THE GOULD BELT

Infrared image of one region of the star-forming clouds that extend from Perseus
through the Taurus-Auriga complex to Orion. Image courtesy T. Preibisch

The Gould Belt is visible to observers on Earth as a ring of young stars and nebulae completely surrounding the Solar System. It was first described in the Nineteenth Century by the Englishman John Herschel (son of William Herschel, who discovered Uranus) and the American Benjamin Gould, after whom the structure is named. In 1874, Gould characterized this formation as a "great circle or zone of bright stars" that "seems to gird the sky, intersecting with the Milky Way at the Southern Cross" (quoted in Crosswell 2005).

More recent observations have established that the Gould Belt is a key structural feature of the Orion Arm, the region of the Milky Way Galaxy in which we live. It is an elliptical disk of hydrogen and other gases, inclined to the plane of the larger Galactic disk by an angle of about 17.2 degrees. Its long axis is about 750 parsecs, and its short axis is about 470 parsecs. Its age is estimated as 30 to 50 million years (all values from Perrot & Grenier 2003). In astronomical terms, therefore, the Gould Belt is a very young formation -- much more recent, for example, than the Jurassic Period (145-200 million years ago), when large dinosaurs roamed the Earth.

Schematic of the Gould Belt by Perrot & Grenier, 2003

Schematic view of the Gould Belt by Christophe Perrot and Isabelle Grenier, A&A 2003 404: 519-531.

This diagram represents the Gould Belt in a flattened perspective, as viewed from above the plane of the Milky Way's disk. The triangle and the six-pointed star mark the Belt center and the position of our Solar System, respectively; "GC" marks the direction of the Galactic Center. The open circles represent nearby associations of bright O and B stars. The shaded circles represent clouds of molecular hydrogen. The thicker ellipse traces the current rim of the Belt, while the arrows indicate the direction of the rim's expansion. The thinner ellipse traces a 1982 estimate of the location of the Belt's rim.

Schematic of the Local Bubble by Lallement and colleagues, 2003

Edge-on view of the Local Bubble, also known as the Local Chimney because of its elongated shape. In relation to the axis of the Milky Way's rotation, the local distribution of interstellar gas has the same inclination as the Gould Belt. It seems likely that the Local Bubble is a transitory structure created by supernovae born in the expanding starburst clouds of the Gould Belt. The Galactic Center is to the right; Galactic North is up. R. Lallement et al., A&A 2003 411: 447-464.

Gould Belt Gallery