335 research outputs found

### Gravitomagnetic Accelerators

We study a simple class of time-dependent rotating Ricci-flat cylindrically
symmetric spacetime manifolds whose geodesics admit gravitomagnetic jets. The
helical paths of free test particles in these jets up and down parallel to the
rotation axis are analogous to those of charged particles in a magnetic field.
The jets are attractors. The jet speed asymptotically approaches the speed of
light. In effect, such source-free spacetime regions act as "gravitomagnetic
accelerators".Comment: 4 pages, 2 figures; v2: reference added; v3: slightly expanded
version accepted for publication in Phys. Lett.

### Tidal Dynamics in Kerr Spacetime

The motion of free nearby test particles relative to a stable equatorial
circular geodesic orbit about a Kerr source is investigated. It is shown that
the nonlinear generalized Jacobi equation can be transformed in this case to an
autonomous form. Tidal dynamics beyond the critical speed c/sqrt(2) is studied.
We show, in particular, that a free test particle vertically launched from the
circular orbit parallel or antiparallel to the Kerr rotation axis is tidally
accelerated if its initial relative speed exceeds c/sqrt(2). Possible
applications of our results to high-energy astrophysics are briefly mentioned.Comment: 15 pages, 3 figures; v2: slightly expanded version accepted for
publication in CQ

### On the Ionization of a Keplerian Binary System by Periodic Gravitational Radiation

The gravitational ionization of a Keplerian binary system via normally
incident periodic gravitational radiation of definite helicity is discussed.
The periodic orbits of the planar tidal equation are investigated on the basis
of degenerate continuation theory. The relevance of the Kolmogorov-Arnold-Moser
theory to the question of gravitational ionization is elucidated, and it is
conjectured that the process of ionization is closely related to the Arnold
diffusion of the perturbed system.Comment: 19 pages, REVTEX Style, To appear in JM

### Ultrarelativistic Motion: Inertial and Tidal Effects in Fermi Coordinates

Fermi coordinates are the natural generalization of inertial Cartesian
coordinates to accelerated systems and gravitational fields. We study the
motion of ultrarelativistic particles and light rays in Fermi coordinates and
investigate inertial and tidal effects beyond the critical speed c/sqrt(2). In
particular, we discuss the black-hole tidal acceleration mechanism for
ultrarelativistic particles in connection with a possible origin for
high-energy cosmic rays.Comment: 13 pages, 3 figures, slightly expanded version accepted for
publication in Class. Quantum Gra

### Tidal effects on magnetic gyration of a charged particle in Fermi coordinates

We examine the gyration motion of a charged particle, viewed from a reference
observer falling along the Z axis into a Schwarzschild black hole. It is
assumed that the magnetic field is constant and uniform along the Z axis, and
that the particle has a circular orbit in the X-Y plane far from the
gravitational source. When the particle as well as the reference observer
approaches the black hole, its orbit is disrupted by the tidal force. The final
plunging velocity increases in the non-relativistic case, but decreases if the
initial circular velocity exceeds a critical value, which is approximately
0.7c. This toy model suggests that disruption of a rapidly rotating star due to
a velocity-dependent tidal force may be quite different from that of a
non-relativistic star. The model also suggested that collapse of the orbit
after the disruption is slow in general, so that the particle subsequently
escapes outside the valid Fermi coordinates.Comment: 10 pages, 12 figure

### Chaos in the Kepler System

The long-term dynamical evolution of a Keplerian binary orbit due to the
emission and absorption of gravitational radiation is investigated. This work
extends our previous results on transient chaos in the planar case to the three
dimensional Kepler system. Specifically, we consider the nonlinear evolution of
the relative orbit due to gravitational radiation damping as well as external
gravitational radiation that is obliquely incident on the initial orbital
plane. The variation of orbital inclination, especially during resonance
capture, turns out to be very sensitive to the initial conditions. Moreover, we
discuss the novel phenomenon of chaotic transition.Comment: RevTeX, 22 pages, 6 figure

### Invariant tori for periodically perturbed oscillators

The response of an oscillator to a small amplitude periodic excitation is discussed. In particular, sufficient conditions are formulated for the perturbed oscillator to have an invariant torus in the phase cylinder. When such an invariant torus exists, some perturbed solutions are in the basin of attraction of this torus and are thus entrained to the dynamical behavior of the perturbed system on the torus. In particular, the perturbed solutions in the basin of attraction of the invariant torus are entrained to a subharmonic or to a quasi periodic motion

- â€¦