Period Changes as a Tool to Study Unseen Components Around Eclipsing Binaries

Abstract

Observational detection of a strically periodic orbital period variation of a binary star system can be considered as a strong evidence on the existence of an unseen component stars around the binary system. Unseen components of eclipsing binary systems cause the light time effect as displacement of the times of eclipse minimum light in a sinousoidal fasion with the period(s) equal to the period(s) of revolution of the unseen component(s). The method may reveal strong evidence even on the unseen large planets or completely dark black hole components of close binary systems. But in the absence of any additional evidence supporting the presence of third component(s), the conclusion that these systems are triple (or multiple) is still considered to be premature at present. In the present study I will review the recent work on the periodic orbital period variation of eclipsing binaries considered to be the light time effect due to unseen component stars around binary systems.