SIGOs, a Proposed Progenitor to Globular Clusters, and their Connections to Gravitational Wave Anisotropies

Supersonically Induced Gas Objects (SIGOs) are structures with little to no dark matter component predicted to form at the early Universe, in regions that had large relative velocities between baryons and dark matter at the time of recombination. They have been suggested to be the progenitors of present-day globular clusters. In this work, we study the formation and abundance of SIGOs semi-analytically to model the global abundance of SIGOs. Significantly, we find that the expected number density of SIGOs is consistent with observed globular cluster number densities. Furthermore, if SIGOs are indeed the progenitors of globular clusters, these results suggest the possibility of a large-scale anisotropy in the abundance of globular clusters in the Universe. Importantly, because globular clusters were proposed to be natural formation sites for gravitational wave sources from binary black hole mergers, we show that SIGOs should imprint an anisotropy on the gravitational wave signal on the sky, consistent with SIGOs’ distribution.