Cypress College ASTR 116 Homework
Astronomy 116, Homework CHAPTER 15 (A) Normal and Active Galaxies.
Due:
Print Last, First Name and date on the small Scantron in INK. Print
your last name in BIG BLOCK letters on the back of the Scantron.
Use a No. 2 pencil to fill out Scantron. Read the chapter.
Look at the videos and simulations in the CD-ROM. Answer all True/False and
Fill in the Blank questions. Then answer the following questions and
turn in your Scantron only. Choose the best answer.
1. How many galaxies are believed to exist?
- a) 1 billion
- b) 10 billion
- c) 50-100 billion
- d) 1 trillion
2. What property is common to all spiral galaxies?
- a) Ongoing star formation.
- b) The disk, the bulge, and the halo.
- c) Abundant interstellar gas.
- d) all of the above
- e) none of the above
3. The shape of, and stars found in, elliptical galaxies are most similar
to the ______ of spiral galaxies.
- a) disc
- b) spiral arms
- c) bulge
- d) halo
4. (True/False) Some galaxies contain only young stars.
5. Why does the Cepheid distance technique have limited usefulness beyond
25 Mpc?
- a) Distant galaxies are seen in the past, when Cepheid variables behaved
differently than they do today.
- b) Distant galaxies are so young they do not contain Cepheids.
- c) Cepheids are too faint to be seen.
- d) The light variability of Cepheids diminishes with distance so that
at large distances they do not appear to vary.
6. Most galaxies are
- a. normal
- b. active
- c. neither, about half are normal and hald are active.
7. Radio lobes in lobe radio galaxies can be as large as _____ across.
- a) 1 kpc
- b) 10 kpc
- c) 100 kpc
- d) 1 Mpc or more
8. In a lobe radio galaxy, the ultimate energy source for the entire galaxy
is thought to reside:
- a) In the lobes.
- b) In the galaxy's center.
- c) In the jets.
- d) all of the above
- e) none of the above
9. Why are quasars called "quasi-stellar"?
- a) Their spectra strongly resemble the spectra of stars.
- b) They are ordinary stars located at vast distances from Earth.
- c) They look like stars on photographs.
- d) Like the stars visible in our night sky, quasars reside within
the
- boundaries of the Milky Way.
10. All quasars have
- a. redshift
- b. blueshift
- c. some have a redshift, while others have a blueshift.
11. What is implied about an active galaxy or quasar that varies its energy
output rapidly?
- a) There are many separate sources of energy in the object.
- b) The source of energy must be numerous supernovae occurring.
- c) The source of energy must be relatively small.
- d) The energy source must be rapidly rotating.
12. What is the most likely source of energy for active galaxies and quasars?
- a) Large clusters of very massive, luminous stars.
- b) A single supermassive, superluminous star.
- c) Accretion onto a supermassive black hole.
- d) Numerous supernovae from rapid star formation in young galaxies.
13. A billion solar mass black hole has a radius of only _______.
- a) 20 A.U.
- b) 15 pc
- c) 150 km
- d) 3 pc
- e) 150,000 A.U.
14. Not only does the central engine of active galaxies and quasars require
a black hole, _______ is also needed to provide the energy radiated.
- a) a very strong magnetic field
- b) a source of very high energy electrons
- c) a high rate of rotation of the black hole
- d) an accretion disk of matter
- e) a companion black hole
15. When mass is accreted into a black hole, how much of its total mass-energy
can be radiated away?
- a) 0.1 percent
- b) 0.7 percent
- c) 20 percent
- d) 50 percent
- e) 100 percent