65 research outputs found
Angular momentum effects in weak gravitational fields
It is shown that, contrary to what is normally expected, it is possible to
have angular momentum effects on the geometry of space time at the laboratory
scale, much bigger than the purely Newtonian effects. This is due to the fact
that the ratio between the angular momentum of a body and its mass, expressed
as a length, is easily greater than the mass itself, again expressed as a
length.Comment: LATEX, 8 page
Generalized pseudo-Newtonian potential for studying accretion disk dynamics in off-equatorial planes around rotating black holes: Description of a vector potential
We prescribe a pseudo-Newtonian vector potential for studying accretion disks
around Kerr black holes. The potential is useful to study the inner properties
of disk not confined to the equatorial plane where general relativistic effect
is indispensable. Therefore, we incorporate the essential properties of the
metric at the inner radii through the pseudo-Newtonian potential derived from
the general Kerr spacetime. The potential, reproducing most of the salient
features of the general-relativity, is valid for entire regime of Kerr
parameter. It reproduces the last stable circular orbit exactly as that in the
Kerr geometry. It also reproduces last bound orbit and energy at last stable
circular orbit with a maximum error ~7% and ~15% respectively upto an orbital
inclination 30 degree.Comment: 22 AASTeX pages including 5 postscript figures; Accepted for
publication in The Astrophysical Journa
Approaches to the Monopole-Dynamic Dipole Vacuum Solution Concerning the Structure of its Ernst's Potential on the Symmetry Axis
The FHP algorithm allows to obtain the relativistic multipole moments of a
vacuum stationary axisymmetric solution in terms of coefficients which appear
in the expansion of its Ernst's potential on the symmetry axis. First of all,
we will use this result in order to determine, at a certain approximation
degree, the Ernst's potential on the symmetry axis of the metric whose only
multipole moments are mass and angular momentum.
By using Sibgatullin's method we analyse a series of exacts solutions with
the afore mentioned multipole characteristic. Besides, we present an
approximate solution whose Ernst's potential is introduced as a power series of
a dimensionless parameter. The calculation of its multipole moments allows us
to understand the existing differences between both approximations to the
proposed pure multipole solution.Comment: 24 pages, plain TeX. To be published in General Relativity and
Gravitatio
Non-Relativistic Limit of Dirac Equations in Gravitational Field and Quantum Effects of Gravity
Based on unified theory of electromagnetic interactions and gravitational
interactions, the non-relativistic limit of the equation of motion of a charged
Dirac particle in gravitational field is studied. From the Schrodinger equation
obtained from this non-relativistic limit, we could see that the classical
Newtonian gravitational potential appears as a part of the potential in the
Schrodinger equation, which can explain the gravitational phase effects found
in COW experiments. And because of this Newtonian gravitational potential, a
quantum particle in earth's gravitational field may form a gravitationally
bound quantized state, which had already been detected in experiments. Three
different kinds of phase effects related to gravitational interactions are
discussed in this paper, and these phase effects should be observable in some
astrophysical processes. Besides, there exists direct coupling between
gravitomagnetic field and quantum spin, radiation caused by this coupling can
be used to directly determine the gravitomagnetic field on the surface of a
star.Comment: 12 pages, no figur
Self-gravitating warped discs around supermassive black holes
We consider warped equilibrium configurations for stellar and gaseous disks
in the Keplerian force-field of a supermassive black hole, assuming that the
self-gravity of the disk provides the only acting torques. Modeling the disk as
a collection of concentric circular rings, and computing the torques in the
non-linear regime, we show that stable, strongly warped precessing equilibria
are possible. These solutions exist for a wide range of disk-to-black hole mass
ratios , can span large warp angles of up to ,
have inner and outer boundaries, and extend over a radial range of a factor of
typically two to four. These equilibrium configurations obey a scaling relation
such that in good approximation \phidot/\Omega\propto M_d/M_{bh} where
\phidot is the (retrograde) precession frequency and is a
characteristic orbital frequency in the disk. Stability was determined using
linear perturbation theory and, in a few cases, confirmed by numerical
integration of the equations of motion. Most of the precessing equilibria are
found to be stable, but some are unstable. The main result of this study is
that highly warped disks near black holes can persist for long times without
any persistent forcing other than by their self-gravity. The possible relevance
of this to galactic nuclei is briefly discussed.Comment: 13 pages, 21 figures, published in MNRA
Phenomenology of the Lense-Thirring effect in the Solar System
Recent years have seen increasing efforts to directly measure some aspects of
the general relativistic gravitomagnetic interaction in several astronomical
scenarios in the solar system. After briefly overviewing the concept of
gravitomagnetism from a theoretical point of view, we review the performed or
proposed attempts to detect the Lense-Thirring effect affecting the orbital
motions of natural and artificial bodies in the gravitational fields of the
Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of
the impact of several sources of systematic uncertainties of dynamical origin
to realistically elucidate the present and future perspectives in directly
measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in
Astrophysics and Space Science (ApSS). Some uncited references in the text
now correctly quoted. One reference added. A footnote adde
On the exhaust of electromagnetic drive
Recent reports about propulsion without reaction mass have been met on one hand with enthusiasm and on the other hand with some doubts. Namely, closed metal cavities, when fueled with microwaves, have delivered thrust that could eventually maintain satellites on orbits using solar power. However, the measured thrust appears to be without any apparent exhaust. Thus the Law of Action-Reaction seems to have been violated. We consider the possibility that the exhaust is in a form that has so far escaped both experimental detection and theoretical attention. In the thruster's cavity microwaves interfere with each other and invariably some photons will also end up co-propagating with opposite phases. At the destructive interference electromagnetic fields cancel. However, the photons themselves do not vanish for nothing but continue in propagation. These photon pairs without net electromagnetic field do not reflect back from the metal walls but escape from the resonator. By this action momentum is lost from the cavity which, according to the conservation of momentum, gives rise to an equal and opposite reaction. We examine theoretical corollaries and practical concerns that follow from the paired-photon conclusion. (C) 2016 Author(s).Peer reviewe
Black hole spin: theory and observation
In the standard paradigm, astrophysical black holes can be described solely
by their mass and angular momentum - commonly referred to as `spin' - resulting
from the process of their birth and subsequent growth via accretion. Whilst the
mass has a standard Newtonian interpretation, the spin does not, with the
effect of non-zero spin leaving an indelible imprint on the space-time closest
to the black hole. As a consequence of relativistic frame-dragging, particle
orbits are affected both in terms of stability and precession, which impacts on
the emission characteristics of accreting black holes both stellar mass in
black hole binaries (BHBs) and supermassive in active galactic nuclei (AGN).
Over the last 30 years, techniques have been developed that take into account
these changes to estimate the spin which can then be used to understand the
birth and growth of black holes and potentially the powering of powerful jets.
In this chapter we provide a broad overview of both the theoretical effects of
spin, the means by which it can be estimated and the results of ongoing
campaigns.Comment: 55 pages, 5 figures. Published in: "Astrophysics of Black Holes -
From fundamental aspects to latest developments", Ed. Cosimo Bambi, Springer:
Astrophysics and Space Science Library. Additional corrections mad
Improved upper bounds on Kaluza–Klein gravity with current Solar System experiments and observations
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