LIGO Seminar

https://caltech.zoom.us/j/87546916051?pwd=aTByZU5WamhUKzlkRVY2bW05bytDdz09

Speaker: Dr. Julian Westerweck

Title: Black hole spectroscopy and beyond no-hair

Abstract: Black hole quasi-normal modes are proving a rich phenomenon in terms of their properties, data-analysis, and potential for discovery of new physics. I present work analysing gravitational-wave data both for the signal of black holes in GR and for several types of alternative quasi-normal modes, covering scalar/vector fields, horizonless objects, and r-modes.

Black hole spectroscopy directly probes the nature of a binary merger's final object by measuring the characteristic spectrum of gravitational-wave modes emitted as it settles down from its perturbed state. This facilitates (no-hair) tests of GR predictions, unexpectedly already using current data. I will discuss some recent advances in analysis methods helping to perform these tests and their results.

In contrast, the presence of additional post-merger signals could reveal more exotic objects or deviations from GR. Scalar- or vector-fields, if present, possess a distinct spectrum of modes, which may couple to and drive gravitational waves with their characteristic frequencies, making them detectable. In current work we aim to constrain their presence in available data and predict future prospects using third-generation instruments.

Exotic compact objects proposed as alternatives to black holes would show characteristic signatures in their post-merger emission. Horizonless compact objects emit at late times weak but long-lived modes following the initial unmodified signal. R-mode oscillations in compact objects consisting of fluid matter produce a similar signal. Employing methods adapted to these long-duration signals, we analyse data from the most promising detections, placing strict bounds on both the location of possible deviations from the Kerr geometry and the proposed fluid's properties.