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Sketch of the effect of a large-amplitude GW traveling parallel to a uniform magnetic field frozen into an ambient ideal plasma, k B 0 at an arbitrary time. Here the
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The propagation of a gravitational wave (GW) through a magnetized plasma is considered. In particular, we study the excitation of fast magnetosonic waves (MSW) by a gravitational wave, using the linearized general-relativistic hydromagnetic equations. We derive the dispersion relation for the plasma, treating the gravitational wave as a perturbatio...
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... Apart from wobbling and merging neutron stars, other potential sources of GWs are coalescing compact binaries or black holes, quasi-normal modes of ringing black holes, the spinning-down effect observed in magnetars due to their enormous magnetic field, etc. (see, e.g., [6][7][8][9][10]). In each and every one of those cases, a potential interaction between GWs and astrophysical plasma present at the spot not only could play an essential role in the final outcome of the messenger's profile, but it could also give rise to new phenomena of particular interest (see, e.g., [11][12][13]), such as, e.g., the excitation of MHD modes-especially of magnetosonic waves (MSWs)-by the GW, i.e., the conversion of gravitational energy into EM energy (and vice versa). Searching for potential resonances in the interaction between MHD modes of magnetized plasma and GWs in a curved spacetime background is an essential first step towards that direction. ...
The general-relativistic (GR) magnetohydrodynamic (MHD) equations for a conductive plasma fluid are derived and discussed in the curved spacetime described by Thorne's metric tensor, i.e., a family of cosmological models with inherent anisotropy due to the existence of an ambient, large-scale magnetic field. In this framework, it is examined whether the magnetized plasma fluid that drives the evolution of such a model can be subsequently excited by a transient, plane-polarized gravitational wave (GW) or not. To do so, we consider the associated set of the perturbed equations of motion and integrate them numerically in order to study the evolution of instabilities triggered by the GW propagation. In particular, we examine to what extend perturbations of the electric and/or the magnetic field can be amplified due to a potential energy transfer from the GW to the electromagnetic (EM) degrees of freedom. The evolution of the perturbed quantities depends on four free parameters, namely, the conductivity of the fluid, σ; the speed of sound square, γ, which in this model may serve also as a measure of the inherent anisotropy; the GW frequency, ω_g ; and the associated angle of propagation with respect to the direction of the magnetic field, θ. We find that GW propagation in the anisotropic magnetized medium under consideration does excite several MHD modes; in other words, there is energy transfer from the gravitational to the EM degrees of freedom that can result in the acceleration of charged particles at the spot and in the subsequent damping of the GW.
... The recent detections of GWs [5][6][7][8] have corroborated the significance of these modes, providing grounds for such a focus. However, also of interest are GW interactions with matter and nonlinear GWs [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. The theory of such waves is more complicated. ...
... where ξ µ is a small vector field. A transformation (25) induces the following transformation of the total metric: ...
... This shows that the reduced field theory induced by the approximate action (24) is not strictly covariant; namely, S generally does change under coordinate transformations (25). These changes are O(a 4 ), so they are beyond the accuracy of our approximation and therefore do not invalidate the reduced theory. ...
Reduced theories of gravitational waves (GWs) often grapple with untangling the physical effects from coordinate artifacts. Here we show how to reinstate gauge invariance within a reduced theory of weakly nonlinear GWs in a general background metric and in the presence of matter. An exactly gauge-invariant ``quasilinear'' theory is proposed, in which GWs are governed by linear equations but also affect the background metric on scales large compared to their wavelength. As a corollary, the gauge-invariant geometrical optics of linear dispersive GWs in a general background is reported. We also show how gauge invariance can be maintained within a given accuracy if nonlinearities are included up to an arbitrary order in the GW amplitude.
... Therefore, the GW-EMW interaction is mainly related with the generation of electric currents in the plasma due to the perturbations in the trajectories of the charged particles by the passage of the GW through the medium [74]. The GW propagation along the direction of the background magnetic field does not generate currents in the plasma [73,74]. ...
... Therefore, the GW-EMW interaction is mainly related with the generation of electric currents in the plasma due to the perturbations in the trajectories of the charged particles by the passage of the GW through the medium [74]. The GW propagation along the direction of the background magnetic field does not generate currents in the plasma [73,74]. ...
... The GW-EMW coupling is more efficient if the waves are in coherence, i.e., if the frequencies satisfy some matching conditions and the relative wave phase remains unaltered for a long time [78]. In fact, this is a resonant condition [65,74,79]. Coherent interaction only requires that the frequencies coincide and that they have identical phase velocity. ...
Coalescence of binary neutron stars (BNSs) is one of the sources of gravitational waves (GWs) able to be detected by ground-based interferometric detectors. The event GW170817 was the first observed in the gravitational and electromagnetic spectra, showing through this joint analysis a certain compatibility with the models of short gamma-ray bursts (sGRBs) to explain the signature of this system. Due to the intense magnetic fields of the neutron stars, the plasma magnetosphere stays strongly magnetized and the propagation of the GW through plasma can excite magnetohydrodynamic (MHD) modes such as Alfv\'en and magnetosonic waves. The MHD modes carry energy and momentum through the plasma, suggesting a mechanism to accelerate the matter during the coalescence of the binaries, explaining some characteristics of the fireball model of the sGRBs. We present a semianalytical formalism to determine the energy transferred by the GW-MHD interaction during the inspiral phase of the stars. Using the inferred physical parameters for GW170817, we show that the energy in the plasma can reach maximum value $\sim 10^{35}\,{\rm J}$ ($\sim 10^{32}\,{\rm J}$) for the Alfv\'en mode (magnetosonic mode) if the angle formed between the background magnetic field and the GW propagation direction is $\theta = \pi / 4$. Particularly, for $\theta = \pi / 2$ only the magnetosonic mode is in coherence with the GWs. In this case, the excited energy in the plasma reaches maximum value $\sim 10^{36} {\rm J}$. If the magnetic field on the surface of the progenitors of the event GW170817 was $\sim 2\times 10^{9}\,{\rm T}$ then energies comparable to those inferred for the GRB 170817A could be obtained. In particular, our semianalytical formalism show consistence with the results obtained by other authors through full general relativistic magnetohydrodynamics (GRMHD) simulations. [ABRIDGED]
... Linear effects of GWs have long been studied in literature [10][11][12], particularly in the context of GW dispersion in gases and plasmas [13][14][15][16][17][18][19]. Some authors have also explored the associated nonlinear phenomena, such as the nonlinear memory effect [20][21][22][23], the contribution of the GW tail from backscattering off the background curvature [20,24], and certain GWplasma interactions [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. However, there remains another fundamental nonlinear effect, the "ponderomotive" effect, that is well-known for electromagnetic interactions [42-45] but has not yet received due attention in GW research. ...
Particles interacting with a prescribed quasimonochromatic gravitational wave (GW) exhibit secular (average) nonlinear dynamics that can be described by Hamilton's equations. We derive the Hamiltonian of this "ponderomotive" dynamics to the second order in the GW amplitude for a general background metric. For the special case of vacuum GWs, we show that our Hamiltonian is equivalent to that of a free particle in an effective metric, which we calculate explicitly. We also show that already a linear GW pulse displaces a particle from its unperturbed trajectory by a finite distance that is independent of the GW phase and proportional to the integral of the pulse intensity. This effect is independent from the nonlinear memory effects that has been known. We calculate the particle displacement analytically and show that our result is in agreement with numerical simulations. We also show how the Hamiltonian of the nonlinear averaged dynamics naturally leads to the concept of the linear gravitational susceptibility of a particle gas with an arbitrary phase-space distribution. We calculate this susceptibility explicitly to apply it, in a follow-up paper, toward studying self-consistent GWs in inhomogeneous media within the geometrical-optics approximation.
... 7 The interaction of GW with electromagnetic fields was investigated by several works (e.g., see Refs. 6,8 ), mainly the Ref., 9 which estimated the amount of energy transferred to MHD wave, by propagation of the monochromatic GW produced by the merger of NSs. The Alfvén wave (AW) is excited by h × , whereas the slow and fast magnetosonic wave (MSW) are coupled to h + of the GW. ...
The gravitational wave, through the strongly magnetized plasma surrounding the neutron stars, in the z-direction, deforms plasma particle rings in ellipses, alternating axes periodically along the direction of the magnetic field (x-axis) and of the y-axis. The uniform field leads to a modulation of the magnetic field, which results in magnetic pressure gradients (magneto-acoustic mode) or in the shear of the magnetic field lines (Alfvén mode). The gravitational wave drives MHD modes and transfers energy to the plasma, can become an important alternative process for the acceleration of baryons to high Lorentz factors observed in short GRBs. The total amount of energy that is transferred from the gravitational wave to the plasma is estimated (≃1040J - 1041 J), with γ≃102. We compare our results with previously obtained results by other works.
... In such investigations, the presence of the magnetic field is vital for mediating the coupling between the GW and the EMW, and a curved background spacetime can also serve as the catalyst. More interestingly for our present study though, it has been noted that currents enabled by the presence of a plasma can also greatly enhance the coupling [22][23][24][25][26][27][28][29][30], through their being disturbed by the GW. It is therefore interesting to examine the possibility of replacing the vacuum electromagnetic field with a strongly magnetized tenuous plasma as the quiescent configuration (in a stationary solution of the so-called force-free electrodynamics, thus no background radiation). ...
We explicitly compute the plasma wave (PW) induced by a plane gravitational wave (GW) travelling through a region of strongly magnetized plasma, governed by force-free electrodynamics. The PW co-moves with the GW and absorbs its energy to grow over time, creating an essentially force-free counterpart to the inverse-Gertsenshtein effect. The time-averaged Poynting flux of the induced PW is comparable to the vacuum case, but the associated current may offer a more sensitive alternative to photodetection when designing experiments for detecting/constraining high frequency gravitational waves. Aside from the exact solutions, we also offer an analysis of the general properties of the GW to PW conversion process, which should find use when evaluating electromagnetic counterparts to astrophysical gravitational waves, that are generated directly by the latter as a second order phenomenon.
... One of them looked at the propagation of gravitational waves linearly coupled to an external magnetic field [18]. It was shown that this configuration triggers magneto-hydrodynamics waves in the plasma [19][20][21][22][23]. Furthermore, the linear nature of the coupling limits the electromagnetic waves to low frequencies, in the best case a few tenths of kHz, which will be easily absorbed by the interstellar medium or plasma. ...
... As a consequence, one needs to associate them with secondary emission mechanisms (e.g., synchrotron radiation) in order to be able to trace the effects of gravitational waves on the strong magnetic fields. The later process can be studied following the mechanisms described in [19][20][21][22][23], and there is work in progress for the special case of strong gravitational fields. ...
Gravitational perturbations of neutron stars and black holes are well known
sources of gravitational radiation. If the compact object is immersed in or
endowed with a magnetic field, the gravitational perturbations would couple to
electromagnetic perturbations and potentially trigger synergistic
electromagnetic signatures. We present a detailed analytic calculation of the
dynamics of coupled gravitational and electromagnetic perturbations for both
neutron stars and black holes. We discuss the prospects for detecting the
electromagnetic waves in these scenarios and the potential that these waves
have for providing information about their source.
... (Please also see, p. 85, of Gertsenshtein, (1962).) Stephenson (2004) also points out that "The topic (of GW to EM conversion and non-gravitational-force generation of GWs) appears to have continued in the main stream of Astrodynamics for some 30 or 40 years now... including the papers of Boccaletti (1970), Gerlach (1974), Zel'dovich (1974, Tatsuo Tokuoka (1975), Macedo and Nelson (1983), Brodin and Marklund (1999), Papadopoulos, et al. (2001), Moortgat (2003) and several others as found on the Internet site: www.gravewave.com." Of course, non-mainstream concepts realize many significant breakthroughs in natural science. ...
An experiment is described for the generation and detection of High‐Frequency Gravitational Waves (HFGWs) in the laboratory utilizing a pair of tabletop X‐ray lasers for generation and a coupling system of semi‐transparent, beam‐splitting membranes with a pulsed Gaussian beam passing through a static magnetic field for detection. The laser axes are coplanar, their pulses are synchronized, and they are aligned in exactly opposite directions. They produce equal and opposite impulsive forces at the laser targets. Essentially, the X‐ray lasers emulate a double‐star orbit. Photons striking a target will produce a jerk (time rate of change of acceleration) and together with a computer controlled logic system will generate a HFGW spike each time the laser pulses are repeated. Specifications are tabulated for several different X‐ray lasers. The focus or concentration point of the gravitational radiation generated by the X‐ray laser pairs is located at the midpoint between the laser targets. The HFGW detecting system, proposed by Chongqing University, is situated at the HFGW focus. A High‐Temperature Superconductor
(HTSC) could might possibly concentrate the peak HFGW flux, potentially up to 4.93×1024 Wm−2 (over a very small detection area). Such large HFGW fluxes may be suitable for future aerospace applications.
... The interaction of gravitational waves (GWs) with the plasma and/or the electromagnetic waves propagating inside the plasma has been studied extensively (DeWitt & Breheme 1960; Cooperstock 1968; Zel'dovich 1974; Gerlach 1974; Grishchuk & Polnarev 1980; Denisov 1978; Macdonald & Thorne 1982; Demianski 1985; Daniel & Tajima 1997; Brodin & Marklund 1999; Servin et al. 2000; Moortgat & Kuijpers 2003). All well-known approaches to the study of the wave-plasma interaction have been used, namely, the Vlasov-Maxwell equations (Macedo & Nelson 1982), the MHD equations (Papadopoulos & Esposito 1981; Papadopoulos et al. 2001; Moortgat & Kuijpers 2003), and the nonlinear evolution of charged particles interacting with a monochromatic GW (Varvoglis & Papadopoulos 1992). The Vlasov-Maxwell equations and the MHD equations were mainly used to investigate the linear coupling of the GW with the normal modes of the ambient plasma, but the normal-mode analysis is a valid approximation only when the GW is relatively weak and the orbits of the charged particles are assumed to remain close to the undisturbed ones. ...
We investigate the non-linear interaction of a strong Gravitational Wave with the plasma during the collapse of a massive magnetized star to form a black hole, or during the merging of neutron star binaries (central engine). We found that under certain conditions this coupling may result in an efficient energy space diffusion of particles. We suggest that the atmosphere created around the central engine is filled with 3-D magnetic neutral sheets (magnetic nulls). We demonstrate that the passage of strong pulses of Gravitational Waves through the magnetic neutral sheets accelerates electrons to very high energies. Superposition of many such short lived accelerators, embedded inside a turbulent plasma, may be the source for the observed impulsive short lived bursts. We conclude that in several astrophysical events, gravitational pulses may accelerate the tail of the ambient plasma to very high energies and become the driver for many types of astrophysical bursts. Comment: 13 pages, 8 figures, accepted to The Astrophysical Journal
Particles interacting with a prescribed quasimonochromatic gravitational wave (GW) exhibit secular (average) nonlinear dynamics that can be described by Hamilton’s equations. We derive the Hamiltonian of this “ponderomotive” dynamics to the second order in the GW amplitude for a general background metric. For the special case of vacuum GWs, we show that our Hamiltonian is equivalent to that of a free particle in an effective metric, which we calculate explicitly. We also show that already a linear plane GW pulse displaces a particle from its unperturbed trajectory by a finite distance that is independent of the GW phase and proportional to the integral of the pulse intensity. We calculate the particle displacement analytically and show that our result is in agreement with numerical simulations. We also show how the Hamiltonian of the nonlinear averaged dynamics naturally leads to the concept of the linear gravitational susceptibility of a particle gas with an arbitrary phase-space distribution. We calculate this susceptibility explicitly to apply it, in a follow-up paper, toward studying self-consistent GWs in inhomogeneous media within the geometrical-optics approximation.
