EM counterparts of recoiling black holes: general relativistic simulations of non-Keplerian discs

TL;DR

This study uses advanced general relativistic simulations to explore electromagnetic signals from recoiling black holes with non-Keplerian discs, revealing potential observable signatures post-merger.

Contribution

First 2D general relativistic hydrodynamics simulations of extended non-Keplerian discs with a new shock detection method, linking black hole recoil properties to electromagnetic emissions.

Findings

Luminosity peaks above 10^{43} erg/s about 30 days after merger.

Recoil velocity and black hole spin influence accretion and emission.

Potential electromagnetic counterparts to black hole mergers identified.

Abstract

We investigate the dynamics of a circumbinary disc that responds to the loss of mass and to the recoil velocity of the black hole produced by the merger of a binary system of supermassive black holes. We perform the first two-dimensional general relativistic hydrodynamics simulations of \textit{extended} non-Keplerian discs and employ a new technique to construct a "shock detector", thus determining the precise location of the shocks produced in the accreting disc by the recoiling black hole. In this way we can study how the properties of the system, such as the spin, mass and recoil velocity of the black hole, affect the mass accretion rate and are imprinted on the electromagnetic emission from these sources. We argue that the estimates of the bremsstrahlung luminosity computed without properly taking into account the radiation transfer yield cooling times that are unrealistically short. At the same time we show, through an approximation based on the relativistic isothermal evolution, that the luminosity produced can reach a peak value above $L \simeq 10^{43} \ {\rm erg/s} $ at about $\sim 30\,{\rm d}$ after the merger of a binary with total mass $M\simeq 10^6 M_\odot$ and persist for several days at values which are a factor of a few smaller. If confirmed by more sophisticated calculations such a signal could indeed lead to an electromagnetic counterpart of the merger of binary black-hole system.