Barnard 68 is a molecular cloud, dark absorption nebula or Bok globule, towards the southern constellation Ophiuchus and well within the Milky Way galaxy at a distance of about 500 light-years, so close that not a single star can be seen between it and the Sun. American astronomer Edward Emerson Barnard added this nebula to his catalog of dark nebulae in 1919. His catalog was published in 1927, at which stage it included some 350 objects. Because of its opacity, its interior is extremely cold, its temperature being about 16 K (−257 °C/-431 °F). Its mass is about twice that of the Sun and it measures about half a light-year across.[2]
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.[3] Careful measurements of the degree of obscuration resulted in a finely sampled and accurate mapping of the dust distribution inside the cloud.[4][5] Observations obtained with Herschel Space Observatory were able to constrain the distribution of the dust component and its temperature even more.[6] 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 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 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.[7]
The cloud's mass is about twice that of the Sun, and it measures about half a light-year across.[2] 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.[8]
The cloud is often confused with Boötes Void although the two have nothing in common, and pictures of Barnard 68 are often erroneously used to illustrate articles about Boötes void.[citation needed]
^ Alves, João; Lada, Charles; Lada, Elizabeth (March 2001). "Seeing the light through the dark" (PDF). The Messenger. 103: 15–20. Bibcode:2001Msngr.103....1A.
^ Alves, João F.; Lada, Charles J.; Lada, Elizabeth A. (January 2001). "Internal structure of a cold dark molecular cloud inferred from the extinction of background starlight". Nature. 409 (6817): 159–161. Bibcode:2001Natur.409..159A. doi:10.1038/35051509. PMID 11196632.
^ Nielbock, Markus; Launhardt, Ralf; Steinacker, Jürgen; et al. (August 2012). "The Earliest Phases of Star formation observed with Herschel (EPoS): The dust temperature and density distributions of B68". Astronomy and Astrophysics. 547: A11. arXiv:1208.4512. Bibcode:2012A&A...547A..11N. doi:10.1051/0004-6361/201219139.
^ Redman, Matt P.; Keto, Eric; Rawlings, J. M. C. (July 2006). "Oscillations in the stable starless core Barnard". Monthly Notices of the Royal Astronomical Society. 370 (1): L1–L5. arXiv:astro-ph/0604056. Bibcode:2006MNRAS.370L...1R. doi:10.1111/j.1745-3933.2006.00172.x.
^Burkert, Andreas; Alves, João (2009). "THE INEVITABLE FUTURE OF THE STARLESS CORE BARNARD 68". The Astrophysical Journal. 695 (2): 1308–1314. arXiv:0809.1457. Bibcode:2009ApJ...695.1308B. doi:10.1088/0004-637X/695/2/1308. ISSN 0004-637X.
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barnard, molecular, cloud, dark, absorption, nebula, globule, towards, southern, constellation, ophiuchus, well, within, milky, galaxy, distance, about, light, years, close, that, single, star, seen, between, american, astronomer, edward, emerson, barnard, add. Barnard 68 is a molecular cloud dark absorption nebula or Bok globule towards the southern constellation Ophiuchus and well within the Milky Way galaxy at a distance of about 500 light years so close that not a single star can be seen between it and the Sun American astronomer Edward Emerson Barnard added this nebula to his catalog of dark nebulae in 1919 His catalog was published in 1927 at which stage it included some 350 objects Because of its opacity its interior is extremely cold its temperature being about 16 K 257 C 431 F Its mass is about twice that of the Sun and it measures about half a light year across 2 Barnard 68Molecular cloudBok globuledark nebulaObservation data J2000 0 1 epochRight ascension17h 22m 38 2s 1 Declination 23 49 34 1 Distance500 2 lyConstellationOphiuchus 2 Physical characteristicsRadius0 25 2 lyDesignationsBarnard 68 LDN 57See also Lists of nebulae Contents 1 Characteristics 2 See also 3 References 4 External linksCharacteristics EditDespite 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 3 Careful measurements of the degree of obscuration resulted in a finely sampled and accurate mapping of the dust distribution inside the cloud 4 5 Observations obtained with Herschel Space Observatory were able to constrain the distribution of the dust component and its temperature even more 6 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 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 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 7 The cloud s mass is about twice that of the Sun and it measures about half a light year across 2 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 8 The cloud is often confused with Bootes Void although the two have nothing in common and pictures of Barnard 68 are often erroneously used to illustrate articles about Bootes void citation needed See also EditFormation and evolution of the Solar SystemReferences Edit a b c LDN 57 SIMBAD Centre de donnees astronomiques de Strasbourg Retrieved 2009 03 01 a b c d e Astronomy Picture of the Day 11 May 1999 Barnard 68 NASA 1999 05 11 Archived from the original on 11 April 2009 Retrieved 2009 03 01 The Dark Cloud B68 at Different Wavelengths European Southern Observatory Retrieved January 30 2012 Alves Joao Lada Charles Lada Elizabeth March 2001 Seeing the light through the dark PDF The Messenger 103 15 20 Bibcode 2001Msngr 103 1A Alves Joao F Lada Charles J Lada Elizabeth A January 2001 Internal structure of a cold dark molecular cloud inferred from the extinction of background starlight Nature 409 6817 159 161 Bibcode 2001Natur 409 159A doi 10 1038 35051509 PMID 11196632 Nielbock Markus Launhardt Ralf Steinacker Jurgen et al August 2012 The Earliest Phases of Star formation observed with Herschel EPoS The dust temperature and density distributions of B68 Astronomy and Astrophysics 547 A11 arXiv 1208 4512 Bibcode 2012A amp A 547A 11N doi 10 1051 0004 6361 201219139 Redman Matt P Keto Eric Rawlings J M C July 2006 Oscillations in the stable starless core Barnard Monthly Notices of the Royal Astronomical Society 370 1 L1 L5 arXiv astro ph 0604056 Bibcode 2006MNRAS 370L 1R doi 10 1111 j 1745 3933 2006 00172 x Burkert Andreas Alves Joao 2009 THE INEVITABLE FUTURE OF THE STARLESS CORE BARNARD 68 The Astrophysical Journal 695 2 1308 1314 arXiv 0809 1457 Bibcode 2009ApJ 695 1308B doi 10 1088 0004 637X 695 2 1308 ISSN 0004 637X External links Edit Wikimedia Commons has media related to Barnard 68 The Black Cloud Ken Croswell C18O abundance in the nearby globule Barnard 68 ESO 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 Astrophile Lucky strike turns a dark cloud into a star 6 September 2012Portals Astronomy Stars Spaceflight Outer space Solar System Retrieved from https en wikipedia org w index php title Barnard 68 amp oldid 1129731758, wikipedia, wiki, book, books, library,
