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;