jpicciri wrote:I've read many explanations for runaway stars that involve a supernova that then "releases" its companion star.
Doesn't the companion still revolve around the center of mass? Does the runaway happen after the supernova
remnants pass the orbit of the companion star? I'm not understanding the kinematics.
The mass that ends up outside the orbit of the star is effectively a shell, and it therefore exerts no net gravitational force on any objects inside it. So there is an effective loss of mass, with the consequence that the runaway star ends up converting its elliptical orbit to a hyperbolic one (meaning it's traveling very nearly in a straight line once it's far from its sibling binary).