M101: The Pinwheel Galaxy . ... Observational evidence indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass and condensed gas which continue to orbit the galaxy center. ... One result is that M101, also called the Pinwheel Galaxy, has several extremely bright star-forming regions (called HII regions ) spread across its spiral arms. M101 is so large that its immense gravity distorts smaller nearby galaxies. ... NASA Official: Jay Norris. ...