Chapter 17

What do astronomers mean when they say that we are all "star stuff"?
A) that life would be impossible without energy from the Sun
B) that Earth formed at the same time as the Sun
C) that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores
D) that the Sun formed from the interstellar medium: the "stuff" between the stars
E) that the Universe contains billions of stars

C) that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores

Which two energy sources can help a star maintain its internal thermal pressure?
A) nuclear fusion and gravitational contraction
B) nuclear fission and gravitational contraction
C) nuclear fusion and nuclear fission
D) chemical reactions and gravitational contraction
E) nuclear fusion and chemical reactions

A) nuclear fusion and gravitational contraction

What type of star is our Sun?
A) low-mass star
B) intermediate-mass star
C) high-mass star

A) low-mass star

What is the range of star masses for high-mass stars?
A) between 500 and about 1,000 solar masses
B) between 200 and about 500 solar masses
C) between 8 and about 100 solar masses
D) between 2 and about 10 solar masses
E) between 2 and about 5 solar masses

C) between 8 and about 100 solar masses

What can we learn about a star from a life track on an H-R diagram?
A) how long ago it was born
B) when it will die
C) where it is located
D) what surface temperature and luminosity it will have at each stage of its life
E) all of the above

D) what surface temperature and luminosity it will have at each stage of its life

Which of the following statements about degeneracy pressure is not true?
A) Degeneracy pressure varies with the temperature of the star.
B) Degeneracy pressure can halt gravitational contraction of a star even when no fusion is occurring in the core.
C) Degeneracy pressure keeps any protostar less than 0.08 solar mass from becoming a true, hydrogen-fusing star.
D) Degeneracy pressure arises out of the ideas of quantum mechanics.
E) Degeneracy pressure supports white dwarfs against gravity.

A) Degeneracy pressure varies with the temperature of the star.

All of the following are involved in carrying energy outward from a star's core except
A) convection.
B) radiative diffusion.
C) conduction.
D) neutrinos.

C) conduction.

Which stars have convective cores?
A) low-mass stars
B) intermediate-mass stars
C) high-mass stars
D) all of the above
E) none of the above

C) high-mass stars

Which of the following spectral types is more likely to be a flare star?
A) KIII
B) MV
C) GV
D) I
E) BII

B) MV

Which of the following properties make flare stars so active?
A) fast rotation rates
B) deep convection zones
C) convecting cores
D) strong stellar winds
E) both A and B

E) both A and B

What happens when a star exhausts its core hydrogen supply?
A) Its core contracts, but its outer layers expand and the star becomes bigger and brighter.
B) It contracts, becoming smaller and dimmer.
C) It contracts, becoming hotter and brighter.
D) It expands, becoming bigger but dimmer.
E) Its core contracts, but its outer layers expand and the star becomes bigger but cooler and therefore remains at the same brightness.

A) Its core contracts, but its outer layers expand and the star becomes bigger and brighter.

What is happening inside a star while it expands into a subgiant?
A) It is fusing hydrogen into helium in the core.
B) It is fusing hydrogen into helium in a shell outside the core.
C) It is fusing helium into carbon in the core.
D) It is fusing helium into carbon in a shell outside the core.
E) It is not fusing any element; it is contracting and heating up.

B) It is fusing hydrogen into helium in a shell outside the core.

Compared to the star it evolved from, a red giant is
A) hotter and brighter.
B) hotter and dimmer.
C) cooler and brighter.
D) cooler and dimmer.
E) the same temperature and brightness.

C) cooler and brighter.

At approximately what temperature can helium fusion occur?
A) 100,000 K
B) 1 million K
C) a few million K
D) 100 million K
E) 100 billion K

D) 100 million K

Why does a star grow larger after it exhausts its core hydrogen?
A) The outer layers of the star are no longer gravitationally attracted to the core.
B) Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward.
C) Helium fusion in the core generates enough thermal pressure to push the upper layers outward.
D) Helium fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward.
E) The internal radiation generated by the hydrogen fusion in the core has heated the outer layers enough that they can expand after the star is no longer fusing hydrogen.

B) Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward.

How many helium nuclei fuse together when making carbon?
A) 2
B) 3
C) 4
D) varies depending on the reaction
E) none of the above

B) 3

The helium fusion process results in the production of
A) hydrogen.
B) oxygen.
C) carbon.
D) nitrogen.
E) iron.

C) carbon.

What happens after a helium flash?
A) The core quickly heats up and expands.
B) The star breaks apart in a violent explosion.
C) The core suddenly contracts.
D) The core stops fusing helium.
E) The star starts to fuse helium in a shell outside the core.

A) The core quickly heats up and expands.

What is a carbon star?
A) a red giant star whose atmosphere becomes carbon-rich through convection from the core
B) a star that fuses carbon in its core
C) another name for a white dwarf, a remnant of a star made mainly of carbon
D) a star that produces carbon by fusion in its atmosphere
E) a star that is made at least 50 percent of carbon

A) a red giant star whose atmosphere becomes carbon-rich through convection from the core

What is a planetary nebula?
A) a disk of gas surrounding a protostar that may form into planets
B) what is left of the planets around a star after a low-mass star has ended its life
C) the expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star
D) the molecular cloud from which protostars form
E) the expanding shell of gas that is left when a white dwarf explodes as a supernova

C) the expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star

What happens to the core of a star after a planetary nebula occurs?
A) It contracts from a protostar to a main-sequence star.
B) It breaks apart in a violent explosion.
C) It becomes a white dwarf.
D) It becomes a neutron star.
E) none of the above

C) It becomes a white dwarf.

Which of the following sequences correctly describes the stages of life for a low-mass star?
A) red giant, protostar, main-sequence, white dwarf
B) white dwarf, main-sequence, red giant, protostar
C) protostar, red giant, main-sequence, white dwarf
D) protostar, main-sequence, white dwarf, red giant
E) protostar, main-sequence, red giant, white dwarf

E) protostar, main-sequence, red giant, white dwarf

Compared to the star it evolved from, a white dwarf is
A) hotter and brighter.
B) hotter and dimmer.
C) cooler and brighter.
D) cooler and dimmer.
E) the same temperature and brightness.

B) hotter and dimmer.

Most interstellar dust grains are produced in
A) the Big Bang.
B) the interstellar medium.
C) the atmospheres of red giant stars.
D) supernova explosions.
E) the solar nebula.

C) the atmospheres of red giant stars.

During which stage is the star's energy supplied by gravitational contraction?
A) ii
B) iii
C) v
D) vi
E) viii

A) ii

During which stage does the star have an inert (nonburning) helium core?
A) iii
B) iv
C) vi
D) vii
E) viii

B) iv

During which stage does the star have an inert (nonburning) carbon core?
A) ii
B) iii
C) iv
D) vi
E) viii

E) viii

Which stage lasts the longest?
A) i
B) iii
C) iv
D) vi
E) viii

B) iii

What will happen to the star after stage viii?
A) It will explode in a supernova.
B) It will begin burning carbon in its core.
C) It will eject a planetary nebula.
D) It will collapse to make a neutron star.
E) It will gain mass until it collapses under its own weight.

C) It will eject a planetary nebula.

In the end, the remaining core of this star will be left behind as
A) a white dwarf made primarily of carbon and oxygen.
B) a white dwarf made primarily of silicon and iron.
C) a neutron star.
D) a black hole.
E) a supernova.

A) a white dwarf made primarily of carbon and oxygen.

Based on its main-sequence turnoff point, the age of this cluster is
A) less than 1 billion years.
B) about 1 billion years.
C) about 2 billion years.
D) about 10 billion years.
E) more than 15 billion years.

D) about 10 billion years.

Which statement about this cluster is not true?
A) It is likely to be located in the halo of the galaxy.
B) It contains some stars that are burning helium in their cores.
C) It is the type of cluster known as an open cluster of stars.
D) It probably contains no young stars at all.
E) It is likely to be spherical in shape.

C) It is the type of cluster known as an open cluster of stars.

Consider the star to which the arrow points. How is it currently generating energy?
A) by gravitational contraction
B) by hydrogen shell burning around an inert helium core
C) by core hydrogen fusion
D) by core helium fusion combined with hydrogen shell burning
E) by both hydrogen and helium shell burning around an inert carbon core

B) by hydrogen shell burning around an inert helium core

Consider the star to which the arrow points. Which of the following statements about this star is not true?
A) It is significantly less massive than the Sun.
B) It is larger in radius than the Sun.
C) It is brighter than the Sun.
D) Its surface temperature is lower than the Sun's.
E) Its core temperature is higher than the Sun's.

A) It is significantly less massive than the Sun.

What is the CNO cycle?
A) the process by which helium is fused into carbon, nitrogen, and oxygen
B) the process by which carbon is fused into nitrogen and oxygen
C) a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts
D) the period of a massive star's life when carbon, nitrogen, and oxygen are fusing in different shells outside the core
E) the period of a low-mass star's life when it can no longer fuse carbon, nitrogen, and oxygen in its core

C) a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts

Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?
A) hydrogen
B) oxygen
C) silicon
D) iron
E) uranium

D) iron

What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure?
A) The core contracts and becomes a white dwarf.
B) The core contracts and becomes a ball of neutrons.
C) The core contracts and becomes a black hole.
D) The star explodes violently, leaving nothing behind.
E) Gravity is not able to overcome neutron degeneracy pressure.

C) The core contracts and becomes a black hole.

What types of stars end their lives with supernovae?
A) all stars that are red in color
B) all stars that are yellow in color
C) stars that are at least several times the mass of the Sun
D) stars that are similar in mass to the Sun
E) stars that have reached an age of 10 billion years

C) stars that are at least several times the mass of the Sun

Which of the following statements about stages of nuclear burning (i.e., first-stage hydrogen burning, second-stage helium burning, etc.) in a massive star is not true?
A) Each successive stage of fusion requires higher temperatures than the previous stages.
B) As each stage ends, the core shrinks further.
C) Each successive stage creates an element with a higher atomic weight.
D) Each successive stage lasts for approximately the same amount of time.

D) Each successive stage lasts for approximately the same amount of time.

Suppose the star Betelgeuse (the upper left shoulder of Orion) were to become a supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?
A) Because the supernova event destroys the star, Betelgeuse would suddenly disappear from view.
B) We'd see a cloud of gas expanding away from the position where Betelgeuse used to be. Over
a period of a few weeks, this cloud would fill our entire sky.
C) Betelgeuse would remain a dot of light but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.
D) Betelgeuse would suddenly appear to grow larger in size, soon reaching the size of the full moon. It would also be about as bright as the full moon.

C) Betelgeuse would remain a dot of light but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.

Which event marks the beginning of a supernova?
A) the onset of helium burning after a helium flash in a star with mass comparable to that of the Sun
B) the sudden outpouring of X rays from a newly formed accretion disk
C) the sudden collapse of an iron core into a compact ball of neutrons
D) the beginning of neon burning in an extremely massive star
E) the expansion of a low-mass star into a red giant

C) the sudden collapse of an iron core into a compact ball of neutrons

After a supernova event, what is left behind?
A) always a white dwarf
B) always a neutron star
C) always a black hole
D) either a white dwarf or a neutron star
E) either a neutron star or a black hole

E) either a neutron star or a black hole

Why is Supernova 1987A particularly important to astronomers?
A) It occurred only a few dozen light-years from Earth.
B) It provided the first evidence that supernovae really occur.
C) It provided the first evidence that neutron stars really exist.
D) It was the first supernova detected in nearly 400 years.
E) It was the nearest supernova detected in nearly 400 years.

E) It was the nearest supernova detected in nearly 400 years.

You discover a binary star system in which one member is a 15MSun main-sequence star and the other star is a 10MSun giant. Why should you be surprised, at least at first?
A) It doesn't make sense to find a giant in a binary star system.
B) The odds of ever finding two such massive stars in the same binary system are so small as to make it inconceivable that such a system could be discovered.
C) The two stars in a binary system should both be at the same point in stellar evolution; that is, they should either both be main-sequence stars or both be giants.
D) The two stars should be the same age, so the more massive one should have become a giant first.
E) A star with a mass of 15MSun is too big to be a main-sequence star.

D) The two stars should be the same age, so the more massive one should have become a giant first.

You discover a binary star system in which one member is a 15MSun main-sequence star and the other star is a 10MSun giant. How do we believe that a star system such as this might have come to exist?
A) The giant must once have been the more massive star but transferred some of its mass to its companion.
B) Despite the low odds of finding a system with two such massive stars, there is nothing surprising about the fact that such systems exist.
C) The two stars probably were once separate but became a binary when a close encounter allowed their mutual gravity to pull them together.
D) The main-sequence star probably is a pulsating variable star and therefore appears to be less massive than it really is.
E) Although both stars probably formed from the same clump of gas, the more massive one must have had its birth slowed so that it became a main-sequence star millions of years later than its less massive companion.

A) The giant must once have been the more massive star but transferred some of its mass to its companion.

Why do scientists think that our solar system must have formed sometime after nearby supernovae explosions?
A) Existence of heavy elements
B) Solar temperature too low
C) Our Sun is a G-type star
D) They don't—scientists believe our Sun is among the first generation of stars.

A) Existence of heavy elements