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:
“That those tribes [the Sac and Fox Indians] cannot exist surrounded by our settlements and in continual contact with our citizens is certain. They have neither the intelligence, the industry, the moral habits, nor the desire of improvement which are essential to any favorable change in their condition.”
—Andrew Jackson (1767–1845)