The Effect of Impact Parameters on the Formation of Massive Black Hole Binaries in Galactic Mergers

TL;DR

This study uses N-body simulations to explore how impact parameters and stellar density influence the timing and formation of massive black hole binaries during galaxy mergers, revealing deviations from previous theories.

Contribution

It provides new insights into the effects of impact parameters and stellar density on MBHB formation timing, challenging prior assumptions.

Findings

Lower stellar density leads to greater deviation in MBHB formation timing.

Higher stellar density and small impact parameters cause MBHs to move directly into each other's cores.

Timing of dual MBHs entering dynamical radius can differ from MBHB formation timing.

Abstract

By employing N-body simulations, we inestigate the formation of massive black hole binaries (MBHBs) through the sinking of two massive black holes (MBHs) during galaxy mergers. With different impact parameters and different central stellar density of the progenitor galaxies, we analyze the orbits of the MBHs from the beginning of the merger until the time when the bound MBHB forms. Contrary to the previous theory that the timing of the dual MBHs entering their dynamical radius is similar as the timing of the formation of the bound MBHB, we find that these two timings could deviate when the central stellar density of the progenitors galaxies are lower. On the other hand, when the central stellar density of the progenitor galaxies is higher and the mergers have small impact parameters, each MBHs would move directly into the core radius of the other progenitor galaxies, and therefore cause a variation in the timings of the MBHB formation.