Modeling Black Hole Merges

Modeling Black Hole Merges
Steve Nadis reported in Quanta this week on some progress in the numerical modeling of black hole dynamics. Black holes are fun geometric objects to study, but anything with time dependence is prohibitively complicated without a computer. General Relativity is complicated!

Progress in modeling mergers of black holes - or black holes absorbing other objects - has accelerated in the past decade. For good reason, gravitational wave observatories have become sensitive enough to detect these events.

The latest development is perhaps the most amusing - at least to theorists. By modeling one of a pair of black holes as a “point mass”, calculations were simplified

Black holes defining property - the event horizon - is necessarily NOT a point. Nevertheless, the disparity in size between a supermassive black hole and a stellar mass black hole suggested that such an approximation may not be entirely inappropriate. Comparing the speedy, point mass approximation with cumbersome, full-sized calculations for a orbiting pair of black holes with a mass ratio around 3, remarkable level of fidelity was maintained (errors within 1%!!). This suggests the approximation may well give reasonable results for systems with a larger mass difference. Highly asymmetric mass ratios - like ten to one and beyond - are currently too extreme for most traditional, numerical approaches.