Accretion processes in magnetically and tidally perturbed Schwarzschild   black holes
  We study the accretion process in the region of the Preston-Poisson space-time describing a Schwarzschild black hole perturbed by asymptotically uniform magnetic field and axisymmetric tidal structures. We find that the accretion disk shrinks and the marginally stable orbit shifts towards the black hole with the perturbation. The radiation intensity of the accretion disk increases, while the radius where radiation is maximal remains unchanged. The spectrum is blue-shifted. Finally, the conversion efficiency of accreting mass into radiation is decreased by both the magnetic and the tidal perturbations. 
Zolt\'an Kov\'acs, L\'aszl\'o \'Arp\'ad Gergely, M\'aty\'as Vas\'uth
gr-qc astro-ph.CO