MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) 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
2) 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
3) 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.
4) 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.
5) 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.
6) 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
7) 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.
8) White dwarfs are so called because
A) the are both very hot and very small.
B) they are the end-products of small, low-mass stars.
C) they are the opposite of black holes.
D) it amplifies the contrast with red giants.
E) they are supported by electron degeneracy pressure.
9) Which of the following is closest in mass to a white dwarf?
A) the Moon B) the Earth C) Jupiter D) the Sun
10) Suppose a white dwarf is gaining mass because of accretion in a binary system. What
happens if the mass someday reaches the 1.4-solar-mass limit?
A) The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy.
B) The white dwarf, which is made mostly of carbon, suddenly becomes much hotter in temperature and therefore is able to begin fusing the carbon. This turns the white dwarf back into a star supported against gravity by ordinary pressure.
C) The white dwarf immediately collapses into a black hole, disappearing from view.
D) A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the material from reaching it in the first place.
11) What kind of pressure supports a white dwarf?
A) neutron degeneracy pressure
B) electron degeneracy pressure
C) thermal pressure
D) radiation pressure
E) all of the above
12) After a massive star supernova, 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
13) From an observational standpoint, what is a pulsar?
A) a star that slowly changes its brightness, getting dimmer and then brighter with a period
of anywhere from a few hours to a few weeks
B) an object that emits flashes of light several times per second or more, with near perfect
regularity
C) an object that emits random "pulses" of light that sometimes occur only a fraction of a
second apart and other times stop for several days at a time
D) a star that changes color rapidly, from blue to red and back again
14) What causes the radio pulses of a pulsar?
A) The star vibrates.
B) As the star spins, beams of radio radiation sweep through space. If one of the beams crosses
the Earth, we observe a pulse.
C) The star undergoes periodic explosions of nuclear fusion that generate radio emission.
D) The star's orbiting companion periodically eclipses the radio waves emitted by the main
pulsar.
E) A black hole near the star absorbs energy and re-emits it as radio waves.
15) How does a black hole form from a massive star?
A) During a supernova, if a star is massive enough for its gravity to overcome neutron
degeneracy of the core, the core will be compressed until it becomes a black hole.
B) Any star that is more massive than 8 solar masses will undergo a supernova explosion and
leave behind a black-hole remnant.
C) If enough mass is accreted by a white-dwarf star so that it exceeds the 1.4-solar-mass limit, it
will undergo a supernova explosion and leave behind a black-hole remnant.
D) If enough mass is accreted by a neutron star, it will undergo a supernova explosion and leave
behind a black-hole remnant.
E) A black hole forms when two massive main-sequence stars collide.
16) What do we mean by the singularity of a black hole?
A) There are no binary black holes each one is isolated.
B) An object can become a black hole only once, and a black hole cannot evolve into anything
else.
C) It is the center of the black hole, a place of infinite density where the known laws of physics
cannot describe the conditions.
D) It is the edge of the black hole, where one could leave the observable universe.
E) It is the "point of no return" of the black hole; anything closer than this point will not be
able to escape the gravitational force of the black hole.
17) If you were to come back to our Solar System in 6 billion years, what might you expect
to find?
A) a red giant star
B) a white dwarf
C) a rapidly spinning pulsar
D) a black hole
E) Everything will be pretty much the same as it is now.
18) What kinds of objects lie in the disk of our galaxy?
A) open clusters
B) O and B stars
C) old K and M stars
D) gas and dust
E) all of the above
19) Harlow Shapley concluded that the Sun was not in the center of the Milky Way Galaxy by
A) looking at the shape of the "milky band" across the sky.
B) mapping the distribution of stars in the galaxy.
C) mapping the distribution of globular clusters in the galaxy.
D) mapping the distribution of gas clouds in the spiral arms.
E) looking at other nearby spiral galaxies.
20) All the iron on Earth originated from
A) white dwarfs.
B) nuclear fusion within the cores of low-mass stars.
C) nuclear fusion within the cores of high-mass stars.
D) the Big Bang, when the universe first began.
E) the bombardment of comets in the late stages of planet formation.
21) What is the most common form of gas in the interstellar medium?
A) molecular hydrogen
B) molecular helium
C) atomic hydrogen
D) atomic helium
E) ionized hydrogen
22) Compared with our Sun, most stars in the halo are
A) young, red, and dim and have fewer heavy elements.
B) young, blue, and bright and have much more heavy element material.
C) old, red, and dim and have fewer heavy elements.
D) old, red, and dim and have much more heavy element material.
E) old, red, and bright and have fewer heavy elements.
23) Which types of galaxies have a clearly defined spheroidal component?
A) spirals only
B) ellipticals only
C) lenticulars only
D) irregulars only
E) all but irregulars
24) How does a lenticular galaxy differ from a normal spiral galaxy?
A) It has no bulge.
B) It has an elongated bulge resembling a bar more than a sphere.
C) It is flatter in shape.
D) It has no gas or dust.
E) It has no spiral arms.
25) Why are Cepheid variables important?
A) Cepheid variables are stars that vary in brightness because they harbor a black hole.
B) Cepheids are pulsating variable stars, and their pulsation periods are directly related to
their true luminosities. Hence, we can use Cepheids as "standard candles" for distance
measurements.
C) Cepheids are a type of young galaxy that helps us understand how galaxies form.
D) Cepheids are supermassive stars that are on the verge of becoming supernovae and therefore allow us to choose candidates to watch if we hope to observe a supernova in the near future.
26) How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove
that the "spiral nebulae" were actually entire galaxies?
A) There are no Cepheids in the Milky Way, so his discovery proved that it had to be in another galaxy.
B) He measured the stellar parallax of the Cepheid in Andromeda, was able to determine the
distance to it, and showed that it was far outside the Milky Way Galaxy.
C) He used main-sequence fitting to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
D) From the period-luminosity relation for Cepheids, he was able to determine the distance to
Andromeda and show that it was far outside the Milky Way Galaxy.
E) Since a Cepheid is a type of luminous galaxy, when he found it in Andromeda he was able to
prove that Andromeda was a separate galaxy from the Milky Way.
27) What is Hubble's law?
A) The longer the time period between peaks in brightness, the greater the luminosity of the
Cepheid variable star.
B) The recession velocity of a galaxy is directly proportional to its distance from us.
C) The recession velocity of a galaxy is inversely proportional to its distance from us.
D) The faster a spiral galaxy's rotation speed, the more luminous it is.
E) The faster a spiral galaxy's rotation speed, the less luminous it is.
28) What is the primary practical difficulty that limits the use of Hubble's law for measuring
distances?
A) Redshifts of galaxies are difficult to measure.
B) The recession velocities of distant galaxies are so great that they are hard to measure.
C) We do not know Hubble's constant very accurately yet.
D) Hubble's law is only useful theoretically; it is difficult to use in practice.
E) The motion of the Earth relative to the Milky Way is difficult to account for.
29) How do observations of distant galaxies help us learn about galaxy evolution?
A) Observations at different distances show galaxies of different ages and therefore different
stages of evolution.
B) We can observe the birth of galaxies.
C) We can observe the evolution of a single galaxy over time.
D) We can observe two galaxies merging and what the result is, helping us learn how mergers
affect evolution.
E) We can see what our galaxy used to look like and therefore theorize about the physical
processes that led to its current appearance.
30) What is a quasar?
A) a starlike object that actually represents a bright patch of gas in the Milky Way
B) a very large galaxy thought to be formed by the merger of several smaller galaxies,
typically found in the center of a galaxy cluster
C) a specialized astronomical instrument for observing distant stars.
D) the extremely bright center of a distant galaxy, thought to be powered by a massive black
hole
E) another name for very bright stars of spectral type O
1) Answer: A
2) Answer: C
3) Answer: B
4) Answer: C
5) Answer: D
6) Answer: C
7) Answer: E
8) Answer: A
9) Answer: D
10) Answer: A
11) Answer: B
12) Answer: E
13) Answer: B
14) Answer: B
15) Answer: A
16) Answer: C
17) Answer: B
18) Answer: E
19) Answer: C
20) Answer: C
21) Answer: C
22) Answer: C
23) Answer: E
24) Answer: E
25) Answer: B
26) Answer: D
27) Answer: B
28) Answer: C
29) Answer: A
30) Answer: D
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