Publication date: Dec 2007
Abstract:
Rotating black holes in the brany universe of the Randall-Sundrum type
with infinite additional dimension are described by the Kerr geometry
with a tidal charge b representing the interaction of the brany black
hole and the bulk spacetime. We investigate the role of the tidal charge
in the orbital resonance model of quasiperiodic oscillations (QPOs) in
black hole systems. The orbital Keplerian frequency ν_{K} and the
radial and vertical epicyclic frequencies ν_{r}, ν_{θ} of
the equatorial, quasicircular geodetical motion are discussed, and the
local maxima of their radial profiles related to Keplerian accretion
discs are given, assuming the inner edge of the disc located at loci of
the innermost stable circular geodesic. The resonant conditions are
given for possible direct (parametric) resonances of the oscillations
with the radial and vertical epicyclic frequencies and for some trapped
oscillations of the warped discs with resonant combinational frequencies
involving the Keplerian and radial epicyclic frequencies. It is shown,
how the tidal charge could influence matching of the observational data
indicating the 3:2 frequency ratio observed in GRS 1915+105 microquasar
with prediction of the orbital resonance model. The "magic"
dimensionless black hole spin enabling presence of strong resonant
phenomena at the radius, where ν_{K}:ν_{θ}:ν_{r} =
3:2:1, is determined in dependence on the tidal charge. Such strong
resonances could be relevant even in sources with highly scattered
resonant frequencies, as those expected in Sgr A*.
Authors:
Stuchlík, Zdeněk; Kotrlová, Andrea;