**Wednesday Weekly Seminar - meeting**

Spectroscopy for asymmetric binary black hole mergers

Dr Jahed Abedi (University of Stavanger)

22 MAY 2024

11:00 - 12:00

Abstract:

Spectroscopy and spectral analysis are widely used today for studying various objects using both optical and acoustic waves. All objects have natural frequencies based on their composition and structure, including black holes, which exhibit quasi-normal modes (QNMs) that can be detected through gravitational waves in binary black hole (BBH) mergers. Einstein's theory predicts how black holes vibrate and what QNM frequencies are allowed. Observing more than one ringdown mode (QNM) can test a fundamental prediction of Einstein's theory. I am a member of an international team engaged in black hole spectroscopy, and our most recent discovery, detailed in Abedi et al. 2023 and Capano et al. 2023, provides compelling observational evidence for a multimode black hole ringdown spectrum observed during the gravitational wave event GW190521. This event showed two spectroscopic lines, corresponding to natural frequencies of 63 Hz and 98 Hz, disappearing after only 0.02 seconds. In this study, we evaluated various tests to assess the reality of this finding. We found a strong correlation between mass ratio and Bayesian factor for gravitational wave modes. The Bayesian factor values and the time dependence, along with the peak time of mode (3,3,0), match with what was found with the analysis of the actual GW190521 event, especially for systems with high mass ratios. If more signals like GW190521 are observed, it may necessitate revisions to astronomical models, opening up a new field of research—spectroscopy with gravitational waves.

**Link to join the webinar:**

https://meet.google.com/fnv-dfkk-ghb

**Link:**https://meet.google.com/fnv-dfkk-ghb