Binary System Mass Transfer

When stars are part of a binary system it is possible for the two to sometimes transfer stellar mass between each other. This occurs when one of the two stars grows too large. It is similar to an equilibrium maintaining system. In order to maintain steady states for each star there will occur a transfer of mass from one to the other. This effect has in fact been quite well measured. For example it is know the limit to which the star can grow without departing some of its mass on its companion star. The limit is known as the Roche Lobe. The Roche Lobe is the minimum distance from the star wherein mass remains gravitationally bound to the star. When the star reaches this limit it begins its transfer. In fact the point which this transfer occurs is at the first Lagrangian point.

Above is a depiction of mass transfer where the donor star creates an accretion disk around the other star. This is a typical method of mass transfer, however not the only. At times rather than creating an accretion disk, mass can be delivered directly on to the recipient star. Another outcome would be for the donning star to release its mass elsewhere such as solar winds.

Below I have two equations are the equations for the Roche Lobe radius of Mass 1 of a binary system. Note the dependence of these equations on the masses of the two stars and their ratio.