A) gas and dust
B) old K and M stars
C) open clusters
D) O and B stars
E) all of the above
G) A) and B)
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A) in the spiral arms
B) everywhere throughout the galactic disk
C) within the halo
D) in the central bulge
F) C) and D)
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A) They have orbits randomly inclined and in different directions relative to the galactic center.
B) They follow spiral paths along the spiral arms.
C) They follow orbits that move up and down through the disk, typically taking them about 50,000 light- years above and below the disk on each orbit.
D) They all orbit in roughly the same plane and in the same direction.
F) A) and B)
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A) The older the star, the bluer its color.
B) The younger the star, the higher its mass.
C) The older the star, the faster its orbital speed.
D) The older the star, the lower its abundance of heavy elements.
E) The less massive the star, the older it is.
G) B) and C)
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Using the orbital velocity law, related ...View Answer
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B) False
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B) False
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A) It absorbs all wavelengths of light.
B) It prevents us from seeing most of the galactic disk with visible and ultraviolet light.
C) It produces so much visible light that it blocks our view of anything beyond it.
D) It has no effect on visible- light observations, but prevents us from studying the galactic center with radio waves or X- rays.
F) A) and C)
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A) molecular hydrogen
B) ionized hydrogen
C) carbon monoxide
D) atomic hydrogen
E) helium
G) D) and E)
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A) The disk is composed of stars orbiting in the same plane, same direction.
B) Globular clusters are compact groups of thousands of stars.
C) The disk is composed of stars of many different ages.
D) The halo is full of old stars orbiting in many different directions.
F) B) and D)
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A) Halo stars formed from gas containing few heavy elements, the elements needed to create terrestrial planets like the Earth.
B) Halo stars formed directly from gas in the halo without forming a planetary disk.
C) Halo stars formed from gas containing lots of heavy elements and few of the light elements needed to create terrestrial planets like the Earth.
D) Planets around stars are extremely rare in our Galaxy.
E) Halo stars are all very low mass stars that cannot hold onto planets.
G) B) and C)
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A) a dense cluster of young, hot stars
B) a gigantic X- ray binary system
C) an enormous collection of dark matter, explaining why we detect no light at all from the galactic center
D) a 3 to 4 million solar mass black hole
F) All of the above
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B) False
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A) red giant in globular cluster M13
B) a red main- sequence star in the disk of the Milky Way
C) None of these choices
E) A) and C)
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A) Given how easily dust grains can form, 10 percent is a surprisingly low fraction.
B) There is nothing surprising about the 10 percent figure because dust grains are the material from which stars are born.
C) The fraction of 10 percent is surprisingly high because dust grains can form only at low temperatures.
D) 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.
F) A) and C)
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A) by the winds of massive stars and supernovae explosions
B) by the collapse of a gas cloud to form stars
C) by collisions between the Milky Way and satellite dwarf galaxies
D) by the rapidly rotating magnetic fields of pulsars
E) by the ejection of planetary nebulae from low- mass stars
G) A) and E)
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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 using the law of conservation of angular momentum to calculate the orbital speeds of nearby stars
D) by estimating the amount of gas and dust in between the stars
F) None of the above
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A) The spiral arms will eventually dissipate and fade away, since they are a temporary phenomenon that should only last for a million years or so.
B) The spiral arms will eventually unwind, as centripetal forces send the stars flying outwards into intergalactic space.
C) The spiral arms will seem to "wind up," to wrap more and more tightly around the center of the Galaxy.
D) Stars will move through the spiral arms, bunching up closer as they pass through. Young hot stars will form and die within the arms before having a chance to move out.
F) B) and D)
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Since stars that are traveling along wit...View Answer
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A) 2%
B) 0) 002%
C) 98%
D) 70%
F) B) and C)
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