Question

1. practice: galactic - scale studies

respond to the following based on your reading.
question 1
how can you infer the existence of dark matter in a massive galaxy or in a cluster?
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question 2
briefly describe why different types of universes would produce different shifts in the light observed from distant galaxies.
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question 3
explain why the galactic disk appears blue and the galactic bulge appears red.

Explanation:

Question 1: The existence of dark matter in a massive galaxy or cluster can be inferred from the observed gravitational effects on visible matter. For example, the rotational speeds of stars in galaxies are much higher than what would be expected based on the amount of visible matter alone. This suggests the presence of additional, unseen mass (dark matter) providing the extra gravitational pull.
Question 2: Different types of universes (e.g., expanding, contracting, static) would produce different shifts in the light from distant galaxies due to the Doppler - like effects related to the relative motion between the source (galaxy) and the observer. In an expanding universe, light from distant galaxies is redshifted as the space between them and us stretches.
Question 3: The galactic disk appears blue because it contains young, hot, massive stars that emit more blue - light. The galactic bulge appears red because it contains older stars with lower surface temperatures that emit more red - light.

Answer:

Question 1: By observing the gravitational effects on visible matter, such as unexpected rotational speeds of stars in galaxies.
Question 2: Due to Doppler - like effects related to the relative motion between the galaxy and the observer, which varies depending on the type of universe (e.g., expansion causes redshift in an expanding universe).
Question 3: The disk has young, hot blue - emitting stars, while the bulge has older, cooler red - emitting stars.