Question 1

As a protostar evolves towards becoming a main-sequence star, its core temperature will

Accepted Answer

A)  always increase. 
B)  always decrease. 
C)  first increase, then decrease. 
D)  first decrease, then increase. 
E)  always be the same value. 
A)  always increase. 
B)  always decrease. 
C)  first increase, then decrease. 
D)  first decrease, then increase. 
E)  always be the same value.

Question 2

Interstellar extinction refers to

Accepted Answer

A)  planets in interstellar space absorbing starlight. 
B)  light being absorbed by dust in interstellar space. 
C)  asteroid impacts that result in mass extinctions of life. 
D)  the emission of red light by interstellar dust. 
E)  hot interstellar gas clouds that cause mass extinctions of life. 
A)  planets in interstellar space absorbing starlight. 
B)  light being absorbed by dust in interstellar space. 
C)  asteroid impacts that result in mass extinctions of life. 
D)  the emission of red light by interstellar dust. 
E)  hot interstellar gas clouds that cause mass extinctions of life.

Question 3

What primarily makes it difficult to observe the process of star formation?

Accepted Answer

A)  Star formation occurs in dusty regions. 
B)  Forming stars have low luminosities. 
C)  Forming stars do not shine at any wavelength until they become T Tauri stars. 
D)  The star formation process happens so quickly. 
E)  Forming stars are too small to be seen. 
A)  Star formation occurs in dusty regions. 
B)  Forming stars have low luminosities. 
C)  Forming stars do not shine at any wavelength until they become T Tauri stars. 
D)  The star formation process happens so quickly. 
E)  Forming stars are too small to be seen.

Question 4

Why do many stars form from a single molecular cloud?

Accepted Answer

Small density fluctuations in the parent

Question 5

Because angular momentum must be conserved, as a gas cloud contracts due to gravity it will also

Accepted Answer

A)  spin slower. 
B)  spin faster. 
C)  increase in temperature. 
D)  decrease in temperature. 
E)  stay the same temperature. 
A)  spin slower. 
B)  spin faster. 
C)  increase in temperature. 
D)  decrease in temperature. 
E)  stay the same temperature.

Question 6

A protostar may evolve into either a main-sequence star or a

Accepted Answer

A)  molecular cloud. 
B)  gas giant planet. 
C)  Herbig-Haro object. 
D)  brown dwarf. 
E)  white dwarf. 
A)  molecular cloud. 
B)  gas giant planet. 
C)  Herbig-Haro object. 
D)  brown dwarf. 
E)  white dwarf.

Question 7

In the figure shown below, the portion of the H-R diagram corresponding to the Hayashi track
of a 1 MSUN star is shown.Temperature increases toward the left, and luminosity increases toward the top of the diagram.Even though the temperature of the protostar is hardly changing as it approaches the main sequence, its luminosity is decreasing.Why?

Accepted Answer

The luminosity of a star,L,depends on it

Question 8

A surprising fact about a 1 MSUN protostar is that, even though nuclear reactions have not yet started in their cores, they are ________ than the Sun

Accepted Answer

A)  hotter 
B)  rotating faster 
C)  smaller 
D)  denser 
E)  more luminous 
A)  hotter 
B)  rotating faster 
C)  smaller 
D)  denser 
E)  more luminous

Question 9

Suppose a protostar shrinks in size from 100 RSUN down to 20 RSUN while maintaining a constant temperature.By what factor does its luminosity decrease?

Accepted Answer

Suppose the original luminosity of the s

Question 10

Why can't very bright protostars be seen in visible light?

Accepted Answer

They are cool,so they emit mos

Question 11

What is the energy source that powers brown dwarf stars?

Accepted Answer

Brown dwarfs shine because they are stil

Question 12

At what wavelength(s) are H II regions most clearly visible, and why do H II regions mark the regions where new stars are currently being formed?

Accepted Answer

H II regions are best seen at H-alpha wi

Question 13

If you could watch stars forming out of a gas cloud, which stars would form first?

Accepted Answer

A)  low-mass stars 
B)  medium-mass stars 
C)  high-mass stars 
D)  stars with low temperatures 
E)  stars of different types would form at random times. 
A)  low-mass stars 
B)  medium-mass stars 
C)  high-mass stars 
D)  stars with low temperatures 
E)  stars of different types would form at random times.

Question 14

When winds blow the gas away from a forming protostar, the protostar

Accepted Answer

A)  expands rapidly to 100 times its original size. 
B)  is revealed as a main-sequence star. 
C)  becomes visible as a T Tauri star. 
D)  is unable to reach the main sequence. 
E)  becomes a brown dwarf. 
A)  expands rapidly to 100 times its original size. 
B)  is revealed as a main-sequence star. 
C)  becomes visible as a T Tauri star. 
D)  is unable to reach the main sequence. 
E)  becomes a brown dwarf.

Question 15

Warm ionized gas in the interstellar medium appears ________ when imaged in the optical region of the electromagnetic spectrum.

Accepted Answer

A)  red 
B)  yellow 
C)  white 
D)  blue 
E)  dark 
A)  red 
B)  yellow 
C)  white 
D)  blue 
E)  dark

Question 16

The interstellar medium is divided into three different kinds of gas clouds.These are

Accepted Answer

A)  cold gas at 100 K, warm gas at 8000 K, and hot gas at about 1 million K. 
B)  warm gas at 8000 K, hot gas at 1 million K, and superhot gas at 10 million K. 
C)  warm gas at 5000 K, warm-hot gas at 100,000 K, and hot gas at about 1 million K. 
D)  cold gas at 100 K, cool gas at 1000 K, and warm gas at 8000 K. 
E)  cold gas at 100 K, hot gas at 1 million K, and superhot gas at 10 million K. 
A)  cold gas at 100 K, warm gas at 8000 K, and hot gas at about 1 million K. 
B)  warm gas at 8000 K, hot gas at 1 million K, and superhot gas at 10 million K. 
C)  warm gas at 5000 K, warm-hot gas at 100,000 K, and hot gas at about 1 million K. 
D)  cold gas at 100 K, cool gas at 1000 K, and warm gas at 8000 K. 
E)  cold gas at 100 K, hot gas at 1 million K, and superhot gas at 10 million K.

Question 17

Objects with masses from 0.01 MSUN to 0.08 MSUN are very different from the Sun because they

Accepted Answer

A)  do not have strong enough gravity to form planets. 
B)  have much higher temperatures than the Sun. 
C)  cannot successfully execute the proton-proton chain reactions. 
D)  form much faster than the Sun did. 
E)  do not exhibit sunspots. 
A)  do not have strong enough gravity to form planets. 
B)  have much higher temperatures than the Sun. 
C)  cannot successfully execute the proton-proton chain reactions. 
D)  form much faster than the Sun did. 
E)  do not exhibit sunspots.

Question 18

If the surface of a star cools, the number of H - ions ________ and the atmosphere becomes more ________.

Accepted Answer

A)  decreases; opaque 
B)  decreases; transparent 
C)  increases; transparent 
D)  increases; opaque 
E)  stays the same; transparent 
A)  decreases; opaque 
B)  decreases; transparent 
C)  increases; transparent 
D)  increases; opaque 
E)  stays the same; transparent

Question 19

The thermal energy of a contracting protostar comes from

Accepted Answer

A)  thermonuclear energy. 
B)  rotational kinetic energy. 
C)  chemical energy. 
D)  gravitational potential energy. 
E)  radiation energy. 
A)  thermonuclear energy. 
B)  rotational kinetic energy. 
C)  chemical energy. 
D)  gravitational potential energy. 
E)  radiation energy.

Question 20

The red emission (bright region at the top) in the figure shown below is due to

Accepted Answer

A)  carbon monoxide (CO). 
B)  warm, neutral hydrogen. 
C)  molecular hydrogen (H2). 
D)  ionized hydrogen (H II region). 
E)  dust. 
A)  carbon monoxide (CO). 
B)  warm, neutral hydrogen. 
C)  molecular hydrogen (H2). 
D)  ionized hydrogen (H II region). 
E)  dust.

Exam 15: The Interstellar Medium and Star Formation

As a protostar evolves towards becoming a main-sequence star, its core temperature will

Interstellar extinction refers to

What primarily makes it difficult to observe the process of star formation?

Why do many stars form from a single molecular cloud?

Because angular momentum must be conserved, as a gas cloud contracts due to gravity it will also

A protostar may evolve into either a main-sequence star or a

A surprising fact about a 1 MSUN protostar is that, even though nuclear reactions have not yet started in their cores, they are ________ than the Sun

Suppose a protostar shrinks in size from 100 RSUN down to 20 RSUN while maintaining a constant temperature.By what factor does its luminosity decrease?

Why can't very bright protostars be seen in visible light?

What is the energy source that powers brown dwarf stars?

At what wavelength(s) are H II regions most clearly visible, and why do H II regions mark the regions where new stars are currently being formed?

If you could watch stars forming out of a gas cloud, which stars would form first?

When winds blow the gas away from a forming protostar, the protostar

Warm ionized gas in the interstellar medium appears ________ when imaged in the optical region of the electromagnetic spectrum.

The interstellar medium is divided into three different kinds of gas clouds.These are

Objects with masses from 0.01 MSUN to 0.08 MSUN are very different from the Sun because they

If the surface of a star cools, the number of H - ions ________ and the atmosphere becomes more ________.

The thermal energy of a contracting protostar comes from

The red emission (bright region at the top) in the figure shown below is due to

Thinking Like an Astronomer

Patterns in the Skymotions of Earth and the Moon

Motion of Astronomical Bodies

Gravity and Orbits

Light

The Tools of the Astronomer

The Formation of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquidthe Giant Planets

Planetary Moons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

Our Starthe Sun

Evolution of Low-Mass Stars

Evolution of High-Mass Stars

Relativity and Black Holes

Galaxies

The Milky Waya Normal Spiral Galaxy

The Expanding Universe

Cosmology

Large-Scale Structure in the Universe

Life

Filters

A surprising fact about a 1 M_SUN protostar is that, even though nuclear reactions have not yet started in their cores, they are ________ than the Sun

Suppose a protostar shrinks in size from 100 R_SUN down to 20 R_SUN while maintaining a constant temperature.By what factor does its luminosity decrease?

Objects with masses from 0.01 M_SUN to 0.08 M_SUN are very different from the Sun because they

If the surface of a star cools, the number of H ^- ions and the atmosphere becomes more .