Ch. 14 Quiz
•What does our galaxy look like?
The Milky Way Galaxy consists of a thin disk about 100,000
light-years in diameter with a central bulge and a spherical region called the
halo that surrounds the entire disk. The disk contains the gas and dust of the interstellar
medium, while the halo contains very little gas.
• How do stars orbit in our galaxy?
Stars in the disk all orbit the galactic center in about the
same plane and in the same direction. Halo and bulge stars also orbit the
center of the galaxy, but their orbits are randomly inclined to the disk of the
galaxy.
• How does our galaxy recycle gas into stars?
Stars are born from the gravitational collapse of gas clumps
in molecular clouds. Near the ends of their lives, stars more massive than our
Sun create elements heavier than hydrogen and helium and expel them into space
via supernovae and stellar winds. The supernovae and winds create hot bubbles
in the interstellar medium, but the gas within these bubbles gradually slows
and cools as they expand. Eventually, this gas cools enough to collect into
clouds of atomic hydrogen.
•Where do stars tend to form in our galaxy?
Active star-forming regions, marked by the presence of hot, massive
stars and ionization nebulae, are found preferentially in spiral arms. The
spiral arms represent regions where a spiral density wave has caused gas clouds
to crash into each other, thereby compressing them and making star formation
more likely.
•What clues to our galaxy’s history do halo stars hold?
The halo generally contains only old, low-mass stars with a
much smaller proportion of heavy elements than stars in the disk. Thus, halo
stars must have formed early in the galaxy’s history, before the gas settled
into a disk.
• How did our galaxy form?
The galaxy probably began as a huge blob of gas called a protogalactic
cloud. Gravity caused the cloud to shrink in size, and conservation of angular momentum
caused the gas to form the spinning disk of our galaxy. Stars in the halo formed
before the gas finished collapsing into the disk.
•What lies in the center of our galaxy?
Motions of stars near the center of our galaxy suggest that
it contains a black hole about 3 to 4 million times as massive as the Sun. The
black hole appears to be powering a bright source of radio emission.
*Who is Andrea M. Ghez?
She is an American Astronomer and professor in the department
of Physics and Astronomy at UCLA
*Who observed stars moving close to the speed of light in
the center of our galaxy?
Andrea M. Ghez
*Where was Dr. Ghez born?
New York City on June 16th 1965
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