Orbital effects of a monochromatic plane gravitational wave with ultra-low frequency incident on a gravitationally bound two-body system

Abstract

We analytically compute the long-term orbital variations of a test particle orbiting a central body acted upon by an incident monochromatic plane gravitational wave. We assume that the characteristic size of the perturbed two-body system is much smaller than the wavelength of the wave. Moreover, we also suppose that the wave's frequency n g is much smaller than the particle's orbital one n b . We make neither a priori assumptions about the direction of the wavevector b k nor on the orbital configuration of the particle. While the semi-major axis a is left unaffected, the eccentricity e, the inclination I, the longitude of the ascending node Ω, the longitude of pericenter ϖ and the mean anomaly M undergo non-vanishing long-term changes of the form dW=dt ¼ FðK ij ; e; I; X; xÞ; W ¼ e; I; X; -; M, where K ij ; i; j ¼ 1; 2; 3 are the coefficients of the tidal matrix K. Thus, in addition to the variations of its orientation in space, the shape of the orbit would be altered as well. Strictly speaking, such effects are not secular trends because of the slow modulation introduced by K and by the orbital elements themselves: they exhibit peculiar long-term temporal patterns which would be potentially of help for their detection in multidecadal analyses of extended data records of planetary observations of various kinds. In particular, they could be useful in performing independent tests of the inflation-driven ultra-low gravitational waves whose imprint may have been indirectly detected in the Cosmic Microwave Background by the Earthbased experiment BICEP2. Our calculation holds, in general, for any gravitationally bound two-body system whose orbital frequency n b is much larger than the frequency n g of the external wave, like, e.g., extrasolar planets and the stars orbiting the Galactic black hole. It is also valid for a generic perturbation of tidal type with constant coefficients over timescales of the order of the orbital period of the perturbed particle.

Detecting stochastic gravitational waves with binary resonance

“…For long-duration GW signals, these imprints accumulate over time, eventually giving rise to observable deviations which can be used to infer the GW amplitude, turning the binary into a dynamical GW detector. This idea has a long history [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], and has been used to search for GWs with the orbit of the binary pulsar B1913+16 [34]. 1 Nonetheless, this binary GW resonance effect has received relatively little attention in the GW community, and, we feel, has not yet been exploited to its full potential.…”