Spiral Galaxy

space · stars · galaxies · cosmic

Spinning disk shape. Spiral galaxies look like giant pinwheels because they have a flat disk of stars, gas, and dust that slowly rotates around a central hub. The whole thing spins like a cosmic merry-go-round.

Bright central bulge. At the heart of every spiral galaxy is a dense clump of stars called the bulge. This glowing core is much brighter and packed with far more stars than the rest of the disk.

Faint outer halo. Surrounding each spiral galaxy is a ghostly, dimmer halo of stars that's much harder to see. Many of these outlying stars live in tight spheres called globular clusters.

Hubble's discovery. A scientist named Edwin Hubble first described spiral galaxies in 1936 in a book called The Realm of the Nebulae. His system for sorting galaxies is still used by scientists today.