Deck 11: The Formation and Structure of Stars

Question 1

The factors that resist collapse in a gas cloud are

A) I,III,& V
B) I,IV,& V
C) II,III,& IV
D) II,IV,& V
E) III,IV,& V

Answer 1

I,IV,& V

Question 2

Protons and neutrons are held together in the nucleus by

A) the weak force.
B) the gravitational force.
C) the electrostatic force.
D) the strong force.
E) the opacity.

Answer 2

the strong force.

Question 3

The proton-proton chain needs high temperature because

A) of the ground state energy of the hydrogen atom.
B) of the presence of helium atoms.
C) the protons must overcome the Coulomb barrier.
D) of the need for low density.
E) the neutrinos carry more energy away than the reaction produces.

Answer 3

the protons must overcome the Coulomb barrier.

Question 4

The free-fall contraction of a molecular cloud

A) can be initiated by shock waves from supernovae.
B) can be initiated by nearby spectral type G stars.
C) can be initiated by the rotation of the cloud.
D) causes the cloud to become transparent to ultraviolet radiation.
E) causes the particles in the cloud to decrease the speed with which they move.

Question 5

What causes the outward pressure that balances the inward pull of gravity in a star?

A) the outward flow of energy
B) the opacity of the gas
C) the temperature of the gas
D) the density of the gas
E) c and d

Question 6

____ is the thermonuclear fusion of hydrogen to form helium operating in the cores of massive stars on the main sequence.

A) The CNO cycle
B) The proton-proton chain
C) Hydrostatic equilibrium
D) The neutrino process
E) none of the above

Question 7

The region of the sun just below the photosphere

A) is undergoing thermonuclear fusion using the proton-proton chain.
B) is undergoing thermonuclear fusion using the CNO cycle.
C) is transporting energy to the photosphere by convection.
D) is not in hydrostatic equilibrium.
E) a and c above

Question 8

The diagram below is an HR diagram.The line indicates the location of the main sequence.Which of the five labeled locations on the HR diagram indicates a luminosity and temperature similar to that of a T Tauri star?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 9

____ are small luminous nebulae excited by nearby young stars.

A) T Tauri stars
B) Herbig-Haro objects
C) O associations
D) WIMPS
E) Giant molecular clouds

Question 10

Interstellar gas clouds may collapse to form stars if they

A) have very high temperatures.
B) encounter a shock wave.
C) rotate rapidly.
D) are located near main sequence spectral type K and M stars.
E) all of the above

Question 11

Main sequence O stars have convective cores because

A) they fuse hydrogen in the CNO cycle.
B) they fuse hydrogen in the proton-proton chain.
C) they contain mostly hydrogen.
D) they have very cool cores.
E) they have very large magnetic fields.

Question 12

Convection is important in stars because it

A) increases the temperature of the star.
B) mixes the gases of the star.
C) transports energy outward in the star.
D) carries the neutrinos to the surface of the star where they can escape.
E) b and c

Question 13

The nuclear reactions in a star's core remain under control so long as

A) luminosity depends on mass.
B) pressure depends on temperature.
C) density depends on mass.
D) weight depends on temperature.
E) temperature depends on mass.

Question 14

The BN object in the Orion molecular cloud is believed to be

A) a star cluster hidden in dust clouds.
B) a forming star nearing the main sequence.
C) a low-mass star fusing hydrogen in its interior.
D) a low-density gas cloud heated by a shock wave.
E) a black hole radiating large amounts of x-ray radiation.

Question 15

In the proton-proton chain

A) no neutrinos are produced.
B) energy is released because a helium nucleus has a greater mass than a hydrogen nucleus.
C) no photons are produced.
D) carbon serves as a catalyst for the nuclear reaction.
E) energy is produced in the form of gamma rays and the velocity of the created nuclei.

Question 16

The central cores of massive main sequence stars

A) produce energy by the proton-proton chain.
B) have a very low opacity.
C) transmit energy outward by convection.
D) burn their nuclear fuels more slowly than low mass main sequence stars.
E) have lower temperatures than the central cores of low mass main sequence stars.

Question 17

If the sun produces energy by the proton-proton chain,then the center of the sun must have a temperature of at least

A) 10⁴ K
B) 10⁷ K
C) 10¹⁰ K
D) 10¹³ K
E) 10¹⁶ K

Question 18

____ occurs when most of the material collapsing to form a protostar has fallen into a disk around the star,and a strong wind from the warm protostar ejects material from its poles.

A) An emission nebula
B) Hydrostatic equilibrium
C) The proton-proton chain
D) The thermonuclear fusion of hydrogen
E) A bipolar flow

Question 19

The carbon-nitrogen-oxygen cycle

A) operates at a slightly lower temperature than the proton-proton chain.
B) is most efficient in a star less massive than the sun.
C) occurs when carbon and oxygen combine to form nitrogen,which produces energy.
D) produces the energy responsible for bipolar flows.
E) combines four hydrogen nuclei to form one helium nucleus,which produces energy.

Question 20

Opacity is

A) the balance between the pressure and force of gravity inside a star.
B) the force that binds protons and neutrons together to form a nucleus.
C) the force that binds an electron to the nucleus in an atom.
D) a measure of the ease with which photons can pass through a gas.
E) the temperature and density at which a gas will undergo thermonuclear fusion.

Question 21

The central cores of which type of star is the lowest temperature?

A) protostars.
B) massive main sequence stars
C) low mass main sequence stars.

Question 22

Ionization from the ____ in the Orion Nebula makes it glow.

A) planets
B) coolest star
C) hottest star

Question 23

Nuclear fusion in stars is controlled by the dependence of density on mass.

Question 24

The youngest stars in the Orion Nebula and other star-forming regions also show

A) circumstellar disks
B) jets
C) Both answers "a" and "b"

Question 25

The Great Nebula in Orion

A) is a Herbig-Haro object.
B) is a reflection nebula.
C) is an emission nebula.
D) contains only young low mass stars.
E) is believed to be about 5 billion years old.

Question 26

As a star begin to form the initial energy source is from

A) nuclear fusion.
B) nuclear fission.
C) gravitational potential energy.
D) magnetic fields.

Question 27

While on the main sequence a star's primary energy source comes from

A) nuclear fusion.
B) nuclear fission.
C) gravitational potential energy.
D) magnetic fields.

Question 28

The H-R diagram of a very young star cluster shows ....

A) only high luminosity main sequence stars
B) only low luminosity main sequence stars
C) only protostars
D) both protostars and high luminosity main sequence stars

Question 29

Ionization from the ____ in the Orion Nebula makes it glow.

A) planets
B) coolest star
C) hottest star

Question 30

The sun has a core in which energy travels outward primarily by radiation.

Question 31

Ninety percent of all stars fuse helium and lie on the main sequence.

Question 32

Hydrostatic equilibrium refers to the balance between weight and pressure.

Question 33

Some young star clusters contain large numbers of T Tauri stars.

Question 34

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

A) temperature.
B) mass.
C) age.
D) luminosity.

Question 35

The sun makes most of its energy by the CNO cycle.

Question 36

The H-R diagram of a young star cluster shows

A) that high mass stars have not yet reached the main sequence yet.
B) that low mass stars have not yet reached the main sequence yet.
C) mainly giant stars.
D) no stars since none have reached the main sequence yet.

Question 37

What force(s)are responsible for the collapse of an interstellar cloud?

A) nuclear
B) gravity
C) electric
D) magnetic
E) Both c and d

Question 38

T Tauri stars are believed to be young,high mass main sequence stars.

Question 39

The hottest stars in the Orion Nebula ____________hydrogen gas and make it _____________.

A) ionize,glow
B) neutralize,glow
C) ionize,swallow the star

Question 40

Energy flows by radiation or convection inside stars but almost never by conduction.

Question 41

Energy transport by ____________________ is important when photons cannot readily travel through a gas.

Question 42

____________________ is the resistance of a gas to the flow of radiation.

Question 43

Ionization from the ____________________ star in the Orion nebula makes it ____________________ brightly.

Question 44

In the collapse of a protostar ____________________ energy is converted to ____________________ energy.

Question 45

Stars with masses greater than 1.1 solar masses use the ____________________ to convert H into He and energy.

Question 46

Pre-main sequence stars are above and to the right of the main sequence.

Question 47

High mass stars evolve more slowly to the main sequence than lower mass stars.

Question 48

The condition of ____________________ means that the force due to gravity pushing down on a layer is exactly equal to the pressure pushing outward on that layer.

Question 49

The Orion region contains young main sequence stars and an emission nebula,but the original molecular cloud they formed out of has been dispersed.

Question 50

Most stars generate their energy by the thermonuclear fusion of ____________________ to form ____________________.

Question 51

A(n)____________________ is a cool,dense cloud of dust and gas that is undergoing gravitational contraction.

Question 52

A star on the ____________________ generates enough energy from nuclear fusion to halt gravitational collapse.