"Now there is a development I'd not heard of before. Fascinating."
Erasmus wrote: What they meant anyway was that momentum is conserved.
I was going to write that too, but I was busy with a prior comment. In physics you always have conservation of energy and conservation of momentum. Even though there's no physical contact, think of recoil from a firearm when it's shot.
Of course there is physical contact. The bullet is in the chamber touching something or else the slug would go forward and the casing would go backward. The bullet goes forward and the backward force is transferred through the casing into the firearm mechanism, some of which might be used to activate a semi auto feature and the rest going into your wrist or your shoulder.
Anyway, regardless of how it is said, 'momentum is conserved' is like saying the truck moved because it has round wheels.
I would be more apt to believe that half the star was sucked into the 'black hole' and the remaining half was spinning round the vortex so fast that centrifugal force ejected it our past the Scharzhild (sp?) radius, possible at a much higher speed than it was entering.