Tuesday, January 31, 2012

Barnard 68 Bok globule

Barnard 68. Dark absorption nebula 
Molecular cloud in the constellation of Ophiuchus
APOD 29.1. 2012

Barnard 68 molecular cloud is only 500 light-years away and therefore the hydrogen in it is dense enough to block all visible spectrum starlight coming from behind it. It looks like a black hole. The name is from the catalogue of 350 dark clouds created by the American astronomer Edward Emerson Barnard (1857–1923). The cloud has the estimated mass of two suns and is about half light-year across.

Bok globule
Barnard 68 is a small molecular cloud and thus a very small Bok globule.

Bok globules are dark clouds of dense cosmic dust and gas in which star formation sometimes takes place. Bok globules are found within H II regions, and typically have a mass of about 2 to 50 solar masses contained within a region about a light year or so across (about 4.5 × 1047 m³, see Orders of magnitude (volume)). They contain molecular hydrogen (H2), carbon oxides and helium, and around 1% (by mass) of silicate dust. Bok globules most commonly result in the formation of double or multiple star systems.

 See APOD 12.6.2012 for a fascinating color image of Thackeray's globules IC 2944 taken by the 4-m Victor Blanco telescope at Cerro Tololo Inter-American ObservatoryChile.

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