Deck 9: The Formation and Structure of Stars

Question 1

_________ are small luminous nebulae excited by nearby young stars.

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

Answer 1

Herbig-Haro objects

Question 2

________ 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

Answer 2

The CNO cycle

Question 3

The visual pink glow of the Great Nebula in Orion

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

Answer 3

is an emission nebula of thin gas.

Question 4

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)dark cloud silhouetted against background stars
E)molecular absorption lines in the spectra of cool stars

Question 5

The lower edge of the main-sequence band is known as ________ and represents the location in the H-R diagram at which stars begin their lives as main-sequence stars.

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

Question 6

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 the gas
C)the high temperature of the gas
D)the high density of the gas
E)the high temperature and the high density of the gas

Question 7

________ 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. Other minor fusion reactions do occur in these objects. They fall in a gap between the low-mass M dwarf stars and the massive planets in which nuclear fusion never occurs.

A)Brown dwarfs
B)Herbig-Haro objects
C)Bok globules
D)T-Tauri star
E)Main-sequence stars

Question 8

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

Question 9

________ 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 outflow

Question 10

There is a main-sequence mass-luminosity relation because

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

Question 11

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

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.
E)unchanged in brightness or apparent color.

Question 12

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 13

Protostars are difficult to observe because

A)the protostar stage is very short.
B)they are surrounded by cocoons of gas and dust.
C)they radiate mainly in the infrared.
D)the protostar stage is very short, they are surrounded by cocoons of gas and dust, and they radiate mainly in the infrared.
E)they are all so far away that the light hasn't reached us yet.

Question 14

The average star spends ________ of its lifetime on the main sequence.

A)1%
B)2%
C)10%
D)20%
E)90%

Question 15

The carbon-nitrogen-oxygen cycle

A)operates at a slightly lower temperature than the proton-proton chain.
B)is most efficient in 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 16

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 other choices are correct.

Question 17

The H-R diagram main-sequence of stars has a limit at the lower-mass or energy-output end because

A)low-mass stars form from the interstellar medium very rarely.
B)low-mass objects are composed primarily of solids, not gases.
C)pressure does not depend on temperature in degenerate matter.
D)the lower limit represents when the radius of the star would be zero.
E)there is a minimum temperature for hydrogen nuclear fusion (the definition of a star).

Question 18

Emission nebulae are also called ________ because they are composed of ionized hydrogen.

A)HI regions
B)HII regions
C)Bok globules
D)HeI regions
E)reflection nebulae

Question 19

The diagram below is an H-R diagram. The line indicates the location of the main sequence. Which of the five labeled 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
E)5

Question 20

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)mixes the gases of the star and transports the energy outward in the star.

Question 21

The lowest-mass object that can initiate thermonuclear fusion of hydrogen has a mass of about

A)1 solar masses.
B)80 solar masses.
C)8 solar masses.
D)0.08 solar masses.
E)0.001 solar masses.

Question 22

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 23

The creation of ________ require(s) that a young hot star (T ≈ 25,000 K) be relatively nearby.

A)emission nebulae
B)HI regions
C)molecular clouds
D)the cool gas of the interstellar medium
E)21-cm radiation

Question 24

________ are small dark nebulae about 1 light-year in diameter that contain 10 to 1,000 solar masses.

A)HI regions
B)HII regions
C)Emission nebulae
D)Bok globules
E)Reflection nebulae

Question 25

Stars are born in

A)reflection nebulae.
B)dense molecular clouds.
C)HII regions.
D)the intercloud medium.
E)the local bubble.

Question 26

If the dust around a protostar radiates most strongly at 30 microns or 30,000 nm, what is the approximate temperature of that dust Hint: T in K = 3,000,000/wavelength in nm or use Wien's Law.

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

Question 27

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

A)The magnetic fields are strongest there.
B)The temperature is the hottest in the center.
C)The density of material is very high in the center.
D)The temperature is the hottest in the center and the density of material is very high in the center.
E)FALSE; Nuclear fusion reactions can take place in the core and corona where temperatures are high enough.

Question 28

Absorption lines due to the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density because

A)the lines are blue shifted.
B)the lines are red shifted.
C)the lines are extremely broad.
D)the lines are extremely narrow.
E)the lines are much darker than the stellar lines.

Question 29

What is the lifetime on the main sequence of a 2-solar-mass star compared to the approximately 10-billion-year life of our Sun Pick the best answer.

A)1.8 × 1011 years
B)1.8 × 1010 years
C)1.8 × 108 years
D)1.8 × 106 years
E)1.8 × 103 years

Question 30

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

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

Question 31

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

A)age
B)distance from the galactic center
C)mass
D)space motion
E)radius

Question 32

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 33

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)the temperature and the density of the gas

Question 34

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 35

Absorption lines due to interstellar gas

A)are wider than the lines from stars because the gas is hotter than most stars.
B)are narrower than the lines from stars because the gas has a lower pressure than stars.
C)indicate that the interstellar medium contains dust.
D)indicate that the interstellar medium is expanding away from the Sun.
E)None of the other choices are correct.

Question 36

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

A)hydrostatic equilibrium
B)nuclear fusion reaction in the core
C)protostar life begins
D)hydrostatic equilibrium and nuclear fusion reaction in the core

Question 37

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 38

A jet has an angular length of 10 seconds of arc and flows from a star at a distance of 2,000 pc. How far does this jet extend away from the star

A)20,000 pc
B)20,000 AU
C)20, 000 ly
D)20,000 miles
E)20,000 km

Question 39

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

A)circumstellar disks.
B)jets.
C)circumstellar disks and jets.

Question 40

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

A)3.2 × 107 years
B)320 years
C)3.2 × 1012 years
D)1× 109 years
E)1 × 1011 years

Question 41

The above visual wavelength image is of a ___________, which is a(n) _________.

A)dark nebula, empty space
B)reflection nebula, dark cloud
C)Bok globule, empty space
D)emission nebula, dark cloud

Question 42

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

A)protostars.
B)massive main-sequence stars.
C)white dwarf stars.

Question 43

A ZAMS star evolves __________ and to the __________ on the H-R diagram because ________________.

A)downward, left, the core expands which causes the outer layers to expand
B)upward, right, the core contracts which causes the outer layers to expand
C)upward, left, the core expands which causes the outer layers to contract
D)downward, right, the core contracts which causes the outer layers to contract

Question 44

The above image is an example of a/an ____________.

A)cluster of stars producing reflection nebula
B)T association
C)OB association
D)Trapezium cluster

Question 45

A ZAMS star is located _______________________.

A)above the main sequence
B)on the upper edge of the main sequence
C)in the middle of the main sequence
D)on the lower edge of the main sequence

Question 46

in the following image, the blue color is from a/an ____________ nebula whereas the pink color is from a/an ___________ nebula.

A)dark, reflection
B)reflection, emission
C)emission, dark
D)emission, reflection

Question 47

In the following visible + near infrared image, the white color is the ______, the red color is the __________, and the lack of white color (or black color) sandwiched between the upper white half-moon shape and the lower white half-moon shape is _________________.

A)star, jet, the infrared part
B)disk, Herbig-Haro object, empty space
C)surface disk, jet, the dense dust disk
D)None of the other choices are correct.

Question 48

What evidence indicates protostars have formed

A)jets
B)bipolar outflows
C)protostellar disks
D)All of the other choices are correct.

Question 49

The image on the right indicates star formation that we cannot see in the wavelength band on the left. The image on the left is a/an __________ wavelength image of the ___________ wavelength image on the right.

A)radio, infrared
B)infrared, visual
C)visual, infrared
D)infrared, radio

Question 50

The hottest star in the Orion Nebula ____________hydrogen gas and makes it _____________.

A)ionizes; glow
B)neutralizse; glow
C)ionizes; swallow the star

Question 51

The above image is an example of a ________.

A)protostellar disk
B)YSO
C)protostar
D)Herbig-Haro object

Question 52

If in a gas the opacity is high, then energy transport is by _____________.

A)conduction
B)convection
C)radiation
D)All of the other choices are correct.

Question 53

Which of the following energy transport processes involves mass motions of material

A)radiation
B)conduction
C)convection
D)All of the other choices are correct.

Question 54

In the Herbig-Haro object shown above, the Herbig-Haro is the ___________.

A)red jet
B)white/blue colored interstellar medium the red jet runs into
C)dusty disk containing a newborn star and the red jet
D)All of these choices are correct.

Question 55

Which of the following is a method of energy transport

A)convection
B)radiation
C)conduction
D)All of the other choices are correct.

Question 56

The above reactions are of the ___________________.

A)proton-proton fusion chain
B)hydrogen-hydrogen fusion chain
C)CNO cycle
D)All of the other choices are correct.

Question 57

Which is the correct evolutionary order

A)protostar, ZAMS, YSO
B)protostar, YSO, ZAMS
C)ZAMS, protostar, YSO
D)ZAMS, YSO, protostar

Question 58

You would like to see through the dust in a cloud to find protostars. Which band of the electromagnetic spectrum would you need to look in

A)infrared
B)visual
C)UV
D)X-ray

Question 59

What is the correct fraction of dust to gas in the interstellar medium

A)1/99
B)10/90
C)50/50
D)90/10

Question 60

in the following cartoon image of Orion, where would you find the Orion nebula

A)below the belt (i.e., three white stars) but above the lower right blue and lower left white stars
B)above the belt (i.e., three white stars) but below the upper red and the upper white stars
C)in the belt, that is, among the three white stars
D)outside the white lines

Question 61

You would use the 21-cm radio emission line to map out ____________.

A)the interstellar medium
B)molecular clouds
C)atomic hydrogen clouds
D)All of the other choices are correct.

Question 62

The above visual wavelength image of the Trapezium cluster shows _________.

A)main sequence and protostars
B)protostars and YSOs
C)YSOs and ZAMS
D)ZAMS and protostars

Question 63

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 64

The interstellar medium is made of ___ % dust and ___ % gas.

A)1, 99
B)0, 100
C)100, 0
D)5, 95

Question 65

Which of the following in not a factor that prevents molecular cloud contraction

A)thermal motion
B)a force exerted by a magnetic field
C)orbital motion
D)turbulence

Question 66

Star may appear fainter due to the interstellar medium. This effect is known as ____________________.

A)interstellar reddening
B)interstellar extinction
C)interstellar absorption line
D)interstellar dust

Question 67

The above image is an example of a/an _________ nebula.

A)dark
B)emission
C)Bok globule
D)reflection

Question 68

The densest, coldest clouds are called _____________.

A)reflection nebula
B)dark nebula
C)Bok globules
D)molecular clouds

Question 69

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

Question 70

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

Question 71

Stars are born in ______________________.

A)molecular clouds
B)atomic hydrogen clouds
C)emission nebula
D)reflection nebula

Question 72

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

Question 73

How long can a 1-solar-mass star live

A)0.5 solar lifetimes
B)1 solar lifetime
C)2 solar lifetimes
D)10 solar lifetimes

Question 74

The above image is a/an _________ wavelength image of a reflection nebula.

A)infrared
B)visual
C)radio
D)X-ray

Question 75

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

Question 76

The interstellar medium is made of ______________.

A)gas
B)dust
C)gas and dust
D)None of these choices are correct.

Question 77

A spectral line produced in the atmosphere of a star may be seen as broad whereas interstellar _______________ lines are very narrow.

A)absorption
B)continuous
C)emission
D)All of the other choices are correct.

Question 78

To initiate star formation in a cloud, you need a __________.

A)slow contraction of a molecular cloud
B)rotating molecular cloud
C)magnetic field
D)shock

Question 79

How long can a four-solar-mass star live

A)1 solar lifetime
B)0.03125 solar lifetimes
C)3 solar lifetimes
D)None of the other choices are correct.

Question 80

A star has crossed the birth line and thus that star is now called a ________________.

A)main-sequence star
B)protostar
C)YSO
D)ZAMS