Question 1

What is the most common form of gas in the interstellar medium?

Accepted Answer

A)  atomic hydrogen
B)  molecular hydrogen
C)  molecular helium
D)  ionized hydrogen
E)  atomic helium

Question 2

The galactic center lies in the direction of which constellation?

Accepted Answer

A)  the Big Dipper
B)  Sagittarius
C)  Taurus
D)  Leo
E)  Orion

Question 3

How do low mass stars transport newly formed elements into the interstellar medium?

Accepted Answer

A)  stellar winds
B)  F supernova explosions
C)  formation of planetary nebula
D)  A and B
E)  A and C

Question 4

Where does most star formation occur in the Milky Way today?

Accepted Answer

A)  in the bulge
B)  in the spiral arms
C)  uniformly throughout the Galaxy
D)  in the Galactic center
E)  in the halo

Question 5

What is the best evidence for an extremely massive black hole in the center of the Milky Way?

Accepted Answer

A)  We observe stars vanishing in the center of the Galaxy as they are sucked into the black hole.
B)  The orbits of stars in the center of the galaxy indicate that the presence of 3 to 4 million solar mass object in a region no larger than our Solar System.
C)  The center of our galaxy hosts a pulsar that is spinning so fast that it could only be a black hole.
D)  Huge amounts of X- rays are pouring out of the center of the galaxy.

Question 6

Why do stars in the disk of a spiral galaxy orbit in roughly the same direction, in the same plane in space?

Accepted Answer

A)  The gas that formed the stars was shaped as a giant, rotating disk.
B)  Collisions between the stars caused their motions to organize into a general, spinning disk direction.
C)  After the stars formed, gravity pulled the stars down into a plane in space, all orbiting a supermassive black hole.
D)  It is pure coincidence; the stars just happen to be going in the same direction.

Question 7

Which of the following does not accurately describe what we observe toward the Galactic center?

Accepted Answer

A)  At X- rays, we see faint emission from an accretion disk around a black hole.
B)  At radio wavelengths, we see giant gas clouds threaded by powerful magnetic fields.
C)  At infrared wavelengths, we see a massive star cluster.
D)  At optical wavelengths, we see a cluster of old, red stars.

Question 8

Which of the following properties is more likely to be a characteristic of a halo star in the Milky Way, not a disk star?

Accepted Answer

A)  It has a low ratio of iron to hydrogen.
B)  It is moving very slowly relative to the Sun's motion.
C)  It could be quite young.
D)  It orbits the center of the Milky Way galaxy.

Question 9

Where do most dust grains form?

Accepted Answer

A)  in molecular clouds
B)  in planetary nebulae
C)  in supernovae
D)  in the winds of red giant stars
E)  all of the above

Question 10

What is the most abundant molecule in interstellar clouds besides molecular hydrogen?

Accepted Answer

A)  carbon monoxide
B)  water
C)  ammonia
D)  methane
E)  molecular helium

Question 11

How do high- mass stars make it more difficult for a molecular cloud to form more stars?

Accepted Answer

A)  Ultraviolet photons heat the gas.
B)  Radiation pressure pushes ionized gas away.
C)  Ultraviolet photons ionize the gas.
D)  Strong winds push gas away.
E)  All of the above

Question 12

What do halo stars do differently from disk stars?

Accepted Answer

A)  They orbit the galactic center with many different inclinations, while disk stars all orbit in nearly the same plane.
B)  They remain stationary, quite unlike disk stars that orbit the galactic center.
C)  They orbit the center of the galaxy at much lower speeds than disk star.
D)  Halo stars explode as supernovae much more frequently than disk stars.

Question 13

Most nearby stars move relative to the Sun at speeds below about 30 km/s. Suppose you observe a nearby star that is moving much faster than this (say, 300 km/s) . Which of the following is a likely explanation for its high speed?

Accepted Answer

A)  It is a very high mass star.
B)  It is a very young star, recently formed.
C)  It is probably a halo star that is currently passing through the disk.
D)  It has been pushed to high speed by the shock wave from a nearby supernova.

Question 14

Approximately how long does it take the sun to go through a full cycle of passing above and below the plane of the galaxy?

Accepted Answer

A)  a few thousand years
B)  a few hundred years
C)  a few million years
D)  a few tens of millions of years

Question 15

Observing our galaxy at radio wavelengths allows us to see through the dust in the disk that obscures our view.

Accepted Answer

A) True 
 B)False

Question 16

The Sun lives in which component of the Milky Way?

Accepted Answer

A)  the disk
B)  the bulge
C)  the halo
D)  a globular cluster A

Question 17

On a dark summer night in the northern hemisphere, we can see the Milky Way, but we can't see the center of the Milky Way. Why not?

Accepted Answer

A)  There are no stars in the center of the Milky Way, just a supermassive black hole.
B)  Interstellar dust and gas absorb and scatter visible light.
C)  We are in the center of the Milky Way.
D)  The center of the Milky Way does not emit enough visible light. B

Question 18

The image of our galaxy in radio emission from carbon monoxide maps the distribution of molecular clouds. Which of the following would give a similar picture of our galaxy?

Accepted Answer

A)  visible light, showing the edges of supernova bubbles
B)  visible light, which is closest to how the night sky appears from Earth
C)  X- rays from hot gas bubbles in the disk
D)  21- cm- line radio emission from atomic hydrogen
E)  infrared emission from interstellar dust grains E

Question 19

Harlow Shapley concluded that the Sun was not located at the center of the Milky Way Galaxy by

Accepted Answer

A)  looking at the shape of the "milky band" across the sky.
B)  looking at other nearby spiral galaxies.
C)  mapping the distribution of globular clusters in the galaxy.
D)  mapping the distribution of gas clouds in the spiral arms.
E)  mapping the distribution of stars in the galaxy.

Question 20

Suppose you discovered a star made purely of hydrogen and helium. How old do you think it would be? Explain.

Accepted Answer

A star made of only hydrogen and helium ...

Exam 15: Our Galaxy

What is the most common form of gas in the interstellar medium?

Correct AnswerverifiedShow Answer

The galactic center lies in the direction of which constellation?

Correct AnswerverifiedShow Answer

How do low mass stars transport newly formed elements into the interstellar medium?

Correct AnswerverifiedShow Answer

Where does most star formation occur in the Milky Way today?

Correct AnswerverifiedShow Answer

What is the best evidence for an extremely massive black hole in the center of the Milky Way?

Correct AnswerverifiedShow Answer

Why do stars in the disk of a spiral galaxy orbit in roughly the same direction, in the same plane in space?

Correct AnswerverifiedShow Answer

Which of the following does not accurately describe what we observe toward the Galactic center?

Correct AnswerverifiedShow Answer

Which of the following properties is more likely to be a characteristic of a halo star in the Milky Way, not a disk star?

Correct AnswerverifiedShow Answer

Where do most dust grains form?

Correct AnswerverifiedShow Answer

What is the most abundant molecule in interstellar clouds besides molecular hydrogen?

Correct AnswerverifiedShow Answer

How do high- mass stars make it more difficult for a molecular cloud to form more stars?

Correct AnswerverifiedShow Answer

What do halo stars do differently from disk stars?

Correct AnswerverifiedShow Answer

Most nearby stars move relative to the Sun at speeds below about 30 km/s. Suppose you observe a nearby star that is moving much faster than this (say, 300 km/s) . Which of the following is a likely explanation for its high speed?

Correct AnswerverifiedShow Answer

Approximately how long does it take the sun to go through a full cycle of passing above and below the plane of the galaxy?

Correct AnswerverifiedShow Answer

Observing our galaxy at radio wavelengths allows us to see through the dust in the disk that obscures our view.

Correct AnswerverifiedShow Answer

The Sun lives in which component of the Milky Way?

Correct AnswerverifiedA

On a dark summer night in the northern hemisphere, we can see the Milky Way, but we can't see the center of the Milky Way. Why not?

Correct AnswerverifiedB

The image of our galaxy in radio emission from carbon monoxide maps the distribution of molecular clouds. Which of the following would give a similar picture of our galaxy?

Correct AnswerverifiedE

Harlow Shapley concluded that the Sun was not located at the center of the Milky Way Galaxy by

Correct AnswerverifiedShow Answer

Suppose you discovered a star made purely of hydrogen and helium. How old do you think it would be? Explain.

Correct AnswerverifiedA star made of only hydrogen and helium ...View AnswerShow Answer

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A star made of only hydrogen and helium ...
View Answer