SPIRAL   STRUCTURE   OF   THE   MILKY   WAY   GALAXY

Conjectural view of the spiral structure of the Milky Way Galaxy - Click to visit the Orion Arm

Artist R. Hurt's conception of the structure of the Milky Way Galaxy
Image courtesy NASA/JPL-Caltech/R. Hurt; labels added

This schematic view represents our Galaxy as a barred spiral with two major arms and several minor, irregular arms and spurs. In reality, the Milky Way may be still more asymmetrical, given its history of violent interactions with satellite galaxies. For potential lookalikes, see Milky Way Twins.

The red circle marks the location of the Solar System, approximately 8.5 kiloparsecs (28,000 light years) from the Galactic Center. Although our system is often described as orbiting on the outskirts of the Milky Way, it is actually located midway between the core and the edge, along a spur of the minor Sagittarius Arm. Our local region of the galaxy is typically known as the Orion Arm.

Spiral arms are standing waves rather than permanent structures. All stars and nebulae in the Galaxy orbit the Galactic Center, but they travel at varying speeds with varying degrees of eccentricity and inclination. The spiral arms are simply the areas where gas and dust accumulate, encouraging the formation of new stars.

This conception of Galactic structure is based on recent studies by Robert Benjamin and colleagues, using the Spitzer Space Telescope. See NASA's news release; see also these publications:

Benjamin RA, Churchwell E, Babler BL, et al. (2005) First GLIMPSE results on the stellar structure of the Galaxy. Astrophysical Journal, 630: L149-L152.

Benjamin RA. (2008) The Spiral Structure of the Galaxy: Something Old, Something New... In Beuther, Linz, Henning, eds. Massive Star Formation: Observations Confront Theory. ASP Conference Series, Vol. 387, 375-380.




All text is copyright Raymond Harris 2006-2008. Image credits appear in the accompanying caption.