Parametrized ringdown spin expansion coefficients: a data-analysis framework for black-hole spectroscopy with multiple events

Understand

Black-hole spectroscopy is arguably the most promising tool to test gravity in extreme regimes and to probe the ultimate nature of black holes with unparalleled precision.

• These tests are currently limited by the lack of a ringdown parametrization that is both robust and accurate.
• We develop an observable-based parametrization of the ringdown of spinning black holes beyond general relativity, which we dub ParSpec (Parametrized Ringdown Spin Expansion Coefficients).
• This approach is perturbative in the spin, but it can be made arbitrarily precise (at least in principle) through a high-order expansion.