Short Questions about Galaxies

  1. (a) What is the Astronomy definition of "metals"?
    (b) What does the fraction of metals observed in a star tell you about the gas that the star formed from?
    Assume that the amount of each element in the outer parts of a star is the same as in the cloud of gas from which it formed.

  2. Describe two differences between the two major populations of stars (labelled Population I and Population II) in terms of properties of the stars or where they are found. (Aside from the difference in the fraction of metals in the stars).

  3. Why must the star responsible for an HII region be a hot star rather than a cool star?

  4. Why wouldn't you expect to detect strong 21 cm emission from an HII region?

  5. How does the diffuse light in the galaxy compare to the average color of bright stars in the galaxy?

  6. If the distribution of globular clusters was even in all directions, as viewed from Earth, whaere would the Sun be in the Galaxy?

  7. What is the evidence that most of the mass in our Galaxy lies in some as-yet-undetected form?

  8. Why are young stars mostly found in the disk of our Galaxy?

  9. Describe the density wave theory of spiral arms.

  10. Briefly characterize the three major types of galaxies according to the Hubble system of classification:
    (Treat barred and unbarred galaxies as one type).
    (a) In terms of the shape of the Galaxies.
    (b) In terms of what they contain in gas and stars.

  11. What is it in clusters of galaxies that produces the X-rays we observe coming from the clusters?

  12. Describe what we think is the fundamental power source for Quasars.

  13. We believe galaxies we see close to us might be different to galaxies we see very far away. The galaxies far away were a lot younger when the light we see coming from them was made.

    a) Explain how you might expect the young age of distant galaxies to make them appear different to the old ones near us.

    b) Describe how the rapid movement of distant galaxies away from us due to the expansion of the universe makes them appear different.

  14. Supernova type Ia (caused by exploding white dwarfs) are used as standard candles to measure the distance to far galaxies. Briefly describe how this works.