A three-dimensional representation of the Roche potential in a binary star with a mass ratio of 2, in the co-rotating frame.  The droplet-shaped figures in the equipotential plot at the bottom of the figure are called the Roche lobes of each star.  L1, L2 and L3 are the points of Lagrange where forces cancel out. Mass can flow through the saddle point L1 from one star to its companion, if the donor star fills its Roche lobe.
Marc van der Sluys
CC BY 2.5
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