Astronomy Chapter 21 Concept Quiz – Flashcards

We can study how galaxies evolve because ______.

Which of the following statements is not an assumption used in models of galaxy formation? 1. Gas contracted to form the disks of galaxies before any stars were born. 2. Some regions in the universe were slightly more dense than others. 3. The universe is expanding. 4. The universe started out filled almost uniformly with hydrogen and helium.

One possible explanation for a galaxy's type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interactions, we'd expect this galaxy to be ______.

Two ways in which the starting conditions in a protogalactic cloud might cause it to become an elliptical (rather than spiral) galaxy are if the cloud begins with either:

Which of the following phenomena are not thought to be results of collisions or other interactions between galaxies? 1. Starbursts. 2. The fact that spiral galaxies have both disk and halo components. 3. The fact that elliptical galaxies are more common in clusters of galaxies than outside clusters. 4. The presence of very large, central dominant galaxies in clusters of galaxies.

If the Andromeda Galaxy collided with the Milky Way, what would most likely happen to Earth?

Interactions among galaxies are also thought to influence a galaxy's type in at least some cases. Which of the following does not support the idea that interactions can shape galaxies? 1.The presence of features such as "tails" extending out of galaxies, bridges between galaxies, and rings of stars around galaxies. 2. Computer modeling of collisions between galaxies. 3. The fact that galaxies with distorted appearances are more common at great distances than nearby. 4. The fact that more distant galaxies have larger redshifts.

Which characteristic is not generally true of a starburst galaxy? 1. Supernovae occur so frequently that their effects combine to drive a galactic wind that blows material into intergalactic space. 2. Its rate of star formation is many times higher than the rate of star formation in the Milky Way. 3. The observed features of the starburst are thought to be caused by the presence of a supermassive black hole in the galaxy's center. 4. The observed features that cause us to classify it as a "starburst" must be only temporary phenomena in the galaxy's history.

Why should galaxy collisions have been more common in the past than they are today?

A quasar's spectrum is hugely redshifted. What do most astronomers think this large redshift tells us about the quasar?

A few decades ago, there was great controversy among astronomers over the question of quasar distances, with some arguing that quasars are much nearer than application of Hubble's law would seem to imply. Why do nearly all astronomers now agree that quasars really are quite far away?

Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply?

Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?

All of the following observations are real. Which one does not support the theory that active galactic nuclei are powered by accretion disks around massive black holes? 1. X-ray emission from active galactic nuclei can vary significantly in times as short as a few days. 2. Spectra of active galactic nuclei show that clouds of gas are orbiting a central object at very high speed. 3. The most luminous active galactic nuclei have huge redshifts. 4. The total luminosity of an active galactic nucleus can be as high as about 10 billion times that of the Sun.

Central black holes can be very efficient for converting the mass-energy of infalling matter to thermal energy in the accretion disk. Roughly what percentage of the mass-energy can be converted to other forms of energy as matter falls into a black hole?

The observed relationship between the masses of central black holes and the bulge masses of galaxies implies that:

Quasar spectra often show many absorption lines that all appear to be due to the same electron transition (such as level 1 to level 2 in hydrogen) but that fall at different wavelengths in the spectrum. Why do we think this is the case?