Deck 7: The Structure and Formation of Stars

Question 1

What can initiate the free-fall contraction of a molecular cloud?

A)shock waves from supernovae
B)nearby spectral type G stars
C)the rotation of the cloud
D)the cloud becoming transparent to ultraviolet radiation

Answer 1

shock waves from supernovae

Question 2

Which of the following relationships is the key to nuclear reactions in a star's core remaining under control?

A)Luminosity depends on mass.
B)Pressure depends on temperature.
C)Density depends on mass.
D)Weight depends on temperature.

Answer 2

Pressure depends on temperature.

Question 3

What is the source of the pink glow within the Great Nebula in Orion?

A)a Herbig-Haro object
B)a reflection nebula made of dust
C)young low-mass stars
D)an emission nebula made of gas

Answer 3

an emission nebula made of gas

Question 4

Which of the following are small luminous nebulae excited by young stars nearby?

A)T Tauri stars
B)Bok globules
C)O associations
D)Herbig-Haro objects

Question 5

What happens in the carbon-nitrogen-oxygen (CNO)cycle?

A)Carbon nuclei are split 3 ways to make helium nuclei.
B)Carbon and oxygen combine to form nitrogen, which produces energy.
C)Carbon and nitrogen combine to form oxygen and energy.
D)Four hydrogen nuclei combine to form one helium nucleus and energy.

Question 6

Because they are composed of ionized hydrogen,emission nebulae have another name - what is that name?

A)HI regions
B)HII regions
C)Bok globules
D)HeI regions

Question 7

How much of its lifetime does the average star spend on the main sequence?

A)1%
B)10%
C)20%
D)90%

Question 8

What is opacity?

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 temperature and density at which a gas will undergo thermonuclear fusion
D)a measure of the resistance to the flow of radiation (photons) through a gas

Question 9

Why is the presence of massive stars in the Orion Nebula an indication that star formation is currently occurring?

A)The Orion Nebula contains large amounts of gas and dust.
B)Massive stars have short lives, so they must have formed recently.
C)Massive stars trigger star formation in nearby gas clouds.
D)The Orion Nebula contains large numbers of brown dwarfs and supernova remnants.

Question 10

What happens in the proton-proton chain?

A)Two protons are fused to make a helium nucleus.
B)Three protons are fused to make a lithium nucleus.
C)A helium nucleus is split into four protons.
D)Four protons are fused to make a helium nucleus.

Question 11

What causes the outward gas pressure that balances the inward pull of gravity in a main-sequence star?

A)the rapid outward flow of gas
B)the rapid inward flow of gas
C)the high temperature and density of the gas
D)the low mass of helium nuclei

Question 12

The lower edge of the main-sequence band represents the location in the H-R diagram at which stars begin their lives as main-sequence stars.What is it called?

A)the zero-age main sequence
B)the birth line
C)the Coulomb barrier
D)the evolutionary track

Question 13

Refer to the H-R diagram.Which of the points represents a star in which the proton-proton chain is occurring?

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

Question 14

Under what conditions might interstellar gas clouds collapse to form stars?

A)if they encounter a shock wave
B)if they have very high temperatures
C)if they rotate rapidly
D)if they are located near main-sequence spectral type K and M stars

Question 15

Refer to the H-R diagram.Which of the points represents a star in which the CNO cycle is occurring?

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

Question 16

On this H-R diagram,the line indicates the location of the main sequence.Which of the four labelled locations on the H-R diagram indicates a luminosity and temperature similar to that of a T Tauri star?

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

Question 17

Why are protostars difficult to observe?

A)The protostar stage is very long.
B)They are all so far away that the light hasn't reached us yet.
C)Most of their radiation is in the form of X-rays.
D)They are surrounded by cocoons of gas and dust.

Question 18

Why is convection important in stars?

A)because it mixes the star's gases and increases the temperature of the star
B)because it mixes the star's gases and transports energy outwards
C)because it carries energy toward the core of the star
D)because it carries the neutrinos to the surface of the star where they can escape

Question 19

What is the term for the process that fuses hydrogen into helium in the cores of massive main-sequence stars?

A)the CNO cycle
B)the proton-proton chain
C)hydrostatic equilibrium
D)the neutrino process

Question 20

Which of the following are star-like objects that contain less than 0.08 solar masses and will never raise their core temperatures high enough that the proton-proton chain can begin?

A)brown dwarfs
B)Herbig-Haro objects
C)Bok globules
D)T Tauri stars

Question 21

What occurs when some of the material collapsing to form a protostar is ejected from its poles?

A)A protoplanetary disk forms.
B)The star stops collapsing.
C)The T Tauri phenomenon occurs.
D)Jets extend into the interstellar medium.

Question 22

What would a H-R diagram of a young star cluster show?

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

Question 23

What is the approximate mass of the lowest mass object that can initiate the thermonuclear fusion of hydrogen?

A)0.08 solar mass
B)1 solar mass
C)8 solar masses
D)80 solar masses

Question 24

As a human with a temperature of about 310 K,you radiate most strongly at a wavelength of about 10 micrometres.If the dust around a protostar radiates most strongly at 30 micrometres,what is the approximate temperature of that dust?

A)100,000 K
B)10,000 K
C)1000 K
D)100 K

Question 25

As a star begins to form,what is its primary energy source?

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

Question 26

What is the lifetime of a 10 solar mass star on the main sequence?

A)3.2×10⁷ years
B)1×10⁹ years
C)1×10¹¹ years
D)3.2×10¹² years

Question 27

While on the main sequence,what is a star's primary energy source?

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

Question 28

The Sun has an expected main-sequence lifetime of about 10¹⁰ years.What is the lifetime on the main sequence of a 2 solar mass star?

A)1.8×10⁶ years
B)1.8×10⁹ years
C)1.8×10¹⁰ yearsα
D)1.8×10¹¹ years

Question 29

Absorption lines due to the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density.How do they show this?

A)The lines are blue shifted.
B)The lines are red shifted.
C)The lines are extremely broad.
D)The lines are extremely narrow.

Question 30

Due to the dust in the interstellar medium,how will a distant star will appear to an observer on Earth?

A)brighter and cooler than it really is
B)brighter and hotter than it really is
C)fainter and cooler than it really is
D)fainter and hotter than it really is

Question 31

Why is there a main sequence mass-luminosity relation?

A)because helium fusion produces carbon
B)because more massive stars support their larger weight by making more energy
C)because the helium flash occurs in degenerate matter
D)because all stars on the main sequence have about the same radius

Question 32

How can molecular clouds be observed?

A)by using infrared telescopes to detect ionized gas in the clouds
B)by using X-ray telescopes to observe the X-ray radiation from the molecules in the cloud
C)by using radio telescopes to observe the emission from CO molecules in the clouds
D)by using radio telescopes to observe the 21-cm radiation from hydrogen

Question 33

Which of the following is NOT evidence of the existence of an interstellar medium?

A)extinction of light from distant stars
B)very narrow calcium absorption lines in the spectra of O and B stars
C)reddening of more distant stars
D)molecular absorption lines in the spectra of cool stars

Question 34

Stars with masses below a certain threshold produce most of their energy via the proton-proton chain.What is that threshold?

A)0.01 solar masses
B)0.1 solar masses
C)1.1 solar masses
D)11 solar masses

Question 35

Which of the following are small dark nebulae about 1 light year in diameter,with masses from 10 to 1,000 solar masses?

A)HII regions
B)emission nebulae
C)Bok globules
D)reflection nebulae

Question 36

The formation of one of the following phenomena requires that a young hot star (T =25,000 K)be relatively close by.Which one?

A)emission nebulae
B)HI regions
C)molecular clouds
D)21-centimetre radiation

Question 37

What causes the dimming of starlight in the interstellar medium?

A)dust particles
B)ionized hydrogen
C)neutral hydrogen
D)molecular gas

Question 38

How do absorption lines from interstellar gas compare to absorption lines from stars?

A)They are wider than the lines from stars because the gas is hotter than most stars.
B)They are narrower than the lines from stars because the gas has a lower pressure than stars.
C)They indicate that the interstellar medium contains different elements than stars do.
D)They indicate that interstellar medium clouds have high velocities.

Question 39

Where are stars born?

A)reflection nebulae
B)dense molecular clouds
C)HII regions
D)the intercloud medium

Question 40

Why does the main sequence have a limit at the lower end?

A)Low mass stars form from the interstellar medium very rarely.
B)Low mass objects are composed primarily of solids, not gases.
C)The lower limit represents a star with zero radius.
D)A minimum temperature is required for hydrogen nuclear fusion to take place.

Question 41

How did observations at the Sudbury Neutrino Observatory solve the solar neutrino problem?

A)They showed that the "missing neutrinos" had changed into a different type.
B)They showed that other experiments had mis-counted the number of solar neutrinos.
C)They showed that models for the number of neutrinos produced by the Sun were wrong.
D)They showed that neutrinos were not escaping from the core of the Sun.

Question 42

Why do higher mass stars live shorter lives on the main sequence than lower mass stars?

A)Higher mass stars burn through their nuclear fuel faster.
B)Lower mass stars don't get their energy from nuclear fusion like higher mass stars do.
C)Higher mass stars have less hydrogen fuel to burn.
D)Lower mass stars spend a longer time evolving to the main sequence.

Question 43

Which of the following factors explain why infrared telescopes are used to observe protostars?

A)density and composition
B)density and the presence of dust
C)temperature and the presence of dust
D)temperature and luminosity

Question 44

Why does the proton-proton chain need high temperatures?

A)High temperatures increase the ground state energy of the hydrogen atom.
B)High temperatures increase the velocity of the protons so they can overcome the Coulomb barrier.
C)High temperatures lower the density of the gas.
D)High temperatures allow the neutrinos to carry more energy away than the reaction produces.

Question 45

What evidence can be used to show that space is not a vacuum?

A)ultraviolet radiation emitted by dust
B)narrow emission lines seen in stellar spectra
C)the presence of bright nebulae
D)the blue colour of stars seen near dark regions

Question 46

What must occur for an object to be considered a main-sequence star?

A)Hydrostatic equilibrium ends.
B)Nuclear fusion reactions in the core begin.
C)Helium flash occurs in the core.
D)Gravitational contraction begins.

Question 47

Which of the following is the best example of energy transport by conduction?

A)Your feet are warmed when you hold them in front of a fire.
B)Your feet are warmed when you wear socks.
C)Your feet get cold when you stand on a cold floor.
D)Your feet get cold when you hold them over a cool air vent.

Question 48

Star clusters are important to the study of stellar evolution because all the stars in a given cluster have one thing in common.What is it?

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

Question 49

What is the name of the process by which the Sun turns mass into energy?

A)nuclear fission
B)nuclear fusion
C)convection
D)radiation

Question 50

What force is responsible for the collapse of an interstellar cloud?

A)nuclear
B)gravity
C)electric
D)magnetic

Question 51

What does solving equations on a computer have to do with making a stellar model?

A)The equations apply the laws of stellar structure at locations within the star.
B)Equations can describe the H-R diagram and a star's location on it.
C)The mass-luminosity equation tells you how to find a star's luminosity given its mass.
D)Equations are used to model the nuclear reactions inside a star.

Question 52

Consider two stars of the same mass: star 1 has just moved on to the main sequence,and star 2 is about to leave it.How are these two stars different?

A)Star 2 has more helium in its core and a hotter surface.
B)Star 2 has more helium in its core and a cooler surface.
C)Star 1 is more luminous and has a hotter surface.
D)Star 1 is more luminous and has a cooler surface.

Question 53

How does the temperature inside a star determine how energy flows inside it?

A)The radiation rate depends on temperature.
B)The dependence of opacity on temperature makes convection happen.
C)The dependence of opacity on temperature makes conduction happen.
D)The temperature determines how much energy is produced at each layer.

Question 54

Why do nuclear fusion reactions only take place in the interior of a star?

A)The magnetic fields are strongest there.
B)The temperature and density are highest in the centre.
C)The core is the only place where hydrogen is found.
D)The strong nuclear force is only active in the centres of stars.

Question 55

What happens to light as it passes through dark nebulae?

A)transmission
B)emission
C)reflection
D)absorption

Question 56

What is produced in the proton-proton chain?

A)two hydrogen nuclei, a single helium nucleus and energy in the form of visible light
B)four hydrogen nuclei and energy in the form of gamma rays
C)a helium nucleus and energy in the form of gamma rays
D)two hydrogen nuclei and energy in the form of visible light

Question 57

In which option below are the stellar types sorted from shortest to longest main-sequence lifetime?

A)O, A, K, M
B)A, B, F, G
C)K, F, B, O
D)B, A, M, G

Question 58

What concept explains why both fusion and fission release energy?

A)proton-proton chain energy
B)Coulomb barrier energy
C)strong force energy
D)nuclear binding energy

Question 59

What characteristic of a star primarily determines its location on the main sequence?

A)age
B)distance from the galactic centre
C)mass
D)radius

Question 60

Which of the following is considered to be the best explanation for the missing solar neutrinos?

A)The Sun is fusing helium but not hydrogen.
B)Nuclear reactions do not produce neutrinos as fast as theory predicts.
C)The Sun may contain matter we haven't yet identified.
D)Neutrinos may oscillate between three different flavours.

Question 61

What does the strong force do?

A)It binds electrons to the nucleus in an atom.
B)It holds the Moon in orbit around the Earth.
C)It creates the magnetic field associated with sunspots.
D)It binds protons and neutrons together to form a nucleus.

Question 62

When energy is carried by the bulk motion of matter,that is called ____________________.

Question 63

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

Question 64

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

Question 65

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

Question 66

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

Question 67

Why are emission nebulae associated with young stars?

A)Young stars have not moved far from the gaseous nebulae where they were born.
B)Only hot stars can ionize nearby gas; hot stars are high-mass, so must be young.
C)The dust that makes emission nebulae glow is destroyed by old stars.
D)Young stars produce the blue light that is scattered by emission nebulae.

Question 68

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

Question 69

The pressure of an interstellar gas cloud depends on the cloud's ____________________ and ____________________.

Question 70

A(n)____________________ is a subatomic particle produced in nuclear fusion that can travel through the Sun and escape to space without interacting with any particles in the Sun.

Question 71

Which of the following is most similar in size to a brown dwarf?

A)the planet Jupiter
B)a red dwarf
C)a white dwarf
D)a Bok globule

Question 72

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

Question 73

____________________ appear reddish in colour due to the light emitted by the Balmer series of the hydrogen atom.

Question 74

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

Question 75

Stars with masses greater than 1.1 solar masses use the ____________________ to convert hydrogen into helium and produce energy

Question 76

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

Question 77

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

Question 78

What is the term for a group of 10 to 100 stars that formed at the same time but are so widely scattered in space their mutual gravity cannot hold them together?

A)a globular cluster
B)an open cluster
C)an association
D)a spherical component

Question 79

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

Question 80

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