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Ch. 19 Our Sun_ along with most of the stars in our neighborhood

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Ch. 19 Our Sun_ along with most of the stars in our neighborhood Powered By Docstoc
					Ch. 19
Our Sun, along with most of the stars in our neighborhood probably formed about
    a few million years ago.

    billions of years ago.

    at the beginning of the universe.

    10 million years ago.

    hundreds of millions of years ago.
Correct
What makes the subject of star formation so difficult and complex?
   Stars live too long to be observed from birth to death.

    It is so slow that no visible proof of it exists.

    Shock waves disrupt the orderly evolution of stars.

    Star formation is too expensive to study in detail.

    Clouds, fragments, protostars, stars, and nebulae all interact and influence each other.
Correct

Which event marks the birth of a star?
    formation of the planetary nebula

    formation of a photosphere

    instability in an interstellar cloud

    fusion of hydrogen atoms into helium atoms

    collapse of an interstellar cloud
Correct
What is the force that keeps a main sequence star from blowing apart?
   The strong force

    Magnetism

    Gravitation

    Radiation pressure

    Electron degeneration pressure
Correct

What happens when an interstellar cloud fragment shrinks?
   It first becomes opaque.

    Density rises.

    Temperature rises.
    Pressure rises.

    all of the above
Correct
During a protostar's T Tauri phase, it
    changes its spin direction.

    may develop very strong winds.

    expands dramatically.

    begins a period of reduced activity.

    lies on the main sequence.
Correct
A newly formed protostar will radiate primarily at which wavelength?
    x-ray

    ultraviolet

    radio

    infrared

    visible light
Correct
How long does it take for a star like our Sun to form?
   fifty million years

    100 thousand years

    two million years

    4.6 billion years

    one billion years

A typical protostar may be several thousand times more luminous than the Sun. What is the source of this
energy?
    from the release of gravitational energy as the protostar continues to shrink

    the ionization of the gas as it heats up

    nuclear fusion in its core

    chemical combustion of hydrocarbons

    from nearby hot stars or supernovae that have initiated the star formation process
Correct
As a star forms, the photosphere first appears:
    when the protostar forms.

    when contraction slows down.
    when nuclear fires ignite.

    when the planetary nebula is expelled.

    when the star reaches the main sequence.
Correct
What is characteristic of a main sequence star?
   It has rapid rotation and a strong stellar wind.

    It has a mass less than the Sun's.
    Nuclear fusion in the core varies due to the amount of gravitational contraction that occurs and which
    heavy elements are produced.
    The rate of nuclear energy generated in the hydrogen to helium fusing core equals the rate radiated
    from the surface.
    All of the above are correct.
Correct
At what stage of evolution do T Tauri stars occur?
    when a protostar is on the verge of becoming a main sequence star

    just prior to the protostar stage

    after the star has established itself as a main sequence star

    just after the planetary nebula is expelled

    just as the collapsing cloud becomes luminous
Correct
On an H-R diagram, a protostar would be
    below and near the right side of the main sequence.

    on the main sequence at the extreme lower right.

    below and to the left of the main sequence.

    above and near the upper left of the main sequence.

    above and to the right of the main sequence.
Correct
Most stars in our part of the Galaxy are formed
    alone.

    in associations of thousands of stars across a spiral arm of the Galaxy.

    in a singular event just after the Big Bang.

    in globular clusters of millions of stars.

    in open clusters of a few dozen.
Correct
Most stars in our part of the Galaxy are formed
    alone.
    in associations of thousands of stars across a spiral arm of the Galaxy.

    in a singular event just after the Big Bang.

    in globular clusters of millions of stars.

    in open clusters of a few dozen.
Correct
Most stars in our part of the Galaxy are formed
    alone.

    in associations of thousands of stars across a spiral arm of the Galaxy.

    in a singular event just after the Big Bang.

    in globular clusters of millions of stars.

    in open clusters of a few dozen.
Correct
What is the force that keeps a main sequence star from collapsing on itself?
   The strong force

    Magnetism

    Gravitation

    Radiation pressure

    Electron degeneration pressure
Correct
What is the force that keeps a main sequence star from collapsing on itself?
   The strong force

    Magnetism

    Gravitation

    Radiation pressure

    Electron degeneration pressure
Correct
Stars form from a collapsing cloud that fragments into smaller and smaller pieces. This process takes
about
    a few million years.

    100 million years.

    100,000 years.

    25,000 years.

    10,000 years.
Correct
A collapsing cloud fragment that will form a star of one solar mass (like our Sun) has a mass of about
       40
    10 solar masses.

    200 solar masses.

    2 solar masses.
       20
    10 solar masses.

    10 solar masses.
Correct
In the collapsing cloud fragment stage (stage 2) of star formation, the size of the cloud fragment is about
     10,000 times the size of the solar system.

    100 times the size of the solar system.

    the size of the solar system.

    10 times the size of the solar system.

    1,000 times the size of the solar system.
Correct
During stage 3 of star formation, the dense, opaque region at the center of the cloud is called a
    zero-age main sequence star.

    T Tauri star.

    Herbig-Haro object.

    protoplanetary nebula.

    protostar.
Correct
A stage 4 object can be plotted on the H-R diagram. At this stage, the star will appear
     in the middle left of the diagram.

    just on the bottom right of the main sequence.

    down and to the left of where it will be when it is a main sequence star.

    in the middle right of the diagram.

    in the middle of the main sequence.
Correct
From stage 4 to stage 7 of star formation, the object plotted on the H-R diagram moves so that
    its luminosity decreases, while its temperature increases.

    its luminosity decreases, while its temperature stays the same.

    its luminosity increases, while its temperature increases.

    its luminosity increases, while its temperature stays the same.

    its luminosity stays the same, and its temperature stays the same.
Correct
Stage 4 of star formation is when the object can exhibit violent surface activity producing extremely strong
protostellar winds. This phase is also called the
     T Tauri phase.

    protostar phase.

    brown dwarf phase.

    Herbig-Haro phase.

    protoplanetary

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

    temperature of the nebula

    mass of the nebula

    rotation of the nebula

    magnetism of the nebula
Correct
A cloud fragment too small to form a star becomes:
     a Herbig Haro object.

    a brown dwarf.

    a black hole.

    a red giant.

    a T Tauri object.
Correct
How long does it take an M class star to reach the main sequence, compared to a solar type star?
   about twenty times longer

    a tenth as long

    about the same, 30 million years

    about twice as long

    longer than the age of the Galaxy
Correct
How long does it take an O-type star to form, compared to the time for a solar-type star to form?
   30 times longer

    300 times longer

    about the same time

    1/30 as long
     1/300 as long
Correct
Which relationship concerning the mass of protostars is false?
    The more massive ones will reach the main sequence first.

     The more massive ones will be the hottest and most luminous.

     The more massive ones create a lot of ultraviolet as well as visible light.

     The more massive ones are so luminous they ionize the gas, hence red H II regions.

     The more massive ones one will be made of the heaviest elements.
Correct
A cloud fragment too small to collapse into a main sequence star becomes a
     white dwarf.

     brown dwarf.

     T Tauri object.

     pulsar.

     planet of another star.
Correct
Which is characteristic of globular star clusters?
    no remaining MS stars, but millions of white dwarfs

     only brown dwarfs in a yellow ball 100 ly across

     old age and hundreds of thousands of stars, only about 30 ly wide

     bright blue main sequence stars, and thousands of them

     a mix of old and young stars, about 100,000 ly across
Correct
The single most important determinant of the temperature, density, radius, luminosity, and pace of
evolution of a protostar is its
    magnetic field.

     mass.

     chemical composition.

     spin.

     molecular composition.
Correct
A fragment of a collapsing gas cloud that comes to equilibrium with a central temperature of 4 million K
will become a
      stage 1 protostar.

     black hole.
    black dwarf.

    brown dwarf.

    T Tauri star.
Correct
Higher mass protostars enter the main sequence
    faster and at a higher luminosity and temperature.

    slower and at a higher luminosity and temperature.

    faster and at a lower luminosity and temperature.

    at the same rate, but at a higher luminsoity and temperature.

    slower and at a lower luminosity and temperature.
Correct
Besides mass the other factor that influences where a star appears on the main sequence is
    chemical composition of the cloud.

    distance from Earth.

    the type of cluster the star is formed in.

    the motion of the star.

    number of stars in the cluster.
Correct
If the initial interstellar cloud in star formation has a mass sufficient to form hundreds of stars, how does a
single star form from it?
     One star forms at its center and blows the rest of the matter back into space.

    The cloud is disrupted by rotation so that it reduces its mass down to that of a typical star.

    A supernova blows the cloud up and dissipates the majority of the gas.

    The cloud fragments into smaller clouds and forms many stars at one time.
    One star forms and the rest of the matter goes into making planets, moons, and other objects of a
    solar system.
Correct
How are T Tauri stars characterized observationally?
   by very rapid rotation

    by very high temperatures

    by sudden changes in their brightness

    by very high magnetic fields and large starspots

    They are newly-formed stars that are short period binaries.
Correct
Which of these is NOT typical of a condensing protostar?
    more infrared than visible light given off from the cocoon of dust around the star

    fusion of helium into carbon in their cores

    dusty disks around their equators

    magnetic fields producing polar flows

    Herbig-Haro objects projecting a light year out in space
Correct
What kind of variable stars are pre-Main Sequence stars undergoing gravitational contraction and
exhibiting erratic changes in their luminosities?
    T Tauri

    Cepheid

    R Coronae Borealis

    Herbig-Haro

    RR Lyrae
Correct
In stage 6 or 7 of the formation of a large cluster of stars, a nebula is formed around the cluster. This
happens because
    there are massive O and B stars emitting high energy photons that ionize the remainder of the cloud.

    the stars are out of their coccoons of dust and their radiation ionizes the gas from the original cloud.

    the number of stars is so great and so intense that the gas from the original cloud is ionized.
    there are thousands of sun-like stars with planets around them and the formation of planets ionizes
    the leftover gas.
    there are brown dwarfs everywhere in between the stars, so the gas is lit up by their low-intensity
    light.
Correct
The stars found in nebulae like the Orion nebula probably formed about
    a few million years ago.

    billions of years ago.

    at the beginning of the universe.

    10 million years ago.

    hundreds of millions of years ago.
Correct
Which of these is NOT a source of the shock waves that lead to protostars?
    radiation from the OB stars in emission nebulae

    expanding planetary nebula shells

    expanding Herbig-Haro objects

    collisions between galaxies
    violent supernovae explosions
Correct
Most stars in the Milky Way probably formed
    in clusters in the Galaxy's spiral arms.

    alone.

    in the galactic Nucleus, then migrated outward later.

    in intergalactic space, then were swept up into the Galaxy.

    from planetary nebulae.
Correct
Why are star clusters almost ideal "laboratories" for stellar studies?
   Stars in clusters are all relatively young and therefore shine brightly.

    Stars in clusters have the same age, similar composition, and are at the same distance away.

    Like our Sun, stars in clusters are always located in the plane of the Milky Way Galaxy.

    Their combined light makes them much easier to spot from a distance.

    All stars in the cluster are the same size and luminosity.
Correct
When a typical open cluster forms, which type of stars are formed most often?
   red giants

    white dwarfs

    solar type stars of class G

    low mass M type dwarfs

    OB associations
Correct
What are the characteristics of globular cluster stars?
   old age and hundreds of thousands to millions of member stars

    hundreds of light years across, with bright OB stars dominant

    a few hundred stars, most still on the main sequence

    no main sequence stars left, with billions of member stars

    no stars as hot as our Sun
Correct
What are the characteristics of an open cluster of stars?
   mostly found above and below the galactic plane

    old age and millions of members

    a few hundred, mainly main sequence stars

    all stars are much more massive than our Sun
    all stars are

Star clusters have been observed within dark nebulae with:
     infrared observations.

    optical movies made over decades.

    radio interferometers.

    ultraviolet light creating the emission nebulae.

    the Chandra X-Ray observatory.
Correct
All globular clusters in our Milky Way are about how old?
      around ten billion years old

    less than a million years

    ten-fifty million years old

    a variety of ages, from newly born to twenty billions years old

    one to three billion years old

The most important fact about a cluster of stars that makes them useful for studying star formation is that
    all the stars are the same spectral type.

    all the stars have the same chemical composition.

    all the stars formed at about the same time.

    all the stars are at the same distance from Earth.

    all the stars formed from the same cloud.

				
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