1.

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

2.	Which of the following would NOT be found in higher-than-average densities in an interstellar nebula? A. electrons B. neutrinos C. dust D. protons

3.

We see an emission nebula predominantly in A. blue light, originally emitted by stars within the nebula but scattered by dust. B. light emitted over a wide range of wavelengths by dust grains that have been heated by radiation from embedded stars. C. light emitted by molecules in the dense clouds of gas surrounding the stars in the nebula. D. the Balmer Ha red line, from recombination of electrons with nuclei in ionized hydrogen.

4.	An H II region is a region of A. ionized hydrogen around one or more O and B stars. B. molecular hydrogen inside a giant molecular cloud. C. neutral, atomic hydrogen in interstellar space. D. gas and dust formed by the explosion of a massive star.

5.

The blue color of a reflection nebula is produced by A. light emitted by the gas cloud that is Doppler-shifted as the cloud moves rapidly toward us. B. the continuum emission of very hot gas and dust. C. emission from specific transitions in hydrogen gas. D. selective scattering from very small dust grains.

6.	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

7.

What determines whether a particular region of an interstellar cloud can collapse and form a star? A. only the temperature, because higher temperatures act to prevent collapse B. the relative concentration of dust to hydrogen gas in the cloud, because the dust is the major trigger that initiates collapse C. the amount of gravity pulling inward compared to gas pressure pushing outward D. the amount of mass in the cloud alone, because this determines the strength of gravity, which will act unopposed on the cloud

8.

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.

9.	The major source of energy in the pre–main-sequence life of the Sun was A. gravitational. B. nuclear fusion. C. chemical burning of carbon atoms. D. nuclear fission.

10.

Protostars with masses of more than about 4 times the mass of the Sun maintain approximately constant luminosity through their pre–main-sequence lifetimes. This is because A. the star contracts as its surface temperature decreases, and the change in surface area compensates for the change in energy emitted per unit area. B. the surface temperature increases as the star contracts, and the change in energy emitted per unit area compensates for the change in surface area. C. they contract too rapidly for their temperature and luminosity to change significantly. D. they are too massive to contract significantly, thus keeping luminosity constant.

11.

A brown dwarf is A. an object intermediate between a planet and a star, with not enough mass to begin nuclear reactions in its core. B. a general name for objects similar to the planet Jupiter. C. any star whose blackbody spectrum peaks in the brown region of the visible spectrum. D. a star of less than about 1.5 solar masses at the very end of its life, after it has cooled to near-invisibility.

12.	What is believed to be the maximum mass that a star can have? A. There appears to be no physical limit. B. about 1000 solar masses C. about 200 solar masses D. about 5 solar masses

13.

What is a T Tauri star? A. a young, irregularly variable, G, K, or M type star that is ejecting gas B. a giant or supergiant star that varies regularly in brightness C. a giant or supergiant star that varies randomly in brightness D. a massive O or B type star that ionizes hydrogen in interstellar space

14.

The characteristics of an open cluster of stars are A. many thousands of stars, all very old, with very little evidence of elements heavier than helium, and no evidence of dust or gas in their vicinity. B. many thousands of stars, of very different ages, but the same chemical composition. C. a few hundred stars, often very young and still embedded in the gas and dust from which they were formed. D. many thousands of stars, mostly binary, of different ages.

15.	Infrared stars within the Orion Nebula are examples of which stage of stellar evolution? A. protostar and young star B. supernova remnants C. red giant D. planetary nebula

16.	In which part of the electromagnetic spectrum are molecules most easily detected? A. visible light B. ultraviolet light C. X rays D. radio waves

17.

If you were to look at one kilogram of material taken from the surface of the Sun and 1 kilogram taken from the center, which of the following statements would be true of these two 1 kilogram masses? A. The kilogram from the surface would contain more hydrogen than the one from the center. B. Neither of them would contain any hydrogen. C. They both would contain the same amount of hydrogen. D. The kilogram from the surface would contain less hydrogen than the one from the center.

18.	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

19.	In terms of nuclear reactions, what is the next stage of a star's life after the end of hydrogen burning in the core? A. hydrogen burning in a thin shell around the core B. helium burning in the core C. carbon burning D. death (it becomes either a supernova or a white dwarf)

20.

When a star leaves the main sequence and expands toward the red giant region, what is happening inside the star? A. Hydrogen burning is taking place in a spherical shell just outside the core; the core itself is almost pure helium. B. Hydrogen burning is taking place in a spherical shell just outside the core; the core has not yet started thermonuclear reactions and is still mostly hydrogen. C. Helium burning is taking place in a spherical shell just outside the core; the core itself is almost pure carbon and oxygen. D. Helium is being converted into carbon and oxygen in the core.

21.	What will be the diameter of the Sun when core helium burning begins? A. half its present size B. the size of the Earth C. about the size of the Earth's orbit D. twice its present size

22.	What rates of mass loss are typical from red giant stars? A. 10-3 solar masses per year B. Red giant stars do not suffer mass loss. C. 1 solar mass per year D. 10-7 solar masses per year

23.

Degeneracy occurs when A. magnetic fields inhibit the motion of charged particles in sunspots. B. solar wind particles ionize atoms in the 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.

24.

Horizontal-branch stars, which have a range of temperatures with luminosities between 50 and 100 times that of the Sun, are in what stage of their lives? A. hydrogen shell burning, with a degenerate helium core B. core helium burning C. gravitational contraction before the start of core hydrogen burning D. core hydrogen burning

25.	In which direction in the Hertzsprung-Russell diagram does the position occupied by a star move when helium burning begins in the star's core? A. toward the lower right B. toward the lower left C. toward the upper right D. toward the upper left

26.

Within a globular cluster, what would you expect to find in the population of stars? A. a full range of stars from bright blue to dim red, with no bright red giant stars but significant amounts of dust and gas B. a full mixture of bright blue supergiant and red giant stars, in addition to white dwarfs and dim red stars C. mainly white dwarf stars surrounded by the remnant dust and gas from the planetary nebular stages of dying stars but no faint red stars, red giants, or bright blue stars D. many red giants, white dwarfs, and dim red stars but no bright blue stars or dust and gas

27.

In describing a star, what does the adjective "metal-poor" mean? A. The star has a low abundance of all elements in its spectrum. B. The star has a low abundance of all elements heavier than hydrogen in its spectrum. C. The star may or may not have a low abundance of carbon in its spectrum, but it is definitely weak in iron. D. The star has a low abundance of all elements heavier than hydrogen and helium in its spectrum.

28.

What is a Cepheid variable star? A. a high-mass star that pulsates regularly in brightness B. one of several classes of stars that pulsate randomly in brightness C. a star that normally remains constant in brightness but occasionally flares up in brightness by several magnitudes D. a low-mass, horizontal-branch star that pulsates regularly in brightness

29.

The components of a binary star, particularly if they are close, can influence each other in various ways. Which of the following is NOT likely to be an effect of one star on its companion? A. Mass can be transferred from one star to its companion. B. Intense radiation from a hot star can produce nuclear reactions on the surface of a cooler companion and initiate a nova explosion. C. The gravitational force of one star will make its companion move in an orbit, rather than remaining stationary. D. A very hot star can heat part of its cooler companion to produce a hot spot.

30.

The shape of the cross-section of the Roche lobes around a close binary star system, taken through the centers of the stars, is A. two unequal ellipses that touch at the center of the lobes. B. an ellipse, with a star at each focus. C. a sphere, centered on the center of mass of the star system. D. a figure-eight.

31.

The most important development in the interior of a star of moderate mass which leads to the red giant phase is A. a runaway nuclear furnace and eventual explosion in the star's interior, destroying the star and leaving only a rapidly expanding shell of gas. B. the cessation of hydrogen "burning" in the core, leading to core contraction and overall star expansion. C. expansion of the whole star, leading to lower temperatures throughout the star and the turnoff of the nuclear furnace in the core. D. contraction of the whole star, which quenches the nuclear furnace in the core and leads to cooling of the surface.

32.

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.

33.	In terms of a star's evolutionary life, an asymptotic giant branch (AGB) star is in the A. helium core-burning phase. B. helium shell-burning phase. C. pre-main sequence phase. D. hydrogen shell-burning phase prior to helium ignition in the core.

34.

The excess carbon in the surface layers of a "carbon star," compared to that at the surface of the Sun, is a result of A. neutrinos, which escape easily from the core of a star but react with the cool hydrogen at its surface to form carbon. B. helium flash, in which the explosion blasts carbon from the core into the surface layers. C. dredge-up, in which the convective envelope transports material from a star's core to its surface. D. mass loss, which strips away the outer envelope from an old star and reveals the carbon-rich core.

35.

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.

36.

A planetary nebula is created A. over several hundred years, during mass transfer in a close binary star system. B. in seconds, during the helium flash in a low-mass star. C. slowly over 10,000 years or more, due to thermal pulses in a low-mass star. D. in hours or less, during the explosion of a massive star.

37.	What fraction of the material returned to the interstellar medium of a galaxy by stars is contributed by planetary nebulae as they eject their shells? A. 15% B. only about 1 part in a million C. less than 1% D. 80%, or most of the returned material

38.	The object seen at the center of a planetary nebula is A. an accretion disk around a black hole. B. a planet in the process of forming. C. composed almost entirely of neutrons, and is spinning rapidly. D. the former core of a red giant star, now a white dwarf star.

39.

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.

40.	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.

41.	The energy generation process inside a white dwarf star is A. the combining of protons and electrons to form neutrons within its core. B. the helium flash—very efficient and rapid helium fusion. C. nonexistent; a white dwarf star is simply cooling by radiating its original heat. D. hydrogen fusion.

42.

Because it has ceased nuclear burning in its interior and therefore no longer generates energy, why is it that a white dwarf does not shrink rapidly under the force of gravity as it cools? A. The rapid reduction of radius before the white-dwarf phase produces a very rapid rotation, thereby generating a large centrifugal force which prevents the star from shrinking. B. The very low luminosity of a white dwarf means that it cools slowly and maintains a high temperature and therefore a high internal pressure which opposes gravity. C. The star has lost so much mass in earlier phases that the remaining mass generates insufficient gravitational force to produce further shrinkage. D. The electrons within it are in a degenerate state and will not allow further shrinkage.

43.

White dwarf stars of different masses have radii or sizes for which A. the more massive the star, the larger it is. B. the sizes are the same for all stellar masses. C. the sizes start out the same for all masses, but the more massive stars shrink fastest. D. the more massive the star, the smaller it is.

44.	Which nuclear fusion cycle follows the helium fusion phase as a massive star evolves? A. silicon "burning" B. carbon "burning" C. iron "burning" D. oxygen "burning"

45.	Very heavy elements beyond iron in the periodic table are formed in the interiors of massive stars by what process in general? A. triple a process B. neutron capture C. splitting of heavier elements by nuclear fission D. CNO cycle of nuclear fusion

46.

A high-mass star near the end of its life undergoes successive cycles of energy generation within its core in which gravitational collapse increases the temperature to the point where a new nuclear fusion cycle generates sufficient energy to stop the collapse. This process does not work beyond the silicon fusion cycle which produces iron. Why is this? A. The pressure from high-energy photons and neutrinos at the very high core temperatures reached at this stage of development is finally sufficient to halt the collapse. B. The density is so great that the iron nuclei are effectively touching one another and the collapse cannot continue. C. Fusion of iron nuclei into heavier nuclei requires energy rather than producing excess energy and therefore will not produce the additional gas pressure to halt the collapse. D. Electrostatic forces between the highly charged iron nuclei are sufficient to overcome the collapse and stabilize the stellar core.

47.

What is photodisintegration? A. heating and ejection of mass from the surface of a normal star by the radiation from a neutron star orbiting it B. destruction of a star by the pressure of radiation inside it C. splitting apart of atomic nuclei by high-energy gamma rays D. ejection of a neutron or proton from an atomic nucleus, accompanied by the emission of a gamma ray

48.	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.

49.

What new method has recently provided astronomers with new information about the behavior of stars beneath their surfaces, for example, the collapse of the inner core of a star undergoing supernova explosion and the nuclear reactions in the interior of the Sun? A. neutrino astronomy B. visible light spectroscopy C. X-ray astronomy and photography D. radio astronomy

50.

Neutrino detectors for astronomical purposes are built and operated deep underground to A. shield them from other high-energy radiation from space and from neutrinos produced locally by cosmic rays or by natural radioactivity B. reduce the effect of rotational speed produced by Earth's rotation, because the sensitive neutrino detection techniques are adversely affected by Doppler shifts. C. utilize the gravitational focusing of neutrinos that occurs in the Earth's core. D. ensure that they are absolutely light-tight, because they depend on the detection of very faint flashes of light.

51.

A Type Ib supernova is believed to result from the A. collapse of a blue supergiant star to form a black hole. B. explosion of a massive star that has lost its hydrogen-rich outer layers through a stellar wind or by mass transfer in a binary star system. C. explosion of a white dwarf in a binary star system after matter transferred to it from its companion has increased its mass above the Chandrasekhar limit. D. explosion of a massive, hydrogen-rich star after silicon burning has produced a core of iron nuclei.

52.

The explosion of a supernova appears to leave behind A. a rapidly expanding shell of gas and a central neutron star. B. a rapidly rotating shell of gas, dust, and radiation, but no central object. C. a rapidly expanding shell of gas and a compact white dwarf star at its center. D. nothing, the explosion changes all the matter completely into energy, which then radiates into space at the speed of light.

This is the end of the test. When you have completed all the questions and reviewed your answers, press the button below to grade the test.