Grand design spiral galaxy
Grand design spiral galaxies are spiral galaxies with very clear, continuous spiral arms that wrap around much of the disk. Their arms stand out as the main, well-defined structure, unlike galaxies with patchy or multi-arm patterns. The arms are strong sites of star formation, hosting many bright, hot, short-lived stars.
About 10% of known spiral galaxies (as of 2002) are grand design spirals. Notable examples include the Whirlpool Galaxy (M51), Phantom Galaxy (M74), Bode’s Galaxy (M81), the Southern Pinwheel (M83), Pinwheel Galaxy (M101), Fireworks Galaxy (NGC 6946), and IC 342 (The Hidden Galaxy).
Density wave theory is the leading explanation for why these arms are so well defined. It was proposed by Chia-Chiao Lin and Frank Shu in 1964, and the term “grand design” appeared in a 1966 follow-up paper. The idea is that spiral arms are density waves that rotate around the galaxy at different speeds than the stars. As gas and stars move through the disk, gravity piles material into the dense arms, causing gas clouds to collapse and form new stars. Stars can move in and out of the arms, so the pattern is long-lasting even as individual stars change position.
This page was last edited on 3 February 2026, at 18:11 (CET).