DDA 2015 – Bringing Black Holes Together: Plunging through the Final Parsec

This is one of a series of notes taken during the 2015 meeting of the AAS Division on Dynamical Astronomy, 3-7 May, at CalTech. An index to this series (all the papers presented at the meeting) is here.

Kelly Holley-Bockelmann (Vanderbilt)




  • How to bringBHs together: three¬†phases
    • Galaxy mergers sinkBHs through dynamical friction
      • $\sim 10^5$ pc
    • Sink closer via 3-body scattering
      • Quinlan 1997
      • dynamical friction no longer operating
      • $\sim 10$ pc, $\sim 10^{10}$ yr(!?)
    • Finally, GW complete the merger
      • $\sim 10^{-5}$ pc
  • Problem: once loss coneis depleted by 3-body scattering, it can only be refilled by 2-body relaxation
    • Merger stalls at $\sim 1$ pc
      • hence the “final parsec problem”
    • Begelman, Blandford, & Rees 1980, Makino 1997, Merritt & Milos 2005
  • Solution: galaxies are not idealized gas-free, stable, equilibrium systems!
    • Mayer et al. 2007: galaxies have gas; gas drives theBHs closer
      • drag(?)
      • spiral wave torques
      • problem: AGN feedback
    • Ostriker,Binney, & Silk 1989: galaxies aretriaxial
      • triaxiality introduces new mechanisms for phase space transport
        • chaos
        • Berczik et al. 2005
      • gets you to grav radiation regime
    • Khan,KHB,Berczik, and Just 2013: test limits of 3-body scattering
      • N-body sims
      • gas-poor, non-rotating, axisymmetric potential
      • still takes too long (2.5 Gyr)
      • found special orbits to fill loss cone
        • because near BH the potential istriaxial
          • even closer, is spherical
        • $\rightarrow$ changes in shape are important
      • add rotation $\rightarrow$ merger goes faster (yay)
        • axisymmetric, counter-rotating: ~100 Myr
          • but eccentricities very high

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