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 21, Problem 37Q
To determine
The time after which the two stars will collide.
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velocity curve for a double line
spectroscopic binary is shown in the sketch.
The system is viewed edge-on, i.e., with an
inclination angle of i 90°, so that the
maximum possible Doppler shifts for this
system are observed.
400
SPo
= , Ain i
300
200
l0o = v Ain i
100
-100
-200
-300
400
0 1 2 3 4
10
Time (days)
Find the speed of star 2 in km/s.
Doppler Velocity
(2esu)
Time left 1:45:56
A star has initially a radius of 680000000 m and a period of rotation about its axis of 33 days.
Eventually it changes into a neutron star with a radius of only 45000 m and a period of 0.3 s.
Assuming that the mass has not changed, find
Assume a star has the shape of a sphere.
(Suggestion: do it with formula first, then put the numbers in)
[Recommended time : 5-8 minutes]
(a) the ratio of initial to final angular momentum (Li/Lf)
Oa. 2.17E+15
Ob. 24
Oc. 0.0416
Od. 4.61E-16
(b) the ratio of initial to final kinetic energy
Oa. 4.85E-23
Ob. 396000
Oc. 2.53E-6
Od. 2.06E+22
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…
Chapter 21 Solutions
Universe: Stars And Galaxies
Ch. 21 - Prob. 1QCh. 21 - Prob. 2QCh. 21 - Prob. 3QCh. 21 - Prob. 4QCh. 21 - Prob. 5QCh. 21 - Prob. 6QCh. 21 - Prob. 7QCh. 21 - Prob. 8QCh. 21 - Prob. 9QCh. 21 - Prob. 10Q
Ch. 21 - Prob. 11QCh. 21 - Prob. 12QCh. 21 - Prob. 13QCh. 21 - Prob. 14QCh. 21 - Prob. 15QCh. 21 - Prob. 16QCh. 21 - Prob. 17QCh. 21 - Prob. 18QCh. 21 - Prob. 19QCh. 21 - Prob. 20QCh. 21 - Prob. 21QCh. 21 - Prob. 22QCh. 21 - Prob. 23QCh. 21 - Prob. 24QCh. 21 - Prob. 25QCh. 21 - Prob. 26QCh. 21 - Prob. 27QCh. 21 - Prob. 28QCh. 21 - Prob. 29QCh. 21 - Prob. 30QCh. 21 - Prob. 31QCh. 21 - Prob. 32QCh. 21 - Prob. 33QCh. 21 - Prob. 34QCh. 21 - Prob. 35QCh. 21 - Prob. 36QCh. 21 - Prob. 37QCh. 21 - Prob. 38QCh. 21 - Prob. 39QCh. 21 - Prob. 40QCh. 21 - Prob. 41QCh. 21 - Prob. 42QCh. 21 - Prob. 43QCh. 21 - Prob. 44QCh. 21 - Prob. 45QCh. 21 - Prob. 46QCh. 21 - Prob. 47QCh. 21 - Prob. 48QCh. 21 - Prob. 49QCh. 21 - Prob. 50QCh. 21 - Prob. 51QCh. 21 - Prob. 52QCh. 21 - Prob. 53QCh. 21 - Prob. 54QCh. 21 - Prob. 55QCh. 21 - Prob. 56QCh. 21 - Prob. 57QCh. 21 - Prob. 58QCh. 21 - Prob. 59QCh. 21 - Prob. 60QCh. 21 - Prob. 61QCh. 21 - Prob. 62QCh. 21 - Prob. 63QCh. 21 - Prob. 64QCh. 21 - Prob. 65QCh. 21 - Prob. 66QCh. 21 - Prob. 67QCh. 21 - Prob. 68QCh. 21 - Prob. 69QCh. 21 - Prob. 70QCh. 21 - Prob. 71QCh. 21 - Prob. 72QCh. 21 - Prob. 73QCh. 21 - Prob. 74QCh. 21 - Prob. 75Q
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- What is the escape velocity Vesc of a 1.4M⊙ 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_forwarda double line The velocity curve for spectroscopic binary is shown in the sketch. The system is viewed edge-on, i.e., with an inclination angle of i = 90°, so that the maximum possible Doppler shifts for this system are observed. 400 U, Aini 300 200 oo - v Ain i 100 -100 -200 -300 400 o 1 2 3 +s 7 8 10 Time (daye) Find the orbital period of this binary in days. Doppler Velocity (2esun)arrow_forwardA 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.arrow_forward
- velocity curve for a double line spectroscopic binary is shown in the sketch. The system is viewed edge-on, i.e., with an inclination angle of i = 90°, so that the maximum possible Doppler shifts for this system are observed. 400 300 So = U, Ani 200 t0 = v Ain i 100 -100 -200 -300 400 O 1 2 3 1 s 1 8: 10 Time (days) Find the orbital period of this binary in days. Doppler Velocity (krn/sec)arrow_forwardA star has initially a radius of 660000000 m and a period of rotation about its axis of 34 days. Eventually it changes into a neutron star with a radius of only 35000 m and a period of 0.2 s. Assuming that the mass has not changed, find Assume a star has the shape of a sphere. (Suggestion: do it with formula first, then put the numbers in) [Recommended time : 5-8 minutes] (a) the ratio of initial to final angular momentum (Li/Lf) Oa. 5.22E+15 Ob. 24.2 Oc. 0.0413 Od. 1.91E-16 (b) the ratio of initial to final kinetic energy Oa. 1.3E-23 Activate V Go to Setting Ob. 607000 Oc. 1.65E-6 e here to searcharrow_forwardwhat is the answer for sub item (b) if the radius of the neutron star is 69.601 km? (express your answer in the proper SI unit ans without scientific notation)arrow_forward
- what is the answer for sub-item (b) if the radius of the neutron star is 68.283 km? (express your answer in the proper SI unit and without scientific notation)arrow_forwardA star has initially a radius of 780000000 m and a period of rotation about its axis of 22 days. Eventually it changes into a neutron star with a radius of only 25000 m and a period of 0.1 s. Assuming that the mass has not changed, find Assume a star has the shape of a sphere. (Suggestion: do it with formula first, then put the numbers in) [Recommended time : 5-8 minutes] (a) the ratio of initial to final angular momentum (Li/Lf) a. 1.85E+16 b. 51.2 c. 0.0195 d. 5.4E-17 (b) the ratio of initial to final kinetic energy a. 2.84E-24 b. 371000 c. 2.69E-6 d. 3.52E+23arrow_forwardA star has initially a radius of 640000000 m and a period of rotation about its axis of 20 days. Eventually it changes into a neutron star with a radius of only 50000 m and a period of 0.2 s. Assuming that the mass has not changed, find Assume a star has the shape of a sphere. (Suggestion: do it with formula first, then put the numbers in) [Recommended time : 5-8 minutes] (a) the ratio of initial to final angular momentum (Li/Lf) Oa. 1.42E+15 Ob. 19 Oc. 0.0527 Od. 7.06E-16 (b) the ratio of initial to final kinetic energy Oa. 8.18E-23 Ob. 456000 Oc. 2.19E-6 Od. 1.22E+22 52%arrow_forward
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