Universe
11th Edition
ISBN: 9781319039448
Author: Robert Geller, Roger Freedman, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 19, Problem 6CC
To determine
The safety valve for the main-sequence star’s nuclear reactions and the reason for its absence in the red giant in which the core is supported by degenerate-electron pressure.
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A red giant that was originally a 9.5MSun main-sequence star loses a solar mass in 100,000 years via a superwind. What is this mass loss rate in units of solar masses per year? (the answer is not 0.000095 solar masses per year).
Additionally, at this mass loss rate, what will the red giant's mass be after 0.5 million years? (Enter your answer as a multiple of MSun.)
Use
t =
1
M2.5
to compute the life expectancy of a 0.6-solar-mass star. (A solar lifetime is approximately 10 billion years.) yrWhy might this be an underestimate if the star is fully mixed by convection?
a) If the star is fully mixed its mass will be much larger than 0.6 solar masses.
b) If the star is fully mixed its mass will be much smaller than 0.6 solar masses.
c) If the star is fully mixed it will be able to use a larger portion of its hydrogen in fusion than the Sun.
d) If the star is fully mixed it will be able to use a smaller portion of its hydrogen in fusion than the Sun.
A main sequence star of mass 25 M⊙has a luminosity of approximately 80,000 L⊙. a. At what rate DOES MASS VANISH as H is fused to He in the star’s core? Note: When we say “mass vanish '' what we really mean is “gets converted into energy and leaves the star as light”. Note: approximate answer: 3.55 E14 kg/s b. At what rate is H converted into He? To do this you need to take into account that for every kg of hydrogen burned, only 0.7% gets converted into energy while the rest turns into helium. Approximate answer = 5E16 kg/s c. Assuming that only the 10% of the star’s mass in the central regions will get hot enough for fusion, calculate the main sequence lifetime of the star. Put your answer in years, and compare it to the lifetime of the Sun. It should be much, much shorter. Approximate answer: 30 million years.
Chapter 19 Solutions
Universe
Ch. 19 - Prob. 1CCCh. 19 - Prob. 2CCCh. 19 - Prob. 3CCCh. 19 - Prob. 4CCCh. 19 - Prob. 5CCCh. 19 - Prob. 6CCCh. 19 - Prob. 7CCCh. 19 - Prob. 8CCCh. 19 - Prob. 9CCCh. 19 - Prob. 10CC
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