Quelltext der Seite Barnard 68

{{Infobox Astronomisches Objekt
|            Typ = Dunkelnebel<ref name=SIMBAD />, [[Molekülwolke]]<ref name=SIMBAD />
|           Name = Barnard 68
|           Bild = [[Datei:Barnard 68.jpg|300px]]
|       Bildtext = Aufnahme des [[Very Large Telescope]]
|      Sternbild = Oph
|            Rek = 17/22/38.2
|            Dek = -/23/49/34
|           Size = 3
|        Caption = Barnard 68
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|           magB = 
|         Winkel = 
|     Entfernung = 500 Lj
|      Paraname1 = Zugehörigkeit
|      Paradata1 = [[Milchstraße]]
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|          Masse = 
|    Durchmesser = 0,5
|      Entdecker = 
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|       Weiteres = 
|        Katalog = Barnard&nbsp;68&nbsp;• LDN&nbsp;57
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|      RekDekRef = <ref name=SIMBAD>{{cite web|url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=barnard+68&submit=SIMBAD+search|title=SIMBAD Astronomical Database (Barnard 68)|publisher=Centre de Données astronomiques de Strasbourg|accessdate=2009-03-01}}</ref>
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|  EntfernungRef = <ref name=APOD />
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'''Barnard 68''' ist eine [[Dunkelwolke]] beziehungsweise [[Bok-Globule]]. Sie liegt in dem südlichen Sternbild [[Schlangenträger]] und ist etwa 500 [[Lichtjahr]]e entfernt. Das Innere der Wolke ist sehr kalt, die Temperatur liegt bei rund 16&nbsp;K (−257&nbsp;°C). Die Gesamtmasse entspricht etwa der doppelten Sonnenmasse, wobei die Wolke eine Ausdehnung von einem halben Lichtjahr hat.<ref name="APOD">{{APOD|en|990511|Molecular Cloud Barnard 68}}</ref>

Die Katalogbezeichnung der Dunkelwolke geht darauf zurück, dass der Astronom [[Edward Emerson Barnard]] sie 1919 in seinem 1927 publizierten und 350 Objekte umfassenden Katalog von Dunkelnebeln aufnahm.
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== Characteristics ==
{{For|more information about Dark Clouds|Dark cloud}}
Despite being opaque at visible-light wavelengths, use of the [[Very Large Telescope]] at [[Cerro Paranal]] has revealed the presence of about 3,700 blocked background Milky Way stars, some 1,000 of which are visible at infrared wavelengths.<ref>ESO, [http://www.eso.org/public/outreach/press-rel/pr-1999/phot-29b-99-normal.jpg The Dark Cloud B68 at Different Wavelengths]</ref> Careful measurements of the degree of obscuration resulted in a finely sampled and accurate mapping of the dust distribution inside the cloud. Having a dark cloud in the solar neighbourhood greatly facilitates observation and measurement. If not disrupted by external forces, the stability of dust clouds is a fine balance between outward pressure caused by the [[Hydrostatic equilibrium|heat or pressure]] of the cloud's contents, and inward gravitational forces generated by the same particles (see [[Jeans instability]] and [[Bonnor-Ebert mass]]). This causes the cloud to wobble or oscillate in a manner not unlike that of a large soap bubble or a water-filled balloon which is jiggled. In order for the cloud to become a star, gravity must gain the upper hand long enough to cause the collapse of the cloud and reach a temperature and density where [[Nuclear fusion|fusion]] can be sustained. When this happens, the much smaller size of the star's envelope signals a new balance between greatly increased gravity and radiation pressure. <ref>arXiv, [http://arxiv.org/abs/astro-ph/0604056v1 Oscillations in the stable starless core Barnard 68]</ref> 

The cloud's mass is about twice that of the Sun, and it measures about half a light-year across. <ref name="APOD"/> Barnard 68's well-defined edges and other features show that it is on the verge of gravitational collapse within the next 100 000 years or so, and is on its way to becoming a star.
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== Weblinks ==
{{Commonscat|Barnard 68}}
* [http://kencroswell.com/theblackcloud.html The Black Cloud - Ken Croswell] (englisch)
* [http://www.aanda.org/articles/aa/pdf/2002/31/aa2297.pdf C18O abundance in the nearby globule Barnard 68] (englisch)
* [https://www.eso.org/public/news/eso0102/ ESO: How to Become a Star - ESO Telescopes Provide Most Detailed View Ever Into a Dark Cloud] (englisch, 10. Januar 2001)

== Einzelnachweise ==
<references />

[[Kategorie:Dunkelwolke]]