Revision 1

Superseded · first revision · record

Title: Do remnant black hole ringdown tones match Kerr at percent precision?
Plain: A newly merged black hole rings like a bell at frequencies fixed by its mass and spin if it is a Kerr black hole. Measuring two or more tones in one event tests this directly.
Precise: For merger remnants, measure the complex frequencies of at least two independent quasinormal modes, for example $(l,m,n) = (2,2,0)$ together with $(2,2,1)$, $(3,3,0)$ or $(4,4,0)$, and constrain the fractional deviations $\delta f$ and $\delta \tau$ from Kerr values for a common mass and spin. The target is $\mid\delta f\mid, \mid\delta \tau\mid$ below 0.01. An answer is the measured deviations with uncertainties from a catalog of events.
Settled by: Multi-mode ringdown measurements with percent-level frequency and damping-time constraints from next-generation ground detectors or LISA.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: partially-resolved
Status note: GW250114 gave two modes at $4.1\,\sigma$ with the overtone frequency consistent with Kerr to plus or minus $30\,\text{percent}$ and the damping rate unconstrained (LIGO-Virgo-KAGRA 2025).
Posed since: 2004