Intermediate mass black holes in AGN discs – I. Production and growth

By B. McKernan, K. Ford, Wladimir Lyra, H. Perets. 2012

262 citations recorded by the source corpus.

Here we propose a mechanism for efficiently growing intermediate mass black holes (IMBH) in discs around supermassive black holes. Stellar mass objects can efficiently agglomerate when facilitated by the gas disc. Stars, compact objects and binaries can migrate, accrete and merge within discs around supermassive black holes. While dynamical heating by cusp stars excites the velocity dispersion of nuclear cluster objects (NCOs) in the disc, gas in the disc damps NCO orbits. If gas damping dominates, NCOs remain in the disc with circularized orbits and large collision cross-sections. IMBH seeds can grow extremely rapidly by collisions with disc NCOs at low relative velocities, allowing for super-Eddington growth rates. Once an IMBH seed has cleared out its feeding zone of disc NCOs, growth of IMBH seeds can become dominated by gas accretion from the active galactic nucleus (AGN) disc. However, the IMBH can migrate in the disc and expand its feeding zone, permitting a super-Eddington accretion rate to continue. Growth of IMBH seeds via NCO collisions is enhanced by a pile-up of migrators. We highlight the remarkable parallel between the growth of IMBH in AGN discs with models of giant planet growth in protoplanetary discs. If an IMBH becomes massive enough it can open a gap in the AGN disc. IMBH migration in AGN discs may stall, allowing them to survive the end of the AGN phase and remain in galactic nuclei. Our proposed mechanisms should be more efficient at growing IMBH in AGN discs than the standard model of IMBH growth in stellar clusters. Dynamical heating of disc NCOs by cusp stars is transferred to the gas in an AGN disc helping to maintain the outer disc against gravitational instability. Model predictions, observational constraints and implications are discussed in a companion paper (Paper II).

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/2a53ab470ee80c9751450103d4147fc10ba74cd1

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In Astronomy and Astrophysics

1. Michela Mapelli
2. Ilya Mandel
3. D. Holz
4. Maya Fishbach
5. Mario Spera
6. N. Giacobbo
7. B. Metzger
8. Zoltán Haiman

In Instrumentation

1. Ilya Mandel
2. Maya Fishbach
3. D. Holz
4. Michela Mapelli
5. E. Thrane
6. Colm Talbot
7. W. Farr
8. T. Bulik

Citations in the corpus

• Formation and Evolution of Compact-object Binaries in AGN Disks (2019, background): “Our simulation results confirm previous assumptions on the possibility of mass growth of BHs through mergers in AGN disks (McKernan et al. 2012, 2014; Yang et al. 2019a).”
• Rapid and Bright Stellar-mass Binary Black Hole Mergers in Active Galactic Nuclei (2016, background): “Further, massive stars can form near galactic centers, e.g., in AGN disks (Goodman & Tan 2004; Levin 2007; McKernan et al. 2012; Stone et al. 2016), providing an additional source of black holes to the nucleus.”
• Observational evidence for intermediate-mass black holes (2017, background): “• Accretion disks in AGN IMBHs could also be found in the accretion disks of AGN if they grow in a man- ner similar to planets in protoplanetary disks (McKernan et al. 2011a, 2012, 2014; Bellovary et al. 2016).”
• Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo (2018, background): “…Antonini & Rasio 2016; Petrovich & Antonini 2017), evolution of hierarchical triple systems(Antonini et al. 2014, 2017; Kimpson et al. 2016; Liu & Lai 2018), gas drag and stellar scattering in accretion disks surrounding supermassive BHs(McKernan et al. 2012; Bartos et al. 2017; Stone et al. 2017).”
• Accretion into the central cavity of a circumbinary disc (2012, background): “The assumption 8 In principle, less massive BHs may grow from the accretion discs around the primary (McKernan et al. 2012); the long-term evolution of such systems would be worthy of further study. that the binary is embedded in a thin disc allows us to make the following additional constraints on…”
• Rates of compact object coalescences (2021, background): “IMBH mergers may be a natural consequence of binary or dynamical evolution (e.g., Amaro-Seoane and Santamaŕıa, 2010; McKernan et al., 2012; Belczynski et al., 2014), and the gravitational waves from mergers of few hundred solar-mass IMBHs could be detected by current instruments (Veitch et al.,…”
• Constraining Stellar-mass Black Hole Mergers in AGN Disks Detectable with LIGO (2017, background): “Thus an overall fraction fd=fco+fg of nuclear BHs end up embedded in the disk, and quickly have their orbits damped and circularized by gas drag (e.g., McKernan et al. 2012).”