10,800 research outputs found
Master equation solutions in the linear regime of characteristic formulation of general relativity
From the field equations in the linear regime of the characteristic
formulation of general relativity, Bishop, for a Schwarzschild's background,
and M\"adler, for a Minkowski's background, were able to show that it is
possible to derive a fourth order ordinary differential equation, called master
equation, for the metric variable of the Bondi-Sachs metric. Once ,
another Bondi-Sachs potential, is obtained from the field equations, and is
obtained from the master equation, the other metric variables are solved
integrating directly the rest of the field equations. In the past, the master
equation was solved for the first multipolar terms, for both the Minkowski's
and Schwarzschild's backgrounds. Also, M\"adler recently reported a
generalisation of the exact solutions to the linearised field equations when a
Minkowski's background is considered, expressing the master equation family of
solutions for the vacuum in terms of Bessel's functions of the first and the
second kind. Here, we report new solutions to the master equation for any
multipolar moment , with and without matter sources in terms only of the
first kind Bessel's functions for the Minkowski, and in terms of the Confluent
Heun's functions (Generalised Hypergeometric) for radiative (nonradiative) case
in the Schwarzschild's background. We particularize our families of solutions
for the known cases for reported previously in the literature and find
complete agreement, showing the robustness of our results.Comment: 19 page
Gravitational radiation by point particle eccentric binary systems in the linearised characteristic formulation of general relativity
We study a binary system composed of point particles of unequal masses in
eccentric orbits in the linear regime of the characteristic formulation of
general relativity, generalising a previous study found in the literature in
which a system of equal masses in circular orbits is considered. We also show
that the boundary conditions on the time-like world tubes generated by the
orbits of the particles can be extended beyond circular orbits. Concerning the
power lost by the emission of gravitational waves, it is directly obtained from
the Bondi's News function. It is worth stressing that our results are
completely consistent, because we obtain the same result for the power derived
by Peters and Mathews, in a different approach, in their seminal paper of 1963.
In addition, the present study constitutes a powerful tool to construct
extraction schemes in the characteristic formalism to obtain the gravitational
radiation produced by binary systems during the inspiralling phase.Comment: 16 pages, 2 figures, DOI 10.1007/s10714-016-2038-
Point Particle Binary System with Components of Different Masses in the Linear Regime of the Characteristic Formulation of General Relativity
A study of binary systems composed of two point particles with different
masses in the linear regime of the characteristic formulation of general
relativity in a Minkowski background is provided. The present paper generalizes
a previous study find in the literature. The boundary conditions at the world
tubes generated by the particle's orbits are explored, when the metric
variables are decomposed in spin-weighted spherical harmonics. The power lost
by the emission of gravitational waves is computed using the News Bondi's
functions. The power found is nothing but the well-known result for the power
obtained by Peters and Mathews in a different approach. This agreement shows
the consistency of the approach considered here. The contribution to the
gravitational radiation of several multipole terms is also shown.Comment: 16 pages, 3 figure
Gravitational wave background from neutron star phase transition
We study the generation of a stochastic gravitational wave (GW) background
produced by a population of neutron stars (NSs) which go over a hadron-quark
phase transition in its inner shells. We obtain, for example, that the NS phase
transition, in cold dark matter scenarios, could generate a stochastic GW
background with a maximum amplitude of , in the
frequency band for stars forming at
redshifts of up to We study the possibility of detection of this
isotropic GW background by correlating signals of a pair of Advanced LIGO
observatories.Comment: 17 pages, 5 figure
A New Method to Calculate the Stochastic Background of Gravitational Waves Generated by Compact Binaries
In the study of gravitational waves (GWs), the stochastic background
generated by compact binary systems are among the most important kinds of
signals. The reason for such an importance has to do with their probable
detection by the interferometric detectors [such as the Advanced LIGO (ALIGO)
and Einstein Telescope (ET)] in the near future. In this paper we are concerned
with, in particular, the stochastic background of GWs generated by double
neutron star (DNS) systems in circular orbits during their periodic and
quasi--periodic phases. Our aim here is to describe a new method to calculate
such spectra, which is based on an analogy with a problem of Statistical
Mechanics. Besides, an important characteristic of our method is to consider
the time evolution of the orbital parameters.Comment: 10 pages, 2 figure
Stochastic Background of Gravitational Waves Generated by Eccentric Neutron Star Binaries
Binary systems emit gravitational waves in a well-known pattern; for binaries
in circular orbits, the emitted radiation has a frequency that is twice the
orbital frequency. Systems in eccentric orbits, however, emit gravitational
radiation in the higher harmonics too. In this paper, we are concerned with the
stochastic background of gravitational waves generated by double neutron star
systems of cosmological origin in eccentric orbits. We consider in particular
the long-lived systems, that is, those binaries for which the time to
coalescence is longer than the Hubble time (Gyr). Thus, we consider
double neutron stars with orbital frequencies ranging from to
Hz. Although in the literature some papers consider the
spectra generated by eccentric binaries, there is still space for alternative
approaches for the calculation of the backgrounds. In this paper, we use a
method that consists in summing the spectra that would be generated by each
harmonic separately in order to obtain the total background. This method allows
us to clearly obtain the influence of each harmonic on the spectra. In
addition, we consider different distribution functions for the eccentricities
in order to investigate their effects on the background of gravitational waves
generated. At last, we briefly discuss the detectability of this background by
space-based gravitational wave antennas and pulsar timing arrays.Comment: 6 pages, 5 figure
The rings of Chariklo under close encounters with the giant planets
The Centaur population is composed by minor bodies wandering between the
giant planets and that frequently perform close gravitational encounters with
these planets, which leads to a chaotic orbital evolution. Recently, the
discovery of two well-defined narrow rings was announced around the Centaur
10199 Chariklo. The rings are assumed to be in the equatorial plane of Chariklo
and to have circular orbits. The existence a well-defined system of rings
around a body in such perturbed orbital region poses an interesting new
problem. Are the rings of Chariklo stable when perturbed by close gravitational
encounters with the giant planets? Our approach to address this question
consisted of forward and backward numerical simulations of 729 clones of
Chariklo, with similar initial orbits, for a period of 100 Myrs. We found, on
average, that each clone suffers along its lifetime more than 150 close
encounters with the giant planets within one Hill radius of the planet in
question. We identified some extreme close encounters able to significantly
disrupt or to disturb the rings of Chariklo. About 3% of the clones lose the
rings and about 4% of the clones have the ring significantly disturbed.
Therefore, our results show that in most of the cases (more than 90%) the close
encounters with the giant planets do not affect the stability of the rings in
Chariklo-like systems. Thus, if there is an efficient mechanism that creates
the rings, then these structures may be common among these kinds of Centaurs.Comment: 11 pages. Accepted for publication in AP
The Gravitational Wave Background From Coalescing Compact Binaries: A New Method
Gravitational waves are perturbations in the spacetime that propagate at the
speed of light. The study of such phenomenon is interesting because many
cosmological processes and astrophysical objects, such as binary systems, are
potential sources of gravitational radiation and can have their emissions
detected in the near future by the next generation of interferometric
detectors. Concerning the astrophysical objects, an interesting case is when
there are several sources emitting in such a way that there is a superposition
of signals, resulting in a smooth spectrum which spans a wide range of
frequencies, the so-called stochastic background. In this paper, we are
concerned with the stochastic backgrounds generated by compact binaries (i.e.
binary systems formed by neutron stars and black holes) in the coalescing
phase. In particular, we obtain such backgrounds by employing a new method
developed in our previous studies.Comment: 8 pages, 2 figure
Forecast constraints on gravity with gravitational waves from compact binary coalescences
The direct detection of gravitational waves (GWs) opened a new chapter in the
modern cosmology to probe possible deviations from the general relativity (GR)
theory. In the present work, we investigate for the first time the modified GW
form propagation from the inspiraling of compact binary systems within the
context of gravity in order to obtain new forecasts/constraints on the
free parameter of the theory. First, we show that the modified waveform differs
from the GR waveform essentially due to induced corrections on the GWs
amplitude. Then, we discuss the forecasts on the gravity assuming
simulated sources of GWs as black hole binaries, neutron star binaries and
black hole - neutron star binary systems, which emit GWs in the frequency band
of the Advanced LIGO (aLIGO) interferometer and of the third generation
Einstein Telescope (ET). We show that GWs sources detected within the aLIGO
sensitivity can return estimates of the same order of magnitude of the current
cosmological observations. On the other hand, detection within the ET
sensitivity can improve by up to 2 orders of magnitude the current bound on the
gravity. Therefore, the statistical accuracy that can be achieved by
future ground based GW observations, mainly with the ET detector (and planed
detectors with a similar sensitivity), can allow strong bounds on the free
parameter of the theory, and can be decisive to test the theory of gravitation.Comment: 13 pages, 9 captioned figures. Version published in PR
Formation of the G-ring arc
Since 2004, the images obtained by Cassini spacecraft's on-board cameras have
revealed the existence of several small satellites in the Saturn system. Some
of these small satellites are embedded in arcs of particles. While these
satellites and their arcs are known to be in corotation resonances with Mimas,
their origin remains unknown. This work investigates one possible process for
capturing bodies into a corotation resonance, which involves raising the
eccentricity of a perturbing body. Therefore, through numerical simulations and
analytical studies, we show a scenario that the excitation of Mimas'
eccentricity could capture particles in a corotation resonance and given a
possible explanation for the origin for the arcs.Comment: 8 pages, 7 figures and 1 tabl
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