Orion Spur

Orion spur

The So System is located within the Orion spur. Although not a spiral arm, the Orion spur is nevertheless a major Milky Way structure that crosses the Perseus arm, linking the Sagittarius and Outer arms.

Such spurs connecting two or more spiral arms are a common feature of spiral galaxies.

The Orion spur is sometimes confusingly called the Orion arm or the Local arm.

The Orion spur is a branch off from the Sagittarius arm at or near the intense radio source W51, which is a large complex of star formation regions and supernova remnants.

It continues through the Cygnus X complex of star formation regions, which includes Cyg OB2, one of the most luminous OB associations known in the local group of galaxies. It passes through the Rift dust clouds and into an expanding ring of bright star formation regions called the Gould belt. The Gould belt includes the Orion molecular cloud and the Sol System (which is much older than the Gould belt and is just passing through).

The Gum nebula supernova remnant dominates the Orion spur just past the Gould belt. Beyond the Gum nebula, the spur forks. The main branch transits the Perseus arm in the direction of the constellation Canis Major and terminates in or near the Outer arm. A smaller branch forms the complex of molecular clouds and star formation regions called the Vela Molecular Ridge.

The Perseus transit at the other end of the Orion spur is described in a major 2008 survey paper on the structure of the Milky Way in the third quadrant.