Just consider the following; A large object, say a sun or neutron star, is traveling through the universe at near the speed of light (let's say 99% of c). This super massive object is on a collision course with a fixed/static super massive object relative to the body in motion. When the eminent impact occurs, the dynamic object will transfer it's momentum to the static body, Newtons third law, almost like astronomical scale newton balls. The problem is, how is the relativistic mass converted into kinetic energy, assuming that the transfer is not instantaneous and occurs over a span of time. To me it would seem as though energy potential is lost all together as it decelerates because the relativistic mass is not transferred as it dissipates exponentially while the force is not transferred exponentially. If someone could please help explain how the relativistic momentum/mass is converted to kinetic energy that would alleviate the spitting psyche headache. I know I'm wrong because energy must be conserved, but would like someone to explain how. Thanks.