Deck 19: Star Formation: a Traumatic Birth

Question 1

If a star is spinning rapidly, this may limit its final mass.

Answer 1

True

Question 2

At the end of the Kelvin-Helmholtz contraction, a star is hundreds of times brighter than itwill be as a main sequence star.

Answer 2

True

Question 3

The fundamental difference between a protostar and a star is that the latter has nuclear fusionas its energy source and the former does not.

Answer 3

True

Question 4

The evolution of a protostar slows significantly as it approaches the main sequence.

Question 5

The birth of stars is a battle between gravity and radiation pressure.

Question 6

Rotation and magnetism both play key roles in protostar formation.

Question 7

A stage 4 protostar may temporarily be thousands of times more luminous than the Sun.

Question 8

Rotation causes the cocoon of dust to flatten into a dusty disk around protostars.

Question 9

Magnetic fields enhance the collapse of a gas cloud in star formation with bipolar flows.

Question 10

It takes about 1032 hydrogen atoms to make a star.

Question 11

As a protostar evolves from stage 4 to stage 6, it gets hotter but much less bright.

Question 12

Stars evolve to the upper left along the main sequence, after forming in the middle.

Question 13

A protostar of 20 solar masses will probably turn into a type O main sequence star.

Question 14

Brown dwarfs most commonly form in the nebular disk around another object, much like aplanet.

Question 15

Rotation of the protostar helps generate the magnetic fields and bipolar flows.

Question 16

Many of the brightest stars we see are only a few million years old.

Question 17

Collisions between galaxies tend to destroy, not create, stars.

Question 18

A protostar of 20 solar masses should form a star that will stay on the main sequence twentytimes longer than our Sun.

Question 19

Type M stars evolve to the main sequence faster than our G type Sun.

Question 20

Brown dwarfs are failed stars, never igniting their hydrogen fusion.

Question 21

As a star forms, the photosphere first appears:

A)when the planetary nebula is expelled.
B)when the protostar forms.
C)when contraction slows down.
D)when nuclear fires ignite.
E)when the star reaches the main sequence.

Question 22

What is the force that keeps a main sequence star from collapsing on itself?

A)magnetism
B)gravitation
C)the strong force
D)radiation pressure
E)electron degeneration pressure

Question 23

A newly formed protostar will radiate primarily at which wavelength?

A)visible light
B)X-ray
C)infrared
D)ultraviolet
E)radio

Question 24

Stars form from a collapsing cloud that fragments into smaller and smaller pieces. Thisprocess takes about:

A)10,000 years.
B)25,000 years.
C)100,000 years.
D)a few million years.
E)100 million years.

Question 25

Which event marks the birth of a star?

A)formation of the planetary nebula
B)fusion of hydrogen atoms into helium atoms
C)collapse of an interstellar cloud
D)formation of a photosphere
E)instability in an interstellar cloud

Question 26

At what stage of evolution do T Tauri stars occur?

A)just as the collapsing cloud becomes luminous
B)when a protostar is on the verge of becoming a main sequence star
C)just prior to the protostar stage
D)just after the planetary nebula is expelled
E)after the star has established itself as a main sequence star

Question 27

What is the force that keeps a main sequence star from blowing apart?

A)magnetism
B)gravitation
C)the strong force
D)radiation pressure
E)electron degeneration pressure

Question 28

What happens when an interstellar cloud fragment shrinks?

A)It first becomes opaque.
B)Density rises.
C)Temperature rises.
D)Pressure rises.
E)all of the above

Question 29

Most stars are usually formed singularly or as binaries, not in clusters.

Question 30

A typical protostar may be several thousand times more luminous than the Sun. What is thesource of this energy?

A)chemical combustion of hydrocarbons
B)nuclear fusion in its core
C)from the release of gravitational energy as the protostar continues to shrink
D)the ionization of the gas as it heats up
E)from nearby hot stars or supernovae that have initiated the star formation process

Question 31

On an H-R diagram, a protostar would be:

A)above and to the right of the main sequence.
B)below and to the left of the main sequence.
C)below and near the right side of the main sequence.
D)above and near the upper left of the main sequence.
E)on the main sequence at the extreme lower right.

Question 32

During a protostar's T Tauri phase, it:

A)begins a period of reduced activity.
B)expands dramatically.
C)lies on the main sequence.
D)may develop very strong winds.
E)changes its spin direction.

Question 33

How long does it take for a star like our Sun to form?

A)100 thousand years
B)two million years
C)fifty million years
D)one billion years
E)4.6 billion years

Question 34

Our Sun, along with most of the stars in our neighborhood, probably formed:

A)a few million years ago.
B)about 10 million years ago.
C)hundreds of millions of years ago.
D)billions of years ago.
E)at the beginning of the universe.

Question 35

Shock waves from supernovae disrupt an interstellar cloud and prevent it from forming stars.

Question 36

Most stars, probably all stars, formed:

A)in a binary system.
B)in a triple system.
C)in a cluster of stars.
D)all by themselves.
E)There is no theory to predict this.

Question 37

Which statement about the stages of starbirth is FALSE?

A)At stage 1, only the cloud exists.
B)By stage 3, the star has formed a photosphere.
C)Nuclear reactions begin in the core by stage 4.
D)The T Tauri wind is prevalent in stage 5.
E)By stage 7, the star has reached the main sequence.

Question 38

Most stars in our part of the Galaxy are formed:

A)alone.
B)in open clusters of a few dozen.
C)in associations of thousands of stars across a spiral arm of the Galaxy.
D)in globular clusters of millions of stars.
E)in a singular event just after the Big Bang.

Question 39

What is characteristic of a main sequence star?

A)It has a mass less than the Sun's.
B)It has rapid rotation and a strong stellar wind.
C)Nuclear fusion in the core varies due to the amount of gravitational contraction that occursand which heavy elements are produced.
D)The rate of nuclear energy generated in the hydrogen to helium fusing core equals the rateradiated from the surface.
E)All of the above are correct.

Question 40

What makes the subject of star formation so difficult and complex?

A)It is so slow that no visible proof of it exists.
B)Star formation is too expensive to study in detail.
C)Stars live too long to be observed from birth to death.
D)Clouds, fragments, protostars, stars, and nebulae all interact and influence each other.
E)Shock waves disrupt the orderly evolution of stars.

Question 41

Which relationship concerning the mass of protostars is FALSE?

A)The more massive ones will reach the main sequence first.
B)The more massive ones will be the hottest and most luminous.
C)The more massive ones will be made of the heaviest elements.
D)The more massive ones are so luminous they ionize the gas, hence red H II regions.
E)The more massive ones create a lot of ultraviolet as well as visible light.

Question 42

The single most important determinant of the temperature, density, radius, luminosity, andpace of evolution of a protostar is its:

A)chemical composition.
B)magnetic field.
C)spin.
D)mass.
E)molecular composition.

Question 43

Higher mass protostars enter the main sequence:

A)faster and at a higher luminosity and temperature.
B)faster and at a lower luminosity and temperature.
C)slower and at a higher luminosity and temperature.
D)slower and at a lower luminosity and temperature.
E)at the same rate, but at a higher luminosity and temperature.

Question 44

From stage 4 to stage 7 of star formation, the object plotted on the H-R diagram moves sothat:

A)its luminosity decreases, while its temperature increases.
B)its luminosity decreases, while its temperature stays the same.
C)its luminosity increases, while its temperature increases.
D)its luminosity increases, while its temperature stays the same.
E)its luminosity stays the same, and its temperature stays the same.

Question 45

A cloud fragment too small to form a star becomes:

A)a red giant.
B)a black hole.
C)a brown dwarf.
D)a T Tauri object.
E)a Herbig-Haro object.

Question 46

The red evolutionary track illustrated in the figure above (similar to fig 19.6 in your textbook),that goes from point 4 to 5 to 6 to 7 shows:

A)a star nearing the end of its life and becoming a red giant.
B)a star nearing the end of its life and becoming a white dwarf.
C)a protostar forming into a main sequence star.
D)the changes that happen to a star during its red giant phase.
E)the locations on the H-R diagram for a small cluster of stars.

Question 47

Stage 4 of star formation is when the object can exhibit violent surface activity producingextremely strong protostellar winds. This phase is also called the:

A)protostar phase.
B)Herbig-Haro phase.
C)brown dwarf phase.
D)T Tauri phase.
E)protoplanetary nebula phase.

Question 48

A collapsing cloud fragment that will form a star of one solar mass (like our Sun)has a massof about:

A)2 solar masses.
B)10 solar masses.
C)200 solar masses.
D)1020 solar masses.
E)1040 solar masses.

Question 49

A fragment of a collapsing gas cloud that comes to equilibrium with a central temperature of4 million K will become a:

A)black hole.
B)brown dwarf.
C)black dwarf.
D)T Tauri star.
E)stage 1 protostar.

Question 50

How long does it take an O-type star to form, compared to the time for a solar-type star toform?

A)1/300 as long
B)1/30 as long
C)about the same time
D)30 times longer
E)300 times longer

Question 51

How long does it take an M class star to reach the main sequence, compared to a solar typestar?

A)a tenth as long
B)about the same, 30 million years
C)about twice as long
D)about twenty times longer
E)longer than the age of the Galaxy

Question 52

What is the key factor that determines the temperature, density, radius, luminosity, and paceof evolution of a protostellar object?

A)composition of the nebula
B)rotation of the nebula
C)mass of the nebula
D)temperature of the nebula
E)magnetism of the nebula

Question 53

If the initial interstellar cloud in star formation has a mass sufficient to form hundreds ofstars, how does a single star form from it?

A)One star forms at its center and blows the rest of the matter back into space.
B)The cloud fragments into smaller clouds and forms many stars at one time.
C)One star forms and the rest of the matter goes into making planets, moons, and other objectsof a solar system.
D)The cloud is disrupted by rotation so that it reduces its mass down to that of a typical star.
E)A supernova blows the cloud up and dissipates the majority of the gas.

Question 54

During stage 3 of star formation, the dense, opaque region at the center of the cloud is calleda

A)Herbig-Haro object.
B)T Tauri star.
C)protostar.
D)protoplanetary nebula.
E)zero-age main sequence star.

Question 55

A cloud fragment too small to collapse into a main sequence star becomes a:

A)white dwarf.
B)pulsar.
C)T Tauri object.
D)brown dwarf.
E)planet of another star.

Question 56

In the collapsing cloud fragment stage (stage 2)of star formation, the size of the cloudfragment is about:

A)the size of the solar system.
B)10 times the size of the solar system.
C)100 times the size of the solar system.
D)1,000 times the size of the solar system.
E)10,000 times the size of the solar system.

Question 57

Which is characteristic of globular star clusters?

A)old age and hundreds of thousands of stars, only about 30 ly wide
B)no remaining MS stars, but millions of white dwarfs
C)only brown dwarfs in a yellow ball 100 ly across
D)bright blue main sequence stars, and thousands of them
E)a mix of old and young stars, about 100,000 ly across

Question 58

While a star develops from a protostar to a main sequence star, a higher mass star'sevolutionary track, compared to the evolutionary track of a lower mass star:

A)shows that the high mass protostar forms into a star at the same location on the mainsequence.
B)shows that the high mass protostar forms into a redder star on the main sequence.
C)shows that the high mass protostar forms into a bluer star on the main sequence.
D)shows that the evolutionary track of these stars cross as they develop into a main sequencestar.
E)tells us nothing about the main sequence star that will form.

Question 59

Besides mass, the other factor that influences where a star appears on the main sequence is:

A)distance from Earth.
B)number of stars in the cluster.
C)chemical composition of the cloud.
D)the motion of the star.
E)the type of cluster the star is formed in.

Question 60

A stage 4 object can be plotted on the H-R diagram. At this stage, the star will appear:

A)in the middle left of the diagram.
B)in the middle right of the diagram.
C)just on the bottom right of the main sequence.
D)down and to the left of where it will be when it is a main sequence star.
E)in the middle of the main sequence.

Question 61

Most stars in the Milky Way probably formed:

A)alone.
B)in intergalactic space, then were swept up into the Galaxy.
C)in clusters in the Galaxy's spiral arms.
D)from planetary nebulae.
E)in the galactic Nucleus, then migrated outward later.

Question 62

In stage 6 or 7 of the formation of a large cluster of stars, a nebula is formed around thecluster. This happens because:

A)the number of stars is so great and so intense that the gas from the original cloud is ionized.
B)the stars are out of their cocoons of dust and their radiation ionizes the gas from the originalcloud.
C)there are brown dwarfs everywhere in between the stars, so the gas is lit up by their low-intensity light.
D)there are thousands of Sun-like stars with planets around them and the formation of planetsionizes the leftover gas.
E)there are massive O and B stars emitting high energy photons that ionize the remainder of thecloud.

Question 63

Protostars can be observed in:

A)the Crab Nebula.
B)the Andromeda Galaxy.
C)the Orion Nebula.
D)our Solar System.
E)the Helix Nebula.

Question 64

All globular clusters in our Milky Way are about how old?

A)less than a million years
B)ten to fifty million years old
C)one to three billion years old
D)around ten billion years old
E)a variety of ages, from newly born to twenty billions years old

Question 65

Atomic bomb tests demonstrated which aspect of star formation?

A)a shock wave surrounding and compressing a molecular cloud
B)the ignition of fusion that changes a protostar to a star
C)a protostar's movement on the Hayashi track
D)the fragmentation of a molecular cloud
E)a shock wave pushing a molecular cloud from one side

Question 66

Brown dwarfs are most easily detected on which portion of the electromagnetic spectrum?

A)X-ray
B)ultraviolet
C)visible light
D)infrared
E)radio

Question 67

The stars found in nebulae like the Orion Nebula probably formed:

A)a few million years ago.
B)about 10 million years ago.
C)hundreds of millions of years ago.
D)billions of years ago.
E)at the beginning of the universe.

Question 68

Most open clusters in our Milky Way are about how old?

A)less than a million years old
B)There's no specific age for an open cluster; stars in a single open cluster vary greatly in age.
C)less than a billion years old
D)around ten billion years old
E)a variety of ages, from newly born to twenty billions years old

Question 69

Brown dwarfs form:

A)in the nebular disk around another object.
B)outside of a galaxy.
C)in planetary nebulae.
D)as the result of a supernova.
E)in their own contracting fragment of a molecular cloud.

Question 70

What are the characteristics of globular cluster stars?

A)no stars as hot as our Sun
B)old age and hundreds of thousands to millions of member stars
C)no main sequence stars left, with billions of member stars
D)a few hundred stars, most still on the main sequence
E)hundreds of light-years across, with bright OB stars dominant

Question 71

The most important fact about a cluster of stars that makes them useful for studying starformation is that:

A)all the stars formed from the same cloud.
B)all the stars formed at about the same time.
C)all the stars are at the same distance from Earth.
D)all the stars have the same chemical composition.
E)all the stars are the same spectral type.

Question 72

Whether an object is a brown dwarf or a planet can be determined by:

A)the mass of the object.
B)the temperature of the object.
C)the composition of the object.
D)the diameter of the object.
E)whether the object is inside or outside of the galaxy.

Question 73

Which of these is NOT typical of a condensing protostar?

A)magnetic fields producing polar flows
B)dusty disks around their equators
C)Herbig-Haro objects projecting a light-year out in space
D)fusion of helium into carbon in their cores
E)more infrared than visible light given off from the cocoon of dust around the star

Question 74

Star clusters have been observed within dark nebulae with:

A)optical movies made over decades.
B)radio interferometers.
C)infrared observations.
D)the Chandra X-ray Observatory.
E)ultraviolet light creating the emission nebulae.

Question 75

What kind of variable stars are pre-Main Sequence stars undergoing gravitational contractionand exhibiting erratic changes in their luminosities?

A)R Coronae Borealis
B)RR Lyrae
C)Cepheid
D)T Tauri
E)Herbig-Haro

Question 76

What are the characteristics of an open cluster of stars?

A)mostly found above and below the galactic plane
B)old age and millions of members
C)a few hundred, mainly main sequence stars
D)All stars are much more massive than our Sun.
E)All stars are about the same age and luminosity.

Question 77

How are T Tauri stars characterized observationally?

A)by sudden changes in their brightness
B)by very high temperatures
C)by very high magnetic fields and large starspots
D)by very rapid rotation
E)They are newly formed stars that are short period binaries.

Question 78

Why are star clusters almost ideal "laboratories" for stellar studies?

A)All stars in the cluster are the same size and luminosity.
B)Their combined light makes them much easier to spot from a distance.
C)Stars in clusters have the same age, similar composition, and are at the same distance away.
D)Stars in clusters are all relatively young and therefore shine brightly.
E)Like our Sun, stars in clusters are always located in the plane of the Milky Way Galaxy.

Question 79

Which of these is NOT a source of the shock waves that lead to protostars?

A)radiation from the OB stars in emission nebulae
B)expanding Herbig-Haro objects
C)expanding planetary nebula shells
D)violent supernovae explosions
E)collisions between galaxies

Question 80

When a typical open cluster forms, which type of stars are formed most often?

A)solar type stars of class G
B)OB associations
C)red giants
D)low mass M type dwarfs
E)white dwarfs