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Astronomy exam 3 > Chapter 9 > Flashcards

Chapter 9 Flashcards

1
Q

With respect to visible wavelength observations in the interstellar medium, select all of the correct statements from the following list.

Most interstellar dust is hydrogen.

Most interstellar gas and dust is concentrated in the plane of our Milky Way Galaxy.

Interstellar dust absorbs the shorter wavelengths of starlight, leaving the longer, redder wavelengths.

Reflection nebulae shine for reasons similar to those that make our sky blue.

Absorption lines from distant stars tend to be very narrow, due to repeated passages through interstellar gas.

Emission nebulae glow from their own energy.

Dark nebulae block out starlight.

A

Most interstellar gas and dust is concentrated in the plane of our Milky Way Galaxy.

Reflection nebulae shine for reasons similar to those that make our sky blue.

Dark nebulae block out starlight.

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2
Q

With respect to the observation of the interstellar medium at wavelengths longer and shorter than that of visible light, select all of the correct statements from the following list.

Giant molecular clouds observed at radio wavelengths are almost pure hydrogen.

Material observed at wavelengths longer than that of visible light is usually cool.

The source of hot gas observed at X-ray wavelengths is not known.

Interstellar dust is observed at ultraviolet wavelengths.

The 21-cm radio observations are of neutral hydrogen.

Much interstellar dust between stars is not visible.

All interstellar material is
cool.

A

Material observed at wavelengths longer than that of visible light is usually cool.

The 21-cm radio observations are of neutral hydrogen.

Much interstellar dust between stars is not visible.

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3
Q

Based on interactions between stars and the matter between them, select all of the correct statements from the following list.

Molecular clouds are where stars are born.
Much interstellar dust comes from stellar atmospheres.

Coronal gas is ejected from supernova explosions.

Supernova explosions cause currents in the interstellar medium.

The intercloud medium is cool.

Molecular clouds are of very low density.

Clouds of neutral hydrogen are huge.

A

Molecular clouds are where stars are born.
Much interstellar dust comes from stellar atmospheres.

Coronal gas is ejected from supernova explosions.

Supernova explosions cause currents in the interstellar medium.

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4
Q

The dust in a molecular cloud has a temperature of about 80 K. At what wavelength in nm does it emit the maximum energy? (Hint: Consider blackbody radiation.)

A

36,250

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5
Q

If the total extinction through a dark nebula is 9 magnitudes, what fraction of photons makes it through the cloud? (Hint: Consider the definition of the magnitude scale.)

A

0.00025

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6
Q

What is responsible for the extinction and reddening of starlight?

A

dust grains with diameters near the wavelength of light

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7
Q

Which wavelengths of starlight ionize the cool hydrogen atoms in the interstellar medium?

A

ultraviolet

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8
Q

What type of spectra is obtained from a reflection nebula?

A

absorption line spectra

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9
Q

Why are interstellar absorption lines so much thinner than stellar absorption lines?

A

Most interstellar gas is at a lower temperature than that of stellar atmospheres and the density of interstellar gas is less than that of stellar atmospheres.

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10
Q

What do forbidden lines tell us about the gas in the interstellar medium?

A

The density of interstellar gas is very low.

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11
Q

The abundances of chemical elements in the interstellar medium, based on absorption lines, are the same as that of the sun for hydrogen, carbon, and oxygen. However, calcium and iron have a lower abundance in the interstellar medium than on the sun. Why?

A

Calcium and iron are stored in dust grains of the interstellar medium.

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12
Q

Hot emission nebulae are somewhat red, and cool reflection nebulae are blue. Why are these colors different from what Wien’s law tells us about the radiation emitted by a black body?

A

All of these choices are correct.

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13
Q

How can the HII intercloud medium be much hotter than neutral HI clouds and yet have about the same pressure?

A

The HI clouds have greater density.

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14
Q

What wavelength band is observed to map the distribution of carbon monoxide (CO) molecules?

A

radio

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15
Q

Why is locating the tracer CO molecule important in the study of the interstellar medium?

A

It gives the location of molecular hydrogen.

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16
Q

What type of hydrogen emits 21 - cm radiation?

A

cool atomic hydrogen

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17
Q

At what wavelength can we best observe the hot coronal gas component of the interstellar medium?

A

X-ray

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18
Q

What effect do dust grains have on the gas in a giant molecular cloud?

A

Dust grains shield molecules from destructive ultraviolet radiation and gas atoms can find partners on the surfaces of dust grains and form molecules.

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19
Q

Which of the following lists the four components of the interstellar medium in order from low to high TEMPERATURE?

A

molecular cloud, HI cloud, HII intercloud medium, coronal gas

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20
Q

Which of the following lists the four components of the interstellar medium in order from low to high DENSITY?

A

coronal gas, HII intercloud medium, HI cloud, molecular cloud

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21
Q

Carbon monoxide (CO) molecules absorb thermal energy through collisions with other molecules inside giant molecular clouds. Each CO molecule de-excites by emitting a radio photon with a wavelength of 2.6 mm. What affect does this process have on the giant molecular cloud?

A

It cools the cloud.

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22
Q

What affect does a supernova event have on the interstellar medium?

A

All of these choices are correct.

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23
Q

The best vacuum chambers on Earth can reach densities of about 1,000,000 atoms per cubic centimeter. Which of the four components of the interstellar medium has lower densities than such a chamber?

A

the hot coronal gas, HII intercloud medium, HI clouds, and molecular clouds

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24
Q

What is found in the spaces between the stars?

A

clouds of gas and dust

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25
Q

What evidence is there of what occupies the space between stars?

A

emissions from ionized gas and dimming of light from distant stars passing through dust

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26
Q

Which is the same as an HII region?

A

ionized H gas cloud around a star

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27
Q

Which looks blueish in color?

A

a reflection nebula

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28
Q

Which looks pinkish in color?

A

an ionized H gas cloud around a star

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29
Q

Which is scattering shorter wavelength visual light?

A

interstellar dust

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30
Q

What is a forbidden spectral line?

A

a line from a transition that is almost never observed in laboratories on Earth

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31
Q

What does the observation of forbidden lines in interstellar clouds tell astronomers?

A

Interstellar clouds are of very low density.

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32
Q

What causes the blueish color of reflection nebulae?

A

All of these choices are correct.

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33
Q

What effect does interstellar dust have on the light from distant stars?

A

It scatters away the shorter wavelengths and causes extinction.

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34
Q

How does light from distant stars look different than light from nearby stars?

A

It looks both dimmer and redder.

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35
Q

Compared to nearby stars, the visual spectra of very distant stars

A

have additional narrow absorption lines.

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36
Q

What is the reason for the narrowness of the interstellar absorption lines in the spectra of very distant stars?

A

Interstellar gas is of very low density.

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37
Q

What would happen if light from a distant star passed through hot interstellar gas?

A

They would be no different than normal. It is density, not temperature, that affects the width of spectral lines.

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38
Q

Which of the following has the highest temperature?

A

intercloud medium

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39
Q

Which has the highest density?

A

molecular clouds

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40
Q

How can HI clouds and the intercloud medium have similar pressures?

A

HI clouds are much cooler but more dense than the intercloud medium.

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41
Q

What does the shape of the 21-cm radio emission line of neutral hydrogen tell you about the interstellar medium?

A

its density

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42
Q

Coronal gas in our galaxy is ________ produced by ________.

A

partially ionized gas in the interstellar medium; energy from hot stars and supernova explosions

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43
Q

The dark area in the picture is doing which of the following?

A

blocking out light from nearby stars

44
Q

The pink area in the picture is doing which of the following?

A

absorbing light from nearby stars and emitting it again

45
Q

What is the pink area in the above picture?

A

emission nebula

46
Q

Of the following components of the interstellar medium, which has the longest primary wavelengths at which they are observed or discovered?

A

neutral HI between stars

47
Q

Of the following components of the interstellar medium, which is observed to be hottest?

A

coronal gas

48
Q

Of the following components of the interstellar medium, which is observed to be most dense?

A

molecular clouds

49
Q

Based on the creation of stars from the interstellar medium, select all of the correct statements from the following list.

Most protostars can be detected by the jets of gas they emit.

Gas will heat up as it collapses.

There is no evidence that star formation is a continuous process.

Protostars are observable at visible wavelengths.

Gravity causes molecular clouds to contract.

There is no resistance to the contraction in a molecular cloud caused by gravity.

Stars are born from the gas and dust of the interstellar medium.

A

Gas will heat up as it collapses.

Gravity causes molecular clouds to contract.

Stars are born from the gas and dust of the interstellar medium.

50
Q

Based on the source of stellar energy, select all of the correct statements from the following list.

The CNO cycle requires a higher temperature than the proton-proton cycle.

The sun’s energy comes from the CNO cycle.

A helium atom is more massive than four hydrogen atoms.

More massive stars make energy with the proton-proton cycle.

Many stars make energy with the proton-proton cycle.

The leftover mass in both the proton-proton cycle and the CNO cycle is converted to energy.

The CNO cycle is more efficient than the proton-proton cycle.

A

The CNO cycle requires a higher temperature than the proton-proton cycle.
Many stars make energy with the proton-proton cycle.

The leftover mass in both the proton-proton cycle and the CNO cycle is converted to energy.

The CNO cycle is more efficient than the proton-proton cycle.

51
Q

With respect to stellar structure, select all of the correct statements from the following list.

Energy in a star flows from the core to the surface.

Less massive stars produce energy with the CNO cycle.

Conduction is an important method of energy transport in stars.

The weight pressing down on a layer of gas in a star is balanced by the pressure in the gas.

More massive stars produce energy with the proton-proton cycle.

Stars are hotter in their cores than on their surfaces.

The interior of the lowest-mass stars transfers energy mostly through convection.

A

Energy in a star flows from the core to the surface.

The weight pressing down on a layer of gas in a star is balanced by the pressure in the gas.

Stars are hotter in their cores than on their surfaces.

The interior of the lowest-mass stars transfers energy mostly through convection.

52
Q

Based on the Orion Nebula, select all of the correct statements from the following list.

Many stars in the Orion Nebula are surrounded by disks of gas and dust.

There is evidence that the stars in the Orion Nebula are young.

The Orion Nebula is an emission nebula.

The Orion Nebula shines only from reflection of the light from the stars within it.

Evidence of active star formation is found at ultraviolet wavelengths.

There is much more of the Orion Nebula than is visible.

The fact that many stars in the Orion Nebula are surrounded by disks of gas and dust proves that these disks are long-lasting.

A

Many stars in the Orion Nebula are surrounded by disks of gas and dust.

There is evidence that the stars in the Orion Nebula are young.

The Orion Nebula is an emission nebula.

There is much more of the Orion Nebula than is visible.

53
Q

The ring ejected by the supergiant star in the figure has a radius of about 5 seconds of arc. If the cluster is 18,000 light years from Earth, what is the radius of the ring in light years?

A

0.436

54
Q

The figure shows the CNO nuclear reactions in stars from top to bottom. In the CNO series of reactions, the net result of the reaction is the conversion of four ____ nuclei into one _____ nucleus.

A

1H; 4He

55
Q

The figure shows the CNO nuclear reactions in stars from top to bottom. In the CNO series of reactions, the number of ______ nuclei is decreased, the number of ______ nuclei stays the same, and the number of ______ is increased.

A

1H; 12C; 4He

56
Q

In which component of the interstellar medium do new stars form?

A

molecular clouds

57
Q

What force causes the contraction of a cloud of interstellar matter to form a star?

A

gravitational force

58
Q

Which factor resists the contraction of a cloud of interstellar matter?

A

All of these choices are correct.

59
Q

What triggers the gravitational collapse of material inside a molecular cloud?

A

a passing shock wave

60
Q

What is the source of a shock wave that passes through a molecular cloud and triggers star formation?

A

All of these choices are correct.

61
Q

What happens to the temperature and density inside a collapsing protostar?

A

Temperature and density both increase.

62
Q

What is a protostar’s energy source?

A

gravitational energy

63
Q

What characteristic of the collapsing cloud that forms a protostar allows it to also form a protostellar disk?

A

rotation

64
Q

At what wavelengths can we observe the early stages of protostar formation?

A

infrared

65
Q

What eventually halts the slow contraction of a newly forming star?

A

nuclear fusion

66
Q

The gestation period for humans is 40 weeks. What was the gestation period for our sun? That is, how much time passed between the onset of gravitational collapse and the sun’s arrival on the main sequence?

A

about 30 million years

67
Q

According to the figure shown here, the protosun was cooler yet much more luminous than the sun is now. How can this be true?

A

The protosun was much larger.

68
Q

What evidence do we have that the Orion region is actively forming stars?

A

All of these choices are correct.

69
Q

How does the CNO cycle differ from the proton-proton chain?

A

The CNO cycle requires a higher temperature than the proton-proton chain and the rate of the CNO cycle is more temperature sensitive than the proton-proton chain.

70
Q

Examine this figure that shows the steps of the CNO cycle. How does the energy produced in one cycle of the CNO cycle compare to that produced in one cycle of the proton-proton chain?

A

The CNO cycle produces the same amount of energy per cycle as the proton-proton chain.

71
Q

Which stars produce most of their energy by the CNO cycle?

A

upper main-sequence stars

72
Q

Which method of energy transport is NOT important inside most stars?

A

conduction

73
Q

How does the extreme temperature sensitivity of the CNO cycle affect a star’s interior?

A

The CNO cycle generation zone occupies a very small region and CNO cycle stars have convective cores and radiative envelopes.

74
Q

Examine this model of main-sequence stars of different masses. How does a seven-solar-mass star differ from a one-solar-mass star like the sun?

A

The convective and radiative zones are switched.

75
Q

What prevents the enormous amount of energy released from the fusion reactions at a star’s core from blowing the star apart?

A

gravity

76
Q

What would happen in the interior of a normal star if gravity were to shrink the star’s size a small amount?

A

All of these choices are correct.

77
Q

Where in the sun is the law of hydrostatic equilibrium at work?

A

at every point inside the sun

78
Q

Which is the cause of the contraction of a cloud of interstellar gas?

A

gravity

79
Q

Which does not resist the contraction of interstellar gas?

A

All of these resist the contraction

80
Q

Which is not a way that a giant molecular cloud can be triggered to collapse?

A

turbulence

81
Q

Which is a way that a giant molecular cloud can be triggered to collapse?

A

the spiral structure of a galaxy

82
Q

The Orion region contains massive, short-lived stars. Massive, short-lived stars are evidence of which of the following?

A

Strictly speaking, that star formation happened very recently.

83
Q

Jets of gas emitted from the center of dusty disks are evidence of which of the following?

A

That protostars really exist.

84
Q

Stars surrounded by short-lived disks of gas and dust are evidence of which of the following?

A

All of these choices are correct.

85
Q

As cold gas in interstellar space contracts, which of the following occurs?

A

All of these choices are correct.

86
Q

What are small nebulae that fluctuate in brightness called?

A

Herbig-Haro objects

87
Q

Which is evidence that protostars are surrounded by disks?

A

All of these choices are correct.

88
Q

Which is not a difference between the CNO cycle and the proton-proton cycle?

A

The CNO cycle produces a helium nucleus.

89
Q

Which is a similarity between the CNO cycle and the proton-proton cycle?

A

They both produce helium nuclei.

90
Q

Which is true about the cores of stars that use the CNO cycle?

A

They are small and convective.

91
Q

Which is true about the outer layers of stars that use the CNO cycle?

A

They are radiative only.

92
Q

Where in a star is energy generated?

A

the core

93
Q

How does energy get to the surface of a star?

A

it could be more than one of these, depending on the mass of the star

94
Q

How does a star’s energy get into space?

A

radiation

95
Q

The most massive stars use ______ to get energy to their surface.

A

radiation

96
Q

The least massive stars use ______ to get energy to their surface.

A

The least massive stars use ______ to get energy to their surface.

97
Q

At any layer in a star, the weight pressing down is _____ the pressure in the gas.

A

equal to

98
Q

At any layer in a star, the weight pressing down is balanced by the pressure in the gas. What is this state called?

A

hydrostatic equilibrium

99
Q

Which must be true for the equilibrium state of stars like our sun to be maintained?

A

The inner layers of the star must be hotter than the outer layers.

100
Q

The “thermostat” in a star is a relationship between which of the following?

A

pressure and temperature

101
Q

How does the “thermostat” of a star regulate nuclear fusion in the core?

A

All of these choices are correct.

102
Q

The star in the figure appears to be ejecting a jet of gas. What is happening to this star?

A

Infalling material in a disk around the star is interacting with the spinning star.

103
Q

This object is probably which of the following?

A

Herbig-Haro object

104
Q

Consider the three stars described here: Convection, Convection-Radiation, Radiation-Convection. The method of energy transfer is listed in order from the center of each star outward.

Which of these main-sequence stars transfers energy via radiation throughout most of its interior?

A

3.5 solar masses

105
Q

Consider the three stars described here: convection, convection-radiation, radiation-convection. The method of energy transfer is listed in order from the center of each star outward.

Which of these main-sequence stars gives off the most energy per second?

A

7 solar masses

Astronomy exam 3 (3 decks)

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