COLLOQUIUM: "Lunar Gravitational-wave Antenna" by Jan Harms (GSSI)


Future GW detectors like LISA and the proposed Einstein Telescope and Cosmic Explorer will herald a new era of GW science and astronomy. Together with pulsar timing arrays and inflationary probes, a frequency band spanning over 20 decades will be under observation. However, these detectors leave important gaps for GW detections, most notably the decihertz band, which would open exciting possibilities for GW cosmology and multi-messenger astronomy. The decihertz band is seen as technologically very challenging to cover. Space-borne concepts like DECIGO have been proposed, but it is not yet clear how to realize the required technologies for such detectors. In 2020, a new detector concept, the Lunar Gravitational-wave Antenna (LGWA) was proposed. The idea is to monitor vibrations of the Moon caused by GWs, which was first conceived by Joseph Weber for the Lunar Surface Gravimeter deployed on the Moon in 1972 by the crew of Apollo 17. Key of LGWA is an ultra-sensitive, cryogenic vibration sensor with sub-femtometer sensitivity in the decihertz band. An array of at least four of these sensors is to be deployed in a permanently shadowed region at the lunar north or south pole. The Moon is known to be several orders of magnitude quieter in terms of seismic perturbations than Earth, and the array serves to further reduce the extremely weak seismic background predicted from meteoroid impacts and moonquakes. In this way, LGWA becomes a technologically feasible concept fully exploiting the unique lunar environment and with the capability to achieve the first GW detections in the decihertz band.