Braking--Radiation: An Energy Source for a Relativistic Fireball
  If the Schwarzschild black-hole is moving rectilinearly with uniform 3-velocity and suddenly stops, according to a distant observer, then we demonstrate that this observer will see a spherical light--like shell or "relativistic fireball" radiate outwards with energy equal to the original kinetic energy of the black-hole. 
C. Barrabes, P. A. Hogan