ACTIVE GALAXIES and QUASARS -------------------------- The most likely reason that clusters of galaxies have more elliptical than spiral galaxies is that in the high density cluster environment $a) spirals merge to form ellipticals. b) intracluster gas strips galaxies of the gas needed for star formation. c) near-misses between galaxies makes them rounder. d) galaxies are older and their brighter disk stars have burned out. At high redshift, a larger fraction of galaxies are "active" (show signs of powerful luminous nuclei) than at low redshift. Therefore, we can safely say that a) all galaxies go through an active phase, and more galaxies in the past were active than now. $b) some galaxies go through an active phase and more galaxies in the past were active than now. c) all galaxies are either active or normal. d) galaxies may become active more than once in their lifetimes. At high redshift, a larger fraction of galaxies are "active" (show signs of powerful luminous nuclei) than at low redshift. If galaxies only become active when they collide or interact with nearby galaxies, then it might be true that a) there were more interactions in the past, and activity fades away. b) the number of distinct galaxies in the Universe decreases with time. c) galaxies were closer together in the past. $d) all of the above. The large doppler velocity widths of broad emission lines in active galaxies (Seyferts and quasars) could NOT be created by hot emitting clouds that are a) swirling at high velocities around a black hole. b) falling into the neighborhood of a black hole. c) being ejected into a broad cone or disk-shaped wind. $d) being ejected along a narrow-angled jet. Narrow absorption lines in the spectra of distant quasars could be caused by clouds of gas on the a) near side of the quasar with large random velocities but small bulk velocities. $b) near side of the quasar with small random velocities but large bulk velocities. c) far side of the quasar with large random velocities but small bulk velocities. d) far side of the quasar with small random velocities but large bulk velocities. Seyferts and quasars are both types of active galaxies, harboring powerful luminous nuclei. Quasar nuclei appear to be more luminous, and therefore their black holes a) are accreting matter at a higher rate. b) are more massive. c) are less obscured along our sightline. $d) any of the above. The word "quasar" comes from "quasi-stellar". What makes quasars quasi-stellar is that they can have a a) proper motion seen between images taken at 2 epochs. b) Doppler velocity shift evident in their spectra. $c) point-like appearance in an image. d) binary companion. The wide variety of spectra observed from different active nuclei of galaxies appear may result from a) how many neutron stars they contain. b) the amount of dust in our Galaxy blocking the view. $c) the angle at which we view each nucleus. e) whether or not the galaxy has a close companion. One method you could use to search for a high-mass black hole at the center of a galaxy is to look for a) a black dot at the galaxy's nucleus. b) a very high luminosity star. $c) a very large range of Doppler shifts around the nucleus. d) distortion in the shapes of stars near the nucleus. Rapid variability in the luminous nuclei of quasars is evidence that the emission region must be $a) small. b) large. c) moving rapidly. d) exploding. The powerful nuclei of quasars and Seyfert galaxies cannot be dominated by starlight because nuclear fusion in a group of stars could not account for the quasar's observed a) rapid variability. b) luminosity. c) compact size. $d) all of the above The distance to the point-like quasars is found from a) comparing their apparent and absolute magnitude. b) the apparent magnitudes of their supernovae. c) their parallax measured with radio telescopes. $d) their redshift and the Hubble law. If the large redshifts of quasars were NOT caused by the cosmological expansion, then bright quasars could possibly be explained as a) distant objects that are very luminous. $b) nearby luminous objects exploding outward from the Milky Way. c) bright nearby objects severely reddened by intervening dust. d) distant objects severely reddened by intervening dust. Quasars are more likely powered by accretion onto a supermassive black hole than by stars because accretion is a) the only natural way to produce radio and x-ray emission. $b) a much more efficient means than fusion of extracting energy from matter. c) possible in the early universe before stars even formed. d) responsible for destroying and engulfing stars.