Barnard 68

Despite being opaque at visible-light wavelengths, use of the Very Large Telescope at Cerro Paranal has revealed the presence of about 3,700 obscured background Milky Way stars, some 1,000 of which are only visible at infrared wavelengths.{{cite web |url=http://www.eso.org/public/images/eso9934b/ |title= The Dark Cloud B68 at Different Wavelengths |publisher= European Southern Observatory|accessdate= January 30, 2012}} Careful measurements of the degree of obscuration resulted in a finely sampled and accurate mapping of the dust distribution inside the cloud.

{{cite journal

|title=Seeing the light through the dark

|last1=Alves|first1=João

|last2=Lada|first2=Charles

|last3=Lada|first3=Elizabeth

|journal=The Messenger

|date=March 2001

|volume=103

|pages=15–20

|bibcode=2001Msngr.103....1A

|url=http://www.eso.org/sci/publications/messenger/archive/no.103-mar01/messenger-no103-1-1.pdf

}}

{{cite journal

|title=Internal structure of a cold dark molecular cloud inferred from the extinction of background starlight

|last1=Alves|first1=João F.

|last2=Lada|first2=Charles J.

|last3=Lada|first3=Elizabeth A.

|journal=Nature

|date=January 2001

|volume=409

|issue=6817

|pages=159–161

|bibcode=2001Natur.409..159A

|doi=10.1038/35051509

|pmid=11196632

|s2cid=4318459 }} Observations obtained with the Herschel Space Observatory were able to constrain the distribution of the dust component and its temperature even more.

{{cite journal

|author1=Nielbock, Markus |author2=Launhardt, Ralf |author3=Steinacker, Jürgen |title= The Earliest Phases of Star formation observed with Herschel (EPoS): The dust temperature and density distributions of B68

|journal=Astronomy and Astrophysics

|date=August 2012

|arxiv = 1208.4512

|doi=10.1051/0004-6361/201219139

|bibcode = 2012A&A...547A..11N |display-authors=etal

|volume=547

|pages=A11|s2cid=40817221 }} Having a dark cloud in the solar neighborhood 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 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 like 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 cloud to collapse and reach a temperature and density where 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.

{{cite journal

|last1= Redman|first1=Matt P.

|last2= Keto|first2=Eric

|last3= Rawlings|first3=J. M. C.

|title= Oscillations in the stable starless core Barnard

|journal=Monthly Notices of the Royal Astronomical Society

|date=July 2006

|volume=370

|issue=1

|pages=L1–L5

|bibcode=2006MNRAS.370L...1R

|arxiv = astro-ph/0604056

|doi=10.1111/j.1745-3933.2006.00172.x

|doi-access=free

|s2cid=7654075

}}

The cloud's mass is about twice that of the Sun, and it measures about half a light-year across. Barnard 68's well-defined edges and other features show that it is on the verge of gravitational collapse, followed by becoming a star within the next 200,000 years or so.{{cite journal|last1=Burkert|first1=Andreas|last2=Alves|first2=João|title=The Inevitable Future of the Starless Core Barnard 68 |journal=The Astrophysical Journal|volume=695|issue=2|year=2009|pages=1308–1314|issn=0004-637X|doi=10.1088/0004-637X/695/2/1308|arxiv = 0809.1457 |bibcode = 2009ApJ...695.1308B |s2cid=18851013 }}

The cloud is often confused with the Boötes Void, although the two have nothing in common. Pictures of Barnard 68 are often erroneously used to illustrate articles about the Boötes Void.{{cite news|last=Felton|first=James|date=1 August 2022|title=A Giant Hole In The Universe: Just What Is The Boötes Void?|url=https://www.iflscience.com/a-giant-hole-in-the-universe-just-what-is-the-botes-void-64689|work=IFLScience|access-date=11 September 2023|quote=...Barnard 68, which – if the Internet is to be believed (which it's not) – is 'an empty void in space so big that if you traveled across it you wouldn’t bump into anything for 752,536,988 years'.}}

• Formation and evolution of the Solar System
• Dark Horse Nebula

{{Reflist}}

{{Commons category|Barnard 68}}

• [http://kencroswell.com/theblackcloud.html The Black Cloud] - Ken Croswell
• [http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/full/2002/31/aa2297/aa2297.right.html C18O abundance in the nearby globule Barnard 68]
• ESO, [http://eso.org/public/news/eso0102/ How to Become a Star - ESO Telescopes Provide Most Detailed View Ever Into a Dark Cloud], 10 January 2001 (accessed 1 March 2009)
• New Scientist, [https://www.newscientist.com/article/dn22248-astrophile-lucky-strike-turns-a-dark-cloud-into-a-star.html Astrophile: Lucky strike turns a dark cloud into a star], 6 September 2012

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Category:Dark nebulae

Category:Ophiuchus