Radiation interference from sources rotating around Schwarzschild black   holes
  We investigate the influence of the spacetime curvature on the interference of the radiation emitted by an ensemble of scalar sources in circular motion around a Schwarzschild black hole. We pay particular attention to the transition from the radiating to the non-radiating regime as the number of sources increases. 
Raissa F. P. Mendes and George E. A. Matsas
gr-qc