Black hole high mass X-ray binary microquasars at cosmic dawn

Theoretical models and observations suggest that primordial Stellar Black Holes (Pop-III-BHs) were prolifically formed in HMXBs, which are powerful relativistic jet sources of synchrotron radiation called Microquasars (MQs).

If a smooth synchrotron cosmic radio background (CRB) reported with ARCADE 2, and the large excess amplitude of HI absorption at z~17 reported by EDGES, believed to be boosted by a CRB, are confirmed, they would be the first observational signatures of large populations of BH-HMXB-MQs at cosmic dawn.

Pop-III BH-HMXB-MQs precede supernovae, neutron stars and dust. BH-HMXB-MQs promptly inject hard X-rays and relativistic jets into the IGM, which overtake the HII regions ionized by progenitor Pop-III stars, heating and partially ionizing the IGM over larger distance scales.

BH-HMXBs are channels for the formation of BBHs. The large masses of GWs-BBHs relative to X-ray-BH masses, and the high rates of BBH-mergers, are consistent with high formation rates of BH-HMXBs and BBHs at cosmic dawn.