2. Explain the different mechanisms that power the internal heating of a giant star, a main sequence star, a giant planet, a terrestrial planet, and a moon.

List the following 5 terms in order through a stars life cycle (starting with the sun), through the remainder of its lifetime: a. Black dwarf b. Planetary nebula c. Red giant d. Star (Sun) e. White dwarf

12. A star with spectral type MO has a surface temperature of 3750 K and a radius of 0.63 Rsun: How many times more luminous is this star than the Sun? (if it is less luminous enter a number less than one) Answer: Submit All Answers Last Answer: 0.0923 Incorrect, tries 1/5. Hint: Use the Luminosity equation, which says that L is proportional to R^2 T^4. If you keep these as ratios compared to the sun, your L will also come out as a ratio compared to the Sun. This star has a mass of 0.4 Msun- Using the simple approximation that we made in class, what is the main sequence lifetime of this star? You may assume that the lifetime of the sun is 1010 yr. Answer: Submit All Answers Compare this to the lifetime of a MO star listed in Table 22.1 (computed using a more sophisticated approach). Is the value you calculated in the previous problem longer or shorter than what is reported in the table? (L for longer, S for shorter) (You only get one try at this problem.) Answer: Submit All Answers

What is the lifetime of a 10-solar-mass star on the main sequence?   a. 3.2 × 107 years   b. 320 years   c. 3.2 × 1012 years   d. 1 × 109 years   e. 1 × 1011 years

A star such as our Sun will eventually evolve to a “red giant” star and then to a “white dwarf” star. A typical white dwarf is approximately the size of Earth, and its surface temperature is about 2.4 × 104 K. A typical red giant has a surface temperature of 3.2 × 103 K and a radius ~90000 times larger than that of a white dwarf. Take the radius of the red giant to be 6 × 1010 m.  What is the average radiated power per unit area of the red giant?_________W/m2 What is the average radiated power per unit area of the white-dwarf?________W/m2 What is the total power radiated by the red giant? _________W What is the total power radiated by the white dwarf? ________W     Please show full work!   Thank you!

Which of the following binary star systems cannot exist? A. A 1 solar-mass main sequence star and a 4 solar mass red giant with a size 100 times smaller than the orbital distance. B. A 15 solar-mass main sequence star and a 10 solar mass red giant with a size 100 times smaller than the orbital distance. C. A 1 solar-mass main sequence star and a 4 solar-mass main sequence star. D. A 2 solar-mass main sequence star and a 1 solar mass red giant with a size a few times smaller than the orbital distance.