If the collapse produces an explosion, the neutron star can be left behind. If the collapse is complete, a black hole results. Smaller orbits have shorter period. The total mass of the two stars can be determined by measuring the period of the orbit and the distance between the stars. Roche Lobes - Region of gravitational dominance of stars in a double system.
More massive star reaches out further, has the largest lobe.
Inner Lagrangian Point Connection point between Roche Lobes, point through which mass can be transferred between stars. Outer Lagrangian Points - Region beyond which matter orbits both stars or flows out of the system. The evolved star is the less massive. Resolution - mass has been transferred between the stars. Most massive star of close pair evolves first, fills its Roche lobe and some of its mass begins to leak through inner lagrangian point to the companion star.