Question 1

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

Accepted Answer

When seen edge-on, a spiral galaxy appears as a thick, straight line of light with a central bulge due to the disk and central bulge structure of the galaxy.

Question 2

Why is it strange to find spiral arms in spiral galaxies (see Figure 13-24,Comins,Discovering the Essential Universe,6th ed.)?

Accepted Answer

The differential rotation of galaxies should cause the spiral arms to wind up and blend into the rest of the galaxy over time, making their persistence a puzzle.

Question 3

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?

Accepted Answer

Sb galaxies are characterized by having a nuclear region of moderate size and arms that are moderately wound, fitting the description given.

Question 4

A spiral galaxy is observed edge-on so that the spiral arms cannot be seen clearly.Is it possible to classify this galaxy using the Hubble classification scheme?

Accepted Answer

The Hubble classification scheme allows for the classification of spiral galaxies based on the size of the nuclear bulge, which can be observed even when the galaxy is edge-on.

Question 5

A typical spiral galaxy has _____ stars in a disk of diameter _____ ly.

Accepted Answer

This is the most accurate estimate based on current observations of spiral galaxies, which have on average about 100 billion stars in a disk that is roughly 100,000 light years in diameter. Option B is incorrect because a diameter of 1000 light years is too small for a typical spiral galaxy. Option C is incorrect because 10⁹ stars is too few for a typical spiral galaxy, and a disk diameter of 10⁶ light years is too large. Option D is also incorrect because 10⁶ stars is too few for a typical spiral galaxy.

Question 6

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?

Accepted Answer

Galaxies with a large nuclear region and tightly wound arms are classified as Sa type in the Hubble sequence. This classification indicates a spiral galaxy with relatively little space between the arms and a prominent central bulge.

Question 7

How does the winding dilemma affect flocculent spirals?

Accepted Answer

Flocculent spirals are characterized by patchy, irregular star formation that is not significantly influenced by the winding dilemma, which primarily concerns the persistence of spiral arms in galaxies with differential rotation.

Question 8

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

Accepted Answer

An Sa galaxy is classified as a spiral galaxy with a large central bulge and tightly wound spiral arms.

Question 9

In the self-propagating star formation theory:

Accepted Answer

The answer of In the self-propagating star formation theory:
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Question 10

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?

Accepted Answer

Spiral galaxies are classified based on the tightness of their spiral arms, the size of their central bulge, and the presence of a bar. The galaxies described in the question have loosely wound arms and a small nuclear region, which suggests they belong to the Sc type. A Sa galaxy would have tightly wound arms and a large bulge, while an SBb galaxy would have a bar and moderately wound arms. An Sb galaxy would have moderately wound arms and a medium-sized bulge.

Question 11

The typical diameter of a spiral galaxy is about:

Accepted Answer

The typical diameter of a spiral galaxy is about 100,000 light-years, which is 10⁵ ly.

Question 12

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?

Accepted Answer

The presence of well-defined lanes of stars and gas clouds indicates the presence of a well-formed spiral structure. Additionally, the round shape and a nuclear region of uniform brightness are also characteristic of spiral galaxies, particularly grand-design spirals. The galaxy cannot be classified as elliptical due to the presence of spiral arms, and cannot be classified as irregular due to the well-defined structure. Flocculent spirals have less distinct spiral arms, making them less likely to have "long, curved, well-defined lanes."

Question 13

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

Accepted Answer

The influence of black holes does not play a role in self-propagating star formation. The other choices (B, C, and D) are all mechanisms that can spread star formation over a region.

Question 14

Ans: C
Section: 13-9
-One difficulty with the density wave theory is that:

Accepted Answer

The difficulty with the density wave theory is that we are unsure of the mechanism that produces the energy output necessary to sustain the density wave.

Question 15

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?

Accepted Answer

The presence of poorly defined lanes in the outer region indicates that the galaxy is spiral in shape. However, the fact that these lanes are fuzzy and poorly defined suggests that the spiral arms are not as tightly wound as in grand-design spirals. This is characteristic of flocculent spirals, which have a more patchy appearance. The round nuclear region with uniform brightness is also common in flocculent spirals.

Question 16

What is the dilemma about the spiral-arm structure of a typical spiral galaxy?

Accepted Answer

The answer of What is the dilemma about the spiral-arm...

Question 17

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

Accepted Answer

The Andromeda Galaxy (M31) is a spiral collection of stars, dust, and gas that is approximately 200,000 ly across. It is one of the closest galaxies to our Milky Way and can be seen with the naked eye from Earth.

Question 18

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

Accepted Answer

The theory of self-propagating star formation proposes that the spiral arms of a galaxy are created by the formation of O and B type stars. In flocculent spiral galaxies, the spiral arms are broad and poorly defined because they lack the long-lived star clusters found in grand-design spirals. Instead, the spiral arm segments are defined only by the relatively short-lived O and B type stars.

Question 19

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?

Accepted Answer

The size of the nuclear bulge is directly related to the tightness of the spiral arms, as spiral galaxies with tighter arms tend to have larger nuclear bulges. This parameter can be easily seen even when the spiral arms cannot be observed due to the galaxy's orientation. The overall spectral color, intrinsic brightness, and diameter of the galaxy would not provide direct information about the tightness of the spiral arms.

Question 20

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

Accepted Answer

Grand-design Sb galaxies are characterized by their well-defined spiral arms that are not too tightly wound, fitting the description given.

Quiz 13: The Galaxies