Gravitational-wave parameter estimation to the Moon and back: massive binaries and the case of GW231123

TL;DR

The paper investigates the potential of the Lunar Gravitational-Wave Antenna (LGWA), a deci-Hz detector deployed on the Moon, to observe massive BBHs and enable multiband science with ground-based observatories. Using Bayesian parameter estimation on simulated populations and a GW231123-like injection, it shows that LGWA could detect a substantial fraction of LVK events and provide thousands of detections per year when combined with 2G/3G networks, while offering long in-band observations that dramatically improve chirp-mass measurements and sky localization. The study highlights that a single deci-Hz observatory can self-triangulate and constrain spins and inclinations with high precision, and that multiband analyses will sharpen the inferred BBH mass spectrum and formation channels. Overall, opening the deci-Hz band promises transformative gains for GW astronomy, including early warning and archival searches, though practical challenges in duty cycle, calibration, and waveform systematics must be addressed in a coherent multiband framework.

Abstract

We study the prospects of the Lunar Gravitational-Wave Antenna (LGWA), a proposed deci-Hz GW detector, to observe binary black holes (BBHs) and enable multiband science with ground-based detectors. We assess the detectability of the events observed by current instruments up to the GWTC-4.0 data release, and of simulated populations consistent with the latest reconstruction by the LIGO-Virgo-KAGRA Collaboration. We find that LGWA alone would have been able to observe more than one third of the events detected so far, and that it could detect $\sim\!90$ events merging in the ground-based band per year out to redshifts $z\sim3-5$. Current detectors at design sensitivity and 100% duty cycle could detect thousands of BBHs per year, with one to a few hundred multiband counterparts in LGWA. Third-generation (3G) detectors can observe most of the BBHs detected by LGWA merging in their frequency band in the simulated mass range $7\,{\rm M}_\odot\lesssim M_{\rm tot}\lesssim 600\,{\rm M}_\odot$, enabling systematic joint analyses of hundreds of events. The short time to merger from the deci-Hz band to the Hz-kHz band (typically months to a year) allows for early warning, targeted follow-up, and archival searches. Multiband observations of intermediate-mass BBHs in the deci-Hz band are particularly promising. We perform an injection study for a GW231123-like system (the most massive BBH detection to date, which accumulates $\sim 10^5$ inspiral cycles in LGWA) and show that deci-Hz observations can measure the chirp mass even better than 3G instruments and yield good sky localization and inclination measurement, even with a single observatory. Opening the deci-Hz band would substantially improve the prospects of GW astronomy for intermediate-mass BBHs.

Figures (4)

• Figure 1: Sensitivity curves for the various detectors considered in this work, and representative massive BBH signals (see text).
• Figure 2: Inverse cumulative distribution of the number of sources as a function of the SNR for the detectors (and detector networks) considered in this work. The solid lines are the cumulative distributions corresponding to the maximum likelihood estimated for the reference population model used in Ref. LIGOScientific:2025pvj, while the shaded bands enclose the maximum and minimum value across 1000 simulated catalogs with varying hyperparameters. For reference, we further report the cumulative distribution of the SNRs for the sources in GWTC-3 KAGRA:2021vkt and GWTC-4 LIGOScientific:2025slb.
• Figure 3: Histogram of the redshift distribution of the simulated catalog for events detected with ${\rm SNR}\geq8$ using the different detectors and networks considered in this work. The solid lines report the population corresponding to the maximum likelihood estimated in Ref. LIGOScientific:2025pvj for the reference population model, while the shaded bands enclose the maximum and minimum value across 1000 simulated catalogs with varying hyperparameters. For reference, we further report the distribution of maximum-likelihood redshifts for the sources in GWTC-3 KAGRA:2021vkt and GWTC-4 LIGOScientific:2025slb.
• Figure 4: Results for our injection study of a GW231123-like event at the various networks considered in this work. We also report the posterior released by LVK for the IMRPhenomXPHM, the same one used in our analysis. In the right panel we show the results for some intrinsic parameters: chirp mass, mass ratio $q=m_2/m_1$, and spin magnitudes and tilts of the two objects. The inset zooms in the marginal ${\cal M}_c$ distribution. In the right panel we show the results for some extrinsic parameters: sky position, luminosity distance, inclination, polarization angle and time of coalescence (the latter centered on the injection value). The inset zooms in on the sky position distribution, with a right ascension reference centered on the injection value.