No abstract available

No abstract available

No abstract available

[en] This is the first of two papers on the energy-extraction processes near a Kerr black hole immersed in a magnetic field. In this paper we shall consider the consequences of a dipole field extending to infinity matched on to a uniform field in the interior which contains the Kerr black hole. The magnetic fields considered are perturbative in nature. The matching of the fields is imperative owing to the ''no-hair theorem'' and the second law of black-hole physics. Two intriguing situations arising in this context are discussed, namely, (1) the second law of black-hole physics and (2) the law of conservation of energy in an energy-extraction process. At first sight both these laws seem to be violated. These issues arise basically because in the presence of the magnetic field there can exist negative-energy states even for L>0 particles. These issues get resolved by realizing that it is the sign of P/sub c/phi = L-eA/sub cphi/ and not L which determines a corotating or counterrotating orbit. It is also shown that negative-energy states can exist away from the horizon in the presence of either of the fields, the dipole and the uniform, thus favoring energy-extraction processes away from the black hole. This type of energy extraction is solely a consequence of the magnetic field. Also, a fairly detailed analysis of the effective-potential curves is provided, mainly relevant to the existence of negative energies and energy extraction. The formalism of the energy-extraction process will be considered in the second paper

No abstract available

[en] We present a class of spherically symmetric hypersurfaces in the Kruskal extension of the Schwarzschild space-time. The hypersurfaces have constant negative scalar curvature, so they are hyperboloidal in the regions of space-time which are asymptotically flat

[en] Recently, Bañados, Silk and West (BSW) demonstrated that the extremal Kerr black hole can act as a particle accelerator with arbitrarily high center-of-mass energy (E_C_M) when the collision takes place near the horizon. The rotating Hayward’s regular black hole, apart from Mass (M) and angular momentum (a), has a new parameter g (g>0 is a constant) that provides a deviation from the Kerr black hole. We demonstrate that for each g, with M=1, there exist critical a_E and r_H"E, which corresponds to a regular extremal black hole with degenerate horizons, and a_E decreases whereas r_H"E increases with increase in g. While a< a_E describe a regular non-extremal black hole with outer and inner horizons. We apply the BSW process to the rotating Hayward’s regular black hole, for different g, and demonstrate numerically that the E_C_M diverges in the vicinity of the horizon for the extremal cases thereby suggesting that a rotating regular black hole can also act as a particle accelerator and thus in turn provide a suitable framework for Plank-scale physics. For a non-extremal case, there always exist a finite upper bound for the E_C_M, which increases with the deviation parameter g.

[en] We show that the angular momentum area inequality 8π|J| ≤ A for weakly stable minimal surfaces would apply to I⁺-regular many-Kerr solutions, if any existed. Hence, we remove the undesirable hypothesis in the Hennig-Neugebauer proof of non-existence of well-behaved two-component solutions. (paper)

[en] We numerically solve the inhomogeneous Zerilli-Moncrief and Regge-Wheeler equations in the time domain. We obtain the gravitational waveforms produced by a point particle of mass μ traveling around a Schwarzschild black hole of mass M on arbitrary bound and unbound orbits. Fluxes of energy and angular momentum at infinity and the event horizon are also calculated. Results for circular orbits, selected cases of eccentric orbits, and parabolic orbits are presented. The numerical results from the time-domain code indicate that, for all three types of orbital motion, black hole absorption contributes less than 1% of the total flux, so long as the orbital radius r_p(t) satisfies r_p(t)>5M at all times

[en] In this work we compute the self-force experienced by a static non-minimally-coupled scalar charge outside a Schwarzschild black hole. We find that the finite part of this self-force is zero. Our no-self-force result is in disagreement with a previous result of Zel'nikov and Frolov, who have suggested that there is a non-zero finite-part of the self-force on a nonminimally-coupled charge in Schwarzschild spacetime. We are able to show that the omission of an unusual flux in their calculation was responsible for their (incorrect) result