7 research outputs found
Basic properties of toroidal structures in Kerr--de Sitter backgrounds
Perfect fluid tori with uniform distribution of the specific angular momentum
orbiting the Kerr-de Sitter black holes or naked singularities are studied.
Closed equipotential surfaces corresponding to stationary toroidal discs are
allowed only in the spacetimes admitting stable circular geodesics. The last
closed surface crosses itself in the cusp(s) enabling outflow(s) of matter from
the torus due to the violation of hydrostatic equilibrium. The repulsive
cosmological constant, , implies the existence of the outer cusp
(with a stabilizing effect on the tori because of "excretion", i.e., outflow of
matter from the torus into the outer space) and the strong collimation of open
equipotential surfaces along the rotational axis. Both the effects take place
nearby the so-called static radius where the gravitational attraction is just
balanced by the cosmic repulsion. The plus-family discs (which are always
corotating in the black-hole backgrounds but can be counterrotating, even with
negative energy of the fluid elements, in some naked singularity backgrounds)
are thicker and more extended than the minus-family ones (which are always
counterrotating in all backgrounds). If the parameters of naked-singularity
spacetimes are very close to the parameters of extreme black-hole spacetimes,
the family of possible disc-like configurations includes members with two
isolated discs where the inner one is always a counterrotating accretion disc.
Mass estimates for tori with nonrelativistic adiabatic equation of state give
limits on their central mass-density, for which the approximation of test fluid
is adequate.Comment: Updated version of the Section talk at Albert Einstein Century
International Conference at Palais de l'Unesco, Paris, France, 18-23 July,
2005; to appear in the Proceedings; AIP style files included; 8 page
Toroidal LNRF-velocity profiles in thick accretion discs orbiting rapidly rotating Kerr black holes
We show that in the equatorial plane of marginally stable thick discs (with
uniformly distributed specific angular momentum the orbital velocity relative
to the locally non-rotating frames (LNRF) has a positive radial gradient in the
vicinity of black holes with spin a>0.99979. The change of sign of the velocity
gradient occurs just above the center of the thick toroidal discs, in the
region where stable circular geodesics of the Kerr spacetime are allowed. The
global character of the phenomenon is given in terms of topology changes of the
von Zeipel surfaces (equivalent to the equivelocity surfaces in the tori with
constant specific angular momentum distribution). Toroidal von Zeipel surfaces
exist around the circle corresponding to the minimum of the equatorial LNRF
velocity profile, indicating a possibility of development of some vertical
instabilities in those parts of marginally stable tori with positive gradient
of the LNRF velocity. Eventual oscillatory frequencies connected with the
phenomenon are given in a coordinate-independent form.Comment: Updated version of the Section talk at Albert Einstein Century
International Conference at Palais de l'Unesco, Paris, France, 18-23 July,
2005; to appear in the Proceedings; AIP style files included; 8 page
Non-monotonic Keplerian velocity profiles around near-extreme braneworld Kerr black holes
We study the non-monotonic Keplerian velocity profiles related to locally
non-rotating frames (LNRF) in the field of near-extreme braneworld Kerr black
holes and naked singularities in which the non-local gravitational effects of
the bulk are represented by a braneworld tidal charge and the 4D geometry
of the spacetime structure is governed by the Kerr-Newman geometry. We show
that positive tidal charge has a tendency to restrict the values of the black
hole dimensionless spin admitting existence of the non-monotonic Keplerian
LNRF-velocity profiles; the non-monotonic profiles exist in the black hole
spacetimes with tidal charge smaller than (and spin larger than
). With decreasing value of the tidal charge (which need not be only
positive), both the region of spin allowing the non-monotonicity in the
LNRF-velocity profile around braneworld Kerr black hole and the velocity
difference in the minimum-maximum parts of the velocity profile increase
implying growing astrophysical relevance of this phenomenon
Relativistic and Newtonian fluid tori with electric charge
We discuss the effects of electric charging on the equilibrium configurations
of magnetized, rotating fluid tori around black holes of different mass. In the
context of gaseous/dusty tori in galactic nuclei, the central black hole
dominates the gravitational field and it remains electrically neutral, while
the surrounding material acquires some electric charge and exhibits
non-negligible self-gravitational effect on the torus structure. The structure
of the torus is influenced by the balance between the gravitational and
electromagnetic forces. A cusp may develop even in Newtonian tori due to the
charge distribution.Comment: 5 pages, 1 figure; to appear in Proceedings of the 15th Marcel
Grossman Meeting on General Relativity - the session AC3 on "Accretion Discs
and Jets" by Eva Hackmann & Audrey Trova (Rome, 1-7 July 2018), edited by
Elia Battistelli, Robert T. Jantzen, and Remo Ruffini, in preparatio
Fish Tank Granuloma Caused by Mycobacterium marinum in Two Aquarists: Two Case Reports
Mycobacterium marinum, the cause of chronic systemic infections in fish, occasionally causes granulomatous skin and soft tissue lesions in humans. Cutaneous mycobacterial infection in two patients owing to unusual circumstances is presented in this report. The first patient was infected through improper hygienic behavior, while infection in the second patient was previously misdiagnosed as rheumatoid arthritis and treated with methylprednisolone for a period of three months, which resulted in a rare systemic spread of M. marinum into the bones of the hand, testis, and epididymis. Simultaneously, screening for possible sources of M. marinum infection in patients' aquaria revealed positive fish harboring VNTR profiles identical to those obtained for clinical isolates from patients