Astronomy 10Spring 2000

Homework #6

Due in one week.

Be careful of units and use appropriate precision. Be sure to explain your reasoning on each problem, so you can get partial credit for your work. Answers without explanations are not acceptable. You are encouraged to work together, but please write this up yourself.

1) If it took a terawatt of power (1012 watts) to keep the Enterprise running at warp speed, how much antimatter would be used up per second? Compare this power output to the luminosity of the Sun. (Notes: to produce a power of 1 watt requires using 1 joule every second. The formula E=mc2 yields joules if the mass is in kilograms and the speed of light is in m/s. The warp engines supposedly work by combining equal amounts of matter as antimatter for power.)

2) Examine the analysis of the Sun's lifetime in the book (p. 395). Now estimate the lifetime (in years) for a star with 0.1 solar masses, which shines with 10-4 solar luminosities. Don't forget that such stars are fully convective, so they can mix all their fuel into the core. Which star would this one be on the HR diagram below?

3) Compare the life of a 20 solar mass star to the life of the Sun. Point out the main similarities and the main differences. When something is different, give a short explanation as to why. Cover the physical appearance and internal structure of each, at each phase of evolution, and the timescales involved. We are not looking for a regurgitation of details you find in the book; this should be a short "executive summary".

4)In the HR diagram below, identify which stars best satisfy these descriptions: 

(you can use a star more than once, or not at all) 

a) the hottest 

b) the coolest 

c) the lowest mass 

d) the highest mass 

e) the biggest 

f) the smallest 

g) main sequence star like the Sun 

h) a red giant 

 

 

 

 

 

 

 

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