... AM CVn stars . ... Flare stars . ... Gavin Ramsay . ... Unlike the Sun, most stars in our Galaxy orbit another star: these systems are called binary stars. Generally it takes many years for the two stars to orbit around each other. However, there is a group of binary systems (called AM CVn or ultra compact binaries) which have an orbital period less than one hour. ... Although there is now over 50 AM CVn binaries known, the theoretical models still predict far more many systems. ...