Constraints on Kerr-Newman black holes from merger-ringdown gravitational-wave observations

TL;DR

This paper develops a model to analyze the post-merger gravitational-wave signals of charged black holes, constraining their charge-to-mass ratio using LIGO-Virgo data and simulations, with implications for testing beyond Standard Model physics.

Contribution

The authors introduce a new template incorporating charge effects into black hole merger-ringdown analysis, enabling constraints on black hole charge from gravitational-wave observations.

Findings

Current data cannot distinguish charged from uncharged black holes.

A 90th percentile bound of q < 0.33 on charge-to-mass ratio for GW150914.

Future observations could detect charge ratios above approximately 0.3 to 0.5.

Abstract

We construct a template to model the post-merger phase of a binary black hole coalescence in the presence of a remnant $U(1)$ charge. We include the quasi-normal modes typically dominant during a binary black hole coalescence, $(\ell,m,n) = \{(2,2,0), (2,2,1)\}$ and also present analytical fits for the quasinormal mode frequencies of a Kerr-Newman black hole in terms of its spin and charge, here also including the $(3,3,0)$ mode. Aside from astrophysical electric charge, our template can accommodate extensions of the Standard Model, such as a dark photon. Applying the model to LIGO-Virgo detections, we find that we are unable to distinguish between the charged and uncharged hypotheses from a purely post-merger analysis of the current events. However, restricting the mass and spin to values compatible with the analysis of the full signal, we obtain a 90th percentile bound $\bar{q} < 0.33$ on the black hole charge-to-mass ratio, for the most favorable case of GW150914. Under similar assumptions, by simulating a typical loud signal observed by the LIGO-Virgo network at its design sensitivity, we assess that this model can provide a robust measurement of the charge-to-mass ratio only for values $\bar{q} \gtrsim 0.5$; here we also assume that the mode amplitudes are similar to the uncharged case in creating our simulated signal. Lower values, down to $\bar{q} \sim 0.3$, could instead be detected when evaluating the consistency of the pre-merger and post-merger emission.