Assessing Selection Effects on the Observed Compact Object Mass Gap in Galactic X-ray Binaries

Determine whether observational or evolutionary selection effects inherent to the detection of Galactic X-ray binaries can produce the observed gap in compact object masses, thereby explaining the apparent paucity of objects in this mass range without invoking a true astrophysical absence.

Background

Dynamical mass measurements of Galactic X-ray binaries have long suggested a paucity of compact objects between roughly 3–5 solar masses, often referred to as the lower mass gap. However, observational pipelines and evolutionary pathways for X-ray binaries may bias detections against systems in this range, calling into question whether the gap is physical or observational.

The detection of GW230529, whose primary mass likely resides in the purported gap, adds evidence that this region is populated. Yet, the role of selection effects in creating or exaggerating the gap in X-ray binary observations remains unresolved, motivating a targeted assessment of these biases.