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Test 1: February 2015
Course: ASTR 1P02, Section 2
Examination date: 6 February 2015
Time of Examination: 20:30 – 21:20
Number of pages: 10
Number of students: 958
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)
(b)
(c)
(d)
* less than
about the same as
greater than
[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
.
(a)
(b)
(c)
(d)
and end their lifetimes as
led zeppelins, green giants
* protostars, white dwarfs
white dwarfs, red dwarfs
red giants, white dwarfs
3. Giant molecular clouds
(a) are clouds that contain mainly giant dust flakes composed of molecules, with only
a little gas.
(b) are clouds that contain mainly gas, with only a few giant molecular dust mites.
(c) * are clouds of gas and dust that are relatively large in size and contain ordinary
sized molecules.
(d) are clouds of gas and dust that could be any size and contain giant molecules.
4. Reflection nebulae appear
(a) red, because they scatter red light more effectively than blue light.
(b) * blue, because they scatter blue light more effectively than red 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.
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5. Dark nebulae can be observed because
(a) they emit a significant amount of ultraviolet electromagnetic radiation.
(b) * they emit a significant amount of infrared 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 are
(a) * relatively cool, which allows hydrogen atoms to bind into molecules.
(b) relatively hot, which allows hydrogen atoms to bind into molecules.
(c) extremely hot, which allows giant molecules to form.
(d) frigidly cold, which allows giant ice crystals to form.
8. Giant molecular clouds range in size
(a) from about 15 AU to about 600 AU.
(b) from about 15 million km to about 600 million km.
(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.]
9. As a clump of gas contracts to form a protostar, its core heats up. If the core temperature reaches about
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
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10. The protostar phase of a star’s life is
(a) * shorter for higher mass stars.
(b) longer for higher mass stars.
(c) [It depends on the size of the molecules comprising the star.]
(d) [It depends on the whims of the head office of ProtoStar Inc.]
11. A brown dwarf is
(a) a character in the Disney movie Snow White and the Dwarf Stars.
(b) a white dwarf that has cooled near the end of its life.
(c) a red dwarf that has cooled near the end of its life.
(d) * a protostar that never gets hot enough for hydrogen fusion to take place.
12. Low-mass stars fuse hydrogen into helium primarily through the
(a) * proton-proton chain.
(b) CNO cycle.
(c) Krebs cycle.
(d) HH fusion mechanism.
13. 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.
14. 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
15. 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
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16. High-mass stars fuse hydrogen into helium primarily through the
(a) proton-proton chain.
(b) * CNO cycle.
(c) Krebs cycle.
(d) HH fusion mechanism.
17. 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.
18. The core of a white dwarf consists mainly of
(a) hydrogen and helium, with a smattering of heavy elements.
(b) an iron core, with concentric rings of lighter elements.
(c) primarily neutrons, covered by a thin layer of heavy elements.
(d) * carbon and oxygen.
19. 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.]
20. Planetary nebulae often appear approximately ring-like because
(a) they are formed in much the same way that cigarette-smokers blow smoke rings.
(b) strong magnetic fields cause jets of ejected material that align the nebulae into
rings.
(c) they form in the same way as other planetary ring systems, such as the rings
around Saturn.
(d) * they are approximately spherical shells, and only appear ring-like because of
our viewing perspective.
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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. The main factor preventing the further collapse of a white dwarf is
(a) extremely high core temperature.
(b) extremely low core temperature.
(c) * electron degeneracy pressure.
(d) neutron degeneracy pressure.
(e) [White dwarfs have a tendency to expand, not contract.]
23. For a star made of degenerate matter, the pressure depends only on
(a) * density.
(b) mass.
(c) radius.
(d) temperature.
24. 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.
25. 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.
26. 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.
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27. 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.
28. 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.
29. 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.
30. Nucleosynthesis of very heavy elements occurs during the life cycle of
(a) low-mass stars.
(b) medium-mass stars.
(c) * high-mass stars.
(d) all stars.
31. 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.
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32. The dense core of a supergiant star at the end of its red giant phase is supported
against collapse by
(a) * electron degeneracy pressure.
(b) neutron degeneracy pressure.
(c) high pressure caused by the extremely high density and temperature of the core.
(d) high pressure caused by intense gravity of the massive star.
33. 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.
34. 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.
35. 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.]
36. 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 3M that is a strong source of
X-rays.
(b) an invisible companion having a mass of at least 3M that is a strong source of
radio waves.
(c) an invisible companion having a mass of at least 3M that is a strong source of
microwaves.
(d) an overdribbling ball-stopper who is a weak source of assists.
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37. 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.
38. The general shape of the Milky Way is
(a) * a disk with a central bulge and a spherical halo.
(b) a cone with a central bulge and an ellipsoidal halo.
(c) a cylinder with a central bulge and a conical halo.
(d) a helix with a central bulge and a spiral halo.
39. 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.
40. 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
41. 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
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42. 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
43. Most of the Milky Way’s gas and dust is found in its
(a) cone.
(b) cylinder.
(c) * disk.
(d) halo.
(e) helix.
44. Population I stars have a
stars.
concentration of heavy elements than Population II
(a) lower
(b) * higher
(c) [The concentrations are about equal.]
(d) [Neither population has stars that contain any heavy elements.]
45. The Sun orbits around the centre of the Milky Way about once every
(a) 230,000 years.
(b) 2.3 million years.
(c) 23 million years.
(d) * 230 million years.
46. Stars in the halo of the Milky Way move in
(a) highly elliptical orbits, all in the same orientations, like a flock of birds.
(b) * highly elliptical orbits, with no apparent organization, like bees in a beehive.
(c) helical orbits, like a submerging school of fish.
(d) arc-like orbits, like a breaching pod of whales.
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47. Astronomers determine the masses of various parts of the Milky Way by
(a) carefully measuring the motions of stars and then using Newton’s formulation of
Kepler’s first law.
(b) carefully measuring the motions of stars and then using Newton’s formulation of
Kepler’s second law.
(c) * carefully measuring the motions of stars and then using Newton’s formulation
of Kepler’s third law.
(d) looking them up in Encyclopaedia Galactica.
48. “Rotation curves” for stars at various positions in the Milky Way, first measured by
Vera Rubin, do not match observed luminous matter in the galaxy. This is strong
evidence for the presence of
(a) the LMC gyre, which contains an enormous number of discarded toasters and TV
sets.
(b) * dark matter in the Milky Way.
(c) a giant black hole at the centre of the Milky Way.
(d) an enormous number of neutrinos streaming through the Milky Way.
49. The compression waves in the Milky Way’s spiral arms move around the galaxy
(a) * more slowly than stars.
(b) more rapidly than stars.
(c) at about the same speed as stars.
(d) [Compression waves in the Milky Way’s spiral arms don’t move.]
50. The average distance between stars in the Milky Way is about
(a) * a few light years.
(b) a few hundred light years.
(c) a few thousand light years.
(d) a few million light years.