Late-time tails in nonlinear evolutions of merging black holes

It has been known for many years, that the boundary condition alter the tails of scalar radiation in spherically symmetric spacetimes. It was however an open question to which extent this result generalises to gravitational waves in vacuum. Using the pseudospectral SpEC code we we uncover for the first time late-time gravitational-wave tails in fully nonlinear 3+1 dimensional numerical relativity simulations.

We achieve this result by exploiting the strong magnification of late-time tails due to binary eccentricity and showcase here the tail presence in head-on configurations for several mass ratios close to unity. The impact of the boundary conditions is uncovered in a systematic study, showing that the boundary conditions are the primary source for errors in the tails.

The simulations are also compared to perturbative evolutions, which display striking agreement with full nonlinear ones.