Roche-lobe overflow occurs in a binary system when a star fills its Roche-lobe (often by expanding during the later stages of stellar evolution). Models show that in systems such as this, any material that passes beyond the Roche-lobe of the star will flow onto the binary companion, often by way of an accretion disk. This occurs through the inner Lagrangian point where the gravity of the two stars cancels, and is responsible for a number of astronomical phenomena including cataclysmic variables, Type Ia supernovae, and many X-ray binary systems.