Name: __________________________ Date: _____________


1.
Certain stages of stellar evolution, such as birth of a protostar and post-main sequence red giant evolution, come about because of an imbalance between gravity and
A.
high-energy neutrino pressure.
B.
radiation intensity.
C.
the centrifugal force from rotation.
D.
internal gas pressure.


2.
The total lifespan of the Sun is believed to be
A.
a few million years.
B.
half a billion years.
C.
12 billion years.
D.
infinite.


3.
The space between stars is now known to contain
A.
large quantities of dust that absorb light but no gas, either atomic or molecular.
B.
gas, made up of atoms, molecules, and dust particles.
C.
a perfect vacuum.
D.
variable amounts of gas but no dust, because dust forms only in planetary systems near stars.


4.
Which are the two most abundant elements in the universe?
A.
hydrogen and helium
B.
nitrogen and oxygen
C.
hydrogen and oxygen
D.
hydrogen and carbon


5.
Protostars are
A.
stars made almost entirely out of protons.
B.
objects with masses less than about 0.08 solar masses, which do not have enough mass to become true stars.
C.
old stars, contracting after using up all of their available hydrogen fuel.
D.
very young objects, still contracting before becoming true stars.


6.
Protostars are stars
A.
that are slowly contracting and cooling.
B.
whose surfaces are slowly expanding while their cores are contracting.
C.
that are slowly contracting and heating up.
D.
that are slowly heating up and expanding.


7.
What is a protostar?
A.
a contracting sphere of gas produced by the collapse of an interstellar cloud with, as yet, no nuclear reactions occurring in its interior
B.
a shell of gas left behind from the explosion of a star as a supernova
C.
a small, cold, interstellar cloud before it collapses to become a star
D.
a star near the end of its life, just before it explodes as a supernova


8.
The source of a protostar's heat is
A.
gravitational energy, released as the star contracts.
B.
gravitational energy, released as the protostar expands.
C.
nuclear reactions converting helium to carbon and oxygen in its core.
D.
nuclear reactions converting hydrogen into helium in its core.


9.
A star's evolutionary track is
A.
its movement when plotted on a Hertzsprung-Russell diagram, as it evolves in luminosity and temperature.
B.
its motion through the dark, dense cloud from which it was formed, marked by a visible channel swept free of dust and gas.
C.
the line across the Hertzsprung-Russell diagram denoting stars identified as main-sequence stars.
D.
its movement when plotted on a map of the galaxy as it takes part in the overall galactic rotation.


10.
How long does it take for a 1-solar-mass star to pass through the pre–main-sequence phase?
A.
200,000 years
B.
20,000,000 years
C.
20,000 years
D.
20 billion years


11.
The total time that the Sun will spend as a main-sequence star is
A.
at least 200 billion years (2 × 1011 years)
B.
about 10 billion years (1010 years)
C.
about 10 million years (107 years)
D.
about 1 million years


12.
What places a limit on the lifetime of a star?
A.
loss of the mass, and therefore of nuclear fuel, of the star into space by stellar winds
B.
amount of available nuclear fuel it contains
C.
collisions between stars in a galaxy are sufficiently frequent that all stars will eventually be destroyed in this way.
D.
buildup of spin as it evolves and contracts means that the star will eventually spin apart


13.
Through nuclear reactions in their cores, stars on the main sequence convert
A.
hydrogen to helium.
B.
helium to hydrogen.
C.
helium to carbon.
D.
carbon to iron.


14.
All stars on the main sequence
A.
are at a late stage of evolution after the red giant stage.
B.
are changing slowly in size by gravitational contraction.
C.
generate energy by hydrogen fusion in their centers.
D.
have approximately the same age to within a few million years.


15.
At what stage of its evolutionary life is the Sun?
A.
post-main sequence—red giant (cool) phase
B.
before main sequence—variable star
C.
main sequence—middle age
D.
just before supernova stage


16.
Which group of stars in the H-R diagram would be labeled “zero-age main sequence”?
A.
stars that have just collapsed from the interstellar medium
B.
stars that are just beginning to convert helium into carbon in their cores
C.
stars that contain no processed elements (elements heavier than hydrogen or helium)
D.
stars that have just started converting hydrogen to helium in their cores


17.
The total time the Sun will spend as a main-sequence star is
A.
about 1 million years.
B.
about 10 billion years.
C.
at least 200 billion years.
D.
about 4.5 million years.


18.
Why does the core of the Sun contain more helium and less hydrogen than the surface material of the Sun?
A.
Thermonuclear reactions have converted much of the original hydrogen in the core into helium.
B.
The hydrogen has been lifted out of the core by the Sun's magnetic field.
C.
Helium is heavier than hydrogen and has sunk toward the center in a process of chemical differentiation.
D.
Helium condensed more easily, so the core became helium-rich when the Sun was first forming. Vast quantities of hydrogen were added only after the core became massive enough.


19.
The evolution of a star is controlled mostly by its
A.
initial mass.
B.
location in the galaxy.
C.
surface temperature.
D.
chemical composition.


20.
What is the most important quantity on which the lifetime of a star depends?
A.
temperature of the star's corona
B.
abundance of heavy elements in the star
C.
star's speed of rotation
D.
mass of the star


21.
What is a red giant?
A.
a large, red star burning hydrogen into helium in its core
B.
a protostar in the “upper right” part of the Hertzsprung-Russell diagram
C.
a large emission nebula
D.
a star burning hydrogen into helium in a shell around the core


22.
After a star becomes a red giant, hydrogen fusion
A.
no longer occurs.
B.
occurs in the core.
C.
occurs in a shell around the core.
D.
occurs only during the helium flash.


23.
What makes a red giant star so large?
A.
The helium-rich core has expanded, pushing the outer layers of the star outward.
B.
The star has many times more mass than the Sun.
C.
Red giants are rapid rotators, and centrifugal force pushes the surface of the star outward.
D.
The hydrogen-burning shell is heating the envelope and making it expand.


24.
Which of the following are not very young stars or prestellar objects?
A.
protostars
B.
red giants
C.
T Tauri stars
D.
infrared emitting stars in gas and dust clouds


25.
The temperature at which thermonuclear reactions begin to convert helium into carbon (helium burning) is
A.
15 million K.
B.
1 million K.
C.
1 billion K.
D.
100 million K.


26.
What is the dominant nuclear reaction during helium burning in a star?
A.
4 He fusing into C
B.
He + 4H combining into C
C.
3 He fusing into C
D.
2 He fusing into C


27.
Degeneracy occurs when
A.
magnetic fields inhibit the motion of charged particles in sunspots.
B.
solar wind particles ionize atoms in Earth's upper atmosphere.
C.
thermonuclear reactions halt the contraction of a protostar.
D.
electrons inside a star resist being pushed closer together than a certain limit.


28.
The helium flash results from
A.
the high temperature in the helium core of a blue (spectral class O or B) supergiant star.
B.
electron degeneracy or quantum crowding in the core of a low-mass red giant star.
C.
the sudden release of energy in strong magnetic fields near a sunspot.
D.
the sudden onset of nuclear reactions at the end of the protostar phase of a star's life.


29.
If you make a list of the 100 brightest stars in the sky you will find that most of them are
A.
white dwarfs.
B.
main sequence stars.
C.
giants and supergiants.
D.
brown dwarfs.


30.
If you make a list of the 100 nearest stars in the sky you will find that most of them are
A.
white dwarfs.
B.
main sequence stars.
C.
giants and supergiants.
D.
brown dwarfs.


31.
The age of a cluster can be found by
A.
observing its position in the sky with respect to the Sun.
B.
measuring its speed of motion relative to the Sun.
C.
carrying out a number count of the stars in the cluster.
D.
determining the turnoff point on the main sequence of its HR diagram.


32.
How do the stars in a star cluster change with time?
A.
The stars with the greatest heavy-element content evolve the most rapidly.
B.
The highest-mass stars evolve the most quickly.
C.
The lowest-mass stars evolve the most quickly.
D.
All stars in it evolve at the same rate.


33.
When does the Helium Flash occur?
A.
when helium fusion begins in a low mass star
B.
when a planetary nebula is formed
C.
when a Type II supernova is formed
D.
when a pulsar is formed


34.
The structure of the deep interior of a low-mass star near the end of its life is
A.
a carbon-oxygen core, a shell undergoing fusion of helium nuclei, and a surrounding dormant hydrogen shell.
B.
an inactive hydrogen core and a helium shell undergoing nuclear fusion, surrounded by a carbon-oxygen shell.
C.
a turbulent mixture of hydrogen, helium, carbon, and oxygen in which only helium continues to undergo nuclear fusion.
D.
a helium core surrounded by a thin hydrogen shell undergoing nuclear fusion, with very small concentrations of heavier nuclei.


35.
The characteristics of red supergiant stars are a
A.
brightness of 10,000 Suns and a diameter of about that of Mars's orbit.
B.
brightness of the Sun and size of about that of Mercury's orbit.
C.
brightness of about 1 million Suns and a diameter of the whole solar system.
D.
brightness of about 10,000 Suns and a diameter of 1/10 of that of the Sun.


36.
A planetary nebula is
A.
a contracting spherical cloud of gas surrounding a newly formed star, in which planets are forming.
B.
the expanding nebula formed by the supernova explosion of a massive star.
C.
an expanding gas shell surrounding a hot, white dwarf star.
D.
a disk-shaped nebula of dust and gas from which planets will eventually form, easily photographed around relatively young stars.


37.
A planetary nebula is
A.
the spherical cloud of hot gas produced by a supernova explosion.
B.
the disk of material in which planets are forming around a star other than the Sun.
C.
a shell of ejected gases, glowing by fluorescence caused by ultraviolet light from a hot but dying central star.
D.
a gas cloud surrounding a planet after its formation and before the formation of the planet's moons.


38.
Planetary nebulae are so-named because
A.
these extended objects, often green-colored, looked like planets when first seen by nineteenth-century observers through their telescopes.
B.
the ejected material is rich in carbon and oxygen, necessary elements for the manufacture of planets in the nebulae surrounding stars.
C.
they rotate slowly and condense into planetary objects around a central star.
D.
their spectra appear to be similar to the spectrum of the giant gas planets in our own solar system.


39.
A white dwarf is
A.
an object like Jupiter which was not massive enough to become a star.
B.
a low-mass star at the end of its life.
C.
a hot, main-sequence star.
D.
a type of protostar.


40.
A white dwarf star, the surviving core of a low-mass star toward the end of its life, can be found on the Hertzsprung-Russell diagram
A.
below and to the left of the main sequence.
B.
at the bottom end of the main sequence, along which it has evolved throughout its life.
C.
at the upper left end of the main sequence, because its surface temperature is extremely high.
D.
above and to the right of the main sequence, because it evolved there after its hydrogen-burning phase.


41.
A white dwarf star is about the same size as
A.
the Earth.
B.
the Sun.
C.
the total solar system.
D.
New York City.


42.
Which physical phenomenon keeps a white dwarf star from collapsing inward on itself?
A.
electron degeneracy or “quantum crowding”
B.
normal gas pressure
C.
convection currents or updrafts from the nuclear furnace
D.
the physical size of the neutrons


43.
Supernovae are of particular importance in theories of stellar evolution because
A.
they are one of the few known mechanisms for producing the heaviest elements.
B.
the Sun will probably go through a supernova phase.
C.
there are several supernovae in the immediate vicinity of the Sun.
D.
they always result in black holes.


44.
A typical supernova, in the hours following its explosion, is as bright as
A.
1000 typical spiral galaxies.
B.
an entire galaxy.
C.
1000 Sun-like stars.
D.
a million Sun-like stars.


45.
The neutrino is
A.
a very small asteroid-like body orbiting the Sun that is very difficult to see.
B.
a heavy nuclear particle, easily detected.
C.
an elusive subatomic particle, having very little or no mass and difficult to detect.
D.
another name for an anti-electron or positron.


46.
A Type II supernova is the
A.
explosion of a single massive star after silicon burning has produced a core of iron nuclei.
B.
explosion of a red giant star as a result of the helium flash in the core.
C.
collapse of a blue supergiant star to form a black hole.
D.
explosion of a white dwarf in a binary star system after mass has been transferred to it from its companion.


47.
Can a white dwarf explode?
A.
Only if another star collides with it; and stars are so far apart in space that this is unlikely ever to have happened in our galaxy.
B.
Yes, but only if nuclear reactions in the white dwarf core reach the stage of silicon burning, producing iron.
C.
No; white dwarfs are held up by electron degeneracy pressure, and this configuration is stable against collapse or explosion.
D.
Yes, but only if it is in a binary star system.


48.
The Crab Nebula is
A.
a supernova remnant.
B.
a planetary nebula surrounding a hot star.
C.
the active nucleus of a spiral galaxy.
D.
a cool pre-stellar gaseous nebula.


49.
Pulsars are
A.
pulsating white dwarfs.
B.
pulsating neutron stars.
C.
pulsating black holes.
D.
rotating neutron stars.


50.
Why is Cygnus X-1 thought to be a black hole?
A.
It has pulled matter from its companion star into an accretion disk around itself.
B.
No light has ever been observed to come from it.
C.
It emits X-rays that flicker on time scales of a hundredth of a second.
D.
It is physically smaller than Earth, but its mass is too large to be a neutron star or white dwarf.