Publication date: Mar 2004
Abstract:
Equatorial motion of test particles in Kerr de Sitter spacetimes is
considered. Circular orbits are determined, their properties are
discussed for both black-hole and naked-singularity spacetimes, and
their relevance for thin accretion disks is established. The circular
orbits constitute two families that coalesce at the so-called static
radius. The orientation of the motion along the circular orbits is, in
accordance with case of asymptotically flat Kerr spacetimes, defined by
relating the motion to the locally nonrotating frames. The minus-family
orbits are all counterrotating, while the plus-family orbits are usually
corotating relative to these frames. However, the plus-family orbits
become counterrotating in the vicinity of the static radius in all Kerr
de Sitter spacetimes, and they become counterrotating in the vicinity of
the ring singularity in Kerr de Sitter naked-singularity spacetimes with
a low enough rotational parameter. In such spacetimes, the efficiency of
the conversion of the rest energy into heat energy in the geometrically
thin plus-family accretion disks can reach extremely high values
exceeding the efficiency of the annihilation process. The transformation
of a Kerr de Sitter naked singularity into an extreme black hole due to
accretion in the thin disks is briefly discussed for both the
plus-family and minus-family disks. It is shown that such a conversion
leads to an abrupt instability of the innermost parts of the plus-family
accretion disks that can have strong observational consequences.
Authors:
Stuchlík, Zdeněk; Slaný, Petr;