Question 1

An H II region looks red, just as the metal filaments in a toaster glow red when heated. Are these colors produced in the same way?

Accepted Answer

A) Yes, both come from the blackbody spectrum, described by Wien's law and the law of Stefan and Boltzmann. 
B) Not exactly, the metal spectrum peaks in the infrared, but there is enough spillover into the visible to make the object look red. The H II region's blackbody curve actually peaks in the red. 
C) No, the metal's red is produced by a blackbody curve. The H II region glows red because of a specific emission line in hydrogen. 
D) No, the H II region's red is produced by a blackbody curve. The metal glows red because of a specific emission line in iron. 
A) Yes, both come from the blackbody spectrum, described by Wien's law and the law of Stefan and Boltzmann. 
B) Not exactly, the metal spectrum peaks in the infrared, but there is enough spillover into the visible to make the object look red. The H II region's blackbody curve actually peaks in the red. 
C) No, the metal's red is produced by a blackbody curve. The H II region glows red because of a specific emission line in hydrogen. 
D) No, the H II region's red is produced by a blackbody curve. The metal glows red because of a specific emission line in iron. C

Question 2

Some protostars, when they evolve onto the main sequence, employ radiation to carry material outward from the core to some region midway through the star. Convection then carries the energy outward to the surface. Which stars show this characteristic?

Accepted Answer

A) only the smallest, with masses less than about 0.4 M ? 
B) intermediate masses, from about 0.4 M ? up to about 4 M ? 
C) the largest, with masses above about 4 M ? 
D) all of them 
A) only the smallest, with masses less than about 0.4 M ? 
B) intermediate masses, from about 0.4 M ? up to about 4 M ? 
C) the largest, with masses above about 4 M ? 
D) all of them B

Question 3

When a carbon monoxide (CO) molecule emits a radio photon of 2.6-mm wavelength, what happens to the molecule?

Accepted Answer

A) The molecule changes its rate of rotation. 
B) An electron in the molecule "flips" or reverses its direction of spin with respect to the plane of the molecule. 
C) An electron in the molecule jumps to a lower orbit. 
D) An electron in the molecule jumps to a higher orbit. 
A) The molecule changes its rate of rotation. 
B) An electron in the molecule "flips" or reverses its direction of spin with respect to the plane of the molecule. 
C) An electron in the molecule jumps to a lower orbit. 
D) An electron in the molecule jumps to a higher orbit. A

Question 4

Suppose the light leaving a star has equal intensities in the blue and the red. The starlight passes through a dust cloud on its journey to Earth. When you observe the light reaching Earth you will find the:

Accepted Answer

A) blue part of the spectrum will be more intense than the red. 
B) red part of the spectrum will be more intense than the blue. 
C) blue and red intensities will still be equal, and they will be undiminished from the intensities that left the star. 
D) blue and red intensities will still be the same, although they will both be diminished from the intensities that left the star. 
A) blue part of the spectrum will be more intense than the red. 
B) red part of the spectrum will be more intense than the blue. 
C) blue and red intensities will still be equal, and they will be undiminished from the intensities that left the star. 
D) blue and red intensities will still be the same, although they will both be diminished from the intensities that left the star.

Question 5

How long does it take for a 1-M ? star to pass through the pre-main-sequence phase?

Accepted Answer

A) 100,000 years 
B) 10 million years 
C) 10,000 years 
D) 10 billion years 
A) 100,000 years 
B) 10 million years 
C) 10,000 years 
D) 10 billion years

Question 6

What is the difference between a giant molecular cloud and an H II region?

Accepted Answer

A) They are two names for the same thing. 
B) The hydrogen in a giant molecular cloud is in molecular form. The hydrogen in an H II region is in ionized atomic form. 
C) A giant molecular cloud is an H II region on a much larger scale. 
D) A giant molecular cloud is a bright spot within an H II region. 
A) They are two names for the same thing. 
B) The hydrogen in a giant molecular cloud is in molecular form. The hydrogen in an H II region is in ionized atomic form. 
C) A giant molecular cloud is an H II region on a much larger scale. 
D) A giant molecular cloud is a bright spot within an H II region.

Question 7

What is the relationship between stellar mass and position on the main sequence of the Hertzsprung-Russell diagram?

Accepted Answer

A) The most massive stars appear in the center of the main sequence while less massive main-sequence stars are brighter or dimmer than these stars as a consequence of their higher or lower temperatures. 
B) The more massive the star, the higher up on the main sequence the star will appear. 
C) The main sequence defines a line of stars whose masses are about 1 Mε , while stars of different masses appear on either side of the main sequence. 
D) The less massive the star, the higher up on the main sequence the star will appear. 
A) The most massive stars appear in the center of the main sequence while less massive main-sequence stars are brighter or dimmer than these stars as a consequence of their higher or lower temperatures. 
B) The more massive the star, the higher up on the main sequence the star will appear. 
C) The main sequence defines a line of stars whose masses are about 1 Mε , while stars of different masses appear on either side of the main sequence. 
D) The less massive the star, the higher up on the main sequence the star will appear.

Question 8

What is a proplyd?

Accepted Answer

A) a protoplanetary disk around a young star 
B) a protostar hidden inside a dense shell of dust 
C) a bright nebula formed in the bipolar outflow from a T Tauri star 
D) an amoeba-like creature thought to inhabit ethane lakes on Saturn's moon, Titan 
A) a protoplanetary disk around a young star 
B) a protostar hidden inside a dense shell of dust 
C) a bright nebula formed in the bipolar outflow from a T Tauri star 
D) an amoeba-like creature thought to inhabit ethane lakes on Saturn's moon, Titan

Question 9

How does a 15-M ? star evolve in the first 105 years after it becomes a protostar?

Accepted Answer

A) Its temperature remains relatively cool at about 4000 K, but its luminosity decreases by a factor of 100. 
B) Its brightness and temperature remain approximately constant as it stabilizes into a nuclear-heated star on the main sequence. 
C) Its brightness remains constant, while its surface temperature increases by a factor of 10. 
D) Its brightness increases by about a factor of 104, because its temperature increases by a factor of 10, moving it upward along the main sequence. 
A) Its temperature remains relatively cool at about 4000 K, but its luminosity decreases by a factor of 100. 
B) Its brightness and temperature remain approximately constant as it stabilizes into a nuclear-heated star on the main sequence. 
C) Its brightness remains constant, while its surface temperature increases by a factor of 10. 
D) Its brightness increases by about a factor of 104, because its temperature increases by a factor of 10, moving it upward along the main sequence.

Question 10

Some protostars, when they evolve onto the main sequence, employ convection to carry material outward from the core to some region midway through the star. Radiation then carries the energy outward to the surface. Which stars show this characteristic?

Accepted Answer

A) only the smallest, with masses less than about 0.4 M ? 
B) intermediate masses, from about 0.4M ? up to about 4 M ? 
C) the largest, with masses above about 4 M ? 
D) all of them 
A) only the smallest, with masses less than about 0.4 M ? 
B) intermediate masses, from about 0.4M ? up to about 4 M ? 
C) the largest, with masses above about 4 M ? 
D) all of them

Question 11

The pillars of M16, shown in Figure 18-20 of Universe, 11th ed., are eroding from:

Accepted Answer

A) intense electromagnetic radiation from the newly forming stars within the cocoons. 
B) ultraviolet radiation from nearby O and B stars. 
C) radioactivity. 
D) bipolar jets from within the pillars. 
A) intense electromagnetic radiation from the newly forming stars within the cocoons. 
B) ultraviolet radiation from nearby O and B stars. 
C) radioactivity. 
D) bipolar jets from within the pillars.

Question 12

A particular giant molecular cloud has a mass of 400,000 M ? . What is the mass of helium in this cloud?

Accepted Answer

A) 4000 M ? 
B) 300,000 M ? 
C) 392,000 M ? 
D) 100,000 M ? 
A) 4000 M ? 
B) 300,000 M ? 
C) 392,000 M ? 
D) 100,000 M ?

Question 13

What are the dimensions of a typical dark nebula of gas and dust within which a star might form?

Accepted Answer

A) a few thousand M ? inside a diameter of about 10 pc, or about 30 ly 
B) about 10 M ? inside a diameter of about 10 pc 
C) 1 or 2 M ? inside a diameter of about 100 au, about the size of the solar system 
D) a few thousand M ? inside about 1 au, Earth's orbit 
A) a few thousand M ? inside a diameter of about 10 pc, or about 30 ly 
B) about 10 M ? inside a diameter of about 10 pc 
C) 1 or 2 M ? inside a diameter of about 100 au, about the size of the solar system 
D) a few thousand M ? inside about 1 au, Earth's orbit

Question 14

Hot O and B stars embedded in an emission nebula emit a great deal of ultraviolet radiation. But UV radiation is not visible to the unaided eye. So where does the visible red color come from?

Accepted Answer

A) A small fraction of the radiation produced by O and B stars is in the visible. However, the total luminosity is so large that this small fraction gives color to the entire nebula. 
B) The UV radiation is redshifted by the Doppler effect, so we see it as visible. 
C) The UV radiation is reddened by passing through interstellar dust until it is visible. 
D) The UV radiation causes hydrogen to be ionized. When the electron and proton reunite, visible light is produced. 
A) A small fraction of the radiation produced by O and B stars is in the visible. However, the total luminosity is so large that this small fraction gives color to the entire nebula. 
B) The UV radiation is redshifted by the Doppler effect, so we see it as visible. 
C) The UV radiation is reddened by passing through interstellar dust until it is visible. 
D) The UV radiation causes hydrogen to be ionized. When the electron and proton reunite, visible light is produced.

Question 15

Astronomers use the symbol H II to mean:

Accepted Answer

A) neutral hydrogen. 
B) ionized hydrogen. 
C) molecular hydrogen (with two atoms). 
D) deuterium (hydrogen with a nucleus of two particles: one neutron and one proton). 
A) neutral hydrogen. 
B) ionized hydrogen. 
C) molecular hydrogen (with two atoms). 
D) deuterium (hydrogen with a nucleus of two particles: one neutron and one proton).

Question 16

Which of the following molecules is likely to be the most common in interstellar space?

Accepted Answer

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

Question 17

Main-sequence stars do not have masses larger than about 200 M ? The reason that stars of larger mass do not exist is that:

Accepted Answer

A) nothing can prevent such stars from collapsing directly into black holes. 
B) the thermonuclear reactions in such stars proceed so rapidly that the star explodes. 
C) such stars contract directly to become planet-like objects. 
D) they rapidly become very luminous and are quickly disrupted by the resulting very high internal pressure. 
A) nothing can prevent such stars from collapsing directly into black holes. 
B) the thermonuclear reactions in such stars proceed so rapidly that the star explodes. 
C) such stars contract directly to become planet-like objects. 
D) they rapidly become very luminous and are quickly disrupted by the resulting very high internal pressure.

Question 18

How do low-mass protostars (< 4 M ? ) evolve in the H-R diagram?

Accepted Answer

A) temperature decreasing at approximately constant luminosity 
B) temperature increasing at approximately constant luminosity 
C) luminosity decreasing at approximately constant temperature 
D) luminosity increasing at approximately constant temperature 
A) temperature decreasing at approximately constant luminosity 
B) temperature increasing at approximately constant luminosity 
C) luminosity decreasing at approximately constant temperature 
D) luminosity increasing at approximately constant temperature

Question 19

A particular giant molecular cloud has a mass of 400,000 M ? . What is the mass of hydrogen in this cloud?

Accepted Answer

A) 100,000 M ? 
B) 4000 M ? 
C) 392,000 M ? 
D) 300,000 M ? 
A) 100,000 M ? 
B) 4000 M ? 
C) 392,000 M ? 
D) 300,000 M ?

Question 20

Early in its lifetime a 1-M ? protostar will have 100 times the Sun's luminosity. How is this possible?

Accepted Answer

A) The first nuclear reactions in a protostar are more energetic than the later hydrogen to helium fusion. 
B) The initial temperature is low but the protostar's radius is large. 
C) Although small, the protostar's initial temperature is high. 
D) The Kelvin-Helmholtz contraction, the protostar's first energy generation mechanism, is more efficient than nuclear fusion. 
A) The first nuclear reactions in a protostar are more energetic than the later hydrogen to helium fusion. 
B) The initial temperature is low but the protostar's radius is large. 
C) Although small, the protostar's initial temperature is high. 
D) The Kelvin-Helmholtz contraction, the protostar's first energy generation mechanism, is more efficient than nuclear fusion.

Exam 18: The Birth of Stars

An H II region looks red, just as the metal filaments in a toaster glow red when heated. Are these colors produced in the same way?

Some protostars, when they evolve onto the main sequence, employ radiation to carry material outward from the core to some region midway through the star. Convection then carries the energy outward to the surface. Which stars show this characteristic?

When a carbon monoxide (CO) molecule emits a radio photon of 2.6-mm wavelength, what happens to the molecule?

Suppose the light leaving a star has equal intensities in the blue and the red. The starlight passes through a dust cloud on its journey to Earth. When you observe the light reaching Earth you will find the:

How long does it take for a 1-M ? star to pass through the pre-main-sequence phase?

What is the difference between a giant molecular cloud and an H II region?

What is the relationship between stellar mass and position on the main sequence of the Hertzsprung-Russell diagram?

What is a proplyd?

How does a 15-M ? star evolve in the first 105 years after it becomes a protostar?

Some protostars, when they evolve onto the main sequence, employ convection to carry material outward from the core to some region midway through the star. Radiation then carries the energy outward to the surface. Which stars show this characteristic?

The pillars of M16, shown in Figure 18-20 of Universe, 11th ed., are eroding from:

A particular giant molecular cloud has a mass of 400,000 M ? . What is the mass of helium in this cloud?

What are the dimensions of a typical dark nebula of gas and dust within which a star might form?

Hot O and B stars embedded in an emission nebula emit a great deal of ultraviolet radiation. But UV radiation is not visible to the unaided eye. So where does the visible red color come from?

Astronomers use the symbol H II to mean:

Which of the following molecules is likely to be the most common in interstellar space?

Main-sequence stars do not have masses larger than about 200 M ? The reason that stars of larger mass do not exist is that:

How do low-mass protostars (< 4 M ? ) evolve in the H-R diagram?

A particular giant molecular cloud has a mass of 400,000 M ? . What is the mass of hydrogen in this cloud?

Early in its lifetime a 1-M ? protostar will have 100 times the Sun's luminosity. How is this possible?

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

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Cosmology: The Origin and Evolution of the Universe

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How does a 15-M ? star evolve in the first 10⁵ years after it becomes a protostar?