STEADY-STATE SHOCKS IN AN ACCRETION DISC AROUND A KERR BLACK-HOLE

Results of numerical simulations of shock solutions in a geometrical thin accretion disc around a Kerr black hole (BH) are presented. Using the smoothed particle hydrodynamics (SPH) technique, the influence of the central object is included by means of an effective potential, which is known to mimic the external Kerr geometry very well. We first present the theory of standing shock formation in an accretion disc around a Kerr black hole, and show that the results of our numerical simulation agree very well with the theoretical results. Using the pseudo-potential, our analysis gives at least a semi-quantitative insight into what a true general relativistic computation might reveal. The location of the shocks is found to be different for the co-rotating and the counter-rotating flows. Compared to accretion in the vicinity of a non-rotating BH, the position of the shock is shifted inwards for prograde accretion and outwards for retrograde accretion. We find that the shocks in an inviscid flow are very stable. We also remove the ambiguity prevalent regarding the location and stability of shocks in adiabatic flows. Finally we sketch some of the astrophysical consequences of our findings in relation to accretion discs in active galactic nuclei (AGN) and quasars.