Concept explainers
(a)
The lifetime of a star; compare it with given values in Table 12.1.
(a)
Answer to Problem 38QAP
The lifetime of star is
Explanation of Solution
Write the expression for lifetime of a main sequence star.
Here,
The above expression shows that the lifetime of star is inversely proportional to the mass of main-sequence star. Greater the mass of star compared to the Sun is; less would be its lifetime.
Conclusion:
Substitute
Thus, the lifetime of star is
(b)
The lifetime of a star; compare it with given values in Table 12.1.
(b)
Answer to Problem 38QAP
The lifetime of star is
Explanation of Solution
Write the expression for lifetime of a main sequence star.
Here,
The above expression shows that the lifetime of star is inversely proportional to the mass of main-sequence star. Greater the mass of star compared to the Sun is; less would be its lifetime.
Conclusion:
Substitute
Thus, the lifetime of star is
(c)
The lifetime of a star; compare it with given values in Table 12.1.
(c)
Answer to Problem 38QAP
The lifetime of star is
Explanation of Solution
Write the expression for lifetime of a main sequence star.
Here,
The above expression shows that the lifetime of star is inversely proportional to the mass of main-sequence star. Greater the mass of star compared to the Sun is; less would be its lifetime.
Conclusion:
Substitute
Thus, the lifetime of star is
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Chapter 12 Solutions
Understanding Our Universe
- As we have discussed, Sirius B in the Sirius binary system is a white dwarf with MB ∼ 1M , LB ∼ 0.024L ,and rB ∼ 0.0084r . For such a white dwarf, the temperature at the center is estimated to be ∼ 107 K.If Sirius B’s luminosity were due to hydrogen fusion, what is the upper limit of the mass fraction of thehydrogen in such a white dwarf?Step 1: Calculate the observed energy production rate per unit mass (remember luminosity is energy outputper unit time).Step 2: Use the per unit mass energy generation rate of hydrogen fusion (via PP chain) to estimate thepossible hydrogen mass fraction given the condition at the center of the white dwarf.arrow_forward(a) Estimate the Eddington luminosity of a 0.072 M, star and compare your answer to the main-sequence luminosity given in Problem 21. Assume k = 0.001 m² kg¯'. Is radia- tion pressure likely to be significant in the stability of a low-mass main-sequence star? (b) If a 120 Mo star forms with log1o T. = 4.727 and log1o(L/Lo) = 6.252, estimate its Eddington luminosity. Compare your answer with the actual luminosity of the star.arrow_forwardFor the PP chain 0.7% of the mass participating in nuclear fusion is liberated as energy which produces a star's luminosity. Assume that the core of a main sequence star consists of 10% of its total mass. Hence, estimate the lifetime of a star on the main sequence in terms of its luminosity L/L. Give your answer in years. You may use the observed mass-luminosity relation L x M³.5, where M is the star's total mass. Using typical values, calculate estimates for the main sequence lifetime of a KO star and a 05 star. Describe briefly why your estimate might be more accurate for K stars compared to O stars.arrow_forward
- Use t = 1 M2.5 to compute the life expectancy of a 0.8-solar-mass star. (A solar lifetime is approximately 10 billion years.)arrow_forward5.15. We observe a binary system in which the tw stars are 1 and 2 arc sec, respectively, from the center of mass. The system is 10 pc from us. The period is 33 yr. What are the masses of the two stars, assuming that i = 90°?arrow_forwardIf a 1.40 MSun neutron star has a radius of 10.0 km, what is the radius (in km) of a 2.15 MSun neutron star? (Use the mass-radius relationship R ∝ M−1/3) What is the escape velocity (in km/s) from the surface of a 1.5 M neutron star? From a 3.0 M neutron star? (Hint: Use the formula for escape velocity, Ve = 2GM r ; make sure to express quantities in units of meters, kilograms, and seconds. Assume a neutron star has a radius of 11 km and assume the mass of the Sun is 1.99 ✕ 1030 kg.) 1.5 M neutron star km/s3.0 M neutron star km/sarrow_forward
- What is the escape velocity Vesc of a 1.4?⊙ neutron star if its radius is 12 km? Express your answer as a multiple of the speed of light (i.e., compute Vesc/c, where c= 2.9979 x 105 km/s). [Hint: you will need to recall the formula for escape speed from the surface of an object. This was discussed when we covered planetary atmospheres.]arrow_forwardFinally estimate the lifetime of an M0 spectral type star if the total mass of the star is M = 0.51M⊙ , and it has a total luminosity L = 7.7× 10−2L⊙. Make the same assumptions as the previous two problems. How does your calculated Main Sequence lifetime for the M0 type star compare to the Main Sequence lifetime you calculated for the Sun?arrow_forwardA star with spectral type A0 has a surface temperature of 9600 K and a radius of 2.2 RSun. How many times more luminous is this star than the Sun? (if it is less luminous enter a number less than one) This star has a mass of 3.3 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. Compare this to the lifetime of a A0 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.)arrow_forward
- A star with mass m, period Ti = 30 days, and radius ri = 1E4 km collapses into a neutron star (Links to an external site.) with a radius of rf = 3 km. Our goal will be to determine the period Tf of the neutron star. Useful formulae: Li=Lf; L=Iω; ω=2πf=2π/T; Isphere=2/5mr^2. 1.How much angular momentum Li does the star have before it collapses? 2. What is the rotation rate ωi of the star before collapsing? 3. Suppose we model the star as a solid sphere of radius ri with moment of inertia 2/5mri2 (a good assumption). What does our description of Li read now? 4.How much angular momentum Lf does the star have after it collapses? 5. What is the rotation rate ωf of the star after collapsing? 6.The new object, a neutron star, is also shaped like a sphere. What does Lf read? Group of answer choices 7.Assuming angular momentum is conserved during collapse (also a good assumption), what is our prediction for the period of the neutron star, Tf? 8. What is Tf in units of days? 9. What…arrow_forwardwhat is the answer for sub-item (b) if the radius of the neutron star is 6.676 km? (express your answer in the proper SI unit and without scientific notation) (b)What is the average density of a neuron star that has the same mass as the sun but a radius of only 20.0 km?arrow_forward= A star population is composed of stars with masses in the range between 1M and 150M. The initial mass function is = 0 (M/M)-2.3, where o (Mo). The luminosity of a star = (M/M) 3.3. Calculate the percentage of the total luminosity of the stars in the population which is produced by stars with mass between 120M and 150M. scales with its mass as L/Larrow_forward
- Stars and Galaxies (MindTap Course List)PhysicsISBN:9781337399944Author:Michael A. SeedsPublisher:Cengage Learning