Chapter 17

Select the correct sequence for cosmic structures, from smallest to largest. a. galaxy, galaxy group, galaxy cluster, supercluster, cosmic web b. cosmic web, galaxy, galaxy cluster, galaxy group, supercluster c. galaxy, galaxy cluster, galaxy group, cosmic web, supercluster d. galaxy, galaxy cluster, galaxy group, supercluster, cosmic web e. cosmic web, galaxy, galaxy group, galaxy cluster, supercluster

Which of the following provide(s) evidence of dark matter? Choose all that apply. a. the Solar System b. galaxies c. galaxy clusters d. superclusters e. black holes

Which statement about the observed expansion of space-time is true? a. Observers in all galaxies should see farther galaxies receding from them faster than nearer galaxies. b. since we see all galaxies receding from the Milky Way, we must be near the center of the Universe. c. On average, all galaxies appear to be receding at the same speed. d. The farther away galaxies are, the more slowly they appear to recede e. Space-time is expanding out toward the limits of the Universe.

The term Local Group refers to a group of a. planets. b. stars. c. galaxies. d. galaxy clusters. e. astronomers working on a redshift survey.

If \(H\) were \(90 \mathrm{km} / \mathrm{s} / \mathrm{Mpc},\) how would the estimated age of the Universe change from current estimates? a. The value would be the same. b. The value would be larger. c. The value would be smaller. d. The value can't be determined from the information given. e. The value would depend on the density of the Universe.

From what you've learned about the stages of evolution of the Universe, and given the very best instruments available to detect light in visible wavelengths on Earth, what would be the earliest time frame or event that could be captured? a. the instant of the Big Bang b. within 300,000 years after the Big Bang c. the birth of the first galaxy d. the end of the Dark Ages e. none of the above

What does a redshift of \(z=0\) mean? a. The object is almost at the edge of the Universe. b. The object is nearly 14 billion years old. c. The object is not moving. d. The object shows no redshift. e. The object is obscured from our view by the plane of the Milky Way.

Which of the following is not characteristic of rich galaxy clusters? a. Their diameters are measured in megaparsecs. b. They can have more than 1,000 members. c. They contain many galaxy groups. d. They are gravitationally bound. e. They contain mostly spiral galaxies.

Which of the following is not indicated by the observation of an Einstein ring? a. the presence of dark matter b. a large mass between the observer and the source object for the ring c. a source object with a circular shape d. dark matter with a symmetric distribution e. curved space-time

Redshift surveys are difficult and time-consuming to obtain. Which of the following factors does not contribute to that difficulty? a. lack of evidence showing that redshifts imply expansion b. dim light from galaxies observed c. number of objects to be observed d. need for specialized equipment e. need for a large amounts of telescope time

Which of the following statements about the cosmic web is not true? a. It is filamentary. b. It is isotropic. c. It is homogeneous. d. It shows no voids. e. It resembles a sponge.

Which of the following is true of an object with a redshift of \(z=5 ?\) a. Its spectrum shows longer wavelengths than is expected for specific elements. b. It is receding faster than an object with \(z=6\). c. It is only a few light-years away. d. It may be significantly closer than a second object with \(z=5\). e. It is farther away than an object with \(z=7\).

Which of the following were the earliest to form in the evolution of the Universe? a. \(1-M_{\text {sum }}\) stars b. galaxies c. supermassive stars d. protoquasars e. intermediate-mass black holes

Which of the following is/are expanding as the Universe expands? Choose all that apply. a. the Solar System b. galaxies c. galaxy clusters d. galaxy superclusters e. space-time

X-ray halos of galaxy clusters consist primarily of which of the following? a. neutral hydrogen gas b. hot, ionized gas c. brown dwarfs d. supernova remnants e. X-ray radiation

If the Local Group had begun forming with more total mass and at a higher density than it did, which of the following would not be true? a. More galaxy mergers would likely have occurred. b. The largest galaxy (Andromeda) might have been even larger. c. More satellite galaxies would likely be found around the spiral galaxies. d. The galaxies would have started moving relative to each other at higher velocities. e. The ratio of luminous to dark matter would likely have been greater.

If the rate of expansion of the Universe had been increasing since the Big Bang, how would the calculated age of the Universe differ from the value attained using the currently observed Hubble constant? a. It would be less than with constant expansion. b. It would be greater than with constant expansion. c. Without knowing the rate of change, it is not possible to determine d. There would be no change, because the rate of expansion is taken into account in the current calculation. e. It would be a meaningless calculation, since astronomers now have definitively determined the true age of the Universe.

What specific piece(s) of evidence for dark matter do astronomers find? Choose all that apply. a. They calculate more mass in various large-scale structures than is visible as luminous matter. b. They observe large dark regions between galaxies. c. Galactic rotation curves do not match expectations based on mass and radius. d. X-ray halos in galaxy clusters have too much pressure to be gravitationally bound by the observed luminous matter in the clusters. e. Galaxies appear dimmer than expected.

Which statement(s) about redshift and look-back time is/are true? Choose all that apply. a. The greater the redshift, the greater the look-back time. b. The smaller the value of \(z\), the shorter the look-back time. c. Objects with greater redshift appear younger than they actually are today. d. Look-back time is limited by the speed of light and the age of the Universe. e. The greater the redshift, the closer the look-back time approaches the Big Bang.

True/False: Gravitational lensing means that objects can appear shifted from their expected positions.

Explain what redsbift means as it applies to the study of galaxies.

What galaxy types are found in the Local Group, and how are they arranged?

What is required for the formation of an Einstein ring?

What are redshift surveys? Name some notable examples. How are their results used?

Define the terms homogencous and isotropic.

Explain why there are no nearby quasars.

How do deep-field images contribute to our understanding of the evolution of the Universe?

Explain the term cold dark matter.

The first Star Wars movie series began with the phrase "Long, long ago in a galaxy far, far away...". What do you understand now about the scope of how long ago and how far away that could have been?

Estimate the age of the Universe, in years, using a value of \(81.5 \mathrm{km} / \mathrm{s} / \mathrm{Mpc}\) for Hubble's constant.

The average velocity for galaxies in a galaxy cluster is \(850 \mathrm{km} / \mathrm{s}\). The diameter of the cluster is 3.2 Mpc. How long, in years, would it take a galaxy to cross the cluster?

An astronomer calculated that the recession velocity of a galaxy was \(65,000 \mathrm{km} / \mathrm{s},\) by noting the redshift of a spectral line whose rest wavelength is \(420 \mathrm{nm}\). At what wavelength, in nanometers, did he observe the spectral line? (See Going Further \(16.1 .\) )