Contact Binary: Stars that touch each other

A contact binary is a binary star system whose constituent stars are so close that they touch each other or have merged to share their gaseous envelopes.

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.

They can be classified into four distinct groups based on the characteristics of their common atmospheres: late-type low mass systems (W UMa systems) with common convective atmospheres, early-type massive systems with common radiative atmospheres, mix- or intermediate-type systems consisting of a cooler component with a convective stellar atmosphere and a hotter companion with a radiative stellar atmosphere, and supergiant contact systems with very deep common convective atmospheres.

There’s also one very peculiar group called double contact systems. In these systems, each of their components is being in contact with its respective critical equal potential surface but the components are not in physical contact with each other! Mostra meno