Deck 11: Formation and Structure of Stars

Question 1

The temperature at the core of a star must be at least 1 million degrees Kelvin before fusion can begin.

Answer 1

False

Question 2

Main sequence O stars have convective cores because they fuse hydrogen in the proton-proton chain.

Answer 2

False

Question 3

When a large gas cloud starts to collapse in a free-fall due to gravity, it will start to cool down as it contracts because of the atoms fall inward.

Answer 3

False

Question 4

When a large gas cloud starts to collapse in a free-fall due to gravity, the cloud will ____.

A) increase in temperature
B) decrease in temperature
C) rotate slower
D) remain at the same temperature
E) become unstable and breakup

Question 5

One trigger that could start the gravitational contraction of a molecular cloud to form stars is a passing shock wave.

Question 6

Stellar winds and _____ will eventually blow away the protostellar disk and remnant cocoons of a protostar apart.

A) gas jets
B) magnetic fields
C) shock waves
D) radiation pressure
E) gravity waves

Question 7

One of the major star forming regions in space is the Orion Nebula.

Question 8

Four of following are factors that must be overcome by a large molecular cloud before gravitational contraction can begin. Which one is the exception?

A) thermal energy of the gas
B) magnetic field of the ISM
C) rotation of the gas cloud
D) intense radiation from a nearby star
E) turbulence in the ISM

Question 9

The proton-proton chain for fusing hydrogen into helium is a much more complicated process than the CNO Cycle for fusing hydrogen into helium.

Question 10

The Sun, a one-solar-mass star, will take approximately how many years to go from protostar to main-sequence star?

A) 160,000 years
B) 700,000 years
C) 8 million years
D) 30 million years
E) 100 million years

Question 11

One of the factors that a large molecular cloud must overcome in order for gravitational contraction to begin is the thermal energy of the gas.

Question 12

After a protostar has progressed in its development, it will have a dense inner part and an outer envelope called a(n) ____.

A) outer-protostar
B) Bok globules
C) upper proto-sphere
D) cocoon nebulae
E) planetary nebulae

Question 13

Convection is important in stars because it transports energy outward in the star.

Question 14

A protostar will continue to collapse due to gravity until it reaches the main sequence, and then gravitational collapse will stop when _____ begins.

A) the formation of star-globulars
B) atoms degenerate at the core of the star
C) the fusion of hydrogen
D) the fusion of helium
E) the fission of hydrogen

Question 15

One of the factors that a large molecular cloud must overcome in order for gravitational contraction to begin is rotation of the gas cloud.

Question 16

Where is the Trapezium found?

A) in the constellation Trapium
B) in the Orion Nebula
C) in all protostars
D) in all cocoon nebulae
E) in the Bok globules

Question 17

As the protostar contracts gravitationally, it will rotate faster and faster and produce a(n) ____.

A) protostellar globular
B) young stellar object (YSO)
C) protostellar envelope
D) cocoon nebula
E) protostellar disk

Question 18

Which trigger could start the gravitational contraction of a molecular cloud?

A) a faster rotation of the molecular cloud
B) an intense magnetic field
C) the collision of molecular clouds
D) intense radiation from a nearby star
E) a nearby spectral type G star

Question 19

Low-mass stars like the Sun transport energy near their surface using convection.

Question 20

The ISM magnetic field is typically about 0.0001 times as strong as Earth's magnetic field at its surface.

Question 22

How do low-mass stars in the lower region of the main sequence produce their energy?

A) by fusing hydrogen using the proton-proton chain
B) by fusing hydrogen using the CNO cycle (carbon-nitrogen-oxygen)
C) by fusing hydrogen using both the CNO cycle and the proton-proton chain
D) by fusing hydrogen using the HNO cycle (hydrogen-nitrogen-oxygen)
E) by fusing helium using the HeNO cycle (helium-nitrogen-oxygen)

Question 23

Eighty percent of the stars on the H-R diagram are on the main sequence, and that is because the star is in hydrostatic equilibrium due to the _____.

A) degenerate property of hydrogen
B) degenerate property of helium
C) Hertzsprung-Russell principle
D) fusion of hydrogen
E) fusion of helium

Question 24

What is the resistance of a gas to the flow of radiation?

A) degeneracy
B) conduction
C) opacity
D) hydrostatic pressure
E) gravitational pressure

Question 25

Hydrostatic equilibrium is the balance between _____________ and radiation _____________.

Question 26

During the main-sequence lifetime of a star of any mass, the core of the star will be composed mainly of ____.

A) hydrogen
B) helium
C) carbon
D) hydrogen and helium
E) helium and carbon

Question 27

When a large gas cloud starts to collapse in a free-fall due to gravity, the rotation rate will ______________.

Question 28

The proton-proton chain needs a high temperature because the protons must overcome the _____________.

Question 29

Our Sun took about ________ years from the collapse of its parent molecular cloud to become a main-sequence star.

A) 30
B) 30,000
C) 5 million
D) 30 million
E) 1 billion

Question 30

List three processes energy can be transported between regions.

Question 31

How do large-mass stars in the upper region of the main sequence produce energy?

A) by fusing hydrogen using the proton-proton chain
B) by fusing hydrogen using the CNO cycle (carbon-nitrogen-oxygen)
C) by fusing hydrogen using both the CNO ccle and the proton-proton chain
D) by fusing hydrogen using the HNO ccle (hydrogen-nitrogen-oxygen)
E) by fusing helium using the HeNO ccle (helium-nitrogen-oxygen)

Question 32

When a large gas cloud starts to collapse in a free-fall due to gravity, the temperature of the gas will _____________.

Question 33

Pre-main-sequence stars (not protostars) on the H-R diagram are _____.

A) above and to the right of supergiants
B) below and to the left of the main sequence
C) below and to the left of white dwarfs
D) above and to the right of the main sequence
E) not on the H-R diagram yet

Question 34

T Tauri stars are understood to be relatively low-mass __________.

A) dust cocoons
B) protostars
C) Herbig-Haro objects
D) nebulae
E) associations

Question 35

Stars with masses equal to or less than 1.1 solar masses use the _____________ to convert H into He for their energy source.

Question 36

The nuclear reactions in a star's core burn steadily so long as the relationship between _____________ and_____________ is stable.

Question 37

There are several triggers that could start the gravitational contraction of a molecular cloud and subsequent star formation.  List two of these triggers.

Question 38

What is a protostar and how does it get its energy?

Question 39

Which atom is not a part of the CNO cycle?

A) lithium
B) hydrogen
C) nitrogen
D) oxygen
E) helium

Question 40

What is the difference between the proton-proton chain and the CNO cycle?

Question 41

Before a giant molecular cloud can contract gravitationally, it must overcome four physical factors that resist compression.  What are these four factors?

Question 42

Describe the concept of a "birth line" and identify where it falls on the H-R diagram.

Question 43

Energy flows by radiation or convection inside normal stars but almost never by _____________ because radiation or convection is much more efficient.

Question 44

Columns of gas in a nebula that point back toward a young, massive star are called _______________.

Question 45

Hydrostatic equilibrium in a newborn star is regulated by a very unique thermostat called the _____________ thermostat.

Question 46

How does a gas cloud become hot enough to ignite nuclear reactions?

Question 47

Briefly describe the pressure-temperature thermostat in stars.

Question 48

The force responsible for the collapse of an interstellar cloud is_____________.

Question 49

Star clusters are important to the study the stellar evolution because stars in a given cluster have the same _____________.