QUIZ - 4.9.13

1. How do we measure stellar masses?

• We measure stellar masses by using Newton's version of Kepler's third law. This law tells us that total mass of a binary system, if we can measure the orbital period (p) and average orbital separation of the system (a). 

2. What are giants, supergiants, and white dwarfs?

• All stars become larger and redder after core hydrogen is exhausted: giants and supergiants. Most stars end up as tiny white dwarfs after fusion has ceased.

3. What are the two types of star clusters?

• Two types of star clusters would be open clusters and globular clusters. Open clusters are loosely packed and contain up to a few thousand stars. Globular clusters are densely packed and contain hundreds of thousands of stars.  

4. How do we measure the age of a star cluster?

• A star cluster's age roughly equlas the life expectancy of its most massive stars still on the main sequence. 

5. Do we know any star cluster 14 billion years old, or older?

• YES, all of the stars in a globular cluster formed at roughly the same time, thus they can serve as cosmic clocks. The oldest globular clusters contain only stars less massive than 0.7 solar masses. These low mass stars are much dimmer than the Sun. This observation suggests that the oldest globular clusters are between 11 and 18 billion years old. The uncertainty in this estimate is due to the difficulty in determining the exact distance to a globular cluster (hence, an uncertainty in the brightness (and mass) of the stars in the cluster). Another source of uncertainty in this estimate lies in our ignorance of some of the finer details of stellar evolution. Presumably, the universe itself is at least as old as the oldest globular clusters that reside in it.

6. Which star has a longer life, small mass star, or big mass star?

• A star's life cycle is determined by its mass. The larger its mass, the shorter its life cycle. Therefore, a small mass star has a longer life.

7. Which star is hotter, small mass star, or big mass star?

• The big mass star is hotter.

8. Which star is bluer, small mass star, or big mass star?

• The big mass star is bluer.

9. Which star is closer, the Sun, or Proxima Centaurus?

• The Sun is the closest star to us.

10. What is the age of the Universe?

• The Universe is estimated to be between 12 to 14 Billion years old.