Physics at Virginia

"Ringdown overtones in black hole binary mergers"

Roberto Cotesta , John Hopkins University
[Host: Kent Yagi]

The gravitational-wave signal emitted by the black-hole remnant resulting from a binary merger such as GW190514 consists in a superposition of damped sinu- soids known as quasinormal modes. Besides the “fundamental" mode (the one with the longest damping time), it is important to detect the so-called “over- tones" (modes with shorter damping time), because a measurement of their frequencies could allow us to identify the remnant as a Kerr black hole. We discuss theoretical and observational issues in the analysis of ringdown over- tones. We present theoretical arguments showing that the spacetime is not well described as a linearly perturbed black hole close to the peak of the waveform amplitude. Then we analyze GW150914 post-merger data to understand if recent ringdown overtone detection claims are robust. We find no evidence in favor of an overtone in the data after the waveform peak. Around the peak, the log-Bayes factor does not indicate the presence of an overtone, while the support for a non-zero amplitude is sensitive to changes in the starting time much smaller than the overtone damping time. This suggests that claims of an overtone detection are noise-dominated. We perform GW150914-like injections in neighboring segments of the real detector noise, and we show that noise can indeed induce artificial evidence for an overtone.


Gravity Seminar
Monday, November 21, 2022
1:30 PM
Physics, Room 313

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