Gravitational wave mergers of accreting binary black holes in AGN discs

Abstract

Binary black hole (BBH) evolution in the discs of active galactic nuclei (AGN) is a promising channel for gravitational wave (GW)-driven mergers. It is however unclear whether binaries interacting with the surrounding disc undergo orbital contraction or expansion. We develop a simple analytic model of accreting BBHs in AGN discs to follow the orbital evolution from the disc-dominated regime at large separations into the GW-driven regime at small separations (the coupled `disc+GW'-driven evolution). We obtain that accreting binaries expand in thick discs with aspect ratio greater than a critical value ($>h_{\mathrm{crit}}$); whereas accreting binaries contract and eventually merge in thin discs ($<h_{\mathrm{crit}}$). Interestingly, accreting BBHs can experience faster mergers compared to non-accreting counterparts, with a non-monotonic dependence on the disc aspect ratio. The orbital contraction is usually coupled with eccentricity growth in the disc-dominated regime, which lead to accelerated inspirals in the GW-driven regime. We quantify the resulting BBH merger timescales in AGN discs (${\tau }_{\mathrm{merger}}\sim 10^5-10^7$ yr) and estimate the associated GW merger rates ($\mathcal{R}\sim (0.2-5){\text{Gpc}}^{-3}{\text{yr}}^{-1}$). Overall, accreting binaries may efficiently contract and merge in thin discs, hence this particular BBH-in-AGN channel may provide a non-negligible contribution to the observed GW merger event rate.

published in MNRAS

References in corpus (15)

• One Channel to Rule Them All? Constraining the Origins of Binary Black Holes using Multiple Formation Pathways
• Hydrodynamic Torques in Circumbinary Accretion Disks
• Four eccentric mergers increase the evidence that LIGO--Virgo--KAGRA's binary black holes form dynamically
• Binary black hole mergers in AGN accretion discs: gravitational wave rate density estimates
• Black Hole Binary Formation in AGN Discs: From Isolation to Merger
• Binary Black Hole Merger Rates in AGN Disks versus Nuclear Star Clusters: Loud beats Quiet
• Gas dynamical friction as a binary formation mechanism in AGN discs
• Hot Circumsingle Disks Drive Binary Black Hole Mergers in Active Galactic Nucleus Disks
• Can stellar-mass black hole growth disrupt disks of active galactic nuclei? The role of mechanical feedback
• Long-term evolution of supercritical black hole accretion with outflows: a subgrid feedback model for cosmological simulations
• The maximum accretion rate of a protoplanet: how fast can runaway be?
• Evolution of binary black holes in AGN accretion discs: Disc-binary interaction and gravitational wave emission
• Black hole - black hole total merger mass and the origin of LIGO/Virgo sources
• Retention of Long-Period Gas Giant Planets: Type II Migration Revisited
• Limits on electromagnetic counterparts of gravitational wave-detected binary black hole mergers

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