Honors Astronomy Sem 2 Final: Bodecker – Flashcards

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question
The light we see from the Sun comes from which layer?
answer
photosphere
question
What natural barrier tries to prevent two protons from combining?
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electromagnetic repulsion
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Which is the weakest of the fundamental forces?
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the gravitational force
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When the chromosphere can be seen during a solar eclipse, what is its color?
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red
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How many planet Earths could fit inside the Sun?
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A million
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From where does most of the solar wind flow?
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coronal holes
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What is the net result of the proton-proton chain?
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4 hydrogens are fused into 1 helium, 2 neutrinos + energy
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In the proton-proton cycle, what fraction of the hydrogen's mass doesn't end up as helium?
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.007
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The density of the Sun is similar to which object?
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Jupiter
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What is the size of a typical granule or convection cell seen in the photosphere?
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1,000 km
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Why couldn't you stand on the Sun's surface?
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The Sun doesn't have a solid surface.
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By what mechanism does radiation reach the Sun's surface from its interior?
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Convection
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What is the meaning of the "solar constant"?
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the solar energy reaching Earth per unit area per unit time
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Which of the following is NOT a property of neutrinos?
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never interact with matter
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Why are scientists bothered by the small number of neutrinos they detect coming from the Sun?
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They are not detecting the number of neutrinos predicted by current theories.
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Which is the strongest of the fundamental forces?
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the force that binds atomic nuclei
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What is it about the Sun's corona that astronomers don't understand?
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The corona is much hotter than layers of the Sun that are closer to the solar interior.
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How would sunspots appear if you could magically remove them from the Sun?
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They would shine bright orange in color.
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The numbers of sunspots and their activity peak about every:
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eleven years
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The critical temperature to initiate the proton-proton cycle in the cores of stars is:
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10 million K
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Loops of glowing hydrogen seen hanging out over the solar limb during totality are:
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prominences
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The _______ Minimum was a period of solar inactivity between 1645 and 1715.
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Maunder
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The pattern of rising hot gas cells all over the photosphere is called:
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Granulation
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The ESA satellite which gave us our most accurate distances to stars is called:
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Hipparcos
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If two stars differ in brightness by 5 magnitudes, the light ratio received by us is ______ to 1.
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100✕
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In comparing first magnitude Deneb with second magnitude Polaris, we find that:
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Deneb appears 2.5✕ brighter to us than does Polaris
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What are the two most important intrinsic properties used to classify stars?
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Luminosity and surface temperature.
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If a star has a parallax of 0.05", then its distance in light years is about:
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66 light years
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If a star is found by spectroscopic observations to be about 500 parsecs distant, its parallax is:
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.002"
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Hipparcos observations have given us good data on stars out to about:
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200 parsecs
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About how many stars has Hipparcos given us accurate distance data on?
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a million, those with parallaxes of .005" or larger
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Which of the following spectral types is the hottest?
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G2
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While Sirius, the Dog Star, is type AO, a star just a step hotter than M0 is a related:
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K9
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The Hertzsprung-Russell Diagram plots ______ against the spectral type or temperature.
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luminosity or absolute magnitude
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Two stars which differ by 5 magnitudes in apparent brightness have the same parallax; thus, one star must be intrinsically ______ times as luminous as the other.
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a hundred
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Stellar masses are determined directly by observation of the orbits and periods of ______ stars.
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all types of bianary
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In what range of masses are most stars found?
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.1 to 20 solar masses
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Why are star clusters almost ideal "laboratories" for stellar studies?
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Stars in clusters have the same age, similar composition, and are at the same distance away.
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Perhaps the greatest of the Greek astronomers, _______ compiled the first catalog of stars, accurately measured their positions, and defined the basic system of stellar brightnesses.
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Hipparcos
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Which of the following spectral types is the hottest?
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O9
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Which of these pairs of spectral types is most similar in temperature?
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K9 and M0
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What physical property of a star does the spectral type measure?
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temperature
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The star's color index is a quick way of determining its:
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temperature
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Which of the following is the most common type of star?
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main sequence
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Which of the following apparent magnitudes is the brightest?
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-1.1
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What is the absolute magnitude of our Sun?
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+4.8
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What is the single most important characteristic in determining the course of a star's evolution?
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mass
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The absolute magnitude of a star is its brightness as seen from a distance of:
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1o parsecs
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Which statement about stellar motion is incorrect?
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proper motion is measured over intervals of exactly six months
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If the radial velocity were -3 km/sec, and the transverse velocity were +4 km/sec, then:
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the space velocity would be 5 km/sec.
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What characteristic of the stars in a binary system can be determined by knowing the period of the stars' common orbit and the distance between them?
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mass
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Which type of binary can have their sizes measured directly by photometry?
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eclipsing
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Upon what data do measurements of sizes of eclipsing binaries depend?
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their Doppler shifts and the duration of stages of the eclipse
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The HR diagram can be a plot of _________.
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absolute magnitude versus color index
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What is the typical main sequence lifetime of a B-type star?
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20 million years
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What is the typical main sequence lifetime of a G-type star?
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10 billion years
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What is the typical main sequence lifetime of a M-type star?
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a trillion years
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A nearby star has a parallax of 0.2 arc seconds. What is its distance?
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5 pc
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Procyon lies about 13 light years distant, thus its parallax is about:
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0.25"
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In the H-R diagram, the bright blue-white stars that dominate the naked eye sky lie to the:
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upper left quadrant
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On the H-R diagram, the Sun lies:
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about the middle of the main sequence
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On the H-R diagram, white dwarfs lie Sirius B and Procyon B lie:
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to the lower left
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On the H-R diagram, red supergiants like Betelguese lie:
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the top right
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______ have masses like that of the Sun, and radii like that of the Earth.
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white dwarfs
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What is proper motion?
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It is the annual apparent motion of a star across the sky.
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In order to turn a star's proper motion into its space velocity, we must also know:
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its distance and radial velocity
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Which of the following best describes the size and distance relationship of our Sun and the nearest star?
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Two golfballs separated by 100 kilometers.
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Compared to the size of the Sun, in what range of sizes are most stars found?
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0.01 to 100 solar radii
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How might the most common occurring stars be described, based on our stellar neighborhood?
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M-type main sequence stars
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What are the characteristics of an open cluster of stars?
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a few hundred, mainly main sequence stars
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What are the characteristics of globular cluster stars?
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old age and hundreds of thousands of stars
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What makes the subject of star formation so difficult and complex?
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Stars live too long to be observed from birth to death.
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A typical protostar may be several thousand times more luminous than the Sun. What is the source of this energy?
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From the release of gravitational energy as the protostar continues to shrink.
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Which of these is not typical of a condensing protostar?
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fusion of helium into carbon in their cores
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What is the critical temperature at which hydrogen can fuse into helium in the star's core?
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10 million K.
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What happens when an interstellar cloud fragment shrinks?
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all
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What is characteristic of a main sequence star?
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The rate of nuclear energy generated in the core equals the rate radiated from the surface.
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Most stars probably formed:
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in clusters
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How long does it take for a star like our Sun to form?
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50 million years
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Which relationship concerning the mass of protostars is false?
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The more massive ones glow red, accounting for the color of H II regions.
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What is the key factor that determines the temperature, density, radius, luminosity, and pace of evolution of a protostellar object?
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Mass
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When an H II region is observed, it signals what stage in stellar formation?
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Depending on their masses, the stars inside may be at different stages of formation.
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What is the size of a typical interstellar cloud that is dense enough to form stars?
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10 pc
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As a star forms, the photosphere first appears:
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When the protostar forms
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For gravity to contract a spinning interstellar cloud, there needs to be sufficient:
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Mass
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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?
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The cloud fragments into smaller clouds and forms many stars at one time.
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A cloud fragment too small to form a star becomes:
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A brown dwarf
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Which event marks the birth of a star?
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Fusion of hydrogen atoms into helium atoms.
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At what stage of evolution do T Tauri stars occur?
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When a protostar is on the verge of becoming a main sequence star.
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How many hydrogen atoms does it take to make a typical star?
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10^57
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How are T Tauri stars characterized observationally?
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By sudden changes in their brightness.
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Evidence for star formation theory comes from:
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Studying different objects at different stages and piecing together an evolutionary picture.
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How long does it take an M-type star to form, compared to the time for a solar-type star to form? `
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20 times as long.
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When a typical open cluster forms, which type of stars are formed most often?
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low mass M type dwarfs
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A star will evolve "off the main sequence" when it uses up which of the following?
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most of the hydrogen in the core
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On the main sequence, massive stars do which of the following?
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burn their hydrogen fuel more rapidly than the Sun
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When the Sun is on the red-giant branch, it will be found where on the H-R diagram?
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upper right
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After the core of a Sun-like star starts to fuse helium on the horizontal branch, the core becomes which of the following?
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hotter
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When the Sun leaves the main sequence, it will become which of the following?
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brighter
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A star like the Sun will end up as what?
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a white dwarf
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The order of evolutionary stages of a star like the Sun would be Main Sequence, giant, planetary nebula, and finally ______.
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none of these
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The helium flash converts helium to the heavier element _____.
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carbon
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How many helium atoms must be fused at 100 million K in the helium flash?
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three
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Which of the following best describes the evolutionary track followed in the HR diagram for the most massive stars?
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horizontally right
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What is used, observationally, to determine the age of a star cluster?
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the luminosity at the main-sequence turnoff
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What is the source of pressure in the core of a red giant that resists the force of gravity?
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electrons which have become incompressible
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In a white dwarf, we have packed the mass of the Sun into the volume of Earth, so the density is:
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a million times that of the Sun.
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What, in addition to its HR diagram, is needed to age-date a star cluster?
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theoretical models of stellar evolution
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What characteristic of a star cluster is used to determine its age?
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The main sequence turnoff.
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The brightest stars of a young open cluster will be:
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massive blue main sequence stars
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In globular clusters, the brightest stars will be:
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red supergiants
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A high-mass star dies more violently than a low-mass star because:
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It generates more heat and its core eventually collapses.
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A ______ is a relatively gentle mass-loss event which allows a star to peacefully readjust its structure into a white dwarf configuration.
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planetary nebula
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Which of these will the Sun probably become in the very distant future?
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planetary nebula
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The evolution of stars appears inevitable. But what likely circumstance can radically alter this evolutionary sequence?
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The stars can be in a short period binary system.
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Which statement is true, in terms of stellar evolution?
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Sooner or later, gravity wins.
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Can a star become a red giant more than once?
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Yes
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Which statement about blue stragglers is false?
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They are much more massive than any other stars known.
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If one star of a binary fills its Roche lobe and is spilling matter onto the other, then the system is a:
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mass-transfer binary
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If two stellar cores share a single envelope, we have a:
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contact bianary
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What results from the mass loss from K and M red giants?
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The wind is rich in dust particles and molecules, including diamonds.
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In a star cluster, just as the most massive stars are evolving into giants and supergiants, what is happening for the lowest mass stars?
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They are just starting to approach the zero-age main sequence.
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Luminous hot stars and luminous cool stars:
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have stellar winds, but each are driven by a different source.
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What is a typical age for a globular cluster?
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12 billion years
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What temperature is needed to fuse helium?
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100 million K
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What are black dwarfs?
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cooled off white dwarfs
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Which of the following is true regarding planetary nebulae?
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They are the ejected envelopes of highly evolved low-mass stars.
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The Roche lobe of a star in a binary star system:
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is, in terms of the star's gravity, its "zone of influence."
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What is a planetary nebula?
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The ejected envelope of a red giant surrounding a stellar core remnant.
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Astronomers talk about "low-mass" and "high-mass" stars with regard to their evolution. In units of solar masses, what is the dividing line, that is, the lowest mass for a high-mass star?
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8 solar masses
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What inevitably forces a star like the Sun to evolve away from being a main sequence star?
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It builds up a core of hellium
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In the evolution of massive stars, what is the significance of the temperature 600 million K?
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The ejected envelope of a red giant surrounding a stellar core remnant.
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A star spends most of its life:
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as a main sequence star.
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What is the significance of 100 million K to the core of a star?
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Temperature need to start triple alpha process and turn helium into carbon.
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The "helium flash" occurs at what stage in stellar evolution?
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red giant
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Just as a low-mass main sequence star runs out of fuel in its core, it actually becomes brighter. How is this possible?
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The core contracts, raising the temperature of the region of hydrogen shell-burning.
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A white dwarf can dramatically increase in brightness only when which of the following applies?
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It has another star nearby.
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Which of the following stars will become hot enough to form elements heavier than oxygen?
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A Star that is eight times more massive than the Sun.
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When does a massive star become a supernova?
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When it forms iron in its core.
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An observable supernova should occur in our Galaxy how often?
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about once every century
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Which one of the following does not provide evidence that supernovae have occurred in our Galaxy?
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The existence of binary stars in our Galaxy.
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Most of the carbon in our bodies originated where?
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the core of a red-giant star
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The silver atoms found in jewelry originated where?
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a supernova
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A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object?
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Nova
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For a nova to occur, the system must have already been a:
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mass-transfer bianary
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Which type of heavy atomic nuclei are most common, and why?
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Even numbered elements, for helium is "giant food" for everything beyond itself.
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Nearly all the elements found in our environment were formed inside stars, except for:
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Hydrogen and Hellium
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The production of which element in the core of a highly evolved giant leads to type II supernovae?
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iron
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Why does neutron capture work?
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Neutrons have no repulsive barrier to overcome in combining with positively charged nuclei.
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What is the only way that a white dwarf can suddenly explode in a type I supernova?
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if it is a member of a mass-transfer binary
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What is stellar nucleosynthesis?
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The formation of heavier elements inside stars.
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Of the elements in your body, the only one not formed in stellar nucleosynthesis is:
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hydrogen
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How long does it take a stellar iron core to collapse?
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one second
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The heaviest nuclei of all are formed:
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By neutron capture during a supernova explosion
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An iron core cannot support a star because:
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Iron cannot fuse with other nuclei to produce energy.
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What direct evidence do astronomers have that supports the heavy element formation in stars?
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all of these
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What was most surprising about SN1987A?
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The parent star was a B supergiant, not a red supergiant.
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The upper mass limit of 1.4 solar masses for white dwarfs won a Nobel prize for:
answer
Chandrasekhar
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The Chandrasekhar mass limit is ______.
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1.4 solar masses
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A 20 solar mass star has a main sequence lifetime of 10 million years, yet its iron core exists for only about how long?
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less than a day
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As a star evolves, heavier elements tend to form by various processes. Which of the following is not one of these processes?
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Neutronization
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The iron we commonly find in our surroundings came from this source.
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decay of nickel-56 and cobalt-56 in a supernova remnant
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What is the reason a type-II supernova slows its dimming after about 2 months?
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Energy is released from the decay of radioactive cobalt-56 to iron-56.
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The transformation of cobalt 56 into iron 56 is an example of:
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the weak force and nuclear fission
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The making of abundant iron nuclei is typical of:
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type II supernova
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What made supernova 1987a so useful to study?
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all of these
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Where was supernova 1987a located?
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In our companion galaxy, the Large Magellanic Cloud
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Which of these is least likely to happen?
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recurrent supernova of type I
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Which of these is the likely progenitor of a type I supernova?
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a mass-transfer binary, with the white dwarf already at 1.3 solar masses
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Which of these is the likely progenitor of a type II supernova?
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an evolved red giant which is just starting to make silicon in its core
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Which of the following does not fit a type I supernova?
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Implosion-explosion of the core of a massive star.
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A star can be a supernova:
answer
once
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The supernova that formed M-1, the Crab Nebula, was observed in what year?
answer
1054 AD by the Chinese
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What is the total energy radiated by a supernova equal to?
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1 billion suns
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The total energy emitted by the brightest nova explosions is about:
answer
1 million suns
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What produces a type-I supernova?
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Mass transfer to a white dwarf in a binary where the Chandrasekhar mass is exceeded.
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When helium capture occurs with a carbon-12 nucleus, what results?
answer
oxygen-16
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When two silicon-28 nuclei fuse, the initial result is:
answer
nickel-56
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What evidence is there that supernovae really have occurred?
answer
All of these
question
When a stellar iron core collapses, large numbers of neutrinos are formed, then:
answer
They immediately pass through the core and escape to space.
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A recurrent nova can eventually build up to a:
answer
type I supernova
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In order of visual luminosity at the start, which is most luminous?
answer
type I supernova
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Which of these do not depend on a mass-transfer binary to occur?
answer
a type II supernova
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The alpha process tends to produce chiefly:
answer
even numbered elements
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Which of the following is not an argument for Cygnus X-1's being a true black hole?
answer
The mass of the visible B star is even greater than Cygnus X-1, at around 30 solar masses.
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What explanation does general relativity provide for gravity?
answer
Gravity is a result of curved spacetime.
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What makes the Crab pulsar somewhat unusual among pulsars in general?
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It is rather bright at visible wavelengths.
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Three terrestrial planetary-sized masses have been discovered orbiting what type of object?
answer
a millisecond pulsar
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What compelling evidence links pulsars to neutron stars?
answer
Only a small rotating source of radiation is thought to be able to emit precisely timed pulses such as those from pulsars.
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The key to identifying a black hole candidate in a binary system is the following:
answer
the unseen companion in the system must have a sufficiently high mass
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Which of these is least likely to exist?
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a 1.8 solar mass white dwarf
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Almost half of all known millisecond pulsars are found in what type of object?
answer
globular clusters
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Who discovered the first object that eventually became known as a pulsar?
answer
Jocelyn Bell
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Who received the Nobel Prize in Physics for relating pulsars to neutron star formation?
answer
Anthony Hewish.
question
The supernova of 1054 AD produced:
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a pulsar with a period of 33 milliseconds, visible optically.
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Which of the following is not a property of the first discovered pulsar (nor any other pulsar)?
answer
emissions only in the visible part of the spectrum
question
In the Lighthouse model,
answer
if the beams sweeps across us, we can observe the pulse.
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What are X-ray bursters?
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They are neutron stars on which accreted matter builds up, then explodes in a violent nuclear explosion.
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What is Cygnus X-1?
answer
a leading candidate for being a black hole
question
X-ray bursters occur in binary star systems. What are the two types of stars that must be present to make up such an object?
answer
a main sequence or giant star and a neutron star
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Which of the following are attracted by gravity?
answer
all of these
question
Which of the following can actually escape a black hole?
answer
nothing
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What would happen if mass is continually added to a 1.4 solar mass neutron star?
answer
The star would eventually become a black hole.
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What would happen if mass is added to a 1.4 solar mass white dwarf?
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The star would erupt as a type I supernova.
question
Which statement about gamma ray bursts is not correct?
answer
They are a scaled up version of the X-ray bursts, with more massive stars involved.
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In a "hypernova", the very energetic supernova creates a:
answer
black hole
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While perhaps affected by rotation and magnetism, we think the lower limit for black holes is:
answer
Schwartzchild's limit of 3 solar masses.
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When we use Hubble's law to estimate the age of the universe, which of the following is true of the answer?
answer
the answer is the same for all galaxies
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Olber's paradox is resolved by which of the following?
answer
the finite age of the universe
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On the basis of our current best estimate of the present mass density of the universe, astronomers think which of the following?
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the universe is infinite in extent and will expand forever
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Because almost all of the galaxies are redshifted, we know that:
answer
the universe is expanding
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The redshift of galaxies in the universe is correctly interpreted as:
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Space itself is expanding with time; the wavelengths of photon are stretched while they travel through space.
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From the 1970's through the 1990's, the accepted value of H was almost doubled. This meant:
answer
the Hubble Time was halved.
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What does the Hubble law imply about the history of the universe?
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The universe started expanding at some time in the past; the universe has an age.
question
The cosmic microwave background is important mostly because:
answer
It confirmed a major prediction made by the Big Bang theory.
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Who was involved in the discovery of the cosmic microwave background radiation?
answer
Bell Labs and Princeton
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The universe has three possible futures. Which one is correct depends only on the average density of matter in the universe. Why is this?
answer
The density of matter determines the strength of gravity, which decelerates the expansion over time.
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The presently accepted values for Hubble constant gives which range of ages for the universe?
answer
10 to 20 billion years
question
What is the meaning of a "closed" universe?
answer
The universe will someday stop expanding and start to collapse.
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Homogeneity and isotropy, taken as assumptions regarding the structure and evolution of the universe, are known as:
answer
The cosmological principle.
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In which of the following models will the universe stop expanding?
answer
Closed universe.
question
The geometry of a closed universe, in two dimensions, resembles which one of the following?
answer
The surface of a sphere.
question
What is the meaning of isotropic?
answer
The same in all directions.
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The darkness of the night sky in a seemingly infinite universe is addressed in:
answer
Olbers' Paradox.
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The explanation for the darkness of the night sky is that (select all that apply):
answer
-the Big Bang means the universe is not infinitely old or large. -the energy of the distant galaxies has been weakened in their red shifting.
question
If the density of the universe is less than critical, then:
answer
the universe will "survive" to expand forever.
question
For a Hubble constant of 65 km/s/Mpc, the critical density is about:
answer
8 ✕ 10-27 kg/m3
question
Recent work with supernovae at great distances suggests the universe may in fact be accelerating its expansion, a startling discovery attributed to a new:
answer
dark energy
question
In the critical universe now proposed, the ratio of matter/energy is about:
answer
35/65
question
According to their H-R diagram turn-off points, the oldest globular clusters are about:
answer
12 billion years old
question
The satellite most responsible for studying the microwave universe is:
answer
COBE
question
For a spatially flat (Euclidean) universe, o is:
answer
1.0
question
If the presently accepted value of o = 0.3 is indeed correct, then the universe will:
answer
expand forever
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