UniverseTenth Edition

Chapter 19Stellar Evolution: On and After

the Main Sequence

Roger Freedman • Robert Geller • William Kaufmann III

Clicker Questions

Stars with larger masses haveA. longer main-sequence lifetimes than smaller mass

stars because they have more fuel. B. shorter main-sequence lifetimes than smaller mass

stars because although they have more fuel, they use it much faster.

C. longer main-sequence lifetimes than smaller mass stars because they can fuse more elements.

D. shorter main-sequence lifetimes than smaller mass stars because they have a smaller core in which nuclear reactions can occur.

Q19.1

Stars with larger masses haveA. longer main-sequence lifetimes than smaller mass

stars because they have more fuel. B. shorter main-sequence lifetimes than smaller mass

stars because although they have more fuel, they use it much faster.

C. longer main-sequence lifetimes than smaller mass stars because they can fuse more elements.

D. shorter main-sequence lifetimes than smaller mass stars because they have a smaller core in which nuclear reactions can occur.

A19.1

Approximately how long will a 3-solar-mass star spend on the main sequence?A. 3 times the Sun’s main-sequence lifetimeB. 0.33 times the Sun’s main-sequence

lifetime C. 0.13 times the Sun’s main-sequence

lifetime D. 0.11 times the Sun’s main-sequence

lifetime E. 0.064 times the Sun’s main-sequence

lifetime Q19.2

Approximately how long will a 3-solar-mass star spend on the main sequence? A. 3 times the Sun’s main-sequence lifetimeB. 0.33 times the Sun’s main-sequence

lifetime C. 0.13 times the Sun’s main-sequence

lifetime D. 0.11 times the Sun’s main-sequence

lifetime E. 0.064 times the Sun’s main-sequence

lifetime A19.2

Why does the core of a star contract during its time on the main sequence?

A. The temperature of the core decreases, which causes contraction.

B. The temperature of the core increases, which causes contraction.

C. As neutrinos build up in the core, the pressure decreases.

D. The number of particles in the core decreases (four hydrogen nuclei are fused into one helium nucleus).

E. The number of particles in the core increases (starting with protons, reactions produce heavier nuclei, positrons, and neutrinos).

Q19.3

Why does the core of a star contract during its time on the main sequence? A. The temperature of the core decreases,

which causes contraction. B. The temperature of the core increases,

which causes contraction. C. As neutrinos build up in the core, the

pressure decreases.D. The number of particles in the core

decreases (four hydrogen nuclei are fused into one helium nucleus).

E. The number of particles in the core increases (starting with protons, reactions produce heavier nuclei, positrons, and neutrinos).

A19.3

When hydrogen fusion in the core of the Sun ends, the Sun will move off the main sequence. As a result, the surface temperature of the Sun will ______ and the diameter of the Sun will ______.

A. decrease / decrease B. increase / increase C. decrease / increase D. increase / decrease E. increase / remain constant

Q19.4

When hydrogen fusion in the core of the Sun ends, the Sun will move off the main sequence. As a result, the surface temperature of the Sun will ______ and the diameter of the Sun will ______.

A. decrease / decrease B. increase / increase C. decrease / increase D. increase / decrease E. increase / remain constant

A19.4

Helium fusion takes place in the core of a red giant star. These fusion reactions produce A. iron. B. hydrogen. C. lithium and

carbon. D. carbon and

oxygen.E. beryllium and

carbon. Q19.5

Helium fusion takes place in the core of a red giant star. These fusion reactions produceA. iron. B. hydrogen. C. lithium and

carbon. D. carbon and

oxygen.E. beryllium and

carbon. A19.5

A certain star has 100 times the luminosity of the Sun and a surface temperature of 3500 K. What type of star is it?

A. A high-mass main-sequence star B. A low-mass main-sequence star C. A red giant D. A red dwarfE. A white dwarf

Q19.6

A certain star has 100 times the luminosity of the Sun and a surface temperature of 3500 K. What type of star is it?

A. A high-mass main-sequence star B. A low-mass main-sequence star C. A red giant D. A red dwarfE. A white dwarf

A19.6

Horizontal-branch stars are stars that have left the main sequence. Inside such stars A. no fusion is occurring in the core, and

hydrogen fusion is occurring in a shell around the core.

B. both core helium fusion and shell hydrogen fusion are taking place.

C. helium fusion is occurring in the core, and there is no hydrogen fusion.

D. both core hydrogen fusion and shell helium fusion are taking place.Q19.7

Horizontal-branch stars are stars that have left the main sequence. Inside such stars A. no fusion is occurring in the core, and

hydrogen fusion is occurring in a shell around the core.

B. both core helium fusion and shell hydrogen fusion are taking place.

C. helium fusion is occurring in the core, and there is no hydrogen fusion.

D. both core hydrogen fusion and shell helium fusion are taking place.A19.7

Cepheid variable stars are very luminous and can be observed over very large distances. Why are such stars important to astronomers?

A. They confirm the theory of nuclear fusion as the energy source for stars.

B. They can be used as distance indicators because their luminosity can be determined from their period.

C. Such stars are unstable and are about to become supernovae.

D. Their age can be determined directly from their period.

E. They are always found in binary systems.

Q19.8

Cepheid variable stars are very luminous and can be observed over very large distances. Why are such stars important to astronomers?

A. They confirm the theory of nuclear fusion as the energy source for stars.

B. They can be used as distance indicators because their luminosity can be determined from their period.

C. Such stars are unstable and are about to become supernovae.

D. Their age can be determined directly from their period.

E. They are always found in binary systems.

A19.8

Cepheid variable stars pulsate regularly in size and luminosity. During the part of a Cepheid’s pulsation cycle in which the star’s outer layers are expanding, the surface temperature of the star ______ and the peak wavelength of light emitted by the star ______. A. decreases / decreases B. increases / increases C. decreases / increases D. increases / decreases E. increases / remains constant

Q19.9

Cepheid variable stars pulsate regularly in size and luminosity. During the part of a Cepheid’s pulsation cycle in which the star’s outer layers are expanding, the surface temperature of the star ______ and the peak wavelength of light emitted by the star ______. A. decreases / decreases B. increases / increases C. decreases / increases D. increases / decreases E. increases / remains constant

A19.9

This graph shows the light curve of δ Cephei. The average period of this variable star is about

A. 1 dayB. 3.5 daysC. 4.4 daysD. 5.4 daysE. 6.4 days

Q19.10

This graph shows the light curve of δ Cephei. The average period of this variable star is about

A. 1 dayB. 3.5 daysC. 4.4 daysD. 5.4 daysE. 6.4 days

A19.10

Which of the following statements is correct? A. Population I stars were some of the first

stars created, and these stars swept up all the metals in the universe.

B. Population I stars were created recently in our universe after supernovae enriched the interstellar medium with metals.

C. A Population I star manufactured metals in its nuclear core, and these metals were carried to the surface of the star by convection.

D. A Population I star had a high-mass binary companion. The companion went through its evolutionary cycle quickly, then exploded as a supernova and showered its companion with metals.

Q19.11

Which of the following statements is correct? A. Population I stars were some of the first

stars created, and these stars swept up all the metals in the universe.

B. Population I stars were created recently in our universe after supernovae enriched the interstellar medium with metals.

C. A Population I star manufactured metals in its nuclear core, and these metals were carried to the surface of the star by convection.

D. A Population I star had a high-mass binary companion. The companion went through its evolutionary cycle quickly, then exploded as a supernova and showered its companion with metals.

A19.11

The stars in a cluster all formed at about the same time. A particular cluster of stars is found to have only high-mass stars on the main sequence. The most likely reason for this isA. no low-mass stars formed in this cluster. B. all of the low-mass stars have since finished

burning their fuel and died. C. there has not yet been enough time for low-

mass stars to evolve from protostars to join the main sequence.

D. all the low-mass stars in the cluster have combined to make high-mass stars.

E. the low mass stars are too faint to be seen.Q19.12

The stars in a cluster all formed at about the same time. A particular cluster of stars is found to have only high-mass stars on the main sequence. The most likely reason for this isA. no low-mass stars formed in this cluster. B. all of the low-mass stars have since finished

burning their fuel and died. C. there has not yet been enough time for low-

mass stars to evolve from protostars to join the main sequence.

D. all the low-mass stars in the cluster have combined to make high-mass stars.

E. the low mass stars are too faint to be seen.A19.12

We know that globular clusters are very old. This is because they contain

A. many high-mass main-sequence stars. B. numerous H II regions. C. no high-mass main-sequence stars. D. equal numbers of low-mass and high-mass

stars. E. no red stars.

Q19.13

We know that globular clusters are very old. This is because they contain

A. many high-mass main-sequence stars. B. numerous H II regions. C. no high-mass main-sequence stars. D. equal numbers of low-mass and high-mass

stars. E. no red stars.

A19.13