Bodies contained in these objects are analogized to cars moving through a traffic jam in a common (-5[1])explanation of a theory resolving their “winding problem.” Lin and Shu’s density wave theory describes these objects, 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. (-5[1])Both (10[1])prongs (-5[1])of Hubble’s “tuning fork” diagram contain these objects, some of which are barred. The central bulges (-5[1])of these objects contain supermassive black holes. (10[2])For 10 points, name these disk-shaped (-5[1])systems of stars, gas, and dark matter, exemplified by Andromeda (10[1])and the Milky Way. ■END■ (10[4]0[1])