A) The 10% figure is too high because there are not enough heavy elements to make that much dust.
B) It is reasonable because we already know that interstellar dust obscures our view through the disk of the galaxy.
C) The 10% figure is too low because most of the mass of the galaxy is in the form of interstellar dust.
D) It seems reasonable as long as we assume that red giant stars-which produce dust grains in their stellar winds-are more common than we thought.
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A) very old
B) found inside molecular clouds
C) very young
D) blue or white in color
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A) cannot travel through the gas.
B) travel so slowly that they are undetectable.
C) can travel through the gas, but the very low density of the interstellar medium makes them inaudible.
D) travel extremely quickly and are therefore very loud.
E) can travel through the halo interstellar medium but not the disk of the galaxy.
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A) 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.
B) Although dark matter emits no visible light, it can be seen with radio wavelengths, and such observations confirm that the halo is full of this material.
C) Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk, suggesting that the halo is full of dark matter.
D) Our view of distant galaxies is sometimes obscured by dark blotches in the sky, and we believe these blotches are dark matter located in the halo.
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A) molecular hydrogen
B) molecular helium
C) atomic hydrogen
D) atomic helium
E) ionized hydrogen
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A) G star
B) M star
C) K star
D) O star
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A) microscopic particles of carbon and silicon
B) ozone "smog"
C) hydrogen and helium atoms
D) tiny grains of water ice
E) the same tiny particles found in household dust
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A) In the spiral arms
B) Everywhere throughout the galactic disk
C) In the central bulge
D) Within the halo
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A) looking at the shape of the "milky band" across the sky.
B) mapping the distribution of stars in the galaxy.
C) mapping the distribution of globular clusters in the galaxy.
D) mapping the distribution of gas clouds in the spiral arms.
E) looking at other nearby spiral galaxies.
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A) It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium.
B) It is the idea that stars in close binary systems can exchange gas with one another.
C) It is the set of nuclear reactions by which heavy elements are produced in the cores of massive stars.
D) It describes the orbits of the stars and interstellar medium around the center of the galaxy.
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A) 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
B) By counting the number of stars visible in this region of the galaxy
C) By estimating the amount of gas and dust in between the stars
D) By using the law of conservation of angular momentum to calculate the orbital speeds of nearby stars
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A) 1%
B) 10%
C) 50%
D) 98%
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Since stars that are traveling along wit...View Answer
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During a star's lifetime, it fuses hydro...View Answer
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A) The orbits of stars in the center of the galaxy indicate that the presence of 3 to 4 million solar mass object in a region no larger than our Solar System.
B) Huge amounts of X-rays are pouring out of the center of the galaxy.
C) The center of our galaxy hosts a pulsar that is spinning so fast that it could only be a black hole.
D) We observe stars vanishing in the center of the Galaxy as they are sucked into the black hole.
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A) Amazing filaments of radio emission swirling around the center of the galaxy
B) The existence of the Milky Way itself: the mass of the black hole is essential to gravitationally bind the galaxy together, so it doesn't fly apart.
C) The gigantic bursts of X-ray energy from a mysterious dark object
D) The motions of stars around a mysterious dark object
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A) open clusters
B) O and B stars
C) old K and M stars
D) gas and dust
E) all of the above
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A) A 3 to 4 million solar mass black hole
B) A gigantic X-ray binary system
C) A dense cluster of young, hot stars
D) An enormous collection of dark matter, explaining why we detect no light at all from the galactic center
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