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.
Famous quotes containing the word contact:
“Yet for all that, there is nothing in me of a founder of a religion—religions are affairs of the rabble; I find it necessary to wash my hands after I have come into contact with religious people.”
—Friedrich Nietzsche (1844–1900)