Gravitational waves to the Moon: prospects and science case

Since their first direct detection a decade ago, gravitational waves have emerged as a powerful tool to study our Universe. The discoveries during the first three observing runs of the LIGO, Virgo, and KAGRA interferometers already had an extraordinary impact on astrophysics, cosmology, and fundamental physics, and the fourth run is ongoing.

Current and future ground-based interferometers are sensitive over a frequency range from a few Hz to a few kilo-Hz, while PTA experiments cover the nano-Hz region, and upcoming space-based missions like LISA will observe sources in the milli-Hz band. A missing link in the gravitational-wave landscape is the deci-Hz band, bridging the gap between LISA and ground-based observatories, and several different detector concepts have been proposed throughout the years to cover this band.

An especially tantalizing possibility is represented by lunar-based observatories, which leverage the Moon's low seismic noise relative to Earth and potential for cryogenic operation in permanently shadowed regions. I will present the two proposed lunar-borne experiments: the inertial sensor-based Lunar Gravitational-Wave Antenna (LGWA) and the laser strainmeter-based Laser Interferometer Lunar Antenna (LILA). After presenting their mission concept and features, I will discuss the promising deci-Hz science case, focusing on the observation of compact binaries, tidal disruption events, supernovae, and stochastic backgrounds of astrophysical and cosmological origin.