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Black hole ringdown: the importance of overtones (1903.08284v2)

Published 19 Mar 2019 in gr-qc

Abstract: It is possible to infer the mass and spin of the remnant black hole from binary black hole mergers by comparing the ringdown gravitational wave signal to results from studies of perturbed Kerr spacetimes. Typically these studies are based on the fundamental quasinormal mode of the dominant $\ell=m=2$ harmonic. By modeling the ringdown of accurate numerical relativity simulations, we find that the fundamental mode alone is insufficient to recover the true underlying mass and spin, unless the analysis is started very late in the ringdown. Including higher overtones associated with this $\ell=m=2$ harmonic resolves this issue, and provides an unbiased estimate of the true remnant parameters. Further, including overtones allows for the modeling of the ringdown signal for all times beyond the peak strain amplitude, indicating that the linear quasinormal regime starts much sooner than previously expected. A model for the ringdown beginning at the peak strain amplitude can exploit the higher signal-to-noise ratio in detectors, reducing uncertainties in the extracted remnant quantities. Tests of the no-hair theorem should consider incorporating overtones in the analysis.

Citations (134)

Summary

  • The paper demonstrates that including quasinormal mode overtones is crucial for accurately analyzing the black hole ringdown phase from gravitational wave signals.
  • Incorporating multiple overtones allows for unbiased estimation of remnant black hole parameters from earlier in the ringdown, improving analysis potential.
  • This refined modeling enhances parameter estimation accuracy and holds significant implications for testing General Relativity using gravitational wave observations.

Overview of the Significance of Overtones in Black Hole Ringdown

The paper "Black hole ringdown: the importance of overtones" addresses a critical aspect of gravitational wave signals resulting from binary black hole (BBH) mergers, focusing primarily on the ringdown phase. This phase, characterized by quasinormal mode (QNM) oscillations of the remnant black hole, provides a direct link to its mass and spin. The authors argue that previous analyses have underestimated the role of QNM overtones in the accurate modeling of the ringdown phase, potentially leading to systematic biases in estimating the remnant's parameters.

Key Findings and Contributions

The paper's primary contribution is the methodological inclusion of QNM overtones beyond the fundamental mode to analyze the ringdown gravitational wave signal more thoroughly. The authors demonstrate that solely relying on the fundamental mode of the gravitational wave signal is inadequate for accurately inferring the true mass and spin of the remnant black hole at earlier times. This inadequacy is particularly glaring unless the analysis commences significantly after the peak strain amplitude of the signal. By incorporating higher overtones in their models, the researchers achieve unbiased estimates of remnant parameters from earlier in the ringdown, signifying that linear perturbation theory can be applied much earlier than previously believed.

Numerical Results and Analysis

Through rigorous modeling using numerical relativity simulations, the authors identify that overtones are not merely auxiliary components but substantially influence the early ringdown regime. They determine that the inclusion of multiple overtones (up to seven in their analysis) provides an optimal fit for the gravitational waveforms, notably reducing mismatches between theoretical predictions and numerical simulations. This enhancement enables analysis of the ringdown signal from the peak strain amplitude onwards, enhancing the potential for accurate parameter estimation and reducing uncertainties due to higher signal-to-noise ratios observed in detectors like LIGO and Virgo.

Implications for Testing General Relativity

These findings have substantial implications for tests of General Relativity (GR), specifically concerning black hole properties and the no-hair theorem. By enabling more precise extraction of QNM frequencies, including their subtly decaying overtones, these models underscore the plausibility of black-hole spectroscopy even in contemporary observational settings. This advancement could significantly impact how gravitational wave astrophysics tests GR and understands the final remnant characteristics following a BBH merger.

Theoretical and Practical Implications

From a theoretical perspective, acknowledging the influence of overtones refines current understandings of black hole dynamics post-coalescence. Practically, the research highlights a pivotal step for gravitational wave astrophysics, suggesting that observing overtones in detector data could serve as new benchmarks for verifying predictions about black holes.

Future Research Directions

The paper opens avenues for future research, suggesting the need to explore a broader parameter space, including different mass ratios and spin configurations of the initial binary components. Further investigation into the observational impacts of additional angular modes and cross-validation with real gravitational wave data could fortify the current understanding of these phenomena. The authors also hint at extending their findings to more general astrophysical scenarios, considering the potential effect of systematic noise and the influence of detector characteristics on the accuracy of these inferences.

In conclusion, the paper provides a comprehensive analysis underscoring the critical role of overtones in black hole ringdown analysis, offering a more robust framework for gravitational wave parameter estimation and tests of GR. Researchers in gravitational wave astronomy would benefit from these insights, understanding the broader implications for black hole physics and astrophysical observations.

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