Gouldian belt

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The Gouldian Belt is a large-scale arrangement of young stars , star formation regions as well as HI , HII and dark clouds . The structure with an extension of more than 2000 light years , for which the English name Gould Belt or Gould's Belt is mostly used in German-language publications , was named after the American astronomer Benjamin Gould . The sun is located within the belt (but is not one of them), so that the belt next to the Milky Way has the largest extent of any deep sky object in the sky.

geometry

The Gouldian belt has an approximately elliptical shape with semi-axes of 354 ± 5 ​​and 232 ± 5 pc (1154 and 756 ly), a height of 60 pc (about 200 ly) and an inclination of about 18 to 21 ° to the plane of the Milky Way (The information differs for different determination methods). The center of the belt lies in the Perseus OB3 group , a member of the Cassiopeia-Taurus Association . The position of the sun lies within the belt roughly in the middle between Per OB3 and the Sco OB2 , part of the Scorpius-Centaurus Association .

The belt expands and rotates around its center so that its eccentricity increases due to the differential galactic rotation, i.e. H. the semi-major axis grows faster than the semi-minor axis.

Origin and development

For the age of the structure, dynamic observations give a value of 20 to 30 million years, while age determinations of the stars give an age of about 60 million years. The development process is not yet understood; several scenarios are discussed. Various scenarios assume that the passage of a cloud through the Milky Way plane at high speed triggered the first phase of star formation. A series of supernovae then formed the belt. The best candidate for this first star formation region is the approximately 35 million year old Perseus OB3 group. Other models are based, among other things, on the expansion of a super-bubble, which, in addition to the Gouldian belt, is also viewed as a forerunner for the Pleiaden Group and the Local Arm.

history

John Herschel first pointed out in 1847 that many bright stars (especially the stars of the Scorpius-Centaurus Association ) in the night sky are not aligned along the plane of the Milky Way, but on a slightly inclined line. In 1874 Benjamin Gould , after whom this structure is named today, examined this distribution more closely and determined for the first time the inclination of the belt in relation to the plane of the Milky Way. In the 1960s, Per Olof Lindblad discovered that the outside of the belt was surrounded by an expanding HI ring . The spatial extent of the structure was determined for the first time in 1974. In the 1980s, many dark clouds were also assigned to this structure.

Known members

A number of well-known, easily observable stars are members of the Gouldian Belt, for example:

  • Antares , brightest star in the constellation Scorpio
  • Shaula (Lambda Scorpii), Scorpio's second brightest star

literature

  • Grenier, Isabelle: The Gould Belt, star formation, and the local interstellar medium, Proc. of the 39th Rencontres de Moriond , 2004, The Young Local Universe ( pdf )

Web links