The orientations of the binary black holes in GWTC-3

It is expected that the orientations of gravitational-wave sources are isotropically distributed. However, there are multiple effects that could cause this to not be the case, including deviations from general relativity and contamination of the gravitational-wave transient catalog with terrestrial sources. In this paper, we examine whether this is the case for the angle between the line-of-sight connecting Earth and the source and the source angular momentum (the source “inclination”). We find that the current catalog is strongly consistent with an isotropic distribution.