Concept explainers
(a)
The luminosity at
(a)
Answer to Problem 44QP
The luminosity at
Explanation of Solution
In terms of solar units, the luminosity law is given by,
Here,
Radius in solar units is,
Temperature in solar units is,
Using the expressions for
Conclusion:
Substitute
Therefore, luminosity at
(b)
The luminosity at
(b)
Answer to Problem 44QP
The luminosity at
Explanation of Solution
From (a), the equation for
Conclusion:
Substitute
Therefore, luminosity at
(c)
The luminosity at
(c)
Answer to Problem 44QP
The luminosity at
Explanation of Solution
From (a), the equation for
Conclusion:
Substitute
Therefore, luminosity at
(d)
The luminosity at
(d)
Answer to Problem 44QP
The luminosity at
Explanation of Solution
From (a), the equation for
Conclusion:
Substitute
Therefore, luminosity at
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Chapter 16 Solutions
21st Century Astronomy
- 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.)arrow_forwardIf a T Tauri star is the same temperature as the Sun but is eighteen times more luminous, what is its radius relative to the Sun? (Hint: Use the luminosity-radius-temperature relation: L L = R R 2 T T 4 .) R R =arrow_forward15: A star has a parallax angle of 0.0270 arcseconds and an apparent magnitude of 4.641. What is the distance to this star? Answer: 37 16: What is the absolute magnitude of this star? Answer:1.8 17: Is this star more or less luminous than the Sun? Answer "M" for More luminous or "L" for Less luminous. (HINT: the absolute magnitude of the Sun is 4.8) Answer: M 18: What is the luminosity of this star? (HINT: The luminosity of the Sun is 3.85×1026 W.) Please answer question #18, #15-17 are correct, the photos provide the work for them.arrow_forward
- If the nuclear fusion reaction of converting 4 H → He occurs at an efficiency of 0.7%, and that mass is converted into energy according to the equation E = mc2, then estimate the Main Sequence lifetime of the Sun (spectral type G2) in years if the Sun (⊙) has a surface luminosity L⊙ = 3.839°ø1033 erg. Assume the Sun’s core (10% of the total mass) is converted from H into He. The Sun’s mass is M⊙ = 1.9891 °ø 1033 g.arrow_forwardIf the Sun were replaced by a white dwarf with a surface temperature of 10,000 K and a radius equal to Earth’s, how would its luminosity compare to that of the Sun?arrow_forwardBefore the star that became SN 1987A exploded, it evolved from a red supergiant to a blue supergiant while remaining at the same luminosity. As a red supergiant, its surface temperature would have been approximately 4000 K, while as a blue supergiant, its surface temperature was 16,000 K. How much did the radius change as it evolved from a red to a blue supergiant?arrow_forward
- Why do you think astronomers have suggested three different spectral types (L, T, and Y) for the brown dwarfs instead of M? Why was one not enough?arrow_forwardAppendix J lists the stars that appear brightest in our sky. Are most of these hotter or cooler than the Sun? Can you suggest a reason for the difference between this answer and the answer to the previous question? (Hint: Look at the luminosities.) Is there any tendency for a correlation between temperature and luminosity? Are there exceptions to the correlation?arrow_forwardHow would a white dwarf that formed from a star that had an initial mass of 1 MSunbe different from a white dwarf that formed from a star that had an initial mass of 9 MSun?arrow_forward
- How much would you weigh if you were suddenly transported to the white dwarf Sirius B? You may use your own weight (or if don’t want to own up to what it is, assume you weigh 70 kg or 150 lb). In this case, assume that the companion to Sirius has a mass equal to that of the Sun and a radius equal to that of Earth. Remember Newton’s law of gravity: F=GM1M2/R2 and that your weight is proportional to the force that you feel. What kind of star should you travel to if you want to lose weight (and not gain it)?arrow_forwardWhat physical properties are different for an M giant with a luminosity of 1000 LSunand an M dwarf with a luminosity of 0.5 LSun? What physical properties are the same?arrow_forwardPlasketts binary system consists of two stars that revolve in a circular orbit about a center of mass midway between them. This statement implies that the masses of the two stars are equal (Fig. P11.19). Assume the orbital speed of each star is |v|=220km/s and the orbital period of each is 14.4 days. Find the mass M of each star. (For comparison, the mass of our Sun is 1.99 1030 kg.)arrow_forward
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