# Black Hole High Mass X-ray Binary Microquasars at Cosmic Dawn

## TL;DR

This paper proposes that primordial black hole high-mass X-ray binaries (HMXBs) in the early universe significantly contributed to cosmic radio background and IGM heating, influencing early structure formation and gravitational wave sources.

## Contribution

It introduces a model linking early black hole HMXBs to cosmic radio background, IGM heating, and binary black hole formation, providing a unified explanation for several observations.

## Key findings

- HMXBs at cosmic dawn produce a radio background consistent with EDGES data.
- Early BH-HMXBs significantly heat and ionize the IGM over large scales.
- High formation rates of BH-HMXBs explain observed gravitational wave black hole mergers.

## Abstract

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). Large populations of BH-HMXB-MQs at cosmic dawn produce a smooth synchrotron cosmic radio background (CRB) that could account for the excess amplitude of atomic hydrogen absorption at z~17, recently reported by EDGES. BH-HMXB-MQs at cosmic dawn precede supernovae, neutron stars and dust. BH-HMXB-MQs promptly inject hard X-rays and relativistic jets into the IGM, which overtake the slower expanding 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 Binary-Black-Holes (BBHs). The large masses of BBHs detected by gravitational waves, relative to the masses of BHs detected by X-rays, and the high rates of BBH-mergers, are consistent with high formation rates of BH-HMXBs and BBHs in the early universe.