Electromagnetic Emission and Orbital Evolution of Eccentric Supermassive Black Hole Binaries in Retrograde Disks
Abstract
Circumbinary disks around supermassive black hole binaries (SMBHBs) are expected to form across a broad range of inclinations, with retrograde configurations potentially a common occurrence. Here we present the first grid-based hydrodynamical simulations of retrograde circumbinary disks around eccentric SMBHBs, solving an energy equation that balances viscous and shock heating against blackbody radiative cooling. We investigate different initial disk Mach numbers ℳa ∈ {10, 20, 40} and consider binary eccentricities eb∈[0.0, 0.8], finding that multiple stable states exist for the same binary eccentricity and Mach number. These states differ by the sense of rotation of their minidisks; both retrograde (↓↓), both prograde (↑↑), or one of each (↑↓), a property set by the initial conditions. Our findings indicate that each state produces qualitatively distinct orbital evolution: ↓↓ and ↑↓ minidisks drive circular inspirals whereas ↑↑ minidisks drive eccentric inspirals with potentially observable eccentricity in the LISA band. We measure the electromagnetic emission produced by the disk, finding that a binary of mass Mb=8×106M⊙ at redshift z=1 would be detectable by both current and upcoming optical and UV instruments. We demonstrate that the time- and azimuthally-averaged disk profiles are well described by 1D models, which naturally set a cavity radius within which angular momentum transport is dominated by Reynolds stresses rather than viscosity.
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BibTeX
@misc{oneill2026electromagnetic,
title = {{Electromagnetic Emission and Orbital Evolution of Eccentric Supermassive Black Hole Binaries in Retrograde Disks}},
author = {David ONeill and Mark J. Avara and Christopher Tiede and Daniel J. DOrazio and Zoltan Haiman and Andrew MacFadyen},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.09314},
eprint = {2609.09314},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.09314},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Electromagnetic Emission and Orbital Evolution of Eccentric Supermassive Black Hole Binaries in Retrograde Disks
AU - David ONeill
AU - Mark J. Avara
AU - Christopher Tiede
AU - Daniel J. DOrazio
AU - Zoltan Haiman
AU - Andrew MacFadyen
PY - 2026
DA - 2026/09/08
PB - arXiv
DO - 10.48550/arxiv.2609.09314
UR - https://arxiv.org/abs/2609.09314
AB - Circumbinary disks around supermassive black hole binaries (SMBHBs) are expected to form across a broad range of inclinations, with retrograde configurations potentially a common occurrence. Here we present the first grid-based hydrodynamical simulations of retrograde circumbinary disks around eccentric SMBHBs, solving an energy equation that balances viscous and shock heating against blackbody radiative cooling. We investigate different initial disk Mach numbers ℳ_a ∈ {10, 20, 40} and consider binary eccentricities e_b∈[0.0, 0.8], finding that multiple stable states exist for the same binary eccentricity and Mach number. These states differ by the sense of rotation of their minidisks; both retrograde (↓↓), both prograde (↑↑), or one of each (↑↓), a property set by the initial conditions. Our findings indicate that each state produces qualitatively distinct orbital evolution: ↓↓ and ↑↓ minidisks drive circular inspirals whereas ↑↑ minidisks drive eccentric inspirals with potentially observable eccentricity in the LISA band. We measure the electromagnetic emission produced by the disk, finding that a binary of mass M_b=8×10^6M_⊙ at redshift z=1 would be detectable by both current and upcoming optical and UV instruments. We demonstrate that the time- and azimuthally-averaged disk profiles are well described by 1D models, which naturally set a cavity radius within which angular momentum transport is dominated by Reynolds stresses rather than viscosity.
ER -