Contact binary
Encyclopedia
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 envelope
s. 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.
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, a contact binary is a binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
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
W Ursae Majoris
W Ursae Majoris is a variable star in the constellation Ursa Major. It is an eclipsing contact binary whose two component stars share a common outer layer, and is the prototype of a class of contact binary variables known as W Ursae Majoris variables...
.
Contact binaries are sometimes confused with common envelope
Common envelope
In astronomy, a common envelope refers to a short-lived phase in the evolution of a binary star in which the largest of the two stars has initiated unstable mass transfer to its companion star. Mass transfer is unstable when the radius of the donor star expands more rapidly or shrinks less...
s. 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.
See also
- Binary starBinary starA binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
- Binary system (astronomy)Binary system (astronomy)A binary system is an astronomical term referring to two objects in space which are so close that their gravitational interaction causes them to orbit about a common center of mass. Some definitions A binary system is an astronomical term referring to two objects in space (usually stars, but also...
- Common envelopeCommon envelopeIn astronomy, a common envelope refers to a short-lived phase in the evolution of a binary star in which the largest of the two stars has initiated unstable mass transfer to its companion star. Mass transfer is unstable when the radius of the donor star expands more rapidly or shrinks less...
- Contact binary (asteroid)Contact binary (asteroid)In the study of asteroids, a contact binary is caused when two asteroids gravitate toward each other until they touch, forming an oddly-shaped single body. Asteroids suspected of being contact binaries include the unusually elongated 624 Hektor and the bilobated 216 Kleopatra and 4769 Castalia...