Exploring the outer limits of Numerical Relativity

We perform a first exploration of black-hole binary evolutions using full nonlinear numerical relativity techniques at separations large enough that low-order post-Newtonian expansions are expected to be very accurate. As a case study, we evolve an equal-mass nonspinning black-hole binary in a quasicircular orbit at an initial coordinate separation of $r=100M$. We measured the orbital period of the binary and find $T=6422M$. We perform convergent simulations at three different grid resolutions and complete two, one and a half, and one and a quarter orbits for the low, medium and high resolutions, respectively. The orbital motion agrees with post-Newtonian predictions to within $1\%$. We discuss on how to improve this accuracy in future simulations. The results are relevant for the generation of long-term waveforms for detection and analysis of gravitational waves by the next generation of detectors.