Black Hole Binary Detection Landscape for the Laser Interferometer Lunar Antenna (LILA): Signal-to-Noise Calculations & Science Cases

Abstract

The Laser Interferometer Lunar Antenna (LILA) is a proposed gravitational-wave project aiming to take full advantage of the Moon's environment to access the deci-Hz band and detect intermediate-mass black hole (IMBH) binaries of mass $\sim 10^2-10^6 \, M_{\odot}$ (arXiv:2508.11631). With an observational period of 4 years, LILA can extend its IMBH detection horizon to the very early Universe, directly probing the first population of massive black holes ($z \sim 20-30$). LILA could also detect intermediate-mass-ratio inspiral systems with a total mass of $\sim 10^4 - 10^6 \, M_{\odot}$ and a mass ratio of $\sim 10^{-4} - 10^{-2}$. LILA can discover IMBH binaries months to years before merger with measurable eccentricity residuals retained from their formation, providing crucial early warning for multi-messenger and multi-band follow-up. The high SNR ($\gtrsim 100$) events detectable with LILA would enable strong-field tests of gravity. With these capabilities, LILA will provide important insights into the formation and evolution of massive black holes, as well as the astrophysical environments and evolutionary pathways of black hole binaries. LILA will also complement current LIGO/Virgo/KAGRA detections of pair-instability mass gap events, hierarchical merger candidates, and light IMBH mergers, while expanding the upper envelope of discovered black holes with stellar origin to masses of $\gtrsim 250 \, M_{\odot}$.