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Register a new userEfficient asymptotic frame selection for binary black hole spacetimes using asymptotic radiation
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Added by
Richard O'Shaughnessy
Publication date
2011
fields
Physics
and research's language is
English
Authors
R. OShaughnessy
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Previous studies have demonstrated that gravitational radiation reliably encodes information about the natural emission direction of the source (e.g., the orbital plane). In this paper, we demonstrate that these orientations can be efficiently estimated by the principal axes of <L_a L_b>, an average of the action of rotation group generators on the Weyl tensor at asymptotic infinity. Evaluating this average at each time provides the instantaneous emission direction. Further averaging across the entire signal yields an average orientation, closely connected to the angular components of the Fisher matrix. The latter direction is well-suited to data analysis and parameter estimation when the instantaneous emission direction evolves significantly. Finally, in the time domain, the average <L_a L_b> provides fast, invariant diagnostics of waveform quality.
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In this article we show that the asymptotic iteration method (AIM) allows one to numerically find the quasinormal modes of Schwarzschild and Schwarzschild de Sitter (SdS) black holes. An added benefit of the method is that it can also be used to calculate the Schwarzschild anti-de Sitter (SAdS) quasinormal modes for the case of spin zero perturbations. We also discuss an improved version of the AIM, more suitable for numerical implementation.
Usually, interpretation of redshift in static spacetimes (for example, near black holes) is opposed to that in cosmology. In this methodological note we show that both explanations are unified in a natural picture. This is achieved if considering the static spacetime one (i) makes a transition to a synchronous frame, (ii) returns to the original frame by means of local Lorentz boost. To reach our goal, we consider a rather general class of spherically symmetric spacetimes. In doing so, we construct frames that generalize the well-known Lemaitre and Painlev{e}--Gullstand ones and elucidate the relation between them. This helps to understanding in an unifying approach, how gravitation reveals itself in different branches of general relativity. This can be useful for general relativity university courses.
In this work, we investigate the Hawking radiation in higher dimensional Reissner-Nordstrom black holes as received by an observer, resides at infinity. The frequency-dependent transmission rates, which deform the thermal radiation emitted in the vicinity of the black hole horizon, are evaluated numerically. Apart from the case of four-dimensional spacetime, the calculations are extended to higher dimensional Reissner-Nordstrom metrics, and the results are found to be somewhat sensitive to the spacetime dimension. In general, it is observed that the transmission coefficients practically vanishes when the frequency of the emitted particle approaches zero. It increases with increasing frequency and eventually saturates to some value. For four-dimensional spacetime, the above result is shown to be mostly independent of the metrics parameter, neither of the orbital quantum number of the particle, once the location of the event horizon, $r_h$, and the product of the charges of the black hole and the particle $qQ$ are given. For higher-dimensional cases, on the other hand, the convergence becomes more slowly. Moreover, the difference between states with different orbital quantum numbers is found to be more significant. As the magnitude of the product of charges $qQ$ becomes more significant, the transmission coefficient exceeds one. In other words, the resultant spectral flux is amplified, which results in an accelerated process of black hole evaporation. The relation between the calculated outgoing transmission coefficient with existing results on the greybody factor is discussed.
The analysis of gravitino fields in curved spacetimes is usually carried out using the Newman-Penrose formalism. In this paper we consider a more direct approach with eigenspinor-vectors on spheres, to separate out the angular parts of the fields in a Schwarzschild background. The radial equations of the corresponding gauge invariant variable obtained are shown to be the same as in the Newman-Penrose formalism. These equations are then applied to the evaluation of the quasinormal mode frequencies, as well as the absorption probabilities of the gravitino field scattering in this background.
We investigate here the behavior of a few spherically symmetric static acclaimed black hole solutions in respect of tidal forces in the geodesic frame. It turns out that the forces diverge on the horizon of cold black holes (CBH) while for ordinary ones, they do not. It is pointed out that Kruskal-like extensions do not render the CBH metrics nonsingular. We present a CBH that is available in the Brans-Dicke theory for which the tidal forces do not diverge on the horizon and in that sense it is a better one.
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