Deck 15: Our Galaxy: the Milky Way

Question 1

Where are the most metal-rich stars found in the Milky Way?

A) in the disk near the Sun
B) at the center
C) in the halo
D) in globular clusters

Answer 1

at the center

Question 2

Studying standard candles in globular clusters offered the first conclusive proof that our galaxy was much ________ than originally believed.

A) smaller
B) rounder
C) larger
D) flatter

Answer 2

larger

Question 3

In general,open clusters are found in the ________ of the Milky Way; globular clusters are found in the ________ of the Milky Way.

A) disk; disk
B) halo; halo
C) disk; halo
D) halo; disk

Answer 3

disk; halo

Question 4

Which of the following statements is NOT a property of a globular cluster?

A) consists of hundreds of thousands of stars
B) contains old stars
C) loosely gravitationally bound
D) tightly gravitationally bound

Question 5

Why do we know that at least one generation of stars formed and died before the Milky Way's globular clusters formed?

A) All globular clusters reside in the disk of the Milky Way.
B) No globular cluster has zero heavy elements.
C) Globular clusters are 9 billion to 10 billion years old.
D) No globular cluster is older than 12 billion years.

Question 6

The chemical composition of a star's atmosphere tells us:

A) how much nuclear burning has gone on in the star.
B) the star's evolutionary stage.
C) the chemical composition of the cloud from which the star formed.
D) all of the above

Question 7

The distance to the center of the Milky Way cannot be measured directly.Which of the following reasons is the best explanation for this fact?

A) There are no variable stars in the galactic center.
B) The supermassive black hole emits no light.
C) Clouds of gas and dust obscure our view.
D) The center is too bright to measure accurately.

Question 8

The discovery of the period-luminosity relationship for variable stars allowed them to be used as standard candles.Who made this important discovery?

A) Ejnar Hertzsprung
B) Henrietta Leavitt
C) Henry Norris Russell
D) Harlow Shapley

Question 9

Cosmic rays are:

A) photons with even higher energy than gamma rays.
B) high-velocity particles produced in novae.
C) primarily protons with very high energies.
D) synchrotron emission from strong magnetic fields.

Question 10

Open star clusters primarily inhabit which part of spiral galaxies?

A) disk
B) halo
C) bulge
D) nucleus

Question 11

Which of the following regions of the electromagnetic spectrum is best used to study structure in the Milky Way?

A) gamma rays
B) radio
C) ultraviolet
D) X-rays

Question 12

What type of standard candle is used to determine distances to globular clusters?

A) RR Lyrae stars
B) Cepheid variable stars
C) T Tauri stars
D) Type Ia supernovae

Question 13

In a star that has a chemical abundance similar to the Sun,what percentage of its mass is made of heavy elements?

A) 0.02 percent
B) 0.2 percent
C) 2 percent
D) 20 percent

Question 14

Where in the Milky Way would we look to find lots of gas and dust?

A) disk
B) globular clusters
C) halo
D) The gas and dust is uniformly distributed in the Milky Way.

Question 15

Harlow Shapley showed that ________ form a spherical halo that is not centered on the Solar System,disproving the idea that the Sun was the center of the Milky Way Galaxy.

A) 21-cm emission from neutral hydrogen gas
B) globular clusters
C) open clusters
D) X-ray-emitting hot gas

Question 16

Which of the following statements is NOT a property of an open cluster?

A) contains hundreds to thousands of stars
B) includes young stars
C) loosely gravitationally bound
D) tightly gravitationally bound

Question 17

Why is 21-cm radiation the best way to map the spiral arms in the Milky Way?

A) The molecular hydrogen gas that produces this emission is concentrated in the spiral arms.
B) These photons, which are produced by neutral hydrogen, penetrate the dense clouds of gas and dust in the disk.
C) This synchrotron emission is produced by supernovae, which are concentrated in the spiral arms.
D) Radio telescopes are easier to operate than optical telescopes, and observations can be made even during the daytime.

Question 18

In which part of the Milky Way would you find little or no neutral hydrogen,no current star formation,and stars that are older than 10 billion years?

A) the halo
B) the disk
C) the galactic center
D) the solar neighborhood

Question 19

The Milky Way Galaxy is a(n)________ galaxy.

A) irregular
B) elliptical
C) barred spiral
D) lenticular

Question 20

Globular clusters,when compared to open clusters,generally:

A) are located closer to the center of the Milky Way.
B) are younger in age.
C) have fewer amounts of heavy elements.
D) all of the above

Question 21

How have astronomers measured the mass of the black hole at the center of our galaxy?

A) using the rotation curve derived from 21-cm emission
B) by observing the motions of stars near the center of the galaxy
C) by measuring the brightness of the quasar
D) by measuring the Doppler shift of Sagittarius A*

Question 22

The fact that the Milky Way has orbiting companion galaxies and is currently "eating" one of them is evidence that:

A) all galaxies are blueshifted with respect to the Milky Way.
B) galaxies form by mergers of smaller protogalaxies.
C) the Milky Way is the center of the universe.
D) we cannot learn anything from this evidence

Question 23

Observations of Doppler shifts toward the center of the galaxy show on one side hydrogen clouds are blueshifted while on the other side hydrogen clouds are redshifted.This is the pattern of the rotation velocity of a:

A) cube.
B) disk.
C) sphere.
D) Cannot determine shape from information given.

Question 24

Which of the following statements about the history of the Milky Way is correct?

A) The Milky Way was much larger in the past.
B) The Milky Way evolved from smaller clumps of stars.
C) The Milky Way has not evolved.
D) The Milky Way is expanding.

Question 25

Which of the following is closest to the mass of the supermassive black hole at the center of the Milky Way Galaxy?

A) 400 solar masses
B) 40,000 solar masses
C) 4 million solar masses
D) 4 billion solar masses

Question 26

What is the main observational difficulty in observing the shape of the Milky Way?

Question 27

Which of the following methods is used to measure the velocity and direction of motion of gas in the galaxy?

A) Doppler effect
B) main-sequence fitting on an H-R diagram
C) parallax
D) transit method

Question 28

If the Large Magellanic Cloud is orbiting the Milky Way in a circular orbit with a speed of 175 km/s and a distance of 165,000 light-years from the center,how long would it take for the Large Magellanic Cloud to complete one orbit around the Milky Way?

A) 600 million years
B) 1.8 billion years
C) 3.5 billion years
D) 17 billion years

Question 29

What is the evidence that the Milky Way must have formed when the gas within a huge "clump" of dark matter collapsed?

A) the number of nearby dwarf galaxies
B) the properties of globular clusters
C) the supermassive black hole at the center of the Milky Way
D) all of the above

Question 30

Magnetic fields in the Milky Way are concentrated in the disk because:

A) halo stars are incapable of producing strong magnetic fields.
B) the fields are tied to the charged particles in dense molecular clouds.
C) gravity forces them to sink to the center of the disk.
D) supernovae explosions continually force them toward the middle of the disk.

Question 31

How do we observe the supermassive black hole at the center of our galaxy?

A) Directly. We can see the dark circle inside its event horizon.
B) Directly. We can see the light that the black hole emits.
C) Indirectly. We can observe its gravitational effects on the nearby gas and stars.
D) We cannot make any observations of the supermassive black hole at the center of our galaxy.

Question 32

Because of the ages of globular clusters in the Milky Way,we think our galaxy's early formation history was characterized by:

A) one single cloud of gas gently collapsing and star formation proceeding slowly within it.
B) one single cloud of gas that rapidly collapsed and turned most of its gas into stars.
C) merging of protogalactic fragments that stimulated a high rate of star formation.
D) slow merging of protogalactic fragments after they had already turned most of their gas into stars.

Question 33

Sagittarius A*,the radio source located at the center of our galaxy,is believed to be a:

A) massive star cluster.
B) supernova remnant.
C) quasar.
D) supermassive black hole.

Question 34

Our Milky Way Galaxy shares the following property in common with other galaxies.

A) Most of the mass in our galaxy is in the form of dark matter.
B) Most of the mass in our galaxy is in the form of dust.
C) Most of the mass in our galaxy is in the form of hydrogen.
D) Most of the mass in our galaxy is in the form of stars.

Question 35

What is ripping apart the Sagittarius dwarf spheroidal galaxy?

A) a supermassive black hole at its center
B) the energetic decay of a WIMP
C) a violent episode of star formation
D) the gravitational tidal force of the Milky Way

Question 36

The Milky Way is part of the Local Group of galaxies.Which of the following statements best describes the Local Group?

A) a vast network of thousands of galaxies
B) the Milky Way and its orbiting companion galaxies
C) about 50 galaxies, including Andromeda and many dwarf galaxies
D) the Milky Way and its halo of globular clusters

Question 37

What observed property of the Milky Way suggests that it contains a large amount of matter NOT in the form of stars?

A) the rotation curve
B) the velocities of the open star clusters
C) the number and shape of the spiral arms
D) the thickness of the disk

Question 38

The center of the Milky Way was an active galactic nucleus in the past.What direct observational evidence supports this?

A) gamma-ray bubbles extending thousands of light-years above and below the galactic plane
B) rapid motions of stars near the galactic center
C) X-ray emission near the galactic center
D) All of the above.

Question 39

Which of the following are NOT found in our galaxy's halo?

A) globular clusters
B) planetary nebulae
C) RR Lyrae stars
D) clouds emitting 21-cm radiation

Question 40

Most of the mass in our galaxy is in the form of:

A) stars
B) gas
C) dust
D) dark matter

Question 41

Describe the differences between the ages and chemical abundances of globular and open star clusters.

Question 42

Describe a scale model of the disk of the Milky Way using a scale in which 1 cm = 1,000 light-years.Note that the diameter of the disk is approximately 100,000 light-years,the thickness of young stars is 500 light-years,and the thickness of the older stars is 4,000 light-years.

Question 43

How does the H-R diagram of a globular star cluster show that its age is very old? Provide a sketch of an H-R diagram for a globular cluster.

Question 44

Explain how a standard candle allows you to determine the distance to an object.What is it that you have to measure or know about the standard candle to derive its distance?

Question 45

How does the H-R diagram of an open cluster show that its age is very young? Provide a sketch of an H-R diagram for an open cluster.

Question 46

Describe the population of globular star clusters in the Milky Way: how many are there,where do they reside in the Milky Way,and how do their ages and chemical abundances compare to the Sun?

Question 47

Why can the observed chemical abundance of a star tell you something about its age?

Question 48

Where would we find the stars with the richest abundance of massive elements? Where would we find those with the smallest amounts of massive elements? Why?

Question 49

Describe the basic scenario that describes the formation and evolution of the Milky Way,including a description of how the halo and disk formed.

Question 50

How do we know that globular cluster stars were not the first stars that formed in our galaxy?

Question 51

Sketch an edge-on view of the Milky Way.Label the locations of the bulge,disk,and halo.

Question 52

Why is the supermassive black hole in the center of our galaxy not an AGN right now? Could it be active in the future? Why or why not?

Question 53

Astronomers use data about stars near the very center of the Milky Way to argue that there must be a supermassive black hole at the center of the galaxy.Describe the method that is used.