Lctr 15 (my answers) – Flashcards
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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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What is the thickness of the disk of the Milky Way?
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1,000 light years
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What makes up the interstellar medium?
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gas and dust
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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 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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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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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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Approximately how long does it take the Sun to orbit the center of the Milky Way Galaxy?
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230 million years
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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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On a dark summer night in the northern hemisphere, we can see the Milky Way but we can't see the center of the Milky Way. Why not?
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Interstellar dust and gas absorb and scatter visible light.
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The Sun lives in which component of the Milky Way?
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The disk
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The very first stars in the universe were made of:
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hydrogen and helium.
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What affects the average orbital speed of a star in our galaxy?
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The mass of the galaxy inside its orbit and size of its orbit (radius)
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What show radio waves from carbon monoxide that we can be used to map the Milky Way Galaxy?
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molecular clouds
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How does the diameter of the disk of Milky Way Galaxy compare to its thickness?
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The diameter is about 100 times as great as the thickness.
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The Sun's location in the Milky Way Galaxy is
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in the galactic disk, roughly halfway between the center and the outer edge of the disk
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How do disk stars orbit the center of the galaxy?
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They all orbit in the same direction with a little up-and-down motion.
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How do we know the total mass of the Milky Way Galaxy that is contained within the Sun's orbital path?
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By applying Newton's version of Kepler's third law (or the equivalent orbital velocity law) to the Sun's orbit around the center of the Galaxy
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Most stars in the Milky Way's halo are
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very old
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If we could see our own galaxy from 2 million light-years away, it would appear
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as a flattened disk with a central bulge and spiral arms
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Which of the following statements comparing halo stars to our Sun is not true?
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Most stars in the halo have either died or are in their final stages of life, while the Sun is only in about the middle of its lifetime.
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What show long-wavelength infrared emission lines that we can be used to map the Milky Way Galaxy?
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where young stars are heating dust grains
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What reveals infrared light that we can be used to map the Milky Way Galaxy?
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stars whose visible light is blocked by gas clouds
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What happens after many generations of the star-gas-star cycle?
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The heavy element abundance increases, the amount of gas decreases.
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What do we call the bright, sphere-shaped region of stars that occupies the central few thousand light-years of the Milky Way Galaxy?
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the galaxy's bulge
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What do we mean by the interstellar medium?
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The gas and dust that lies in between the stars in the Milky Way galaxy
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What show gamma rays that we can be used to map the Milky Way Galaxy?
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where cosmic rays from supernovae collide with atomic nuclei in gas clouds
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What do we mean by the star-gas-star cycle?
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It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium.
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How do bulge stars orbit the center of the galaxy?
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They have orbits randomly and in different directions relative to the galactic center.
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Most stars in the Milky Way's disk
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have heavy-element proportions of about 2 %, like our Sun
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Which of the following models best explains why our galaxy has spiral arms?
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The spiral arms are a wave of star formation caused by wave of density propagating outward through the disk of the galaxy.
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What do halo stars do differently from disk stars?
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They orbit the galactic center with many different inclinations, while disk stars all orbit in nearly the same plane.
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Over time, the star-gas-star cycle leads the gas in the Milky Way to
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have a greater abundance of heavy elements
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Spiral arms appear bright because
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they contain more hot young stars than other parts of the disk
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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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Which of the following does not accurately describe what we observe toward the Galactic center?
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at optical wavelengths, we see a cluster of old, red stars
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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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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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What elements do astronomers consider heavy elements?
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all elements besides hydrogen and helium
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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 is the most common form of gas in the interstellar medium?
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atomic hydrogen
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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.
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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, gamma-ray, X-ray, infrared, and radio wavelengths from the center can be detected and used to determine the conditions there.
