Binary Star

Mass exchange binaries are short period pairs whose components are virtually in contact with each other so that they interact with each other; their large gaseous atmospheres may touch forming a figure eight in three dimensions. Sometimes the atmospheres overlap to such an extent that they make an envelope around the entire system. Mass from one component flows into the other resulting in mass loss and exchange. This in turn affects a change in the period of revolution of the pair. Generally, the components are at different stages in their evolutionary track. X-ray binaries described below are also binaries that exchange mass. Much remains to be done to understand the details of the physics of the interaction.