Authors: Adam Pound, Eric Poisson, Bernhard G. Nickel
Date: Thu, 29 Sep 2005
Abstract: A small body moving in the field of a much larger black hole and subjected to its own gravity moves on an accelerated world line in the background spacetime of the large black hole. The acceleration is produced by the body's gravitational self-force, which is constructed from the body's retarded gravitational field. The adiabatic approximation to the gravitational self-force is obtained instead from the half-retarded minus half-advanced field; it is known to produce the same dissipative effects as the true self-force. We argue that the adiabatic approximation is limited, because it discards important conservative terms which lead to the secular evolution of some orbital elements. We argue further that this secular evolution has measurable consequences; in particular, it affects the phasing of the orbit and the phasing of the associated gravitational wave. Our argument rests on a simple toy model involving a point electric charge moving slowly in the weak gravitational field of a central mass; the charge is also subjected to its electromagnetic self-force. In this simple context the true self-force is known explicitly and it can cleanly be separated into conservative and radiation-reaction pieces. We observe that the conservative part of the self-force produces a secular regression of the orbit's periapsis. We explain how the conclusions reached on the basis of the toy model can be extended to the gravitational self-force, and to fast motions and strong fields. While the limitations of the adiabatic approximation are quite severe in a post-Newtonian context in which the motion is slow and the gravitational field weak, they appear to be less so for rapid motions and strong fields.
Authors: John T Whelan
Date: Tue, 27 Sep 2005
Abstract: The response of a cross-correlation measurement to an isotropic stochastic gravitational-wave background depends on the observing geometry via the overlap reduction function. If one of the detectors being correlated is a resonant bar whose orientation can be changed, the response to stochastic gravitational waves can be modulated. I derive the general form of this modulation as a function of azimuth, both in the zero-frequency limit and at arbitrary frequencies. Comparisons are made between pairs of nearby detectors, such as LIGO Livingston-ALLEGRO, Virgo-AURIGA, Virgo-NAUTILUS, and EXPLORER-AURIGA, with which stochastic cross-correlation measurements are currently being performed, planned, or considered.
Authors: Steve Drasco, Scott A. Hughes
Date: Mon, 26 Sep 2005
Abstract: Using black hole perturbation theory, we calculate the gravitational waves produced by test particles moving on bound geodesic orbits about rotating black holes. The orbits we consider are generic - simultaneously eccentric and inclined. The waves can be described as having radial, polar, and azimuthal "voices", each of which can be made to dominate by varying eccentricity and inclination. Although each voice is generally apparent in the waveform, the radial voice is prone to overpowering the others. We also compute the radiative fluxes of energy and axial angular momentum at infinity and through the event horizon. These fluxes, coupled to a prescription for the radiative evolution of the Carter constant, will be used in future work to adiabatically evolve through a sequence of generic orbits. This will enable the calculation of inspiral waveforms that, while lacking certain important features, will approximate those expected from astrophysical extreme mass ratio captures sufficiently well to aid development of measurement algorithms on a relatively short timescale.
Authors: B. Kocsis (ELTE), Z. Frei (ELTE), Z. Haiman (Columbia), K. Menou (Columbia)
Date: Thu, 22 Sep 2005
Abstract: The gravitational waves (GW) emitted during the coalescence of supermassive black holes (SMBHs) in the mass range 10ˆ4-10ˆ7 M_sun will be detectable out to high redshifts with LISA. We calculate the size and orientation of the three-dimensional error ellipse in solid angle and redshift within which the LISA event could be localized using the GW signatures alone. We take into account uncertainties in LISA's measurements of the luminosity distance and direction to the source, in the background cosmology, in weak gravitational lensing magnification due to inhomogeneities along the line of sight, and potential source peculiar velocities. We find that weak lensing errors exceed other sources of uncertainties by nearly an order of magnitude. Under the plausible assumption that BH mergers are accompanied by gas accretion leading to Eddington-limited quasar activity, we then compute the number of quasars that would be found in a typical LISA error volume, as a function of BH mass and redshift. We find that low redshifts offer the best opportunities to identify quasar counterparts to cosmological standard sirens, and that the LISA error volume will typically contain a single near-Eddington quasar at z=1. This will allow a straightforward test of the hypothesis that BH mergers are accompanied by bright quasar activity and, if the hypothesis proves correct, will guarantee the identification of a unique quasar counterpart. This would yield unprecedented tests of the physics of SMBH accretion, and offer an alternative method to precisely constrain cosmological parameters [abridged].
Authors: Kostas Glampedakis
Date: Wed, 7 Sep 2005
Abstract: In this review article I attempt to summarise past and present-ongoing-work on the problem of the inspiral of a small body in the gravitational field of a much more massive Kerr black hole. Such extreme mass ratio systems, expected to occur in galactic nuclei, will constitute prime sources of gravitational radiation for the future LISA gravitational radiation detector. The article's main goal is to provide a survey of basic celestial mechanics in Kerr spacetime and calculations of gravitational waveforms and backreaction on the small body's orbital motion, based on the traditional ‘flux-balance’ method and the Teukolsky black hole perturbation formalism.
Authors: Denis Defrere, Andreas Rathke
Date: Wed, 7 Sep 2005
Abstract: The Doppler tracking data from two deep-space spacecraft, Pioneer 10 and 11, show an anomalous blueshift, which has been dubbed the "Pioneer anomaly". The effect is most commonly interpreted as a real deceleration of the spacecraft - an interpretation that faces serious challenges from planetary ephemerides. The Pioneer anomaly could as well indicate an unknown effect on the radio signal itself. Several authors have made suggestions how such a blueshift could be related to cosmology. We consider this interpretation of the Pioneer anomaly and study the impact of an anomalous blueshift on the Laser Interferometer Space Antenna (LISA), a planned joint ESA-NASA mission aiming at the detection of gravitational waves. The relative frequency shift (proportional to the light travel time) for the LISA arm length is estimated to 10E-16, which is much bigger than the expected amplitude of gravitational waves. The anomalous blueshift enters the LISA signal in two ways, as a small term folded with the gravitational wave signal, and as larger term at low frequencies. A detail analysis shows that both contributions remain undetectable and do not impair the gravitational-wave detection. This suggests that the Pioneer anomaly will have to be tested in the outer Solar system regardless if the effect is caused by an anomalous blueshift or by a real force.
Authors: A. Stroeer, A. Vecchio, G. Nelemans
Date: Wed, 21 Sep 2005
Abstract: The Laser Interferometer Space Antenna (LISA) will provide the largest observational sample of (interacting) double white dwarf binaries, whose evolution is driven by radiation reaction and other effects, such as tides and mass transfer. We show that, depending on the actual physical parameters of a source, LISA will be able to provide very different quality of information: for some systems LISA can test unambiguously the physical processes driving the binary evolution, for others it can simply detect a binary without allowing us to untangle the source parameters and therefore shed light on the physics at work. We also highlight that simultaneous surveys with GAIA and/or optical telescopes that are and will become available can radically improve the quality of the information that can be obtained.
Authors: L.-M. Lin, K. S. Cheng, M.-C. Chu, W.-M. Suen
Date: Thu, 15 Sep 2005
Abstract: (Abridged) We study the gravitational radiation from gravitational collapses of rapidly rotating neutron stars induced by a phase-transition from normal nuclear matter to a mixed phase of quark and nuclear matter in the core of the stars. The study is based on self-consistent three dimensional hydrodynamic simulations with Newtonian gravity and a high resolution shock capturing scheme, and the quadrupole formula of gravitational radiation. The quark matter of the mixed phase is described by the MIT bag model and the normal nuclear matter is described by an ideal fluid equation of state (EOS). 1. We determined the magnitudes of the emitted gravitational waves for several collapse scenarios. 2. We determined the types and frequencies of the fluid oscillation modes excited by the process. In particular, we find that the gravitational wave signals produced by the collapses are dominated by the fundamental quadrupole and quasi-radial modes of the final equilibrium configurations. In some collapse scenarios, we find that the oscillations are damped out within a few dynamical timescales due to the growth of differential rotations and the formation of strong shock waves. 3. We showed that the spectrum of the gravitational wave signals is sensitive to the EOS, implying that the detection of such gravitational waves could provide useful constraints on the EOS of newly born quark stars. 4. For the range of rotation periods we have studied, we found no sign of the development of nonaxisymmetric dynamical instabilities in the collapse process.
Authors: D. Bar
Date: Wed, 14 Sep 2005
Abstract: We represent and discuss a theory of gravitational holography in which all the involved waves; subject, reference and illuminator are gravitational waves (GW). Although these waves are so weak that no terrestrial experimental set-ups, even the large LIGO, VIRGO, GEO and TAMA facilities, were able up to now to directly detect them they are, nevertheless, known under certain conditions (such as very small wavelengths) to be almost indistinguishable (see P. 962 in Ref. 18) from their analogue electromagnetic waves (EMW). We, therefore theoretically, show, using the known methods of optical holography and taking into account the very peculiar nature of GW, that it is also possible to reconstruct subject gravitational waves.
Authors: Réjean J. Dupuis (for the LIGO Scientific Collaboration)
Date: Tue, 6 Sep 2005
Abstract: An overview of the searches for gravitational waves from radio pulsars with LIGO and GEO is given. We give a brief description of the algorithm used in these targeted searches and provide end-to-end validation of the technique through hardware injections. We report on some aspects of the recent S3/S4 LIGO and GEO search for signals from several pulsars. The gaussianity of narrow frequency bands of S3/S4 LIGO data, where pulsar signals are expected, is assessed with Kolmogorov-Smirnov tests. Preliminary results from the S3 run with a network of four detectors are given for pulsar J1939+2134.
© M. Vallisneri 2012 — last modified on 2010/01/29
Tantum in modicis, quantum in maximis