The complex evolution of supermassive black holes in cosmological simulations

TL;DR

This paper introduces advanced cosmological simulations that accurately model the complex dynamics of supermassive black holes, including binary formation, eccentricities, and gravitational wave emission, within evolving galaxies.

Contribution

It presents a novel simulation approach using the KETJU code to self-consistently resolve SMBH dynamics and their interactions with galaxy-scale processes.

Findings

Most SMBH binaries form with high eccentricities (0.6-0.95).

Circular binary models are inadequate for typical SMBH binary evolution.

The simulations capture complex SMBH behaviors like gravitational wave emission and Lidov-Kozai oscillations.

Abstract

We present here self-consistent zoom-in simulations of massive galaxies forming in a full cosmological setting. The simulations are run with an updated version of the KETJU code, which is able to resolve the gravitational dynamics of their supermassive black holes, while simultaneously modelling the large-scale astrophysical processes in the surrounding galaxies, such as gas cooling, star formation and stellar and AGN feedback. The KETJU code is able to accurately model the complex behaviour of multiple SMBHs, including dynamical friction, stellar scattering and gravitational wave emission, and also to resolve Lidov-Kozai oscillations that naturally occur in hierarchical triplet SMBH systems. In general most of the SMBH binaries form at moderately high eccentricities, with typical values in the range of e =0.6-0.95, meaning that the circular binary models that are commonly used in the literature are insufficient for capturing the typical binary evolution.