Glossary term: Galactic Disk

Description: The galactic disk is the disk component of the Milky Way that contains stars, gas, and dust in circular coplanar motion around the galactic center. The galactic disk is very thin compared to its diameter of about 100,000 light years. It is sometimes divided into two components: the thin disk which is about 1000 light years thick and the thick disk about 5000 light years thick. Whether the thick disk is a separate component of the galaxy or an extension of the thin disk is a matter of debate amongst astronomers. The thin disk has four spiral arms where the rate of star formation is relatively high. The disk is surrounded by a large galactic halo.

Although the Milky Way is well studied its precise structure is still a matter of some debate, particularly near the core where the large density of stars and extinction due to interstellar material makes study difficult.

Many other galaxies, including spiral and lenticular galaxies, have their own galactic disks.

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