1. The visible disk of the Galaxy is about 100,000 light-years in diameter and 2000 light-years thick. If about five supernovae explode in the Galaxy each century, how often on the average would you...

1. The visible disk of the Galaxy is about 100,000 light-years in diameter and 2000 light-years thick. If about five supernovae explode in the Galaxy each century, how often on the average would you expect to see a supernova within 1000 light-years of the Sun?

2. Give reasons for the rapid rise in the Galaxy’s rotation curve (see Figure 15-18) at distances close to the galactic center.

Figure 15-18