Janusz Karkowski

Universality and backreaction in a general-relativistic accretion of steady fluids

The spherically symmetric steady accretion of polytropic perfect fluids onto a black hole is the simplest flow model that can demonstrate the effects of backreaction. The analytic and numerical investigation reveals that backreaction keeps intact most of the characteristics of the sonic point. For any such system, with the free parameter being the relative abundance of the fluid, the mass accretion rate achieves maximal value when the mass of the fluid is 1/3 of the total mass. Fixing the total mass of the system, one observes the existence of two weakly accreting regimes, one overabundant and the other poor in fluid content.

Bondi accretion onto cosmological black holes

In this paper we investigate a steady accretion within the Einstein-Straus vacuole, in the presence of the cosmological constant. The dark energy damps the mass accretion rate and --- above certain limit --- completely stops the steady accretion onto black holes, which in particular is prohibited in the inflation era and after (roughly)

Spinning Q-balls in the complex signum-Gordon model

10^{12}

Luminosity, selfgravitation and nonuniqueness of stationary accretion

years from Big Bang (assuming the presently known value of the cosmological constant). Steady accretion would not exist in the late phases of the Penroses scenario - known as the Weyl curvature hypothesis - of the evolution of the Universe.

Penrose inequality for gravitational waves

Rotational excitations of compact Q-balls in the complex signum-Gordon model in 2+1 dimensions are investigated. We find that almost all such spinning Q-balls have the form of a ring of strictly finite width. In the limit of large angular momentum M{sub z}, their energy is proportional to |M{sub z}|{sup 1/5}.

Rotating systems, universal features in dragging and antidragging effects, and bounds of angular momentum

Aims. We show the existence of two branches of solutions bifurcating from a point with maximal luminosity. Methods. We investigate a Newtonian description of accreting compact bodies with hard surfaces, including luminosity and selfgravitation of polytropic perfect fluids. This nonlinear integro-differential problem is studied numerically. Its reduced version simplifies (under appropriate boundary conditions) to an algebraic relation between luminosity and the gas abundance in stationary, spherically symmetric flows and it can be dealt with analytically. Results. There exist – for a given luminosity, asymptotic mass and asymptotic temperature – two sub-critical solutions that bifurcate from an extremal point. They differ by the fluid content and the mass of the compact centre. Their relevance to Thorne- u Zytkow stars is discussed.

Comments on tails in Schwarzschild spacetimes

We investigate an axially symmetric asymptotically flat vacuum self-gravitating system. A class of initial data with apparent horizon was numerically constructed. The examined solutions satisfy the Penrose inequality. The prior analysis of a massive system and the present results suggest that either massive or source-free configurations fulfil the Penrose inequality.

Binding energy of static perfect fluids

We consider stationary, axially symmetric toroids rotating around spinless black holes, assuming the general-relativistic Keplerian rotation law, in the first post-Newtonian approximation. Numerical investigation shows that the angular momentum accumulates almost exclusively within toroids. It appears that various types of dragging (anti-dragging) effects are positively correlated with the ratio

Waves in Schwarzschild spacetimes: how strong can be imprints of the spacetime curvature

M_\mathrm{D}/m

Backscattering of electromagnetic and gravitational waves off Schwarzschild geometry

(