ASTRONOMY 123
Exam II
Answers
1. The absorption of smaller galaxies into larger ones is called
a. galactic cannibalism
2. Collisions between galaxies:
b. may cause bursts of star formation
3. What is the Great Wall?
c. a large sheet of galaxies, one of the largest known
structures in the universe.
4. The Cartwheel Galaxy and the Antennae are examples of
b. collisions of galaxy
5. Galaxies in collision can result in
a. Starburst galaxies
b. Ejection of stars
c. Galactic cannibalism
--> d. All of the above
6. What is a supercluster?
b. A cluster of clusters of galaxies
7. What is the Einstein Cross?
a. evidence for gravitational lensing
8. The cosmic microwave background radiation was discovered
a. with a low-noise radio antenna
9. The present temperature of the cosmic microwave background radiation is
a. 2.7 K
10. The Cosmological Assumptions include all of the following except
c. The universe is infinite
11. The existence of the cosmic microwave background radiation implies
b. the universe had a hot, dense period in the past
12. The Universality of Physical Laws means
d. The same physical laws apply to all localities at all times
13. Which of the following is an observed property of the cosmic microwave
background radiation?
d. Its spectrum matches a blackbody spectrum
14. We know the "center" of the universe from
d. The concept of "center" of the universe does not exist
in our modern view
15. How old is the universe
a. about 14 billion years
16. A closed universe is
c. finite and unbounded
17. An open universe is
c. infinite and unbounded
18. Double quasars confirm the theory of
d. general relativity
19. Images of young, background galaxies, warped by the gravitational field
of a foreground galaxy cluster are
c. blue arcs
20. A thought experiment suggesting the entire night sky should be as
bright as the Sun
c. Olbers's Paradox
21. A double quasar is explained by
a. the gravitational-lens effect
22. The eventual fate of the universe depends on
b. its density
23. The Big Bang
a. was an expansion of space
b. happened about 14 billion years ago
c. involved the entire universe
---> d. all of the above
24. What is the approximate value of "Omega nought" (Ω0)?
b. 1
25. What is a gravitational lens?
a. light is bent by matter
26. About how old was the universe when it had cooled to 3000 K?
c. 400,000 years
27. What theory explains the curvature of space?
d. Einstein's General Theory of Relativity
28. What is the approximate fraction of the critical density represented by
normal matter?
a. 0.05
29. During the Big Bang, which of the following elements was formed in the
largest quantity
---> a. helium
b. uranium
c. iron
d. gold
30. The existence of the cosmic microwave background implies
b. the universe had a hot, dense period in the past
(Question 30 is a repeat of question 11 above!)
31. Dark matter is thought to make up ___ percent of all matter in
the universe. (Note, in this you ignore the presence of dark energy.)
d. more than 80
32. What might arise from vacuum energy?
b. A cosmological constant
33. Galaxies in clusters
b. Sometimes collide
34. The evolutionary path of galaxies
c. is not simple, depending on the details of collisions
35. What do we learn from analysis of Planck data?
a. Age of the universe
b. Total energy-mass density (Ω0)
c. Fractions of ordinary matter, dark matter, and dark energy
---> d. All of the above
36. The first evidence of dark energy came from
a. Measurements of distant supernovae
37. Dark energy is responsible for
b. An accelerating expansion of the universe
38. The possible geometries of the universe in Einstein's General Theory are
d. flat, open, or closed
39. What was the temperature of the universe when it was 400,000 years old?
b. 3000 K
40. Which of the following supports the Big Bang?
a. Hubble's Law
b. Existence of Quasars
c. Cosmic microwave background
---> d. All of the above
41. The Cosmological Principle states
c. On a large scale, the universe is homogeneous and isotropic
42. The largest structures seen in the universe are
c. 200 - 300 Mpc in size
43. Dark matter is likely mostly composed of
b. undiscovered exotic subatomic particles
44. A galaxy left alone will evolve slowly, in a predictable way.
a. Ellipticals will become fainter and redder as stars burn out
45. Geometry of the universe if the density of matter is less than the
critical density
b. open universe
46. Supermassive black holes
b. are commonly found at the centers of galaxies
47. In surveys of galaxies, bubbles of galaxies are found to surround
unpopulated regions called
a. voids
48. The bullet cluster is an example of
c. the collision of two galaxy clusters
49. A relationship between supermassive black holes and host galaxies is
d. the more massive the host galaxies, the more massive its
black hole
50. Assumed property of the universe which says the number of galaxies in
a volume of space is the same no matter where that volume is
d. homogeneous
51. Quantity introduced by Einstein to make his equations describe a static
universe
a. cosmological constant
52. Mass in galaxies and clusters inferred from rotation curves and other techniques
b. dark matter
53. Geometry of the universe if the density of matter is greater than the
critical density
a. closed universe
54. Assumed property of the universe which says it is the same in all directions
c. isotropic
55. Grouping of several clusters of galaxies into a larger unit
b. supercluster
56. Galaxy in which a violent event has caused an intense period of star formation
a. starburst galaxy
57. A galaxy left alone will evolve slowly, in a predictable way.
b. Spirals will remain bluish as long as there is new star
formation
58. Possible galaxy composed almost entirely of dark matter, emitting
virtually no visible light
d. dark galaxy
59. The concept that galaxies grew through repeated merging of smaller objects
d. hierarchical merging
60. Galaxy rotation curves suggest
a. galaxies contain large amounts of dark matter
61. The distance from Earth to the Great Wall is
d. about 100,000,000 pc
62. Geometry of the universe if its density is equal to the critical density
c. flat universe
SHORT ANSWER QUESTIONS
1. What contributes most of the density of the universe?
Dark Energy
2. If the Hubble constant is 20 km/s/Mly, how fast will a galaxy at a
distance of 100 Mly years appear to be receding from us?
20 km/s/Mly × 100 Mly
= 2,000 km/s
3. If the Hubble constant is 20 km/s / Mly, at what look-back time will a
galaxy appear to be receding from us at the speed of light?
Hubble's Law: Speed = H × Distance
Distance = Speed / H
= 300,000 km/s / 20 km/s/Mly
= 15,000 Mly = 15 billion light-years
Look back time = 15 billion years
4. In a closed universe, how does the density of the universe compare to
the critical density?
The density is greater than the critical density
5. What is the name of the thought experiment suggesting that if the universe
were homogeneous, infinite, and unchanging, the entire sky would be as bright
as the surface of the Sun?
Olbers' Paradox
6. What is the name of Einstein's "fudge factor" which he invented to create
a static universe in his equations?
Cosmological constant
7. What object is thought to be at the center of a quasar?
Supermassive black hole