Significant challenges for astrophysical inference with next-generation gravitational-wave observatories

Abstract

The next generation of gravitational-wave observatories will achieve unprecedented strain sensitivities with an expanded observing band. They will detect Oð105Þ binary neutron star (BNS) mergers every year, the loudest of which will be in the band for ≈90 minutes with signal-to-noise ratios ≈1500. We show that subtleties arising from the rotation of the Earth and the free-spectral range of gravitational-wave interferometers dramatically increases the complexity of next-gen BNS signals compared to the one-minute signals seen by LIGO-Virgo. Reduced-order quadrature, a compression method currently relied upon to speed up the most expensive BNS calculations, may no longer be effective in determining the astrophysical parameters of next-gen BNS signals. We carry out reduced-order inference on a simulated next-gen BNS signal taking into account the Earth’s rotation and the observatories’ free-spectral range. We show that reduced-order modeling becomes impractical, and the full problem becomes computationally infeasible, when we include data below ≈16 Hz—a part of the observing band that is critical for precise sky localization. We discuss potential paths toward solving this complex problem.