AST HOMEWORKS EXAM 3 | 132 ACTUAL
QUESTIONS AND ANSWERS WITH RATIONALE |
ALREADY GRADED A+ | NEW UPDATE 2025
Applying Newton's version of Kepler's third law (or the orbital velocity law) to the
a star orbiting 40,000 light-years from the center of the Milky Way galaxy allows us
to determine ______. - ANSWER the mass of the Milky Way Galaxy that lies
within 40,000 light-years of the galactic center
The kinetic energy Ekinetic of an amount of mass M traveling at a velocity v is
given by the formula Ekinetic=Mv^2/2. The total kinetic energy of the matter
ejected from a supernova explosion is about 10^44 joules.
Determine the typical speed at which that matter is ejected from a supernova
with a mass of 28 MSun. - ANSWER vdebris = 1.9×10^6 m/s
Sort each item into the appropriate bin according to whether it is more common
in spiral arms or about equally common within and between the spiral arms in a
spiral galaxy's disk. - ANSWER More common in spiral arms:
-young stars
-star formation
-dense, dusty gas clouds
-ionization nebulae
Equally common within and between spiral arms:
-old stars
,Click the icon "Spiral arm and star motion" in the interactive figure and watch the
animation of the galaxy's rotation over several hundred million years. Which of
the following statements accurately describe the motion? - ANSWER -
Individual stars move in and out of spiral arms over time.
-Individual stars orbit around the center of the galaxy.
Watch the video that comes up when you click the icon "Star formation in spiral
arms" in the interactive figure. Which of the following best describes what spiral
arms are? - ANSWER Spiral arms are waves of higher density that move
outward through a galaxy, triggering star formation as they pass.
What evidence suggests that most of the mass of the Milky Way is in the form of
dark matter? - ANSWER The orbital speeds of stars far from the galactic center
are surprisingly high.
Which of the following models best explains why our galaxy has spiral arms? -
ANSWER The spiral arms are a wave of star formation caused by a wave of
density propagating outward through the disk of the galaxy.
Why do disk stars bob up and down as they orbit the galaxy? - ANSWER
because the gravitational pull of other disk stars always pulls them toward the disk
How would you expect a star that formed recently in the disk of the galaxy to
differ from one that formed early in the history of the disk? - ANSWER It
should have a higher fraction of elements heavier than hydrogen and helium.
, What are the dark blobs (indicated by the red arrows) in this photograph from the
Hubble Space Telescope? - ANSWER Cold, dense molecular clouds in which
stars are forming.
How does the interstellar medium affect our view of most of the galaxy? -
ANSWER It prevents us from seeing most of the galactic disk with visible and
ultraviolet light.
How do disk stars orbit the center of the galaxy? - ANSWER They all orbit in
roughly the same plane and in the same direction.
Where are most of the Milky Way's globular clusters found? - ANSWER in the
halo
Which part of the galaxy has gas with the hottest average temperature? -
ANSWER the halo
The most common form of gas in the disk of the Milky Way galaxy is _________. -
ANSWER atomic hydrogen gas
How do we determine the Milky Way's mass outside the Sun's orbit? -
ANSWER from the orbits of stars and gas clouds orbiting the galactic center at
greater distances than the Sun
How should we expect the Milky Way's interstellar medium to be different in 50
billion years than it is today? - ANSWER The total amount of gas will be much
less than it is today.
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