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<p><b>Neue Seite</b></p><div>{{Infobox Astronomisches Objekt<br />
| Typ = Dunkelnebel<ref name=SIMBAD />, [[Molekülwolke]]<ref name=SIMBAD /><br />
| Name = Barnard 68<br />
| Bild = [[Datei:Barnard 68.jpg|300px]]<br />
| Bildtext = Aufnahme des [[Very Large Telescope]]<br />
| Sternbild = Oph<br />
| Rek = 17/22/38.2<br />
| Dek = −/23/49/34<br />
| Size = 3<br />
| Caption = Barnard 68<br />
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| Entfernung = 500 Lj<br />
| Paraname1 = Zugehörigkeit<br />
| Paradata1 = [[Milchstraße]]<br />
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| Durchmesser = 0,5<br />
| Entdecker = <br />
| Entd-Datum = <br />
| Weiteres = <br />
| Katalog = Barnard&nbsp;68&nbsp;• LDN&nbsp;57<br />
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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|language=en}}</ref><br />
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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 9&nbsp;[[Kelvin]] (−264&nbsp;[[Grad Celsius|°C]]).<ref>{{Literatur |Autor=M. Nielbock, R. Launhardt, J. Steinacker, A. M. Stutz, Z. Balog |Titel=The Earliest Phases of Star formation (EPoS) observed with Herschel : the dust temperature and density distributions of B68 |Sammelwerk=Astronomy & Astrophysics |Band=547 |Datum=2012-11 |ISSN=0004-6361 |DOI=10.1051/0004-6361/201219139 |Seiten=A11 |Online=https://www.aanda.org/10.1051/0004-6361/201219139 |Abruf=2019-08-23}}</ref><ref>{{Literatur |Autor=A. Roy, Ph. André, P. Palmeirim, M. Attard, V. Könyves |Titel=Reconstructing the density and temperature structure of prestellar cores from Herschel data: A case study for B68 and L1689B |Hrsg= |Sammelwerk=Astronomy & Astrophysics |Band=562 |Nummer= |Auflage= |Verlag= |Ort= |Datum=2014 |ISBN= |ISSN=0004-6361 |DOI=10.1051/0004-6361/201322236 |Seiten=A138 |Online=https://www.aanda.org/10.1051/0004-6361/201322236 |Abruf=2019-08-23}}</ref> Die Gesamtmasse entspricht etwa der doppelten Sonnenmasse, wobei die Wolke eine Ausdehnung von einem halben Lichtjahr hat.<ref name="APOD">{{Astronomy Picture of the Day|en|990511|Molecular Cloud Barnard 68}}</ref><br />
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Die Katalogbezeichnung der Dunkelwolke geht darauf zurück, dass der Astronom [[Edward Emerson Barnard]] sie 1919 in seinen 1927 publizierten, 350 Objekte umfassenden Katalog von Dunkelnebeln aufnahm.<br />
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== Characteristics ==<br />
{{For|more information about Dark Clouds|Dark cloud}}<br />
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> <br />
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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.<br />
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== Weblinks ==<br />
{{Commonscat|Barnard 68}}<br />
* [http://kencroswell.com/theblackcloud.html The Black Cloud – Ken Croswell] (englisch)<br />
* [http://www.aanda.org/articles/aa/pdf/2002/31/aa2297.pdf C18O abundance in the nearby globule Barnard 68] (englisch)<br />
* [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)<br />
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== Einzelnachweise ==<br />
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[[Kategorie:Dunkelwolke]]</div>imported>SchlurcherBot