Astro 20 Chapter 12
____ galaxies have a great many short spiral segments branching from the spiral arms.
Flocculent
The center of our galaxy lies in the direction of (but far beyond) the stars in the constellation of
Sagittarius.
____ in other galaxies should contain luminous O and B stars if they are like the Milky Way.
The spiral arms
The first stars to form in our galaxy
had highly elongated elliptical orbits.
The traditional "top-down" theory of the formation of our galaxy cannot explain why
not all globular clusters are the same age. the youngest globular clusters are in the outer halo. the oldest stars are metal poor but not completely metal free. streams and rings of scattered stars are in the halo. (all of the above)
Why are Cepheid variable stars important in our study of the Milky Way galaxy?
Cepheid variable stars are stars that periodically brighten and dim. Their brightness periods can be used to determine their distance, which is useful for astronomers studying the distance of the Milky Way galaxy.
Who first used RR Lyrae variable stars to determine distances in the Milky Way?
Harlow Shapley
How did Harlow Shapley use the period-luminosity relationship of RR Lyrae variables to determine the size of the Milky Way galaxy?
He found the distances to globular clusters distributed about the center of the galaxy.
Who first determined that the energy/sec emitted by the luminosity of Cepheid variable stars is larger when the variation of their period is longer?
Henrietta Leavitt
The orbits of population I stars I. are confined to disk of the galaxy. II. are very elliptical. III. are nearly circular. IV. are randomly inclined to the disk of the galaxy.
I & III
Population II stars I. are primarily found in the disk of the galaxy. II. contain more heavy metals than population I stars. III. are primarily old low mass stars. IV. are located in globular clusters.
III & IV
Why does the rotation of our galaxy suggest that it is more massive than previously thought?
If the galaxy was a similar size to our solar system, then the speed of the rotations away from the center would be slower, which is called Keplerian motion. But in the Milky Way, orbital velocities are constant or increasing the greater the distance from the center, implying that the galaxy has a lot more mass.
How do theories of the origin of the Milky Way explain its halo?
Originally, the Milky Way started off as a spherical cloud of gas, stars, and star clusters. Over time, this sphere contracted toward its equator until it was a flat disk. The Milky Way's halo is the remnants of the spherical shape before it flattened. This is called the top-down or the monolithic collapse hypothesis.
Why does the average chemical composition of stars now forming differ from that of older stars?
Population I stars contain more metal than Population II stars because Population II stars were formed much earlier in the galaxy. Back when these stars were formed, there wasn't enough metal to incorporate into the star. But now that many of these old stars have died, their metallic remnants were used to form new stars.
____ of the Milky Way contains mostly old (population II) stars and globular clusters.
The spherical halo component
How does the traditional theory of the formation of the galaxy explain the origin of globular clusters?
They formed early on during the free-fall collapse of the proto-galactic material.
What evidence do we have that the center of our galaxy is a powerful source of energy?
When the nucleus is observed with infrared and radio wavelengths, the images show material such as stars orbiting around the nucleus at high speeds. Supernova remnants exist at the nucleus, along with huge amounts of stars and dust. Astronomers suggest that there is a supermassive black hole at the center of the galaxy, weighing about 4 million solar masses.
The central areas of our Milky Way Galaxy contain
a nuclear bulge of stars. a bar of stars. a radio wave emitting "whirlpool" of gas. a several million solar mass black hole. (all of the above)
If the spiral density wave were the only thing producing spiral arms, it would be expected that
all galaxies would have only two smooth spiral arms.
The traditional "top-down" theory states that the galaxy formed
as a large spherical cloud of gas that was rotating very slowly.
If a star with a large peculiar proper motion and/or speed with respect a typical disk star is found, what other property would you expect it to have?
low luminosity poor metal content compared to the Sun old age (all of the above)
The age of the Milky Way galaxy has been estimated to be at least 13 billion years based on
observations of globular clusters.
Our galaxy is suspected to be surrounded by a galactic halo or corona because the disk of the galaxy
rotates faster than expected in its outer region.
Pulsating variable stars are useful in determining
the distance to globular clusters.
Radio maps of our galaxy show spiral arms because
the gas in spiral arms is denser.
