Astronomy 1002
Homework #7
 
 


 

1. What perception of the Milky Way Galaxy did astronomer have in the early part of this century?

a) They believed that the Earth rested inside concentric spheres, with the Milky Way stars fixed to the outermost sphere.

b) They believed that the Milky Way was one of billions of galaxies in the universe.

c) They believed that the Sun was roughly in the center of the Milky Way.

d) They believed that, because the Sun was at the center of the Milky Way, it was impossible to see the rest of the universe.


 

2. Harlow Shapley determined the location of the center of the Galaxy by observations of:

a) Cepheids.

b) Globular clusters.

c) The spiral arms.

d) A visually bright, massive, object around which all objects in the Galaxy move.


 

3. Which is the correct description of the Sun's location within the Milky Way?

a) At the outer edge of the galactic bulge but in the plane of the disc.

b) In the disc but at its outer edge.

c) Above the disc and about one-third of the galactic radius from the center.

d) In the disc and about one-half a galactic radius from the center.


 

4. What two observations of an object allow for a determination of the Milky Way's mass?

a) Object's mass and velocity.

b) Object's age and distance from the galactic center.

c) Object's mass and age.

d) Object's velocity and distance from the galactic center.


 

5. What type of variable star is used to determine the distances to globular clusters?

a) RR Lyrae stars

b) Cepheids

c) T Tauri

d) flare stars

e) novae


 

6. Which of the following is not found in the Galaxy's halo?

a) globular clusters

b) old stars

c) stars with random, three dimensional orbits

d) red stars

e) emission nebulae containing young stars


 

7. The object located at the very center of the Galaxy is believed to be a ________.

a) a large cluster of stars

b) an enormous emission nebula

c) a black hole

d) a massive supernova

e) a massive star formation region


 

8. About how many galaxies are believed to exist?

a) 20 million

b) 2 billion

c) 20 billion

d) 2 trillion


 

9. What property is common to all spiral galaxies?

a) Ongoing star formation.

b) The disk, the bulge, the halo, and the corona.

c) Abundant interstellar gas.

d) all of the above

e) none of the above


 

10. Why does the Cepheid distance technique have limited usefulness beyond 5 Mpc?

 

a) Distant galaxies are seen in the past, when Cepheid variables behaved differently than they do today.

b) Distant galaxies are so young they do not contain Cepheids.

c) Cepheids are too faint to be seen.

d) The light variability of Cepheids diminishes with distance so that at 5 Mpc they do not appear to vary.


 

11. Collisions between galaxies:

a) Turn ellipticals into spirals.

b) May cause bursts of star formation.

c) Cause large numbers of stars to collide and explode.

d) Never occur.


 

12. What is the Great Wall?

a) It is not a structure but a distance beyond which astronomers cannot view galaxies.

b) It is the time before the universe started expanding; a time about which we can never know anything.

c) It is a large sheet of galaxies measuring 70 Mpc by 200 Mpc.

d) It is an enormous intergalactic cloud of dust and gas that hides more distant galaxies.


 

  13. Which of the following is the Hubble Law?

a) The greater the distance to a galaxy, the greater its redshift.

b) The greater the distance to a galaxy, the fainter it is.

c) The more distant a galaxy is, the younger it appears.

d) Most galaxies belong to a cluster; most clusters are part of a super cluster.


 

14. What does the Hubble Law measure?

a) The rate of expansion of the universe.

b) How galaxies are distributed in the universe.

c) How light gets fainter with increasing distance.

d) Light travels at a finite speed; we see objects the way they were when the light left them, not the way they are when we make our observation.


 

15. Which type of galaxy has a small bulge and loose, poorly defined spiral pattern?

a) S0

b) Sc

c) Sa

d) SBa

e) Sb


 

16. How many solar masses a year must a black hole consume to power a 1040 W quasar?

a) 1

b) 10

c) 100

d) 1000


 

17. In a lobe radio galaxy, the ultimate energy source for the entire radio source is thought to reside:

a) In the lobes.

b) In the galaxy's center.

c) In the jets.

d) all of the above

e) none of the above


 

18. Which of the following is not a characteristic of active galaxies?

a) They are generally more luminous than fairly bright normal galaxies.

b) Their energy emission can be explained as the accumulated emission of billions of stars.

c) Their energy output can be highly variable.

d) They often exhibit jets and other signs of explosive activity.

e) Their optical spectra may show broad emission lines, indicating rapid internal motion.


 

19. Why is the energy source of Seyfert galaxies thought to be extremely compact?

a) Their energy is totally nonstellar in origin.

b) Their spectra are like those produced by ordinary stars.

c) They vary on rapid time scales.

d) Seyferts can be seen clearly; we can see that the energy source is compact.


 

20. The look-back time of an object is directly related to its:

a) Distance.

b) Variability.

c) Luminosity.

d) Size.


 

21. What was discovered about the spectra of quasars?

a) The emission lines were from completely unknown elements.

b) The emission lines were formed by completely new processes never before observed.

c) They contained normal emission lines that were highly red shifted.

d) For the first time, stars were discovered to have radio emission lines.


 

22. What is the most likely source of energy for active galaxies and quasars?

a) Large clusters of very massive, luminous stars.

b) A single supermassive, superluminous star.

c) Accretion onto a supermassive black hole.

d) Numerous supernovae from rapid star formation in young galaxies.


 

23. Quasars have their distances measured by what technique?

a) Cepheids

b) Tully-Fisher relation

c) Supernovae

d) parallax

e) Hubble law


 

24. Because all of the galaxies are redshifted, we know that:

a) We are at the center of the universe.

b) The universe is expanding.

c) The sky is dark at night.

d) all of the above

e) none of the above


 

25. Homogeneity and isotropy, taken as assumptions regarding the structure and evolution of the universe, are known as:

a) The Hubble Law.

b) Riemannian geometry.

c) Grand Unified Theory.

d) The cosmological principle.


 

26. In which of the following models will the universe stop expanding?

a) Open universe.

b) Closed universe.

c) Critical universe.

d) all of the above

e) none of the above


 

 

27. What does the Hubble law imply about the history of the universe?

a) The universe started expanding at some time in the past; the universe has an age.

b) The universe has been expanding forever; it is infinitely old.

c) The Milky Way galaxy is at the exact location where the universe started to expand.

d) Before the universe started to expand, it had collapsed and expanded many times before.


 

28. The cosmic microwave background is important mostly because:

a) Its detection represented a major technological advance.

b) It confirmed a major prediction made by the Big Bang theory.

c) It showed that the universe is open.

d) It showed that the universe is closed.


 

29. The universe has three possible futures. Which one is correct depends only on the average density of matter in the universe. Why is this?

a) The density of matter determines the strength of gravity, which decelerates the expansion over time.

b) The density of matter determines the rate of formation of black holes which will eventually collapse the universe.

c) The density of matter tells astronomers whether new matter is constantly forming, thereby producing a steady-state.

d) If the density is sufficiently high, the geometry of space may be curved.


 

30. What is the meaning of a "closed" universe?

a) The universe will expand forever.

b) The universe will someday stop expanding and start to collapse.

c) The universe will stop expanding in an infinite amount of time.

d) The universe is in a steady-state.


 

31. The redshift of galaxies in the universe is correctly interpreted as:

a) A Doppler shift due to the motions of the galaxies through space.

b) An "aging" of the light.

c) Space itself is expanding with time; the wavelengths of photon are stretched while they travel through space.

d) The difference in temperatures of distant and nearby galaxies.


 

32. Why didn't an abundance of elements heavier than helium form in the early universe?

a) The expansion of the universe caused the temperature and density to drop too low for fusion to occur.

b) Heavier elements did form, but they didn't survive the process that made the earliest stars and galaxies.

c) The laws of physics prohibit the formation of elements heavier than helium, except in the confined environments of stellar interiors.

d) all of the above

e) none of the above


 

33. Currently, most of the mass of the universe is believed to consist of:

a) Protons and neutrons.

b) Dark matter.

c) The stars.

d) Black holes.