Why do merging black holes hide their predicted afterglow?

After two black holes merge, relativity predicts a slowly decaying 'tail' in the gravitational-wave signal — yet numerical simulations of circular mergers rarely show it. The culprit is spectral structure: a source oscillating at a well-defined frequency exponentially suppresses the tail by a factor tied to how narrowband the signal is. This explains why head-on and eccentric mergers, which produce broader-spectrum signals, do show tails — and why circular mergers don't.