An ultra-cool dwarf is a stellar or sub-stellar object that has an effective temperature lower than 2,700 K (2,430 °C; 4,400 °F).[1] This category of dwarf stars was introduced in 1997 by J. Davy Kirkpatrick, Todd J. Henry, and Michael J. Irwin. It originally included very low mass M-dwarf stars with spectral types of M7 but was later expanded to encompass stars ranging from the coldest known to brown dwarfs as cool as spectral type T6.5. Altogether, ultra-cool dwarfs represent about 15% of the astronomical objects in the stellar neighborhood of the Sun.[2] One of the best known examples is TRAPPIST-1.[3]
Size comparison of the Sun (at left) and TRAPPIST-1 (an ultra-cool dwarf)
Models of the formation of planets suggest that due to their low masses and the small size of their proto-planetary disks, these stars could host a relatively abundant population of terrestrial planets ranging from Mercury-sized to Earth-sized bodies, rather than a population of super-Earths and Jupiter-massed planets. The discovery of the TRAPPIST-1 planetary system, consisting of seven Earth-sized planets, would appear to validate this accretion model.[4]
Due to their slow hydrogen fusion, when compared to other types of low-mass stars the life spans of ultra-cool dwarfs are estimated to be at least several hundred billion years, with the smallest among them living for about 12 trillion years. As the age of the universe is only 13.8 billion years, all ultra-cool dwarf stars are therefore in the early portions of their life-cycles. Models predict that at the ends of their lives the smallest of these stars will become blue dwarfs rather than expanding into red giants.[5]
Magnetic propertiesedit
After the detection of bursts of radio emission from the M9 ultracool dwarf LP 944-20 in 2001, a number of astrophysicists began observation campaigns at the Arecibo Observatory and the Very Large Array to search for additional objects emitting radio waves. To date hundreds of ultra-cool dwarfs have been observed with these radio telescopes and of these stars, more than a dozen radio-emitting ultra-cool dwarfs have been identified.[6] These surveys indicate that approximately 5-10% of ultracool dwarfs emit radio waves. These observation campaigns identified the noteworthy 2MASS J10475385+2124234, which has a temperature of 800-900 K making it the coolest known radio-emitting brown dwarf. 2MASS J10475385+2124234 is a T6.5 brown dwarf that retains a magnetic field with a strength greater than 1.7 kG, making it some 3000 times more intense than Earth's magnetic field.[7]
Referencesedit
^Gillon, Michaël; Jehin, Emmanuël; Lederer, Susan M; Delrez, Laetitia; De Wit, Julien; Burdanov, Artem; Van Grootel, Valérie; Burgasser, Adam J; Triaud, Amaury H. M. J; Opitom, Cyrielle; Demory, Brice-Olivier; Sahu, Devendra K; Bardalez Gagliuffi, Daniella; Magain, Pierre; Queloz, Didier (2016). "Temperate Earth-sized planets transiting a nearby ultracool dwarf star". Nature. 533 (7602): 221–4. arXiv:1605.07211. Bibcode:2016Natur.533..221G. doi:10.1038/nature17448. PMC5321506. PMID 27135924.
^Cantrell, Justin R.; Henry, Todd J.; White, Russel J. (13 September 2013). "The Solar Neighborhood Xxix: The Habitable Real Estate of Our Nearest Stellar Neighbors". The Astronomical Journal. 146 (4): 99. arXiv:1307.7038. Bibcode:2013AJ....146...99C. doi:10.1088/0004-6256/146/4/99. S2CID 44208180.
^Gillon, Michaël (May 5, 2017). "Ultra-Cool Dwarf Stars May Host Planets With Ultra-Cool Life". Vice.com. Retrieved 27 April 2020.
^"NASA Telescope Reveals Largest Batch of Earth-Size, Habitable-Zone Planets Around Single Star". NASA. Retrieved 2017-11-19.
^Adams, F. C.; P. Bodenheimer; G. Laughlin (2005). "M dwarfs: planet formation and long term evolution". Astronomische Nachrichten. 326 (10): 913–919. Bibcode:2005AN....326..913A. doi:10.1002/asna.200510440.
^Route, M.; Wolszczan, A. (20 October 2016). "The Second Arecibo Search for 5 GHz Radio Flares from Ultracool Dwarfs". The Astrophysical Journal. 830 (2): 85. arXiv:1608.02480. Bibcode:2016ApJ...830...85R. doi:10.3847/0004-637X/830/2/85. S2CID 119279978.
^Route, M.; Wolszczan, A. (10 March 2012). "The Arecibo Detection of the Coolest Radio-flaring Brown Dwarf". The Astrophysical Journal Letters. 747 (2): L22. arXiv:1202.1287. Bibcode:2012ApJ...747L..22R. doi:10.1088/2041-8205/747/2/L22. S2CID 119290950.
External linksedit
UltracoolSheet: Catalog containing over 3,000 ultracool dwarfs and directly imaged exoplanets
Database of Ultracool Parallaxes: Predecessor of the UltracoolSheet
January 01, 1970
ultra, cool, dwarf, ultra, cool, dwarf, stellar, stellar, object, that, effective, temperature, lower, than, this, category, dwarf, stars, introduced, 1997, davy, kirkpatrick, todd, henry, michael, irwin, originally, included, very, mass, dwarf, stars, with, s. An ultra cool dwarf is a stellar or sub stellar object that has an effective temperature lower than 2 700 K 2 430 C 4 400 F 1 This category of dwarf stars was introduced in 1997 by J Davy Kirkpatrick Todd J Henry and Michael J Irwin It originally included very low mass M dwarf stars with spectral types of M7 but was later expanded to encompass stars ranging from the coldest known to brown dwarfs as cool as spectral type T6 5 Altogether ultra cool dwarfs represent about 15 of the astronomical objects in the stellar neighborhood of the Sun 2 One of the best known examples is TRAPPIST 1 3 Size comparison of the Sun at left and TRAPPIST 1 an ultra cool dwarf Models of the formation of planets suggest that due to their low masses and the small size of their proto planetary disks these stars could host a relatively abundant population of terrestrial planets ranging from Mercury sized to Earth sized bodies rather than a population of super Earths and Jupiter massed planets The discovery of the TRAPPIST 1 planetary system consisting of seven Earth sized planets would appear to validate this accretion model 4 Due to their slow hydrogen fusion when compared to other types of low mass stars the life spans of ultra cool dwarfs are estimated to be at least several hundred billion years with the smallest among them living for about 12 trillion years As the age of the universe is only 13 8 billion years all ultra cool dwarf stars are therefore in the early portions of their life cycles Models predict that at the ends of their lives the smallest of these stars will become blue dwarfs rather than expanding into red giants 5 Magnetic properties editAfter the detection of bursts of radio emission from the M9 ultracool dwarf LP 944 20 in 2001 a number of astrophysicists began observation campaigns at the Arecibo Observatory and the Very Large Array to search for additional objects emitting radio waves To date hundreds of ultra cool dwarfs have been observed with these radio telescopes and of these stars more than a dozen radio emitting ultra cool dwarfs have been identified 6 These surveys indicate that approximately 5 10 of ultracool dwarfs emit radio waves These observation campaigns identified the noteworthy 2MASS J10475385 2124234 which has a temperature of 800 900 K making it the coolest known radio emitting brown dwarf 2MASS J10475385 2124234 is a T6 5 brown dwarf that retains a magnetic field with a strength greater than 1 7 kG making it some 3000 times more intense than Earth s magnetic field 7 References edit Gillon Michael Jehin Emmanuel Lederer Susan M Delrez Laetitia De Wit Julien Burdanov Artem Van Grootel Valerie Burgasser Adam J Triaud Amaury H M J Opitom Cyrielle Demory Brice Olivier Sahu Devendra K Bardalez Gagliuffi Daniella Magain Pierre Queloz Didier 2016 Temperate Earth sized planets transiting a nearby ultracool dwarf star Nature 533 7602 221 4 arXiv 1605 07211 Bibcode 2016Natur 533 221G doi 10 1038 nature17448 PMC 5321506 PMID 27135924 Cantrell Justin R Henry Todd J White Russel J 13 September 2013 The Solar Neighborhood Xxix The Habitable Real Estate of Our Nearest Stellar Neighbors The Astronomical Journal 146 4 99 arXiv 1307 7038 Bibcode 2013AJ 146 99C doi 10 1088 0004 6256 146 4 99 S2CID 44208180 Gillon Michael May 5 2017 Ultra Cool Dwarf Stars May Host Planets With Ultra Cool Life Vice com Retrieved 27 April 2020 NASA Telescope Reveals Largest Batch of Earth Size Habitable Zone Planets Around Single Star NASA Retrieved 2017 11 19 Adams F C P Bodenheimer G Laughlin 2005 M dwarfs planet formation and long term evolution Astronomische Nachrichten 326 10 913 919 Bibcode 2005AN 326 913A doi 10 1002 asna 200510440 Route M Wolszczan A 20 October 2016 The Second Arecibo Search for 5 GHz Radio Flares from Ultracool Dwarfs The Astrophysical Journal 830 2 85 arXiv 1608 02480 Bibcode 2016ApJ 830 85R doi 10 3847 0004 637X 830 2 85 S2CID 119279978 Route M Wolszczan A 10 March 2012 The Arecibo Detection of the Coolest Radio flaring Brown Dwarf The Astrophysical Journal Letters 747 2 L22 arXiv 1202 1287 Bibcode 2012ApJ 747L 22R doi 10 1088 2041 8205 747 2 L22 S2CID 119290950 External links editUltracoolSheet Catalog containing over 3 000 ultracool dwarfs and directly imaged exoplanets Database of Ultracool Parallaxes Predecessor of the UltracoolSheet Retrieved from https en wikipedia org w index php title Ultra cool dwarf amp oldid 1188180382, wikipedia, wiki, book, books, library,
