Exam 15: Our Galaxy

A) become denser and hotter
B) become denser and have a greater abundance of heavy elements
C) have a lower abundance of heavy elements
D) have a greater abundance of heavy elements

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A) The diameter is about 100 times as great as the thickness.
B) The diameter and thickness are roughly equal.
C) The diameter is about 100,000 times as great as the thickness.
D) The diameter is about 10 times as great as the thickness.

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A) very near the galactic center
B) in the halo of the galaxy, about 28,000 light- years above the galactic disk
C) at the very outer edge of the galactic disk
D) in the galactic disk, roughly halfway between the center and the outer edge of the disk

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A) H2O
B) H2
C) CO
D) NH3

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From within the central bulge of the gal...

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A) globular clusters
B) X- ray binaries
C) high- mass, red supergiant stars
D) young stars

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A) We must look at the centers of other (external) galaxies and assume that they are similar to the Milky Way.
B) High- resolution photographs obtained by the Hubble Space Telescope have revealed the galactic center using visible light.
C) 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.
D) The gas and dust in the Milky Way prevent any type of direct observation of the galactic center, but theoretical models allow us to predict what is happening there.

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A) 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.
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) 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.
D) 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.

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A) The 10% figure is too high because there are not enough heavy elements to make that much dust.
B) The 10% figure is too low because most of the mass of the galaxy is in the form of interstellar dust.
C) It is reasonable because we already know that interstellar dust obscures our view through the disk of the galaxy.
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) 2 billion years
B) 200 million years
C) 2 million years
D) 200,000 years
E) 20,000 years

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A) the gas and dust that lie in between the stars in the Milky Way galaxy
B) the middle section of the Milky Way galaxy
C) the name of an oracle who can channel messages from beings that live near the star called Vega
D) the dust that fills the halo of the Milky Way galaxy

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A) gas and dust
B) K and M stars
C) O and B stars
D) open clusters
E) all of the above

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A) 10%
B) 1%
C) 50%
D) 98%

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A) elements that are heavier than iron
B) elements that are heavier than hydrogen
C) elements that are heavier than uranium
D) elements that are heavier than carbon
E) all elements besides hydrogen and helium

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A) 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.
B) Although dark matter emits no visible light, we have detected its radio emissions.
C) The orbital speeds of stars far from the galactic center are surprisingly high.
D) Our view of distant galaxies is often obscured by dark blotches, which are presumably made of dark matter.

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A) amazing filaments of radio emission swirling around the center of the galaxy
B) the gigantic bursts of X- ray energy from a mysterious dark object
C) 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.
D) the motions of stars around a mysterious dark object

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A) the Keck I telescope on the summit of Mauna Kea
B) the Hubble Space Telescope
C) the SOFIA airborne infrared observatory
D) the Chandra X- ray Observatory

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