Download Assignment 10

Assignment 10
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
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1. Where would you look for the youngest stars in the Milky Way Galaxy?
a. in the halo
b. where there is dark matter
c. in the disk
d. in the nuclear bulge
e. you can't fool me; my chances of finding a very young star are the same, wherever in the Galaxy I look
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2. Objects orbiting around the center of the Milky Way obey Kepler's 3rd Law. This means that:
a. the pull of gravity gets stronger and stronger as you get further away from the center
b. larger clusters of stars will orbit the center more quickly than smaller ones
c. the closer a star is to the center, the longer it will take to go around
d. a cloud of gas or star that is further from the center will generally take more time to orbit
e. the orbits of all objects around the Galaxy are in the shape of a circle
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3. What of the following statements is part of our best modern theory about how galaxies like ours come to have spiral arms?
a. spiral arms are caused by chains of black holes which are drawing in a lot of material
b. spiral arms are just a coincidence; very few other galaxies have them
c. we have spiral arms because our galaxy is presently merging with another galaxy about our size
d. spiral arms are places where the density of material is much higher (like a traffic jam)
e. spiral arms are regions where a whole series of old globular clusters have come together, like pearls on a necklace
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4. Our Milky Way Galaxy is what type of galaxy?
a. spiral
b. elliptical
c. dwarf elliptical
d. irregular
e. none of the above
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5. How do astronomers measure the mass that the Galaxy contains inside the orbit of the Sun?
a. they count the number of stars one by one and multiply by the average mass of a star
b. they add up all the observations at 21­cm wavelengths (because the mass of hydrogen gas is far greater than the mass in all the stars)
c. they measure the distance to the center of the Galaxy and the period of the Sun's orbit and then use Kepler's Third Law
d. they measure the masses of many other spiral galaxies nearby and then take an average
e. you can't fool me; there is no way to get the mass of something as big as our Galaxy
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6. Astronomers believe that the center of our Galaxy has a black hole with enough mass inside to make almost 3 million Suns! How do astronomers think a black hole could acquire so much mass?
a. the Galaxy formed from one supergiant star, and most of what is left of it is now in the black hole
b. the black hole at the center is really another galaxy that our Milky Way swallowed; none of its material comes from our own Galaxy
c. the center of our Galaxy is a much more crowded region than where the Sun is found; we still see material falling toward the center and material has fallen in for billions of years
d. this black hole contains only dark matter, and we know dark matter is concentrated toward the center of our Galaxy; none of it can be found near the outer regions of the Milky Way
e. no one can think of a way to make a black hole this massive; that's why most astronomers are skeptical about the observations that indicate that our Galaxy has such a black hole
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7. Which type of galaxy is observed to contain mostly older stars?
a. spiral
b. elliptical
c. dwarf elliptical
d. irregular
e. none of the above
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8. In a distant galaxy, whose light is just arriving from 9 billion light years away, our spectroscope should reveal that the most common element is
a. helium
b. carbon
c. hydrogen
d. iron
e. Einsteinium
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9. What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?
a. parallax
b. Cepheid variables
c. using the x­ray emission from the entire galaxy
d. finding the redshift and using Hubble's Law
e. the turnoff point of the main sequence on an H­R diagram
____ 10. Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the
a. brighter it looks
b. bluer its color
c. the later in its life we are seeing it
d. the larger its halo is
e. the faster it is moving away from us
____ 11. The Andromeda Galaxy (our nearest spiral neighbor) has spectral lines that show a blue shift. From this we may conclude that:
a. the universe is no longer expanding
b. this particular galaxy is moving toward us
c. this galaxy has merged with the Milky Way and is now part of it
d. this particular galaxy is moving away from us
e. this galaxy has an unusual number of very bright and hot O­type stars in it
____ 12. Which of the following statements about the implications of Hubble's Law is FALSE?
a. the law implies that the whole universe must be expanding
b. the law can be used to measure distances to remote galaxies for which we can measure a Doppler shift
c. the law does NOT require us to be at the center of the expanding universe
d. if you were observing the universe from a distant galaxy, you would NOT see all the galaxies (except those in your own group) moving away from YOU
e. although galaxies move away from each other, they themselves are not expanding in size
____ 13. The type of galaxy that sometimes has a distinct bar of stars running across the central region is
a. spiral
b. elliptical
c. dwarf elliptical
d. irregular
e. all of the above can have clear, distinct central bars
____ 14. The type of galaxy that consists almost entirely of old stars and is thus less blue (more yellow and reddish) than the other types is:
a. spiral
b. elliptical
c. irregular
d. barred spiral
e. all of the above consist almost entirely of old stars
____ 15. If quasars often resemble little blue stars, what was it about them that so surprised astronomers when they were discovered?
a. their surface temperatures were among the lowest measured
b. they show absolutely no lines in the spectrum
c. they vary their brightness with a period (time­scale) of seconds
d. they were all located in globular clusters
e. their spectral lines were at first hard to recognize and then turned out to have large redshifts
____ 16. The astronomer who first solved the problem of the strange redshifts seen in quasar spectra and thus helped us understand that the quasars must be distant objects was
a. Carl Sagan
b. Maarten Schmidt
c. Edwin Hubble
d. S. Chandrasekhar
e. Vesto Slipher
____ 17. A Congressman from Texas visits our National Observatory in Tucson, Arizona, and wants to be shown an object in the universe with the "biggest damn redshift you ever saw". What type of object should the astronomers show him?
a. a comet in the Kuiper Belt
b. one of the galaxies in our Local Group of galaxies
c. a star with a very low surface temperature
d. a quasar
e. an active galaxy that is in a rich cluster of galaxies just beyond the Local Group
____ 18. Today we know that what all quasars have in common is that they appear to be small sources of energy with
a. strong radio emission
b. variations in luminosity with a period of seconds
c. redshifts that indicate they are far away
d. tremendous proper motion (apparent motion across the sky)
e. gravitational lenses clearly visible around them
____ 19. What method would astronomers use to find the distance to a remote quasar?
a. parallax
b. Cepheid variables
c. using a Type I supernova explosion as a standard "bulb"
d. finding the redshift and using Hubble's Law
e. the turnoff point of the main sequence
____ 20. After several decades of observation, astronomers have concluded that quasars are
a. very powerful and compact sources of energy at the centers of distant galaxies
b. projectiles shot out of our own Galaxy and moving out into intergalactic space
c. energetic collisions of comets in the Oort Cloud
d. anti­matter stars in the halo of the Milky Way Galaxy
e. a completely baffling mystery with no hint of an answer
____ 21. Today, astronomers find compelling evidence that the energy source of the quasars and active galaxies is
a. antimatter and matter colliding at the center of a galaxy
b. chain reactions of supernova explosions
c. matter falling toward a supermassive black hole at the center of a galaxy
d. the left­over (and stored) energy of the big bang explosion
e. you can't fool me; astronomers have no compelling explanation for what the energy source is for the quasars ­­ they are completely baffled
____ 22. How do astronomers now explain the fact that the energy emitting regions for quasars are so small?
a. quasars are just optical illusions caused by gravitational lensing effects
b. quasars are the result of three or four galaxies colliding: the collision squeezes the quasar to become much smaller than it normally would be
c. quasars are the result of matter falling into a black hole; the event horizons of black holes are extremely small
d. quasars are caused by the actions of neutron stars and neutron stars have been squeezed so much that they are very, very small
e. you can't fool me, there is no plausible explanation for the small sizes of quasar energy regions
____ 23. Active radio galaxies can display
a. strong emission from a small central source
b. long jets of radio emissions
c. two lobes (regions of radio emission) that can be quite far from the galaxy's center
d. all of the above
e. none of the above
____ 24. A friend of yours who is a science fiction fan hears you talk about the fact that astronomers now believe that the mechanism for the large energy output of quasars involves a supermassive black hole. He challenges you, saying something like "Oh come on, every science fiction fan knows that nothing, not even light, can escape from a black hole! How can a black hole be an energy source!?" How would you respond to his objection?
a. you're right, my explanation doesn't make sense; I wonder why astronomers didn't think of that?
b. light can't escape from the event horizon of a regular black hole; but it can easily escape from the event horizon of a supermassive black hole
c. it isn't light that escapes from the black holes in quasars, but x­rays and gamma­rays, which work by completely different rules
d. the energy we see from quasars comes from regions where matter is falling in still outside the event horizon
e. quasars act like gravitational lenses and bend spacetime until light and other radiation CAN emerge from a black hole in unexpected ways
Assignment 10
Answer Section
MULTIPLE CHOICE
1. ANS: C
3. ANS: D
5. ANS: C
+
7. ANS: B
9. ANS: D
11. ANS: B
13. ANS: A
15. ANS: E
17. ANS: D
19. ANS: D
21. ANS: C
23. ANS: D