Publikace ÚTF

“Almost all” seems to be known about isolated stationary black holes in
asymptotically flat space-times and about the behaviour of test matter and fields in
their backgrounds. The black holes likely present in galactic nuclei and in some
X-ray binaries are commonly being represented by the Kerr metric, but actually
they are not isolated (they are detected only thanks to a strong interaction with
the surroundings), they are not stationary (black-hole sources are rather strongly
variable) and they also probably do not live in an asymptotically flat universe. Such
“perturbations” may query the classical black-hole theorems (how robust are the
latter against them?) and certainly affect particles and fields around, which can have
observational consequences. In the present contributionwe examine howthe geodesic
structure of the static and axially symmetric black-hole space-time responds to the
presence of an additional matter in the form of a thin disc or ring. We use several
different methods to show that geodesic motion may become chaotic, to reveal the
strength and type of this irregularity and its dependence on parameters. The relevance
of such an analysis for galactic nuclei is briefly commented on.