The Cosmic Perspective, Chapter 17

1) 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

2) 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

3) What type of star is our Sun?

A) low-mass star

B) intermediate-mass star

C) high-mass star

A

4) 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

5) 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

6) 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

7) 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

8) 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

9) 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

10) 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

11) 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

12) 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

13) 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

14) 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

15) 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

16) 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

17) The helium fusion process results in the production of

A) hydrogen.

B) oxygen.

C) carbon.

D) nitrogen.

E) iron.

C

18) 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

19) 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

20) 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

21) 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

23) 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

24) 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

How does a star's mass affect its fusion rate?

Higher-mass stars have hotter cores, leading to faster fusion, higher luminosity, and shorter lifetimes

Why do high-mass stars use the CNO cycle instead of the proton-proton chain?

Their hotter cores allow hydrogen to fuse using carbon, nitrogen, and oxygen as catalysts.

What are the life stages of a low-mass star?

A: Protostar → Main sequence → Red giant → Helium flash → Horizontal branch → Double shell fusion → Planetary nebula → White dwarf.

What triggers the helium flash in low-mass stars?

The core supported by degeneracy pressure heats up until helium fusion begins explosively.

What happens after core helium fusion ends in low-mass stars?

Double shell fusion occurs—He → C shell fusion and H → He shell fusion—until the outer layers are ejected.

Why is iron the "dead end" of fusion?

Fusion reactions involving iron do not release energy; iron has the lowest mass per nuclear particle.

How are elements heavier than iron formed?

Through neutron capture during a supernova explosion.

What happens during multiple shell fusion in high-mass stars?

Elements like Ne, Mg, Si, and others fuse in concentric shells surrounding an iron core.

What causes a core-collapse supernova in high-mass stars?

Iron builds in the core, and when degeneracy pressure fails, the core collapses, triggering a supernova.

What are the remnants of high-mass star deaths?

Neutron stars or black holes, depending on mass.

What is the Crab Nebula?

A supernova remnant from an explosion observed in A.D. 1054.

How do stars in close binary systems evolve differently?

Mass transfer alters their evolutionary paths. The originally more massive star can become a subgiant by transferring mass.

What’s unusual about the Algol binary system?

The more evolved star is less massive, due to past mass transfer.