21st Century Astronomy
6th Edition
ISBN: 9780393428063
Author: Kay
Publisher: NORTON
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Chapter 22, Problem 7QP
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The correct statement
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1. The current (critical) density of our universe is pe = 10-26kg/m³. Assume the universe is
filled with cubes with equal size that each contain one person of m = 100kg. What would
the length of the side of such a cube have to be in order to give the correct critical density?
How many hydrogen atoms would you need in a box of 1 m³ to reach the critical density?
The matter we know, which consists mostly of hydrogen, constitutes only 4.8% of the current
critical energy density of our universe. So how many hydrogen atoms are actually in a box
of 1 m3 in our universe? Deep space is very empty and a much better vacuum than we can
obtain on earth in a laboratory.
The age of the universe can be determined if
a.
the universe is flat.
b.
the amount of dark matter in the universe can be accurately determined.
c.
the rate of recession of the galaxies in the Local Group can be accurately determined.
d.
the temperature of the cosmic background radiation can be accurately determined.
e.
the Hubble constant and density of the universe can be accurately determined.
The density of the universe is
a.
equal to the critical density if the universe is closed.
b.
equal to the critical density if the universe is flat.
c.
greater than the critical density if the universe is flat.
d.
greater than the critical density if the universe is open.
e.
none of the above.
Chapter 22 Solutions
21st Century Astronomy
Ch. 22.1 - Prob. 22.1CYUCh. 22.2 - Prob. 22.2CYUCh. 22.3 - Prob. 22.3CYUCh. 22.4 - Prob. 22.4CYUCh. 22.5 - Prob. 22.5CYUCh. 22 - Prob. 1QPCh. 22 - Prob. 2QPCh. 22 - Prob. 3QPCh. 22 - Prob. 4QPCh. 22 - Prob. 5QP
Ch. 22 - Prob. 6QPCh. 22 - Prob. 7QPCh. 22 - Prob. 8QPCh. 22 - Prob. 9QPCh. 22 - Prob. 10QPCh. 22 - Prob. 11QPCh. 22 - Prob. 12QPCh. 22 - Prob. 13QPCh. 22 - Prob. 14QPCh. 22 - Prob. 15QPCh. 22 - Prob. 16QPCh. 22 - Prob. 17QPCh. 22 - Prob. 18QPCh. 22 - Prob. 19QPCh. 22 - Prob. 20QPCh. 22 - Prob. 21QPCh. 22 - Prob. 22QPCh. 22 - Prob. 24QPCh. 22 - Prob. 28QPCh. 22 - Prob. 29QPCh. 22 - Prob. 31QPCh. 22 - Prob. 32QPCh. 22 - Prob. 33QPCh. 22 - Prob. 34QPCh. 22 - Prob. 35QPCh. 22 - Prob. 36QPCh. 22 - Prob. 37QPCh. 22 - Prob. 38QPCh. 22 - Prob. 39QPCh. 22 - Prob. 40QPCh. 22 - Prob. 41QPCh. 22 - Prob. 42QPCh. 22 - Prob. 43QPCh. 22 - Prob. 44QPCh. 22 - Prob. 45QP
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, physics and related others by exploring similar questions and additional content below.Similar questions
- 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_forwardAn 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!arrow_forwardWe know that dark matter must exist in galaxies. If not, many of the stars in a galaxy would ... a.Expand and go supernova due to the expansion of the Universe b.Fly away from the galaxy because the stars’ velocities are so large, and the galaxy would not have enough gravity to hold onto them c.Orbit the center of the galaxy normally d.Spiral in toward the center of the galaxy because most of the galaxy’s mass would be toward the centerarrow_forward
- If the universe is closed and finite, then a. the universe has a center and an edge. b. the universe will expand forever. c. the final fate of the universe will be very cold and of extremely low density. d. the space-time of the universe is negatively curved. e. none of the above are true.arrow_forwardIf our universe is expanding, what are the implications for the separation between two stars within our galaxy? A. The two stars are moving farther apart. B. The two stars are moving closer together. C. The distance between the two stars is unaffected. D. The question is impossible to answer without more information.arrow_forwardGalaxy seeds around which galaxies, clusters, and walls grew may have been a. caused by hot dark matter. b. caused by baryons. c. the result of the separation of the electromagnetic and weak forces. d. the result of freezing water molecules shortly after the universe became transparent to photons. e. caused by microscopic random fluctuations in the infant universe.arrow_forward
- Quasi-stellar objects were first detected as a. double-lobed spiral galaxies. b. faint points of light with peculiar emission spectra. c. large regions of X-ray emissions. d. starlike objects with normal stellar emission spectra. e. galaxies with normal stellar emission spectra.arrow_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_forwardBased on what you have learned about galaxy formation from a protogalactic cloud (and similarly star formation from a protostellar cloud), the fact that dark matter in a galaxy is distributed over a much larger volume than luminous matter can be explained by I. Dark matter does not emit EM radiations. II. The pressure of an ideal gas decreases when temperature drops. III. The temperature of an ideal gas decreases when its thermal energy decreases. A. I only B. I and III only C. II and III only D. I, II and III Is the answer C? Thank you!arrow_forward
- Which of the following might you expect to be an additional consequence of the fact that galaxies contain more mass than expected?A. The gravitational force between galaxies is greater than expected.B. Galaxies appear less bright than expected.C. Galaxies are farther away than expected.D. There are more galaxies than expected.arrow_forwardIn 1998, it was announced that the expansion of the universe is accelerating. What does this imply from the perspective of the big bang? a. A force exists that we knew nothing about causes the expansion. b. The universe must be closed. c. The universe is finite. d. The amount of dark matter must be far less than the amount of normal matter. e. The universe must be infinitely old.arrow_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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