Spiral Galaxies

Spiral galaxies have flat rotating disks with sweeping arms of gas, dust, and young blue stars. The arms are not permanent structures — they are density waves, regions of compressed gas that trigger star formation as material passes through them. Our own Milky Way is a spiral galaxy.

Barred spirals have an elongated bar of stars across their center, with arms spiraling from the bar's ends. The Milky Way is a barred spiral. The bar channels gas toward the center, fueling star formation and feeding the central black hole.