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:
“Whatever my own practice may be, I have no doubt that it is a part of the destiny of the human race, in its gradual improvement, to leave off eating animals, as surely as savage tribes have left off eating each other when they came in contact with the more civilized.”
—Henry David Thoreau (1817–1862)