arXiv subjects

Amos Ori

Publications and source records attributed to Amos Ori.

63 records · Page 4Linked to original sources

arXiv1997

Transmission and reflection coefficients for a scalar field inside a charged black hole

Using the late-time expansion we calculate the leading-order coefficients describing the evolution of a massless scalar field inside a Reissner-Nordstrom black hole. These coefficients may be interpreted as the reflection and transmission coefficients for scalar-field modes propagating from the event horizon to the Cauchy horizon. Our results agree with those obtained previously by Gursel et al by a different method.

gr-qc↗

arXiv1997

Analytic study of the null singularity inside spherical charged black holes

We study analytically the features of the Cauchy horizon (CH) singularity inside a spherically-symmetric charged black hole, nonlinearly perturbed by a self-gravitating massless scalar field. We derive exact expressions for the divergence rate of the blue-shift factors, namely the derivatives in the outgoing direction of the scalar field $Φ$ and the area coordinate $r$. Both derivatives are found to grow along the contracting CH exactly like $1/r$. Our results are valid everywhere along the CH singularity, up to the point of full focusing. These exact analytic expressions are verified numerically.

gr-qc↗

arXiv1997

Late-time evolution of nonlinear gravitational collapse

We study numerically the fully nonlinear gravitational collapse of a self-gravitating, minimally-coupled, massless scalar field in spherical symmetry. Our numerical code is based on double-null coordinates and on free evolution of the metric functions: The evolution equations are integrated numerically, whereas the constraint equations are only monitored. The numerical code is stable (unlike recent claims) and second-order accurate. We use this code to study the late-time asymptotic behavior at fixed $r$ (outside the black hole), along the event horizon, and along future null infinity. In all three asymptotic regions we find that, after the decay of the quasi-normal modes, the perturbations are dominated by inverse power-law tails. The corresponding power indices agree with the integer values predicted by linearized theory. We also study the case of a charged black hole nonlinearly perturbed by a (neutral) self-gravitating scalar field, and find the same type of behavior---i.e., quasi-normal modes followed by inverse power-law tails, with the same indices as in the uncharged case.

gr-qc↗

arXiv1995

Radiation-reaction-induced evolution of circular orbits of particles around Kerr Black Holes

It is demonstrated that, in the adiabatic approximation, non-Equatorial circular orbits of particles in the Kerr metric (i.e. orbits of constant Boyer-Lindquist radius) remain circular under the influence of gravitational radiation reaction. A brief discussion is given of conditions for breakdown of adiabaticity and of whether slightly non-circular orbits are stable against the growth of eccentricity.

gr-qc↗

arXiv1995

Remarks on the formation of black holes in non-symmetric gravity

In a recent paper, we discussed the formation of black holes in non-symmetric gravity. That paper was then criticized by Cornish and Moffat. In the present paper, we address the arguments raised by Cornish and Moffat. In summary, we do not see any reason to doubt the validity of our former conclusions.

gr-qc↗

arXiv1995

Radiative Evolution of Orbits Around a Kerr Black Hole

We propose a simple approach for the radiative evolution of generic orbits around a Kerr black hole. For a scalar-field, we recover the standard results for the evolution of the energy $E$ and the azimuthal angular momentum $L_z$ . In addition, our method provides a closed expression for the evolution of the Carter constant $Q$.

gr-qc↗

arXiv1995

On the formation of black holes in non-symmetric gravity

It has been recently suggested that the Non-symmetric Gravitational Theory (NGT) is free of black holes. Here, we study the linear version of NGT. We find that even with spherical symmetry the skew part of the metric is generally non-static. In addition, if the skew field is initially regular, it will remain regular everywhere and, in particular, at the horizon. Therefore, in the fully-nonlinear theory, if the initial skew-field is sufficiently small, the formation of a black hole is to be anticipated.

gr-qc↗

arXiv1995

Are physical objects necessarily burnt up by the blue sheet inside a black hole?

The electromagnetic radiation that falls into a Reissner-Nordstrom black hole develops a ``blue sheet'' of infinite energy density at the Cauchy horizon. We consider classical electromagnetic fields (that were produced during the collapse and then backscattered into the black hole), and investigate the blue-sheet effects of these fields on infalling objects within a simplified model. These effects are found to be finite and even negligible for typical parameters.

gr-qc↗

arXiv1992

The Last Three Minutes: Issues in Gravitational Wave Measurements of Coalescing Compact Binaries

Gravitational-wave interferometers are expected to monitor the last three minutes of inspiral and final coalescence of neutron star and black hole binaries at distances approaching cosmological, where the event rate may be many per year. Because the binary's accumulated orbital phase can be measured to a fractional accuracy $\ll 10^{-3}$ and relativistic effects are large, the waveforms will be far more complex, carry more information, and be far harder to model theoretically than has been expected. Theorists must begin now to lay a foundation for extracting the waves' information.

astro-ph↗