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Test 1: February 2015
Course: ASTR 1P02, Section 2
Examination date: 9 February 2015
Time of Examination: 11:00 – 11:50
Number of pages: 10
Number of students: 30
Time limit: 50 min
Instructor: S. D’Agostino
ANSWERS.
Correct alternatives are indicated by *.
Each question is worth 1 mark. Total number of marks: 50.
1. If the mass of Star A is greater than the mass of Star B, then the lifetime of Star A is
the lifetime of Star B.
(a) * less than
(b) about the same as
(c) greater than
(d) [There is not enough information given; the lifetime of a star also depends on its
spectral nebulosity.]
2. Most medium-mass stars begin their lifetimes as
.
and end their lifetimes as
(a) led zeppelins, green giants
(b) white dwarfs, red dwarfs
(c) red giants, white dwarfs
(d) * protostars, white dwarfs
3. Reflection nebulae appear
(a) * blue, because they scatter blue light more effectively than red light.
(b) red, because they scatter red light more effectively than blue light.
(c) blurry, because astronomers who observe them tend to drink Molson Canadian
more often than Blue Light.
(d) shiny, because they contain a high density of flakes of dust that have been coated
with nearly-pure metals.
4. Giant molecular clouds are
(a) extremely hot, which allows giant molecules to form.
(b) extremely cold, which allows giant ice crystals to form.
(c) * relatively cool, which allows hydrogen atoms to bind into molecules.
(d) relatively hot, which allows hydrogen atoms to bind into molecules.
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5. Dark nebulae can be observed because
(a) * they emit a significant amount of infrared electromagnetic radiation.
(b) they emit a significant amount of ultraviolet electromagnetic radiation.
(c) they emit red light because electrons recombine with protons and then make
transitions to lower energy levels.
(d) they contain a significant amount of dark matter that can be detected using dark
matter CCDs attached to radio telescopes.
6. Emission nebulae appear
(a) yellow, because they emit a significant amount of yellow electromagnetic radiation.
(b) blue, because they emit a significant amount of blue and ultraviolet electromagnetic radiation.
(c) * red, because electrons recombine with protons and then make transitions to
lower energy levels, emitting red light in the process.
(d) dark, because they contain a significant amount of dark matter that can be detected using CCDs attached to radio telescopes.
7. Giant molecular clouds range in size
(a) from about 15 million km to about 600 million km.
(b) from about 15 AU to about 600 AU.
(c) from about 15 billion km to about 600 billion km.
(d) * from about 15 light years to about 600 light years.
(e) [It depends on the size of the molecules in the cloud.]
8. As a clump of gas contracts to form a protostar, its core heats up. If the core temperature reaches
then fusion of hydrogen into helium begins, and the protostar
becomes a main sequence star.
(a) 100,000 degrees K
(b) 1 million degrees K
(c) * 10 million degrees K
(d) 100 million degrees K
9. A brown dwarf is
(a) a character in the Disney movie Snow White and the Dwarf Stars.
(b) * a protostar that never gets hot enough for hydrogen fusion to take place.
(c) a white dwarf that has cooled near the end of its life.
(d) a red dwarf that has cooled near the end of its life.
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10. Low-mass stars fuse hydrogen into helium primarily through the
(a) HH fusion mechanism.
(b) * proton-proton chain.
(c) CNO cycle.
(d) Krebs cycle.
11. The primary net result of Hydrogen fusion in the core of a star is that
(a) *four protons are fused into one Helium nucleus and energy is released.
(b) four neutrons are fused into one Helium nucleus and energy is released.
(c) four protons are fused into one Helium nucleus and energy is absorbed.
(d) four neutrons are fused into one Helium nucleus and energy is absorbed.
12. Low-mass main-sequence stars are found in this part of the H-R diagram:
(a) upper-left
(b) upper-right
(c) lower-left
(d) * lower-right
13. High-mass main-sequence stars are found in this part of the H-R diagram:
(a) * upper-left
(b) upper-right
(c) lower-left
(d) lower-right
14. High-mass stars fuse hydrogen into helium primarily through the
(a) HH fusion mechanism.
(b) proton-proton chain.
(c) * CNO cycle.
(d) Krebs cycle.
15. The luminosity of a star is nearly constant while it stays on the main sequence, but in
the long run there is
(a) * a very gradual increase in luminosity.
(b) a very gradual decrease in luminosity.
(c) a periodic change in luminosity.
(d) [It depends on the size of the molecules that make up the star.]
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16. In the late stages of the life of a star like the Sun, the star goes through the following
phases, in order:
(a) yellow giant phase, first red giant phase, second red giant phase
(b) yellow giant phase, pulsar phase, red giant phase
(c) * first red giant phase, yellow giant phase, second red giant phase
(d) first red giant phase, yellow dwarf phase, second red giant phase
17. A pulsar is
(a) a Cepheid variable.
(b) an RR Lyrae variable.
(c) a white dwarf that spins very rapidly.
(d) * a neutron star that spins very rapidly.
18. A planetary nebula forms from
(a) the initial “clumping” in a giant molecular cloud, resulting in further collapse
which forms a protostar.
(b) material falling into a dwarf star from a neighbouring star in a binary system.
(c) * the stellar material ejected when the core of a medium-sized star collapses into
a white dwarf.
(d) the interstellar medium accreted around a large planet, eventually becoming the
planet’s rings.
19. The core of a white dwarf consists mainly of
(a) hydrogen and helium, with a smattering of heavy elements.
(b) * carbon and oxygen.
(c) an iron core, with concentric rings of lighter elements.
(d) primarily neutrons, covered by a thin layer of heavy elements.
20. Nuclear fusion takes place in a white dwarf mainly in
(a) its core.
(b) the region just outside the core (“helium flash”).
(c) near the surface, driven by electron degeneracy.
(d) * [Virtually no nuclear fusion occurs in a white dwarf.]
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21. The average density (i.e., mass density) of a white dwarf is
(a) less than the average density of the Sun.
(b) a little greater than the average density of the Sun.
(c) a little greater than the average density of the Earth.
(d) * much, much greater than the average density of the Earth.
22. For a star made of degenerate matter, the pressure depends only on
(a) * density.
(b) mass.
(c) radius.
(d) temperature.
23. For a star made of degenerate matter, the larger the mass
(a) the larger the radius.
(b) * the smaller the radius.
(c) the larger the temperature.
(d) the smaller the temperature.
24. The Chandrasekhar limit is
(a) the maximum number of pastries Mrs. Chandrasekhar allowed Mr. Chandrasekhar
to eat after dinner.
(b) * the maximum mass for a degenerate stellar object.
(c) the maximum density for a degenerate stellar object.
(d) the maximum temperature for a degenerate stellar object.
25. The range of observed sizes for white dwarfs is approximately
(a) between the size of a hippopotamus and the size of Donald Trump’s ego.
(b) between the heights of Grumpy and Bashful.
(c) * between the radius of the Earth and twice the radius of the Earth.
(d) between the radius of the Sun and twice the radius of the Sun.
26. White dwarfs dim and eventually become black dwarfs
(a) after a few tens of thousands of years.
(b) after a few tens of millions of years.
(c) after a few hundreds of millions of years.
(d) * over a time scale similar to the current age of the universe.
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27. A type Ia supernova occurs because of
(a) the core collapse of a medium-mass star.
(b) the core collapse of a high-mass star.
(c) * matter from a nearby star falling onto the surface of a white dwarf, becoming
compressed and heated, and eventually resulting in an explosion.
(d) matter from a nearby star falling onto the surface of a neutron star, becoming
compressed and heated, and eventually resulting in an explosion.
28. A type II supernova occurs because of
(a) the core collapse of a medium-mass star.
(b) * the core collapse of a high-mass star.
(c) matter from a nearby star falling onto the surface of a white dwarf, becoming
compressed and heated, and eventually resulting in an explosion.
(d) matter from a nearby star falling onto the surface of a neutron star, becoming
compressed and heated, and eventually resulting in an explosion.
29. A mature supergiant star at the end of its red giant phase has
(a) an apple core.
(b) a carbon core.
(c) * an iron core.
(d) an oxygen core.
(e) a silicon core.
30. Neutron stars have densities that are
(a) about 10 times as dense as white dwarfs.
(b) about 100 times as dense as white dwarfs.
(c) about 1000 times as dense as white dwarfs.
(d) * much, much denser than any of the other alternatives listed here.
31. The Schwarzschild radius is
(a) the smallest possible radius of a white dwarf.
(b) the smallest possible radius of a neutron star.
(c) the radius of the region around a neutron star within which X-ray bursts occur.
(d) * the radius of the region around a black hole within which not even light can
escape.
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32. Neutron stars with masses greater than about 3 solar masses do not exist because
neutron degeneracy pressure is not strong enough to balance gravity, and so
(a) the neutron star explodes into a Type II supernova.
(b) the neutron star explodes into a Type Ib supernova.
(c) * the neutron star collapses into a black hole.
(d) [No star is massive enough to produce such a massive stellar remnant.]
33. One type of indirect observational evidence for black holes is a binary system consisting
of a normal star and
(a) * an invisible companion having a mass of at least 3 M that is a strong source
of X-rays.
(b) an invisible companion having a mass of at least 3 M that is a strong source of
radio waves.
(c) an invisible companion having a mass of at least 3 M that is a strong source of
microwaves.
(d) an overdribbling ball-stopper who is a weak source of assists.
34. The first astronomer to observe that the Milky Way consists of a very large number of
faint stars was
(a) Tycho Brahe.
(b) * Galileo Galilei.
(c) Johannes Kepler.
(d) Buzz Lightyear.
(e) Isaac Newton.
35. The general shape of the Milky Way is
(a) a cone with a central bulge and an ellipsoidal halo.
(b) a cylinder with a central bulge and a conical halo.
(c) * a disk with a central bulge and a spherical halo.
(d) a helix with a central bulge and a spiral halo.
36. Harlow Shapley determined our location in the Milky Way by measuring the distances
to
(a) * globular clusters.
(b) open clusters.
(c) closed clusters.
(d) zodiacal clusters.
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37. Harlow Shapley determined our location in the Milky Way by measuring certain dispioneered by Henrietta Swan Leavitt.
tances using the method of
(a) * Cepheid variables
(b) RR Lyrae variables
(c) Mira variables
(d) Type Ia supernovae
38. Leavitt’s method is based on her observation that there is a relationship between
for the variable stars that she studied.
(a) * period and luminosity
(b) luminosity and mass
(c) mass and temperature
(d) temperature and radius
39. The diameter of the Milky Way is approximately
(a) 100 light years
(b) 1,000 light years
(c) 10,000 light years
(d) * 100,000 light years
(e) 1,000,000 light years
40. Stars in the halo of the Milky Way move in
(a) * highly elliptical orbits, with no apparent organization, like bees in a beehive.
(b) highly elliptical orbits, all in the same orientations, like a flock of birds.
(c) helical orbits, like a submerging school of fish.
(d) arc-like orbits, like a breaching pod of whales.
41. The iron core of a high-mass star collapses when
(a) when it is ignited by the helium flash.
(b) * its mass exceeds the Chandrasekhar limit.
(c) when the triple-alpha process begins.
(d) when the CNO cycle stops.
42. A type II supernova occurs when
(a) helium starts fusing to carbon in the core of the star.
(b) a regular star is swallowed by a black hole.
(c) * a high-mass star explodes.
(d) mass transfer pushes the mass of a white dwarf to the maximum value it can have.
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43. Because of type II supernovae
(a) the resulting burst of neutrinos keeps the galaxy from collapsing.
(b) * elements heavier than iron are synthesized and elements heavier than helium
are dispersed through space.
(c) hydrostatic equilibrium within the galaxy is maintained.
(d) the hydrogen gulf stream within the galactic atmosphere is maintained.
44. A neutron star is supported against gravitational collapse by
(a) thermal neutrinos.
(b) non-thermal neutralinos.
(c) electron degeneracy pressure.
(d) * neutron degeneracy pressure.
(e) strong nuclear forces.
45. Pulsars were discovered by
(a) * Jocelyn Bell.
(b) Arthur Stanley Eddington.
(c) Albert Einstein.
(d) Harlow Shapley.
(e) Fritz Zwicky.
46. Einstein’s general theory of relativity is a theory of gravity based on the idea that
matter and energy bend space-time. An early observational confirmation of the theory
was carried out during an expedition to see the 1919 solar eclipse in South Africa, led
by
(a) Jocelyn Bell
(b) * Arthur Stanley Eddington.
(c) Edwin Hubble.
(d) Harlow Shapley.
(e) Fritz Zwicky.
47. As a spinning star contracts, its spin rate
(a) decreases.
(b) * increases.
(c) doesn’t change.
(d) [Stars don’t spin.]
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48. When lighter nuclei fuse during a supernova explosion to form a gold nucleus,
(a) * energy is absorbed.
(b) energy is released.
(c) there is no absorption or release of energy.
(d) [Such processes do not occur in supernova explosions.]
49. Astronomers measure distances to distant galaxies using
(a) pulsars.
(b) black holes
(c) * type Ia supernovae
(d) type II supernovae
50. The centre of the Milky Way is unobservable at visible wavelengths because
(a) it is too far away.
(b) * it is obscured by massive clouds of gas and dust.
(c) it is obscured by a massive black hole.
(d) it is covered by an invisibility cloak.