We study dynamics and radiation generation in the last few orbits and merger of a binary black hole system, applying recently developed techniques for simulations of moving black holes. Our analysis of the gravitational radiation waveforms and dynamical black hole trajectories produces a consistent picture for a set of simulations with black holes beginning on circular-orbit trajectories at a variety of initial separations. We find profound agreement at the level of 1% among the simulations for the last orbit, merger and ringdown. We are confident that this part of our waveform result accurately represents the predictions from Einstein's General Relativity for the final burst of gravitational radiation resulting from the merger of an astrophysical system of equal-mass nonspinning black holes. The simulations result in a final black hole with spin parameter a/m = 0.69. We also find good agreement at a level of roughly 10% for the radiation generated in the preceding few orbits.

We present new techniqes for evolving binary black hole systems which allow the accurate determination of gravitational waveforms directly from the wave zone region of the numerical simulations. Rather than excising the black hole interiors, our approach follows the "puncture" treatment of black holes, but utilzing a new gauge condition which allows the black holes to move successfully through the computational domain. We apply these techniques to an inspiraling binary, modeling the radiation generated during the final plunge and ringdown. We demonstrate convergence of the waveforms and good conservation of mass-energy, with just over 3% of the system's mass converted to gravitional radiation.PACS numbers: 04.25. Dm, 04.30.Db, 04.70.Bw, 95.30.Sf, 97.60.Lf Coalescing comparable mass black hole binaries are prodigious sources of gravitational waves. The final merger of these systems, in which the black holes leave their quasicircular orbits and plunge together to produce a highly distorted black hole that "rings down" to a quiescent Kerr state, will produce a strong burst of gravitational radiation. Such mergers are expected to be among the strongest sources for ground-based gravitational wave detectors, which will observe the mergers of stellar-mass and intermediate mass black hole binaries, and the spacebased LISA, which will detect mergers of massive black hole binaries. Observations of these systems will provide an unprecedented look into the strong-field dynamical regime of general relativity. With the first-generation of ground-based interferometers reaching maturity and LISA moving forward through the formulation phase, the need for accurate merger waveforms has become urgent.Such waveforms can only be obtained through 3-D numerical relativity simulations of the full Einstein equations. While this has proven to be a very challenging undertaking, new developments allow an optimistic outlook. Full 3-D evolutions of binary black holes, in which regions within the horizons have been excised from the computational grid, have recently been carried out. Using co-rotating coordinates, so that the holes remain fixed on the grid as the system evolves, a binary has been evolved through a little more than a full orbit [1] as well as through a plunge, merger, and ringdown [2], though without being able to extract gravitational waveforms. More recently, a simulation in which excised black holes move through the grid in a single plunge-orbit, merger, and ringdown has been accomplished, with the calculation of a waveform [3].In this Letter, we report the results of new simulations of inspiraling binary black holes through merger and ringdown. These have been carried out using new techniques which allow the black holes to move through the coordinate grid without the need for excision [17].Using fixed mesh refinement, we are able to resolve both the dynamical region where the black holes inspiral (with length scales ∼ M , where M is the total system mass) and the outer regions where the gravitational waves propagate (leng...

We present an accurate approximation of the full gravitational radiation waveforms generated in the merger of noneccentric systems of two nonspinning black holes. Utilizing information from recent numerical relativity simulations and the natural flexibility of the effective-one-body (EOB) model, we extend the latter so that it can successfully match the numerical relativity waveforms during the last stages of inspiral, merger, and ringdown. By ''successfully'' here, we mean with phase differences & 8% of a gravitational-wave cycle accumulated by the end of the ringdown phase, maximizing only over time of arrival and initial phase. We obtain this result by simply adding a 4-post-Newtonian order correction in the EOB radial potential and determining the (constant) coefficient by imposing high-matching performances with numerical waveforms of mass ratios m 1 =m 2 1, 3=2, 2 and 4, m 1 and m 2 being the individual blackhole masses. The final black-hole mass and spin predicted by the numerical simulations are used to determine the ringdown frequency and decay time of three quasinormal-mode damped sinusoids that are attached to the EOB inspiral-(plunge) waveform at the EOB light ring. The EOB waveforms might be tested and further improved in the future by comparison with extremely long and accurate inspiral numerical relativity waveforms. They may be already employed for coherent searches and parameter estimation of gravitational waves emitted by nonspinning coalescing binary black holes with groundbased laser-interferometer detectors.

Recent developments in numerical relativity have made it possible to reliably follow the coalescence of two black holes from near the innermost stable circular orbit to final ringdown. This opens up a wide variety of exciting astrophysical applications of these simulations. Chief among these is the net kick received when two unequal mass or spinning black holes merge. The magnitude of this kick has bearing on the production and growth of supermassive black holes during the epoch of structure formation, and on the retention of black holes in stellar clusters. Here we report the first accurate numerical calculation of this kick, for two nonspinning black holes in a 1.5 : 1 mass ratio, which is expected on the basis of analytic considerations to give a significant fraction of the maximum possible recoil. We have performed multiple runs with different initial separations, orbital angular momenta, resolutions, extraction radii, and gauges. The full range of our kick speeds is 86-116 km s , and the Ϫ1 most reliable runs give kicks between 86 and 97 km s . This is intermediate between the estimates from two Ϫ1 recent post-Newtonian analyses and suggests that at redshifts , halos with masses Շ will have 9 z տ 10 10 M , difficulty retaining coalesced black holes after major mergers.

We review the tests of general relativity that will become possible with space-based gravitational-wave detectors operating in the ∼ 10−5 − 1 Hz low-frequency band. The fundamental aspects of gravitation that can be tested include the presence of additional gravitational fields other than the metric; the number and tensorial nature of gravitational-wave polarization states; the velocity of propagation of gravitational waves; the binding energy and gravitational-wave radiation of binaries, and therefore the time evolution of binary inspirals; the strength and shape of the waves emitted from binary mergers and ringdowns; the true nature of astrophysical black holes; and much more. The strength of this science alone calls for the swift implementation of a space-based detector; the remarkable richness of astrophysics, astronomy, and cosmology in the low-frequency gravitational-wave band make the case even stronger.