Question 1

The temperature inside a Bok globule, where star formation may be taking place, is:

Accepted Answer

A) about 10,000 K. 
B) about 100 K. 
C) significantly less than 1 K. 
D) about 10 K. 
A) about 10,000 K. 
B) about 100 K. 
C) significantly less than 1 K. 
D) about 10 K.

Question 2

Dark nebulae have temperatures around 10 K and emit mostly in the millimeter range. Are these values consistent with blackbody radiation?

Accepted Answer

A) Wien's law predicts a peak wavelength of a few millimeters, so this emission is consistent with blackbody radiation. 
B) Wien's law predicts a peak wavelength of a few meters, so this emission is not consistent with blackbody radiation. 
C) Wien's law predicts a peak wavelength of less than 1 mm, so this millimeter radiation must come from specific molecular sources. 
D) Wien's law predicts a peak wavelength in the x-ray range, so this emission is not consistent with blackbody radiation. 
A) Wien's law predicts a peak wavelength of a few millimeters, so this emission is consistent with blackbody radiation. 
B) Wien's law predicts a peak wavelength of a few meters, so this emission is not consistent with blackbody radiation. 
C) Wien's law predicts a peak wavelength of less than 1 mm, so this millimeter radiation must come from specific molecular sources. 
D) Wien's law predicts a peak wavelength in the x-ray range, so this emission is not consistent with blackbody radiation.

Question 3

The lowest mass that a protostar can have and still become a star (i.e., start thermonuclear reactions in its core) is:

Accepted Answer

A) about one-half M ? 
B) slightly less than 1/100 m ? 
C) slightly less than 1/10 m ? 
D) 8/10 M ? 
A) about one-half M ? 
B) slightly less than 1/100 m ? 
C) slightly less than 1/10 m ? 
D) 8/10 M ?

Question 4

If a protostar of 1 M ? has a luminosity 100 times that of the Sun and a radius 20 times that of the Sun, what is its surface temperature? (The Sun's surface temperature is 5800 K.)

Accepted Answer

A) 2000 K 
B) 2900 K 
C) 4100 K 
D) 5800 K 
A) 2000 K 
B) 2900 K 
C) 4100 K 
D) 5800 K

Question 5

What is the similarity in physical principle between the mechanism at work in an emission nebula and that in a household fluorescent light bulb?

Accepted Answer

A) Both depend on atomic ionization and subsequent recombination of atoms to produce light, mainly in specific spectral lines. 
B) The spectral lines they produce from hydrogen gas are the same in both the nebula and the fluorescent tube. 
C) Both depend on heating of a neutral gas to produce a continuum spectrum. 
D) Both depend on electrical energy to heat a gas; in a fluorescent bulb electric energy comes from the household supply, whereas in the emission nebula electrical energy arises from rapid motion of ionized gases. 
A) Both depend on atomic ionization and subsequent recombination of atoms to produce light, mainly in specific spectral lines. 
B) The spectral lines they produce from hydrogen gas are the same in both the nebula and the fluorescent tube. 
C) Both depend on heating of a neutral gas to produce a continuum spectrum. 
D) Both depend on electrical energy to heat a gas; in a fluorescent bulb electric energy comes from the household supply, whereas in the emission nebula electrical energy arises from rapid motion of ionized gases.

Question 6

The bright stars at the center of an H II region (an emission nebula) are mostly:

Accepted Answer

A) young O and B stars. 
B) red supergiants. 
C) hot white dwarfs. 
D) T Tauri stars. 
A) young O and B stars. 
B) red supergiants. 
C) hot white dwarfs. 
D) T Tauri stars.

Question 7

How many different kinds of molecules have been discovered in interstellar space?

Accepted Answer

A) fewer than two dozen 
B) about 75 
C) more than 200 
D) nearly 1000 
A) fewer than two dozen 
B) about 75 
C) more than 200 
D) nearly 1000

Question 8

A small emission nebula contains about how many solar masses of material?

Accepted Answer

A) 1 
B) 100 
C) 10,000 
D) 1 million 
A) 1 
B) 100 
C) 10,000 
D) 1 million

Question 9

What is the dominant spectral emission line from an emission nebula in visible light?

Accepted Answer

A) Hα 
B) There are no spectral line features emitted by this nebula, because the light is scattered continuum starlight from embedded stars. 
C) the sodium D lines 
D) Lymanα 
A) Hα 
B) There are no spectral line features emitted by this nebula, because the light is scattered continuum starlight from embedded stars. 
C) the sodium D lines 
D) Lymanα

Question 10

Protostars with masses of less than about 4 times the mass of the Sun evolve at approximately constant surface temperature through most of their pre-main-sequence lifetimes. This is because:

Accepted Answer

A) they contract too rapidly for their temperature and luminosity to change significantly. 
B) they are not massive enough to contract significantly and luminosity remains constant. 
C) the luminosity increases as the surface area decreases. 
D) the luminosity decreases as the surface area decreases. 
A) they contract too rapidly for their temperature and luminosity to change significantly. 
B) they are not massive enough to contract significantly and luminosity remains constant. 
C) the luminosity increases as the surface area decreases. 
D) the luminosity decreases as the surface area decreases.

Question 11

The blue color of a reflection nebula is produced by:

Accepted Answer

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. 
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.

Question 12

The predominant color of an emission nebula is:

Accepted Answer

A) red, from the hydrogen Balmer Hα line. 
B) blue, from scattering of light from hot stars by dust particles. 
C) green-yellow from the 530.3 nm emission line of ionized iron, equivalent to that from the hot solar corona. 
D) a continuum of all colors, the combined light from all the stars in the nebula. 
A) red, from the hydrogen Balmer Hα line. 
B) blue, from scattering of light from hot stars by dust particles. 
C) green-yellow from the 530.3 nm emission line of ionized iron, equivalent to that from the hot solar corona. 
D) a continuum of all colors, the combined light from all the stars in the nebula.

Question 13

The ratio of molecular hydrogen to carbon monoxide in interstellar space is about:

Accepted Answer

A) 10 to 1. 
B) 500 to 1. 
C) 1000 to 1. 
D) 10,000 to 1. 
A) 10 to 1. 
B) 500 to 1. 
C) 1000 to 1. 
D) 10,000 to 1.

Question 14

The jets of bipolar outflow associated with many protostars are formed by the protostar's:

Accepted Answer

A) magnetic field. 
B) gravitational field. 
C) nearby hot O and B stars. 
D) central black hole. 
A) magnetic field. 
B) gravitational field. 
C) nearby hot O and B stars. 
D) central black hole.

Question 15

Newborn O and B stars carve out H II regions that expand into the giant molecular cloud in which the stars exist. Suppose a G-type star is also formed. What role does it play in this process?

Accepted Answer

A) The G-type star, too, will help in creating the H II region, but it does not contribute as much energy as the hotter stars. 
B) The G-type star does not produce enough ultraviolet radiation to ionize significant amounts of hydrogen. 
C) The G-type star does not produce enough infrared radiation to ionize significant amounts of hydrogen. 
D) G-type stars are never formed in the initial group of stars within a giant molecular cloud. They are only formed later when the interstellar medium has been enriched by the initial group. 
A) The G-type star, too, will help in creating the H II region, but it does not contribute as much energy as the hotter stars. 
B) The G-type star does not produce enough ultraviolet radiation to ionize significant amounts of hydrogen. 
C) The G-type star does not produce enough infrared radiation to ionize significant amounts of hydrogen. 
D) G-type stars are never formed in the initial group of stars within a giant molecular cloud. They are only formed later when the interstellar medium has been enriched by the initial group.

Question 16

What recent evidence has indicated that the initial condensation that occurred in a gas and dust cloud to produce the Sun was caused by a nearby supernova explosion?

Accepted Answer

A) the abnormal velocity of the Sun with respect to the spiral arm in which it is located, indicating a major disturbance in the past 
B) meteorites containing heavy elements produced only in supernova explosions 
C) a vast shell of gas moving outward at a great speed from a position in our galaxy near to the Sun 
D) a layer of Earth's crust containing abnormal amounts of the rare metal iridium 
A) the abnormal velocity of the Sun with respect to the spiral arm in which it is located, indicating a major disturbance in the past 
B) meteorites containing heavy elements produced only in supernova explosions 
C) a vast shell of gas moving outward at a great speed from a position in our galaxy near to the Sun 
D) a layer of Earth's crust containing abnormal amounts of the rare metal iridium

Question 17

Typical jets of bipolar outflow last for:

Accepted Answer

A) 10 years. 
B) 1000 years. 
C) 100,000 years. 
D) 10 million years. 
A) 10 years. 
B) 1000 years. 
C) 100,000 years. 
D) 10 million years.

Question 18

What is the characteristic color of an emission nebula?

Accepted Answer

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

Question 19

The main factor that determines the rate at which a protostar evolves is its:

Accepted Answer

A) initial mass, smaller masses evolving faster. 
B) initial mass, larger masses evolving faster. 
C) initial composition. 
D) environment, protostars with binary companions evolving much faster. 
A) initial mass, smaller masses evolving faster. 
B) initial mass, larger masses evolving faster. 
C) initial composition. 
D) environment, protostars with binary companions evolving much faster.

Question 20

Those interior regions of a protostar that are relatively cool are more likely to transport energy by:

Accepted Answer

A) conduction, because the atoms are close enough together to act as a solid. 
B) convection, because the hydrogen tends to form the H- ion, a good absorber of radiation. 
C) radiation, because the atoms move too slowly at these temperatures for convection to be effective. 
D) radiation, because low temperature atoms produce copious amounts of visible light. 
A) conduction, because the atoms are close enough together to act as a solid. 
B) convection, because the hydrogen tends to form the H- ion, a good absorber of radiation. 
C) radiation, because the atoms move too slowly at these temperatures for convection to be effective. 
D) radiation, because low temperature atoms produce copious amounts of visible light.

Exam 18: The Birth of Stars

The temperature inside a Bok globule, where star formation may be taking place, is:

Dark nebulae have temperatures around 10 K and emit mostly in the millimeter range. Are these values consistent with blackbody radiation?

The lowest mass that a protostar can have and still become a star (i.e., start thermonuclear reactions in its core) is:

If a protostar of 1 M ? has a luminosity 100 times that of the Sun and a radius 20 times that of the Sun, what is its surface temperature? (The Sun's surface temperature is 5800 K.)

What is the similarity in physical principle between the mechanism at work in an emission nebula and that in a household fluorescent light bulb?

The bright stars at the center of an H II region (an emission nebula) are mostly:

How many different kinds of molecules have been discovered in interstellar space?

A small emission nebula contains about how many solar masses of material?

What is the dominant spectral emission line from an emission nebula in visible light?

Protostars with masses of less than about 4 times the mass of the Sun evolve at approximately constant surface temperature through most of their pre-main-sequence lifetimes. This is because:

The blue color of a reflection nebula is produced by:

The predominant color of an emission nebula is:

The ratio of molecular hydrogen to carbon monoxide in interstellar space is about:

The jets of bipolar outflow associated with many protostars are formed by the protostar's:

Newborn O and B stars carve out H II regions that expand into the giant molecular cloud in which the stars exist. Suppose a G-type star is also formed. What role does it play in this process?

What recent evidence has indicated that the initial condensation that occurred in a gas and dust cloud to produce the Sun was caused by a nearby supernova explosion?

Typical jets of bipolar outflow last for:

What is the characteristic color of an emission nebula?

The main factor that determines the rate at which a protostar evolves is its:

Those interior regions of a protostar that are relatively cool are more likely to transport energy by:

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