21st Century Astronomy
6th Edition
ISBN: 9780393428063
Author: Kay
Publisher: NORTON
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Question
Chapter 21, Problem 39QP
(a)
To determine
The distance at which galaxy is situated.
(b)
To determine
The age of the universe at the look back time of galaxy.
(c)
To determine
The scale factor of the universe.
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Students have asked these similar questions
An astronomer observed the motions of some galaxies. Based on his observations, he made the following statements. Which one of them is most likely to be false? Take Hubble's constant to be 67 km/s/Mpc.
A. A galaxy observed to be moving away from us at a speed of 70 km/s is at a distance of about 1 Mpc from us.
B. A galaxy observed to be moving away from us at a speed of 700 km/s is at a distance of about 10 Mpc from us.
C. A galaxy observed to be moving away from us at a speed of 7000 km/s is at a distance of about 100 Mpc from us.
D. A galaxy observed to be moving away from us at a speed of 70000 km/s is at a distance of about 1 Gpc from us.
Is the answer D? Thank you!
If a galaxy is 9.0 Mpc away from Earth and recedes at 488 km/s, what is H0 (in km/s/Mpc)?
km/s/Mpc
What is the Hubble time (in yr)?
years
How old (in yr) would the universe be, assuming space-time is flat and the expansion of the universe has not been accelerating?
How would acceleration change your answer?
A.If the expansion of the Universe has been accelerating, the Universe could be substantially younger than the value entered above.
BIf the expansion of the Universe has been accelerating, the Universe could be substantially older than the value entered above.
The matter density in the Universe today
is Pm = -27 kg m-3. What would
2.7 x 10
be the value of the density parameter,
2o, if the Hubble constant had the value
Ho = 38 km/s/Mpc? Assume the Universe
does not contain dark energy and choose
the option below that best matches your
answer.
Select one:
O a.
0.1
O b. 2.
О с.
1.
O d. 0.7
О е.
0.5
Chapter 21 Solutions
21st Century Astronomy
Ch. 21.1 - Prob. 21.1CYUCh. 21.2 - Prob. 21.2CYUCh. 21.3 - Prob. 21.3ACYUCh. 21.3 - Prob. 21.3BCYUCh. 21.4 - Prob. 21.4CYUCh. 21 - Prob. 1QPCh. 21 - Prob. 2QPCh. 21 - Prob. 3QPCh. 21 - Prob. 4QPCh. 21 - Prob. 5QP
Ch. 21 - Prob. 6QPCh. 21 - Prob. 7QPCh. 21 - Prob. 8QPCh. 21 - Prob. 9QPCh. 21 - Prob. 10QPCh. 21 - Prob. 11QPCh. 21 - Prob. 12QPCh. 21 - Prob. 13QPCh. 21 - Prob. 14QPCh. 21 - Prob. 15QPCh. 21 - Prob. 16QPCh. 21 - Prob. 17QPCh. 21 - Prob. 18QPCh. 21 - Prob. 19QPCh. 21 - Prob. 20QPCh. 21 - Prob. 21QPCh. 21 - Prob. 23QPCh. 21 - Prob. 24QPCh. 21 - Prob. 25QPCh. 21 - Prob. 26QPCh. 21 - Prob. 27QPCh. 21 - Prob. 28QPCh. 21 - Prob. 29QPCh. 21 - Prob. 30QPCh. 21 - Prob. 31QPCh. 21 - Prob. 32QPCh. 21 - Prob. 33QPCh. 21 - Prob. 34QPCh. 21 - Prob. 35QPCh. 21 - Prob. 36QPCh. 21 - Prob. 37QPCh. 21 - Prob. 38QPCh. 21 - Prob. 39QPCh. 21 - Prob. 40QPCh. 21 - Prob. 41QPCh. 21 - Prob. 42QPCh. 21 - Prob. 43QPCh. 21 - Prob. 44QPCh. 21 - Prob. 45QP
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- Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In this case, A. Galaxy 1 must be twice as big as Galaxy 2. B. we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2. C. we are seeing Galaxy 1 as it looked at a later time in the history of the universe than Galaxy 2. D. Galaxy 2 must be twice as old as Galaxy 1.arrow_forwardIf a quasar has a recessional velocity of 2.7 × 10 5 km/sec and is determined to be 3600 Mpc, what is the Hubble constant based on this quasar alone? a. 50 km/sec/Mpc b. 9.7 × 108 km/sec/Mpc c. 75 km/sec/Mpc d. 0.013 km/sec/Mpc e. 273,600 km/sec/Mpcarrow_forwardThe matter density in the Universe today is ?m=2.7×10−27kgm−3. What would be the value of the density parameter, Ω0, if the Hubble constant had the value H0 = 38 km/s/Mpc?arrow_forward
- If a galaxy is 8.8 Mpc away from Earth and recedes at 498 km/s, what is H0 (in km/s/Mpc)? _______ km/s/Mpc What is the Hubble time (in yr)? _______ yr How would acceleration change your answer? A: If the expansion of the Universe has been accelerating, the Universe could be substantially younger than the value entered above. B: If the expansion of the Universe has been accelerating, the Universe could be substantially older than the value entered above.arrow_forwardRecall that Hubbleʹs law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubbleʹs constant. Suppose H0 = 80 km/s/Mpc. How fast would a galaxy located 800 megaparsecs distant be receding from us? A. 64 Mpc/s B. 64,000 km/s C. 0.1 times the speed of light D. 10 km/s E. 64 km/sarrow_forwardThe mass density of our universe is measured to be about 10-29 kg/m3. If an arbitrary point is chosen as the center, how large is the radius of a spherical surface centered at the point so that the mass enclosed in the surface will become a blackhole observed by someone outside the surface? A. 4.2 trillion light years B. 420 billion light years C. 42 billion light years D. 4.2 billion light years Is the answer D? Thanks!arrow_forward
- What happens when galaxies collide? A. Star collisions will be rare but the shapes of the galaxies will be largely distorted. B. The shapes of the galaxies will be largely distorted and many of the stars of one galaxy will collide with stars of the other galaxy. C. The shapes of the galaxies will be distorted and many stars will collide with stars of the other galaxy, as well as with other stars in the same galaxy. D. Star collisions will be rare and the two galaxies will just pass through each other without any changes. Is the answer A? Thank you!arrow_forwardAssuming that hydrogen fusion requires the Universe to have a temperature of T > 10' K (as measured by the CMB), determine the redshift at which the fusion of hydrogen into helium was just possible as the Universe expanded and cooled. Choose the option below that most closely matches your answer. Select one: Оа. 4000.87 b. 3669723.77 О с 2229723.71 O d. 9748293.14 O e. 4669723.16arrow_forwardWhat are the angular diameters of the following, as seen from Earth? a. The Sun, with radius R = Rsun = 7x10^5 km. b. Betelgeuse, with MV = -5.5 mag, mv = 0.8 mag, and R = 650Rsun. c. The galaxy M31, with R = 30 kpc at a distance D = 0.7Mpc. d. The Coma cluster of galaxies, with R = 3 Mpc at a distance D = 100 Mpc.arrow_forward
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