Clumps of material orbiting a black hole and the QPOs

Abstract

Clumps of material orbiting a black hole may be disturbed, somewhat like comets in the Kuiper belt, to relatively small periastron orbits. Each periastron passage changes the orbital parameters in such a way that the orbit becomes more and more eccentric and the angular momentum approaches the critical value for tidal capture. When this value is reached, the body is suddenly caught by the relativistic potential to the last periastron (occurring at two Schwarzschild radii for a non rotating black hole). In this process the transfer of orbital into internal energy heats the body before it makes a few more turns toward the horizon of the black hole. Because of strong relativistic effects this last bright message from the object is seen as a quasi-periodic flare. Assuming that a black hole may be fed by a large number of such small debris we calculate light curves expected from such events. We investigate the resemblance of the Fourier spectra of such light curves with those of observed QPOs.