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This study examines gravitational waves emitted during binary black hole mergers, specifically analyzing "direct waves" that carry information about the remnant black hole's properties. By filtering out quasinormal mode oscillations from numerical relativity simulations, researchers found that the direct wave's frequency evolves over time and approaches values directly related to the final black hole's rotation rate and surface gravity. The evolution pattern depends on the remnant's spin, with the frequency approaching twice the horizon angular velocity from above for lower spins and from below for higher spins.
Why it matters
Understanding the direct wave component improves our ability to extract physical information about black hole horizons from gravitational wave observations, potentially enabling more precise measurements of remnant black hole properties from LIGO/Virgo detections. This work bridges theoretical predictions about black hole dynamics with observable gravitational wave signals.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
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Abstract: While no signal originating at a black hole’s event horizon can reach future null infinity, information about the horizon and its immediate vicinity can be encoded in asymptotic properties of waves emitted by matter or field perturbations falling toward a growing/forming horizon. Within a response-filtered framework, “direct wave” denotes source-sensitive plunge and remnant-formation information revealed by filtering the black-hole response. Unlike a stationary damped sinusoid with a fixed complex frequency, the direct wave follows the evolving source and has an evolving instantaneous complex frequency tied at late times to the remnant horizon angular velocity $Omega_H$ and surface gravity $kappa_H$. Using rational filters, we remove quasinormal modes from numerical-relativity waveforms to study this evolution. Before numerical contamination, trajectories depend on remnant spin: the real frequency evolves toward $2Omega_H$ from above for lower spins ($chi_flesssim0.7$) and from below for higher spins ($chi_fgtrsim0.7$), while the instantaneous decay rate increases, with best-resolved cases approaching the expected value of $3kappa_H$. As in particle-plunge results, the horizon-controlled value is approached only at late times, as frame dragging controls near-horizon motion. For $chi_fsim0.7$ remnants of non-precessing, comparable-mass binaries, the early-time real frequency is close to $2Omega_H$ because the binary orbital frequency transitions smoothly to the remnant horizon frequency. Finite-time deviations therefore carry information about merger/collapse dynamics rather than undermining the horizon connection. Full direct-wave evolution requires numerical-relativity calibration. We further show that approximate pole-zero pairing in the Kerr response motivates a minimal filter set that suppresses quasinormal-mode features while revealing source-trajectory information.
Source: Complex frequency evolution of direct waves from binary black hole mergers