2 research outputs found
A fast stroboscopic spectral method for rotating systems in numerical relativity
We present a numerical technique for solving evolution equations, as the wave
equation, in the description of rotating astrophysical compact objects in
comoving coordinates, which avoids the problems associated with the light
cylinder. The technique implements a fast spectral matching between two domains
in relative rotation: an inner spherical domain, comoving with the sources and
lying strictly inside the light cylinder, and an outer inertial spherical
shell. Even though the emphasis is placed on spectral techniques, the matching
is independent of the specific manner in which equations are solved inside each
domain, and can be adapted to different schemes. We illustrate the strategy
with some simple but representative examples.Comment: 16 pages, 15 figure
Characteristic extraction in numerical relativity: binary black hole merger waveforms at null infinity
The accurate modeling of gravitational radiation is a key issue for
gravitational wave astronomy. As simulation codes reach higher accuracy,
systematic errors inherent in current numerical relativity wave-extraction
methods become evident, and may lead to a wrong astrophysical interpretation of
the data. In this paper, we give a detailed description of the
Cauchy-characteristic extraction technique applied to binary black hole
inspiral and merger evolutions to obtain gravitational waveforms that are
defined unambiguously, that is, at future null infinity. By this method we
remove finite-radius approximations and the need to extrapolate data from the
near zone. Further, we demonstrate that the method is free of gauge effects and
thus is affected only by numerical error. Various consistency checks reveal
that energy and angular momentum are conserved to high precision and agree very
well with extrapolated data. In addition, we revisit the computation of the
gravitational recoil and find that finite radius extrapolation very well
approximates the result at \scri. However, the (non-convergent) systematic
differences to extrapolated data are of the same order of magnitude as the
(convergent) discretisation error of the Cauchy evolution hence highlighting
the need for correct wave-extraction.Comment: 41 pages, 8 figures, 2 tables, added references, fixed typos. Version
matches published version