Constraining Binary Black Hole Precessional Morphologies at Different Reference Points

Merging binary black holes exhibit precessional motion that can be classified into three categories: Circulating, librating around 0, and librating around pi. This information can be decoded from the gravitational wave signal. Binary systems can transition between morphologies as they spiral inwards, and spin precession effects are more pronounced near merger. The spin morphology reveals information about the binary black holes' formation such as through isolated evolution of massive binary stars and their collapse or through dynamic evolution channels such as capture. In this study, we considered inferring the morphology at a reference point at which the binary has (approximately) a given orbital velocity. Previous studies have instead used a reference point at a given gravitational wave frequency, which corresponds to different orbital velocities depending on the binary's properties. We simulated loud signals for highly spinning binary black holes in the LIGO-Virgo network at its plus-era sensitivity and constrained their precessional morphologies. We then compared the results to those from previous work to see if there are better constraints at this new reference point. We find that one can obtain both better and worse constraints at a fixed orbital velocity than at a fixed gravitational wave frequency. This study will help determine a suitable reference point for constraining binary black hole spin morphologies.