Oct 8: Ho Jung Paik (University of Maryland) on LANGO, the lunar gravitational wave antenna concept
With ground-based interferometers detecting hundreds of gravitational-wave (GW) events, GW astronomy is continuing to blossom. U.S. and European scientists are advancing plans to construct third-generation ground-based interferometers. ESA has proceeded through the mission formulation phase of space-based interferometer in a lower-frequency band, 10‒4 to 0.1 Hz. Despite all these exciting developments, there is still a missing frequency band, 0.1 to 10 Hz. This mid-frequency band is rich with interesting astrophysical events. Coalescence and merger of intermediate-mass black holes occur in this frequency band. Coalescing stellar-mass BHs pass through this frequency band days before they reach the frequency band of LIGO and Virgo. Detection of such signals would enable a mid-frequency detector to issue an advance notice to the high-frequency GW detectors, as well as to optical, X-ray and γ-ray telescopes.
Due to lack of plate tectonics, ocean waves and winds, the Moon is very quiet seismically and provides an ideal environment for GW experiments. We propose LANGO (Lunar Accelerometer Network Gravitational Observatory) to detect GWs in this frequency band. In the first phase, we propose to deploy four sensitive ambient-temperature (250 K) accelerometers in the tetrahedral or in a square configuration on the hemisphere facing the Earth. After successful operation at 250 K, LANGO would be upgraded to a cryogenic (4 K) version with over two orders of magnitude increased sensitivity, with coherent rejection of seismic noise implemented. LANGO is a full-tensor detector, capable of determining the source direction and wave polarization. The cryogenic LANGO could reach sensitivity ≤ 10^-23 Hz^-1/2 at 1-10 Hz. The LANGO accelerometers will be 103-105 times more sensitive than Apollo seismometers. With such sensitivity, LANGO will make great contribution to the advancement of lunar geophysics as well.