Astronomy II (Astr 1020)
Spring 2008
Prof Richard Ignace
HOMEWORK #4
Notes:
You will need a calculator, a pencil, and a standard scantron.
Each question has one correct answer. Choose the best answer for each. Mark your answer on the scantron.
This homework is due at the beginning of class on March 13. Late homeworks will not be accepted.
1. For a star that is 8 times more massive than the Sun, how will its expected Main Sequence lifetime
compare to the Sun?
a) About 8 times longer
b) About 8 times shorter
c) About the same
d) About 64 times shorter
e) About 64 times longer
2. Massive stars (say, greater than a solar mass) have more fuel to burn than stars like the Sun. Why,
then, do they not live as long?
a) They tend to have more heavy elements, and so they begin fusing Iron more rapidly.
b) That’s not true. The more fuel a star has, the longer it will live.
c) Since massive stars tend to form later, they form with proportionally less Hydrogen.
d) Because of their higher core temperatures, they use up their fuel much more rapidly.
3. Why does the fusion of Iron in the core of a star signal the beginning of a supernova?
a) Because when two iron atoms meet, they will fuse to form radioactive Uranium, effectively making
the stellar core a giant fission bomb.
b) Iron fusion releases a tremendous amount of energy, causing the star to blow itself apart.
c) Iron is a catalyst, causing reactions to take place at an accelerated rate, resulting in an explosive
release of energy.
d) Because by this time the star is so hot, it can’t hold itself together.
e) Iron fusion actually takes away energy from the core, causing it to collapse and then rebound,
resulting in a supernova explosion.
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