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 (sixth Edition)
- The center star in the head of the asterism Scorpius is Dschubba. Assume that Dschubba is a spherical blackbody with a surface temperature of 28,000 K and a radius of 5.16 × 109m, located at a distance of 123 parsecs from Earth. Determine the following for Dschubba:(a) luminosity relative to the Sun (note that L = 3.83 × 1026W ).(b) absolute bolometric magnitude (note that M = 4.74).(c) apparent bolometric magnitude.(d) radiant flux at the star’s surface (in SI unit).(e) radiant flux at Earth’s surface (in SI unit).(f) peak wavelength λmax when plotting the plank function against wavelength (in nm)arrow_forwardUsing 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).arrow_forwardA star population is composed of stars with masses in the range between 1M and 150M. The initial mass function is = (M/M)-2.3, where = (Mo). The luminosity of a star scales with its mass as L/L = (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.arrow_forward
- A star has a period of P = 37 days. It has a radius of 5.7 times the radius of the sun. Calculate it's equatorial speed Vrot. Answer: Okm/s Om/s Check A star has a radius of 5.7 times the radius of the sun and a mass of 18 times the mass of the sun. It rotates at 0.7 of the critical speed W, the speed at which it's surface at the equator is actually in orbit. Recall Vrot is calculated at the equator and W= Vrot/Vorb Calculate it's period P. Answer: Odays Ohours Oseconds Checkarrow_forwardIf a neutron Star has a radius of 12 km and a temperature of 8.0 x 10^6 K, how luminous is it? Express your answer in watts and also in solar luminosity units. (Hint: Use the relation L/L= (R/R)^2(T/T)^4 . Use 5,800 K for the surface temperature of the Sun. The luminosity of the sun is 3.83 x 10^26W) luminosity in watts ________ W luminosity in solar luminosity units ______ Larrow_forwardAn M dwarf star of mass 0.1 solar masses, a radius of 0.13 solar radii and a photospheric temperature of 2708 Kelvin. Assuming the dwarf contains the same mixture of elements as the Sun, and that the thermal pressure of the Sun's core is 1.3 x 10^14 N/m^2 estimate the ratio between the thermal pressure in the M dwarf's core versus that of the Sun. select unitsarrow_forward
- 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_forwardConsider a star with more brightness at 280 pc from the Sun. Suppose this star gets exploded as a supernova at a temperature of 18000 K. The absolute bolometric magnitude of this supernova is-12.24. Calculate its diameter by assuming a sphere at maximum light. (Assume the luminosity of Sun as 3.8×1026 W, the mass of thesun as 1.9 ×1030 kg, and surface temperature of Sun as 5778 K).(a) 1.7×108 km(6) 3.5x108 km(c) 5.2x108 km(d) 6.9 x108 kmarrow_forwardA 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!arrow_forward
- A star with a radius 1.5 times that of the Sun has a surface temperature T=9,000 K. Calculate the luminosity of this star and express your answer in units of the Solar luminosity (the Solar luminosity = 3.84 x 1026 W and the Solar radius = 7 x 108 m)arrow_forwardWe will take a moment to compare how brightly a white dwarf star shines compared to a red giant star. For the sake of this problem, let's assume a white dwarf has a temperature around 10,000 K and a red giant has a temperature around 5,000 K. As for their stellar radiatin, the white dwarf has a radius about 1/100th that of the Sun, and a red giant has a radius around 100 times larger than the Sun. With this in mind, how does the luminosity of a red giant star compare to that of a white dwarf (Hint: do not try to enter all of these numbers into the luminosity equation {it won't go well}; instead, remember that you are only interested in the ratio between the two, so all common units and components can be divided out)? Please enter your answer in terms of the luminosity of the red giant divided by the luminosity of the white dwarf and round to two significant figures. Also, please avoid using commas in your answer.arrow_forwardFor 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_forward
- Stars and Galaxies (MindTap Course List)PhysicsISBN:9781337399944Author:Michael A. SeedsPublisher:Cengage LearningFoundations of Astronomy (MindTap Course List)PhysicsISBN:9781337399920Author:Michael A. Seeds, Dana BackmanPublisher:Cengage Learning