Why Galaxies have Spiral Arms?! - The majestic spiral arms of galaxies are a source of wonder, but what exactly causes them to form? Is it the swirling dance of stars as they orbit the galactic center, or something more mysterious? Does the speed at which different parts of the galaxy rotate play a role? And why don't these arms simply wind up and disappear over time? | The Brain Maze

Pan of Spiral Galaxy IC 1954 in Horologium | Hubble Space Telescope

Galaxy Types: From Spirals to Ellipticals