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Collaborators: Hui Li(李晖), Yaping Li(李亚平, Xiangli Lei(雷享礼), Jiancheng Wu（吴建成）

Huazhong Univ of Sci & Tech

Binary-single interactions in AGN disk

Reporter: Mengye Wang (王梦叶)

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2025.03.27

Wang et al. 2025, accepted by ApJ, arXiv:2501.10703

Wang et al. in preparation

Supervisors: Qingwen Wu(吴庆文), Yiqiu Ma（马怡秋）

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Contents

  • Background: BBH merger channels

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  • Simulation of BSI in AGN disk

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  • Simulation of BSI in AGN disk with PN formalism

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  • Summary

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BBH merger channels

Isolated binary star evolution

Dynamical formation channel

Marelli et al. 2020; Bethe & Brown 1998; Belczyński et al. 2002; Dominik et al. 2012; Eldridge & Stanway 2016; Stevenson et al. 2017b; Giacobbo & Mapelli 2018…

BBH formation by three-body encounter

Elwin et al. 2023; Portegies Zwart & McMillan 2000; O’Leary et al. 2006; Downing et al. 2010; Samsing et al. 2014; Ziosi et al. 2014; Rodriguez et al. 2015, 2016a …

GC/NSC

AGN disk channel

McKernan et al. 2014; Bartos et al. 2017; Stone et al. 2017; Yang et al. 2019; Samsing et al. 2021, LYP et al. 2021, LRX et al. 2022, Whitehead et al. 2023…

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AGN disk channels

Gas Assisted BBH formation

Gas Assisted BBH contract

LJR et al. 2023; Whitehead et al. 2023

LYP et al. 2021; Li & Lai et al. 2022, 2023

Dempsey et al. 2022

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Eccentric GW mergers: binary-single interactions(BSI) in AGN disk

Samsing et al. 2022

The 2D coplanar case:

The 3D cluster case:

The fraction of 3-body mergers is about 100 times larger in the 2D disk case compared with the 3D cluster case

The gas effect is ignored

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Contents

  • Background: BBH mergers channels

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  • Hydrodynamical Simulation of BSI in AGN disk

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  • Simulation of BSI in AGN disk with PN formalism

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  • Summary

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Binary-single interactions simulation in AGN disk

Root grid:

AMR: five levels

The maximum refinement zone:

Coupling REBOUND with Athena++ in shearing box

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Gas morphology

Trajectory of three BHs

Snapshots of the gas surface density

arXiv:2501.10703

A high-density region forms during two BHs close encounter

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Energy dissipation during BSI

The power of SMBH and gas:

  • The dense gas causes the pulsed energy dissipation during each close encounter
  • The gas increases the frequency of close encounter during BSI

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Spatial distribution of the gas power

  • After the BHs’ CSDs collide, the gas motion lags behind the BHs.

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  • As the BHs move apart, the lagged gas causes energy dissipation of the three-body system.
  • When two BHs approach, the gas does positive work

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  • When they move apart, the gas does negative work

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The end-state BBHs orbital distribution

  • The gas hardens the end-state-BBH semi-major axis
  • The gas plays a negligible effect on the eccentricity
  • The gas shorten the GW merger timescale of end-state BBHs

 

 

 

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Contents

  • Background: BBH mergers channels

​

  • Simulation of BSI in AGN disk

​

  • Simulation of BSI in AGN disk with PN formalism

​

  • Summary

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Simulation of BSI in AGN disk with PN formalism

Merger events

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The three merger probability in AGN disk

BS : BBH+ single BH

GW : GW megers

ST : stable triple (Hierarchical)

Ion : Ionization

Wang et al. in preparation

The gas increases the three-body merger probability from 4% to 20%

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Summary

We investigate the BSI process within AGN disks using both hydrodynamical and N-body simulations. The primary effects of the gas environment are as follows:

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  • Energy Dissipation: The dense gas within the AGN disk leads to significant energy dissipation within the system

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  • Enhanced Encounters: The presence of gas increases the frequency of encounters during BSI

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  • Increased three-body Merger Rates: The gas environment can amplify the merger rate by a factor of about 5

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