Astronomy 102, Fall 2004
Homework Assignment #8
This homework set is due at the beginning of class on Friday, November 19. It must be turned in by 9:10AM that day. Late homework will not be accepted. This is includes your being late to class!
Staple. If you have more than one page, staple them together; do not just fold the corner. If you have multiple pages and do not staple, I will deduct one point from your score..
The first three problems are required. The remaining problems are optional, and will not be graded; they are here as additional review problems for you. After the homework has been graded, solutions will be posted to all problems.
Please write out the problem statement at the top of your solution. (This is for two reasons; it is so I can know which problems you answered, and that you answered the right problem from the bit. It also will make your graded homework more useful as a study aid later.)
You may consult with other students (as well as with the TAs and professor) on this homework set. However, your final answer should be your own. Do not write down an answer you don't understand, and do not "dictate" an answer to somebody else.
(a)A core-collapse supernova happens in our Galaxy about once every 100 years. Approximately how many neutron stars should there be in our galaxy?
(b)Should the number of white dwarves in our galaxy be much greater, greater, similar, or smaller than the number of neutron stars? Explain.
A supernova typically releases something like 1044 Joules of energy. That's a lot; it's similar to the total energy that the Sun will emit throughout its lifetime.
- (a) In a core-collapse (type II) supernova, where does all of this energy come from?
- (b) In a thermonuclear (type Ia) supernova, where does all of this energy come from?
- Optional, 1-point extra credit: Do the calculations (based on numbers and equations you know from lecture and other material in this course) to show that roughly the right amount of energy is released for each of the mechanisms you identified in (a) and (b).
A cluster of stars formed sometime in the past somewhere in our Galaxy. Typically, when clusters form, the number of stars that form with each mass (i.e. how many 20Msun stars, how many 1Msun stars, how many 0.5Msun stars, etc.) is the same as what is found in young stellar populations anywhere in our galaxy.
Stars spend about 10% of their life as giants.
If you find and look at all the stars in this cluster now, what fraction of the stars do you think will be red giants? (I.e. much more than 10%, more than 10%, about 10%, less than 10%, much less than 10%.) Explain.
The problem below is optional; it need not be turned in, and it will not be graded.
When you look at a globular cluster through a small telescope with your eye, the individual stars you can see are largely red giants.
- (a) Why is this so?
- (b) Why aren't you seeing any high-luminosity massive main sequence stars?
- (c) Is what you are seeing representative of the population of stars in the globular cluster? Why or why not?