Gould Belt
The Gouldsche belt is a large-scale array of young stars, star forming regions, and HI, HII and dark clouds. The structure with more than 2,000 light- years extension, for which in German publications mostly the English name Gould Belt or Gould 's Belt is used, was named after U.S. astronomer Benjamin Gould. The sun is located within the belt (but is not among them ), so that the belt next to the Milky Way has the largest extent of a deep-sky object in the sky.
Geometry
The Gouldsche belt has an approximately elliptical shape with semiaxes of 354 ± 5 and 232 ± 5 pc ( 1154 and 756 Lj ), a height of 60 pc ( 200 light years ) and an inclination of about 18 to 21 ° to the plane of the Milky Way (values differ for different methods of determination ). The center of the belt is located in the Perseus OB3 group, a member of Cassiopeia - Taurus association. The position of the sun lies within the belt about midway between Per OB3 and the Sco OB2, a part of the Scorpius - Centaurus association.
The belt expands and rotates around its center, so that its eccentricity increased by the differential galactic rotation, ie the semi-major axis is growing faster than the small half-axis.
Formation and development
For the age of the structure dynamic considerations provide a value of 20 to 30 million years ago, during the age provisions of the stars provide an age of about 60 million years ago. The creative process is not yet understood, it will be discussed several scenarios. Various scenarios assume that the passage of a cloud at high speed through the galactic plane has triggered a first phase of star formation, the belt was a series of supernovae then formed. The best candidate for this first star-forming region is about 35 million years old Perseus OB3 group. Other models are based inter alia on the expansion of a super-bubble, which is considered in addition to the Gould Belt as the precursor for the Pleiades group and the Local arm.
History
John Herschel in 1847 for the first time pointed out that many bright stars (especially the stars of the Scorpius - Centaurus association ) are not aligned in the night sky along the galactic plane, but on a slightly inclined line. 1874 examined Benjamin Gould, after this structure is named today, this distribution closer and certain first time the inclination of the belt over the galactic plane. In the 1960s, Per Olof Lindblad noted that the outside of the belt is surrounded by an expanding HI ring in the 1980s, many dark clouds of this structure have been assigned. 1974 for the first time, the spatial extent of the structure was determined.
Known members
A number of known, easily observable star is a member of the Gould Belt, for example:
- Antares, brightest star of the constellation Scorpio
- Shaula ( Lambda Scorpii ), the second brightest star in the Scorpio