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Hierarchical Black Hole Mergers in Active Galactic Nuclei
Y Yang1, I Bartos1, V Gayathri1,2
1Department of Physics, University of Florida, P.O. Box 118440, Gainesville, Forida 32611-8440, USA.
Active galactic nuclei (AGN) accretion disks may host black hole mergers. This channel explains hierarchical mergers and black holes exceeding the stellar core collapse mass limit, potentially including GW170729.
Area of Science:
- Astrophysics
- Gravitational Wave Astronomy
Background:
- The origin of stellar-mass black hole mergers detected by LIGO/Virgo remains unclear.
- Understanding these mergers is crucial for black hole astrophysics.
Purpose of the Study:
- To investigate the role of active galactic nuclei (AGN) accretion disks in black hole mergers.
- To explore the possibility of hierarchical mergers within AGN disks.
Main Methods:
- Simulating black hole dynamics within AGN accretion disks with migration traps.
- Analyzing the mass and spin properties of merging black holes.
Main Results:
- Migration traps in AGN disks can facilitate hierarchical black hole mergers.
- Approximately 40% of AGN-assisted mergers may involve black holes heavier than 50 solar masses.
- These mergers produce black hole spins (anti)aligned with the orbital axis.
Conclusions:
- AGN-assisted hierarchical mergers offer a plausible channel for observed black hole mergers.
- The unique spin signatures could distinguish this channel from others.
- The heaviest merger detected, GW170729, might have originated from this AGN channel.
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