Evolution of Massive Blackhole Triples II -- The effect of the BH triples dynamics on the structure of the galactic nuclear

TL;DR

This study uses N-body simulations to show that galaxies with triple black holes have larger, less dense cusps and distinct velocity anisotropies compared to those with binary black holes, revealing observable signatures of their dynamical history.

Contribution

It demonstrates how triple black hole interactions uniquely influence galactic core structures and kinematics, providing potential observational markers.

Findings

Galaxies with triple BHs have larger, less dense cusps.

Presence of significant radial velocity anisotropy in galaxies with triple BHs.

Cusp size depends on triple BH evolution history, unlike binary BHs.

Abstract

In this paper, we investigate the structures of galaxies which either have or have had three BHs using $N$-body simulations, and compare them with those of galaxies with binary BHs. We found that the cusp region of a galaxy which have (or had) triple BHs is significantly larger and less dense than that of a galaxy with binary BHs of the same mass. Moreover, the size of the cusp region depends strongly on the evolution history of triple BHs, while in the case of binary BHs, the size of the cusp is determined by the mass of the BHs. In galaxies which have (or had) three BHs, there is a region with significant radial velocity anisotropy, while such a region is not observed in galaxies with binary BH. These differences come from the fact that with triple BHs the energy deposit to the central region of the galaxy can be much larger due to multiple binary-single BH scatterings. Our result suggests that we can discriminate between galaxies which experienced triple BH interactions with those which did not, through the observable signatures such as the cusp size and velocity anisotropy.