13.0 Learning Objectives

In this chapter, students will learn how to:

• Identify the major techniques used by astronomers to study galaxy evolution and cosmic time, including the use of telescopes, spectra analysis, and look-back time calculations.
• Explain the concept of a “cosmic time machine” and how it enables astronomers to observe galaxies as they were billions of years ago, allowing the reconstruction of galactic evolution over time.
• Apply the knowledge of galaxy collisions and mergers to understand the formation of elliptical and spiral galaxies, and how collisions can trigger starbursts and intense star formation.
• Analyze the differences between galaxy collisions and star collisions, explaining why galaxies can collide while stars within a galaxy rarely do.
• Explain the evidence for the presence of a supermassive black hole at the center of our Galaxy, including the observations of stars’ orbits and the compact radio source Sagittarius A*.
• Explain the difference between quasars and stars in terms of their energy sources, and how the presence of supermassive black holes can account for the observed properties of quasars and AGNs.