Ch 17 Reading/Concept – Flashcards

1) Which of the following stars will live longest? A) a 1-solar-mass star B) a 2-solar-mass star C) a 3-solar-mass star D) a 4-solar-mass star E) a 5-solar-mass star

2) In the context of understanding stellar lives, "high-mass" stars have masses A) more than about 8 times the mass of our Sun. B) more than about 3 times the mass of our Sun. C) more than twice the mass of our Sun. D) more than 20 times the mass of our Sun.

3) Which of the following lists the stages of life for a low-mass star in the correct order? A) protostar, main-sequence star, red giant, planetary nebula, white dwarf B) protostar, main-sequence star, red giant, supernova, neutron star C) protostar, main-sequence star, planetary nebula, red giant D) main-sequence star, white dwarf, red giant, planetary nebula, protostar

4) What happens when a main-sequence star exhausts its core hydrogen fuel supply? A) The entire star shrinks in size. B) The core shrinks while the rest of the star expands. C) The core immediately begins to fuse its helium into carbon. D) The star becomes a neutron star.

5) The main source of energy for a star as it grows in size to become a red giant is A) hydrogen fusion in the central core. B) helium fusion in the central core. C) hydrogen fusion in a shell surrounding the central core. D) gravitational contraction.

6) The overall helium fusion reaction is A) three helium nuclei fuse to form one carbon nucleus. B) two helium nuclei fuse to form one beryllium nucleus. C) two hydrogen nuclei fuse to form one helium nucleus. D) four helium nuclei fuse to form one oxygen nucleus.

7) What is a helium flash? A) The ignition of helium shell burning in a high-mass star with a carbon core. B) A sudden brightening of a low-mass star, detectable from Earth by observing spectral lines of helium. C) It is another name for the helium fusion reaction. D) The sudden onset of helium fusion in the core of a low-mass star.

8) An H-R diagram for a globular cluster will show a horizontal branch—a line of stars above the main-sequence but to the left of the subgiants and red giants. Which of the following statements about these horizontal branch stars is true? A) They have inert (non-burning) carbon cores. B) Their sole source of energy is hydrogen shell burning. C) They generate energy through both hydrogen fusion and helium fusion. D) In a particular star cluster, all horizontal branch stars have the same spectral type.

9) What is a planetary nebula? A) gas created from the remains of planets that once orbited a dead star B) interstellar gas from which planets are likely to form in the not-too-distant future C) the remains of a high-mass star that has exploded D) gas ejected from a low-mass star in the final stage of its life

10) The ultimate fate of our Sun is to A) explode in a supernova. B) become a white dwarf that will slowly cool with time. C) become a rapidly spinning neutron star. D) become a black hole.

11) Which low-mass star does not have fusion occurring in its central core? A) a main-sequence star B) a red giant C) a helium-burning star

12) How are low-mass red giant stars important to our existence? A) These stars manufactured virtually all the elements out of which we and our planet are made. B) These stars generate the energy that makes life on Earth possible. C) These stars manufactured most of the carbon atoms in our bodies. D) These stars provide most of the light that reaches us from globular clusters.

13) Which of the following pairs of atomic nuclei would feel the strongest repulsive electromagnetic force if you tried to push them together? A) helium and helium B) hydrogen and hydrogen C) hydrogen and helium D) hydrogen and deuterium

14) Which of the following stars will certainly end its life in a supernova? A) the Sun B) a red giant star C) a 10-solar-mass star D) a neutron star

15) What is the CNO cycle? A) a set of steps by which four hydrogen nuclei fuse into one helium nucleus B) the process by which helium is fused into carbon, nitrogen, and oxygen C) the process by which carbon is fused into nitrogen and oxygen D) the set of fusion reactions that have produced all the carbon, nitrogen, and oxygen in the universe

16) In order to predict whether a star will eventually fuse oxygen into a heavier element, what do you need to know about the star? A) its luminosity B) its overall abundance of elements heavier than helium C) how much oxygen it now has in its core D) its mass

17) Why is iron significant to understanding how a supernova occurs? A) Iron is the heaviest of all atomic nuclei, and thus no heavier elements can be made. B) Supernovae often leave behind neutron stars, which are made mostly of iron. C) The fusion of iron into uranium is the reaction that drives a supernova explosion. D) Iron cannot release energy either by fission or fusion.

18) After a supernova explosion, the remains of the stellar core A) will always be a neutron star. B) be either a neutron star or a black hole. C) will always be a black hole. D) may be either a white dwarf, neutron star, or black hole

19) Why is Supernova 1987A particularly important to astronomers? A) It is the nearest supernova to have occurred at a time when we were capable of studying it carefully with telescopes. B) It was the first supernova detected in nearly 400 years. C) It provided the first evidence that supernovae really occur. D) It occurred only a few light-years from Earth.

20) Algol consist of a 3.7 MSun main-sequence star and a 0.8 MSun subgiant. Why does this seem surprising, at least at first? A) The two stars in a binary system should both be at the same stage of life; that is, they should either both be main-sequence stars or both be subgiants. B) It doesn't make sense to find a subgiant in a binary star system. C) The two stars should be the same age, so we'd expect the subgiant to be more massive than the main-sequence star. D) A star with a mass of 3.7 MSun is too big to be a main-sequence star.

21) Where does gold (the element) come from? A) It is produced by mass transfer in close binaries. B) It is produced during the supernova explosions of high-mass stars. C) It is produced during the late stages of fusion in low-mass stars. D) It was produced during the Big Bang.

1) Sun is considered to be a A) low-mass star. B) intermediate-mass star C) high-mass star. D) brown dwarf.

2) Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars? A) H-R diagrams of open clusters B) observing a low-mass star over many years C) H-R diagrams of globular clusters D) spacecraft observations of the Sun

3) Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main-sequence star? A) The red giant has a hotter core. B) The red giant's surface is hotter. C) The red giant is more massive. D) Fusion reactions are producing energy at a greater rate in the red giant.

4) Which of the following describes a star with a hydrogen-burning shell and an inert helium core? A) It is a red giant that grows in luminosity until it dies in a planetary nebula. B) It is a subgiant that gradually grows dimmer as its hydrogen-burning shell expands and cools. C) It is a subgiant that grows in luminosity until helium fusion begins in the central core. D) It is what is known as a helium-burning star, which has both helium fusion in its core and hydrogen fusion in a shell.

5) Which of the following observations would not be likely to provide information about the final, explosive stages of a star's life? A) studying the light rings around Supernova 1987A in the Large Magellanic Cloud B) decades of continuous monitoring of red giants in a globular cluster C) observing the structures of planetary nebulae D) neutrino detections from nearby supernovae

6) Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system? A) Supernovae are more common. B) Planetary nebula formation is more common. C) They both occur in about equal numbers. D) It is impossible to say.

11) What will happen to the star after stage VIII? A) Its outer layers will be ejected as a planetary nebula and its core will become a white dwarf. B) It will continue to expand gradually until carbon fusion begins in its core. C) It will explode as a supernova and leave a neutron star or black hole behind. D) It will remain in stage VIII for about 10 billion years, after which its outer layers will shrink back and cool.

12) Carbon fusion occur in high-mass stars but not in low-mass stars because A) the cores of low-mass stars never contain significant amounts of carbon. B) the cores of low-mass stars never get hot enough for carbon fusion. C) only high-mass stars do fusion by the CNO cycle. D) carbon fusion can occur only in the stars known as carbon stars.

13) Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, etc.) in a high-mass star is not true? A) As each stage ends, the core shrinks and heats further. B) Each successive stage creates an element with a higher atomic number and atomic mass number. C) As each stage ends, the reactions that occurred in previous stages continue in shells around the core. D) Each successive stage lasts for approximately the same amount of time.

14) Which event marks the beginning of a supernova? A) the sudden collapse of an iron core into a compact ball of neutrons B) the onset of helium burning after a helium flash C) the beginning of neon burning in an extremely massive star D) the sudden initiation of the CNO cycle

15) 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? A) 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. 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) Because the supernova destroys the star, Betelgeuse would suddenly disappear from view. 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.

16) Suppose that hydrogen, rather than iron, had the lowest mass per nuclear particle. Which of the following would be true? A) Stars would be brighter. B) Stars would be less massive. C) All stars would be red giants. D) Nuclear fusion could not power stars.

17) 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? A) The apparent pattern is thought to be a random coincidence. B) Elements with atomic mass numbers divisible by 4 tend to be more stable than elements in between. C) At the end of a high-mass star's life, it produces new elements through a series of helium capture reactions. D) This pattern in elemental abundances was apparently determined during the first few minutes after the Big Bang.

18) A spinning neutron star has been observed at the center of a A) planetary nebula. B) supernova remnant. C) red supergiant. D) protostar.

19) 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? A) 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. B) 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. 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 two stars are simply evolving normally and independently, and one has become a giant before the other.

20) Tidal forces are very important to the Algol system today, but were not important when both stars were still on the main sequence. Why not? A) Main-sequence stars in a system like the Algol system are small compared to their physical separation. B) Main-sequence stars are too big to be affected by tidal forces. C) Main-sequence stars are too massive to be affected by tidal forces. D) Main-sequence stars are unaffected by tidally-induced mass transfer.