Exam 14: Our Galaxy

A) Two small galaxies that orbit the Milky Way Galaxy
B) Two nebulae located in the disk of the Milky Way galaxy and visible only from the Southern Hemisphere
C) Star-forming clouds found in the constellation Orion
D) The clouds of dust and gas found interspersed in many places throughout the Milky Way Galaxy

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A) Hydrogen gas produces so much visible light that the interstellar medium is opaque, blocking our view of anything beyond it.
B) Dust reflects most light from distant regions of the galaxy back towards the source.
C) Molecules in the interstellar medium absorb all wavelengths of light.
D) The small mixture of dust grains in the interstellar medium absorbs visible light.
E) all of the above

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A) It is pure coincidence; the stars just happen to be going in the same direction.
B) The gas that formed the stars was shaped as a giant, rotating disk.
C) Collisions between the stars caused their motions to organize into a general, spinning disk direction.
D) After the stars formed, gravity pulled the stars down into a plane in space, all orbiting a supermassive black hole.

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

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A) In the interstellar medium
B) In stars and supernovae
C) All were made in the Big Bang, when the universe first began
D) None of the above
E) All of the above

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Using the orbital velocity law, related ...

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A) High-resolution photographs obtained by the Hubble Space Telescope have revealed the galactic center using visible light.
B) 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.
C) 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.
D) We must look at the centers of other (external) galaxies and assume that they are similar to the Milky Way.

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A) 100 light years
B) 1,000 light years
C) 10,000 light years
D) 100,000 light years
E) 1,000,000 light years

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

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A) The stars that formed first could orbit the center of the galaxy in any direction at any inclination.
B) The stars that formed first eventually settled into a galactic disk, circling the center of the galaxy.
C) The protogalactic cloud gradually formed stars, starting from the center of the galaxy working outwards.
D) The protogalactic cloud gradually formed stars, starting from the outer edges of the spiral arms and working inward.

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A) It should have a higher fraction of elements heavier than hydrogen and helium.
B) It should be higher in mass.
C) It should be much brighter.
D) It should orbit the galactic center at a much higher rate of speed.
E) All of the above would be expected.

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A) The mass of the galaxy inside its orbit and size of its orbit
B) The mass and age of the star
C) The star's mass and the mass of the galaxy
D) The mass and age of the galaxy

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A) in supernovae
B) in the winds of red giant stars
C) in planetary nebulae
D) in molecular clouds
E) all of the above

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A) The spiral arms are a wave of star formation caused by wave of density propagating outward through the disk of the galaxy.
B) The spiral arms are composed of groups of stars that are bound together by gravity and therefore always stay together as the galaxy rotates.
C) The spiral arms were imprinted on the galaxy at its birth. Ever since, like a coiling rope, the spiral arms have been wound tighter with each galactic rotation.
D) No model can explain the existence of the arms, which rotate with the galaxy like the fins of a giant pinwheel toy.

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