moon phases

The objects depicted below have one very significant similarity and one equally significant difference. There similarity is in there shape, a globular mass surrounded by a ring. The difference is the Sombrero galaxy (top photo) is trillions of times bigger than Saturn. Why would two objects so vastly different in mass so closely resemble each other in form?

About 4.5 billion years ago an object the size of Mars impacted the Earth. This collision tore a massive piece out of our planet, forming the Pacific basin and casting debris equal to about 1/6 of the Earth into orbit. Because of our rotation this debris formed a equatorial ring, which ultimately colalessed into the moon. Earths' ring was an important component of its' planetary evolution. Does this also happen on a galacic scale?