Ringdown spectroscopy of phenomenologically modified black holes
Spyros Thomopoulos, Sebastian H. Völkel, Harald Pfeiffer
Abstract
The characteristic oscillations of black holes, as described by their<br>quasinormal mode spectrum, play a fundamental role in testing general<br>relativity with gravitational waves. The so-called parametrized QNM framework<br>was introduced to predict perturbative changes in the spectrum due to small<br>deviations from general relativity. In this work, we extend the framework to<br>model time-domain signals and study the excitation of quasinormal modes from<br>the time evolution of initial data. Specifically, we quantify whether the<br>perturbative eigenvalue predictions agree with extracting excited quasinormal<br>modes from such simulations. Addressing this issue is particularly important in<br>the context of agnostic ringdown tests and the possible presence of spectral<br>instabilities, which may diminish the promises of black hole spectroscopy. We<br>find that the extracted quasinormal modes agree well with the perturbative<br>predictions, underlining that these types of modifications can, in principle,<br>be robustly tested from real observations. Moreover, we also report the<br>importance of including late-time tails for accurate mode extractions. Finally,<br>we provide a WKB-inspired analysis supporting the importance of the peak of the<br>scattering potential and show robust scaling relations.<br>