"
These objects have a resonance named for Bertil Lindblad, who identified an objection to existing models of them called the "winding problem." Orbital resonance may result in the high prevalence of active nuclei in the barred variety of these. Predominantly Population II stars are found in the bulges of subclass a, at the center of which a supermassive black hole may exist. A large number of Population I stars, young and blue, may be found in their arms. For 10 points, identify this kind of galaxy, examples of which include the Andromeda Galaxy and the Milky Way.
These objects have a resonance named for Bertil Lindblad, who identified an objection to existing models of them called the "winding problem.
{spiral} galaxies [prompt on galaxies]