Structure of the nucleus of 1928+738

TL;DR

This paper models the VLBI jet of 1928+738, revealing it contains three trajectory families and evidence for two binary black hole systems, with implications for understanding radio quasars and their connection to GAIA.

Contribution

It provides the first detailed modeling indicating the presence of two binary black hole systems in the nucleus of 1928+738 based on VLBI component trajectories.

Findings

Three families of VLBI component trajectories identified.

Two binary black hole systems characterized by specific radii.

Separation of the black hole systems approximately 1.35 mas.

Abstract

Modeling of the trajectories of VLBI components ejected by the nucleus of 1928+738 shows the VLBI jet contains three families of trajectories, i.e. VLBI components are ejected from three different origins. The fit of components C1, C6 and C8 indicates that the nucleus of 1928+738 contains two binary black hole systems. The first binary black hole system is associated with the stationary components Cg and CS and is characterized by a radius $R_{bin,1} \approx 0.220$ mas; both black holes ejected VLBI components quasi regularly between 1990 and 2010. The second binary black hole system is not associated with stationary components and is characterized by a radius $R_{bin,2} \approx 0.140$ mas; it ejected only three VLBI components between 1994 and 1999. The two black hole sytems are separated by $\approx 1.35$ mas. We briefly discuss the consequences of the existence of binary black holes systems in radio quasars to make the link between radio quasars and GAIA.