Astronomy CH 15 quiz – Flashcards
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What is the thickness of the disk of the Milky Way?
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1,000 light years
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Where are most heavy elements made?
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in stars and supernovae
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What makes up the interstellar medium?
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gas and dust
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How can we see through the interstellar medium?
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by observing at wavelengths (high-energy X-rays and long wavelength radio waves) that are not absorbed by interstellar dust
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How are interstellar bubbles made?
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by the winds of massive stars and supernovae explosions
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What produces the 21-cm radio line that we can be used to map the Milky Way Galaxy?
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atomic hydrogen
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Which of the following does not accurately describe what we observe toward the Galactic center? A.At radio wavelengths, we see giant gas clouds threaded by powerful magnetic fields. B.At X-rays, we see faint emission from an accretion disk around a black hole. C.At infrared wavelengths, we see a massive star cluster. D.At optical wavelengths, we see a cluster of old, red stars.
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D.At optical wavelengths, we see a cluster of old, red stars.
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What is the diameter of the disk of the Milky Way?
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100,000 light years
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Approximately how far is the Sun from the center of the galaxy?
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27,000 light-years
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What evidence supports the existence of a black hole at the center of our galaxy?
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The motions of the gas and stars at the center indicate that it contains 4 million solar masses within a region only 3 light-years across.
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What kinds of objects lie in the disk of our galaxy? A.old K and M stars B.O and B stars C.gas and dust D.open clusters E.all of the above
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E.all of the above
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Harlow Shapley concluded that the Sun was not located at the center of the Milky Way Galaxy by
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mapping the distribution of globular clusters in the galaxy.
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The image of our galaxy in radio emission from carbon monoxide maps the distribution of molecular clouds. Which of the following would give a similar picture of our galaxy? A.visible light, which is closest to how the night sky appears from Earth B.infrared emission from interstellar dust grains C.21-cm-line radio emission from atomic hydrogen D.visible light, showing the edges of supernova bubbles E.X-rays from hot gas bubbles in the disk
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B.infrared emission from interstellar dust grains
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How does the interstellar medium obscure our view of most of the galaxy?
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The small mixture of dust grains in the interstellar medium absorbs visible light.
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Where do most dust grains form?
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in the winds of red giant stars
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What elements do astronomers consider heavy elements?
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all elements besides hydrogen and helium
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The galactic center lies in the direction of which constellation?
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Sagittarius
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Why are we unlikely to find Earth-like planets around halo stars in the Galaxy?
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Halo stars formed from gas containing few heavy elements, the elements needed to create terrestrial planets like the Earth.
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If you were to take a voyage through the entire disk of the Milky Way, what kind of material would you spend most of your time in?
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rarefied clouds of atomic hydrogen
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Approximately how long does it take the Sun to orbit the center of the Milky Way Galaxy?
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200 million years
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What kinds of objects lie in the halo of our galaxy?
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globular clusters
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How do we learn about the conditions at the center of our own galaxy, the Milky Way?
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While we cannot see the galactic center with visible or ultraviolet light, radio and X-rays from the center can be detected and used to determine the conditions there.
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Why do we believe that most of the mass of the Milky Way is in the form of dark matter?
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The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo.
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What is Sgr A*?
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a source of bright radio emission in the center of our galaxy
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Where does most star formation occur in the Milky Way today?
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in the spiral arms
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How do low mass stars transport newly formed elements into the interstellar medium?
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stellar winds and formation of planetary nebula
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Compared to our Sun, most stars in the halo are
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old, red, and dim and have fewer heavy elements.
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What is the most abundant molecule in interstellar clouds besides molecular hydrogen?
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carbon monoxide
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What evidence suggests that the protogalactic cloud that formed the Milky Way resulted from several collisions among smaller clouds?
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Halo stars differ in age and heavy-element content, but these variations do not seem to depend on the stars' distance from the galactic center.
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Why has star formation ceased in the galactic halo?
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All of the galaxy's cool gas settled to the galactic plane long ago.
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Approximately how long does it take the sun to go through a full cycle of passing above and below the plane of the galaxy?
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a few tens of millions of years
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What is the most common form of gas in the interstellar medium?
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atomic hydrogen
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How do high-mass stars make it more difficult for a molecular cloud to form more stars? A.Strong winds push gas away. B.Ultraviolet photons ionize the gas. C.Radiation pressure pushes ionized gas away. D.Ultraviolet photons heat the gas. E.All of the above
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E.All of the above
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Compared with stars in the disk, orbits of stars in the halo
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are elliptical, with random orientations.
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Which of the following are signposts of the presence of high mass stars, and thus recent star formation? A.closely spaced low mass stars B.predominantly blue reflection nebulae C.predominantly red ionization nebulae D.closely spaced low mass stars and predominantly blue reflection nebulae E.predominantly red ionization nebulae and predominantly blue reflection nebulae
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E.predominantly red ionization nebulae and predominantly blue reflection nebulae
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How do high mass stars transport newly formed elements into the interstellar medium?
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stellar winds and supernova explosions
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Sound waves in the interstellar medium
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can travel through the gas, but the very low density of the interstellar medium makes them inaudible.
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What causes the sun to "bob" up-and-down in its orbit around the galactic center?
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lack of friction with the low-density interstellar medium and the localized pull of stars within the disk itself
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What is a shock wave?
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a pressure wave that moves faster than the speed of sound
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Suppose you read somewhere that 10 percent of the matter in the Milky Way is in the form of dust grains. Should you be surprised? If so, why?
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The fraction of 10 percent cannot be correct. Dust grains are solid and only 2 percent of the matter in the galaxy is made of anything besides hydrogen and helium.
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Over time, what is the net effect of the star-gas-star cycle in the Milky Way?
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The total mass in the galaxy's interstellar medium is gradually reduced, and the remaining gas is continually enriched in heavy elements.
