8. What is a galaxy?

8.1 Why is it important to understand our galaxy, the Milky Way?

8.2 The shape of the Milky Way

8.2.1 Why was it difficult to determine the shape?

8.2.2 How was the shape finally measured? What were the roles of Shapley and Leavitt? What is a standard candle?

8.3. Other galaxies

8.3.1 Why wasn’t it obvious that there are other galaxies?

8.3.2 Why was it an important question?

8.3.3 How was the question settled? Roles of Curtis, Hubble, and advances in technology

8.3.4 How are distances to galaxies measured?

8.3.4.1 What is the Local Group?

8.3.4.2. What is the galaxy distance ladder? What are the most critical steps on the ladder?

8.3.5.  The interstellar medium

8.3.5.1   How it was discovered

8.3.5.2   Types of nebula

8.3.6. Dark Matter

8.3.6.1 Why do we think spiral galaxies contain a lot of dark matter?

8.3.6.1.1 Where is it within the galaxy?

8.3.6.1.2 What is the dark matter thought to be?

8.3.7  Distribution of galaxies in space

8.3.7.1 What are groups, clusters?

8.3.7.2 What is the overall large scale distribution of galaxies like? How does it relate to galaxy formation?

8.3.7.3 What is gravitational lensing? How does it work? What can we learn from it?

9. Galaxy Characteristics

9.1 Galaxy types

9.1.1  What are the three main types of galaxies?

9.1.2 What parts of a spiral galaxy are seen at different wavelengths?

9.1.3 How are the most distant galaxies different from nearby ones? Why?

9.2 What type of galaxy is the Milky Way?

9.2.1 What is the Milky Way like? – shape, major parts

9.2.2 What are the stellar populations, and what do they tell us about the Milky Way?

9.2.3 How did the Milky Way form? What is the evidence? What gives it its current appearance (e.g., disk, halo, spiral arms)?

9.3 The center of the Milky Way

9.3.1 Why is it important?

9.3.2 What accounts for most of the energy from the Galactic Center?

9.3.3 Why do we believe there is a supermassive black hole there?

9.4 Active Galactic Nuclei

9.4.1 What powers an active galaxy nucleus (AGN)?

9.4.2 What are the observed consequences from an AGN?

9.4.2.1 Strange emission line properties

9.4.2.2 X-ray, radio emission

9.4.2.3 Variability – and what it means

9.4.2.4 Jets, what they are

9.4.2.5 Faster-than-light motions – what causes them

9.4.3 What is a quasar? How were they discovered?

9.4.4 Why are AGNs important?

10. Star formation

10.1   Star formation

10.1.1 Stages of collapse into a protostar

10.1.2   Evolution of a protostar onto the main sequence

10.1.2.1 For objects of stellar mass

10.1.2.2 Masses above or below the stellar range

10.2 Spiral arms in galaxies

10.2.1 What marks spiral arms to make them bright?

10.2.2 How do they form?

10.2.2.1 Density wave theory

10.2.2.2 Sequential star formation

10.3 Mergers and starbursts

10.3.1 Do galaxies collide? What happens to them when they do?

10.3.2 What is a starburst?

10.3.3 How do the stars in a galaxy and its central black hole appear to be linked?