Question 1

The next stage in the life of a star like the Sun, after the main-sequence phase, is

Accepted Answer

A)  the red giant phase. 
B)  the horizontal-branch phase. 
C)  a protostar. 
D)  death (i.e., either a supernova or a white dwarf). 
A)  the red giant phase. 
B)  the horizontal-branch phase. 
C)  a protostar. 
D)  death (i.e., either a supernova or a white dwarf).

Question 2

Astronomers studying stellar evolution draw a curve on a Hertzsprung-Russell diagram called a "birth line". What does the birth line represent?

Accepted Answer

A)  evolutionary track of a 1-solar-mass star (i.e., the Sun) 
B)  coordinates of the initial collapse of dense cores of various initial masses 
C)  coordinates of the transformation of protostars of various masses into pre-main-sequence stars 
D)  coordinates of the transformation of pre-main-sequence stars of various masses into main-sequence stars 
A)  evolutionary track of a 1-solar-mass star (i.e., the Sun) 
B)  coordinates of the initial collapse of dense cores of various initial masses 
C)  coordinates of the transformation of protostars of various masses into pre-main-sequence stars 
D)  coordinates of the transformation of pre-main-sequence stars of various masses into main-sequence stars

Question 3

In which region of the Hertzsprung-Russell diagram does a newly formed protostar first appear when it begins to shine at visible wavelengths?

Accepted Answer

A)  bottom right corner; very low luminosity because it is both small and cool 
B)  center of the main sequence since all protostars begin their lives at this position and move up or down the diagram, depending on their mass as time passes 
C)  right side; relatively large luminosity because of its size but cool temperature 
D)  top left corner; at the top of the main sequence, down which it will progress with time 
A)  bottom right corner; very low luminosity because it is both small and cool 
B)  center of the main sequence since all protostars begin their lives at this position and move up or down the diagram, depending on their mass as time passes 
C)  right side; relatively large luminosity because of its size but cool temperature 
D)  top left corner; at the top of the main sequence, down which it will progress with time

Question 4

When attempting to observe a protostar, which region of the spectrum do astronomers usually use?

Accepted Answer

A)  visible, because protostars do emit visible light 
B)  infrared, because protostars emit only infrared light 
C)  infrared, because these longer wavelengths can penetrate the dust surrounding the protostar 
D)  ultraviolet, because their higher energy photons can penetrate the dust surrounding the protostar 
A)  visible, because protostars do emit visible light 
B)  infrared, because protostars emit only infrared light 
C)  infrared, because these longer wavelengths can penetrate the dust surrounding the protostar 
D)  ultraviolet, because their higher energy photons can penetrate the dust surrounding the protostar

Question 5

Suppose that an astronomical observatory announces the discovery of an object with about 50 times the mass of Jupiter. Since this mass is not enough for the object to be a star, what name would the observatory apply to the object?

Accepted Answer

A)  red dwarf 
B)  infrared dwarf 
C)  brown dwarf 
D)  white dwarf 
A)  red dwarf 
B)  infrared dwarf 
C)  brown dwarf 
D)  white dwarf

Question 6

The stars that last longest are the stars

Accepted Answer

A)  with the largest luminosity and highest temperature, since they take the longest to cool down to invisibility. 
B)  with the largest mass, that is, the largest amount of fuel. 
C)  with the smallest mass. 
D)  of intermediate mass; small-mass stars have little fuel and burn out quickly, while very massive stars burn their fuel very rapidly. 
A)  with the largest luminosity and highest temperature, since they take the longest to cool down to invisibility. 
B)  with the largest mass, that is, the largest amount of fuel. 
C)  with the smallest mass. 
D)  of intermediate mass; small-mass stars have little fuel and burn out quickly, while very massive stars burn their fuel very rapidly.

Question 7

What happens to a star after the start of helium nuclear reactions in its core compared with what it was like before these reactions began?

Accepted Answer

A)  The star is larger and hotter. 
B)  The star is larger and cooler. 
C)  The star is smaller and hotter. 
D)  The star is smaller and cooler. 
A)  The star is larger and hotter. 
B)  The star is larger and cooler. 
C)  The star is smaller and hotter. 
D)  The star is smaller and cooler.

Question 8

Which component in the core of a star undergoing helium fusion leads to the behavior known as the "helium flash?"

Accepted Answer

A)  neutrinos, since it is this component that, in interacting with helium nuclei, triggers the helium flash 
B)  helium, since its density has to be above a certain limit to trigger this explosive event 
C)  electrons, since they control the pressure, and their pressure does not depend on temperature. Under these conditions, buildup of heat can occur without leading to the normal gas expansion and the resulting thermal equilibrium. 
D)  remnant hydrogen since loss of this component allows uncontrolled helium burning rather than a uniform rate of energy production 
A)  neutrinos, since it is this component that, in interacting with helium nuclei, triggers the helium flash 
B)  helium, since its density has to be above a certain limit to trigger this explosive event 
C)  electrons, since they control the pressure, and their pressure does not depend on temperature. Under these conditions, buildup of heat can occur without leading to the normal gas expansion and the resulting thermal equilibrium. 
D)  remnant hydrogen since loss of this component allows uncontrolled helium burning rather than a uniform rate of energy production

Question 9

Degeneracy occurs when

Accepted Answer

A)  electrons inside a star resist being pushed closer together than a certain limit. 
B)  solar wind particles become trapped in Earth's magnetic field. 
C)  magnetic fields inhibit the motion of charged particles in sunspots. 
D)  thermonuclear reactions halt the contraction of a protostar. 
A)  electrons inside a star resist being pushed closer together than a certain limit. 
B)  solar wind particles become trapped in Earth's magnetic field. 
C)  magnetic fields inhibit the motion of charged particles in sunspots. 
D)  thermonuclear reactions halt the contraction of a protostar.

Question 10

The group of stars that is formed when a giant molecular cloud collapses is called a(n)

Accepted Answer

A)  open cluster. 
B)  galaxy. 
C)  constellation. 
D)  gravitational lens. 
A)  open cluster. 
B)  galaxy. 
C)  constellation. 
D)  gravitational lens.

Question 11

Which of these statements characterizes the early stages of a red giant?

Accepted Answer

A)  large, red star that is burning hydrogen into helium in its core 
B)  protostar in the upper right of the Hertzsprung-Russell diagram 
C)  large-emission nebula 
D)  star that is burning hydrogen into helium in a shell around the core 
A)  large, red star that is burning hydrogen into helium in its core 
B)  protostar in the upper right of the Hertzsprung-Russell diagram 
C)  large-emission nebula 
D)  star that is burning hydrogen into helium in a shell around the core

Question 12

The helium flash occurs in a 2-solar-mass star when

Accepted Answer

A)  the core heats up from helium fusion and the gas does not expand to cool down and stabilize the temperature because the gas properties are controlled by degenerate electrons. 
B)  convection within the star carries helium to the surface, where it shows its own characteristic spectrum for the first time. 
C)  hydrogen fusion ceases abruptly, leaving only the fusion of helium to generate energy. 
D)  the core temperature becomes sufficiently high for helium fusion for the first time. 
A)  the core heats up from helium fusion and the gas does not expand to cool down and stabilize the temperature because the gas properties are controlled by degenerate electrons. 
B)  convection within the star carries helium to the surface, where it shows its own characteristic spectrum for the first time. 
C)  hydrogen fusion ceases abruptly, leaving only the fusion of helium to generate energy. 
D)  the core temperature becomes sufficiently high for helium fusion for the first time.

Question 13

When the Sun entered the main sequence, its core was approximately 75 percent hydrogen and 25 percent helium, by mass. What was the ratio of hydrogen nuclei to helium nuclei?

Accepted Answer

A)  3:1 
B)  4:1 
C)  12:1 
D)  16:1 
A)  3:1 
B)  4:1 
C)  12:1 
D)  16:1

Question 14

In some binary star systems, such as $\beta$ Lyrae, essentially no light is seen from the more massive star because the

Accepted Answer

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

Question 15

Why are the stars in an open cluster useful for studying just the EARLY stages of stellar evolution?

Accepted Answer

A)  These stars are all massive and thus erupt in a supernova explosion before the later stages of evolution are reached. 
B)  There are many different paths a star can take after the main sequence, and open clusters contain so few stars that each of these paths is followed by only a few stars, making them statistically unreliable for study. 
C)  The stars in an open cluster tend to dissipate after a few tens of millions of years and cease to be a part of the group. 
D)  These stars all tend to be very small, and after the early stages they begin to experience mass loss and disappear from view. 
A)  These stars are all massive and thus erupt in a supernova explosion before the later stages of evolution are reached. 
B)  There are many different paths a star can take after the main sequence, and open clusters contain so few stars that each of these paths is followed by only a few stars, making them statistically unreliable for study. 
C)  The stars in an open cluster tend to dissipate after a few tens of millions of years and cease to be a part of the group. 
D)  These stars all tend to be very small, and after the early stages they begin to experience mass loss and disappear from view.

Question 16

The next lengthy period in the evolution of a star after hydrogen fusion is helium fusion. What is the main product of this helium fusion?

Accepted Answer

A)  deuterium 
B)  beryllium 
C)  carbon 
D)  oxygen 
A)  deuterium 
B)  beryllium 
C)  carbon 
D)  oxygen

Question 17

What is the difference between a Type I Cepheid ($\delta$ Cepheid star) and a Type II Cepheid?

Accepted Answer

A)  Type I Cepheids are main-sequence stars, while Type II Cepheids are giant stars. 
B)  Type I Cepheids are short-period variables, while Type II Cepheids are long-period variables. 
C)  Only Type I Cepheids have a simple relationship between luminosity and period. 
D)  Type I Cepheids are brighter metal-rich stars, while Type II Cepheids are dimmer metal-poor stars. 
A)  Type I Cepheids are main-sequence stars, while Type II Cepheids are giant stars. 
B)  Type I Cepheids are short-period variables, while Type II Cepheids are long-period variables. 
C)  Only Type I Cepheids have a simple relationship between luminosity and period. 
D)  Type I Cepheids are brighter metal-rich stars, while Type II Cepheids are dimmer metal-poor stars.

Question 18

An astronomer plots the H-R diagram of a star cluster and finds that it contains hot B-type stars on the main sequence and cooler G- and K-type stars noticeably above the main sequence. This cluster is

Accepted Answer

A)  of indeterminate age since the age of the cluster cannot be estimated from the information given. 
B)  impossible because cool stars cannot be above the main sequence when hot stars are on the main sequence. 
C)  old because the G and K stars are already evolving off (away from) the main sequence. 
D)  very young because the G and K stars are still evolving toward the main sequence. 
A)  of indeterminate age since the age of the cluster cannot be estimated from the information given. 
B)  impossible because cool stars cannot be above the main sequence when hot stars are on the main sequence. 
C)  old because the G and K stars are already evolving off (away from) the main sequence. 
D)  very young because the G and K stars are still evolving toward the main sequence.

Question 19

What is an emission nebula, also known as an H II region?

Accepted Answer

A)  region of ionized hydrogen around one or more hot O- and B-type stars 
B)  region of molecular hydrogen inside a giant molecular cloud 
C)  region of neutral, atomic hydrogen in interstellar space 
D)  region of gas and dust formed by the explosion of a massive star 
A)  region of ionized hydrogen around one or more hot O- and B-type stars 
B)  region of molecular hydrogen inside a giant molecular cloud 
C)  region of neutral, atomic hydrogen in interstellar space 
D)  region of gas and dust formed by the explosion of a massive star

Question 20

What is the second MOST abundant element in the interstellar medium (after hydrogen)?

Accepted Answer

A)  helium 
B)  carbon 
C)  nitrogen 
D)  iron 
A)  helium 
B)  carbon 
C)  nitrogen 
D)  iron

The next stage in the life of a star like the Sun, after the main-sequence phase, is

Astronomers studying stellar evolution draw a curve on a Hertzsprung-Russell diagram called a "birth line". What does the birth line represent?

In which region of the Hertzsprung-Russell diagram does a newly formed protostar first appear when it begins to shine at visible wavelengths?

When attempting to observe a protostar, which region of the spectrum do astronomers usually use?

Suppose that an astronomical observatory announces the discovery of an object with about 50 times the mass of Jupiter. Since this mass is not enough for the object to be a star, what name would the observatory apply to the object?

The stars that last longest are the stars

What happens to a star after the start of helium nuclear reactions in its core compared with what it was like before these reactions began?

Which component in the core of a star undergoing helium fusion leads to the behavior known as the "helium flash?"

Degeneracy occurs when

The group of stars that is formed when a giant molecular cloud collapses is called a(n)

Which of these statements characterizes the early stages of a red giant?

The helium flash occurs in a 2-solar-mass star when

When the Sun entered the main sequence, its core was approximately 75 percent hydrogen and 25 percent helium, by mass. What was the ratio of hydrogen nuclei to helium nuclei?

In some binary star systems, such as $\beta$ Lyrae, essentially no light is seen from the more massive star because the

Why are the stars in an open cluster useful for studying just the EARLY stages of stellar evolution?

The next lengthy period in the evolution of a star after hydrogen fusion is helium fusion. What is the main product of this helium fusion?

What is the difference between a Type I Cepheid ( $\delta$ Cepheid star) and a Type II Cepheid?

An astronomer plots the H-R diagram of a star cluster and finds that it contains hot B-type stars on the main sequence and cooler G- and K-type stars noticeably above the main sequence. This cluster is

What is an emission nebula, also known as an H II region?

What is the second MOST abundant element in the interstellar medium (after hydrogen)?

Discovering the Night Sky

Gravitation and the Motion of the Planets

Light and Telescopes

Atomic Physics and Spectra

Exoplanets and the Formation of Planetary Systems

Formation of the Solar System

Earth and the Moon

The Other Terrestrial Planets

The Outer Planets

Vagabonds of the Solar System

The Sun: Our Extraordinary Star

Characterizing Stars

The Death of Stars

Black Holes: Matters of Gravity

The Milky Way Galaxy

Galaxies

Quasars and Other Active Galaxies

Cosmology

Astrobiology

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Exam 13: The Lives of Stars From Birth Through Middle Age

The next stage in the life of a star like the Sun, after the main-sequence phase, is

Astronomers studying stellar evolution draw a curve on a Hertzsprung-Russell diagram called a "birth line". What does the birth line represent?

In which region of the Hertzsprung-Russell diagram does a newly formed protostar first appear when it begins to shine at visible wavelengths?

When attempting to observe a protostar, which region of the spectrum do astronomers usually use?

Suppose that an astronomical observatory announces the discovery of an object with about 50 times the mass of Jupiter. Since this mass is not enough for the object to be a star, what name would the observatory apply to the object?

The stars that last longest are the stars

What happens to a star after the start of helium nuclear reactions in its core compared with what it was like before these reactions began?

Which component in the core of a star undergoing helium fusion leads to the behavior known as the "helium flash?"

Degeneracy occurs when

The group of stars that is formed when a giant molecular cloud collapses is called a(n)

Which of these statements characterizes the early stages of a red giant?

The helium flash occurs in a 2-solar-mass star when

When the Sun entered the main sequence, its core was approximately 75 percent hydrogen and 25 percent helium, by mass. What was the ratio of hydrogen nuclei to helium nuclei?

In some binary star systems, such as β\betaβ Lyrae, essentially no light is seen from the more massive star because the

Why are the stars in an open cluster useful for studying just the EARLY stages of stellar evolution?

The next lengthy period in the evolution of a star after hydrogen fusion is helium fusion. What is the main product of this helium fusion?

What is the difference between a Type I Cepheid ( δ\deltaδ Cepheid star) and a Type II Cepheid?

An astronomer plots the H-R diagram of a star cluster and finds that it contains hot B-type stars on the main sequence and cooler G- and K-type stars noticeably above the main sequence. This cluster is

What is an emission nebula, also known as an H II region?

What is the second MOST abundant element in the interstellar medium (after hydrogen)?

Discovering the Night Sky

Gravitation and the Motion of the Planets

Light and Telescopes

Atomic Physics and Spectra

Exoplanets and the Formation of Planetary Systems

Formation of the Solar System

Earth and the Moon

The Other Terrestrial Planets

The Outer Planets

Vagabonds of the Solar System

The Sun: Our Extraordinary Star

Characterizing Stars

The Death of Stars

Black Holes: Matters of Gravity

The Milky Way Galaxy

Galaxies

Quasars and Other Active Galaxies

Cosmology

Astrobiology

Filters

In some binary star systems, such as $\beta$ Lyrae, essentially no light is seen from the more massive star because the

What is the difference between a Type I Cepheid ( $\delta$ Cepheid star) and a Type II Cepheid?