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# astronomy HW # 10 & 11

UCF Spring 2013 Section 1
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Which of the following is a consequence of Hubble's Law?
A.all galaxies are moving away from us equally fast
B.the more distant a galaxy is from us, the faster it moves away from us
C. more distant galaxies appear younger
D. the Big Bang
E. the closer a galaxy is to us, the faster it moves away from us
B
Which of the following types of galaxies appear reddest in color?
A.spirals
B.irregulars
C.ellipticals
D. lenticulars
C
What is the best way to determine a galaxy's redshift?
A.Take a spectrum of the galaxy, and measure the difference in wavelength of spectral lines from the wavelengths of those same lines as measured in the laboratory.
B.Find the color of the galaxy, and estimate its distance based on how red the galaxy is.
C.Measure the magnitude of the galaxy, estimate its distance, and calculate its redshift using Hubble's Law.
D.Find the galaxy's apparent distance, and look up the redshift based on Hubble's Law.
A
Which of the following best explains why a higher-mass cluster of galaxies causes light from a distant galaxy to bend more than a lower-mass cluster of galaxies?
A.The stronger gravity of a larger cluster curves space itself by a greater amount, and light follows the curvature of space.
B.Light must go around any large collection of galaxies, so it has farther to go around a larger cluster.
C.The stronger gravity of a larger cluster causes photons to accelerate to higher speeds.
A
Does Hubble's law work well for galaxies in the Local Group? Why or why not?
A.No, because galaxies in the Local Group are gravitationally bound together.
B.No, because Hubble did not know the Local Group existed when he discovered his law.
C.Yes, it works so well that we have never detected any measurable deviations from its predictions.
D.No, because we do not know the precise value of Hubble's constant.
A
The most basic difference between elliptical galaxies and spiral galaxies is that ________.
A.elliptical galaxies lack anything resembling the halo of a spiral galaxy
B.elliptical galaxies are very old and spiral galaxies are very young
C.elliptical galaxies have a spheroidal component (of stars distributed spherically about the galactic center), and spiral galaxies do not
D.elliptical galaxies lack anything resembling the disk of a spiral galaxy
D
Based on current estimates of the value of Hubble's constant, how old is the universe?
A.8 to 12 billion years old
B.More than 20 billion years old
C.15 to 20 billion years old
D.12 to 15 billion years old
E.4 to 8 billion years old
D
Listed following are three possible models for the long-term expansion (and possible contraction) of the universe in the absence of dark energy. Rank each model from left to right based on the ratio of its actual mass density to the critical density, from smallest ratio (mass density much smaller than critical density) to largest ratio (mass density much greater than critical density).
critical universe, coasting universe, recollapsing universe
coasting universe, critical universe, recollapsing universe
What is Hubble's law?
A.The recession velocity of a galaxy is inversely proportional to its distance.
B.The faster a spiral galaxy's rotation speed, the less luminous it is.
C.The luminosity of the Cepheid variable star is directly proportional to its pulsation period.
D.The faster a spiral galaxy's rotation speed, the more luminous it is.
E.The recession velocity of a galaxy is directly proportional to its distance.
E
Which statement below correctly describes the relationship between expansion rate and age for the universe?
A.The faster the rate of expansion, the younger the age of the universe.
B.Age is independent of the expansion rate.
C.The faster the rate of expansion, the older the age of the universe.
A
Which types of galaxies have a clearly defined disk component?
A.ellipticals only
B.irregulars only
C.spirals only
D.spirals and lenticulars
E.lenticulars only
D
Compared to spiral galaxies, elliptical galaxies are
A.redder and rounder.
B.bluer and rounder.
C.bluer and flattened.
D.always much smaller.
E.redder and flattened.
A
Why do we call dark matter "dark"?
A. We cannot detect the type of radiation that it emits.
B. It emits no or very little radiation of any wavelength.
C. It emits no visible light.
D. It blocks out the light of stars in a galaxy.
B
What evidence suggests that the Milky Way contains dark matter?
What evidence suggests that the Milky Way contains dark matter?
A. We see many dark voids between the stars in the halo of the Milky Way.
B. We observe clouds of atomic hydrogen far from the galactic center orbiting the galaxy at unexpectedly high speeds, higher speeds than they would have if they felt only the gravitational attraction from objects that we can see.
C. When we observe in different wavelengths, such as infrared or radio, we see objects that don't appear in visible-light observations.
D. When we look at the galactic center, we are able to observe a large black hole that is composed of dark matter.
E. We see many lanes of dark material blocking out the light of stars behind them along the band of the Milky Way.
B
The distribution of the dark matter in a spiral galaxy is
A. predominantly concentrated in the spiral arms.
B. flattened in a disk but about ten times larger than the stellar disk.
C. approximately spherical and about the same size as the galaxy halo.
D. flattened in a disk and about the same size as the stellar disk.
E. approximately spherical and about ten times the size of the galaxy halo.
E
A gravitational lens occurs when
A. dark matter builds up in a particular region of space, leading to a very dense region and an extremely high mass-to-light ratio.
B. a massive object bends light beams that are passing nearby.
C. a massive object causes more distant objects to appear much larger than they should, and we can observe the distant objects with better resolution.
D. a telescope lens is distorted by gravity.
B
Which of the following is not evidence for dark matter?
A. the broad absorption lines found in the spectra of elliptical galaxies
B. the flat rotation curves of spiral galaxies
C. gravitational lensing around galaxy clusters
D. the expansion of the universe
E. X-ray observations of hot gas in galaxy clusters
D
What do we mean when we say that a particle is weakly interacting?
What do we mean when we say that a particle is weakly interacting?
A. It interacts with other particles only through the weakest force, gravity.
B. It interacts with other particles only through the weak force.
C. It interacts only with other weak particles, such as neutrinos.
D. It doesn't interact with any type of baryonic matter.
E. It interacts with other particles only through the weak force and the force of gravity
E
Why isn't the space within our solar system or the Milky Way expanding according to Hubble's Law?
A. Hubble's law of expansion applies only to the space between galaxies.
B. The universe is not old enough for the solar system or Milky Way to have begun their expansion.
C. As we are inside our solar system and the Milky Way, we cannot observe their expansion.
D. The gravity exerted by the solar system and the Milky Way is strong enough to hold them together against the expansion of the universe.
D
What fraction of the mass needed to halt expansion of the universe exists in the form of visible, luminous matter (such as the stars within galaxies)?
What fraction of the mass needed to halt expansion of the universe exists in the form of visible, luminous matter (such as the stars within galaxies)?
A. 10 percent
B. 25 percent
C. less than 1 percent
D. 50 percent
C
The actual matter density of the universe, accounting for all of the luminous matter and all of the dark matter known to exist in galaxies and clusters, is what fraction of the critical density?
The actual matter density of the universe, accounting for all of the luminous matter and all of the dark matter known to exist in galaxies and clusters, is what fraction of the critical density?
A. 100 percent
B. 25 percent
C.10 percent
D. 200 percent
E. 1 percent
B
Which model of the universe gives the youngest age for its present size and expansion rate?
Which model of the universe gives the youngest age for its present size and expansion rate?
A. A re-collapsing universe
B. A coasting universe
C. An accelerating universe
D. A critical universe
E. All models give the same age
A
What might be causing the universe to accelerate?
A.WIMPs
B. White-dwarf supernovae
C. Dark energy
D. Gravitation
E. MACHOs
...
Spiral galaxy rotation curves are generally fairly flat out to large distances. Suppose that spiral galaxies did not contain dark matter. How would their rotation curves be different?
A.The rotation curve would look the same with or without the presence of dark matter.
B. The orbital speeds would rise upward with increasing distance from the galactic center, rather than remaining approximately constant.
C. The orbital speeds would fall off sharply with increasing distance from the galactic center.
D. The rotation curve would be a straight, upward sloping diagonal line, like the rotation curve of a merry-go-round.
C
How does gravitational lensing tell us about the mass of a galaxy cluster?
A. The lensing broadens spectral lines, and we can use the broadening to "weigh" the cluster.
B. The lensing allows us to determine the orbital speeds of galaxies in the cluster, so that we can determine the mass of the cluster from the orbital velocity law.
C. Newton's universal law of gravitation predicts how mass can distort light, so we can apply Newton's law to determine the mass of the cluster.
D. Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it.
D
Which of the following statements best describes the current state of understanding regarding the apparent acceleration of the expansion of the universe?
A. The acceleration is very important in the cosmos today, but the evidence indicates that it will eventually slow down, allowing the universe to recollapse.
B. The acceleration probably is not real, and what we attribute to acceleration is probably just a misinterpretation of the data.
C. The cause of the acceleration is well-understood, and attributed to the particles that make up dark energy.
D. We have moderately strong evidence that the acceleration is real, but essentially no idea what is causing it.
D
Some people wish that we lived in a recollapsing universe that would eventually stop expanding and start contracting. For this to be the case, which of the following would have to be true (based on current understanding)?
A. Neither dark energy nor dark matter really exist.
B. Dark energy is the dominant form of energy in the cosmos.
C. Dark energy exists but dark matter does not.
D. Dark energy does not exist and there is much more dark matter than we are aware of to date.
D