LION: laser interferometer on the moon

Abstract

Gravitational wave astronomy has now left its infancy and has become an important tool for probing the most violent phenomena in our Universe. The LIGO/Virgo-KAGRA collaboration operates ground based detectors which cover the frequency band from 10 Hz to the kHz regime. Meanwhile, the pulsar timing array and the soon to launch LISA mission will cover frequencies below 0.1 Hz, leaving a gap in detectable gravitational wave frequencies. Here we show how a laser interferometer on the moon (LION) gravitational wave detector would be sensitive to frequencies from sub Hz to kHz. We find that the sensitivity curve is such that LION can measure compact binaries with masses between 10 and 100M ⊙ at cosmological distances, with redshifts as high as z = 100 and beyond, depending on the spin and the mass ratio of the binaries. LION can detect binaries of compact objects with higher-masses, with very large signal-to-noise ratios (SNRs), help us to understand how supermassive black holes got their colossal masses on the cosmological landscape, and it can observe in detail intermediate-mass ratio inspirals at distances as large as at least 100 Gpc. Compact binaries that never reach the LIGO/Virgo sensitivity band can spend significant amounts of time in the LION band, while sources present in the LISA band can be picked up by the detector and observed until their final merger. Since LION covers the deci-Hertz regime with such large SNRs, it truly achieves the dream of multi messenger astronomy.

LISA telescope: phase noise due to pointing jitter

“…Let us note that, in a real implementation of the LISA optical metrology system, the telescope essentially produces an image, at the emitting aperture, of the "interface aperture" located on the optical bench (see Sec. 4.4 of [6]). The clipping of the beam does not take place at the telescope output aperture or in the telescope structure, but on the optical bench, at the interface aperture.…”

“…The very low frequency domain is nevertheless extremely interesting from an astrophysical point of view. This is why from the beginning of the GW detection planning era, as soon as the 1970's, various kinds of space antennas, obviously free of terrestrial issues, have been proposed [6,10].…”

“…In this configuration, the amount of scattered light in the optical system is another point to keep under control, as stray light can give rise to noise in the heterodyne phase measurements. Because of the large ratio between the emitted and received powers of light through the same telescope it will be necessary to control scattered light [6,8].…”

How the spherical modes of gravitational waves can be detected despite only seeing one ray

“…The underlying idea for the detection of GWs using interferometers is that of geodesic deviation [2,3,10,13,15]. In this case the motion of two particles moving along close geodesics is considered to describe the effect of a gravitational field by describing how the particles deviate from each other.…”

“…But how does the information about the modes gets into the signal? Obviously the answer is that we get the signal from GW detectors like LIGO, Virgo, KAGRA, TianQin or LISA [2,3,10,13,15]. However, this is only pushing the question to another level.…”