Question 1

When the Sun first becomes a red giant star, its energy generation will be produced by:

Accepted Answer

A) core hydrogen fusion. 
B) shell hydrogen fusion. 
C) core helium fusion. 
D) Kelvin-Helmholtz contraction. 
A) core hydrogen fusion. 
B) shell hydrogen fusion. 
C) core helium fusion. 
D) Kelvin-Helmholtz contraction.

Question 2

The spiral galaxy in which we live is roughly 14 billion years old. For the stars that formed when the galaxy was very young (say, during the first billion years), which of the following statements is true? (See Table 19-1 of Universe, 11th ed.)
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  ​

Accepted Answer

A) Some stars of half the mass of the Sun are still on the main sequence, but most have finished their lives as stars. 
B) All stars of half the mass of the Sun are still on the main sequence. 
C) Some stars of 15 times the mass of the Sun are still on the main sequence, but most have finished their lives as stars. 
D) All stars of 3 times the mass of the Sun are still on the main sequence. 
A) Some stars of half the mass of the Sun are still on the main sequence, but most have finished their lives as stars. 
B) All stars of half the mass of the Sun are still on the main sequence. 
C) Some stars of 15 times the mass of the Sun are still on the main sequence, but most have finished their lives as stars. 
D) All stars of 3 times the mass of the Sun are still on the main sequence.

Question 3

Approximately what fraction of the Sun's main-sequence lifetime has been completed at the present time? (See Table 19-1 of Universe, 11th ed.)
​
  ​

Accepted Answer

A) less than 10% 
B) about 3/4 
C) about 1/4 
D) about 1/2 
A) less than 10% 
B) about 3/4 
C) about 1/4 
D) about 1/2

Question 4

What is the most important quantity on which the lifetime of a star depends?

Accepted Answer

A) temperature of the star's corona 
B) abundance of heavy elements in the star 
C) star's speed of rotation 
D) mass of the star 
A) temperature of the star's corona 
B) abundance of heavy elements in the star 
C) star's speed of rotation 
D) mass of the star

Question 5

If you examine many main-sequence stars, the lifetimes are different. As the luminosity of the star under consideration increases, the star's main-sequence lifetime:

Accepted Answer

A) is unaffected, as lifetime depends only on temperature and mass and not luminosity. 
B) decreases because the star's fuel is being expended at a larger rate. 
C) increases because larger luminosities imply larger masses. 
D) decreases because larger luminosities go with smaller, hotter stars. 
A) is unaffected, as lifetime depends only on temperature and mass and not luminosity. 
B) decreases because the star's fuel is being expended at a larger rate. 
C) increases because larger luminosities imply larger masses. 
D) decreases because larger luminosities go with smaller, hotter stars.

Question 6

RR Lyrae variables are likely to be found in:

Accepted Answer

A) very young clusters, where high-mass stars are undergoing core hydrogen burning. 
B) giant molecular clouds, where protostars are forming from gas and dust clouds. 
C) young-to-intermediate-age clusters, where high-mass stars are undergoing central helium burning. 
D) globular clusters, where low-mass stars are undergoing core helium burning. 
A) very young clusters, where high-mass stars are undergoing core hydrogen burning. 
B) giant molecular clouds, where protostars are forming from gas and dust clouds. 
C) young-to-intermediate-age clusters, where high-mass stars are undergoing central helium burning. 
D) globular clusters, where low-mass stars are undergoing core helium burning.

Question 7

What is the minimum mass necessary in a protostar for it to begin nuclear reactions and become a main sequence star?

Accepted Answer

A) 0.08 M ? 
B) 0.4 M ? 
C) 1.0 M ? 
D) 1.4 M ? 
A) 0.08 M ? 
B) 0.4 M ? 
C) 1.0 M ? 
D) 1.4 M ?

Question 8

When a Cepheid variable star reaches maximum luminosity, which other property of the star does NOT also reach a maximum?

Accepted Answer

A) surface temperature 
B) diameter 
C) outward radial velocity 
D) luminosity 
A) surface temperature 
B) diameter 
C) outward radial velocity 
D) luminosity

Question 9

Suppose that, when the stars in a particular open star cluster are plotted in an H-R diagram, the luminosity of stars at the turnoff point is about 5 times the luminosity of the Sun. Approximately what is the age of this cluster? (See Figure 19-15 of Universe, 11th ed.) ​
  ​

Accepted Answer

A) 100 million years 
B) 1 billion years 
C) 500 million years 
D) 4 billion years 
A) 100 million years 
B) 1 billion years 
C) 500 million years 
D) 4 billion years

Question 10

What causes the core of a star to contract during the main-sequence phase of the star's life?

Accepted Answer

A) The conversion of hydrogen into helium reduces the number of particles in the core. 
B) Convection in the outer layers carries energy out of the core more efficiently as the star ages. 
C) Helium has a larger atomic weight than hydrogen and exerts a stronger gravitational pull on the core. 
D) The rate of core hydrogen burning decreases as the hydrogen is used up, reducing the rate of energy generation. 
A) The conversion of hydrogen into helium reduces the number of particles in the core. 
B) Convection in the outer layers carries energy out of the core more efficiently as the star ages. 
C) Helium has a larger atomic weight than hydrogen and exerts a stronger gravitational pull on the core. 
D) The rate of core hydrogen burning decreases as the hydrogen is used up, reducing the rate of energy generation.

Question 11

If you were to look at 1 kg of material taken from the surface of the Sun and 1 kg taken from the center, which of the following statements would be true of these two 1-kg masses?

Accepted Answer

A) The kilogram from the surface would contain more hydrogen than the one from the center. 
B) Neither of them would contain any hydrogen. 
C) They both would contain the same amount of hydrogen. 
D) The kilogram from the surface would contain less hydrogen than the one from the center. 
A) The kilogram from the surface would contain more hydrogen than the one from the center. 
B) Neither of them would contain any hydrogen. 
C) They both would contain the same amount of hydrogen. 
D) The kilogram from the surface would contain less hydrogen than the one from the center.

Question 12

In some binary star systems, such as $\beta$ (Beta) Lyrae, very little light is seen from the more massive star. This is because the:

Accepted Answer

A) more massive star is still hidden in the dust clouds from which it formed. 
B) more massive star is a black hole, from which light cannot escape. 
C) more massive star is hidden by an accretion disk of material from the less massive star. 
D) orbit of the more massive star keeps it hidden behind the larger but less massive star as seen from Earth. 
A) more massive star is still hidden in the dust clouds from which it formed. 
B) more massive star is a black hole, from which light cannot escape. 
C) more massive star is hidden by an accretion disk of material from the less massive star. 
D) orbit of the more massive star keeps it hidden behind the larger but less massive star as seen from Earth.

Question 13

The Kelvin-Helmholtz contraction supplies significant energy to a star:

Accepted Answer

A) only in the stages before the main sequence. 
B) after the core of a late main-sequence star runs out of hydrogen. 
C) all during the main-sequence lifetime of star. 
D) only when the outer edges of the star collapse inward. 
A) only in the stages before the main sequence. 
B) after the core of a late main-sequence star runs out of hydrogen. 
C) all during the main-sequence lifetime of star. 
D) only when the outer edges of the star collapse inward.

Question 14

Where on the H-R diagram would you expect to find Population I and II stars?

Accepted Answer

A) Each population should be scattered throughout the entire diagram. 
B) Population I stars are restricted to the left (high temperature) side of the diagram, and Population II stars are to the right side. 
C) Population I stars are restricted to the right (low temperature) side of the diagram, and Population II stars are to the left side. 
D) Population I stars are represented across the entire H-R diagram, but Population II stars exist primarily on the right side. 
A) Each population should be scattered throughout the entire diagram. 
B) Population I stars are restricted to the left (high temperature) side of the diagram, and Population II stars are to the right side. 
C) Population I stars are restricted to the right (low temperature) side of the diagram, and Population II stars are to the left side. 
D) Population I stars are represented across the entire H-R diagram, but Population II stars exist primarily on the right side.

Question 15

For a main-sequence star of less than 0.4 M ? , what percentage of the mass of the core still remains as hydrogen after the thermonuclear furnace has transformed hydrogen into helium over its main-sequence lifetime?

Accepted Answer

A) 75% 
B) 35% 
C) 25% 
D) less than 1% 
A) 75% 
B) 35% 
C) 25% 
D) less than 1%

Question 16

The majority of the elements heavier than hydrogen and helium in the universe are believed to have originated in:

Accepted Answer

A) the original Big Bang. 
B) the central cores of stars. 
C) HII regions, under the action of H $\alpha$ light. 
D) giant molecular clouds. 
A) the original Big Bang. 
B) the central cores of stars. 
C) HII regions, under the action of H $\alpha$ light. 
D) giant molecular clouds.

Question 17

The core hydrogen fusion phase will span approximately 12 billion years for a star like the Sun. How long will the core helium fusion phase last?

Accepted Answer

A) 12 billion years 
B) 1 billion years 
C) 100 million years 
D) 1 million years 
A) 12 billion years 
B) 1 billion years 
C) 100 million years 
D) 1 million years

Question 18

Electron degeneracy, a result of the Pauli exclusion principle that prevents electrons from becoming crowded together beyond a certain limit, is important in:

Accepted Answer

A) the core of a low-mass star just before the start of core helium burning. 
B) the core of a low-mass star just before the start of core hydrogen burning. 
C) the core of a low-mass star during core hydrogen burning. 
D) a low-mass protostar evolving toward the main sequence. 
A) the core of a low-mass star just before the start of core helium burning. 
B) the core of a low-mass star just before the start of core hydrogen burning. 
C) the core of a low-mass star during core hydrogen burning. 
D) a low-mass protostar evolving toward the main sequence.

Question 19

The stars at the turnoff point in the H-R diagram of the Hyades star cluster have an absolute magnitude of approximately M = +2, whereas those at the turnoff point in the cluster M41 have M = 0. From this information, we can say with certainty that the Hyades cluster:

Accepted Answer

A) is farther away than M41. 
B) older than M41. 
C) has more stars in it than M41. 
D) younger than M41. 
A) is farther away than M41. 
B) older than M41. 
C) has more stars in it than M41. 
D) younger than M41.

Question 20

In a semidetached binary star system:

Accepted Answer

A) the stars share the same outer atmosphere, but the cores of the two stars do not touch. 
B) one star fills its Roche lobe, while the other does not. 
C) one star orbits the center of mass, while the other moves freely through space. 
D) both stars fill their Roche lobes. 
A) the stars share the same outer atmosphere, but the cores of the two stars do not touch. 
B) one star fills its Roche lobe, while the other does not. 
C) one star orbits the center of mass, while the other moves freely through space. 
D) both stars fill their Roche lobes.

Exam 19: Stellar Evolution: on and After the Main Sequence

When the Sun first becomes a red giant star, its energy generation will be produced by:

The spiral galaxy in which we live is roughly 14 billion years old. For the stars that formed when the galaxy was very young (say, during the first billion years), which of the following statements is true? (See Table 19-1 of Universe, 11th ed.) ​ ​

Approximately what fraction of the Sun's main-sequence lifetime has been completed at the present time? (See Table 19-1 of Universe, 11th ed.) ​ ​

What is the most important quantity on which the lifetime of a star depends?

If you examine many main-sequence stars, the lifetimes are different. As the luminosity of the star under consideration increases, the star's main-sequence lifetime:

RR Lyrae variables are likely to be found in:

What is the minimum mass necessary in a protostar for it to begin nuclear reactions and become a main sequence star?

When a Cepheid variable star reaches maximum luminosity, which other property of the star does NOT also reach a maximum?

Suppose that, when the stars in a particular open star cluster are plotted in an H-R diagram, the luminosity of stars at the turnoff point is about 5 times the luminosity of the Sun. Approximately what is the age of this cluster? (See Figure 19-15 of Universe, 11th ed.) ​ ​

What causes the core of a star to contract during the main-sequence phase of the star's life?

If you were to look at 1 kg of material taken from the surface of the Sun and 1 kg taken from the center, which of the following statements would be true of these two 1-kg masses?

In some binary star systems, such as β\betaβ (Beta) Lyrae, very little light is seen from the more massive star. This is because the:

The Kelvin-Helmholtz contraction supplies significant energy to a star:

Where on the H-R diagram would you expect to find Population I and II stars?

For a main-sequence star of less than 0.4 M ? , what percentage of the mass of the core still remains as hydrogen after the thermonuclear furnace has transformed hydrogen into helium over its main-sequence lifetime?

The majority of the elements heavier than hydrogen and helium in the universe are believed to have originated in:

The core hydrogen fusion phase will span approximately 12 billion years for a star like the Sun. How long will the core helium fusion phase last?

Electron degeneracy, a result of the Pauli exclusion principle that prevents electrons from becoming crowded together beyond a certain limit, is important in:

The stars at the turnoff point in the H-R diagram of the Hyades star cluster have an absolute magnitude of approximately M = +2, whereas those at the turnoff point in the cluster M41 have M = 0. From this information, we can say with certainty that the Hyades cluster:

In a semidetached binary star system:

Astronomy and the Universe

Knowing the Heavens

Eclipses and the Motion of the Moon

Gravitation and the Waltz of the Planets

The Nature of Light

Optics and Telescopes

Comparative Planetology I: Our Solar System

Comparative Planetology II: the Origin of Our Solar System

The Living Earth

Our Barren Moon

Mercury, Venus, and Mars: Terrestrial, yet Unique

Jupiter and Saturn: Lords of the Planets

Jupiter and Saturns Satellites of Fire and Ice

Uranus, Neptune, Pluto, and the Kuiper Belt: Remote Worlds

Asteroids, Comets, and Impacts

Our Star, the Sun

The Nature of the Stars

The Birth of Stars

Stellar Evolution: The Death of Stars

Stellar Remnants: Neutron Stars and Black Holes

Our Galaxy

Galaxies

Quasars and Active Galaxies

Cosmology: The Origin and Evolution of the Universe

Exploring the Early Universe

The Search for Extraterrestrial Life

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The spiral galaxy in which we live is roughly 14 billion years old. For the stars that formed when the galaxy was very young (say, during the first billion years), which of the following statements is true? (See Table 19-1 of Universe, 11th ed.)

Approximately what fraction of the Sun's main-sequence lifetime has been completed at the present time? (See Table 19-1 of Universe, 11th ed.) $Approximately what fraction of the Sun's main-sequence lifetime has been completed at the present time? (See Table 19-1 of Universe, 11th ed.) $

Suppose that, when the stars in a particular open star cluster are plotted in an H-R diagram, the luminosity of stars at the turnoff point is about 5 times the luminosity of the Sun. Approximately what is the age of this cluster? (See Figure 19-15 of Universe, 11th ed.)

In some binary star systems, such as $\beta$ (Beta) Lyrae, very little light is seen from the more massive star. This is because the: