Question 1

What is the minimum temperature for a cloud to excite emission lines from H₂?

Accepted Answer

A) 10 K 
B) 30 K 
C) 100 K 
D) 300 K 
E) 1000 K 
A) 10 K 
B) 30 K 
C) 100 K 
D) 300 K 
E) 1000 K C

Question 2

Photographs of many young stars show long jets of material apparently being ejected from their poles.

Accepted Answer

A) True 
 B)False  True

Question 3

Why are brown dwarfs easier to spot in a young,star forming region like Orion rather than an old group of stars like a globular cluster?

Accepted Answer

Like stars,but even more so,brown dwarfs are more luminous when they are young.They produce infrared radiation from the release of gravitational energy as they collapse and are therefore brighter and easier to see when they are forming.

Question 4

What prevents a brown dwarf from undergoing nuclear fusion?

Accepted Answer

A) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. 
B) There is not enough mass to maintain nuclear reactions in a self-sustaining way. 
C) The surface temperature never rises high enough for the radiation to be trapped and heat their interior to the temperatures required for nuclear fusion. 
D) Radiation pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. 
E) There are too many heavy elements and not enough hydrogen for fusion to occur in a self-sustaining way. 
A) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. 
B) There is not enough mass to maintain nuclear reactions in a self-sustaining way. 
C) The surface temperature never rises high enough for the radiation to be trapped and heat their interior to the temperatures required for nuclear fusion. 
D) Radiation pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. 
E) There are too many heavy elements and not enough hydrogen for fusion to occur in a self-sustaining way.

Question 5

What happens to the surface temperature and luminosity when a protostar undergoes convective contraction?

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 6

The gravitational force in a molecular cloud depends on

Accepted Answer

A) density only. 
B) temperature only. 
C) density and temperature. 
D) composition. 
E) thermal pressure. 
A) density only. 
B) temperature only. 
C) density and temperature. 
D) composition. 
E) thermal pressure.

Question 7

What is the smallest mass a newborn star can have?

Accepted Answer

A) 8 times the mass of Jupiter 
B) 80 times the mass of Jupiter 
C) 800 times the mass of Jupiter 
D) about 1/80 the mass of our Sun 
E) about 1/800 the mass of our Sun 
A) 8 times the mass of Jupiter 
B) 80 times the mass of Jupiter 
C) 800 times the mass of Jupiter 
D) about 1/80 the mass of our Sun 
E) about 1/800 the mass of our Sun

Question 8

Process of Science: Since scientists can't follow the stellar formation process of a single star from start to finish,how do they study solar life cycles?

Accepted Answer

Scientists must draw conclusio

Question 9

What is the approximate range of masses that newborn main-sequence stars can have?

Accepted Answer

A) 0.001 to 150 solar masses 
B) 0.1 to 1,000 solar masses 
C) 0.1 to 150 solar masses 
D) 0.001 to 10 solar masses 
E) 0.1 to 10 solar masses 
A) 0.001 to 150 solar masses 
B) 0.1 to 1,000 solar masses 
C) 0.1 to 150 solar masses 
D) 0.001 to 10 solar masses 
E) 0.1 to 10 solar masses

Question 10

Explain how the balance of gravity versus thermal pressure predicts that a cloud should fragment into many stars.

Accepted Answer

Clouds collapse when their self-gravity

Question 11

Where would a brown dwarf be located on an H-R diagram?

Accepted Answer

A) upper right 
B) on the lower part of the main sequence 
C) below and to the right of the lowest part of the main sequence 
D) lower left 
E) above and to the left of the main sequence 
A) upper right 
B) on the lower part of the main sequence 
C) below and to the right of the lowest part of the main sequence 
D) lower left 
E) above and to the left of the main sequence

Question 12

Which of the following may be caused by a protostellar disk?

Accepted Answer

A) protostellar jets 
B) protostellar winds 
C) accretion of material onto the star 
D) relatively slow protostellar rotation 
E) all of the above 
A) protostellar jets 
B) protostellar winds 
C) accretion of material onto the star 
D) relatively slow protostellar rotation 
E) all of the above

Question 13

The core of a protostar that will eventually become a brown dwarf shrinks until

Accepted Answer

A) the type of pressure called degeneracy pressure becomes important. 
B) its central temperature is high enough to support fusion reactions. 
C) it forms a rocky core. 
D) it radiates brown light. 
A) the type of pressure called degeneracy pressure becomes important. 
B) its central temperature is high enough to support fusion reactions. 
C) it forms a rocky core. 
D) it radiates brown light.

Question 14

What property of a molecular cloud does not counteract gravitational contraction?

Accepted Answer

A) thermal pressure 
B) turbulent motions 
C) magnetic fields 
D) fragmentation 
A) thermal pressure 
B) turbulent motions 
C) magnetic fields 
D) fragmentation

Question 15

Under which circumstances can you be sure that the thermal pressure within a gas cloud is increasing?

Accepted Answer

A) The cloud's temperature and density are both increasing. 
B) The cloud's temperature is increasing and its density is decreasing. 
C) The cloud's temperature and density are both decreasing. 
D) The cloud's temperature is decreasing and its density is increasing. 
E) It is impossible to say. 
A) The cloud's temperature and density are both increasing. 
B) The cloud's temperature is increasing and its density is decreasing. 
C) The cloud's temperature and density are both decreasing. 
D) The cloud's temperature is decreasing and its density is increasing. 
E) It is impossible to say.

Question 16

Using Mathematical Insight 16.1,calculate the minimum mass at which gravity and pressure balance for a cloud composed only of hydrogen and helium that cannot cool below 100 K.Assume that density is the same,300 particles per cubic centimeter,as molecular clouds in the Milky Way.

Accepted Answer

Use the equation
Mbalance= 18 MSun
@#LAT-DLM& with

Question 17

What is the greatest mass a newborn star can have

Accepted Answer

A) 10 solar masses. 
B) 20 solar masses. 
C) 50 solar masses. 
D) a few hundred solar masses. 
A) 10 solar masses. 
B) 20 solar masses. 
C) 50 solar masses. 
D) a few hundred solar masses.

Question 18

What happens to the visible radiation produced by new stars within a molecular cloud?

Accepted Answer

A) It escapes the cloud completely. 
B) It is absorbed by dust grains and heats up the cloud. 
C) It is reflected back onto the protostar,heating it up further. 
D) The blue light is absorbed and the red light transmitted. 
E) It shoots out in bright jets. 
A) It escapes the cloud completely. 
B) It is absorbed by dust grains and heats up the cloud. 
C) It is reflected back onto the protostar,heating it up further. 
D) The blue light is absorbed and the red light transmitted. 
E) It shoots out in bright jets.

Question 19

If a star is extremely massive (well over 100 solar masses),why isn't it likely to survive for long?

Accepted Answer

A) It explodes as a supernova after just a few dozen years. 
B) It may blow itself apart because of radiation pressure. 
C) It eventually divides into two lower-mass stars. 
D) Its great mass will cause it to suck itself into becoming a black hole. 
A) It explodes as a supernova after just a few dozen years. 
B) It may blow itself apart because of radiation pressure. 
C) It eventually divides into two lower-mass stars. 
D) Its great mass will cause it to suck itself into becoming a black hole.

Question 20

Calculations show that gravity begins to overcome thermal pressure in clouds that are

Accepted Answer

A) less massive than the Sun. 
B) more massive than the Sun. 
C) more massive than ten times the Sun. 
D) more massive than a hundred times the Sun. 
E) more massive than a thousand times the Sun. 
A) less massive than the Sun. 
B) more massive than the Sun. 
C) more massive than ten times the Sun. 
D) more massive than a hundred times the Sun. 
E) more massive than a thousand times the Sun.

Exam 16: Star Birth

What is the minimum temperature for a cloud to excite emission lines from H₂?

Photographs of many young stars show long jets of material apparently being ejected from their poles.

Why are brown dwarfs easier to spot in a young,star forming region like Orion rather than an old group of stars like a globular cluster?

What prevents a brown dwarf from undergoing nuclear fusion?

What happens to the surface temperature and luminosity when a protostar undergoes convective contraction?

The gravitational force in a molecular cloud depends on

What is the smallest mass a newborn star can have?

Process of Science: Since scientists can't follow the stellar formation process of a single star from start to finish,how do they study solar life cycles?

What is the approximate range of masses that newborn main-sequence stars can have?

Explain how the balance of gravity versus thermal pressure predicts that a cloud should fragment into many stars.

Where would a brown dwarf be located on an H-R diagram?

Which of the following may be caused by a protostellar disk?

The core of a protostar that will eventually become a brown dwarf shrinks until

What property of a molecular cloud does not counteract gravitational contraction?

Under which circumstances can you be sure that the thermal pressure within a gas cloud is increasing?

Using Mathematical Insight 16.1,calculate the minimum mass at which gravity and pressure balance for a cloud composed only of hydrogen and helium that cannot cool below 100 K.Assume that density is the same,300 particles per cubic centimeter,as molecular clouds in the Milky Way.

What is the greatest mass a newborn star can have

What happens to the visible radiation produced by new stars within a molecular cloud?

If a star is extremely massive (well over 100 solar masses),why isn't it likely to survive for long?

Calculations show that gravity begins to overcome thermal pressure in clouds that are

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