Contact Binaries and Merging Stars

A contact binary is two stars that are so close that their surfaces are touching. In profile, such a system would resemble a peanut. As the two stars orbit each other, they lose momentum, so they eventually spiral together. Such a merger could produce a bright outburst, known as a nova, with the two stars forming a single, more-massive star. It could also produce a supernova explosion, which would completely destroy the two stars.