Chapter 17
Conceptual Quiz
Part A
Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars?
Hint A.1
Study Section 17.2
ANSWER:

Observations of a low-mass star over many years. H-R diagram of an open cluster. Spacecraft visits to the Sun. H-R diagrams of a globular cluster.
Part B
Our Sun is considered to be a ______.
Hint B.1
Study Section 17.1
ANSWER:

low-mass star high-mass star intermediate-mass star brown dwarf
Part C
Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main sequence star?
Hint C.1
Study Section 17.2
ANSWER:

Fusion reactions are producing more energy more rapidly in a red giant star. The red giant is more massive. The red giant is hotter. The red giant has a larger radius.
Part D
What would be a consequence of hydrogen (rather than iron) having the lowest mass per nuclear particle?
Hint D.1
Study Section 17.3
ANSWER:

Stars would be less massive. Stars would be brighter. All stars would be red giants. Nuclear fusion could not power stars.
Part E
What happens to a star when fusion reactions are occurring in shells but not in the core?
Hint E.1
Study Section 17.2
ANSWER:

The inert core loses mass and shrinks. The shells continuously become more luminous as their density, and therefore their fusion rate, increases. The shells maintain a steady output of energy, owing to the thermostat effect maintained by gravitational equilibrium. The inert core increases in mass, heats, and expands.
Part F
Why do tidal forces have little effect on the stars in a system like the Algol system while they are on the main sequence?
Hint F.1
Study Section 17.2 and 17.4.
ANSWER:

Main sequence stars are too massive to be affected by tidal forces. Main sequence stars in a system like the Algol system are small compared to their physical separation. Main sequence stars are too big to be affected by tidal forces. Main sequence stars are unaffected by tidally-induced mass transfer.
Part G
Which of the following observations would not be likely to provide information about the final epoch of a star's life?
Hint G.1
Study Section 17.2 and 17.3
ANSWER:

Measuring the structures of planetary nebulae. Long-term monitoring of main sequence stars Neutrino detections from nearby supernovae. Studying the light rings around Supernova 1987A in the Large Magellanic Cloud.
Part H
Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system?
Hint H.1
Study Section 17.2 and 17.3.
ANSWER:

It is impossible to say. Planetary nebula formation is more common. They both occur in about equal numbers. Supernovae are more common.
Part I
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. During which stage is the star's energy supplied by primarily by gravitational contraction?
Hint I.1
Consider all stages of a star's life, including before it reaches the main sequence stage.
ANSWER:

ii iii v vi viii
Part J
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. During which stage does the star have an inert (non-burning) helium core?
Hint J.1
Study Section 17.2
ANSWER:

vi vii iii iv viii
Part K
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. Which stage lasts the longest?
Hint K.1
Study Section 17.2
ANSWER:

iii vi i iv viii
Part L
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. During which stage does the star have an inert (non-burning) carbon core surrounded by shells of helium and hydrogen burning?
Hint L.1
Study Section 17.2
ANSWER:

viii vi ii iv iii
Part M
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. What will happen to the star after stage viii?
Hint M.1
Study Section 17.2
ANSWER:

It will continue to expand gradually until carbon fusion begins in its core. It will explode as a supernova and leave a neutron star or black hole behind. Its outer layers will be ejected as a planetary nebula and its core will become a white dwarf. It will remain in stage viii for about 10 billion years, after which its outer layers will shrink back and cool.
Part N
What process distributes most of the carbon in the universe?
Hint N.1
Study Section 17.2
ANSWER:

Supernovae Winds from main-sequence stars. Hot star winds Winds from low-mass red giant stars.
Part O
Why can the fusion of carbon occur in intermediate- and high-mass stars but not in low-mass stars?
Hint O.1
Study Sections 17.2 and 17.3
ANSWER:

It is because the cores of low-mass stars never get hot enough for carbon fusion. It is because carbon fusion can occur only in the stars known as carbon stars. It is because only high-mass stars do fusion by the CNO cycle. It is because the cores of low-mass stars never contain significant amounts of carbon.
Part P
Observations show that elements with atomic mass numbers divisible by 4 (such as oxygen--16, neon--20, and magnesium--24) tend to be more abundant in the universe than elements with atomic mass numbers in between. Why do we think this is the case?
Hint P.1
Study Section 17.3
ANSWER:

At the end of a high-mass star's life, it produces new elements through a series of helium capture reactions. Elements with atomic mass numbers divisible by 4 tend to be more stable than elements in between. The apparent pattern is thought to be a random coincidence. This pattern in elemental abundances was apparently determined during the first few minutes after the Big Bang.
Part Q
Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, etc.) in a high-mass star is NOT true?
Hint Q.1
Study Section 17.3
ANSWER:

Each successive stage lasts for approximately the same amount of time Each successive stage creates an element with a higher atomic number and atomic mass number. As each stage ends, the core shrinks and heats further. As each stage ends, the reactions that occurred in previous stages continue in shells around the core.
Part R
Which event marks the beginning of a supernova?
Hint R.1
Study Section 17.3
ANSWER:

The sudden collapse of an iron core into a compact ball of neutrons. The onset of helium burning after a helium flash. The sudden initiation of the CNO cycle. The beginning of neon burning in an extremely massive star.
Part S
Suppose that the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?
Hint S.1
Study Section 17.3
ANSWER:

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. Because the supernova destroys the star, Betelgeuse would suddenly disappear from view. 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. 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.
Part T
A spinning neutron star has been observed at the center of a ______.
Hint T.1
A neutron star can be formed when a star explodes.
ANSWER:

protostar. supernova remnant. planetary nebula. red supergiant.
Part U
You discover a binary star system in which one star is a 15 Msun main-sequence star and the other is a 10 Msun giant. How do we think that a star system such as this might have come to exist?
Hint U.1
Study Section 17.4
ANSWER:

The two stars probably were once separate, but became a binary when a close encounter allowed their mutual gravity to pull them together. 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 stars millions of years later than its less massive companion. The two stars are simply evolving normally and independently, and one has become a giant before the other. The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion.