Question 1

In which of these sites in the universe has a supermassive black hole been proposed to account for recent observations?

Accepted Answer

A)  center of the Milky Way 
B)  center of the Ring Nebula, a planetary nebula in Lyra 
C)  center of the universe, where the Big Bang occurred at the beginning of the universe 
D)  center of the Crab Nebula, an old supernova remnant

Question 2

Which parameters of star motion in the Milky Way are represented by its rotation curve?

Accepted Answer

A)  orbital speed as a function of star distance from the galactic center 
B)  orbital period of the stars as a function of their distance from the galactic center 
C)  orbital speed of the stars as a function of their individual masses 
D)  star position above or below the galactic plane as a function of distance from the galactic center

Question 3

The method Hubble used to determine the distance to the Andromeda Galaxy (M31), thereby establishing the concept of separate and individual galaxies throughout the universe, was the

Accepted Answer

A)  observation of Cepheid variable stars. 
B)  measurement of the redshift of the whole galaxy. 
C)  measurement of stellar parallax, or apparent motion, of stars because of Earth's orbital motion. 
D)  observation of the brightnesses of novae.

Question 4

The galactic halo contains outer and inner shells of stars. How does the outer shell compare to the inner shell?

Accepted Answer

A)  The two shells are virtually identical except for their distance from the galactic nucleus. 
B)  The outer shell contains all of the globular clusters. 
C)  The inner shell contains all of the globular clusters 
D)  The stars of the outer shell are relatively metal-rich.

Question 5

If astronomers aim a radio telescope at a distant spiral arm of the Milky Way Galaxy, they will probably observe a 21-cm line. If they point a large optical telescope at this same region, they will probably not be able to detect the neutral hydrogen that gives rise to the 21-cm radio signal. Why not?

Accepted Answer

A)  Neutral hydrogen is incapable of emitting visible radiation. 
B)  The H  $\alpha$  line-the primary emission of neutral hydrogen-has a much smaller energy than the 21-cm radio wave and thus is harder to detect. 
C)  There is little energy in the depths of space to excite visible radiation from neutral hydrogen. 
D)  The visible light emitted by neutral hydrogen is all absorbed by H II gas regions before reaching the solar system.

Question 6

In the 1780s, Sir William Herschel tried to measure the Sun's position in the Milky Way Galaxy by

Accepted Answer

A)  counting the density of stars in different directions along the Milky Way. 
B)  measuring distances to star clusters and H II regions in the disk of the Galaxy. 
C)  measuring the locations of globular clusters around the Galaxy. 
D)  comparing the Milky Way with the Andromeda Galaxy.

Question 7

Where in space should an astronomer look for a globular cluster?

Accepted Answer

A)  in the Milky Way disk, moving in a circular orbit around the galactic center 
B)  in elliptical galaxies, because they are composed of old stars and do not exist in young systems like spiral galaxies 
C)  in the Milky Way galactic halo, orbiting the galactic center in a long elliptical orbit around the galactic center 
D)  in the asteroid belt

Question 8

Which of these statements correctly describes the rotation of the Milky Way Galaxy?

Accepted Answer

A)  The disk rotates like a solid object (objects at all distances take the same time to complete an orbit), and the globular clusters have random orbits with no net rotation of the halo about the center of the Galaxy. 
B)  Objects in the disk have random orbits with no net rotation of the disk about the center of the Galaxy, and the globular clusters rotate differentially (objects farther from the center take longer to complete an orbit than objects closer to the center). 
C)  The disk rotates differentially (objects farther from the center take longer to complete an orbit than objects closer to the center), and the globular clusters rotate differentially (objects farther from the center take longer to complete an orbit than objects closer to the center). 
D)  The disk rotates differentially (objects farther from the center take longer to complete an orbit than do objects closer to the center), and the globular clusters have random orbits with no net rotation of the halo about the center of the Galaxy.

Question 9

In order to measure the speed of the Sun with respect to the center of the Galaxy, it was necessary to establish a rest frame. What was used to establish this frame?

Accepted Answer

A)  the average of several nearby galaxies 
B)  the globular clusters in the halo because they remain at rest while the Galaxy rotates beneath 
C)  the globular clusters in the halo because their velocities must average to zero 
D)  the Great Attractor because its enormous mass acts like a stationary point

Question 10

When distances were carefully measured from Earth to globular clusters above and below the Milky Way plane (where the 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 11

The dark matter halo is estimated to extend out about 12 times farther from the galactic center than the solar system's position. How does this compare with the distance to the nearest large galaxy, Andromeda (M31), which is 2.2 million light-years away?

Accepted Answer

A)  The dark matter halo reaches only about 1 percent of the way to M31. 
B)  The dark matter halo reaches about one-seventh of the way to M31. 
C)  The dark matter halo just falls short of M31. If the Andromeda Galaxy has its own dark matter halo, the two must overlap. 
D)  Earth's dark matter halo engulfs M31.

Question 12

What is it that makes the study of the structure of the Milky Way Galaxy more difficult than that of much more distant spiral galaxies?

Accepted Answer

A)  The galactic center is visible only from the southern hemisphere, where, until recently, no major telescopes were available for the study of galactic structure. 
B)  The Milky Way appears to be unique, with a structure quite unlike any other galaxy. 
C)  The Sun is within the Galaxy, and its motion confuses the interpretation of the motion of other parts of the Galaxy. 
D)  Most of the Milky Way is hidden behind dense gas and dust clouds in the galactic plane.

Question 13

The vast majority of the stars in the galactic halo are isolated field stars. What is the origin of these stars?

Accepted Answer

A)  These very old stars are left over from the original infall of the material that formed the Galaxy. 
B)  These are stars left over from the formation of the globular clusters. 
C)  These are stars that were moving too fast and were expelled from globular clusters. 
D)  These are the remnants of small galaxies that have been absorbed by the Milky Way Galaxy.

Question 14

The diameter of the Milky Way Galaxy is about

Accepted Answer

A)  100 kpc. 
B)  31 kpc. 
C)  3.1 kpc. 
D)  2 kpc.

Question 15

What type of object has been proposed to explain the tremendous activity detected at the center of the Milky Way Galaxy?

Accepted Answer

A)  giant molecular cloud 
B)  supermassive black hole 
C)  supernova explosion 
D)  rapidly rotating neutron star

Question 16

If the galactic center of the Milky Way is now thought to contain a supermassive black hole, why is the Sun NOT falling into it under the black hole's extreme gravity?

Accepted Answer

A)  The Sun's mass is so small that even the extreme mass concentration at the galactic center will not exert a significant force on it. 
B)  The inward force exerted on the Sun from the black hole is offset by the force exerted outward by the hidden "dark" matter beyond the Sun's orbit. 
C)  The mutual gravitational forces of local stars in the Orion spiral arm are sufficient to overcome the strong inward force and keep the Sun moving in its orbit. 
D)  The Sun has sufficient velocity that it can orbit the galactic center in a circle.

Question 17

In 2006, a Type Ia supernova erupted in the spiral galaxy M100. Its peak apparent magnitude was +13.5, and its absolute magnitude was about -17.5. What do these numbers give for its distance?

Accepted Answer

A)  7 kpc 
B)  10 kpc 
C)  31 kpc 
D)  42 kpc

Question 18

Of the entries in this list of questions about the Milky Way Galaxy, which ONE has been answered at the present time?

Accepted Answer

A)  Did the central black hole form first or did the Galaxy form first? 
B)  Does the Galaxy have a central bar or not? 
C)  What is dark matter? 
D)  What is creating the positrons near the center of the Milky Way?

Question 19

Which of these components of the Milky Way was recently mapped by the Planck satellite?

Accepted Answer

A)  the spiral arms 
B)  the global magnetic field 
C)  an X-shaped set of stars near the galactic center 
D)  atomic hydrogen

Question 20

In determining the distance to a galaxy by using observations of a Cepheid variable star, which of these properties is NOT needed?

Accepted Answer

A)  average brightness or apparent magnitude of the Cepheid 
B)  velocity of the Cepheid via the Doppler effect 
C)  type of spectrum of the Cepheid-whether it is metal-rich or metal-poor 
D)  period of variability of the Cepheid

Exam 16: The Milky Way Galaxy