Testing the wormhole echo hypothesis for GW231123

The short-duration gravitational-wave (GW) event GW231123 has inferred component masses in the pair-instability mass gap and exhibits a burst-like morphology with no clearly inspiral, making it an interesting target for tests beyond the standard binary black hole (BBH) interpretation. In this work, motivated by its phenomenological similarity to GW190521, we test whether GW231123 is compatible with a wormhole-echo scenario by modeling a leading echo pulse with a well-motivated phenomenological sine-Gaussian wavepacket. We perform Bayesian model comparison against a BBH baseline described by the IMRPhenomXPHM-SpinTaylor waveform, and obtain the Bayes factor ratio $\ln B^{\rm Echo}{\rm BBH} = 1.87$, corresponding to weak-to-moderate support for the echo hypothesis. In our previous analysis for GW190521 within the same overall framework, we found $\ln B^{\rm Echo}{\rm BBH} \approx -2.9$, implying a shift of $Δ\ln B \approx 4.8$ between the two events. This sign change indicates that GW231123 is more compatible with a single-pulse echo description than GW190521.

💡 Research Summary

This paper presents a Bayesian model comparison analysis testing whether the short-duration gravitational-wave event GW231123 can be interpreted as a “wormhole echo” rather than a standard binary black hole (BBH) merger. GW231123 is notable for its burst-like morphology lacking a clear inspiral phase and component masses within the pair-instability mass gap, making it a candidate for exotic origins.

Motivated by its similarity to the previously observed event GW190521, the authors hypothesize that GW231123 could be the leading echo pulse from a post-merger wormhole remnant. In this scenario, subsequent echoes are attenuated below detection thresholds, leaving only a single observable pulse. They model this leading echo using a phenomenological sine-Gaussian waveform packet, parameterized by a central frequency (f_n), width (β), and phase (φ). This model is compared against a standard BBH baseline described by the IMRPhenomXPHM-SpinTaylor waveform, which includes spin-precession effects deemed important for this event.

The analysis uses publicly available data from the Hanford and Livingston detectors. Bayesian parameter estimation and model selection are performed using the Parallel Bilby pipeline with the Dynesty nested sampler over a 4-second segment. The key metric is the log Bayes factor, ln B^Echo_BBH, which quantifies the relative evidence for the echo hypothesis over the BBH hypothesis.

Under the BBH hypothesis, the inferred source-frame component masses (m1 ~150 M⊙, m2 ~93 M⊙) confirm the event’s location in the pair-instability mass gap. For the echo hypothesis, the sine-Gaussian parameters are constrained, with a central frequency around 53 Hz.

The model comparison yields ln B^Echo_BBH = +1.87 for GW231123. This positive value indicates weak-to-moderate support for the echo model over the BBH model within the context of this specific analysis. This result contrasts sharply with the authors’ previous finding for GW190521, which gave ln B^Echo_BBH ≈ -2.9, favoring the BBH interpretation. The shift of ΔlnB ≈ 4.8 between the two events suggests that GW231123’s signal morphology is comparatively more compatible with a single-pulse echo description.

The paper carefully notes the limitations of the study. The echo model is a simplified, phenomenological template that does not incorporate spin effects or correlations among multiple echoes. The Bayes factor can also be sensitive to the choice of BBH baseline waveform. Therefore, the result is not conclusive evidence for a wormhole echo but indicates that the hypothesis cannot be ruled out and warrants further investigation. The study exemplifies a methodology for quantitatively testing alternative paradigms in gravitational-wave astronomy against the standard BBH merger model.