Multiple supermassive black hole systems: SKA's future leading role

TL;DR

This paper discusses how the SKA telescope will significantly advance understanding of multiple supermassive black hole systems, their role in galaxy evolution, and gravitational wave background detection through high-resolution imaging and pulsar timing.

Contribution

It highlights SKA's potential to observe SMBH systems across a wide range of separations, improving constraints on galaxy evolution and gravitational wave backgrounds.

Findings

SKA will enable high-resolution imaging of SMBH systems.

Radio-jet morphology can identify close SMBH binaries.

SKA will help trace SMBH binary evolution from galaxy scales to sub-parsec.

Abstract

Galaxies and supermassive black holes (SMBHs) are believed to evolve through a process of hierarchical merging and accretion. Through this paradigm, multiple SMBH systems are expected to be relatively common in the Universe. However, to date there are poor observational constraints on multiple SMBHs systems with separations comparable to a SMBH gravitational sphere of influence (<< 1 kpc). In this chapter, we discuss how deep continuum observations with the SKA will make leading contributions towards understanding how multiple black hole systems impact galaxy evolution. In addition, these observations will provide constraints on and an understanding of stochastic gravitational wave background detections in the pulsar timing array sensitivity band (nanoHz -microHz). We also discuss how targets for pointed gravitational wave experiments (that cannot be resolved by VLBI) could potentially be found using the large-scale radio-jet morphology, which can be modulated by the presence of a close-pair binary SMBH system. The combination of direct imaging at high angular resolution; low-surface brightness radio-jet tracers; and pulsar timing arrays will allow the SKA to trace black hole binary evolution from separations of a galaxy virial radius down to the sub-parsec level. This large dynamic range in binary SMBH separation will ensure that the SKA plays a leading role in this observational frontier.