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. Almost all known contact binary systems are eclipsing binaries; eclipsing contact binaries are known as W Ursae Majoris variables, after their type star, W Ursae Majoris.
Contact binaries are sometimes confused with common envelopes. However, whereas the first refers to a stable configuration of two touching stars in a binary with a typical lifetime of millions to billions of years, the latter describes a dynamically unstable phase in binary evolution which either expels the stellar envelope or merges the binary in a timescale of months to years.
- Contact binary (asteroid), 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
- 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.
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- 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.
- p. 19, Double and Multiple Stars and how to Observe Them, James Mullaney, New York, London: Springer, 2005. ISBN 1-85233-751-6.
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