island universes" and what we refer to today as "galaxies." As we look beyond stars to the galaxies of which they are a part, we will find that

  • Galaxies are classified into different morphological types that are given their shapes by the properties of the orbits of the stars they contain.
  • The arms of spiral galaxies, which form whenever the disk of a spiral galaxy is disturbed, are sites of star formation.
  • Stars and gas account for only a small fraction of the mass of a galaxy; galaxies are mostly composed of an unknown form of "dark matter." Most, and perhaps all, large galaxies have supermassive black holes at their centers.
  • When these supermassive black holes are fed, as during encounters between galaxies, they may blaze forth with the light of thousands of normal galaxies coming from an active galactic nucleus no larger than our own Solar System.

Organize

  1. Read Chapter 18 in your textbook or ebook.
  2. Take the Diagnostic Quiz to assess your understanding of the basic concepts and identify gaps in your understanding of the assigned reading.

Learn

  1. Use the FlashCards to test your memory for new terms.
  2. Review Excursions Box 18.1 on Quasars—When Conventional Thinking Failed.
  3. If your instructor has assigned SmartWork online homework, login from the right navigation pane for additional practice and review.

Connect

  1. Periodic Connections boxes and the Seeing the Forest through the Trees section at the chapter's end draw your attention to recurring themes and help prepare you for concepts explored more fully in subsequent chapters.
  2. Visit Astronomy in the News for breaking news of new discoveries and the opportunity to apply what you've learned in this chapter to real-world (and real Universe) events.


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Organize

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