# Modeling the Black hole Merger of QSO 3C 186

## TL;DR

This paper models the properties of a supermassive black hole merger in quasar 3C 186, using observations of recoil velocity and numerical relativity to estimate mass ratios, spins, and gravitational wave emission.

## Contribution

It provides the first detailed modeling of the black hole merger in 3C 186, constraining progenitor parameters and energy radiated based on observational data and simulations.

## Key findings

- Black holes had comparable masses with q>1/4.
- At least 4% of total mass was radiated as gravitational waves.
- Merger was the most energetic event observed, radiating about 10% of total mass.

## Abstract

Recent detailed observations of the radio-loud quasar 3C 186 indicate the possibility that a supermassive recoiling black hole is moving away from the host galaxy at a speed of nearly 2100km/s. If this is the case, we can model the mass ratio and spins of the progenitor binary black hole using the results of numerical relativity simulations. We find that the black holes in the progenitor must have comparable masses with a mass ratio $q=m_1/m_2>1/4$ and the spin of the primary black hole must be $\alpha_2=S_2/m_2^2>0.4$. The final remnant of the merger is bounded by $\alpha_f>0.45$ and at least $4\%$ of the total mass of the binary system is radiated into gravitational waves. We consider four different pre-merger scenarios that further narrow those values. Assuming, for instance, a cold accretion driven merger model, we find that the binary had comparable masses with $q=0.70^{+0.29}_{-0.21}$ and the normalized spins of the larger and smaller black holes were $\alpha_2=0.94^{+0.06}_{-0.22}$ and $\alpha_1=0.95^{+0.05}_{-0.09}$. We can also estimate the final recoiling black hole spin $\alpha_f=0.93^{+0.02}_{-0.03}$ and that the system radiated $9.6^{+0.8}_{-1.4}\%$ of its total mass, making the merger of those black holes the most energetic event ever observed.