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 19, Problem 7Q
To determine
(a)
The main sequence lifetime of
To determine
(b)
The main sequence lifetime of
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Consider two stars on the main sequence, A and B. Star A has a mass of 6 M⊙. Star B has a mass of 0.3 M⊙. Compute the ratio of main sequence lifetimes for the two stars, TB/TA .
What are the a) luminosity and b)wavelength of maximum emission for a star with a surface temperature is 2,000K and a size of 1.0*108m?
If 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
=
Chapter 19 Solutions
Universe: Stars And Galaxies
Ch. 19 - Prob. 1QCh. 19 - Prob. 2QCh. 19 - Prob. 3QCh. 19 - Prob. 4QCh. 19 - Prob. 5QCh. 19 - Prob. 6QCh. 19 - Prob. 7QCh. 19 - Prob. 8QCh. 19 - Prob. 9QCh. 19 - Prob. 10Q
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- If the Sun is well approximated by a black body with a temperature of 6,000◦ K, then how does its surface brightness compare (ratio) with the surface brightness of a 12,000◦ K star? How about a 3,000◦ K star?arrow_forwardUse 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.arrow_forwardYou receive 8 × 10−9 W/m2 of energy from a star that is 2 parsecs away, it has a V -band apparentmagnitude mV = −1.5. How much more/less flux do you receive from a star with an apparent magnitudemV = 5.3? For the first star, what is its V -band absolute magnitude?arrow_forward
- Assuming that at the end of the He burning phase of the stellar core (r < R_core) has no H or He or other metals and is composed completely of Carbon, X=Y=0, X_c = 1 ; The envelope above the core has a normal stellar composition ( r > R_core). Calculate the length of time in years that a 1M_sol and 10M_sol star will live on the horizontal branch or the time between the start and end of the He burning phase. Assume that the normal relationship between mass and luminosity holds for horizontal branch stars. Please be as detailed as possiblearrow_forwardIf a T Tauri star is the same temperature as the Sun but is seventeen 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)arrow_forwardAssume that when a certain main sequence star becomes a giant gas, its luminosity increases from L to 1000 L and its radius also increases from R to 1000 R. If the initial surface temperature is T, what approximately is the final surface temperature? A. 0.032 T B. 0.18 T C. 0.0010 T D. 0.010 Tarrow_forward
- A 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) 36.854 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.arrow_forward. A star"s position in the sky against distant background objects has shifted by 0.4" in 6 months it returned where it was. what is the stellar parallax p of this star? Ans. p=0.2" b. How far is this star from the Sun?arrow_forwardSuppose we represent an ordinary star as a uniform solid rigid sphere. The star’s initial radius is 644000 km (comparableto the size of our sun). After it collapses, forming a neutron star, its final radius is only 18.3 km! If the original starmakes one complete rotation about its axis once per month (every 30 days), find the neutron star’s period of rotationjust after the original star has collapsed.Tafter = (in s)arrow_forward
- Given the mass of the sun (1.989 x 10^30 kg), calculate the average density of a neutron star with a radius of 45.439 km.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_forwardIf a 100 solar mass star were to have a luminosity of 107 times the Sun’s luminosity, how would such a star’s density compare when it is on the main sequence as an O-type star, and when it is a cool supergiant (M-type)? Use values of temperature from Figure 18.14 or Figure 18.15 and the relationship between luminosity, radius, and temperature as given in Exercise 18.47. Figure 18.15 Schematic HR Diagram for Many Stars. Ninety percent of all stars on such a diagram fall along a narrow band called the main sequence. A minority of stars are found in the upper right; they are both cool (and hence red) and bright, and must be giants. Some stars fall in the lower left of the diagram; they are both hot and dim, and must be white dwarfs. Figure 18.14 HR Diagram for a Selected Sample of Stars. In such diagrams, luminosity is plotted along the vertical axis. Along the horizontal axis, we can plot either temperature or spectral type (also sometimes called spectral class). Several of the brightest stars are identified by name. Most stars fall on the main sequence.arrow_forward
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