Ch. 15 Our Galaxy – Flashcards
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How many stars does the Milky Way galaxy have?
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Over 100 billion stars
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What shape does the Milky Way galaxy have?
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Spiral galaxy
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What are the components of a spiral galaxy?
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Spiral arms, disk, bulge, halo, and, globular clusters
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How thick is the disk?
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1000 light years
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Where do most of the galaxies bright stars reside?
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In the disk
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What is the interstellar medium?
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Clouds of interstellar gas and dust (they obscure our view of the galaxy when we observe with visible light)
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How do disk stars orbit the center of the galaxy?
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In circular paths that all go in the same direction in nearly the same plane
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What causes the up-and-down motion of stars moving around the galaxy?
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From the pull of gravity within the disk
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How long does it take a star to orbit the center of the galaxy?
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200 million years
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How do stars in the halo orbit?
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Their motions are random and in opposite directions
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How do stars in the bulge orbit?
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Some move in random directions and others in the same direction as disk stars
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Where is most of the mass of a galaxy concentrated?
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In the disk
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What were the two lightest elements that formed during the big bang?
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Hydrogen and helium
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Where were the other heavier elements formed?
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In the stars with the help of the interstellar medium
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How is gas recycled in our galaxy?
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Gas from dying stars mixes new elements into the interstellar medium, which slowly cools, making the molecular clouds where stars form. Those stars will eventually return much of their matter to interstellar space.
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Where do stars tend to form in our galaxy?
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Active star-forming regions contain molecular clouds,
hot stars, and ionization nebulae. Much of the star formation in our galaxy happens in the spiral arms.
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What are the characteristics of halo stars?
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They are very old, contain smaller proportions of heavy elements than disk stars, and are low in mass
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How did our galaxy form?
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From a giant gas cloud
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What is the evidence for a black hole at our galaxy's center?
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Orbits of stars near the center of our galaxy indicate that it contains a black hole with 4 million times the mass of the Sun.
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What is the shape of the Milky Way's halo?
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Spherical
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Where are the most of the Milky Way's globular clusters found?
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In the halo
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Why do disk stars bob up and down as they orbit the galaxy?
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gravity of disk stars
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How do we determine the Milky Way's mass outside the Sun's orbit?
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From the orbits of stars and gas clouds orbiting the galactic center at greater distances than the Sun
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Which part of the galaxy contains the coldest gas?
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Disk
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What is the typical percentage (by mass) of elements other than hydrogen and helium in stars that are forming right now in the vicinity of the Sun?
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2%
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Which of these forms of radiation passes most easily through the disk of the Milky Way?
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Infrared light
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Where would you be most likely to find an ionization nebula?
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Disk
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Which kind of star is most likely to be fond in the halo?
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M star
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The best measurements of the mass of the black hole at the galactic center come from what?
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The orbits of stars in the galactic center.
