Pinwheel Galaxy

The Pinwheel Galaxy is a face-on grand design spiral galaxy, presenting one of the most complete views of spiral structure available from Earth. Its nearly perfect face-on orientation makes it an ideal specimen for studying spiral arm morphology, star formation patterns, and disk structure.

The galaxy’s disk spans roughly 170,000 light-years — about twice the diameter of the Milky Way. The Hubble mosaic image, composed of 51 separate ACS pointings, is one of the most detailed images of a spiral galaxy ever assembled and reveals hundreds of individual stellar nurseries and star clusters scattered throughout the arms.

The spiral arms are asymmetric — one arm is considerably more developed than the others — a consequence of the gravitational influence of three nearby companion galaxies (NGC 5474, NGC 5477, NGC 5585). The asymmetry is particularly visible in wide-field images.

The brightest pink regions are giant HII regions — ionized hydrogen clouds surrounding young stellar clusters — some reaching sizes comparable to the Tarantula Nebula in the Large Magellanic Cloud.