Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 20, Problem 21Q
To determine
To define nuclear density and to explain the reason of its significance when a star’s core reaches this density.
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Students have asked these similar questions
The evolutionary track of a medium mass star is shown below. Which cut-away core diagram correctly illustrates the source
of fusion energy when the star is at the indicated position?
(A) H>He
(B)
He>C
(C)
(D)
H>He
H>He
He>C
Не
Temperature
А. (А)
В. (В)
C. (C)
D.(D)
Luminosity -
Using solar units, we find that a star has 4 times the luminosity of the Sun, a mass 1.25 times the mass of the Sun, and a surface temperature of 4090 K (take the Sun's surface temperature to be 5784 K for the sake of this problem). This means the star has a radius of.................... solar radii and is a .................... star (use the classification).
For a main sequence star with luminosity L, how many kilograms of hydrogen is being converted into helium per second? Use the formula that you derive to estimate the mass of hydrogen atoms that are converted into helium in the interior of the sun (LSun = 3.9 x 1026 W).
(Note: the mass of a hydrogen atom is 1 mproton and the mass of a helium atom is 3.97 mproton. You need four hydrogen nuclei to form one helium nucleus.)
Chapter 20 Solutions
Universe: Stars And Galaxies
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- The text says a star does not change its mass very much during the course of its main-sequence lifetime. While it is on the main sequence, a star converts about 10% of the hydrogen initially present into helium (remember it’s only the core of the star that is hot enough for fusion). Look in earlier chapters to find out what percentage of the hydrogen mass involved in fusion is lost because it is converted to energy. By how much does the mass of the whole star change as a result of fusion? Were we correct to say that the mass of a star does not change significantly while it is on the main sequence?arrow_forwardDescribe the evolution of a star with a mass similar to that of the Sun, from the protostar stage to the time it first becomes a red giant. Give the description in words and then sketch the evolution on an HR diagram.arrow_forwardHow do the two types of supernovae discussed in this chapter differ? What kind of star gives rise to each type?arrow_forward
- What is fusion? How does it happen inside a star?arrow_forwardObservations show that stellar luminosity, L, and mass, M, are related by L x M3.5 for main sequence stars. Obtain an expression that relates the main sequence life time and the mass of a star. You should assume that the luminosity is constant throughout a star's main sequence life time, and that the amount of mass converted into energy by a star while it is on the main sequence is given by AM main sequence life time of a 20 Solar mass star given that the Sun is expected to spend 1010 years on the main sequence. Comment on the significance of your answer. fM, where f is a constant. Estimate thearrow_forwardWhich of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, etc.) in a high- mass star is not true? A. As each stage ends, the core shrinks and heats further. B. Each successive stage creates an element with a higher atomic number and atomic mass number. C. As each stage ends, the reactions that occurred in previous stages continue in shells around the core. D.Each successive stage lasts for approximately the same amount of time.arrow_forward
- How can we know that the sun will “die” in about 5 billion years? Choose the correct answer. A. We can see the evolution and death in the spectra B. We can see the entire process as it plays out in a star C. We look at thousands of stars like the sun and can see them in all stages of developmentarrow_forwardThe mass-luminosity relation describes the mathematical relationship between luminosity and mass for main sequence stars. It describes how a star with a mass of 4 M⊙ would have a luminosity of ______ L⊙. If a star has a radius 1/2 that of the Sun and a temperature 4 that of the Sun, how many times higher is the star's luminosity than that of the Sun? (If it is smaller by a factor of 8, you would write 0.125 because 1/8=0.125) If a star has a radius 2 times larger than the Sun's and a luminosity 1/4th that of the Sun, how many times higher is the star's temperature than that of the Sun? (If it is smaller by a factor of 8, you would write 0.125 because 1/8=0.125) If a star has a surface temperature 2 times lower than the Sun's and a luminosity the same as the Sun, how many times larger is the star than the Sun? (If it is smaller by a factor of 8, you would write 0.125 because 1/8=0.125)arrow_forwardWhy is it that we can describe the life cycle of a star and be confident about it?arrow_forward
- This star has a mass of 3.3 MSun. What is the main sequence lifetime of this star? You may assume that the lifetime of the sun is 1010 yr. Hint: The simple relation is that lifetime is proportional to mass divided by luminosity. If you use these quantities in solar masses and solar luminosities, then this relation tells you how many times longer than the Sun the star will live.arrow_forwardQUESTION 16 Use the figure shown below to complete the following statement: A low-mass protostar (0.5 to 8M the mass compared to our sun) remains roughly constant in decreases in until it makes a turn towards the main sequence, as it follows its evolutionary track. Protostars of different masses follow diferent paths on their way to the main sequence. 107 Luminosity (L) 10 105 10 107 10² 101 1 10-1 10-2 10-3 Spectral type 0.01 R 0.001 Re 60 M MAIN SEQUENCE 40,000 30,000 20 Mau 10 Mgun 5 Mun 0.1 Run Ren radius; temperature luminosity; radius 3 Min. 05 BO temperature; luminosity Oluminosity: temperature radius: luminosity 1 M 10,000 6000 Surlace temperature (K) 1,000 Rs 2 M STAR L 0.8 M B5 AO FOGO КБ МБ -10 +10 3000 Absolute visual magnitude andarrow_forwardA Crude Analysis: In about 5 billion years, the Sun is going to look a lot different. Our sun is going to turn into a red-giant, a bigger star whose core temperature is much higher than the Sun's current core temperature (you will learn about the red giants in the coming weeks). Assume the core temperature of the red-giant phase of the Sun does not go beyond 100 million degrees. Do you think the temperature is high enough for helium fusion to occur? Note that this question is about helium fusion not hydrogen fusion. How are you going about proving your claim? Question: What temperature in degrees Kelvin must the red-giant sun be at to allow for the helium-helium interactions to take place not considering the Quantum Mechanical effects (i.e. what temperature would allow helium atoms to breach the helium-helium potential wall without help from Quantum Mechanics)? Use wolfram alpha to find the values for the constants. Round your answer to two decimal places. Your answer i [ Select ] 1.47…arrow_forward
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