2025ApJ...992...16P

We explore the potential of lunar-based gravitational-wave detectors to broaden the multimessenger astrophysics landscape by detecting mergers of massive (M₁, M₂ > 1M_⊙) double white dwarf (WD) binaries. These systems are potential progenitors of Type Ia supernovae and could serve as independent probes of cosmic expansion. We examine two proposed lunar gravitational-wave detector concepts operating in the subhertz band (0.1-1 Hz): the Gravitational-Wave Lunar Observatory for Cosmology (a proxy for suspended test mass detectors) and the Lunar Gravitational-Wave Antenna (a proxy for seismic array detectors). We estimate that these detectors could reach distances of up to ∼1 Gpc for the most massive mergers. We show that lunar detectors could observe up to dozens of massive WD mergers annually, including those originating from globular clusters. Lunar detectors would constrain the masses of these WDs with an unprecedented accuracy of one part in a million. Furthermore, these detectors would provide early warnings weeks before mergers, including sky-localization of square arcminute resolution, enabling a new era of coordinated multimessenger follow-up of electromagnetic transients-whether they evolve into Type Ia supernovae or accretion-induced collapse events.