Electromagnetic Signatures from Supermassive Binary Black Holes Approaching Merger

Abstract

We present fully relativistic predictions for the electromagnetic emission produced by accretion disks surrounding spinning and nonspinning supermassive binary black holes on the verge of merging. We use the code Bothros to post-process data from 3D general relativistic magnetohydrodynamic simulations via ray-tracing calculations. These simulations model the dynamics of a circumbinary disk and the mini-disks that form around two equal-mass black holes orbiting each other at an initial separation of 20 gravitational radii, and evolve the system for more than 10 orbits in the inspiral regime. We model the emission as the sum of thermal blackbody radiation emitted by an optically thick accretion disk and a power-law spectrum extending to hard X-rays emitted by a hot optically thin corona. We generate time-dependent spectra, images, and light curves at various frequencies to investigate intrinsic periodic signals in the emission, as well as the effects of the black hole spin. We find that prograde black hole spin makes mini-disks brighter since the smaller innermost stable circular orbit angular momentum demands more dissipation before matter plunges to the horizon. However, compared to mini-disks in larger separation binaries with spinning black holes, our mini-disks are less luminous: unlike those systems, their mass accretion rate is lower than in the circumbinary disk, and they radiate with lower efficiency because their inflow times are shorter. Compared to a single black hole system matched in mass and accretion rate, these binaries have spectra noticeably weaker and softer in the UV. Finally, we discuss the implications of our findings for the potential observability of these systems.

Misaligned Spinning Binary Black Hole Mergers in Hot Magnetized Plasma

“…The former has been the subject of numerous numerical investigations and explored by several theoretical groups with different techniques: Newtonian (and pseudo-Newtonian) viscous hydrodynamics (MacFadyen & Milosavljević 2008;D'Orazio et al 2016;Tang et al 2018;Tiede et al 2020) and magnetohydrodynamics (MHD; Shi et al 2012;Shi & Krolik 2016), MHD evolution over post-Newtonian spacetime metrics (Noble et al 2012;Zilhão et al 2015;Bowen et al 2017Bowen et al , 2018Noble et al 2021), and fully general relativistic magnetohydrodynamic (GRMHD) simulations (Farris et al 2012;Gold et al 2014aGold et al , 2014b. These works studied the CBD response to MBHB inspirals (Noble et al 2012), the mass feeding to individual "mini-disks" around inspiraling MBHs (Bowen et al 2017(Bowen et al , 2018, and the EM radiation emerging from these systems employing ray-tracing techniques (D'Ascoli et al 2018;Gutiérrez et al 2021). More recently, the impact of the spins of individual BHs on the dynamics of mini-disks was explored by Paschalidis et al (2021) in full GR and by Armengol et al (2021) employing an approximate metric for the spacetime evolution (Combi et al 2021a(Combi et al , 2022.…”

A Geometric Model to Interpret the γ-Ray Quasiperiodic Oscillation of PG 1553+113

“…That evidence reveals that PG 1553+113 most probably hosts a supermassive black hole binary system (e.g., Caproni et al 2017;Tavani et al 2018;Cavaliere et al 2019;Huang et al 2021). Furthermore, in the dual active galactic nucleus system, the complex dynamics associated with orbital motion result in accretion flows onto black holes intrinsically variable (e.g., Gutiérrez et al 2022), which may lead to the accretion rate periodic changes. It is usually thought that the power of the jet is proportional to the accretion power (e.g., Falcke & Biermann 1995).…”

Galaxy fields of LISA massive black hole mergers in a simulated Universe

“…For instance, binaries of 3 × 10 5 M at z ∼ 0.5 the number of orbital cycles is ∼ 85 (∼ 20) 10 hours (1 hour) before the final merger. This quantity is particularly important for observational studies, given that the orbital period of a binary can imprint distinctive variations in the lu-minosity emitted by active MBHBs (Gutiérrez et al 2022;Cattorini et al 2022).…”

“…Days to hours prior to coalescence, the precursor EM emission extends over different wavelengths and is expected to emerge from the circumbinary disc, the mini-discs, and from the hot gas and accretion streams that fill the cavity wall carved by the binary. For instance, the UV radiation produced by the disc components and the X-rays from coronal emission are expected to be the main contributions to the pre-merger EM signal (Tang et al 2018;d'Ascoli et al 2018;Gutiérrez et al 2022). These emissions show periodicities connected to the dynamical coupling of the binary with the circumbinary disc, providing a clear signature of an ongoing merger (Bowen et al 2018;Paschalidis et al 2021;Combi et al 2022).…”