15 research outputs found
Electromagnetic Fields of Separable Space-Times
Carter derived the forms of the metric and the vector potentials of the
space-times in which the relativistic Schrodinger equation for the motion of a
charged particle separates. Here we show that on each `spheroidal' surface a
rotation rate exists such that relative to those rotating axes the electric and
magnetic fields are parallel and orthogonal to the spheroid which is thus an
equipotential in those axes. All the finite Carter separable systems without
magnetic monopoles or gravomagnetic NUT monopoles have the same gyromagnetic
ratio as the Dirac electron.Comment: 9 pages; accepted for publication in Class. Quantum Gra
Theory and astrophysical consequences of a magnetized torus around a rapidly rotating black hole
(Abbrev.) We analyze the topology, lifetime, and emissions of a torus around
a black hole formed in hypernovae and black hole-neutron star coalescence. The
torus is ab initio uniformly magnetized, represented by two counter oriented
current-rings, and develops a state of suspended accretion against a "magnetic
wall" around the black hole. Magnetic stability of the torus gives rise to a
new fundamental limit EB/Ek<0.1 for the ratio of poloidal magnetic field
energy-to-kinetic energy. The lifetime of rapid spin of the black hole is
effectively defined by the timescale of dissipation of black hole-spin energy
in the horizon, and satisfies T= 40s (MH/7MSun)(R/6MH)^4(0.03MH/MT) for a black
hole of mass MH surrounded by a torus of mass MT and radius R. The torus
converts a major fraction Egw/Erot=0.1 into gravitational radiation through a
finite number of multipole mass-moments, and a smaller fraction into MeV
neutrinos and baryon-rich winds. At a source distance of 100Mpc, these
emissions over N=2e4 periods give rise to a characteristic strain amplitude
\sqrt{N}hchar=6e-21. We argue that torus winds create an open magnetic
flux-tube on the black hole, which carries a minor and standard fraction
Ej/Erot=1e-3 in baryon-poor outflows to infinity. We identify this baryon poor
output of tens of seconds with GRBs with contemporaneous and strongly
correlated emissions in gravitational radiation, conceivably at multiple
frequencies. Ultimately, this leaves a black hole binary surrounded by a
supernova remnant.Comment: To appear in ApJ (44p
An Action for Black Hole Membranes
The membrane paradigm is the remarkable view that, to an external observer, a
black hole appears to behave exactly like a dynamical fluid membrane, obeying
such pre-relativistic equations as Ohm's law and the Navier-Stokes equation. It
has traditionally been derived by manipulating the equations of motion. Here we
provide an action formulation of this picture, clarifying what underlies the
paradigm, and simplifying the derivations. Within this framework, we derive
previous membrane results, and extend them to dyonic black hole solutions. We
discuss how it is that an action can produce dissipative equations. Using a
Euclidean path integral, we show that familiar semi-classical thermodynamic
properties of black holes also emerge from the membrane action. Finally, in a
Hamiltonian description, we establish the validity of a minimum entropy
production principle for black holes.Comment: LaTeX, 30 Pages, minor editorial change
Gravitomagnetism and Relative Observer Clock Effects
The gravitomagnetic clock effect and the Sagnac effect for circularly
rotating orbits in stationary axisymmetric spacetimes are studied from a
relative observer point of view, clarifying their relationships and the roles
played by special observer families. In particular Semer\'ak's recent
characterization of extremely accelerated observers in terms of the two-clock
clock effect is shown to be complemented by a similarly special property of the
single-clock clock effect.Comment: 19 pages, LaTeX, IOP macros with package epsf and 1 eps figure, to
appear in Classical and Quantum Gravity, slight revisio
Znajek-Damour Horizon Boundary Conditions with Born-Infeld Electrodynamics
In this work, the interaction of electromagnetic fields with a rotating
(Kerr) black hole is explored in the context of Born-Infeld (BI) theory of
electromagnetism instead of standard Maxwell theory and particularly BI theory
versions of the four horizon boundary conditions of Znajek and Damour are
derived. Naturally, an issue to be addressed is then whether they would change
from the ones given in Maxwell theory context and if they would, how.
Interestingly enough, as long as one employs the same local null tetrad frame
as the one adopted in the works by Damour and by Znajek to read out physical
values of electromagnetic fields and fictitious surface charge and currents on
the horizon, it turns out that one ends up with exactly the same four horizon
boundary conditions despite the shift of the electrodynamics theory from a
linear Maxwell one to a highly non-linear BI one. Close inspection reveals that
this curious and unexpected result can be attributed to the fact that the
concrete structure of BI equations happens to be such that it is
indistinguishable at the horizon to a local observer, say, in Damour's local
tetrad frame from that of standard Maxwell theory.Comment: 38 pages, Revtex, typos corrected, accepted for publication in Phys.
Rev.
The Stretched Horizon and Black Hole Complementarity
Three postulates asserting the validity of conventional quantum theory,
semi-classical general relativity and the statistical basis for thermodynamics
are introduced as a foundation for the study of black hole evolution. We
explain how these postulates may be implemented in a ``stretched horizon'' or
membrane description of the black hole, appropriate to a distant observer. The
technical analysis is illustrated in the simplified context of 1+1 dimensional
dilaton gravity. Our postulates imply that the dissipative properties of the
stretched horizon arise from a course graining of microphysical degrees of
freedom that the horizon must possess. A principle of black hole
complementarity is advocated. The overall viewpoint is similar to that
pioneered by 't~Hooft but the detailed implementation is different.Comment: (some misprints in equations have been fixed), 48 pages (including
figures), SU-ITP-93-1
Coulomb field of an accelerated charge: physical and mathematical aspects
The Maxwell field equations relative to a uniformly accelerated frame, and
the variational principle from which they are obtained, are formulated in terms
of the technique of geometrical gauge invariant potentials. They refer to the
transverse magnetic (TM) and the transeverse electric (TE) modes. This gauge
invariant "2+2" decomposition is used to see how the Coulomb field of a charge,
static in an accelerated frame, has properties that suggest features of
electromagnetism which are different from those in an inertial frame. In
particular, (1) an illustrative calculation shows that the Larmor radiation
reaction equals the electrostatic attraction between the accelerated charge and
the charge induced on the surface whose history is the event horizon, and (2) a
spectral decomposition of the Coulomb potential in the accelerated frame
suggests the possibility that the distortive effects of this charge on the
Rindler vacuum are akin to those of a charge on a crystal lattice.Comment: 27 pages, PlainTex. Related papers available at
http://www.math.ohio-state.edu/~gerlac
Magnetic Alignment Process : A New Mechanism for Extracting Energy from Rotating Black Holes
As a complementary or companion process to the Blandford-Znajek mechanism for
the rotational energy extraction from a Kerr black hole to serve as a viable
model for the central engine of quasar, AGN and even GRB, the magnetic
alignment process is proposed. In contrast to the environment assumed in the
Blandford-Znajek mechanism in which the rotating hole's spin axis and the
asymptotic direction of the magnetic field are aligned, this new process
operates when they are generally misaligned which obviously is the more natural
situation likely to happen. The time scales over which these two processes take
place and the total radiated powers released at the horizon by them have been
estimated and found to be nearly comparable. This may imply that in a random,
non-axisymmetric configuration, the magnetic alignment process would operate
first during which some of the hole's rotational energy is released and upon
completion of the alignment, the Blandford-Znajek mechanism may follow and the
rest of the hole's rotational energy, if any left, would be further released.Comment: 15 pages, Revtex, Comments and a reference adde
Astrophysical Origins of Ultrahigh Energy Cosmic Rays
In the first part of this review we discuss the basic observational features
at the end of the cosmic ray energy spectrum. We also present there the main
characteristics of each of the experiments involved in the detection of these
particles. We then briefly discuss the status of the chemical composition and
the distribution of arrival directions of cosmic rays. After that, we examine
the energy losses during propagation, introducing the Greisen-Zaptsepin-Kuzmin
(GZK) cutoff, and discuss the level of confidence with which each experiment
have detected particles beyond the GZK energy limit. In the second part of the
review, we discuss astrophysical environments able to accelerate particles up
to such high energies, including active galactic nuclei, large scale galactic
wind termination shocks, relativistic jets and hot-spots of Fanaroff-Riley
radiogalaxies, pulsars, magnetars, quasar remnants, starbursts, colliding
galaxies, and gamma ray burst fireballs. In the third part of the review we
provide a brief summary of scenarios which try to explain the super-GZK events
with the help of new physics beyond the standard model. In the last section, we
give an overview on neutrino telescopes and existing limits on the energy
spectrum and discuss some of the prospects for a new (multi-particle)
astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used
to probe new physics beyond the electroweak scale.Comment: Higher resolution version of Fig. 7 is available at
http://www.angelfire.com/id/dtorres/down3.html. Solicited review article
prepared for Reports on Progress in Physics, final versio