Roche Lobe Mass Transfer
Binary star system: gravity + rotation create teardrops of influence
The Roche lobe is the region around each star where its gravity dominates. At the inner Lagrange point L1, gravity balances — matter can flow from one star to the other. When a star expands to fill its Roche lobe (fill = 100%), mass transfer begins. This drives X-ray binaries, cataclysmic variables, and Type Ia supernovae.