1,721,041 research outputs found
Gravitational waves from pulsations of neutron stars described by realistic equations of state
Full text linkIn this work we discuss the time evolution of nonspherical perturbations of a nonrotating neutron star described by a realistic equation of state (EOS). We analyze 10 different EOS for a large sample of neutron star models. Various kinds of generic initial data are evolved and the gravitational signals are computed. We focus on the dynamical excitation of fluid and spacetime modes and extract the corresponding frequencies. We employ a constrained numerical algorithm based on standard finite-differencing schemes which permits stable and long-term evolutions. Our code provides accurate waveforms and allows one to capture, via Fourier analysis, the frequencies of the fluid modes with an accuracy comparable to that of frequency-domain calculations. The results we present here are useful for providing comparisons with simulations of nonlinear oscillations of (rotating) neutron star models as well as test beds for 3D nonlinear codes. © 2008 The American Physical Society
Improved effective-one-body description of coalescing nonspinning black-hole binaries and its numerical-relativity completion
Full text linkModeling the Complete Gravitational Wave Spectrum of Neutron Star Mergers
Full text linkIn the context of neutron star mergers, we study the gravitational wave spectrum of the merger remnant using numerical relativity simulations. Postmerger spectra are characterized by a main peak frequency f_2 related to the particular structure and dynamics of the remnant hot hypermassive neutron star. We show that f_2 is correlated with the tidal coupling constant κ^T_2 that characterizes the binary tidal interactions during the late-inspiral merger. The relation f_2 (κ^T_2) depends very weakly on the binary total mass, mass ratio, equation of state, and thermal effects. This observation opens up the possibility of developing a model of the gravitational spectrum of every merger unifying the late-inspiral and postmerger descriptions
Time delay in binary systems
Full text linkThe aim of this paper is to study the time delay on electromagnetic signals propagating across a binary stellar system. We focus on the antisymmetric gravitomagnetic contribution due to the angular momentum of one of the stars of the pair. Considering a pulsar as the source of the signals, the effect would be manifest both in the arrival times of the pulses and in the frequency shift of their Fourier spectra. We derive the appropriate formulas and we discuss the influence of different configurations on the observability of gravitomagnetic effects. We argue that the recently discovered PSR J0737-3039 binary system does not permit the detection of the effects because of the large size of the eclipsed region
Gravitational waves from nonlinear couplings of radial and polar nonradial modes in relativistic stars
No full textThe postbounce oscillations of newly-born relativistic stars are expected to lead to gravitational-wave emission through the excitation of nonradial oscillation modes. At the same time, the star is oscillating in its radial modes, with a central density variation that can reach several percent. Nonlinear couplings between radial oscillations and polar nonradial modes lead to the appearance of combination frequencies (sums and differences of the linear mode frequencies). We study such combination frequencies using a gauge-invariant perturbative formalism, which includes bilinear coupling terms between different oscillation modes. For typical values of the energy stored in each mode we find that gravitational waves emitted at combination frequencies could become detectable in galactic core-collapse supernovae with advanced interferometric or wideband resonant detectors
Horizon-absorption effects in coalescing black-hole binaries: An effective-one-body study of the nonspinning case
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Factorization and resummation: A new paradigm to improve gravitational wave amplitudes
No full textInternational audienceWe introduce a new resummed analytical form of the post-Newtonian (PN), factorized, multipolar amplitude corrections fℓm of the effective-one-body (EOB) gravitational waveform of spinning, nonprecessing, circularized, coalescing black hole binaries (BBHs). This stems from the following two-step paradigm: (i) the factorization of the orbital (spin-independent) terms in fℓm; (ii) the resummation of the residual spin (or orbital) factors. We find that resumming the residual spin factor by taking its inverse resummed (iResum) is an efficient way to obtain amplitudes that are more accurate in the strong-field, fast-velocity regime. The performance of the method is illustrated on the ℓ=2 and m=(1,2) waveform multipoles, both for a test mass orbiting around a Kerr black hole and for comparable-mass BBHs. In the first case, the iResum fℓm’s are much closer to the corresponding “exact” functions (obtained by numerically solving the Teukolsky equation) up to the light ring than the nonresummed ones, especially when the black-hole spin is nearly extremal. The iResum paradigm is also more efficient than including higher post-Newtonian terms (up to 20PN order): the resummed 5PN information yields per se a rather good numerical or analytical agreement at the last stable orbit and a well-controlled behavior up to the light ring. For comparable mass binaries (including the highest PN-order information available, 3.5PN), comparing EOB with numerical relativity (NR) data shows that the EOB/NR fractional disagreement at merger, without NR calibration of the EOB waveform, is generically reduced by iResum, from 40% of the usual approach to just a few percent. This suggests that EOBNR waveform models for coalescing BBHs may be improved by using iResum amplitudes
A new gravitational wave generation algorithm for particle perturbations of the Kerr spacetime
Full text linkWe present a new approach to solve the 2+1 Teukolsky equation for gravitational perturbations of a Kerr black hole. Our approach relies on a new horizon penetrating, hyperboloidal foliation of Kerr spacetime and spatial compactification. In particular, we present a framework for waveform generation from point-particle perturbations. Extensive tests of a time domain implementation in the Teukode code are presented. The code can efficiently deliver waveforms at future null infinity. The accuracy and convergence of the waveforms' phase and amplitude is demonstrated. As a first application of the method, we compute the gravitational waveforms from inspiraling and coalescing black-hole binaries in the large-mass-ratio limit. The smaller mass black hole is modeled as a point particle whose dynamics is driven by an effective-one-body-resummed analytical radiation reaction force. We compare the analytical, mechanical angular momentum loss (computed using two different prescriptions) to the gravitational wave angular momentum flux. We find that higher-order post-Newtonian corrections are needed to improve the consistency for rapidly spinning binaries. We characterize the multipolar waveform as a function of the black-hole spin. Close to merger, the subdominant multipolar amplitudes (notably the m = 0 ones) are enhanced for retrograde orbits with respect to prograde ones. We argue that this effect mirrors nonnegligible deviations from the circularity of the dynamics during the late-plunge and merger phase. For the first time, we compute the gravitational wave energy flux flowing into the black hole during the inspiral using a time-domain formalism proposed by Poisson. Finally, a self-consistent, iterative method to compute the gravitational wave fluxes at leading-order in the mass of the particle is developed. The method can be used alternatively to the analytical radiation reaction in cases where the analytical information is poor or not sufficient. Specifically, we apply it to compute dynamics and waveforms for a rapidly rotating black hole with dimensionless spin parameter _(â = + 0.9). For this case, the simulation with the consistent flux differs from the one with the analytical flux by ~ 35 gravitational wave cycles over a total of about 250 cycles. In this simulation the horizon absorption accounts for about +5 gravitational wave cycles
Modeling the Dynamics of Tidally Interacting Binary Neutron Stars up to the Merger
Full text linkThe data analysis of the gravitational wave signals emitted by coalescing
neutron star binaries requires the availability of an accurate analytical
representation of the dynamics and waveforms of these systems. We propose an
effective-one-body (EOB) model that describes the general relativistic dynamics
of neutron star binaries from the early inspiral up to merger. Our EOB model
incorporates an enhanced attractive tidal potential motivated by recent
analytical advances in the post-Newtonian and gravitational self-force
description of relativistic tidal interactions. No fitting parameters are
introduced for the description of tidal interaction in the late, strong-field
dynamics. We compare the model energetics and the gravitational wave phasing
with new high-resolution multi-orbit numerical relativity simulations of
equal-mass configurations with different equations of state. We find agreement
within the uncertainty of the numerical data for all configurations. Our model
is the first semi-analytical model which captures the tidal amplification
effects close to merger. It thereby provides the most accurate analytical
representation of binary neutron star dynamics and waveforms currently
available
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