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Budapest, Hungary

Csizmadia P.,RMKI | Laszlo A.,RMKI | Laszlo A.,CERN | Racz I.,RMKI
Journal of Physics: Conference Series | Year: 2010

In the conventional models of astrophysical jets magnetohydrodynamics is believed to play the most role. Recently there were several qualitative arguments emphasizing that the role of pure gravitational effects might be more important than expected before. Here we present some preliminary but quantitate results clarifying the role of gravity in the formation of astrophysical jets. © 2010 IOP Publishing Ltd. Source

Csizmadia P.,RMKI | Kovaacs G.,Eotvos Lorand University | Racz I.,RMKI
Journal of Physics: Conference Series | Year: 2010

A mathematical and numerical framework for the study of dynamical properties of spherically symmetric Einstein-Yang-Mills-Higgs systems is introduced. The quantitative investigations of the time evolution of some simple magnetic monopole type configurations are presented. Long living breather type states are found to develop. © 2010 IOP Publishing Ltd. Source

Gaspar M.E.,RMKI | Racz I.,RMKI
Classical and Quantum Gravity | Year: 2010

As a preparation for the dynamical investigations, this paper begins with a short review of the three-layer gravastar model with distinguished attention to the structure of the pertinent parameter space of gravastars in equilibrium. Then the radial stability of these types of gravastars is studied by determining their response for the totally inelastic collision of their surface layer with a dust shell. It is assumed that the dominant energy condition holds and the speed of sound does not exceed that of the light in the matter of the surface layer. While in the analytic setup the equation of state is kept to be generic, in the numerical investigations three functionally distinct classes of equations of states are applied. In the corresponding particular cases the maximal mass of the dust shell that may fall onto a gravastar without converting it into a black hole is determined. For those configurations which remain stable the excursion of their radius is assigned. It is found that even the most compact gravastars cannot get beyond the lower limit of the size of conventional stars, provided that the dominant energy condition holds in both cases. It is also shown - independent of any assumption concerning the matter interbridging the internal de Sitter and the external Schwarzschild regions - that the better a gravastar in mimicking a black hole the easier is to get the system formed by a dust shell and the gravastar beyond the event horizon of the composite system. In addition, a generic description of the totally inelastic collision of spherical shells in spherically symmetric spacetimes is also provided in the appendix. © 2010 IOP Publishing Ltd. Source

Racz I.,RMKI
Classical and Quantum Gravity | Year: 2010

The global extendibility of smooth causal geodesically incomplete spacetimes is investigated. Denote by γ one of the incomplete non-extendible causal geodesics of a causal geodesically incomplete spacetime (M, gab). First, it is shown that it is always possible to select a synchronized family of causal geodesics and an open neighbourhood μof a final segment of γ in M such that comprises members of Γ, and suitable local coordinates can be defined everywhere on provided that γ does not terminate either on a tidal force tensor singularity or on a topological singularity. It is also shown that if, in addition, the spacetime (M, g ab) is globally hyperbolic, and the components of the curvature tensor, and its covariant derivatives up to order k - 1 are bounded on , and also the line integrals of the components of the kth-order covariant derivatives are finite along the members of Γ - where all the components are meant to be registered with respect to a synchronized frame field on - then there exists a Ck - extension so that for each , which is inextendible in (M, gab), the image, , is extendible in . Finally, it is also proved that whenever γ does terminate on a topological singularity (M, g ab) cannot be generic. © 2010 IOP Publishing Ltd. Source

Racz I.,RMKI | Toth G.Z.,RMKI
Classical and Quantum Gravity | Year: 2011

The late-time behavior of a scalar field on fixed Kerr background is examined in a numerical framework incorporating the techniques of conformal compactification and hyperbolic initial value formulation. The applied code is 1+(1+2) as it is based on the use of the spectral method in the angular directions while in the time-radial section fourth order finite differencing, along with the method of lines, is applied. The evolution of various types of stationary and non-stationary pure multipole initial states are investigated. The asymptotic decay rates are determined not only in the domain of outer communication but along the event horizon and at future null infinity as well. The decay rates are found to be different for stationary and non-stationary initial data, and they also depend on the fall off properties of the initial data toward future null infinity. The energy and angular momentum transfers are found to show significantly different behavior in the initial phase of the time evolution. The quasinormal ringing phase and the tail phase are also investigated. In the tail phase, the decay exponents for the energy and angular momentum losses at I+ are found to be smaller than at the horizon which is in accordance with the behavior of the field itself and it means that at late times the energy and angular momentum falling into the black hole become negligible in comparison with the energy and angular momentum radiated toward I+. The energy and angular momentum balances are used as additional verifications of the reliability of our numerical method. © 2011 IOP Publishing Ltd. Source

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