Deck 17: Galaxies

Question 1

A spiral galaxy is observed edge-on so that its spiral arms are barely visible. The galaxy, however, is observed to have a very large nuclear bulge. Thus, this galaxy

A) is probably type Sa.
B) is probably type Sb.
C) is probably type Sc.
D) cannot be classified if its spiral arms cannot be studied.

Answer 1

is probably type Sa.

Question 2

What is the classification for a spiral galaxy with a small nuclear region and loosely wound arms?

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

Answer 2

Sc

Question 3

A spiral galaxy is observed edge-on so that the spiral arms cannot be seen clearly. Is it possible to classify this into one of the Sa, Sb, and Sc categories?

A) Yes. The classification scheme is also an evolutionary scheme. It is possible to classify galaxies by age, for example, by counting the number of blue supergiants visible along the edge.
B) Yes. The tightness of spiral arms is correlated with the size of the nuclear bulge.
C) Yes. The tightness of spiral arms is correlated with the number of bright H II regions that can be counted along the edge.
D) No. The classification scheme is based on the tightness of spiral arms. If the arms cannot be seen, the galaxy cannot be classified.

Answer 3

Yes. The tightness of spiral arms is correlated with the size of the nuclear bulge.

Question 4

According to the Hubble classification scheme, an Sa galaxy has

A) a large central bulge and tightly wound spiral arms.
B) an irregular shape with no obvious disk or spiral arms.
C) a round or spherical appearance with a smooth light distribution.
D) a small central bulge and loosely wound spiral arms.

Question 5

In a spiral galaxy, the

A) spiral arm tightness is independent of the size of the nuclear bulge; a particular bulge can have a wide range of spiral structure.
B) smaller the nuclear bulge is, the tighter the spiral.
C) tighter the spiral is, the larger the nuclear bulge.
D) larger the nuclear bulge is, the looser the spiral.

Question 6

In spiral galaxies, the tightness of the winding of the spiral arms appears to be related directly to the

A) age of the galaxy, as determined from the age of its individual stars.
B) number of globular clusters in the halo of the galaxy.
C) overall intrinsic size of the galaxy, or the diameter across the spiral arms.
D) size of the central bulge of the galaxy.

Question 7

What is the classification for a spiral galaxy with a moderately sized nuclear region and moderately wound arms?

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

Question 8

An astronomer studying a distant cluster of galaxies finds that several of the galaxies are spiral-shaped, with a nuclear region of moderate size and moderately wound arms. How should the astronomer classify these galaxies?

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

Question 9

A particular galaxy appears round, with a nuclear region of uniform brightness and an outer region that is broken up into curved but fuzzy and poorly defined lanes of stars and light gas clouds. How would this galaxy be classified?

A) elliptical
B) grand-design spiral
C) flocculent spiral
D) irregular

Question 10

What is the basic shape of a spiral galaxy?

A) round, flat disk with long lanes of stars that curve outward from a round, nuclear region bulging out of the disk
B) 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) round, thin disk of uniform brightness with its edges bent up and down into a spiral shape

Question 11

According to the Hubble classification scheme, an Sc galaxy has a(n)

A) round or spherical appearance with a smooth light distribution.
B) large central bulge and tightly wound spiral arms.
C) irregular shape with no obvious disk or spiral arms.
D) small central bulge and loosely wound spiral arms.

Question 12

Suppose the Milky Way Galaxy is 1 of a 1000 billion galaxies and they similarly have, on average, 200 billion stars each. How many stars is that?

A) 2 * 10¹⁹
B) 2 *10²¹
C) 2 *10²³
D) 2 * 10²⁵

Question 13

What is the classification for a spiral galaxy with a large nuclear region and tightly wound arms?

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

Question 14

An astronomer studying a distant cluster of galaxies finds that several of the galaxies are spiral-shaped, with a large nuclear region and tightly wound arms. How should the astronomer classify these galaxies?

A) Sb
B) SBb
C) Sa
D) Sc

Question 15

What does a spiral galaxy look like when seen edge-on?

A) thick, straight line of light with a central light bulge
B) circular, with no evidence of spiral arms since they are hidden by dust and gas
C) thick line curved into a spiral shape
D) thick, straight line with constant thickness

Question 16

A spiral galaxy has well-defined arms that are wound not-too-tightly around its intermediate-size bulge. This is MOST likely a

A) flocculent Sa.
B) grand-design Sb.
C) flocculent Sb.
D) grand-design Sc.

Question 17

Spiral galaxies are classified in terms of increasing tightness of their spiral arms as types Sa, Sb, and Sc. However, many spiral galaxies are aligned edge-on to Earth and their spiral arms cannot be seen. Which other parameter that is directly related to spiral-arm tightness can be easily seen edge-on and can therefore be used to provide this classification?

A) overall spectral color
B) overall intrinsic brightness of the galaxy, or its absolute magnitude
C) size of the nuclear bulge
D) overall diameter of the galaxy

Question 18

An astronomer studying a distant cluster of galaxies finds that several of the galaxies are spiral-shaped, with a small nuclear region and loosely wound arms. How should the astronomer classify these galaxies?

A) Sa
B) SBb
C) Sc
D) Sb

Question 19

The Andromeda Galaxy (M31) is BEST described as a(n)

A) spiral collection of stars, dust, and gas, 200,000 ly across.
B) extension of the Milky Way.
C) vortex surrounding a black hole.
D) gaseous nebula extending for 6° across Earth's sky.

Question 20

What type of galaxy has a nuclear region of more or less uniform brightness from which long lanes of stars curve outward?

A) spiral
B) quasar
C) irregular
D) elliptical

Question 21

Spiral density waves move through a medium that is also moving. The speed of the density waves

A) is greater than the speed of the medium through which they pass.
B) is the same as that of the medium through which they pass, thus forming a rigid spiral pattern.
C) is less than that of the medium through which they pass.
D) varies as the waves go around the galaxy, slowing down while passing through a spiral arm and speeding up in the regions in between.

Question 22

What mechanism is believed to produce flocculent spiral galaxies?

A) satellite galaxies plunging through the disk of the nuclear spiral galaxy
B) self-propagating star formation, where star formation occurs in bursts
C) shock waves from explosive star formation in the nuclear bulge
D) density waves in the interstellar medium

Question 23

In which of these ways is the Milky Way Galaxy different from most spiral galaxies?

A) The Milky Way has only three spiral arms, whereas most spiral galaxies have at least four.
B) The Milky Way has only two spiral arms, whereas most galaxies have at least four.
C) The spiral arms of the Milky Way are far more tightly wound than those in most galaxies.
D) The Milky Way has at least four spiral arms, whereas most spiral galaxies have only two.

Question 24

A particular galaxy appears round, with a nuclear region of uniform brightness and an outer region that is broken up into long, curved, well-defined lanes of stars and light gas clouds. How would this galaxy be classified?

A) elliptical
B) flocculent spiral
C) irregular
D) grand-design spiral

Question 25

What is a probable mechanism for the initial triggering, and the subsequent maintenance, of the density wave that forms the visible arms in spiral galaxies?

A) equivalent of a massive "sound" wave generated at the center of the galaxy by the gravitational energy release at the initial formation of the galaxy, producing progressive compression of material that is shaped by galaxy rotation
B) gravitational influence from the rotating central supermassive black hole at the galactic center of the arm material
C) gravitational interaction from the close passage of another galaxy
D) shock waves from supernova explosions of massive stars within the spiral arms

Question 26

Why do the spiral arms show up so clearly in spiral galaxies?

A) Stars are spread almost uniformly over the galaxy (outside the nuclear bulge), but the brightest stars occur only in the spiral arms, where their brightness and the fact that they illuminate gas clouds make the arms stand out.
B) Stars are spread uniformly over the galaxy, but the dust forms a spiral pattern, absorbing starlight; the spiral arms are the dust-free regions between the dust lanes.
C) The number of stars in the arms is several times larger than in the regions between, so these arms are reasonably distinct.
D) Stars occur only in the spiral arms (and the nuclear bulge), with essentially none between the arms, so the arms show up very distinctly.

Question 27

What mechanism is believed to produce grand-design spiral galaxies?

A) shock waves from explosive star formation in the nuclear bulge
B) density waves in the interstellar medium
C) satellite galaxies plunging through the disk of the nuclear spiral galaxy
D) self-propagating star formation, where star formation occurs in bursts

Question 28

What is a barred spiral galaxy?

A) galaxy with a bar through the nuclear bulge and the spiral arms starting from the ends of the bar
B) spiral galaxy with a straight bar instead of a nuclear bulge
C) galaxy in which the arms form straight bars instead of curved lines
D) galaxy with a bar extending across the entire diameter and the arms starting at various positions along the bar

Question 29

How many stars per cubic parsec are there in the spiral arms of a spiral galaxy compared with the regions between the spiral arms?

A) The density of stars inside spiral arms is more than 100 times that in the regions between the arms.
B) The density of stars inside spiral arms is about twice that in the regions between the arms.
C) There are a lot of stars in the spiral arms and none at all in the regions between the arms.
D) The density of stars inside spiral arms is about 5% more than in the regions between the arms.

Question 30

Which of these accurately characterizes an apparent dilemma in understanding the spiral arm structure of a typical spiral galaxy?

A) The measured speeds of stars in the galaxy are exactly correct for the present spiral structure, having spun the observed tightness of the spiral in the typical lifetime of a galaxy.
B) If the measured speeds of stars in the galaxy had spun the arms into shape, these arms would be far less tightly wound than the observed arms.
C) If the measured speeds of stars in the galaxy had spun the arms into shape, these arms would be far more tightly wound than the observed arms.
D) The measured speeds of material in the spiral arms should not have led to any spiral but should have generated a straight bar rotating like a solid object.

Question 31

According to the theory of self-propagating star formation, the spiral arms of flocculent spiral galaxies are broad and poorly designed because

A) the spiral arms in these galaxies are strongly influenced by the black hole at the center of the galaxy.
B) the density wave has been disrupted by the bar across the center of the galaxy.
C) dust lanes occur in broad bands rather than in the narrow bands found in grand-design spirals.
D) the spiral arm segments are defined only by the relatively short-lived O- and B-type stars.

Question 32

One difficulty with the density wave theory is that

A) the theory fails to explain why a given spiral pattern lasts only a small fraction of the lifetime of a galaxy.
B) the theory fails to provide a mechanism for star formation.
C) astronomers are unsure of the mechanism that produces the energy output necessary to sustain the density wave.
D) the theory fails to explain the distribution of Population I and Population II stars in the galaxy.

Question 33

Why is it surprising to find spiral arms in spiral galaxies?

A) Spiral arms require new stars, and previous new stars should have already used up the interstellar medium; no new stars should be forming now.
B) The variations in speed of the stars across galaxies are not high enough to twist the shape of the arms into a spiral.
C) There is no known mechanism to generate spiral arms.
D) The motions of the stars and differential rotation of the galaxy should have wound their arms tightly and made them blend and disappear.

Question 34

How does the amount of dust and gas in a spiral galaxy vary with the classification of the galaxy?

A) The most loosely wound galaxy, Sc, has the most dust and gas in its arms.
B) All spiral galaxies Sa, Sb, and Sc types have about the same fraction of gas and dust within them, about 4% by mass.
C) Only the most tightly wound spiral galaxies, type Sa, have any dust or gas in them at all.
D) The most loosely wound galaxy, Sc, has the least dust and gas in its arms.

Question 35

In the self-propagating star formation theory

A) spiral arms are formed and sustained primarily by the actions of solar-mass stars because there are so many more of them than there are high-mass stars.
B) spiral arms are poorly defined because they are formed and sustained primarily by the actions of short-lived massive stars.
C) the passage of dust clouds through the spiral arms triggers star formation.
D) spiral structure results with thin, well-defined arms.

Question 36

How does the winding dilemma affect flocculent spirals?

A) The winding dilemma is the basic cause of the chaotic structure in flocculent spirals.
B) The winding dilemma affects only galaxies with flat rotation curves and constant stellar speeds, and this does not include flocculent spirals.
C) Flocculent spirals are dominated by self-propagating star formation in which groups of stars are formed and then fade as the massive luminous stars complete their life cycles. This transient, spotty star-formation pattern is unaffected by the winding dilemma.
D) Flocculent spirals have a whirlpool structure with several centers of rotation, each affected by the winding dilemma. This results in the overall flocculent pattern.

Question 37

Self-propagating star formation requires many mechanisms to spread star formation over a region. Which of these is NOT one of them?

A) the influence of black holes
B) winds from newly formed stars
C) shock waves from supernovae
D) radiation from newly formed stars

Question 38

Which one of these statements about the spiral arms of grand-design spirals is true?

A) The density of matter in the spiral arms is many times the density of the regions in between.
B) The regions between the spiral arms are cloaked in dust, which makes them look dimmer than the spiral arms.
C) The spiral density waves, which move around the galaxy, are transverse waves, moving up and down across the direction of the waves motion like light waves.
D) The spiral arms have almost the same density as the rest of the disk. They are more visible because they contain bright, newly formed stars.

Question 39

Grand-design spiral galaxies

A) have a central bulge that does not rotate.
B) are encompassed within a large lens-shaped disk of dark matter.
C) are orbited by globular clusters that also exhibit star formation.
D) are most often near a companion galaxy.

Question 40

What is the distribution of stars in the spiral arms of a typical spiral galaxy?

A) The density of stars in the arms is far higher than the density of stars between the arms.
B) Far fewer but brighter stars exist in the arms, while many more fainter stars exist between the arms.
C) All the stars of a spiral galaxy are in the arms; there are none at all between the arms.
D) The density of stars is relatively uniform in the disk of the galaxy but is slightly higher within the arms than between them.

Question 41

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?

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

Question 42

Barred galaxies

A) are increasing in number as the universe ages.
B) are mostly leading-arm spirals.
C) all have tightly wound spiral arms.
D) all have spiral arms wound with various degrees of tightness.

Question 43

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

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

Question 44

Arrange these objects in order of increasing size.

A) ultra-compact dwarfs, globular clusters, spiral galaxies
B) globular clusters, ultra-compact dwarfs, spiral galaxies
C) globular clusters, spiral galaxies, ultra-compact dwarfs
D) ultra-compact dwarfs, spiral galaxies, globular clusters

Question 45

What happens in the bar of a barred spiral?

A) The bar rotates like a rigid body with no relative motion of the stars and gas inside.
B) The bar is part of the spiral arm structure, and it is actually a shock wave moving through the relatively rapid circular motion of the individual stars.
C) Stars tend to enter one end of the bar, pass through the bar, and exit the other end.
D) Stars and gas tend to move along highly elliptical orbits within the bars.

Question 46

The Hubble classification description for an S0 galaxy is a

A) small central bulge with loosely wound spiral arms.
B) disk and central bulge with a smooth light distribution and no spiral arms.
C) large central bulge with tightly wound spiral arms.
D) round or spherical shape with a smooth light distribution and no disk or central bulge.

Question 47

How do nearly all spiral galaxies rotate?

A) The arms lead as the galaxy rotates (the arms point forward).
B) Spiral galaxies do not rotate; if they did, the spiral pattern would soon disappear.
C) Astronomers do not know; spiral galaxies rotate far too slowly for them to have seen any motion in the time since galaxies were discovered.
D) The arms trail as the galaxy rotates (the arms point backward).

Question 48

What name is given to a galaxy with a smooth distribution of brightness and a very elongated shape?

A) Sc
B) SBc
C) E0
D) E7

Question 49

What name is given to a galaxy with a smooth distribution of brightness and a round shape?

A) SBa
B) Sa
C) E7
D) E0

Question 50

How does the number of barred spiral galaxies in the universe compare with the number of ordinary spiral galaxies?

A) Barred spirals outnumber ordinary spirals.
B) There are about equal numbers of barred spirals and ordinary spirals.
C) The question is meaningless-barred spirals are simply ordinary spirals seen edge-on.
D) Ordinary spirals outnumber barred spirals.

Question 51

What is the MOST widely accepted Hubble classification of the Milky Way Galaxy?

A) Sab
B) SBa
C) SBab
D) Because of the difficulty of examining the structure of the Milky Way from inside, the Galaxy has not been classified.

Question 52

What is an SBc galaxy?

A) galaxy with a moderate nuclear bulge, moderately wound arms, and a bright core
B) galaxy with a large nuclear bulge and tightly wound arms starting from the ends of a straight bar through the nuclear bulge
C) galaxy with a small nuclear bulge and loosely wound arms coming from the center of the nuclear bulge
D) galaxy with a small nuclear bulge and loosely wound arms starting from the ends of a straight bar through the nuclear bulge

Question 53

What is a lenticular (or S0) galaxy?

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

Question 54

Arrange these objects according to size, largest to smallest.

A) globular clusters, traditional dwarf elliptical, ultra-compact dwarfs
B) globular clusters, ultra-compact dwarfs, traditional dwarf elliptical
C) traditional dwarf elliptical, ultra-compact dwarfs, globular clusters
D) ultra-compact dwarfs, traditional dwarf galaxies, globular clusters

Question 55

Doppler measurements of the motions of stars in nearby spiral and barred galaxies indicate that

A) in most spiral and barred galaxies, the arms trail behind the rotating nucleus.
B) in most spiral and barred galaxies, the arms rotate ahead of the nucleus; that is, spiral and barred galaxies are mostly leading-arm galaxies.
C) in most spiral and barred galaxies, the arms lead the rotation of the nucleus; that is, the arms spin faster than the nucleus.
D) about half of all galaxies have trailing arms-the stars rotate slower than the nucleus-while in the other half, the arms rotate ahead of the nucleus.

Question 56

What is an elliptical galaxy?

A) galaxy with an elliptical outline and a smooth distribution of brightness but no apparent structure
B) spiral galaxy seen from an angle, giving it an elliptical profile
C) galaxy with an elliptical halo when observed at radio wavelengths
D) spiral galaxy with an elliptically shaped nuclear bulge and the spiral arms starting from the ends of the ellipse

Question 57

A grand-design spiral of type SBa has all of these EXCEPT

A) tightly wound spiral arms.
B) a central bar.
C) about 25% gas and dust.
D) a halo of globular clusters.

Question 58

An astronomer studying a cluster of galaxies finds a galaxy that is round and has a disk and central bulge like a spiral galaxy but has no spiral arms. How should the astronomer classify this galaxy?

A) E0
B) E7
C) Sa
D) S0

Question 59

How many barred spiral galaxies are there compared with ordinary spiral galaxies?

A) There are about half as many barred spirals as there are ordinary spirals.
B) There are about twice as many barred spirals as there are ordinary spirals.
C) About 1 in 10 spiral galaxies contains a bar.
D) The numbers are essentially equal.

Question 60

Elliptical galaxies look far less impressive than spiral galaxies because

A) they contain far fewer stars.
B) there are none within this Local Group, so the only elliptical galaxies seen are at very large distances from Earth.
C) they contain no gas and dust clouds or young, hot stars.
D) they are always smaller.

Question 61

Which one of these statements does NOT correctly describe typical elliptical galaxies?

A) Typical elliptical galaxies have a central bulge and a disk but no spiral arms.
B) Typical elliptical galaxies have a smooth light distribution with various degrees of elongation from a circular shape.
C) Typical elliptical galaxies contain primarily low-mass stars.
D) Typical elliptical galaxies cover the entire range of masses from the smallest to the largest galaxies in the universe.

Question 62

Which class of galaxies has the greatest range of sizes in the universe?

A) irregular galaxies
B) ellipticals
C) lenticular galaxies
D) spirals

Question 63

According to the Hubble classification scheme, an E3 galaxy

A) is rounder-looking than an E5 galaxy.
B) has more tightly wound spiral arms than an E5 galaxy.
C) is more elongated than an E5 galaxy.
D) has a shorter central bar in its disk than an E5 galaxy.

Question 64

According to the Hubble classification scheme, an E6 galaxy

A) has more tightly wound spiral arms than an E2 galaxy.
B) has a shorter central bar in its disk than an E2 galaxy.
C) is rounder-looking than an E2 galaxy.
D) is more elongated than an E2 galaxy.

Question 65

According to the Hubble classification scheme, an E4 galaxy has a(n)

A) disk and central bulge with a smooth light distribution and no spiral arms.
B) irregular shape.
C) round or spherical shape with a smooth light distribution and no disk or central bulge.
D) moderately elliptical shape (a flattened circle) with a smooth light distribution.

Question 66

At visible wavelengths, which galaxies are the brightest in the universe?

A) giant elliptical galaxies
B) lenticular galaxies
C) large spiral galaxies like the Milky Way
D) starburst galaxies

Question 67

The largest range of sizes of galaxies is found in which class of galaxies?

A) spiral galaxies
B) irregular galaxies
C) elliptical galaxies
D) starburst galaxies

Question 68

Which of these types of galaxies contains primarily Population II, metal-poor, low-mass, long-lived stars?

A) elliptical galaxies
B) barred spiral galaxies
C) starburst galaxies
D) flocculent spiral galaxies

Question 69

In which category of galaxy do astronomers find the largest galaxies in the universe?

A) lenticular galaxies
B) large spiral galaxies like the Milky Way
C) irregular galaxies
D) elliptical galaxies

Question 70

Which one of these statements is NOT a characteristic of elliptical galaxies?

A) Elliptical galaxies are almost devoid of interstellar gas and dust.
B) Almost all star formation stopped in elliptical galaxies billions of years ago.
C) Different elliptical galaxies appear to be flattened by different amounts.
D) Elliptical galaxies have a disk and a central bulge but no spiral arms.

Question 71

How are the Magellanic Clouds, the two nearby satellite galaxies of the Milky Way Galaxy, classified?

A) elliptical galaxies
B) irregular galaxies
C) flocculent spiral galaxies
D) grand-design spiral galaxies

Question 72

Which one of these properties is NOT typical of elliptical galaxies?

A) old Population II stars
B) old supernova remnants
C) neutron stars
D) dark nebulae

Question 73

Lenticular galaxies, S0, have no spiral arms. What is the difference between an S0 and an elliptical E0, which also has no spiral arms?

A) There is no difference. These are two different designations for the same thing.
B) An S0 will have more gas and dust than an E0.
C) The S0 will contain primarily Population II stars while the E0 has primarily Population I stars.
D) The S0 will be likely to contain supernova remnants while ellipticals never contain supernova remnants.

Question 74

An astronomer studying a galaxy finds that its spectrum shows only old, low-mass, Population II stars, and photographs of the galaxy show little or no interstellar gas or dust. What kind of galaxy is this astronomer studying?

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

Question 75

An elliptical galaxy typically contains which of these kinds of stars?

A) primarily young, metal-rich stars
B) stars of all ages, but all metal-poor
C) primarily old, metal-poor stars
D) stars of all ages from young, metal-rich stars to old, metal-poor stars

Question 76

Which of these galaxy types contain little or no interstellar dust or gas?

A) ellipticals
B) barred spirals
C) irregulars
D) spirals

Question 77

In which of these types of galaxies is star formation no longer occurring?

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

Question 78

Compared to the Milky Way Galaxy, a giant elliptical like M86 has

A) more gas and dust.
B) a higher rate of star formation.
C) more stars.
D) spiral arms that are more loosely wound.

Question 79

What is an E3 galaxy?

A) galaxy with a smooth light distribution and a moderately elongated elliptical shape without a disk or central bulge
B) galaxy with a smooth light distribution and a very elongated elliptical shape without a disk or central bulge
C) galaxy with a smooth light distribution and a moderately elliptical shape, having a pronounced disk and central bulge
D) galaxy with an irregular light distribution and a very elongated shape

Question 80

The biggest and intrinsically brightest galaxies in the universe are members of which group?

A) irregular galaxies
B) barred spirals
C) large spirals
D) ellipticals