282 research outputs found

    On the Stability of the Iterated Crank-Nicholson Method in Numerical Relativity

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    The iterated Crank-Nicholson method has become a popular algorithm in numerical relativity. We show that one should carry out exactly two iterations and no more. While the limit of an infinite number of iterations is the standard Crank-Nicholson method, it can in fact be worse to do more than two iterations, and it never helps. We explain how this paradoxical result arises

    Late-Time Evolution of Charged Gravitational Collapse and Decay of Charged Scalar Hair - II

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    We study analytically the initial value problem for a charged massless scalar-field on a Reissner-Nordstr\"om spacetime. Using the technique of spectral decomposition we extend recent results on this problem. Following the no-hair theorem we reveal the dynamical physical mechanism by which the charged hair is radiated away. We show that the charged perturbations decay according to an inverse power-law behaviour at future timelike infinity and along future null infinity. Along the future outer horizon we find an oscillatory inverse power-law relaxation of the charged fields. We find that a charged black hole becomes ``bald'' slower than a neutral one, due to the existence of charged perturbations. Our results are also important to the study of mass-inflation and the stability of Cauchy horizons during a dynamical gravitational collapse of charged matter in which a charged black-hole is formed.Comment: Latex 15 pages, Revtex.st

    Equilibrium and stability of relativistic cylindrical polytropes

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    We examine the structure and radial stability of infinitely long cylindrical polytropes in general relativity. We show that in contrast with spherical polytropes, all cylindrical polytropes are stable. Thus pressure regeneration is not decisive in determining the behavior of cylindrical systems. We discuss how the behavior of infinite cylinders is qualitatively different from that of finite, asymptotically flat configurations. We argue that the use of infinite cylinders to gain physical insight into the collapse of finite aspherical systems may be misleading. In particular, the ability of pressure and rotation to always halt the collapse of an infinite cylinder to a naked singularity may not carry over to finite systems

    Eclipse mechanisms for binary pulsars

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    The parameters of the new eclipsing millisecond pulsar PSR 1744 - 24A in Terzan 5 are sufficiently different from those of PSR 1957 + 20 that very severe constraints can be put now on the theoretical models and formation scenarios of such systems. Most importantly, the eclipse cannot be caused by refractive effects (either total reflection or bending of the radio signal paths). Instead, they very likely are produced by an absorption mechanism, possibly combined with pulse-smearing effects. A model based on free-free absorption by the gas evaporated from the companion remains viable in spite of difficulties. Independent of the particular eclipse mechanism, the results of some preliminary dynamical calculations of the evaporative flow are discussed

    Late-Time Evolution of Realistic Rotating Collapse and The No-Hair Theorem

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    We study analytically the asymptotic late-time evolution of realistic rotating collapse. This is done by considering the asymptotic late-time solutions of Teukolsky's master equation, which governs the evolution of gravitational, electromagnetic, neutrino and scalar perturbations fields on Kerr spacetimes. In accordance with the no-hair conjecture for rotating black-holes we show that the asymptotic solutions develop inverse power-law tails at the asymptotic regions of timelike infinity, null infinity and along the black-hole outer horizon (where the power-law behaviour is multiplied by an oscillatory term caused by the dragging of reference frames). The damping exponents characterizing the asymptotic solutions at timelike infinity and along the black-hole outer horizon are independent of the spin parameter of the fields. However, the damping exponents at future null infinity are spin dependent. The late-time tails at all the three asymptotic regions are spatially dependent on the spin parameter of the field. The rotational dragging of reference frames, caused by the rotation of the black-hole (or star) leads to an active coupling of different multipoles.Comment: 16 page

    Radiative Tail of Realistic Rotating Gravitational Collapse

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    An astrophysically realistic model of wave dynamics in black-hole spacetimes must involve a non-spherical background geometry with angular momentum. We consider the evolution of gravitational (and electromagnetic) perturbations in rotating Kerr spacetimes. We show that a rotating Kerr black hole becomes `bald' slower than the corresponding spherically-symmetric Schwarzschild black hole. Moreover, our results turn over the traditional belief (which has been widely accepted during the last three decades) that the late-time tail of gravitational collapse is universal. In particular, we show that different fields have different decaying rates. Our results are also of importance both to the study of the no-hair conjecture and the mass-inflation scenario (stability of Cauchy horizons).Comment: 11 page
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