Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 28, Problem 1E
How are distant (young) galaxies different from the galaxies that we see in the universe today?
Expert Solution & Answer
To determine
To explain:
The difference between distant young galaxies and the galaxies that are seen in the universe today.
Explanation of Solution
Introduction:
Distant young galaxies are different from present day galaxies in terms of star formation, composition and shape. Distant galaxies were present at the time when the universe was only 500 million years old while present day galaxy is about 13.8 years old.
Distant galaxies were small as compared to present day galaxy and rate of star formation was very high in young galaxies and they were numerous, less luminous and rich in gas.
Distant galaxies were small and elliptical as at that time, spiral arms, bulges and disks were not there.They contain mostly old stars and they were irregular and smaller than present day galaxies. Present day galaxies are spiral in shape and they contain young stars with interstellar matter.
Formation of larger galaxies is the result of combination of fragment of old galaxies. The color of galaxy indicates the age of star by which it is populated.Blue galaxies contain hot stars and star formation occurs at high rate.
Conclusion:
Thus,Distant galaxies were small as compared to present day galaxy and rate of star formation was very high in young galaxies and they were numerous, less luminous and gas rich.
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Question B3
Consider the following FLRW spacetime:
t2
ds² = -dt² +
(dx²
+ dy²+ dz²),
t2
where t is a constant.
a)
State whether this universe is spatially open, closed or flat.
[2 marks]
b) Determine the Hubble factor H(t), and represent it in a (roughly drawn) plot as a function
of time t, starting at t = 0.
[3 marks]
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to galaxy A.
d) The Friedmann equations are
2
k
8πG
а
4πG
+
a²
(p+3p).
3
a
3
[5 marks]
Use these equations to determine the energy density p(t) and the pressure p(t) for the
FLRW spacetime specified at the top of the page.
[5 marks]
e) Given the result of question B3.d, state whether the FLRW universe in question is (i)
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A conformally…
SECTION B
Answer ONLY TWO questions in Section B
[Expect to use one single-sided A4 page for each Section-B sub question.]
Question B1
Consider the line element
where w is a constant.
ds²=-dt²+e2wt dx²,
a) Determine the components of the metric and of the inverse metric.
[2 marks]
b) Determine the Christoffel symbols. [See the Appendix of this document.]
[10 marks]
c)
Write down the geodesic equations.
[5 marks]
d) Show that e2wt it is a constant of geodesic motion.
[4 marks]
e)
Solve the geodesic equations for null geodesics.
[4 marks]
Page 2
SECTION A
Answer ALL questions in Section A
[Expect to use one single-sided A4 page for each Section-A sub question.]
Question A1
SPA6308 (2024)
Consider Minkowski spacetime in Cartesian coordinates th
=
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(a) Consider the vector with components V" = (1,-1,0,0). Determine V and V. V.
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[2 marks]
Write down the line element, the metric, the Christoffel symbols and the Riemann curvature
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[5 marks]
(c) Determine V", that is, write the object in question A1.a in the coordinate system x'. Verify
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Question A2
[5 marks]
Suppose that A, is a covector field, and consider the object
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Chapter 28 Solutions
Astronomy
Ch. 28 - How are distant (young) galaxies different from...Ch. 28 - What is the evidence that star formation began...Ch. 28 - Describe the evolution of an elliptical galaxy....Ch. 28 - Explain what we mean when we call the universe...Ch. 28 - Describe the organization of galaxies into...Ch. 28 - What is the evidence that a large fraction of the...Ch. 28 - When astronomers make maps of the structure of the...Ch. 28 - How does the presence of an active galactic...Ch. 28 - Describe how you might use the color of a galaxy...Ch. 28 - Suppose a galaxy formed stars for a few million...
Ch. 28 - Given the ideas presented here about how galaxies...Ch. 28 - Can an elliptical galaxy evolve into a spiral?...Ch. 28 - If we see a double image of a quasar produced by a...Ch. 28 - The left panel of Figure 27.1 shows a cluster of...Ch. 28 - Suppose you are standing in the center of a large,...Ch. 28 - Astronomers have been making maps by observing a...Ch. 28 - Human civilization is about 10,000 years old as...Ch. 28 - Given that only about 5% of the galaxies visible...Ch. 28 - Using the information from Example 28.1, how much...Ch. 28 - Using the information from Example 28.1, if...Ch. 28 - Using the information from Example 28.1, how much...Ch. 28 - Galaxies are found in the “walls” of huge voids;...Ch. 28 - Calculate the velocity, the distance, and the...Ch. 28 - Assume that dark matter is uniformly distributed...Ch. 28 - The simulated box of galaxy filaments and...Ch. 28 - The first objects to collapse gravitationally...
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