Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Question
Chapter 27, Problem 23Q
To determine
The factor that will set the limit on the lifetime of our technological civilization.
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Tutorial
A radio broadcast left Earth in 1925. How far in light years has it traveled?
If there is, on average, 1 star system per 400 cubic light years, how many star systems has this broadcast
reached?
Assume that the fraction of these star systems that have planets is 0.30 and that, in a given planetary
system, the average number of planets that have orbited in the habitable zone for 4 billion years is 0.85. How
many possible planets with life could have heard this signal?
Part 1 of 3
To figure out how many light years a signal has traveled we need to know how long since the signal left Earth.
If the signal left in 1925, distance in light years = time since broadcast left Earth.
d = tnow - tbroadcast
d =
light years
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Tutorial
A radio broadcast left Earth in 1923. How far in light
years has it traveled?
If there is, on average, 1 star system per 400 cubic light
years, how many star systems has this broadcast
reached?
Assume that the fraction of these star systems that
have planets is 0.50 and that, in a given planetary
system, the average number of planets that have
orbited in the habitable zone for 4 billion years is 0.40.
How many possible planets with life could have heard
this signal?
Part 1 of 3
To figure out how many light years a signal has
traveled we need to know how long since the signal left
Earth. If the signal left in 1923, distance in light years =
time since broadcast left Earth.
d = tnow - broadcast
d = 97
97 light years
Part 2 of 3
Since the radio signal travels in all directions, it
expanded as a sphere with a radius equal to the
distance it has traveled so far. To determine the
number of star systems this signal has reached, we
need to determine the volume of that sphere.
V, =
Vb…
In a globular cluster, astronomers (someday) discover a star with the same mass as our Sun, but consisting entirely of hydrogen and helium. Is this star a good place to point our SETI antennas and search for radio signals from an advanced civilization?
Group of answer choices
No, because such a star (and any planets around it) would not have the heavier elements (carbon, nitrogen, oxygen, etc.) that we believe are necessary to start life as we know it.
Yes, because globular clusters are among the closest star clusters to us, so that they would be easy to search for radio signals.
Yes, because we have already found radio signals from another civilization living near a star in a globular cluster.
No, because such a star would most likely not have a stable (main-sequence) stage that is long enough for a technological civilization to develop.
Yes, because such a star is probably old and a technological civilization will have had a long time to evolve and develop there.
Chapter 27 Solutions
Universe: Stars And Galaxies
Ch. 27 - Prob. 1QCh. 27 - Prob. 2QCh. 27 - Prob. 3QCh. 27 - Prob. 4QCh. 27 - Prob. 5QCh. 27 - Prob. 6QCh. 27 - Prob. 7QCh. 27 - Prob. 8QCh. 27 - Prob. 9QCh. 27 - Prob. 10Q
Ch. 27 - Prob. 11QCh. 27 - Prob. 12QCh. 27 - Prob. 13QCh. 27 - Prob. 14QCh. 27 - Prob. 15QCh. 27 - Prob. 16QCh. 27 - Prob. 17QCh. 27 - Prob. 18QCh. 27 - Prob. 19QCh. 27 - Prob. 20QCh. 27 - Prob. 21QCh. 27 - Prob. 22QCh. 27 - Prob. 23QCh. 27 - Prob. 24QCh. 27 - Prob. 25QCh. 27 - Prob. 26QCh. 27 - Prob. 27QCh. 27 - Prob. 28QCh. 27 - Prob. 29QCh. 27 - Prob. 30QCh. 27 - Prob. 31QCh. 27 - Prob. 32QCh. 27 - Prob. 33Q
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