On the behaviour of eccentric sub-pc massive black hole binaries embedded in massive discs

Abstract

Using the 3D smoothed particle hydrodynamics code PHANTOM, we investigate the evolution of the orbital properties of massive black hole binaries embedded in massive discs where gravitational instabilities (GIs) triggered by the disc self-gravity are the only source of angular momentum transport. In particular, we investigate the evolution of binaries with different initial eccentricities $e_0=0.05,0.5,0.8$ and mass ratios $q=0.1,0.3,0.9$. Our simulations suggest that there might not be a unique value of critical eccentricity. We find initially more eccentric binaries to tend to higher asymptotic eccentricity values than more circular ones. This implies that there is a range of critical eccentricity values, that depends on the initial condition of the system. In particular, we find the width of this range to be narrower for more unequal binaries. We furthermore measure preferential accretion onto our binaries, finding more accretion onto the primary only for mass ratio $q=0.3$ and eccentricity $e=0.8$. We discuss how this might have implications for the amplitude of the gravitational wave background detected by Pulsar Timing Arrays (PTA) experiments. We finally measure the corresponding value of the viscosity parameter $\alpha$ in our simulations and discuss how this depends on the binary properties.

7 pages, A&A submitted

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• Realistic consecutive galaxy mergers form eccentric PTA sources
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• Effects of eccentricity on accreting binary black holes: MHD simulations in full GR reveal novel periodicities in jet power and synchrotron spectra
• Radiation pressure role in accreting massive black hole binaries
• Spacetime in motion: an evolving relativistic binary black hole metric for GIZMO