Deck 13: The Lives of Stars From Birth Through Middle Age

Question 1

What is the second MOST abundant element in the interstellar medium (after hydrogen)?

A) helium
B) carbon
C) nitrogen
D) iron

Answer 1

helium

Question 2

What are the two MOST abundant elements in the interstellar medium?

A) hydrogen and carbon
B) hydrogen and oxygen
C) hydrogen and helium
D) nitrogen and oxygen

Answer 2

hydrogen and helium

Question 3

The space between stars is known to contain

A) large quantities of dust that absorb and scatter light but no gas, either atomic or molecular.
B) variable amounts of gas but no dust, which forms only in planetary systems near stars.
C) a perfect vacuum.
D) gas, both atomic and molecular, and dust.

Answer 3

gas, both atomic and molecular, and dust.

Question 4

Which of these objects is NOT an abundant physical component of the interstellar medium?

A) atoms and ions
B) molecules
C) dust
D) radioactive elements

Question 5

Which of these methods has NOT yet been used to study the material of the interstellar medium?

A) scattering of starlight
B) collection of dust and gas by spacecraft
C) emission of electromagnetic radiation by atoms and molecules
D) absorption of light from more distant stars

Question 6

Which of these molecules is likely to be the MOST common in interstellar space?

A) OH, hydroxyl
B) H₂, molecular hydrogen
C) CO, carbon monoxide
D) H₂O, water

Question 7

Most interstellar matter is too cold to be observed optically. In which part of the electromagnetic spectrum might its radiation be detected?

A) gamma ray
B) ultraviolet
C) infrared
D) X-ray

Question 8

The light from a distant cloud of gas and dust looks distinctly red to the unaided eye. When a spectrum is taken, the red color is found to come from a single, bright spectral line. Thus, the red color in this situation is due to

A) interstellar reddening.
B) the Balmer spectrum of hydrogen.
C) the Doppler effect.
D) interstellar reddening, the Balmer spectrum of hydrogen, or the Doppler effect.

Question 9

What is the MOST abundant element in the interstellar medium?

A) carbon
B) helium
C) oxygen
D) hydrogen

Question 10

To detect most interstellar material requires

A) optical telescopes.
B) gamma-ray observatories.
C) radio telescopes.
D) ultraviolet detectors.

Question 11

The light from a distant cloud of gas and dust looks distinctly red to the unaided eye. When a spectrum is taken, the short wavelengths are all found to be dimmed in intensity compared with the longer wavelengths, which are all more intense. Thus, the red color in this situation is due to

A) interstellar reddening.
B) the Balmer spectrum of hydrogen.
C) the Doppler effect.
D) any one of these three phenomena.

Question 12

The Pleiades cluster consists of a number of bright stars wrapped in a cloud of gas and dust that appears blue. This cluster is an example of

A) a giant molecular cloud.
B) a dark nebula.
C) a reflection nebula.
D) a stellar "nursery."

Question 13

The light from a distant cloud of gas and dust looks distinctly red to the naked eye. When a spectrum is taken, it is found that many wavelengths that would normally be expected to be in the middle of the spectrum have been shifted into the long-wavelength end of the spectrum. Thus, the red color in this situation is due to

A) interstellar reddening.
B) the Balmer spectrum of hydrogen.
C) the Doppler effect.
D) interstellar reddening, the Balmer spectrum of hydrogen, or the Doppler effect.

Question 14

How have complex molecules such as formaldehyde (H₂CO) been detected in interstellar clouds?

A) by direct sampling by space probes
B) by observing the chemical reactions in which they are created
C) only by theoretical modeling since it is known that the component elements (H, C, O) are present in space
D) by molecular emission lines

Question 15

What do a reflection nebula surrounding a star and Earth's atmosphere have in common?

A) The reflection nebula and Earth's atmosphere both appear blue because of preferred scattering of this color of light.
B) The reflection nebula and Earth's atmosphere both have about the same temperature.
C) The reflection nebula and Earth's atmosphere have almost the same average density of gas.
D) The reflection nebula and Earth's atmosphere both contain the same types of molecules.

Question 16

Which of these common molecules found in interstellar space contains nitrogen atoms but no oxygen?

A) water vapor (H₂O)
B) formaldehyde (H₂CO)
C) methane (CH₄)
D) ammonia (NH₃)

Question 17

Most interstellar matter is too cold to be observed optically. Its radiation is predominantly emitted at longer wavelengths, such as infrared and radio. This behavior is an example of

A) Bode's law.
B) Wien's law.
C) the Stefan-Boltzmann law.
D) Kirchhoff's law.

Question 18

A star cluster at a great distance from the Sun, but inside the Milky Way, appears to be fainter than a similar star cluster at a closer distance. Part of this is the expected result from the inverse square law, but the distant cluster will also appear fainter than expected by distance alone because

A) the photons of light become "tired" and appear less bright as they travel.
B) the cosmological redshift has moved some of the light into the infrared spectral region.
C) star clusters are systematically smaller and hence less bright the farther they are from the galactic center and hence from the Sun.
D) light is scattered and absorbed by interstellar dust and gas between distant clusters and Earth.

Question 19

The apparent reddening of light from stars after its passage through the interstellar medium is caused by

A) the additional contribution to this starlight by emission from hydrogen gas in the interstellar medium.
B) preferential scattering of blue starlight by dust grains.
C) Zeeman shift of the light by the powerful magnetic fields existing within the interstellar medium.
D) scattering of this light from rapidly moving material; the light is Doppler-shifted toward the red end of the spectrum.

Question 20

Interstellar extinction is the

A) assimilation of interstellar matter by stars after gravitational attraction and capture.
B) reduction of the apparent brightness of stars by scattering and absorption of their light by intervening interstellar clouds.
C) wipeout of species on Earth by intense radiation from a nearby supernova.
D) deaths of high-mass stars in the space between other long-lived stars.

Question 21

How is gas distributed in interstellar space?

A) in clumps, concentrated in interstellar clouds
B) concentrated in narrow riverlike streams of gas that circle the Galaxy
C) uniformly distributed through space
D) concentrated around existing stars because of the stars' gravitational pull

Question 22

What is the typical mass of a giant molecular cloud?

A) 10 to 100 solar masses
B) 100 to 1000 solar masses
C) 1000 to 1 million solar masses
D) 1 million to 1 billion solar masses

Question 23

What fraction of the mass of a typical interstellar cloud is helium?

A) 50 percent
B) 2 percent
C) 10 percent
D) 25 percent

Question 24

In which part of the electromagnetic spectrum are molecules in the interstellar medium MOST easily detected?

A) visible light
B) radio waves
C) X-rays
D) ultraviolet light

Question 25

What wavelengths have astronomers used to map and study the distribution of the giant molecular clouds in space?

A) X-ray
B) visible
C) ultraviolet
D) radio

Question 26

What causes the characteristic blue color of a reflection nebula?

A) electrons dropping between energy levels n = 3 and n = 2 in hydrogen atoms
B) electrons dropping between energy levels n = 2 and n = 1 in hydrogen atoms
C) thermal blackbody radiation emitted by the hot gas
D) scattering of starlight from dust grains in the nebula

Question 27

Which of these easily observed molecular species is used as a tracer for the fundamental but difficult to observe H₂ molecules in giant molecular clouds?

A) hydroxyl (OH)
B) water vapor (H₂O)
C) carbon dioxide (CO₂)
D) carbon monoxide (CO)

Question 28

When looking for molecular hydrogen, astronomers actually look for

A) atomic hydrogen.
B) carbon monoxide.
C) carbon dioxide.
D) polycyclic aromatic hydrocarbons (PAHs).

Question 29

In star-forming regions in interstellar space, which molecule is the easiest to detect?

A) ammonia (NH₃)
B) hydrogen (H₂)
C) formaldehyde (H₂CO)
D) carbon monoxide (CO)

Question 30

The mass of a particular interstellar giant molecular cloud is 2 million solar masses. Approximately what is the mass of the hydrogen in this cloud?

A) 40,000 solar masses
B) 1 million solar masses
C) 1.5 million solar masses
D) 1.96 million solar masses

Question 31

The mass of a particular giant molecular cloud in interstellar space is 2 million solar masses. What is the mass of the helium in this cloud?

A) 40,000 solar masses
B) 1 million solar masses
C) 200,000 solar masses
D) 500,000 solar masses

Question 32

Giant molecular clouds, which are major sites of star formation, can be up to about

A) 10 times the size of the solar system and contain 2 to 3 solar masses of material.
B) 10 pc across and contain a few thousand solar masses of material.
C) 100 pc across and contain 2 million solar masses of material.
D) 1000 pc across and contain 100 million solar masses of material.

Question 33

Hydrogen in molecular form, H₂, is thought to be very abundant in gas clouds in space, but these molecules emit radiation relatively inefficiently since they are symmetrical. Which other molecular element occurs in close association with H₂ and is used as a probe for molecular clouds?

A) carbon monoxide (CO)
B) methane (CH₄)
C) water vapor (H₂O)
D) carbon dioxide (CO₂)

Question 34

What fraction of the mass of a typical interstellar cloud is hydrogen?

A) 2 percent
B) almost 50 percent
C) 74 percent
D) 98 percent

Question 35

The density of carbon monoxide is observed in a particular interstellar cloud to be 500 CO molecules per cubic meter. What will be the expected density of molecular hydrogen gas, H₂, in this cloud?

A) 500 million molecules of H₂ per cubic meter
B) 500 molecules of H₂ per cubic meter
C) 5 million molecules of H₂ per cubic meter
D) 50,000 molecules of H₂ per cubic meter

Question 36

Which of these fall within the typical range of dimensions of a giant molecular cloud in interstellar space?

A) mass of about 1000 solar masses in volume with a diameter of about 1000 ly
B) mass of about 1 million solar masses in volume with a diameter of about 100 ly
C) mass of about 1 million solar masses in volume with a diameter of about 100 au, about the size of the solar system
D) mass of about 1000 solar masses in volume with a diameter of about 100 ly

Question 37

What is a typical size for a giant molecular cloud?

A) 100 ly across
B) 1000 ly across
C) anything up to about 1 ly across
D) 5 ly across

Question 38

Which of these important atomic or molecular species is particularly difficult to detect in the interstellar medium?

A) molecular hydrogen (H₂)
B) atomic hydrogen (H)
C) carbon monoxide (CO)
D) water vapor (H₂O)

Question 39

A reflection nebula is made visible by

A) thermal energy emitted as a continuous spectrum by the very hot gas, much like that emitted by a hot body on Earth.
B) light from embedded stars reflected over a wide range of wavelengths toward Earth by crystals of water, methane, and ammonia ices.
C) emission lines from hydrogen, which itself has been ionized by UV light from embedded stars.
D) blue light preferentially scattered by dust grains.

Question 40

What is the characteristic color of a reflection nebula?

A) red
B) yellow
C) green
D) blue

Question 41

What is the ultimate fate of an open star cluster?

A) The shape of the cluster will remain more or less as it is at the present time as the stars in it age and die.
B) The stars in the cluster escape one by one until the cluster no longer exists.
C) Over time the stars collide and merge, eventually creating a black hole.
D) The stars gradually sink toward the center, creating a globular cluster.

Question 42

Open clusters are NOT

A) gravitationally bound.
B) the result of star formation within a single giant molecular cloud.
C) loose groupings of stars of a wide range of ages.
D) known to contain more than about 100 stars.

Question 43

Which wavelength region is MOST useful for investigating the dense cores inside giant molecular clouds?

A) infrared
B) X-ray
C) ultraviolet
D) optical

Question 44

Which of these mechanisms is NOT a common way in which star formation is triggered or started?

A) collisions between interstellar clouds
B) heating of an interstellar cloud by radiation from embedded young stars
C) compression of an interstellar cloud by the shock waves from a supernova explosion
D) compression of an interstellar cloud by the pressure of light from nearby stars

Question 45

What determines whether a particular region of an interstellar cloud can collapse and form a star?

A) temperature, since higher temperatures act to prevent collapse
B) amount of gravity pulling inward compared with gas pressure pushing outward
C) gas density (the ratio of the mass of the cloud over its volume), since density determines how gravity will act on the cloud material
D) amount of mass in the cloud, since mass determines the strength of gravity

Question 46

Which of these mechanisms is NOT thought to be significant in the formation of new stars in the interstellar medium?

A) heating of an interstellar cloud by concentrated beams of neutrinos from nearby stars
B) compression of cold interstellar gas by radiation pressure from light from very bright stars
C) condensation of matter by the shock wave from a nearby supernova
D) collision of two cold interstellar clouds

Question 47

Which of these mechanisms is thought to be ineffective and inefficient in the triggering of star birth in molecular clouds?

A) gravitational contraction of a hot gas cloud
B) collisions between two interstellar clouds
C) supernova explosions and the resultant shock waves
D) radiation pressure from the intense UV radiation from hot stars

Question 48

The Jeans instability describes the

A) explosion of a star at the end of its life, the supernova phenomenon.
B) overcoming of gas pressure by self-gravity in a cold and dense interstellar cloud, to form a star.
C) conditions under which sufficient numbers of neutrinos can trigger the collapse of an interstellar cloud.
D) expansion of a gas cloud after gravitational contraction because of buildup of great heat within the cloud from gravitational potential energy.

Question 49

The distinctive color of a reflection nebula is

A) light of all colors predominantly in the red part of the spectrum, emitted by cool stars and reflected by crystals of water ice surrounding the stars.
B) several specific colors, resulting from fluorescence of atoms excited by ultraviolet radiation emitted by hot stars.
C) blue, caused by the scattering of light from dust grains.
D) red, resulting from the emission of light from hydrogen gas.

Question 50

The group of stars that is formed when a giant molecular cloud collapses is called a(n)

A) open cluster.
B) galaxy.
C) constellation.
D) gravitational lens.

Question 51

The distinct blue color of the nebulosity around stars in young clusters such as the Pleiades (see Figure 13-4 in the text) is caused by

A) atoms of gas emitting light by fluorescence, having been excited by ultraviolet radiation from hot stars.
B) light emitted by interstellar gases but Doppler-shifted by motion toward the observer.
C) starlight reflected by blue-colored interstellar material.
D) starlight scattered and reflected by small dust grains in the interstellar material.

Question 52

What condition is considered sufficient for an interstellar cloud to collapse and form a star or stars (i.e., if this condition holds then the cloud has to collapse)?

A) The cloud must be alone in space (far from stars and other interstellar clouds).
B) Gravity must dominate gas pressure inside the cloud.
C) Gravity must be strong enough to reach all parts of the cloud.
D) The cloud must be cooler than 100 K.

Question 53

The Horsehead Nebula in Orion (see Figure 13-5 in the text) is a distinct dark region surrounded by brighter regions. The Horsehead is an example of

A) an emission nebula.
B) a black hole.
C) a Bok gobule.
D) a dark nebula.

Question 54

Dark nebulae are extreme examples of

A) interstellar extinction.
B) interstellar reddening.
C) emission nebulae.
D) polycyclic aromatic hydrocarbons (PAHs).

Question 55

How do massive stars normally end their lives?

A) Massive stars gradually shrink to the size of Earth.
B) Astronomers don't know how massive stars normally end their lives since their lifetimes are longer than the age of the universe.
C) Massive stars collapse and become black holes.
D) Massive stars explode.

Question 56

The MOST likely places in which stars and planetary systems are forming in the universe are

A) the centers of galaxies.
B) nebulae composed of dense gas and dust.
C) regions surrounding quasars.
D) the rarified space between galaxies.

Question 57

In photographs, the Pleiades open star cluster is surrounded by a bluish haze (see Figure 13-4 in the text). What causes this blue light?

A) starlight scattered from interstellar dust in the star cluster
B) starlight scattered by the light-sensitive grains in the photographic plate when the picture was taken
C) shock waves losing energy to interstellar gas in the star cluster, causing the atoms to emit light
D) starlight absorbed and reemitted by interstellar gas in the star cluster

Question 58

Which of these statements about open star clusters is TRUE?

A) Open star clusters slowly condense into globular clusters as the stars drive off the remaining interstellar dust and gas.
B) One star in an open cluster eventually undergoes a supernova explosion that quickly disperses the other stars.
C) As open star clusters slowly condense, their residual rotation spins them into a flat pancake shape and they become spiral galaxies.
D) The motions of individual stars are such that all open clusters eventually disperse.

Question 59

New stars are formed from

A) hot supernova remnants.
B) activity around black holes in the centers of galaxies.
C) huge, cool dust and gas clouds.
D) pure energy in free space.

Question 60

There are several mechanisms that can trigger star formation in a cold, dark nebula. In each mechanism, the key to star formation is

A) bathing the cold, dark nebula in ultraviolet radiation and sweeping away some of the colder material.
B) compressing the gas and dust so that gravitation will overcome the gas pressure.
C) heating the gas so that gas pressure will overcome gravitation.
D) subjecting the dark nebula to an intense magnetic field so that supersonic jets will form.

Question 61

An open cluster has

A) a few hundred members, often very young and still embedded in the gas and dust from which they were formed.
B) hundreds of thousands of members, all very old, surrounded by very little interstellar gas and dust.
C) a few dozen members, the remnant of a globular cluster of stars from which most of the members have escaped.
D) many thousands of members of different ages.

Question 62

Protostars, when they first form from the interstellar medium, are usually

A) very bright in ultraviolet light due to numerous flares that are hotter and brighter than solar flares.
B) detected by emission lines in their visible spectra, emitted by gas being blown off their surfaces into space.
C) easily detected because their light ionizes the surrounding interstellar gas, or reflection nebulae.
D) hidden from sight by dust clouds that emit infrared radiation.

Question 63

Protostars are slowly

A) expanding at the surface while the core contracts.
B) contracting and heating up.
C) heating up and expanding.
D) contracting and cooling.

Question 64

The major source of energy in the pre-main-sequence life of the Sun was

A) nuclear fusion.
B) burning of carbon atoms.
C) gravitation.
D) nuclear fission.

Question 65

Parts of a supernova remnant become visible

A) because of radioactive elements that were created in the supernova and carried along with the remnant.
B) when large hot stars form within the gas and dust of the remnant and emit radiation, which excites the remaining gas.
C) when they collide with other clouds of gas and dust.
D) when they interact with the galaxy's strong magnetic field.

Question 66

In which one of these locations are clumps of gas MOST likely to be collapsing to form stars?

A) outer part of the solar system
B) globular cluster
C) reflection nebulae
D) giant molecular clouds

Question 67

The solar system could have formed from a

A) nonrotating Bok globule with a relatively low density.
B) rotating Bok globule with a relatively low density.
C) nonrotating Bok globule with a relatively high density.
D) rotating Bok globule with a relatively high density.

Question 68

Star formation takes place in

A) giant molecular clouds.
B) globular clusters.
C) blue reflection nebulae.
D) hot, turbulent gas thrown out in a supernova explosion.

Question 69

Where are protostars MOST likely to form?

A) emission nebulae
B) reflection nebulae
C) dark nebulae
D) planetary nebulae

Question 70

Protostars are

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

Question 71

The Cygnus Loop Nebula is characterized by having an arched, shell-like appearance. The Cygnus Loop is a

A) dark nebula.
B) reflection nebula.
C) supernova remnant.
D) giant molecular cloud.

Question 72

In order to produce protoplanets around a new star within a condensing interstellar cloud, a necessary condition seems to be that the cloud must

A) be rotating.
B) have a relatively high temperature.
C) have no rotational motion at all.
D) contain a high fraction of its mass as dust.

Question 73

What is believed to be the MOST important factor determining whether a collapsing region (dense core) in an interstellar cloud becomes a single-star or a multiple-star system?

A) fraction of heavy elements in the cloud
B) temperature
C) mass of the collapsing region
D) amount of rotation (spin)

Question 74

What is a protostar?

A) sphere of gas after collapse from an interstellar cloud but before nuclear reactions have begun
B) small interstellar cloud before it collapses to become a star
C) star near the end of its life before it explodes as a supernova
D) shell of gas left behind from the explosion of a star as a supernova

Question 75

Where in the universe would one look for a protostar?

A) near black holes
B) in dense dust and gas clouds
C) in the empty space between galaxies
D) in globular clusters of stars

Question 76

The source of MOST of a protostar's heat is

A) gravitational energy released as the protostar expands.
B) nuclear reactions in its core converting helium to carbon and oxygen.
C) gravitational energy released as the star contracts.
D) nuclear reactions in its core converting hydrogen into helium.

Question 77

Which range of electromagnetic radiation is MOST useful for observing newborn protostars in their gas and dust nebulae?

A) infrared
B) visible
C) highly penetrating X-ray
D) radio

Question 78

How does a dense core collapse to become a star?

A) The innermost part collapses first; then the outer part is drawn in by the gravity of the inner part.
B) The collapse is turbulent and chaotic, with no overall pattern.
C) The outer, less dense part falls in first and its weight accelerates the collapse of the inner part.
D) All parts of the cloud accelerate inward more or less smoothly and evenly.

Question 79

At what stage in its life does a star pass through the protostar phase?

A) while it is converting hydrogen into helium in its core
B) when it is expanding in size as a red giant or supergiant
C) after nuclear reactions end in its core but before the red giant phase
D) after dense core collapse but before nuclear reactions begin in its core

Question 80

Accretion of matter in an interstellar cloud leads to

A) a supernova explosion, since accretion is a nuclear process.
B) explosion of this matter when it is attracted to and falls onto the surfaces of stars.
C) the formation of molecules from atomic gases.
D) a protostar.