Astronomy Test 6 - Galaxies & Cosmology 4/25/03 ctr
Please put your name on the back of the last sheet only. Answer all. Good luck!
___ Which distance indicator works with the greatest distance?
1-brightest galaxy in a cluster
2-large globular clusters
3-H II regions
4-Cepheid variable stars
___ The look-back time is
1-how long light from an object takes to reach earth
2-numerically equal to the distance in light years
3-larger for more distant objects
4-all of these
___ If galaxy A is four times more distant than galaxy B, then according to the Hubble law, galaxy A will recede
1-16 times faster
2-4 times faster
3-2 times faster
4-1.4 times faster
___ Which of these collide?
1-galaxies but not stars
2-stars but not galaxies
3-galaxies and stars
4-neither galaxies nor stars
___ Red and yellow stars are found evenly spread throughout the disk, whereas hot blue stars are typically found
1-at the very edge of the galaxy.
2-in the central bulge.
3-only in spiral arms.
4-in the halo.
___ Surprisingly, stars in the outer regions of the Milky Way orbit
1-faster than the inner stars.
2-with roughly the same speed as the inner stars.
3-in a pronounced wavelike, up-and-down motion; they don't orbit the center
4-slower than the inner stars.
___ Although the galactic center appears relatively calm in the direction of Sagittarius to the unaided eye, the motions of gas and stars suggest
1-the galaxy's spiral arms connect at the very center.
2-a million-solar-mass black hole is present.
3-that X-ray binaries are common there.
4-it is filled with colliding dust and gas.
___ Calculations based on stellar evolution suggest that the universe is about
1-15 trillion years old.
2-15 billion years old.
3-15 million years old.
4-15 thousand years old.
___ The most powerful objects in the universe are
___ Surrounding the center of the Milky Way on all sides
2-is the interstellar medium.
3-are old globular clusters.
4-are young, open star clusters.
___ If we could see the Milky Way from 2 million light-years away, it would appear
1-like a single dim star.
2-as a faintly glowing, long band of light.
3-to fill the sky with widely spaced stars.
4-to be a disk with spiral arms.
___ Stars that have high concentrations of elements other than hydrogen and helium likely are
1-formed in molecular clouds.
2-stars found in globular clusters.
3-stars that formed first in the galaxy.
4-recently formed stars.
___ A standard candle is a
1-Pulsating G2 star.
2-light source of known brightness.
3-7-cm wax candle.
___ Extremely small Cepheid-variable stars will have
1-a very low brightness.
2-very large distance measurements.
3-short pulsation periods.
___ From a quasar's red shift, we can infer that it is
___ The side of a rotating galaxy that is moving towards the observer is
___ The observation that stars near the edge of a galaxy orbit as fast as stars near the middle suggests that the galaxy
1-has more gravity than previously thought.
2-is longer than previously thought.
3-has older stars than previously thought.
4-is older than previously thought.
___ In the Milky Way, stars are just the tip of the iceberg. This refers to the idea that
1-the galaxy is likely made mostly of non-luminous matter.
2-there are many more Earth-like planets than stars.
3-brown dwarf stars are more interesting than white dwarf stars.
4-the spectral class of a star tells what material might be orbiting each.
___ How does the average density of the universe affect predicted fate of the universe?
1-The expansion of the universe is unaffected by its density.
2-The increased pressure associated with the matter will cause the universe to expand forever.
3-If the universe is dense enough, it would eventually stop expanding and collapse.
4-The density of the universe is too infinitesimal to affect the expansion of the universe.
1. Draw and label a side view of the Milky Way, showing the parts, the location of the sun, the globular clusters, the number of stars, and the approximate distance across it.
2. How can a balloon with dots marked on it be used to illustrate Hubble's law?
3. The five largest galaxies in a photograph of a nearby cluster average 12 mm across. In a second photograph of another cluster of galaxies, all the galaxies look much smaller.
(a) Why is this?
(b) If the first cluster is 50 million light years away and the five largest galaxies in the second cluster average 2 mm across, about how far away is the second cluster?
4. How does a quasar produce its energy?
5. What are MACHOS and WIMPS? Give an example of each.
6. How did Vera Rubin discover that dark matter must exist? Discuss as fully as you can.
7. Sketch and briefly explain a simple model that shows how the galaxies are arranged in the universe as a whole.