when a star first appears on the H-R diagram, it moves
A up
B down
C to the right
D to the left
a forming star is first detectable as
A a new star in an ordinary field of stars
B a bright region in an otherwise dark cloud
C an infrared emitting region in an interstellar cloud
D a contracting cloud of gas.
a solid object within a collapsing cloud will remain in a stable orbit instead of falling in to the center if
A its density is greater than the density of the rest of the cloud
B its size is greater than a critical value
C its centrifugal force balances the inward force of gravity
D it has an electric charge to repel the surrounding matter
stars that are in the process of forming are difficult to see primarily because:
A they are too cool.
B they are often obscured by surrounding dust.
C they are too small.
D all of the above are true.
a star reaches the main sequence when
A it starts to collapse
B it is a proto star
C nuclear reactions start
D it starts to shine
when a star first appears on the H-R diagram it is
A cool and faint
B cool and bright
C hot and faint
D on the main sequence
the material from which a star forms has an initial temperature that is
A nearly hot enough for fusion reactions
B several thousand degrees
C about room temperature
D very far below freezing
nuclear fusion will start when a proto star's
A surface temperatures and densities are high enough to split apart hydrogen nuclei
B surface temperatures and densities are high enough to force hydrogen nuclei to fuse together
C core temperatures and densities are high enough to split apart hydrogen nu
D core temperatures and densities are high enough to force hydrogen nuclei t fuse together
the initial phase of a star's life, immediately following its formation as a local condensation, is controlled by
A the hydrogen reactions
B the relative abundance of the elements
C gravitational contraction
D fission reactions
mapping of the entire galaxy cannot be done optically because of
A absorption by gas and dust
B stars are not bright enough to see that far away
C appropriate stars cannot be found on those parts of the galaxy far from the sun
D no choice
when a new star like our sun is forming, what is the event that halts the initial gravitational contraction
A the onset of fusion
B the helium flash
C a supernova explosion
D the exhaustion of fuel supplies
the collapse of a forming star is usually halted by
A the increasing pressure forces within the object
B an explosion
C the force of gravity
D the generation of light within the object
pre-main sequence red giants are rarely observed because
A they are of little interest to astronomers
B only very high mass stars go through that evolutionary stage
C stars spend a relatively short time in that evolutionary stage
D they are too faint to be easily observed
t tauri stars are:
A periodic variable stars that have just arrived on the main- sequence.
B periodic variable stars that have not yet reached the main- sequence.
C irregular variable stars that have not yet reached the main-sequence.
D stars that are actually still on the hayashi track.
proto stars begin with a temperature of about
A -300 f
B 300 f
C 100,000 f
D 10**7 f
according to one contemporary model of star formation in the galaxy, massive stars form
A out of giant molecular clouds.
B quickly, in less than a million years.
C in small groups of about 10 stars at a time.
D all of the above.
E none of the above.
a forming star is first detectable as
A an infrared hot spot in a cloud
B a new star
C a large visible cloud of gas
D a black hole
proto stellar collapse
A hydrogen shell burning.
B hydrogen core burning.
C helium shell burning.
D ejection of planetary nebula.
as a star is forming by the condensing of gases, the gases
A cool as they fall.
B heat up as they fall.
C stay about the same temperature.
D any of the above, depending upon the mass involved.
a proto star generates its energy by
A oxidation of carbon.
B fusion of hydrogen to helium.
C fission of uranium.
D conversion of gravitational to thermal energy.
E none of the above.
when a star first appears on the H-R diagram, its actual total brightness, as compared to the sun's current value, is
A much greater
B about the same
C much less
D undetectably fainter
as a new star evolves from cool dust and gas to a hot star, the peak wavelength of its spectrum of electromagnetic radiation will
A increase from visible to infrared wavelengths
B remain the same
C change from the infrared to the visible wavelengths
D change from the ultraviolet to the visible range
in which star is gravity the only source of energy
A main sequence
B pre-main sequence
C post-main sequence red giant
D none of the above
according to contemporary ideas, massive stars form
A in small groups of about ten.
B out of giant molecular clouds.
C in a short time compared to the lives of the stars.
D all of the above.
E none of the above.
the best statement we can make about star formation is that
A stars probably condense from interstellar material.
B stars form from the collisions of many smaller objects in space, like comets and planets.
C all stars formed when the universe started and have not been changing since then.
D we have no idea at all how stars form.
what is the source of energy that results in light emission from a proto star?
A chemical reactions.
B nuclear reactions.
C gravity.
D hydrogen fusion.
E both (b) and (d) above.
the contraction of a star as it reaches the main sequence is halted by
A an explosion at the center of the star
B the rigid structure of the electrons in the center of the star
C the onset of nuclear reactions in the center of the star
D the heating of the outer layers of the star
an object becomes a star when
A it starts to collapse
B it is a proto star
C nuclear reactions start
D hydrogen is exhausted in the center of the star
a star stops its collapsing when forces from the gas pressure and gravitational forces are balanced. what is this state of balance called?
A natural balance.
B newtonian balance.
C hydrostatic equilibrium.
D protostatic equilibrium.
what process raises the core temperature of a proto star to the point where fusion can begin?
A chemical reactions which start at lower temperatures than fusion does
B increased friction among its atoms and molecules
C self-gravitation which boosts the star's core pressure
D self-gravitation which decreases the star's pressure and thus allows the density to rise
proto stars are difficult to observe because
A the proto star stage is very short.
B they are surrounded by cocoons of gas and dust.
C they radiate mainly in the infrared.
D all of these.
when radio astronomers map the disk of our galaxy they are most likely to look at
A "radio" stars
B pulsars
C absorption lines in gas clouds
D no choice
which stars reach the main sequence in the shortest time after their birth
A largest
B reddest
C densest
D most massive
the source of energy in a star which is still forming is
A the proton-proton chain
B the triple alpha process
C the carbon cycle
D gravitational contraction
the contraction of a forming star is halted by
A an explosion in the center of the star
B the rigid structure of the electrons in the center of the star
C the onset of nuclear reactions in the center of the star
D the heating of the outer layers of the star
extremely bright stars must be young because such stars
A are giving out enough light to illuminate their birth processes
B are using up fuel at a great rate and cannot exist for long
C still retain the rapid spinning of the cloud from which they came
D are bright because of the friction with their cloud of origin
as a proto star contracts it moves
A down in the H-R diagram
B up in the H-R diagram
C to the left in the H-R diagram
D to the right in the H-R diagram
as a star begins to form, it collapses because of
A turbulence in the cloud
B matter surrounding the cloud pushing in
C the force of gravity of the cloud
D the random motion of atoms in the cloud
which of the following objects would be useful for mapping the halo
A open clusters
B globular clusters
C associations
D no choice
you are an astronomer who would like to observe a proto-star. which of the following instruments would be of greatest use to you?
A the 5-meter (200-inch) telescope at mt. palomar
B the arecibo radio telescope tuned to a wavelength of 21 centimeters
C the IRAS satellite
D you can't fool me; there is no way to observe proto-stars
radio maps of the galaxy are hampered by
A poor equipment
B assumptions concerning the rotation model of the galaxy
C lack of bright sources
D no choice
a star is considered to begin its main sequence life when
A it starts to collapse.
B its proto star life begins.
C nuclear reactions start.
D it begins to move off the main sequence.
E its planetary system has formed.
the observations of bipolar outflows of gas from regions of star formation in molecular clouds indicate
A newly-born stars move in two directions.
B a ring or torus of material around the young stars.
C hot dust causes the gas to move rapidly.
D every star forms with a planetary system.
prior to reaching the main sequence, a star's energy comes from
A gravitation
B nuclear fusion
C nuclear fission
D black holes
the major source of energy in the early, pre-main sequence life of the sun was
A nuclear fusion
B nuclear fission
C burning of carbon atoms
D gravitational
stars in galactic orbits near the sun appear to stream
A around the galactic center in the direction of the sun's motion
B around the galactic center opposite to the direction of the sun's motion
C toward and away from the galactic center
D no choice
what observational evidence leads to the inference that star birth is occurring now in the milky way galaxy?
A infrared observations of possible proto stars.
B bipolar outflows associated with infrared sources.
C a cluster of infrared sources near the Orion nebula.
D all of the above.
proto stars generate energy through
A nuclear fusion.
B nuclear fission.
C gravitational collapse.
D static discharge.
dark globules are found in
A dark nebulae
B planetary nebulae
C bright emission nebulae
D no choice
the contraction of an interstellar cloud to become a star is caused by
A magnetic forces
B electric forces
C nuclear forces
D gravitational forces
the helmholtz-kelvin theory describes a star obtaining energy from
A gravitational contraction
B nuclear fusion
C nuclear fission
D chemical reactions
what type of objects are the most useful in mapping the distribution of material in the disk of our galaxy?
A young objects
B old objects
C faint objects
D no choice
stars which are just forming (proto stars) radiate most of their energy in
A x-rays
B visible light
C ultraviolet
D infrared
where in the sky would you look for a forming star?
A in dense dust and gas clouds
B in the empty space between galaxies
C near to black holes
D in globular clusters of stars
when a new star like our sun is forming what is the event that halts the initial gravitational contraction?
A the onset of fusion
B the helium flash
C the core becoming degenerate
D the exhaustion of fuel supplies
infrared stars within the Orion nebula are examples of which stage of stellar evolution?
A supernova remnant
B planetary nebula
C proto star and young star
D red giant
star formation can be triggered by which of the following events
A a star passing through an interstellar cloud
B an explosion of a galaxy
C a temporary decrease in the density of a cloud
D a nearby supernova explosion
a collapsing cloud begins to heat up because
A a hot red-giant is concealed inside
B a cool red-giant is concealed inside
C falling particles gain speed, collide, and produce heat
D thermonuclear fusion begins
forming stars in dark, dusty regions may be studied in the _____ spectral region
A x-ray
B ultraviolet
C visual
D infrared
a contracting cloud of gas will never experience fusion if
A it is too far from the galactic center
B its mass is too small
C its internal temperature rises too high
D it contracts too violently
as a forming star contracts
A the particles move faster
B the density increases
C the temperature increases
D all of the above
during the formation of a star, the contraction stops when
A the star collapses into a black hole
B the star collapses into a white dwarf
C hydrogen nuclear reactions turn on
D helium nuclear reactions turn on
forming stars are difficult to observe because
A this stage is too short to be seen
B they are surrounded by cocoons of gas and dust
C they radiate mainly x-rays
D all of these
high mass collapsing gas clouds
A take more time to collapse than low mass clouds
B take less time to collapse than low mass clouds
C take the same amount of time to collapse as low mass clouds
D take an unknown amount of time to collapse
the condensing sun first emitted radiation in what wavelength region?
A x-ray
B ultraviolet
C visual
D infrared
the primary force that plays a major role in the formation of a star is
A magnetism
B electricity
C nuclear binding force
D gravity
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