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 25, Problem 38Q
To determine
The use of the cosmic background
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Estimating the mass of the Milky Way
a) Assuming the Sun moves in a circular orbit of radius 8 kiloparsecs around the center of the Milky Way, and that its orbital speed
is 220 km/s, calculate how many years it takes the Sun to complete one orbit of the Galaxy. Remember to convert kiloparsecs to
kilometers.
b) Using the modified form of Kepler's third law (introduced in Lecture 13, for measuring the combined masses of binary stars),
R³
m+ M = estimate the mass of the Milky Way enclosed within 8 kpc (Sun's orbit radius). The mass of the Milky Way inside
p²
I
the Sun's orbit can be represented as a single mass (M) located at its center, and the mass of the Sun (m) can be considered
infinitesimally small compared to the Milky Way's (i.e., m < M).
c) Is this estimate of the Milky Way's mass an upper or lower limit? Explain your reasoning.
Astronomers frequently say that "there are more stars in the universe than there are grains of sand on all the
beaches on the earth". Given that a typical grain of sand is about 0.5 – 1.0 mm in diameter, estimate the
number of grains of sand on all the earth's beaches. The diameter of the Earth is 12,742 km.
a) About 1011
b) About 1016
c) About 1021.
6.
Assume that a typical galaxy contains about 200 billion stars and that there are more than 150 billion
galaxies in the known universe. Estimate the total number of stars in the universe.
b) About 1022
a) About 1010
c) About 1016.
7.
Compare the values of the number of grains of sand in all earth's beaches (from problem 5) with the
number of stars in the universe (from problem 6) – which is greater?
a) Number of sand grains
b) number of stars
c) they are about the same.
Explain the expanding Universe theory and its relationship to the Big Bang theory?
Chapter 25 Solutions
Universe: Stars And Galaxies
Ch. 25 - Prob. 1QCh. 25 - Prob. 2QCh. 25 - Prob. 3QCh. 25 - Prob. 4QCh. 25 - Prob. 5QCh. 25 - Prob. 6QCh. 25 - Prob. 7QCh. 25 - Prob. 8QCh. 25 - Prob. 9QCh. 25 - Prob. 10Q
Ch. 25 - Prob. 11QCh. 25 - Prob. 12QCh. 25 - Prob. 13QCh. 25 - Prob. 14QCh. 25 - Prob. 15QCh. 25 - Prob. 16QCh. 25 - Prob. 17QCh. 25 - Prob. 18QCh. 25 - Prob. 19QCh. 25 - Prob. 20QCh. 25 - Prob. 21QCh. 25 - Prob. 22QCh. 25 - Prob. 23QCh. 25 - Prob. 24QCh. 25 - Prob. 25QCh. 25 - Prob. 26QCh. 25 - Prob. 27QCh. 25 - Prob. 28QCh. 25 - Prob. 29QCh. 25 - Prob. 30QCh. 25 - Prob. 31QCh. 25 - Prob. 32QCh. 25 - Prob. 33QCh. 25 - Prob. 34QCh. 25 - Prob. 35QCh. 25 - Prob. 36QCh. 25 - Prob. 37QCh. 25 - Prob. 38QCh. 25 - Prob. 39QCh. 25 - Prob. 40QCh. 25 - Prob. 41QCh. 25 - Prob. 42QCh. 25 - Prob. 43QCh. 25 - Prob. 44QCh. 25 - Prob. 45QCh. 25 - Prob. 46QCh. 25 - Prob. 47QCh. 25 - Prob. 48QCh. 25 - Prob. 49QCh. 25 - Prob. 50QCh. 25 - Prob. 51QCh. 25 - Prob. 52QCh. 25 - Prob. 53QCh. 25 - Prob. 54QCh. 25 - Prob. 55Q
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- The figure below shows the spectra of two galaxies A and B. Please can i get help with this questions below: 1. Which of these galaxies has ongoing star formation? How can you tell?2. One of these galaxies has Hubble type E3 while the other is SBb. Which is which? What does the 3 inE3 tell you about the galaxy? What does the SB in SBb tell you about the galaxy?3. What effects would dust have on the two spectra?4. Which galaxy would you expect to have more far-infrared emission? Explarrow_forwardDescribe what is meant by Olbers’ paradox. Explain how it is solved by our modern understanding of the Universe.arrow_forward1. 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.arrow_forward
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