Long-Term Evolution of and X-ray Emission from a Recoiling Supermassive Black Hole in a Disk Galaxy

TL;DR

This study models the long-term motion and X-ray emission of recoiling supermassive black holes in disk galaxies, revealing potential observable luminosities and probabilities of detection based on their trajectories and accretion behavior.

Contribution

It introduces a detailed simulation of recoiling SMBHs in galaxy potentials, including dynamical friction and gas accretion, to predict their X-ray luminosities and observational prospects.

Findings

X-ray luminosity can exceed 3x10^39 erg/s during disk crossings

Luminosity may reach ~10^46 erg/s if ejected into the disk

Probability of detecting luminous recoiling SMBHs in disk galaxies

Abstract

Recent numerical relativity simulations have shown that the emission of gravitational waves at the merger of two black holes gives a recoil kick to the final black hole. We follow the orbits of a recoiling supermassive black hole (SMBH) in a fixed background potential of a disk galaxy including the effect of dynamical friction. If the recoil velocity of the SMBH is smaller than the escape velocity of the galaxy, the SMBH moves around in the potential along a complex trajectory before it spirals into the galactic center through dynamical friction. We consider the accretion of gas onto the SMBH from the surrounding ISM and estimate the X-ray luminosity of the SMBH. We find that it can be larger than 3x 10^39 erg^-1 or the typical X-ray luminosity of ultra-luminous X-ray sources, when the SMBH passes the galactic disk. In particular, the luminosity could exceed ~10^46 erg s^-1, if the SMBH is ejected into the galactic disk. The average luminosity gradually increases as the SMBH spirals into the galactic center. We also estimate the probability of finding recoiling SMBHs with X-ray luminosities of >3x 10^39 erg^-1 in a disk galaxy.