Question 1

Typical gas temperatures in dark Bok globules, the birthplaces of stars, are:

Accepted Answer

A) just below freezing, at -3°C or 270 K. 
B) 100 K. 
C) 10 K. 
D) just above that of the cosmic background radiation, at 3.5 K. 
A) just below freezing, at -3°C or 270 K. 
B) 100 K. 
C) 10 K. 
D) just above that of the cosmic background radiation, at 3.5 K.

Question 2

Astronomers use millimeter wavelength radiation to find giant molecular clouds. What is the source of this millimeter radiation?

Accepted Answer

A) vibrations of the hydrogen atoms in the H2 molecule, the most abundant molecule in giant molecular clouds 
B) emissions from the hot O and B stars newly formed in giant molecular clouds 
C) shock waves formed when solar winds from newly formed stars collide with the gas in giant molecular clouds 
D) rotational energy changes in the CO molecule 
A) vibrations of the hydrogen atoms in the H2 molecule, the most abundant molecule in giant molecular clouds 
B) emissions from the hot O and B stars newly formed in giant molecular clouds 
C) shock waves formed when solar winds from newly formed stars collide with the gas in giant molecular clouds 
D) rotational energy changes in the CO molecule

Question 3

A particular, dense interstellar cloud is about 100 pc across and contains 2 million M ? of material. This cloud would probably be classified as a:

Accepted Answer

A) giant molecular cloud. 
B) cocoon nebula. 
C) Herbig-Haro object. 
D) Bok globule. 
A) giant molecular cloud. 
B) cocoon nebula. 
C) Herbig-Haro object. 
D) Bok globule.

Question 4

Which of the following is NOT a required condition for gas and dust to begin to condense into a protostar?

Accepted Answer

A) low mutual rotation, to avoid spin-off of material from the forming star 
B) low temperature, to maintain low gas pressure in the cloud 
C) higher than average density, to ensure that gravitational attraction is enhanced 
D) high temperature, to ensure that gas atoms and dust particles collide with sufficient energy to stick together 
A) low mutual rotation, to avoid spin-off of material from the forming star 
B) low temperature, to maintain low gas pressure in the cloud 
C) higher than average density, to ensure that gravitational attraction is enhanced 
D) high temperature, to ensure that gas atoms and dust particles collide with sufficient energy to stick together

Question 5

We know that the Pleiades star cluster is relatively old, about 50 million years old. Each of the following helps us to date the Pleiades EXCEPT ONE. Which is the EXCEPTION?

Accepted Answer

A) The Pleiades is not surrounded by an H II region. 
B) The stars are nearly all on the main sequence. 
C) The most massive stars have not yet evolved off the main sequence. 
D) The O and B star association originally formed as part of the cluster is still present. 
A) The Pleiades is not surrounded by an H II region. 
B) The stars are nearly all on the main sequence. 
C) The most massive stars have not yet evolved off the main sequence. 
D) The O and B star association originally formed as part of the cluster is still present.

Question 6

A main-sequence star begins its life with a certain amount of mass, but it eventually evolves into a giant star hundreds of times as large as it was when it was on the main sequence. How is this possible?

Accepted Answer

A) Nuclear reactions result in additional mass. 
B) Stellar evolution involves mergers of stars-and that provides the additional mass needed for expansion. 
C) Additional mass is not needed. As the star expands its density decreases. 
D) Stars are constantly being bombarded by dust, as are the planets; this provides the additional mass needed for expansion. 
A) Nuclear reactions result in additional mass. 
B) Stellar evolution involves mergers of stars-and that provides the additional mass needed for expansion. 
C) Additional mass is not needed. As the star expands its density decreases. 
D) Stars are constantly being bombarded by dust, as are the planets; this provides the additional mass needed for expansion.

Question 7

Which of the following trigger mechanisms for the initiation of stellar formation in gas and dust clouds produces many low-mass stars and only a few high-mass, hot O and B stars?

Accepted Answer

A) passage of the cloud through a black hole 
B) compression caused by the passage of the cloud through a galactic spiral arm 
C) shock wave from a supernova explosion 
D) gravitational condensation of the cloud 
A) passage of the cloud through a black hole 
B) compression caused by the passage of the cloud through a galactic spiral arm 
C) shock wave from a supernova explosion 
D) gravitational condensation of the cloud

Question 8

At what wavelengths have astronomers mapped and studied the distribution of giant molecular clouds in space?

Accepted Answer

A) long radio wavelengths, greater than 20 cm, because molecules are very efficient radio emitters 
B) visible light, using photography 
C) UV, because molecules are efficient UV emitters and the clouds are hot 
D) millimeter wavelengths, using radio telescopes 
A) long radio wavelengths, greater than 20 cm, because molecules are very efficient radio emitters 
B) visible light, using photography 
C) UV, because molecules are efficient UV emitters and the clouds are hot 
D) millimeter wavelengths, using radio telescopes

Question 9

What causes the characteristic red color of an emission nebula?

Accepted Answer

A) thermal (blackbody) radiation with its peak in the visible red part of the spectrum 
B) electrons jumping from the n = 2 energy state to the n = 3 energy state in hydrogen atoms 
C) electrons jumping from the n = 3 energy state to the n = 2 energy state in hydrogen atoms 
D) electrons jumping from the n = 2 energy state to the n = 1 energy state in hydrogen atoms 
A) thermal (blackbody) radiation with its peak in the visible red part of the spectrum 
B) electrons jumping from the n = 2 energy state to the n = 3 energy state in hydrogen atoms 
C) electrons jumping from the n = 3 energy state to the n = 2 energy state in hydrogen atoms 
D) electrons jumping from the n = 2 energy state to the n = 1 energy state in hydrogen atoms

Question 10

What is the predominant atomic or molecular mechanism that produces the light we see from emission nebulae?

Accepted Answer

A) Radio energy from embedded stars excites atoms to high atomic states, and spectral lines are produced as these atoms return to their unexcited states. 
B) Radiation from nearby stars heats the gas, and the gas then emits a continuum spectrum appropriate to its temperature. 
C) Photons of UV and X radiation from very hot embedded stars accelerate electrons by collision, and these accelerating electrons radiate at all wavelengths. 
D) UV light from hot stars ionizes atoms, and the subsequent recombination of electrons with these ions produces spectral lines. 
A) Radio energy from embedded stars excites atoms to high atomic states, and spectral lines are produced as these atoms return to their unexcited states. 
B) Radiation from nearby stars heats the gas, and the gas then emits a continuum spectrum appropriate to its temperature. 
C) Photons of UV and X radiation from very hot embedded stars accelerate electrons by collision, and these accelerating electrons radiate at all wavelengths. 
D) UV light from hot stars ionizes atoms, and the subsequent recombination of electrons with these ions produces spectral lines.

Question 11

The ionization energy of hydrogen is 13.6 electron volts or 2.18 × 10-18 J. A photon emitted from a hot O or B star can ionize hydrogen if it has a wavelength no greater than:

Accepted Answer

A) 2.18 × 10-18 m. 
B) 5.69 × 10-11 m. 
C) 6.54 × 10-10 m. 
D) 9.12 × 10-8 m. 
A) 2.18 × 10-18 m. 
B) 5.69 × 10-11 m. 
C) 6.54 × 10-10 m. 
D) 9.12 × 10-8 m.

Question 12

What does a cocoon nebula do to deserve its name?

Accepted Answer

A) Its gravity prevents the evolving protostar from expanding rapidly and dissipating as a consequence of its very high temperature. 
B) It enhances the visibility of a faint protostar by scattering the light from it, much as a mist spreads and enlarges the light from street lamps. 
C) It hides protostars by absorbing the very large amounts of visible light emitted by them but reemits this energy as infrared radiation. 
D) It absorbs all the electromagnetic radiation from protostars, rendering them invisible until they have melted and evaporated the dust and ionized the gas in the nebula. 
A) Its gravity prevents the evolving protostar from expanding rapidly and dissipating as a consequence of its very high temperature. 
B) It enhances the visibility of a faint protostar by scattering the light from it, much as a mist spreads and enlarges the light from street lamps. 
C) It hides protostars by absorbing the very large amounts of visible light emitted by them but reemits this energy as infrared radiation. 
D) It absorbs all the electromagnetic radiation from protostars, rendering them invisible until they have melted and evaporated the dust and ionized the gas in the nebula.

Question 13

What would be the temperature inside a dense core that is about to collapse to form a star?

Accepted Answer

A) 10 K 
B) 1000 K 
C) less than 1 K 
D) 100 K 
A) 10 K 
B) 1000 K 
C) less than 1 K 
D) 100 K

Question 14

An object that is formed by the gravitational collapse of an interstellar cloud, and is slowly contracting and heating up to become a star, is called a:

Accepted Answer

A) Herbig-Haro object. 
B) red giant star. 
C) cocoon nebula. 
D) protostar. 
A) Herbig-Haro object. 
B) red giant star. 
C) cocoon nebula. 
D) protostar.

Question 15

In photographs, the Pleiades open star cluster is surrounded by a bluish haze (See Figure 18-23 of Universe, 11th ed.(in the text)). What causes this blue light?

Accepted Answer

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

Question 16

What process makes an emission nebula glow?

Accepted Answer

A) electric currents caused by the flow of ionized gas, heating dust particles 
B) free electrons emitting light as they pass close to, and are accelerated by, positively charged ions 
C) light emitted when electrons jump between energy states in hydrogen atoms 
D) high-energy electrons spiraling along magnetic field lines 
A) electric currents caused by the flow of ionized gas, heating dust particles 
B) free electrons emitting light as they pass close to, and are accelerated by, positively charged ions 
C) light emitted when electrons jump between energy states in hydrogen atoms 
D) high-energy electrons spiraling along magnetic field lines

Question 17

When a dark nebula collapses to form a group of stars, what is this stellar group called?

Accepted Answer

A) a galaxy 
B) a constellation 
C) an open cluster 
D) a globular cluster 
A) a galaxy 
B) a constellation 
C) an open cluster 
D) a globular cluster

Question 18

Compared to the air we breathe, how dense is the matter within a typical nebula, such as that in Orion, where star formation is taking place?

Accepted Answer

A) about 10-16 times as dense 
B) about 10-19 times as dense 
C) about the same density-otherwise self-gravity could not form stars from this material 
D) about 10-10 times as dense 
A) about 10-16 times as dense 
B) about 10-19 times as dense 
C) about the same density-otherwise self-gravity could not form stars from this material 
D) about 10-10 times as dense

Question 19

Which of the following processes does NOT lead to star formation?

Accepted Answer

A) compression of a cold interstellar gas-and-dust cloud by the shock wave from a nearby supernova explosion 
B) compression waves passing through interstellar clouds in the arms of spiral galaxies 
C) compression of a hot interstellar gas cloud by its own gravity 
D) compression of a cold part of a large interstellar cloud by another part that contains a group of hot, young, massive stars 
A) compression of a cold interstellar gas-and-dust cloud by the shock wave from a nearby supernova explosion 
B) compression waves passing through interstellar clouds in the arms of spiral galaxies 
C) compression of a hot interstellar gas cloud by its own gravity 
D) compression of a cold part of a large interstellar cloud by another part that contains a group of hot, young, massive stars

Question 20

Star clusters of the same type and structure appear to become fainter than expected, on the basis of the inverse-square law alone, as distance from the Sun increases. This is because:

Accepted Answer

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

Exam 18: The Birth of Stars

Typical gas temperatures in dark Bok globules, the birthplaces of stars, are:

Astronomers use millimeter wavelength radiation to find giant molecular clouds. What is the source of this millimeter radiation?

A particular, dense interstellar cloud is about 100 pc across and contains 2 million M ? of material. This cloud would probably be classified as a:

Which of the following is NOT a required condition for gas and dust to begin to condense into a protostar?

We know that the Pleiades star cluster is relatively old, about 50 million years old. Each of the following helps us to date the Pleiades EXCEPT ONE. Which is the EXCEPTION?

A main-sequence star begins its life with a certain amount of mass, but it eventually evolves into a giant star hundreds of times as large as it was when it was on the main sequence. How is this possible?

Which of the following trigger mechanisms for the initiation of stellar formation in gas and dust clouds produces many low-mass stars and only a few high-mass, hot O and B stars?

At what wavelengths have astronomers mapped and studied the distribution of giant molecular clouds in space?

What causes the characteristic red color of an emission nebula?

What is the predominant atomic or molecular mechanism that produces the light we see from emission nebulae?

The ionization energy of hydrogen is 13.6 electron volts or 2.18 × 10-18 J. A photon emitted from a hot O or B star can ionize hydrogen if it has a wavelength no greater than:

What does a cocoon nebula do to deserve its name?

What would be the temperature inside a dense core that is about to collapse to form a star?

An object that is formed by the gravitational collapse of an interstellar cloud, and is slowly contracting and heating up to become a star, is called a:

In photographs, the Pleiades open star cluster is surrounded by a bluish haze (See Figure 18-23 of Universe, 11th ed.(in the text)). What causes this blue light?

What process makes an emission nebula glow?

When a dark nebula collapses to form a group of stars, what is this stellar group called?

Compared to the air we breathe, how dense is the matter within a typical nebula, such as that in Orion, where star formation is taking place?

Which of the following processes does NOT lead to star formation?

Star clusters of the same type and structure appear to become fainter than expected, on the basis of the inverse-square law alone, as distance from the Sun increases. This is because:

Astronomy and the Universe

Knowing the Heavens

Eclipses and the Motion of the Moon

Gravitation and the Waltz of the Planets

The Nature of Light

Optics and Telescopes

Comparative Planetology I: Our Solar System

Comparative Planetology II: the Origin of Our Solar System

The Living Earth

Our Barren Moon

Mercury, Venus, and Mars: Terrestrial, yet Unique

Jupiter and Saturn: Lords of the Planets

Jupiter and Saturns Satellites of Fire and Ice

Uranus, Neptune, Pluto, and the Kuiper Belt: Remote Worlds

Asteroids, Comets, and Impacts

Our Star, the Sun

The Nature of the Stars

Stellar Evolution: on and After the Main Sequence

Stellar Evolution: The Death of Stars

Stellar Remnants: Neutron Stars and Black Holes

Our Galaxy

Galaxies

Quasars and Active Galaxies

Cosmology: The Origin and Evolution of the Universe

Exploring the Early Universe

The Search for Extraterrestrial Life

Filters

The ionization energy of hydrogen is 13.6 electron volts or 2.18 × 10^-18 J. A photon emitted from a hot O or B star can ionize hydrogen if it has a wavelength no greater than: