Understanding Our Universe
3rd Edition
ISBN: 9780393614428
Author: PALEN, Stacy, Kay, Laura, Blumenthal, George (george Ray)
Publisher: W.w. Norton & Company,
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Chapter 17, Problem 7QAP
To determine
Reason why voids do not contain dark matter.
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Students have asked these similar questions
What is the strongest piece of evidence for the existence of dark matter?
As stars die, they transition to either a supergiant star or a white dwarf
There is a 2.7 K background radiation that permeates the entire universe
The rate of expansion of the universe is increasing
The orbital speed of stars near the edge of galaxies is nearly the same as stars close to the center of the galaxy
What can change the expansion rate of the Universe over time?
Gravity: Attractive forces increase the expansion rate by pulling mass together making gravity stronger.
Gravity decreases the expansion rate, while electromagnetic forces are always repulsive and speed-up expansion.
Attractive forces such as gravity decrease the expansion rate. Repulsive forces would speed-up expansion by pushing spacetime apart.
Nothing, since the expansion rate remains always constant, and it is measured from Hubble's law.
An astronomer in an imaginary Universe observes a small patch of the sky (0.005% of the total) with very deep observations and
finds one million galaxies. How many galaxies can they estimate to be present in the whole Universe?
10 billion
20 billion
50 billion
O 70 billion
Chapter 17 Solutions
Understanding Our Universe
Ch. 17.1 - Prob. 17.1CYUCh. 17.2 - Prob. 17.2CYUCh. 17.3 - Prob. 17.3CYUCh. 17.4 - Prob. 17.4CYUCh. 17.5 - Prob. 17.5CYUCh. 17 - Prob. 1QAPCh. 17 - Prob. 2QAPCh. 17 - Prob. 3QAPCh. 17 - Prob. 4QAPCh. 17 - Prob. 5QAP
Ch. 17 - Prob. 6QAPCh. 17 - Prob. 7QAPCh. 17 - Prob. 8QAPCh. 17 - Prob. 9QAPCh. 17 - Prob. 10QAPCh. 17 - Prob. 11QAPCh. 17 - Prob. 12QAPCh. 17 - Prob. 13QAPCh. 17 - Prob. 14QAPCh. 17 - Prob. 15QAPCh. 17 - Prob. 16QAPCh. 17 - Prob. 17QAPCh. 17 - Prob. 18QAPCh. 17 - Prob. 19QAPCh. 17 - Prob. 20QAPCh. 17 - Prob. 21QAPCh. 17 - Prob. 22QAPCh. 17 - Prob. 23QAPCh. 17 - Prob. 24QAPCh. 17 - Prob. 25QAPCh. 17 - Prob. 26QAPCh. 17 - Prob. 27QAPCh. 17 - Prob. 28QAPCh. 17 - Prob. 29QAPCh. 17 - Prob. 30QAPCh. 17 - Prob. 31QAPCh. 17 - Prob. 32QAPCh. 17 - Prob. 33QAPCh. 17 - Prob. 34QAPCh. 17 - Prob. 35QAPCh. 17 - Prob. 36QAPCh. 17 - Prob. 37QAPCh. 17 - Prob. 38QAPCh. 17 - Prob. 39QAPCh. 17 - Prob. 40QAPCh. 17 - Prob. 41QAPCh. 17 - Prob. 42QAPCh. 17 - Prob. 43QAPCh. 17 - Prob. 44QAPCh. 17 - Prob. 45QAP
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- How are distant (young) galaxies different from the galaxies that we see in the universe today?arrow_forwardWhat percentage of matter is ordinary matter? What percentage is dark matter? What makes up the rest of the Universes density?arrow_forwardA cluster of galaxies is observed to have a recessional velocity of 60,000 km/s. Find the distance to the cluster. (Assume a Hubble constant of 22 km/s per million light-years.)arrow_forward
- We can detect 21-cm emission from other galaxies as well as from our own Galaxy. However, 21-cm emission from our own Galaxy fills most of the sky, so we usually see both at once. How can we distinguish the extragalactic 21-cm emission from that arising in our own Galaxy? (Hint: Other galaxies are generally moving relative to the Milky Way.)arrow_forwardGalaxies are found in the “walls” of huge voids; very few galaxies are found in the voids themselves. The text says that the structure of filaments and voids has been present in the universe since shortly after the expansion began 13.8 billion years ago. In science, we always have to check to see whether some conclusion is contradicted by any other information we have. In this case, we can ask whether the voids would have filled up with galaxies in roughly 14 billion years. Observations show that in addition to the motion associated with the expansion of the universe, the galaxies in the walls of the voids are moving in random directions at typical speeds of 300 km/s. At least some of them will be moving into the voids. How far into the void will a galaxy move in 14 billion years? Is it a reasonable hypothesis that the voids have existed for 14 billion years?arrow_forwardSuppose the stars in an elliptical galaxy all formed within a few million years shortly after the universe began. Suppose these stars have a range of masses, just as the stars in our own galaxy do. How would the color of the elliptical change over the next several billion years? How would its luminosity change? Why?arrow_forward
- We 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_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_forwardAll Radio Galaxies have the following number of plasma jets and lobes a) 2 b) 5 c) 1 d) 4 e)7arrow_forward
- A star at a distance of 50000 light years from the center of a galaxy has an orbital speed of 100 km/s around the galactic center. What is the total mass of the galaxy located at distances smaller than 50000 light years from the center? A. 7.6 ×1010 solar masses B. 4.2 ×1011 solar masses C. 3.5 ×1010 solar masses D. 1.4 ×1011 solar masses Is the answer C? M = (r x v^2) / G = 50000 x 9.46e15 x (100000^2) / 6.67e-11 / 2e30 (the Sun's mass) = 3.55e10 solar massesarrow_forwardIn galaxy clusters, most of the galaxies appear to be elliptical galaxies because They formed in-situ from low-angular-momentum clouds They aren't really elliptical, but they look that way because they are very distant When galaxies collect in clusters, the proximity makes them puffier Galaxies in clusters probably had many merger events in the pastarrow_forwardWhat 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_forward
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