Round 8: Tossup 2

Bodies contained in these objects are analogized to cars moving through a traffic jam in a common explanation of a theory resolving their “winding problem.” Lin and Shu’s density wave (10[1])theory describes these objects, (-5[1])which contain the majority of HII (“H two”) regions. The intrinsic luminosity of these objects is proportional to their asymptotic rotation velocity by the Tully-Fisher relation. Both prongs of Hubble’s “tuning fork” (10[1])diagram contain these objects, (10[1])some of which are barred. The central bulges of these objects (10[1])contain supermassive black (10[1])holes. (10[1])For 10 points, name these disk-shaped systems of stars, gas, and dark matter, exemplified by Andromeda and the Milky Way. ■END■ (10[1])

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