PSc 100:
Study Guide Questions for Week 9



1) A megaparsec is equivalent to

a) 3.26 light years.
b) 206,265 light years.
c) 206,265 AU.
d) 3,260,000 light years.
e) the diameter of the Milky Way.


2) The look-back time is

a) how long the light from an object takes to reach Earth.
b) numerically equal to the distance in light years.
c) smaller for more distant objects.
d) All of the above.
e) a and b above.


3) The mass of a single galaxy might be found by

a) the double galaxy method.
b) the rotation curve method.
c) the cluster method.
d) Any of these methods.
e) None of these methods.


4) Elliptical galaxies contain ...

a) younger stars and more gas and dust than
b) younger stars and less gas and dust than
c) older stars and more gas and dust than
d) older stars and less gas and dust than
e) [The answer depends on the size of the galaxy.]

... spiral galaxies.


5) What is the type of the bright galaxy above?

a) E1
b) E5
c) Sa
d) Sc
e) SBc


6) What is the type of the bright galaxy above?

a) E1
b) E5
c) Sa
d) Sc
e) SBc


7) Which type of galaxies contains large clouds of gas and dust, both old and young stars, but have no obvious spiral arms or nucleus?

a) Irregular.
b) S0.
c) E7.
d) Sa.
e) E0.


8) Voids are

a) regions in an elliptical galaxy where few clouds of gas and dust are found.
b) regions in the Local Group where light from distant galaxies is blocked by gas and dust.
c) regions in a cluster of galaxies where no spiral galaxies are found.
d) empty regions in the Universe that separate filaments of superclusters.
e) regions swept clean by the hot intergalactic medium.


9) Most of the mass in most galaxies is contained in

a) massive O and B stars.
b) HI (neutral hydrogen) regions.
c) HII (ionized hydrogen) regions.
d) dark matter.
e) the disk of the galaxy.


10) Observations of type Ia supernovae can be used to infer a galaxy's

a) mass.
b) luminosity.
c) distance.
d) angular momentum.
e) Hubble type.


11) If a galaxy is receding from us at a velocity of 2,100 km/s, what is its distance from us? (Assume a Hubble constant of 70 km/s/Mpc)


12) Tidal tails are the result of

a) multiple supernova explosions in a galaxy.
b) galaxy cannibalism.
c) the interaction and merging of two similarly-sized galaxies.
d) precessing jets from accretion disks around supermassive black holes in active galaxies.
e) the interaction and merging of two galaxy clusters.


13) Seyfert I galaxies are different from Seyfert II galaxies in the following way:

a) Seyfert IIs are brighter and have broader emission lines.
b) Seyfert IIs have no emission lines.
c) Seyfert IIs have less powerful radio jets.
d) Seyfert IIs have have weaker and narrower emission lines.
e) Seyfert IIs contain less massive black holes in their center.


14) If the red shifts of quasars arise from the expansion of the Universe,

a) quasars must be very small.
b) quasars must be within the Local Group.
c) quasars must be single stars with an extremely large mass.
d) quasars must be moving toward the Earth at a large radial velocity.
e) quasars must be very luminous.


15) The discovery of the gravitational lens effect for distant quasars confirmed

a) that quasars were located within the Local Group of galaxies.
b) that quasars were giant elliptical galaxies at very great distances.
c) Einstein's theory of general relativity, predicting that large masses could bend light.
d) Newton's theory of universal gravitation by showing that the photon was affected by gravity.
e) the existence of supermassive black holes at the center of active galactic nuclei.


16) The image above shows an X-ray image of the central core and the jet of the quasar 3C~273. No jet is observed on the opposite side of the bright central source, because

a) there is no counter-jet in the opposite direction.
b) the counter-jet in the opposite direction is much less energetic than the one we see.
c) the counter-jet in the opposite direction is obscured by gas and dust near the center of the galaxy hosting the quasar.
d) the jet is moving almost at the speed of light, and we only see the component of the jet that is pointing towards us because it is Doppler boosted.
e) the counter-jet is obscured by the thick accretion disk around the central supermassive black hole.


17) If we were observing the quasar shown above Question 16) from a different direction, we might be seeing a

a) radio galaxy.
b) Herbig-Haro object.
c) Seyfert I galaxy.
d) Seyfert II galaxy.
e) planetary nebula.


18) What was the solution to Olbers' Paradox?


19) In the course of the expansion of the Universe,

a) clusters of galaxies are also expanding in size.
b) Galaxies and galaxy clusters are moving along with the expanding space, but keep their individual sizes.
c) galaxies are also expanding as they move along with the expanding Universe.
d) galaxies and clusters of galaxies keep their individual sizes as they expand through the structure of space-time.
e) objects of all size scales are expanding along with the cosmic expansion.


20) The assumptions of homogeneity, isotropy and universality are collectively called the

a) universal law of cosmology.
b) theory of general relativity.
c) equivalence principle.
d) first postulate of cosmology.
e) cosmological principle.


21) According to the theory of general relativity, the curvature of space-time is caused by

a) the presence of massive objects.
b) relativistic motion.
c) the presence of energy in any form.
d) All of the above.
e) a and c above.


22) A high red shift z corresponds to

a) a low luminosity.
b) a low mass.
c) a large look-back time (early cosmological time).
d) a late cosmological time.
e) a small distance.


23) What was the mass percentage of Helium ("the primordial Helium abundance") formed during the big bang?


24) What was the red shift of the Universe that marks the transition between the radiation dominated and the matter dominated era, and what temperature did the Universe have at that time? What happened at that time, and why is it so significant?


25) What could astronomers conclude from the anisotropy of the cosmic microwave background radiation?

a) The Universe has a flat geometry.
b) The Universe had a beginning in time.
c) The Universe does not have a boundary in space.
d) The Universe is accelerating.
e) Most of the matter in the Universe is contained in dark matter.


26) The value of the large-scale mass density of the Universe that would bring the cosmic expansion to a halt at infinity is called the

a) nuclear density.
b) critical density.
c) cosmological density.
d) flat density.
e) neutral density.


27) How could an accelerating Universe be accomodated within the concept of general relativity?

a) By introducing a negative mass density.
b) By abandoning the assumption of homogeneity.
c) By abandoning the assumption of isotropy.
d) By abandoning the equivalence principle.
e) By introducing a non-zero cosmological constant.


Answers to study guide questions


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