Question 1

How do astronomers infer the presence of magnetic fields in molecular clouds?

Accepted Answer

A) by measuring the amount of interstellar reddening 
B) by measuring the Doppler shifts of emission lines from gas clumps in the cloud 
C) by measuring the infrared light emitted by the cloud 
D) by measuring the polarization of starlight passing through the cloud 
E) by measuring the amount by which gravity is reduced 
A) by measuring the amount of interstellar reddening 
B) by measuring the Doppler shifts of emission lines from gas clumps in the cloud 
C) by measuring the infrared light emitted by the cloud 
D) by measuring the polarization of starlight passing through the cloud 
E) by measuring the amount by which gravity is reduced

Question 2

The vast majority of stars in a newly formed star cluster are

Accepted Answer

A) very high-mass,type O and B stars. 
B) red giants. 
C) about the same mass as our Sun. 
D) less massive than the Sun. 
A) very high-mass,type O and B stars. 
B) red giants. 
C) about the same mass as our Sun. 
D) less massive than the Sun.

Question 3

What is a protostar?

Accepted Answer

A) a star that has planets 
B) an intermediate-mass star 
C) a star that is still in the process of forming 
D) a star in its final stage of life 
A) a star that has planets 
B) an intermediate-mass star 
C) a star that is still in the process of forming 
D) a star in its final stage of life

Question 4

About how many times more luminous than our Sun is a young solar mass protostar just beginning convective contraction?

Accepted Answer

A) 2-5 
B) 5-10 
C) 10-100 
D) 100-1000 
E) a million 
A) 2-5 
B) 5-10 
C) 10-100 
D) 100-1000 
E) a million

Question 5

Which of the following statements is probably true about the very first stars in the universe?

Accepted Answer

A) They were made only from hydrogen and helium. 
B) They were made from pure energy. 
C) They were probably orbited only by terrestrial planets,but no jovian planets. 
D) They were made approximately of 98% hydrogen and helium,and 2% of heavier elements. 
A) They were made only from hydrogen and helium. 
B) They were made from pure energy. 
C) They were probably orbited only by terrestrial planets,but no jovian planets. 
D) They were made approximately of 98% hydrogen and helium,and 2% of heavier elements.

Question 6

What species absorbs photons in a protostar's outer layers?

Accepted Answer

A) H 
B) H₂ 
C) H⁺ 
D) H⁻ 
E) dust 
A) H 
B) H₂ 
C) H⁺ 
D) H⁻ 
E) dust

Question 7

Explain why stars form only in molecular clouds,the coldest,densest parts of the interstellar medium.

Accepted Answer

A cloud collapses and ultimately forms s

Question 8

What can we learn about a star from a life track on an H-R diagram?

Accepted Answer

A) the star's age 
B) the surface temperature and luminosity the star will have at each stage of its life 
C) the star's current stage of life 
D) how the star's distance from Earth varies at different times in its life 
A) the star's age 
B) the surface temperature and luminosity the star will have at each stage of its life 
C) the star's current stage of life 
D) how the star's distance from Earth varies at different times in its life

Question 9

According to current understanding,how did the first generation of stars differ from stars born today?

Accepted Answer

A) They contained much more hydrogen and helium than stars born today. 
B) They were much cooler in temperature than most stars born today. 
C) They were much more likely to be members of binary star systems than stars are born today. 
D) They were much more massive than most stars born today. 
A) They contained much more hydrogen and helium than stars born today. 
B) They were much cooler in temperature than most stars born today. 
C) They were much more likely to be members of binary star systems than stars are born today. 
D) They were much more massive than most stars born today.

Question 10

What happens to the surface temperature and luminosity when a protostar radiatively contracts?

Accepted Answer

A) Its surface temperature and luminosity increase. 
B) Its surface temperature remains the same and its luminosity decreases. 
C) Its surface temperature and luminosity decrease. 
D) Its surface temperature decreases and its luminosity increases. 
E) Its surface temperature and luminosity remain the same. 
A) Its surface temperature and luminosity increase. 
B) Its surface temperature remains the same and its luminosity decreases. 
C) Its surface temperature and luminosity decrease. 
D) Its surface temperature decreases and its luminosity increases. 
E) Its surface temperature and luminosity remain the same.

Question 11

Which of the following phenomena is not commonly associated with the star formation process?

Accepted Answer

A) the formation of a spinning disk of material around a protostar 
B) powerful "jets" shooting out along the rotation axis of a protostar 
C) strong winds of particles blowing out into space from a protostar 
D) intense ultraviolet radiation coming from a protostar 
A) the formation of a spinning disk of material around a protostar 
B) powerful "jets" shooting out along the rotation axis of a protostar 
C) strong winds of particles blowing out into space from a protostar 
D) intense ultraviolet radiation coming from a protostar

Question 12

Explain how gas in a protostellar disk spirals onto the central star.

Accepted Answer

Gas in a protostellar disk will orbit li

Question 13

Which of the following discoveries,if they existed,would necessitate a reevaluation of our ideas of stellar formation?

Accepted Answer

A) a cluster of stars that appeared to be 13 billion years old 
B) a 100-solar-mass star 
C) a 0.01-solar-mass star 
D) a molecular cloud without any stars 
E) planetary systems around other stars than our own 
A) a cluster of stars that appeared to be 13 billion years old 
B) a 100-solar-mass star 
C) a 0.01-solar-mass star 
D) a molecular cloud without any stars 
E) planetary systems around other stars than our own

Question 14

Clouds that appear dark in visible light often glow when observed at long infrared wavelengths.

Accepted Answer

A) True 
 B)False

Question 15

What is interstellar reddening?

Accepted Answer

A) Interstellar dust absorbs more red light than blue light,making stars appear redder than their true color. 
B) Interstellar dust absorbs more red light than blue light,making stars appear bluer than their true color. 
C) Interstellar dust absorbs more blue light than red light,making stars appear redder than their true color. 
D) Interstellar dust absorbs more blue light than red light,making stars appear bluer than their true color. 
E) The spectral line shift due to a star's motion through the interstellar medium. 
A) Interstellar dust absorbs more red light than blue light,making stars appear redder than their true color. 
B) Interstellar dust absorbs more red light than blue light,making stars appear bluer than their true color. 
C) Interstellar dust absorbs more blue light than red light,making stars appear redder than their true color. 
D) Interstellar dust absorbs more blue light than red light,making stars appear bluer than their true color. 
E) The spectral line shift due to a star's motion through the interstellar medium.

Question 16

There is no limit to the mass with which a star can be born.

Accepted Answer

A) True 
 B)False

Question 17

When does a protostar become a true star?

Accepted Answer

A) when the star is 1 million years old 
B) when the central temperature reaches 1 million Kelvin 
C) when nuclear fusion begins in the core 
D) when the thermal energy becomes trapped in the center 
E) when the stellar winds and jets blow away the surrounding material 
A) when the star is 1 million years old 
B) when the central temperature reaches 1 million Kelvin 
C) when nuclear fusion begins in the core 
D) when the thermal energy becomes trapped in the center 
E) when the stellar winds and jets blow away the surrounding material

Question 18

Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds?

Accepted Answer

A) visible light 
B) ultraviolet 
C) infrared 
D) blue light 
A) visible light 
B) ultraviolet 
C) infrared 
D) blue light

Question 19

Approximately what core temperature is required before hydrogen fusion can begin in a star?

Accepted Answer

A) 10,000 K 
B) 10 million K 
C) 1 billion K 
D) 10 billion K 
E) 10 trillion K 
A) 10,000 K 
B) 10 million K 
C) 1 billion K 
D) 10 billion K 
E) 10 trillion K

Question 20

What prevents the pressure from increasing as a cloud contracts due to its gravity?

Accepted Answer

A) As the cloud becomes denser,gravity becomes stronger and overcomes the pressure buildup. 
B) The pressure is transferred from the center of the cloud to its outer edges where it can dissipate. 
C) Thermal energy is converted to radiative energy via molecular collisions and released as photons. 
D) Excess pressure is released in jets of material from the young stars. 
E) Once the cloud reaches a critical density,the pressure becomes degenerate and independent of temperature. 
A) As the cloud becomes denser,gravity becomes stronger and overcomes the pressure buildup. 
B) The pressure is transferred from the center of the cloud to its outer edges where it can dissipate. 
C) Thermal energy is converted to radiative energy via molecular collisions and released as photons. 
D) Excess pressure is released in jets of material from the young stars. 
E) Once the cloud reaches a critical density,the pressure becomes degenerate and independent of temperature.

Exam 16: Star Birth

How do astronomers infer the presence of magnetic fields in molecular clouds?

The vast majority of stars in a newly formed star cluster are

What is a protostar?

About how many times more luminous than our Sun is a young solar mass protostar just beginning convective contraction?

Which of the following statements is probably true about the very first stars in the universe?

What species absorbs photons in a protostar's outer layers?

Explain why stars form only in molecular clouds,the coldest,densest parts of the interstellar medium.

What can we learn about a star from a life track on an H-R diagram?

According to current understanding,how did the first generation of stars differ from stars born today?

What happens to the surface temperature and luminosity when a protostar radiatively contracts?

Which of the following phenomena is not commonly associated with the star formation process?

Explain how gas in a protostellar disk spirals onto the central star.

Which of the following discoveries,if they existed,would necessitate a reevaluation of our ideas of stellar formation?

Clouds that appear dark in visible light often glow when observed at long infrared wavelengths.

What is interstellar reddening?

There is no limit to the mass with which a star can be born.

When does a protostar become a true star?

Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds?

Approximately what core temperature is required before hydrogen fusion can begin in a star?

What prevents the pressure from increasing as a cloud contracts due to its gravity?

A Modern View of the Universe

Discovering the Universe for Yourself

The Science of Astronomy

Making Sense of the Universe: Understanding Motion, Energy, and Gravity

Light and Matter: Reading Messages from the Cosmos

Telescopes: Portals of Discovery

Our Planetary System

Formation of the Solar System

Planetary Geology: Earth and the Other Terrestrial Worlds

Planetary Atmospheres: Earth and the Other Terrestrial Worlds

Jovian Planet Systems

Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts

Other Planetary Systems: The New Science of Distant Worlds

Our Star

Surveying the Stars

Star Stuff

The Bizarre Stellar Graveyard

Our Galaxy

Galaxies and the Foundations of Modern Cosmology

Galaxy Evolution

The Birth of the Universe

Dark Matter, Dark Energy, and the Fate of the Universe

Life in the Universe

Celestial Timekeeping and Navigation

Space and Time

Spacetime and Gravity

Building Blocks of the Universe

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