Deck 16: The Milky Way Galaxy

Question 1

What is the approximate diameter of the Milky Way Galaxy in light-years?

A) 10
B) 100
C) 1,000
D) 100,000
E) 1,000,000

Answer 1

100,000

Question 2

What fraction of the Galaxy's mass is in a form that does not emit electromagnetic radiation?

A) about 90%
B) about 50%
C) about 10%
D) zero percent, all of the Galaxy emits some form of light.

Answer 2

about 90%

Question 3

The Sun lies _______ the disk of our Milky Way Galaxy.

A) at the center of
B) about half of the way out in
C) about one-tenth of the way out in
D) in the halo above

Answer 3

about half of the way out in

Question 4

Astronomers measured the location of the Sun in the Milky Way Galaxy by

A) counting the number of stars.
B) plotting the position of globular star clusters.
C) plotting distribution of water molecules.
D) plotting the position of O and B stars.

Question 5

Who was the first to measure the structure of Milky Way using globular clusters?

A) Jacobus Kapteyn
B) Edwin Hubble
C) Harlow Shapley
D) William Herschel

Question 6

One of the reasons that Kapteyn underestimated the size of the Milky Way and Shapley overestimated it is that they did not recognize the ___________.

A) effects of the motion of the Sun from the center
B) dimming effect of interstellar dust
C) age of the globular clusters
D) existence of dark matter

Question 7

The Solar System is located about ___ from the center of the Milky Way.

A) 8 kiloparsecs
B) 8 light-years
C) 8 AU
D) 8 parsecs

Question 8

The Solar System is about 5 billion years old and completes one orbit around the center of the Milky Way in 220 million years. Therefore, we conclude that the Solar system has completed a total of about ___ orbits around the Galactic center.

A) 5
B) 10
C) 22
D) 50

Question 9

The gas and dust in the disk of the Milky Way amount to approximately ____ of the mass of the stars.

A) 15%
B) 30%
C) 50%
D) 90%

Question 10

The estimated age of the Milky Way Galaxy is about ___________.

A) 20 billion years
B) 100,000 years
C) 13 billion years
D) 4.6 billion years

Question 11

The average distance between stars in the neighborhood of the Solar System is about ___________.

A) 4 AU
B) 4 light-years
C) 4 kiloparsecs
D) 4 arc seconds

Question 12

Sir William Herschel counted the number of stars in different directions, and getting similar numbers in each direction along the disk, concluded the Sun was near the center of a disk like collection of stars. Herschel came to the wrong conclusion about the Sun's location because

A) He was predisposed to believe the Sun was in the center of the Milky Way, and ignored data which disagreed with that conclusion.
B) He did not know that interstellar dust made it hard for him to see a large part of the Milky Way's disk.
C) He only counted globular clusters, and not regular stars.
D) The Sun's position in the Milky Way at that particular time was very unusual and skewed his results.

Question 13

The Milky Way is tilted on the sky because

A) it's appearance depends entirely on where you are on Earth.
B) the Solar System is tilted compared to the disk of the Galaxy.
C) the Sun's gravity deflects incoming starlight.
D) the disk of the Galaxy is warped.

Question 14

What does the Milky Way look like on the night sky?

A) a spiral-shaped region of nebulosity
B) a pale band of light scattered with stars that stretches across the sky
C) a uniform scattering of stars throughout the sky
D) The Milky Way is not visible from Earth without a telescope.

Question 15

Roughly how far across is the Milky Way?

A) 25 light-years
B) 25,000 light-years
C) 100,000 light-years
D) 10 million light-years

Question 16

About how much mass does our galaxy contain?

A) 1 million solar masses
B) 1 billion solar masses
C) 10¹¹ solar masses
D) 10²⁰ solar masses

Question 17

What did Harlow Shapley study in order to deduce the Milky Way's size and the Sun's position in it?

A) open star clusters
B) globular star clusters
C) interstellar gas clouds
D) spiral arms

Question 18

Although it hasn't been observed (yet), why do astronomers think that the Milky Way may contain "dark" material?

A) Theory predicts that there should be more black holes than we've so far detected.
B) The Galaxy's gravity seems too big for the mass astronomers can see.
C) Due to its large size, the light from stars on the other side of the Milky Way has not reached us yet.
D) Astronomers have detected neutrinos from unseen sources.

Question 19

One way astronomers deduce that the Milky Way has a disk is that they

A) see stars arranged in a circular region around the north celestial pole.
B) see far more stars along the band of the Milky Way than in other directions.
C) see a large dark circle silhouetted against the Milky Way in the Southern Hemisphere.
D) see the same number of stars in all directions in the sky.
E) None of these choices is correct.

Question 20

The space between the stars is known to contain

A) a large quantity of dust but no gas at all.
B) a variable amount of gas but no dust at all.
C) a perfect vacuum.
D) both gas (atomic or molecular) and dust.

Question 21

Stars in globular clusters belong to Population ___.

A) I
B) II
C) III
D) Zero

Question 22

The Milky Way Galaxy contains about _____ stars. Most of these stars are probably _____.

A) 100 billion; red giants
B) 100 billion; O and B type stars
C) 10 billion; white dwarfs
D) 100 billion; cool dwarfs

Question 23

The majority of stars in the Milky Way appear to be in the _______.

A) O and B spectral type
B) mass range of 0.1 to 0.5 solar masses
C) 6,000 K to 10,000 K temperature range
D) Sagittarius A* region

Question 24

Older red stars are found where in the Galaxy?

A) only in the halo
B) only in the disk
C) only in the bulge
D) all throughout the Galaxy

Question 25

One difference between Population I and Population II stars in the Milky Way is

A) that Pop I stars produce energy by fusion and Pop II by fission.
B) that Pop I stars have very few metals and Pop II stars are metal rich.
C) that Pop I stars have orbits in the disk and Pop II stars have orbits that pass through the disk.
D) that Pop I stars produce energy by fusion and Pop II stars through gravitational contraction.

Question 26

In general, Population I stars are _________ than Population II stars.

A) older
B) younger
C) the same age
D) sometimes older, and sometimes younger

Question 27

In general, Population I stars are ______ and Population II stars are _______.

A) massive; dwarfs
B) dwarfs; massive
C) blue; red
D) red; blue

Question 28

If you made a plot of open clusters on a star map, they would be

A) evenly scattered on the page.
B) concentrated along the Galaxy's disk.
C) clustered away from the Galactic bulge.
D) spherically arranged in a halo.

Question 29

Which statement is not true about open clusters?

A) After a molecular cloud has collapsed and formed many stars, the cloud dissipates and the stars spread out into an open cluster.
B) Open clusters usually contain many blue stars.
C) Open clusters are gravitationally bound and therefore have a spherical shape.
D) Open clusters typically contain dozens to hundreds of stars.

Question 30

Which of the following may explain the failure to observe Population III stars?

A) We do not expect to observe Population III stars, because pure hydrogen and helium stars never formed.
B) Population III stars had their surfaces contaminated by remnants of massive stars.
C) The first stars to be formed in the young Milky Way are too far away to be detected.
D) None of these choices is correct.

Question 31

What is not true of Population I stars?

A) They are old.
B) They are frequently blue.
C) They are high heavy element content.
D) They are found in the disk.

Question 32

A young blue star moving along a circular orbit in the disk is a

A) Pop I star.
B) Pop II star.
C) Pop III star.
D) Pop V star.

Question 33

An old red star moving along a random orbit around the bulge is a

A) Pop I star.
B) Pop II star.
C) Pop III star.
D) Pop V star.

Question 34

What happens when the electron in a hydrogen atom flips its direction of spin, from parallel to anti parallel to that of the proton?

A) Nothing, this transition never occurs.
B) The atom emits 656-nm radiation that gives red color.
C) The atom emits high-energy ultraviolet rays.
D) The atom emits 21-cm radio radiation.

Question 35

Which radiation is the most useful to map the structure of our Galaxy?

A) far ultraviolet
B) 21-cm radio radiation
C) X-rays
D) gamma rays

Question 36

What is an emission nebula?

A) a region of gas around cool K or M type stars
B) a region of ionized gas around hot O or B type stars
C) a region of gas around black holes
D) a gas cloud in globular clusters

Question 37

The typical size of the interstellar dust particles is _________ and they consist of __________.

A) 1 cm; silicates and carbon compounds
B) 1 mm; hydrogen and helium
C) about a micrometer or less; hydrogen and helium
D) about a micrometer or less; silicates and carbon compounds

Question 38

Dust and gas in the Milky Way

A) are spread evenly throughout the halo and disk.
B) are concentrated in a thin layer in the disk.
C) are found in different places: dust primarily in the disk and gas primarily in the halo.
D) are found in different places: gas primarily in the disk and dust primarily in the halo.

Question 39

Why is it not possible to use visible light to investigate the center of our Galaxy?

A) Intervening gas locating in the disk of the Galaxy blocks our view of the Galactic center.
B) The massive black hole located at the center of the Galaxy prevents light from escaping the region.
C) There are no sources of visible light found at the center of the Galaxy.
D) The density of stars toward the Galactic center is so high that it is not possible to see through them.

Question 40

In a telescopic observation of a field of stars, you see an irregularly-shaped dark patch. This is most likely

A) an area where there are no stars.
B) a black hole.
C) the dusty center of a globular cluster.
D) a dark nebula.

Question 41

A bright red nebula is called an HII region when it contains

A) molecular hydrogen gas, H₂.
B) hot hydrogen gas thermally glowing.
C) hydrogen atoms which have been ionized by ultraviolet radiation.
D) hydrogen which is generating 21-cm radio waves.

Question 42

Compared to a cold molecular cloud at 10 K, an HII region has a temperature about

A) 1,000,000 times hotter.
B) 1,000 times hotter.
C) 10 times hotter.
D) the same.

Question 43

We know interstellar matter exits because

A) we can see it in dark clouds and clouds that absorb light.
B) the matter creates narrow absorption lines in the spectra of some stars.
C) we can detect radio waves coming from atoms and molecules in the cold gas.
D) some stars appear red in color despite their temperature.
E) All of these choices are correct.

Question 44

How do we know that some interstellar matter is dust?

A) We can observe the tiny particles with the Hubble Space Telescope.
B) Dust emits X-rays.
C) Dust obscures and reddens starlight.
D) Interstellar matter is composed only of hydrogen gas.

Question 45

What is the difference between an emission and a reflection nebula?

A) Emission nebulas give off their own light; reflection nebulas reflect the light of nearby stars.
B) Generally, emission nebulas appear blue, and reflection nebulas look red.
C) Emission nebulas contain many dying stars; reflection nebulas are stellar nurseries.
D) All of these choices are correct.

Question 46

What is the zone of avoidance?

A) a part of the region of the Solar System where it is too dangerous to send spacecraft
B) a quadrant of the Galaxy where no galaxies exist
C) a part of the sky in which astronomers cannot observe due to bright emission from interstellar dust
D) the region of the sky where no galaxies are seen due to obscuring dust in the Milky Way

Question 47

Which of these objects can be found in the spiral arms of the Galaxy?

A) HII regions
B) Associations
C) Pop I stars
D) dying, red stars
E) All of these choices are correct.

Question 48

According to the density-wave theory, spiral arms are blue because they

A) contain many reflection nebulae from sites of young star formation.
B) contain only young stars, whose formation was triggered by the explosion of older red stars just in front of the spiral arm.
C) contain a lot of young stars formed from clouds compressed by the density wave.
D) have too much metal content to form red stars.

Question 49

The ______ theory offers a likely explanation for the formation of _____.

A) high rotation speed; spiral arms
B) density wave; Galactic bulge
C) density wave; spiral arms
D) high rotation speed; dark matter

Question 50

What is the density-wave model?

A) It is a way of describing the formation of Galactic spiral arms.
B) It is a model who puts on a show at astronomy meetings.
C) It is a description of how light propagates.
D) It is a theory of the origin of the Universe.

Question 51

Astronomers think the Milky Way has spiral arms because

A) they can see them unwinding along the celestial equator.
B) radio maps show that gas clouds are distributed in the disk with a spiral pattern.
C) Pop II stars, hot molecular clouds, and asterisms outline spiral arms.
D) globular clusters outline spiral arms.
E) All of these choices are correct.

Question 52

Astronomers think the Milky Way has spiral arms because

A) they can see them unwinding along the celestial equator.
B) X-ray maps show that dust clouds are distributed in the disk with a spiral pattern.
C) young star clusters, HII regions, and associations outline spiral arms.
D) globular clusters outline spiral arms.
E) All of these choices are correct.

Question 53

Rotational velocity outside the visible boundary of our Galaxy is _____ than would be expected on the basis of observed stars and gas, indicating the presence of _____.

A) zero; a vacuum
B) lower; gas
C) smaller; white dwarfs
D) higher; dark matter

Question 54

Astronomers have measured the Milky Way's mass by

A) observing magnetic fields in the Solar System.
B) using radar.
C) sending unmanned space missions to the center of the Galaxy.
D) observing its gravitational attraction on matter in and near it.

Question 55

Although it hasn't been observed (yet), why do astronomers think that the Milky Way is embedded in a halo of dark matter?

A) Theory predicts that there should be more black holes than we've so far detected.
B) Stars in the outer regions of the Galaxy are orbiting faster than expected.
C) Due to its large size, the light from stars on the other side of the Milky Way has not reached us yet.
D) Astronomers have detected neutrinos from unseen sources.

Question 56

The modified form of Kepler's Third law allows astronomers to determine the Milky Way's ____.

A) mass
B) age
C) composition
D) shape
E) number of spiral arms

Question 57

The radio waves emitted from Sagittarius A* region take how long to travel to Earth?

A) 50,000 years
B) 100,000 years
C) 8.5 years
D) 220 million years

Question 58

Astronomers believe that the massive object at the center of the Milky Way is a black hole because

A) images show an accretion disk surrounding an empty spot.
B) gravitational wave measurements indicate a black hole is there.
C) observations at X-ray waves, infrared waves, and radio waves limit the size of the object to smaller than 10 AU.
D) it is necessary to explain the Galaxy's rotation curve.

Question 59

Astronomers have found the black hole at the center of the Milky Way has a mass of about _________ solar masses.

A) 40
B) 4 hundred thousand
C) 4 million
D) 4 billion

Question 60

What might you find at the center of the Milky Way?

A) a region 10,000 light-years across containing no stars
B) a 10,000 solar mass star whose luminosity is 100 million solar luminosities
C) a black hole with the mass of a few million Suns
D) the first stars that formed in the galaxy

Question 61

Which of the following may explain the failure to observe Population III stars?

A) We do not expect to observe Population III stars, because pure hydrogen and helium stars never formed.
B) Population III stars are shrouded by gas and dust, making them difficult to see.
C) The first stars to be formed in the young Milky Way were very massive and therefore short-lived.
D) None of these choices is correct.

Question 62

Which of the following could NOT be the result of scattering?

A) A star appears dimmer than it is.
B) A star appears redder than it is.
C) A nebula appears bluer than it is.
D) The sky appears blue.
E) None of these choices are correct.

Question 63

The Milky Way has no sharply defined outer edge.

Question 64

Of the normal matter in the Milky Way, the vast majority of the mass is in the form of gas and dust.

Question 65

The estimated age of the Milky Way Galaxy is about 13 billion years.

Question 66

The main parts of the Milky Way Galaxy are the disk, the bulge, and the halo.

Question 67

New surveys suggest brown dwarfs, stars under the critical mass for stable fusion, are probably very rare.

Question 68

Astronomers can measure the diameter of our Milky Way Galaxy by plotting the position of globular star clusters.

Question 69

The Solar System is located about 8 light-years away from the Galactic center.

Question 70

Associations are loose groups of young stars in the spiral arms usually mingled with large clouds of gas and dust.

Question 71

Dust accounts for about 1% of the total mass of interstellar matter.

Question 72

The zone of avoidance is the region around the massive black hole found at the center of the Galaxy.

Question 73

We know that galaxies exist in the zone of avoidance because we can detect them using radio telescopes.

Question 74

The composition of the interstellar gas is very similar to the composition of our Sun.

Question 75

Hydrogen, both in neutral and in molecular form, can be used to map out features of the Galaxy through its emission of 21-cm radiation.

Question 76

The Milky Way shows evidence that over its history it has merged with and "cannibalized" smaller galaxies.