X-Ray Pulsars are magnetized Neutron Stars. In Binary systems, when the Neutron Star enters the accretion regime, it starts to accrete matter from its optical counterpart which acts as the donor here.

Stars in binary systems exist in mathematically defined, adjoined pear-shaped "lobes" called Roche lobes. As massive stars age, they can swell out and fill in their Roche lobe. When this happens ...