ConceptCheck 14-1: If spiral nebulae are closer than some of the stars of our Galaxy, then the evidence presented supports Shapley’s argument that spiral nebulae are within our Galaxy, and not in a large galaxy very far away.
ConceptCheck 14-2: Cepheid variables identified in other galaxies have well-known luminosities, and comparing luminosity to brightness reveals distances to other galaxies.
ConceptCheck 14-3: Sc galaxies have the most active star formation so a sketch would have a smaller central bulge and a relatively large star-forming disk with considerable gas and dust.
ConceptCheck 14-4: In both spiral and barred spirals, the designation a is used for tightly wound arms and c for loosely wrapped arms.
ConceptCheck 14-5: Elliptical galaxies have almost no gas or dust available for the formation of stars.
ConceptCheck 14-6: If the Type Ia supernova appeared to be dimmer because of intervening dust, then astronomers would mistakenly believe that the supernova was farther away and, subsequently, that the galaxy was farther away than it really is.
ConceptCheck 14-7: A galaxy that has almost no variability in the hydrogen light emitted is assumed to be rotating slowly because it has very few stars and must be quite small and have a low luminosity. However, in this case, if it appears bright, then it must be very close to our Galaxy.
ConceptCheck 14-8: Because the base of the distance ladder depends on parallax, all rungs of the ladder are completely dependent on an accurate understanding of brightness as determined by parallax.
ConceptCheck 14-9: Regular clusters have a spherical distribution and are observed to contain significantly more galaxies, most of which lack spiral structures, as compared to irregular clusters that are more spread out, less densely packed but have a wider variety of galaxy shapes included.
ConceptCheck 14-10: No, although on the largest scales, galaxies appear in every direction. Observations of superclusters show they are clumped into uneven groups and into long filaments.
ConceptCheck 14-11: The 54-member Local Group, dominated by the Milky Way Galaxy and the Andromeda Galaxy, contains mostly dwarf ellipticals.
ConceptCheck 14-12: Collisions between gas and dust in colliding galaxies will warm gas, causing it to glow in X-rays.
ConceptCheck 14-13: Simulations suggest that a single galaxy will form with many newly formed stars.
ConceptCheck 14-14: The best evidence is that the rotation curves in galaxies cannot be accounted for by the observed mass and the ability of galaxies and galaxy clusters to gravitationally lens more distant sources of light.
ConceptCheck 14-15: These objects are quite distant, yet profoundly luminous and exhibit emission lines rather than absorption lines.
ConceptCheck 14-16: An object that has a very short period of brightening and dimming can only do so if quite small in diameter, otherwise we would see a gradual brightening and dimming as the light from the closest regions arrives first and the light from the most distant regions arrives later.
ConceptCheck 14-17: Material falling inward toward a supermassive black hole can become so bright that its emitted energy (radiation pressure) can actually prevent more material from approaching the supermassive black hole.
ConceptCheck 14-18: We can observe the rotation curves for nearby galaxies, whereas for quasars, we infer that only a compact supermassive black hole can account for the energy we observe being emitted.
ConceptCheck 14-19: Earlier galaxies appear to have been much smaller, suggesting that today’s large galaxies formed by collisions and combinations of smaller galaxies.
ConceptCheck 14-20: Elliptical galaxies create most of their stars during the initial formation of the galaxy. Metal-rich, Population I stars can only form from the remains of Population II stars, which can only occur in later generations of star formation, which do not occur in elliptical galaxies.
ConceptCheck 14-21: The arms become distorted during collisions, resulting in astronomers observing far fewer spiral galaxies today than in the past.
CalculationCheck 14-1: Using the inverse-square law, if one object is 3 times farther away, it must be 1/32 dimmer, or only 1/9 as bright.
CalculationCheck 14-2: If LEdd = 30,000 (M ÷ M⊙)L⊙, then doubling the mass doubles the Eddington limit.
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