Deck 12: Star Stuff

Question 1

As a solar mass protostar moves on to the main sequence,

A) its surface temperature and luminosity increase.
B) its surface temperature increases and its luminosity decreases.
C) its surface temperature and luminosity decrease.
D) its surface temperature decreases and its luminosity increases.
E) its surface temperature and luminosity remain the same.

Answer 1

B

Question 2

What happens after the 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.

Answer 2

A

Question 3

What did Carl Sagan mean when he said that we are all "star stuff"?

A) that life would be impossible without energy from the Sun
B) that the Earth formed at the same time as the Sun
C) that the carbon, oxygen, and other 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

Answer 3

C

Question 4

No stars are expected with masses greater than 150 times our Sun because

A) molecular clouds do not have enough material to form such massive stars.
B) they would fragment into binary stars because of their rapid rotation.
C) they would generate so much power that they would blow themselves apart.
D) they would shine exclusively at X-ray wavelengths and would be difficult to detect.
E) they would be too massive for hydrogen fusion to occur in their cores.

Question 5

Helium fusion results in the production of

A) hydrogen.
B) oxygen.
C) carbon.
D) nitrogen.
E) iron.

Question 6

Which of the following masses separates low mass stars from high mass stars?

A) About 150 solar masses
B) About 50 solar masses
C) About 2 solar masses
D) About 1 solar mass
E) About 0.08 solar masses

Question 7

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

Question 8

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

Question 9

What is a planetary nebula?

A) a disk of gas surrounding a protostar that may form into planets
B) what is left of its planets after a low-mass star has ended its life
C) the expanding shell of gas that is no longer gravitationally bound 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

Question 10

When does a star become a main-sequence star?

A) when the protostar assembles from its parent molecular cloud
B) the instant when hydrogen fusion first begins in the star's core
C) when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium
D) when a star becomes luminous enough to emit thermal radiation
E) when hydrogen fusion is occurring throughout the star's interior

Question 11

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.

Question 12

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.

Question 13

At approximately what temperature can helium fusion occur?

A) 100,000 K
B) 1 million K
C) 10 million K
D) 100 million K
E) 100 billion K

Question 14

What is the fate of an isolated brown dwarf?

A) It will become a white dwarf.
B) It will become a neutron star.
C) It will become a black hole.
D) It will slowly evaporate to nothing.
E) It will remain a brown dwarf forever.

Question 15

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 is a consequence of the laws of quantum mechanics.

Question 16

What happens when a star like the sun 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.

Question 17

What happens to the core of a star after it ejects a planetary nebula?

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

Question 18

What type of star is our Sun?

A) A low-mass star
B) An intermediate-mass star
C) A high-mass star

Question 19

How many helium nuclei fuse together when making carbon?

A) 2
B) 3
C) 4
D) It varies depending on the reaction
E) Helium cannot fuse into carbon

Question 20

What percentage of a star's total lifetime is spent on the main sequence?

A) 10%
B) 20%
C) 50%
D) 90%
E) 100%

Question 21

After a supernova event occurring in a high-mass star, 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

Question 22

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

Question 23

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.

Question 24

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

Question 25

You discover a binary star system in which one member is a 15 solar mass main-sequence star and the other star is a 10 solar mass giant star. 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.
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 15 solar masses is too big to be a main-sequence star.

Question 26

At the end of its life, 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.

Question 27

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

Question 28

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.

Question 29

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

Question 30

Which of the following statements about the stages of nuclear burning 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 as long as the first, hydrogen fusion stage.

Question 31

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.

Question 32

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

Question 33

Most interstellar dust grains

A) were produced in the Big Bang.
B) are produced in the interstellar medium.
C) are produced in the atmospheres of red giant stars.
D) are produced in supernova explosions.
E) are produced in the cores of low-mass stars

Question 34

Photographs of many young stars show long jets of material apparently being ejected from their poles.

Question 35

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.

Question 36

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.

Question 37

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 4.5 billion years.
D) about 10 billion years.
E) more than 15 billion years.

Question 38

You discover a binary star system in which one member is a15 solar mass main-sequence star and the other star is a 10 solar mass giant star. 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) Other than the very 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.

Question 39

Why is Supernova 1987A particularly important to astronomers?

A) It occurred only a few dozen light-years from Earth.
B) It provided the first observational evidence that supernovae actually occur.
C) It provided the first evidence that neutron stars exist.
D) It was the first supernova detected in nearly 400 years.
E) It was the nearest supernova detected in nearly 400 years.

Question 40

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

Question 41

In any star cluster, stars with lower masses greatly outnumber those with higher masses.

Question 42

Falsifying Scientific Theories: In many simple expositions of the scientific method, it is often stated that if a scientific theory makes an incorrect prediction, it is falsified and must be discarded. Argue against this simple view of the scientific method by using the Algol paradox (Section 12.4) as a case study. In particular, why did astronomers not discard the theory of stellar evolution despite an apparent direct contradiction of a fundamental prediction of stellar evolution, that more massive stars evolve faster than less massive stars?

Question 43

The heaviest element produced by stars or in supernovae is silicon.

Question 44

The Faintest White Dwarfs: All low-mass stars end their lives by forming white dwarfs which evolve by cooling at a constant radius, growing less and less luminous with time. You are about to begin an observing program to look for the faintest white dwarfs in the Milky Way Galaxy. In the course of your observations, will you continue to find white dwarfs that are less and less luminous, or will you ultimately find a population of white dwarfs that are the least luminous ones in the Milky Way? If you answer the latter, what is your interpretation of this result?

Question 45

Stars with high masses live longer than stars with lower masses.

Question 46

All stars that become supernovae will leave behind a neutron star.

Question 47

Historical Supernova: You find an ancient Chinese text that speaks of a "new star" briefly visible in the constellation Sagittarius in the year 1000 B.C. You suspect that the reference is to a supernova explosion. Design an observing program to provide scientific evidence for this hypothesis. What object or objects would you look for in the sky today? What wavelengths of electromagnetic radiation would you use? How would you be sure any object you found exploded (as seen from the Earth) nearly 3000 years ago?

Question 48

Choose from the list below for the following questions. You may use a choice more than once.
A. H fusion by the proton-proton chain
B. H fusion by the CNO cycle
C. helium fusion
D. matter-antimatter annihilation
E. gravitational contraction
Which one provided the energy that made the Sun hot in the first place?

Question 49

The most massive stars generate energy at the end of their lives by fusing iron in their cores.

Question 50

Stars spend about 90% of their lifetime on the main sequence

Question 51

Choose from the list below for the following questions. You may use a choice more than once.
A. H fusion by the proton-proton chain
B. H fusion by the CNO cycle
C. helium fusion
D. matter-antimatter annihilation
E. gravitational contraction
Which method of energy generation is used by the Sun today?

Question 52

Although some photographs show what looks like jets of material near many young stars, we now know that these "jets" actually represent gas from the surrounding nebula that is falling onto the stars.

Question 53

Choose from the list below for the following questions. You may use a choice more than once.
A. H fusion by the proton-proton chain
B. H fusion by the CNO cycle
C. helium fusion
D. matter-antimatter annihilation
E. gravitational contraction
Which process leads to the production of carbon?

Question 54

Briefly describe how a star forms.

Question 55

The helium fusion process works by fusing two helium nuclei into one beryllium nucleus.

Question 56

There is no limit to the mass with which a star can be born.

Question 57

Stellar Evolution as a Scientific Theory: Based on the chapter material, list what you feel are the basic founding assumptions of the theory of stellar evolution. For example, you might list that stars are assumed to be balls of mostly hydrogen gas held together by their own gravity. After this, make another list of as many of the successful predictions of this theory as you can. Based on the comparison of these two lists, how successful a scientific theory would you rate the theory of stellar evolution?

Question 58

Explain how some stars form in binary systems.

Question 59

Our Sun will end its life in a planetary nebula and become a white dwarf.

Question 60

Choose from the list below for the following questions. You may use a choice more than once.
A. H fusion by the proton-proton chain
B. H fusion by the CNO cycle
C. helium fusion
D. matter-antimatter annihilation
E. gravitational contraction
Which method of energy generation provides the source of energy for a protostar?

Question 61

Why are elements with even numbers of protons more abundant, on average, than elements with odd numbers of protons?

A) Because elements are mainly made in fusion reactions with hydrogen nuclei
B) Because when elements split in a fission reaction, they prefer to split with all the protons paired
C) Because elements are mainly made in fusion reactions with helium nuclei
D) There's no explanation, it's something of a mystery to be explained or it may be a coincidence.

Question 62

Consider the "dead end" element for cores of massive stars: why is that element the "dead end"?

A) It can only release energy by fusion.
B) It has the lowest mass per nuclear particle.
C) It has the highest nuclear mass.
D) It has the lowest nuclear mass.
E) It has the highest mass per nuclear particle. F) It can only release energy by fission.

Question 63

(Use diagram of abundance vs atomic number) What process best explains the observed pattern of abundances of elements with atomic numbers between 6 and 20?

A) Fusion reactions with neutrons
B) Radioactive decay of nuclei with odd numbers of protons
C) Fusion reactions with helium nuclei
D) Fusion reactions with hydrogen nuclei

Question 64

Choose from the list below for the following questions. You may use a choice more than once.
A. H fusion by the proton-proton chain
B. H fusion by the CNO cycle
C. helium fusion
D. matter-antimatter annihilation
E. gravitational contraction
Which method of energy generation provides the source of energy for a 10Msᵤn main-sequence star?

Question 65

Choose from the list below for the following questions. You may use a choice more than once.
A. H fusion by the proton-proton chain
B. H fusion by the CNO cycle
C. helium fusion
D. matter-antimatter annihilation
E. gravitational contraction
When a 1-solar-mass star stabilizes as a giant for about a billion years, which method of energy generation occurs in its central core?

Question 66

Which of the following properties describes a low-mass star?

A) Has higher main-sequence luminosities than high mass stars
B) Late in life, fuses carbon into oxygen
C) Ends its life as a supernova
D) Has longer lifetimes than high mass stars

Question 67

What will happen in the Sun immediately after it has exhausted its supply of hydrogen in its core?

A) The helium core will shrink and heat; a shell of hydrogen will start fusing.
B) The helium core will shrink, heat, and start fusing helium to carbon.
C) The core will collapse and a supernova will result.
D) The Sun will turn into a white dwarf and cool off forever.

Question 68

Choose from the list below for the following questions. You may use a choice more than once.
A. H fusion by the proton-proton chain
B. H fusion by the CNO cycle
C. helium fusion
D. matter-antimatter annihilation
E. gravitational contraction
Which one is used by a main-sequence star of spectral type B2?

Question 69

What does the CNO cycle and the hydrogen proton-proton cycle have in common? Choose the best answer to the question.

A) They both are ways to fuse hydrogen nuclei to make helium.
B) They are both nuclear reactions; the CNO cycle makes carbon, nitrogen, and oxygen, and the proton cycle makes helium.
C) They are both cycles in star lives.
D) They both trigger at the same temperature.

Question 70

Lithium, beryllium, and boron are elements with atomic number 3, 4, and 5, respectively. Even though they are three of the five simplest elements, why are they rare compared to many heavier elements?

Question 71

Briefly summarize the stages of life for a low-mass star.

Question 72

Which type of star spends the longest time as a protostar?

A) O star
B) B star
C) M star
D) G star

Question 73

What star is the most likely to have made the atoms of gold in your jewelry or your electronics?

A) A high-mass star
B) A white dwarf
C) The Sun
D) A low-mass star

Question 74

Which type of star spends the shortest time as a main sequence star?

A) O star
B) M star
C) B star
D) G star

Question 75

Briefly summarize the stages of life for a high-mass star.

Question 76

Which element is the dead end for cores of the most massive stars?

A) Iron
B) Lead
C) Hydrogen
D) Oxygen
E) Uranium

Question 77

Do you think it is possible that a 1.5-solar-mass red giant could harbor an advanced civilization? Explain your reasoning.

Question 78

According to this plot, which is the third most abundant element in the universe?

A) Hydrogen
B) Boron
C) Oxygen
D) Lithium
E) Helium

Question 79

Do you think it is possible that a 10-solar-mass main-sequence star could harbor an advanced civilization? Explain your reasoning.

Question 80

Identify the correct sequence of life events for a high mass star.

A) Main sequence, red supergiant, supernova, neutron star
B) Main sequence, red supergiant, neutron star, supernova
C) Red supergiant, main sequence, neutron star, supernova
D) Red supergiant, main sequence, supernova, neutron star