Gravitational waves - tool to observe black holes

Einstein's theory of general relativity predicts ripples in space-time generated by pairs of black holes merging. When galaxies merge, the supermassive black holes thought to be at the centre of large galaxies will inevitably meet. They first dance together, then enter a desperate embrace before they merge.

General relativity predictions suggest that towards the end of their dance, black holes emit gravitational waves. Scientists working on the EU-funded project CBHEO (Connecting numerical simulations of black holes with experiment and observations) have generated 'template' waveforms that should match such astrophysical signals.

The observed waveforms are expected to include the signals from the two black holes spiralling towards each other, as well as their merger and the resulting ring-down. The search templates generated by the CBHEO scientists using numerical relativity and post-Newtonian techniques include all these features.

Specifically, the inspiral portion of the waveform was modelled using analytic post-Newtonian calculations. On the other hand, numerical solutions of the general relativity field equations were required to model the final orbits and black holes merger accurately.

These hybrid waveforms have been added to data recoloured to predictions of the sensitivity curves for the Virgo and the Laser Interferometer Gravitational-Wave Observatory (LIGO). The resulting data were analysed by gravitational wave detection algorithms as part of the Numerical Injection Analysis (NINJA) collaborative effort.

CBHEO scientists also modelled parton-parton collisions produced by merging black holes. This study was motivated by the possibility of black holes forming in the particle collision experiments as predicted by new theories of gravity. The simulations' main output was the amount of energy and angular momentum lost in gravitational waves.

Armed with CBHEO project results about the dynamics of black holes, scientists hope to identify gravitational wave signatures. In turn, as black holes are very hard to observe, information about gravitational waves could prove to be a powerful new tool in astrophysics.