A binary star system where both stars are so close they touch and share a common envelope of material, creating a peanut-shaped configuration. These systems represent the most extreme form of stellar interaction, with material flowing between the stars and orbital periods typically less than one day.
From Latin 'contactus' (touching) and 'binarius' (consisting of two), coined in the mid-20th century as astronomers recognized this extreme configuration. The term reflects the physical contact between stellar surfaces, distinguishing these systems from detached or semi-detached binaries.
Contact binaries are so close they're practically kissing stars! The two stars share the same outer atmosphere and rotate in perfect synchronization, like cosmic dancers locked in an eternal embrace that will eventually lead to their merger into a single star.
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