ConceptChecks
ConceptCheck 23-1: 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 are not themselves large galaxies very far away.
ConceptCheck 23-2: Cepheid variable stars have well-known luminosities, and can even be identified in other galaxies. Comparing a Cepheid’s luminosity to apparent brightness reveals a precise distance to the galaxy.
ConceptCheck 23-3: 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 23-4: In both spiral and barred spirals, the designation a is used for tightly wound arms and c for loosely wrapped arms.
ConceptCheck 23-5: Elliptical galaxies have almost no gas or dust available for the formation of stars.
ConceptCheck 23-6: 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 23-7: A galaxy has a narrow width to its emitted hydrogen light if it rotates slowly. This is because the width arises from the Doppler shift of emitted light from approaching and receding sides of the rotating galaxy. Smaller galaxies rotate more slowly than larger galaxies, which means that galaxies with narrower emission line widths are also smaller. If, as in this question, the galaxy appears bright, than it must be close to our own Galaxy.
ConceptCheck 23-8: 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.
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ConceptCheck 23-9: From Figure 23-17, the farther away the galaxy, the larger its recessional velocity in the Hubble flow. Furthermore, a larger recessional velocity produces a larger redshift, so the farther galaxy has the largest redshift.
ConceptCheck 23-10: The spectral shift toward the shorter blue wavelengths means that the Andromeda Galaxy is moving toward our Milky Way Galaxy.
ConceptCheck 23-11: Rich clusters are observed to contain significantly more galaxies within them than poor clusters.
ConceptCheck 23-12: 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 23-13: The Local Group, dominated by the Milky Way Galaxy and the Andromeda Galaxy, contains about 40 dwarf ellipticals.
ConceptCheck 23-14: Collisions between gas and dust in colliding galaxies will warm gas, causing it to glow in X-rays.
ConceptCheck 23-15: Simulations suggest that a single elliptical galaxy will form with many newly formed stars.
ConceptCheck 23-16: 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 23-17: All matter consisting of neutrons and protons is called “ordinary” matter, so a neutron star is still made of ordinary matter, even though a neutron star is not an ordinary object like a planet or star.
ConceptCheck 23-18: Earlier galaxies appear to have been much smaller, suggesting that today’s large galaxies formed by collisions and combinations of smaller galaxies.
ConceptCheck 23-19: 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 23-20: The arms become distorted during collisions, resulting in astronomers observing far fewer spiral galaxies today than in the past.
CalculationChecks
CalculationCheck 23-1: Because z = the change in wavelength (λ − λ0) divided by the original λ0, z = (725.6 nm − 656.3 nm) ÷ 656.3 nm = 0.11.
CalculationCheck 23-2: Hubble’s Law, v = H0d, can be rearranged as d = v ÷ H0. Using H0 = 73 km/s/Mpc, d = v ÷ H0 = 10,000 km/s ÷ 73 km/s/Mpc = 134 Mpc (million parsecs).