Constraints on charged black holes from merger-ringdown signals in GWTC-3 and prospects for the Einstein Telescope

TL;DR

This study constrains the charge of astrophysical black holes using gravitational wave data, finding no strong evidence for charge with current detectors, but showing future detectors like the Einstein Telescope could significantly improve these constraints.

Contribution

The paper extends previous analyses by including multiple GW events and simulating ET data to demonstrate improved charge constraints and the potential to break charge-spin degeneracy.

Findings

Current GW observations limit black hole charge to Q<0.37 at 90% CL.

Simulated ET data could improve constraints to Q<0.2 at 90% CL.

Including multiple ringdown modes helps break charge-spin degeneracy.

Abstract

Whether astrophysical black holes (BHs) can have charge is a question to be addressed by observations. In the era of gravitational wave (GW) astronomy, one can constrain the charge of a merged BH remnant using the merger-ringdown signal of the GW data. Extending earlier studies, we analyze five GW events in GWTC-3, assuming Kerr-Newman BHs. Our results show no strong evidence for a charged BH, and give a limit on the charge-to-mass-ratio $Q<0.37$ at $90\%$ credible level (CL). Due to the charge-spin degeneracy in the waveform and the limited signal-to-noise ratios (SNRs), it is challenging for LIGO/Virgo/KAGRA observations to provide better constraints. We further simulate data for the Einstein Telescope (ET), where SNRs can be as large as $\sim270$ in the ringdown signal. These simulated events allow us to consider the 220, 221, and 330 ringdown modes altogether, which can help break the charge-spin degeneracy. The analysis of a simulated GW150914-like signal shows that ET can improve the constraints on the charge-to-mass-ratio to $Q \lesssim 0.2$ at $90\%$ CL with one ringdown signal.