245 research outputs found
Exotic orbits due to spin-spin coupling around Kerr black holes
We report exotic orbital phenomena of spinning test particles orbiting around
a Kerr black hole, i.e., some orbits of spinning particles are asymmetrical
about the equatorial plane. When a nonspinning test particle orbits around a
Kerr black hole in a strong field region, due to relativistic orbital
precessions, the pattern of trajectories is symmetrical about the equatorial
plane of the Kerr black hole. However, the patterns of the spinning particles'
orbit are no longer symmetrical about the equatorial plane for some orbital
configurations and large spins. We argue that these asymmetrical patterns come
from the spin-spin interactions between spinning particles and Kerr black
holes, because the directions of spin-spin forces can be arbitrary, and
distribute asymmetrically about the equatorial plane.Comment: 15 pages, 20 figure
Determining the nature of white dwarfs from low-frequency gravitational waves
An extreme-mass-ratio system composed of a white dwarf (WD) and a massive
black hole can be observed by the low-frequency gravitational wave detectors,
such as the Laser Interferometer Space Antenna (LISA). When the mass of the
black hole is around , the WD will be disrupted by the
tidal interaction at the final inspiraling stage. The event position and time
of the tidal disruption of the WD can be accurately determined by the
gravitational wave signals. Such position and time depend upon the mass of the
black hole and especially on the density of the WD. We present the theory by
using LISA-like gravitational wave detectors, the mass-radius relation and then
the equations of state of WDs could be strictly constrained (accuracy up to
). We also point out that LISA can accurately predict the disruption
time of a WD, and forecast the electromagnetic follow-up of this tidal
disruption event.Comment: 7 pages, 2 figure
The gravitational time delay in the field of a slowly moving body with arbitrary multipoles
We calculate the time delay of light in the gravitational field of a slowly
moving body with arbitrary multipoles (mass and spin multipole moments) by the
Time-Transfer-Function (TTF) formalism. The parameters we use, first introduced
by Kopeikin for a gravitational source at rest, make the integration of the TTF
very elegant and simple. Results completely coincide with expressions from the
literature. The results for a moving body (with constant velocity) with
complete multipole-structure are new, according to our knowledge.Comment: 9 pages, no figure
Electromagnetic and gravitational radiation from the coherent oscillation of electron-positron pairs and fields
Integrating equations of particle-number and energy-momentum conservation and
Maxwell field equations, we study the oscillation and drift of electron and
positron pairs coherently with fields after these pairs are produced in
external electromagnetic fields. From the electric current of oscillating
pairs, we obtain the energy spectrum of electromagnetic dipole radiation. This
narrow spectrum is so peculiar that the detection of such radiation can
identify pair production and oscillation in strong laser fields. We also obtain
the energy spectrum of gravitational quadrapole radiation from the
energy-momentum tensor of oscillating pairs and fields. Thus, we discuss the
generation of gravitational waves on the basis of rapid development of strong
laser fields.Comment: 6 pages, 4 figure
Gravitational waves with dark matter minispikes: the combined effect
It was shown that the dark matter(DM) minihalo around an intermediate mass
black hole(IMBH) can be redistributed into a cusp, called the DM minispike. We
consider an intermediate-mass-ratio inspiral consisting of an IMBH harbored in
a DM minispike with nonannihilating DM particles and a small black hole(BH)
orbiting around it. We investigate gravitational waves(GWs) produced by this
system and analyze the waveforms with the comprehensive consideration of
gravitational pull, dynamical friction and accretion of the minispike and
calculate the time difference and phase difference caused by it. We find that
for a certain range of frequency, the inspiralling time of the system is
dramatically reduced for smaller central IMBH and large density of DM. For the
central IMBH with , the time of merger is ahead, which can be
distinguished by LISA, Taiji and Tianqin. We focus on the effect of accretion
and compare it with that of gravitational pull and friction. We find that the
accretion mass is a small quantity compared to the initial mass of the small BH
and the accretion effect is inconspicuous compared with friction. However, the
accumulated phase shift caused by accretion is large enough to be detected by
LISA, Taiji and Tianqin, which indicate that the accretion effect can not be
ignored in the detection of GWs.Comment: 10 pages, 14 figure
Chaos and dynamics of spinning particles in Kerr spacetime
We study chaos dynamics of spinning particles in Kerr spacetime of rotating
black holes use the Papapetrou equations by numerical integration. Because of
spin, this system exists many chaos solutions, and exhibits some exceptional
dynamic character. We investigate the relations between the orbits chaos and
the spin magnitude S, pericenter, polar angle and Kerr rotation parameter a by
means of a kind of brand new Fast Lyapulov Indicator (FLI) which is defined in
general relativity. The classical definition of Lyapulov exponent (LE) perhaps
fails in curve spacetime. And we emphasize that the Poincar\'e sections cannot
be used to detect chaos for this case. Via calculations, some new interesting
conclusions are found: though chaos is easier to emerge with bigger S, but not
always depends on S monotonically; the Kerr parameter a has a contrary action
on the chaos occurrence. Furthermore, the spin of particles can destroy the
symmetry of the orbits about the equatorial plane. And for some special initial
conditions, the orbits have equilibrium points.Comment: 17 pages, 12 figure
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