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In astronomy, a contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes. A binary system whose stars share an envelope may also be called an overcontact binary.〔(contact binary ), David Darling, ''The Internet Encyclopedia of Science''. Accessed on line November 4, 2007.〕〔(overcontact binary ), David Darling, ''The Internet Encyclopedia of Science''. Accessed on line November 4, 2007.〕〔pp. 51–53, ''An Introduction to Astrophysical Fluid Dynamics'', Michael J. Thompson, London: Imperial College Press, 2006. ISBN 1-86094-615-1.〕 Almost all known contact binary systems are eclipsing binaries;〔p. 231, ''Stellar Rotation'', Jean Louis Tassoul, Andrew King, Douglas Lin, Stephen P. Maran, Jim Pringle, and Martin Ward, Cambridge, UK, New York: Cambridge University Press, 2000. ISBN 0-521-77218-4.〕 eclipsing contact binaries are known as W Ursae Majoris variables, after their type star, W Ursae Majoris.〔p. 19, ''Double and Multiple Stars and how to Observe Them'', James Mullaney, New York, London: Springer, 2005. ISBN 1-85233-751-6.〕 Contact binaries are sometimes confused with common envelopes. However, whereas the configuration of two touching stars in a contact binary has a typical lifetime of millions to billions of years, the common envelope is a dynamically unstable phase in binary evolution that either expels the stellar envelope or merges the binary in a timescale of months to years.〔 〕 ==See also== *Contact binary (small Solar System body), two asteroids gravitating toward each other until they touch *Thorne–Żytkow object, a type of star wherein a red giant or supergiant contains a neutron star at its core *VFTS 352 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「contact binary」の詳細全文を読む スポンサード リンク
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