Question 1

One piece of evidence for the existence of dark matter is the:

Accepted Answer

A)  absence of interstellar materials (gas and dust) from elliptical galaxies. 
B)  low count of neutrinos emitted from the center of the Sun. 
C)  scarcity of dwarf ellipticals in the Local Group of galaxies. 
D)  discrepancy between observed mass and the required gravitational binding in rich clusters of galaxies.

Question 2

Seyfert galaxies are:

Accepted Answer

A)  active galaxies with bright, starlike nuclei. 
B)  irregular galaxies with no shape or structure. 
C)  very small elliptical galaxies. 
D)  the largest galaxies in the universe.

Question 3

What is the evidence that indicates to some astronomers that a supermassive black hole exists at the center of the Milky Way Galaxy?

Accepted Answer

A)  A Doppler shift of light from stars in the near neighborhood of the galactic center indicates that the stars are falling inward at very high speeds. 
B)  The Sun's motion in space shows that, if Kepler's law holds for its orbit around the galactic center, there must be a very massive object at the center of the Milky Way. 
C)  No electromagnetic radiation at all comes from the precise position of the galactic center, and it just looks like a dark void in space. 
D)  Measurement of gas clouds orbiting the galactic center at very high speeds indicates that they would rapidly move out of the Galaxy unless some very massive object were holding them in orbit.

Question 4

Many rich,regular clusters of galaxies contain substantial amounts of very hot,intergalactic gas.What is believed to have produced this hot gas?

Accepted Answer

A)  collisions between galaxies in the cluster 
B)  bursts of star formation in merging galaxies 
C)  supernovae (exploding stars) 
D)  jets of gas ejected by supermassive black holes at the centers of the galaxies

Question 5

A radio astronomer points a radio telescope through the Milky Way's disk in a direction directly away from the center of the Galaxy.If the astronomer measures the Doppler shift of the 21-cm radio line of hydrogen from interstellar clouds at several different distances from the Sun along this line of sight,what should be the result? (Figure 13-7 of Comins,Discovering the Essential Universe,6th ed.,may be helpful.)

Accepted Answer

A)  The Doppler shift should have a constant value, regardless of distance, as a result of the Sun's speed of motion around the center of the Galaxy. 
B)  The Doppler shift should be almost zero for all clouds, regardless of distance. 
C)  The Doppler shift should rise to a maximum at some distance, then decrease again. 
D)  The Doppler shift should be larger the farther away the cloud is.

Question 6

Does the halo of the Milky Way Galaxy include other galaxies?

Accepted Answer

A)  No. It is not possible for one galaxy to orbit another galaxy. 
B)  No. The halo is limited to field stars and globular clusters. 
C)  Yes. The halo region includes the Andromeda Galaxy. 
D)  Yes. The halo region includes several small galaxies, among them the Magellanic Clouds, two small, irregular galaxies.

Question 7

One of the consequences of the collision of two galaxies appears to be:

Accepted Answer

A)  a burst of vigorous star birth. 
B)  a very large explosion, similar to but much larger than a supernova, often known as a superdupernova. 
C)  almost nothing since stars are widely separated in each galaxy and the probability of star-star collisions is very small. 
D)  the disappearance of one of them into the central black hole of the other.

Question 8

What would you expect to be the overall color of a globular cluster of stars? Explain.

Accepted Answer

A)  blue because of the contribution from young and very hot stars in the cluster 
B)  red because of the emission of light by the hydrogen gas in H II regions surrounding the stars in the cluster 
C)  red because of the older population of stars in the cluster 
D)  blue because of the scattering of starlight from the dust surrounding the stars in the cluster

Question 9

When distances were carefully measured from Earth to globular clusters above and below the Milky Way plane (where our view of them is not obscured by interstellar dust and gas),the distribution of the clusters was found to be:

Accepted Answer

A)  spherically symmetric about a point in the constellation Sagittarius and concentrated in that direction. 
B)  in a relatively flat disk almost perpendicular to the plane of the Galaxy, with a relatively higher density of clusters toward its center. 
C)  concentrated in the plane of the Milky Way and clustered around the Sun's position, indicating that the Sun is close to the Galaxy's center. 
D)  uniformly distributed throughout space, with no concentration in any area of the Milky Way.

Question 10

The ratio of thickness to diameter of the Milky Way Galaxy is:

Accepted Answer

A)  1/500. 
B)  1/5. 
C)  1/50. 
D)  1/1000.

Question 11

If the black hole in the center of the Milky Way Galaxy were 4 × 10⁶ solar masses,what would be the orbital period of Earth around this hole in an orbit of radius 1 AU (assuming that Newtonian physics and Kepler's third law apply)?

Accepted Answer

A)  less than 1 second 
B)  3 minutes 
C)  4 hours 
D)  5 weeks

Question 12

What is the designation given to a galaxy with a large nuclear bulge and tightly wound arms starting from a bar through the nuclear bulge?

Accepted Answer

A)  Sb 
B)  SBa 
C)  SBc 
D)  Sa

Question 13

The amount of visible matter in a typical cluster of galaxies is:

Accepted Answer

A)  just sufficient to hold the inner regions of the cluster together, but the fringe galaxies are drifting away from this center. 
B)  not sufficient to hold the cluster together by a factor of 2, such that the cluster is slowly spreading out. 
C)  insufficient to hold the cluster together, by about a factor of 10. 
D)  far more than enough to hold the cluster together gravitationally and is slowly concentrating the cluster into a very tight supercluster.

Question 14

Gravitational lensing of distant objects by closer galaxies indicates that the:

Accepted Answer

A)  amount of visible matter in the galaxies accounts for only 10% of the total mass producing the lensing. 
B)  amount of visible matter in the galaxy is about 10 times too great to account for the observed lensing, leading to the idea of negative gravitation within such large-scale structures. 
C)  amount of visible matter in the galaxies is sufficient to account for the gravitational lensing. 
D)  total mass within the galaxies that produces the lensing exceeds the amount of visible matter by a factor of 100.

Question 15

Who was the first person to observe the spiral structure of distant galaxies with a telescope?

Accepted Answer

A)  Sir Isaac Newton 
B)  Sir William Herschel 
C)  William Rosse 
D)  Galileo Galilei

Question 16

What is a lenticular (or S0)galaxy?

Accepted Answer

A)  a galaxy with a central bulge and a disk like a spiral galaxy, but with no spiral arms 
B)  a galaxy with a smooth brightness profile and lacking the central bulge and disk of a spiral galaxy 
C)  a galaxy with a lot of gas and dust and no particular structure 
D)  a spiral galaxy with fuzzy and poorly formed spiral arms

Question 17

Most of the light from a galaxy comes from the inner parts.If this means that most of the galaxy's mass is also in the inner region,then how would we expect the galaxy's speed of rotation to behave in its outer region?

Accepted Answer

A)  The rotation speed should increase with increasing distance from the center. 
B)  The rotation speed should decrease sharply to zero at the outer edge of the visible galaxy. 
C)  The rotation speed should not change appreciably with increasing distance from the center (i.e., a "flat" rotation curve). 
D)  The rotation speed should decrease smoothly with increasing distance from the center.

Question 18

NGC 1265,an active galaxy in the Perseus cluster,is described as a head-tail source because (see Figure 13-62,Comins,Discovering the Essential Universe,6th ed.):

Accepted Answer

A)  it resembles a horse's tail and is located near the Horsehead nebula in Orion. 
B)  the jets are emitted from the radio lobes and stream toward the nucleus, the reverse of what happens in a normal radio galaxy. 
C)  this galaxy is peculiar and is exploding and sending out many jets that interact with the surrounding intergalactic material. 
D)  the two jets interact with the rapidly moving intergalactic medium, which sends them streaming out behind the galaxy in a pair of arcs.

Question 19

What appears to be the central energy-generating system or "engine" that is producing prodigious amounts of energy in the centers of galaxies,active galaxies,and quasars?

Accepted Answer

A)  a steady series of supernova explosions, the late evolutionary stages of massive stars 
B)  a rapidly rotating core of matter, where friction between it and the surrounding matter causes tremendous heat and energy output 
C)  a supermassive black hole, where matter is compressed falling into the hole and heated to extremely high temperatures 
D)  There is no central "engine" in these sources. Their high gravity has focused radiation from many sources beyond them by gravitational lensing and they thus appear to be very bright.

Question 20

What is the basic shape of a spiral galaxy?

Accepted Answer

A)  a round, flat disk with long lanes of stars that curve outward from a round, nuclear region of uniform brightness 
B)  a round, flat disk with long lanes of stars that curve outward from the center of the galaxy 
C)  approximately spherical with long lanes of dark dust clouds curving through it in a spiral pattern 
D)  a round, thin disk of uniform brightness with its edges bent up and down into a spiral shape

Exam 13: The Galaxies