Too small to fail: Measurability of sub-solar mass compact objects with gravitational waves

The detection of a sub-solar mass black hole could yield dramatic new insights into the nature of dark matter, as such objects lack a traditional astrophysical formation mechanism. Gravitational waves allow for the direct measurement of compact object masses during compact object mergers, and we expect the gravitational-wave signal from a low-mass coalescence to remain within the LIGO frequency band for thousands of seconds. However, the analysis of such long signals presents new data analysis challenges, and it remains unclear whether we could confidently measure the properties of a sub-solar mass compact object. To this end, we perform Bayesian parameter estimation on gravitational-wave signals from theoretical sub-solar mass compact object mergers to explore the measurability of their source properties. Using recent likelihood approximation techniques, we find that the LIGO/Virgo detectors during the upcoming O4 observing run will be able to confidently measure sub-solar component masses with signal-to-noise ratios as low as 8 and may even measure higher-order effects like spin precession.